INTERFACE CONTROL DOCUMENT - sdcm.ru · PDF fileSYSTEM OF DIFFERENTIAL CORRECTION AND MONITORING INTERFACE CONTROL DOCUMENT Radiosignals and digital data structure of GLONASS Wide

SYSTEM OF DIFFERENTIAL CORRECTION AND MONITORING

INTERFACE

CONTROL

DOCUMENT

Radiosignals and digital data structure of

GLONASS Wide Area Augmentation System,

System of Differential Correction and Monitoring

(Edition 1)

2012

Edition 1 2012 ICD SDCM

Joint Stock Company "Russian Space Systems"

2

УТВЕРЖДАЮ APPROVED

Командующий Космическими войсками

О.

Head of Federal Space Agency

____________________Vladimir Popovkin

«_______»____________________2012

Interface Control Document

Radiosignals and digital data structure of

GLONASS Wide Area Augmentation System,

System of Differential Correction and Monitoring

(Edition 1)

AGREED

Deputy Head of Federal Space Agency

______________Anatoliy Shilov

«_______»__________2012

First Deputy Director General – Designer

General of Russian Space Systems

__________________Sergey Ezhov

«_______»______________2012



3

From Russian Space Systems From Federal Space Agency

Grigoriy Stupak

A.Terekhov

From Center of programs and planes

realization on rocket and space

engineering

Vyacheslav Dvorkin Vladimir Klimov

Sergey Karutin

S. Andrianov

Sergey Kalinchev

N.M. Volkov

Vladimir Kurshin

Vitaliy Sernov

Daniil Visnyakov



4

Table of contents

1 Introduction .......................................................................................................... 10

1.1 SDCM purpose .............................................................................................. 10

1.2 SDCM components ....................................................................................... 10

1.3 SDCM interface definition ............................................................................ 11

2 GENERAL ........................................................................................................... 13

2.1 ICD definition ................................................................................................ 13

2.2 ICD approval and revision ............................................................................. 13

3 Space Segment of SDCM ..................................................................................... 14

3.1 Space Segment structure ................................................................................ 14

4 General aspects interaction between SDCM and user ......................................... 15

5 Interface of SDCM radiosignals ........................................................................... 17

5.1 L1 signal structure ......................................................................................... 17

5.2 RF signal characteristics of L1 ...................................................................... 17

5.3 C/A codes in L1 SDCM signal ...................................................................... 20

5.4 Convolutional encoding of transmitted digital data ...................................... 23

6 SDCM data format ............................................................................................... 24

6.1 General format information ........................................................................... 24

6.2 Preamble ........................................................................................................ 24

6.3 Message type identifier .................................................................................. 24

6.4 Data field ....................................................................................................... 26

6.5 Messages and Relationship between Message Types ................................... 26

6.6 Data field M(x) .............................................................................................. 27

6.7 Cyclic Redundancy Check ............................................................................ 27



5

7 SDCM data content .............................................................................................. 29

7.1 SDCM testing mode (Message Type 0) ........................................................ 29

7.2 PRN Mask Assignments (Message Type 1) .................................................. 29

7.3 GEO Navigation Message (Message Type 9) ............................................... 33

7.4 GEO Almanac Message Type 17 .................................................................. 34

7.5 Long-term and mixed satellite error corrections (Message Types 24 and 25)37

7.6 Fast corrections Message Types 2-5 ............................................................. 42

7.7 Integrity parameters of fast and long-term corrections (Message Type 6) ... 45

7.8 Ionosphere Grid Point Masks Message Type 18 ........................................... 47

7.9 Ionospheric Delay Corrections Messages Type 26 ...................................... 52

7.10 Degradation parameters (Messages Type 7 and 10) ................................. 54

7.11 SDCM Network Time/UTC/GLONASS Time Offset Parameters

Message Type 12 .......................................................................................... 59

7.12 SDCM Service Message Type 27 ............................................................. 61

7.13 Clock-ephemeris Covariance Matrix Message Type 28 .......................... 64

7.14 Null Message Type 63 and Internal Test Message Type 62 .................... 66

8 Annex А. Definitions of basic a priory and a posteriori parameters for navigation

user equipment accuracy assessment taking into account SDCM data .................. 67

9 Annex B. Basic integrity principles .................................................................... 69

10 Annex C. Tables of SDCM message formats ................................................. 76

11 Annex D. Recommendations on SDCM data use in the navigation algorithm

GLONASS/GPS/SDCM ......................................................................................... 84

12 Annex E. Recommendations on the troposphere model ............................... 102

13 Annex F. Transmission sequence of SDCM messages. ............................... 105



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14 Annex G. Transmission sequence of SDCM messages when changing data

field of used satellites (change of PRN mask) ...................................................... 107

15 Annex I. Definitions of SDCM data application protocols ......................... 108

16 Annnex J. Additional materials and data ...................................................... 124

17 References ..................................................................................................... 127

18 Changes registration list ................................................................................ 128



7

List of acronyms and abbreviations

UE – User Equipment

IMO – International Marine Organization

GEO – Geostationary satellite

GNSS – Global Navigation Satellite System

GSO – Geostationary Orbit

GDOP – Geometric Dilution of Precision

ICAO – International Civil Aviation Organization

II – Integrity Information (of GNSS radionavigation field)

SC – Spacecraft

CI – Correcting Information (corrections to ephemeris and time-and

frequency parameters)

CMS – Command-Measuring System

NUE – Navigation User Equipment

NSC – Navigation Spacecraft

NS – Navigation Satellite

OC – Orbital Constellation

ERP – Earth Rotation Parameters

SW – Software

SS – Space Segment

SDCM – System of Differential Correction and Monitoring

RS – Reference Station

SA – Standard Accuracy

RIRV – Russian Institute of Radionavigation and Time



8

STS – System Time Scale

CS – Central Synchronizer

MCS – Mission Control Center

TFC – Time-and-Frequency Corrections

ECD – Efemeris and Clock Data

AT – Atomic Time

BPSK – Binary Phase-Shifted Key

CRC – Cyclic Redundancy Check

C/A – Coarse Acquisition

ECEF – Earth-Centered Earth-Fixed

ET – Ephemeris Time

DOP – Dilution of Precision

GDOP – Geometric Dilution of Precision

GIVE – Grid Ionospheric Vertical Error

HAL – Horizontal Alert Limit

HDOP – Horizontal Dilution of Precision

HPL – Horizontal Protection Level

IOD – Issue of Data

JD – Julian Date

PDOP – Position Dilution of Precision

PRN – Pseudorandom Number

RAIM – Receiver Autonomous Integrity Monitoring

RMS – Root Mean Square

RTCA – Radio Technical Commission for Aeronautics



9

RTCM – Radio Technical Commission for Maritime Services Special

Committee

SARPs – Standards and Recommended Practices

SBAS – Satellite-Based Augmentation System

SNT – SBAS Network Time

SoL – Safety of Life service

TDOP – Time Dilution of Precision

TTA – Time to Alert

VAL – Vertical Alert Limit

VDOP – Vertical Dilution of Precision

VPL – Vertical Protection Level

UIRE – User Ionospheric Range Error

UERE – User Equivalent Range Error

UDRE – User Differential Range Error

UERRE – User Equivalent Range Rate Error

URA – User Range Accuracy

UT – Universal Time

UTC – Universal Time Coordinated

UTC (SU) – Universal Time Coordinated (SU)



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1 Introduction

1.1 SDCM purpose

1.1.1 The System of Differential Correction and Monitoring

(SDCM) is an SBAS augmentation to the Global Navigation Satellite System

GLONASS for enhancing accuracy and calculating integrity of positioning for

marine, airborne, terrestrial and space users of GLONASS and GPS opened

radiosignals.

1.2 SDCM components

1.2.1 SDCM includes two subsystems:

Constellation of satellites (Space Segment);

Ground-based monitoring and control facilities (Control Segment)

Space Segment includes 3 operating geostationary satellites of multifunctional

Space System Luch, broadcasting SDCM data to users by means of SBAS

radiosignals described in Section 4.

Control Segment includes Center of Differential Correction and Monitoring

(CDCM), ground based facilities transmitting SDCM data to users, Mission Uplink

and Control Center and the network of Reference Stations located worldwide.

Control Segment is responsible for:

Monitoring of opened radionavigation field of GLONASS and GPS

satellites;

continuous correcting (уточнение) of orbits and clocks of GLONASS

and GPS satellites;

generating correcting data and integrity parameters;



11

transmitting corrections and integrity data to users via Space Segment

and ground facilities.

1.3 SDCM interface definition

1.3.1 Fig 1 shows General Interface from Space Segment (of

GLONASS, SDCM and GPS systems) to Navigation User Equipment (NUE). It is

formed by L1 radiosignals of SDCM and opened GLONASS and GPS radiosignals of

L1, L2, L3 and L5 frequency bands.

Figure 1. Interface from Space Segment to NUE for SDCM

GLONASS constellation includes GLONASS-M and GLONASS-K satellites.

GLONASS-M satellites radiate opened navigation radiosignals with frequency

division (OF) in two frequency bands: L1 and L2. Satellites located in opposite points

of the same orbit plane (antipodal), can transmit navigation radiosignals on equal

carrier frequencies.

GLONASS-K satellites of the first phase radiate L3OC opened radiosignals in

L3 frequency band, besides L1OF and L2OF.

Interface of L1OF and L2OF signals radiated by GLONASS-M and

GLONASS-K satellites, regulated by GLONASS ICD «Navigation radiosignal in

bands L1, L2 with open access and frequency division », 2010, Edition 5.2.



12

Interface of L3OC signal radiated by GLONASS-K satellites, regulated by

GLONASS ICD «Navigation radiosignal in band L3 with open access and code

division», 2011, Edition 1.

L1 signal of SDCM СДКМ radiated by geostationary satellites, is

informational and transmits differential corrections and GNSS integrity data to

navigation users.



13

2 GENERAL

2.1 ICD definition

2.1.1 Given Interface Control Document (ICD) specifies

parameters of interface of radiosignals emitted by SDCM Space Segment in L1

frequency band.

2.2 ICD approval and revision

2.2.1 Joint Stock Company “Russian Space Systems” (JSC RSS)

is a developer of ICD and a head responsible for SDCM creation.

JSC RSS is responsible for development, coordination, revision, maintenance

an official distribution of ICD.

ICD shall be approved by duly authorized representatives of Federal Space

Agency (Roskosmos) and enters into effect upon approval by Head of Roskosmos.

In the course of SDCM development its separate parameters can vary. The

developer of ICD bears responsibility for negotiation of the offered modifications

with all responsible sides and for preparation, if necessary, the new edition of the

ICD containing modifications.

Modifications and new editions of the ICD enter into effect upon approval by

Head of Roskosmos.



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3 Space Segment of SDCM

3.1 Space Segment structure

3.1.1 Completely deployed Space Segment includes 3 operating

geostationary satellites (see Table 1).

Table 1. Nominal parameters of SDCM Space Segment

Orbital position Luch-5А Luch -5B Luch -5V

167o E 95

o E 16

o W

PRN 140 125 141

Eccentricity 0 0 0

Inclination (o) 0 0 0

Radius (km) GSO 42164 42164 42164



15

4 General aspects interaction between SDCM and user

Requirements for SDCM Time to alert (TTA) are showed in Annex G

‘Recommendations for using SDCM data in the navigation algorithm

GLONASS/GPS/SDCM (accordingly for state functions of GNSS satellites, principal

differential corrections and accurate differential corrections)”. Figure 2 shows

components of total TTA for both ground and space segments.

Figure 2. Time to alert for SDCM

According to Figure 2 ‘initial event’ in GNSS/SDCM and ‘initial event’ at user

equipment which mean satellite failure are considered simultaneous. Actually it is not

so due to different parameters of receivers. There is little difference, due to receiver

processing, between the time of measured pseudorange distortion and the time when

distorted information is displayed. For simplification, it is not shown in the Figure.



16

Taking into account the local nature of tropospheric delay, all users calculate

their own delays at troposphere. Recommended model for tropospheric delay

calculation is given in Annex D ‘Recommendations for tropospheric model’ (based

on RTCA/DO-229D) nevertheless, other models can also be used, at discretion and

responsibility of the user.

Multipath contribution into positioning error is considerable and affects both

SDCM ground facilities and user equipment. In SDCM ground facilities multipath

effect is decreased as far as it is possible or suppressed to minimize signal errors.

User equipment also should provide for multipath suppression means.

Special means is used in SDCM preventing any ambiguity when using

corrections. It is described in Section 7.5.

In GPS and GLONASS different coordinate systems are used, WGS-84 and

PZ-90.02 respectively. SDCM generates corrections in WGS-84 by matrix

transformation of GLONASS data from PZ-90.02 (see Annex I “SDCM data

protocols definition”).

In SBAS messages SDCM data for GLONASS and GPS are presented in

single time scale, GPS.



17

5 Interface of SDCM radiosignals

5.1 L1 signal structure

5.1.1 L1 signal of SDCM is radiated by three geostationary

satellites, antenna inclination to the north from is 7 o.

5.2 RF signal characteristics of L1

5.2.1 Carrier frequency of L1 signal

Noise –type radiosignal is used at the carrier frequency of 1575,42 MHz with

code division between three geostationary satellites.

5.2.2 Carrier frequency stability

Short-term instability of carrier frequency at the output of the satellite

transmitting antenna shall not exceed 5 × 10-11

when averaging at time intervals of 1-

10 s.

5.2.3 Carrier phase noise

In L1 signal the phase noise spectral density of the non-modulated carrier is

such that in a receiver a phase locked loop of 10 Hz one-sided noise bandwidth

provides the accuracy of carrier phase tracking not worse than 0.1 radian (1σ).

5.2.4 Spurious Transmissions

Spurious transmissions will be at least 40 dB below the unmodulated carrier

power over all frequencies.

5.2.5 Modulation

Transmitted message 250 bps with convolutional encoding at a rate of 500

symbols per second will be added modulo-2 to a 1023-bit pseudo-random noise code.

It will then be bi-phase shift-keyed (BPSK) modulated onto the carrier at a rate of

1,023 Mbps. Symbols of SDCM message (transmission rate of 500 symbols per

second are synchronized with time interval of 1 millisecond of С/А code.



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5.2.6 L1 radiosignal spectrum

Main lobe of L1 signal transmitted by SDCM geostationary satellites will

occupy the bandwidth of 2,046 MHz.

5.2.7 Doppler shift

The Doppler shift of L1 carrier received by stationary user from a SDCM

geostationary satellite, is caused by the satellite motion which in the worst case (end

of life) will be less than 40 meters per second relative to the user and, respectively,

Doppler shift will be less than 210 Hz.

5.2.8 Polarization

L1 signal transmitted by SDCM geostationary satellites will be right-hand

circularly polarized. The ellipticity will be no worse than 2 dB for the angular range

of 9,1 from boresight.

5.2.9 User received signal levels

The power level of the received L1 С/А signal from SDCM geostationary

satellite with the radiated power of 43 3 W, at the output of a 0dBi right-hand

circular polarized antenna will be greater than -158,5 dBW for elevation angle of 5O

or more. The maximum received power level will be greater than -155 dBW in such

an antenna.

Power level response of the received L1 С/А signal for nominal radiated power

and the antenna gain 1 depending from the elevation angle is showed in Table 2 for

ground-based users of north and south latitudes across the meridian of SDCM

geostationary satellite position.



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Table 2. L1 power level response depending from the elevation angle of

geostationary satellite provided that the user and satellite positions have the same

meridian

Elevation angle

(degrees)

Power level

(dBW)

5 -157,0

15 -156,7

25 -156,5

35 -156,3

45 -156,1

55 -156,1

65 -156,1

75 -156,2

85 -156,6

90 -156,9

85 -157,1

75 -157,7

65 -158,5

55 -159,4

45 -160,3

35 -161,1

25 -161,8

15 -162,3

5 -162,7

Estimated coverages of SDCM geostationary satellites are showed in Figure 3.

Gro

un

d-b

ased

use

r in

sou

th l

atit

ud

es

Gro

un

d-b

ased

use

r in

no

rth

lat

itu

des



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Figure 3. Estimated coverages of SDCM geostationary satellites

Edge of coverage is determined by signal level (not less than -158,5 dBW) and

by elevation angle.

5.2.10 Correlation loss

Correlation loss of L1 signal resulting from modulation imperfections and

filtering of inside the satellite will be less than1 dB.

5.3 C/A codes in L1 SDCM signal

5.3.1 Requirements

C/A codes used in L1 SDCM signal will belong to the family of 1023-bit Gold

codes.

5.3.2 C/A codes generation

C/A codes are Gold codes generated by Modulo-2 addition of two 1023 bit

pseudo-random sequences, G1 and G2 generated by two 10 trigger resistors having



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different feedbacks (see Figures 4 and 5): for G1 from triggers 3 and 10; for G2 from

triggers 2, 3, 6, 8, 9, 10.

C/A codes are identified in three ways:

1) PRN number;

2) G2 delay in chips (see Figure 4);

3) Initial G2 state (see Figure 5).

5.3.3 SDCM C/A codes

SDCM uses 3 allowable С/А codes with numbers 125, 140 and 141. Table 3

shows G2 delay figures for given codes (code delay).

Figure 4. Programmable G2 delay



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Figure 5. Programmable initial G2 state

Table 3. Allowable SDCM С/А codes

PRN G2 delay

(chips) Initial G2 state First 10 SDCM chips

125 235 1076 0701

140 456 1653 0124

141 499 1411 0366

Comment. Initial G2 state and first 10 chips of SDCM are written in the

following way: first left figure is 0 or 1 for the first chip, next three figures in octal

counting system present other 9 chips. First 10 chips of SDCM are inverse to initial

G2 state and also presented in octal counting system.



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5.4 Convolutional encoding of transmitted digital data

In L1 signal transmitted by a geostationary satellite, digital data transmitted at

a rate of 250 bit per second are continuously convolutional encoded at a code rate of

500 symbols per second.

Figure 6 shows convolutional encoding.

Figure 6. Convolutional encoding

Comment. In the first part of each bit output switch of the convolutional

encoder is fixed in the lower (1) position.

Data Input

250 BPS

Output symbols 500 SPS

1

2



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6 SDCM data format

6.1 General format information

All SDCM messages are transmitted in blocks by 250 bits (Figure 7): 8

bits – preamble, 6 bits – Message Type, 212 bits – data field, 24 bits – Cyclic

Redundancy Check (CRC) for error detection in the data field.

Direction of data flow from satellite . Most significant bit (MSB) transmitted first

250 Bits – 1 Second

8-Bit Preamble 24-Bits Parity

6-Bit Message Type Iidentifier

212-bit Data Field

Figure 7. Data block format

6.2 Preamble

The distributed preamble will be a 24-bit unique word, distributed over three

successive blocks. These three 8-bit words will be made up of the sequence of bits -

01010011, 10011010, 11000110.

6.3 Message type identifier

Message type identifier consists of 6 binary symbols and defines 64 message

types (0…63), as Table 4 shows. Message type identifier is transmitted by most

significant bit ahead.

Table 4 shows SDCM messages transmitted by geostationary satellites. These

data are transmitted in 250-bit blocks. Each block starts with 8-bit heading

(preamble), then 6-bit message type follows defining the type (or number) of the



25

message. Data field length is 212 bits. At the end of each block 24 parity bits go

allowing checking the validity of received data and in some cases restore the data.

Table 4. SDCM message types

Type Contents

0 Don’t use for safety applications (for SDCM testing)

1 PRN Mask assignments

2–5 SDCM fast corrections

6 GNSS/SDCM integrity information

7 Fast correction degradation factor

8 Reserved for future messages

9 GEO navigation message

10 Degradation parameters (of fast and long-term corrections, ionospheric

delays)

11 Reserved for future messages

12 SDCM network time /UTC offset Parameters

13 to16 Reserved for future messages

17 GEO satellite almanac

18 Ionospheric grid point masks

19 to 23 Reserved for future messages

24 Mixed fast corrections /long-term satellite error corrections

25 Long-term satellite error corrections

26 Ionospheric delay corrections

27 SDCM Service Message

28 Clock-Ephemeris Covariation Matrix Message

29–61 Reserved for future messages

62 Internal Test Message

63 Null message

Above messages are transmitted with different frequency which depends on

information validity time or message urgency. For instance, if uncertainty of any

SDCM GEO satellite is detected, Message Type 0 with respective PRN code is

transmitted immediately. Table 5 shows data update intervasl and aging time within

which different SDCM data can be used.



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Table 5. Time intervals of SDCM messages

Data Message type

Maximum data

update interval

(seconds)

Data aging

time

(seconds)

Testing 0 6 –

PRN mask 1 60 –

Fast corrections 2-5, 24 60 18 *

Long-term

corrections 24, 25 120 360

GEO data 9 120 360

Modification of

parameters 7,10 120 360

Ionospheric

mask 18 300

Ionospheric

corrections 26 300 600

UTC data 12 300 –

Almanac 17 300 –

* For fast corrections aging time is given taking into account additional

transmission of respective data in Message Type 7.

6.4 Data field

Data field comprises 212 binary symbols (bits). Each parameter in the Data

field is transmitted by most significant bit ahead. Structure of digital data in the Data

field and transmitted parameters are defined by a message type to be transmitted and

presented below.

6.5 Messages and Relationship between Message Types

To associate data in different message types, a number of issue of data (IOD)

parameters are used. These parameters include:

GPS IODClock (IODCk) and GPS IODEphemeris (IODEk) indicate

GPS clock and ephemeris issue of data, where k = satellite;



27

GLONASS Data (IODGk) – indicate GLONASS clock and ephemeris

issue of data, where k = satellite;

IOD PRN Mask (IODP) identifies the current PRN mask

IOD Fast Corrections j (IODFj) identifies the current fast corrections,

where j = fast corrections Message Type (Types 2-5);

IOD Ionospheric Grid Point Mask (IODI) – identifies the current

Ionospheric Grid Point Mask;

IOD Service Message (IODS) – identifies the current Service Message

(s) Type 27.

The relationship among the messages is shown in Figure 9.

6.6 Data field M(x)

Data field M(x) of a GEO message (226 bits) is formed by 8-bit preamble, 6-

bit message type identifier and 212-bit data field. Binary bits are arranged in the same

order as transmitted from SDCM satellite, so as to make m1 correspond to the first

transmitted bit of preamble and m226 to the 212 bit of data field.

CRC-code including r bits is arranged so as to make r1 the first transmitted bit

and r24 – the last the first transmitted bit.

6.7 Cyclic Redundancy Check

In each block of transmitted digital data of 250 bits long the last 24 bits are the

bits of Cyclic Redundancy Check (CRC) parity which permits detecting errors during

reception, without correction.

Bits of CRC parity in blocks of digital data are calculated as a remainder, R(x),

from Modulo 2 division of 2 binomials:

mod 2

kx M xQ x R x

G x,

k = 24 – number of redundancy bits in CRC;

M(x) – data field of binary symbols, im presented as the polynomial:



28

226226 225 224 0

1 2 226

1

i

i

i

M x m x m x m x m x

G(x) – code seed:

24 23 18 17 14 11 10 7 6 5 4 3 1G x x x x x x x x x x x x x x

Q(x) – quotient from division;

R(x) – remainder from division comprising control symbols ( ir ) of

cyclical redundancy code (CRC):

23 22 0

1 2 24

1

kk i

i

i

R x r x r x r x r x ; 24k .

Data field M x of 226 bits long is made up by 8-bit preamble, 6-bit message

type identifier and 212-bit data field. Binary bits are arranged in the same order as

transmitted from SDCM satellite, so as to make m1 correspond to the first transmitted

bit of the preamble and m226 to the 212 bit of data field.

CRC-code including r bits is arranged so as to make r1 the first transmitted bit

and r24 – the last transmitted bit.



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7 SDCM data content

7.1 SDCM testing mode (Message Type 0)

The first message type, Message Type 0, will be used during testing SDCM

system or a new satellite. The user can not use the signal of this satellite.

Message Type 0 (see Table 4) – is broadcasted by SDCM during testing phase

at the minimum rate of once per minute.

Message Type 0 informs the user that received data should not be used due to

possible degradation of accuracy and integrity. SDCM testing data will not be used

for safety navigation operations.

During testing phase SDCM can exclude certain message types out from the

list of messages and use null field of Message Type 0 for additional transmission of

fast corrections substituting data field of Message Type 2 for null field of Message

Type 0 (see Table 4).

7.2 PRN Mask Assignments (Message Type 1)

In the form of PRN Mask this message contain the information about all

satellites for which SDCM transmits corrections. It consists of 210-ordered slots

following one after another. Table 6 shows data description of this message.

The length of PRN Mask is nominally restricted by 210 slots but permits

message transmission from 1 to a maximum of 51 satellites from the list presented in

Table 6.



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Table 6. SDCM: Message Type 1

PRN Slot Assignment

1-37 GPS/GPS Reserved PRN

38-61 GLONASS (GLONASS Slot Number plus 37)

62-119 Future GNSS (Galileo)

120-138 GEO/SBAS PRN

139-210 Future GNSS / GEO /SBAS/Pseudosatellites

The field of Message Type 1 is made up as follows (see Figure 8).

Direction of data flow from satellite; Most significant bit (MSB) transmitted first250 bits - 1 second

6-Bit Message Type Identifier ()

8-Bit Preamble

24-Bit

Parity

PRN Mask field for indicating satellites (210 Bits)

IODP (2 Bits)

Figure 8. Structure of Message Type 1 – the list of satellites for which digital

data are transmitted

Preamble, message type identifier and 24 parity bits are defined above

(Sections 6.2, 6.3, 6.7). Issue of Data (IODP) fix transmitted digital data to the

number of the satellite in the list of used satellites. IODP definition is given in Annex

B “Basic principles of integrity”.

Binary bits are arranged in the same order as transmitted from SDCM satellite,

so as to make m1 correspond to the first transmitted bit of preamble and m226 to the

212 bit of data field.

The field of PRN Mask in Message Type 1 indicates for which satellites digital

data are transmitted and determines the list of satellites for which corrections are

transmitted.



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Comment. The first transmitted bit of PRN Mask corresponds to PRN-code

number 1 (definition of the term «the number of PRN-code» is given below).

Code rule for 210 bits in PRN Mask:

0 – data do not exist;

1 – data exist.

In SBAS standard mentioned parameters are transmitted in the following

messages:

– the list of satellites comprises 210 bits in Message Type 1;

– the number of satellite in the list – in messages 24, 25 and 28;

– the number of PRN-code – in message Type 17;

– Issue of data (IODP) in Messages Type 1, 2, 3, 4, 5, 7, 24, 25 and 28.

For satellite identification in SBAS standard the term «the number of PRN-

code» of the satellite is used which unambiguously identify each satellite and its

belonging to systems, as Table 5 shows. The number of PRN-code is formed from the

code of PRN Mask and is equal to the number 1 in the code of PRN Mask.

The list of satellites (PRN Mask): this is 210-ordered position binary code for

definition of those satellite numbers for which SDCM transmits corrections in the

SBAS format. Each of 210 code bits shows whether the satellite having the number

equal to this bit is included in the list or not. For instance, if the bit having the

number 5 is equal to 1, it means that for the satellite with PRN 5 corrections are

generated and transmitted in the current portion of digital data. If the bit is equal to 0,

it means that for the satellite corrections are not transmitted in the current stream of

digital data (but SDCM can transmit these data in digital data flow from another GEO

satellite). Due to restrictions to permissible update time in the SBAS channel each

digital data flow can transmit data maximum for 51 satellites (from 210 satellites

given in Table 7).



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Table 7. PRN Slots applicability to systems

PRN Slot Belonging to a system

0 No satellite

1 – 37 GPS

38 – 61 GLONASS Slot Number plus 37

62 – 119 Not reserved

120 – 138 (158)* , including

125, 140, 141

SBAS including

GEO – SDCM

139 (159) – 210 Not reserved

* Comment. Currently authorized international organizations are in the process

of resolving the issue of enhancing the number of SBAS codes from 19 to 39. After

the decision has been approved SBAS PRN Slots will reserve the numbers 120 – 158.

Figure 9 shows the principle of generating actual numbers of satellite PRN

Slots and defining sequence order of data included in digital data with use of PRN

Mask Slot. The numbers of the satellites not taken into account are indicated as

«empty».

Table 8 shows the structure of Message Type 1 fields (PRN Mask and IODP)

Figure 9. Principle of generating the PRN Mask assignments.

Table 8. Structure of message 1 fields (PRN Mask and IODP)

Field contents Bits Numbers Resolution

For each of 210 bits of

PRN Mask

Mask values:

1 0 or 1

1

IODP: 2 0–3 1



33

7.3 GEO Navigation Message (Message Type 9)

GEO Navigation Message Type 9 comprises ephemeris and time corrections of

a SDCM satellite. SDCM transmits this message in order to provide compatibility

with WAAS navigation equipment produced previously, it is used only for satellite

signal search but not for navigation measurements.

Figure 10 shows the structure of Message Type 9. Table 9 shows Type 9 GEO

Navigation Message parameters. Following symbols used in Figure 10 and Table 9:

Direction of data flow from satellite; Most significant bit (MSB) transmitted first

250 bits - 1 second

8-Bit Preamble

6-Bit Message Type

Identifier ()

Spare (8 Bits)

XG YG ZG GX GY GZ GX GY GZ aGf0 aGf1

t0,GEO

URA

24-Bit

control

Figure10. Structure of Type 9 GEO Navigation Message

t0,GEO – data lock-on time for the range function of a GEO satellite expressed

as the time interval from the midnight of current day.

GGG ZYX – GEO satellite coordinates at t0,GEO.

GGG ZYX – GEO satellite velocity at t0,GEO.

GGG ZYX – GEO satellite acceleration at t0,GEO.

aGf0 – GEO satellite onboard time scale offset relative to the SDCM network

time (SNT), at t0,GEO.

aGf1 – drift rate of GEO satellite onboard time scale relative to SNT.

User Range Accuracy (URA) –Root-mean-square user range error without

taking into account atmosphere effects.



34

Table 9. Navigation Message Type 9

Parameter

No. of

Bits Effective Range

Resolution

Not reserved 8 –– ––

t0,GEO 13 0–86 384 sec 16 sec

URA 4 (see the Comment) ––

XG 30 42 949 673 m 0,08 m

YG 30 42 949 673 m 0,08 m

ZG 25 6 710 886,4 m 0,4 m

17 40,96 m/sec 0,000625 m/sec

17 40,96 m/sec 0,000625 m/sec

18 524,288 m/sec 0,004 m/sec

10 0,0064 m/sec 2 0,0000125 m/sec

2

10 0,0064 m/sec 2 0,0000125 m/sec

2

10 0,032 m/sec 2 0,0000625 m/sec

2

aGf0 12 0,9537 10-6

sec 231

sec

aGf1 8 1,1642 10-10

sec

/ sec

240

sec / sec

Comment. According to the SBAS standard, if URA is equal to 15, range

signal of the satellite can not be used. SDCM does not provide pseudorange

measurements to GEO satellite, therefore in order to provide compatibility with the

equipment produced earlier, URA is defined in SDCM ICD as a constant equal to 15.

7.4 GEO Almanac Message Type 17

Almanac for three satellites will be broadcast in the GEOs Almanac Message

Type 17. These messages will be repeated to include all GEOs. Unused almanacs will

have a PRN number of 0 and should be ignored.

Almanac comprises information about satellite health and state and service

provider ID ensuring uplinking with GEO satellite. Table 10 Service Provider IDs.

GX

GY

GZ

GX

GY

GZ



35

Table 10. Service Provider IDs.

ID Service Provider

0 WAAS

1 EGNOS

2 MSAS

3 GAGAN

4 SDCM

5-15 Reserved

Almanac information including status (transmitted parameters) of each GEO is

transmitted by Message Type 17.

Figure 11 shows the structure of Message Type 17 (with additional information

- Figure 12). Message Type 17 permits transmitting data for 3 GEOs simultaneously.

Satellite identification is effected by a PRN number.

Figure 11. Type 17 GEO Almanac Message Format

Figure 12. Information interpretation for one satellite



36

Comment.

1. The field «Data identifier» in Message Type 17 is always «002».

2. In order to provide compatibility with navigation equipment produced earlier,

the fields of coordinates components and satellite velocity are kept.

Preamble, message type identifier, parity field and PRN number field are

defined above (Sections 6.2, 6.3, 6.7, 7.2).

Table 11 Health and status bits.

Table 11. Health and status bits of a GEO («0» – data transmitted; «1» – data not

transmitted)

Bit 0 (LSB) Ranging –– 1

Bit 1 Accurate corrections 0 1

Bit 2 Broadcast Integrity 0 1

Bit 3 Not reserved –– ––

Bits 4 – 7 Service Provider ID See Table 11

Comment.

SDCM does not provide pseudorange measurements to GEO satellite, therefore

the bit 0 (LSB) is always equal to «1».

Table 12 shows Service provider IDs (establishing belonging of the transmitter

in SBAS coding)

Table 12. Service Provider ID (in SBAS coding)

Identifier Digital data provider

0 WAAS

1 EGNOS

2 MSAS

3 GAGAN

4 SDCM

5–13 Not reserved

14–15 Reserved



37

7.5 Long-term and mixed satellite error corrections (Message Types 24 and

25)

Messages Type 24 and 25 will be broadcast to provide error estimates for slow

varying satellites ephemeris and clock errors. These long-term corrections are mot

applied for GEOs. Instead, the Type 9 GEO Navigation Message will be updated as

required to prevent slow varying GEO satellite errors.

Message Type 24 as well contains information about fast corrections.

Long-term corrections are differential corrections to GEO navigation

ephemeris and clock errors for which update interval shall not exceed 120 sec.

Mixed corrections are the message of SDCM comprising long-term as well as

fast corrections simultaneously (see Section 0) to ephemeris and clock of a navigation

satellite.

Preamble, message type identifier, parity field and PRN number field are

defined above (Sections 6.2, 6.3, 6.7, 7.2).

The structure of Message Type 25 comprising long-term corrections depends

on whether corrections rates-of-change are transmitted or not (in case of their quick

change between received messages). Specific format of transmitted message is

defined in accordance with the code figure in the field “Velocity code”.

Code rule for the field «Velocity code » (1 bit):

0 – corrections ix , iy , iz , , 1i fa are not transmitted (Figure 13 shows the

format of Message Type 25);

1 – corrections ix , iy , iz , , 1i fa are transmitted (Figure 14 shows the

format of Message Type 25).

The following symbols are used when describing Type 24 and 25 Message

formats:

ix – correction to ephemeris for i-satellite along x-axis ;

iy – correction to ephemeris for i-satellite along y-axis;

iz – correction to ephemeris for i-satellite along z-axis;



38

, 0i fa – clock correction for i-satellite;

ix – correction to ephemeris (velocity) for i-satellite along x-axis;

iyδ – correction to ephemeris (velocity) for i-satellite along y-axis;

izδ – correction to ephemeris (velocity) for i-satellite along z-axis;

, 1i fa – frequency correction for i-satellite;

,i LTt – time from the midnight of current day until the user has received the

parameters: , 0, , , , , , и ,i i i i f i i i iflx y z a x y z a in seconds;

t0 – reference time transmitted in Message Types 24-25 provided that the

velocity code is equal to 1.

Figure 13 shows Type 25 Message format for the velocity code equal to 0,

Figure 14 – for the velocity code equal to 1.

Figure 15 shows Type 24 Message format comprising fast and long-term

corrections.


250 Bits - 1 secondVelocity code = 0

IODi (8 Bits)

PRN mask

number

6-Bit Message type identifier

8-Bit Preamble

24-Bits

parity

IODP (2 Bits)

X ZY 0faX Y Z 0fa S

Second half of message

(Data for SC №3 and SC №4)

S = Spare

Data for SC №1Data for SC №2

Figure 13. Type 25 Message format (the velocity code = 0)



39


250 Bits - 1 second

Velocity code = 1

IODi (8 Bits)

PRN mask number IODP (2 Bits)

X ZY 0faX Y Z 1fa

Second half of message

(Data for SC №2)

24-Bits parity


8-Bit Preamble

t0

Data for SC №1

Figure 14. Type 25 Message format (the velocity code = 0 – corrections rate-

of-change are transmitted) – long-term corrections (maximum for 2 satellites).


250 Bits - 1 second

Block identifier (2 Bits)

Fast corrections FCi

(for 6 satellites, by 12 Bits)IODP (2 Bits)

106-bit long-term satellite error

correction Half Message Type 25

6 4 Bit UDREIs

S

IODF (2 Bits)

S – Spare (4 Bits)

8-Bit Preamble


24-Bits parity

Figure 15. Type 24 Message format – mixed (fast and long-term) corrections

Basic provisions of the present standard concerning the transmission of fast

and long-term corrections are the following:

1) long-term corrections to ephemeris for GLONASS and GPS systems are

transmitted: for GLONASS – in PZ-90.02, for GPS – in WGS-84;

2) The following rules are established for long-term corrections.

Issue of data (IODi): factor connecting long-term corrections for i-th satellite

with ephemeris transmitted by this satellite. It is used differently for GLONASS and

GPS.

For GLONASS IODi defines the time period within which GLONASS data

will be used together with SDCM data. This information is included in its two

subfields as shown in Table 13.



40

Table 13. IODi contents for GLONASS satellites

Operation time (V): the time period within which GLONASS ephemeris data

are used (coding step is 30 seconds).

Delay time (L): the time interval starting from the last GLONASS ephemeris

update to the predicted time of receiving the long-term correction by the user

Table 14. Operation time V and delay time L

For GLONASS satellites the user can use long-term corrections only if the time

of receiving last GLONASS ephemeris tr and the time of receiving the long-term

correction by the user tLT meet the following condition:

.LT r LTt L V t t L

For GPS satellites long-term corrections only can be used provided that IODi in

received SDCM corrections coincide with IODE in received GPS ephemeris and with

8 LSB of IODC.

Table 15 shows Type 24 Message format and the effective range within which

its parameters may vary.

Table 16 shows Type 25 Message format and the effective range within which

its parameters may vary for velocity code 0 and Table 17 - for velocity code 1.

5 LSB IODi: identifier V 3 MSB IODi : identifier L

Operation time (see Table 14) Delay time (see Table 14)

Data Bits used Values used Resolution

Operation time (V) 5 30 – 960 sec 30 sec

Delay time (L) 3 0 – 120 sec 30 sec



41

Table 15. Type 24 Mixed fast correction/long-term satellite error corrections message

format

Parameter Bits Effective Range Resolution

Fast corrections (FCi)

(for six satellites) 12 256,000 m 0,125 m

User Differential Range

Error UDREIi

(for six satellites)

4 (see Table 19) (see Table 19)

IODP 2 0–3 1

Fast correction type

identifier 2 0–3 1

IODFj 2 0–3 1

Not reserved 4 — —

Half Message Type 25 106 — —

Table 16. Type 25 long-term satellite error corrections message format (velocity

code = 0)

Parameter Bits Effective

Range Resolution

Velocity code = 0 1 0 1

For two satellites:

PRN musk number 6 0–51 1

Issue of data (IODi) 8 0–255 1

xi 9 ±32 m 0,125 m

yi 9 ±32 m 0,125 m

zi 9 ±32 m 0,125 m

ai,f0 10 ±2–22

sec 2–31

sec

IODP 2 0–3 1




42

Table 17. Type 25 long-term satellite error corrections (velocity code = 1)

Parameter Bits Effective

Range Resolution

For one satellite

Velocity code = 1 1 1 1

PRN musk number 6 0–51 1

Issue of data (IODi) 8 0–255 1

xi 11 ±128 m 0,125 m

yi 11 ±128 m 0,125 m

zi 11 ±128 m 0,125 m

ai,f0 11 ±2–21

sec 2–31

sec

8 ±0,0625

m/sec 2

–11 m/sec

8 ±0,0625

m/sec 2

–11 m/sec

8 ±0,0625

m/sec 2

–11 m/sec

ai,f1 8 ±2–32

sec/sec 2–39

sec/sec

Reference time (t0) 13 0–86 384 sec 16 sec

IODP 2 0–3 1

7.6 Fast corrections Message Types 2-5

Fast corrections contains the information about correction of measured ranges

to navigation satellites. The correction is used as the following expression:

PR t PR t PRC t RRC t tcorrected measured f of of( ) ( ) ( ) ( ),

where:

PRmeasured – measured range to a satellite

PRCf – correction included in Message Types 2-5

t – current time

tof – reference time or time of applicability of the most recent fast correction

( )current previous

of

PRC PRCRRC t

t ,

ixδ

izδ iyδ



43

t = (tof – tof,previous).

This correction permits compensating fast errors when measuring range to a

satellite which arise due to inaccurate predictions of satellite onboard clock offset.

Fast correction also permits compensating errors introduced by selective availability.

Apart from corrections SDCM Message Types 2-5 contain accuracy data –

UDRE (User Differential Range Error), which permits to the user to define

navigation accuracy.

SDCM Message Type 2 contains the data sets for the first 13 satellites

designated in the PRN mask, SDCM Message Type 3 – for satellites 14-26, SDCM

Message Type 4 – for satellites 27-39, SDCM Message Type 5 – for satellites 40-51.

Fast correction (FCi) is a correction for fast errors (clocks) of a satellite which

is added to the measured pseudorange of i-th satellite. In order to transmit fast

corrections for the 51-st satellite 4 types of messages are used in sequence:

Message Type 2 contains the data sets for the first 13 satellites designated in

the PRN mask (13 satellites);

Message Type 3 contains the data sets for satellites 14 - 26 designated in the

PRN mask (13 satellites);

Message Type 4 contains the data sets for satellites 27 - 39 designated in the

PRN mask (13 satellites);

Message Type 5 – contains the data sets for satellites 40 - 51 designated in the

PRN mask (12 satellites).

Types 2-5 fast satellite error corrections formats are identical and given in

Figure 16.



44


250 Bits - 1 second

Fast corrections FC for 13 (12) satellites (by 12 Bits) – seе Table 11


8-Bit Preamble

24-Bits parityIODP (2 Bits)

IODF-j (2Bits)

FC

UDREI errors for 13 (12) satellites (by 12 Bits) – see Table 11

Figure 16. Types 2-5 fast satellite error corrections

Preamble, message type identifier and parity field are defined above (Sections

6.2, 6.3, 6.7).

Fast correction IODFj.

In Messages Type 2, 3, 4 and 5, IODFj is designated respectively IODF2,

IODF3, IODF4 and IODF5. Each 2-bit IODFj sequentially receives the values 010, 110,

210 and 310. When there is no alert condition for any of the satellites in a message

type, sequential change of codes in IODF2, IODF3, IODF4 and IODF5 (each code

sequentially takes on a value: 010, 110 and 210) provides the connection of digital data

from messages type 2-5 with data from Message Type 6 – synchronization method is

presented in Annex B. integrity principles. However, in the case of accuracy

degradation of differential corrections of one or several satellites (digital data for

them are transmitted in Messages Type 2-5, 24), Message Type 6 is also transmitted,

in which the respective value of IODFj; j [2…5] is equal to 3. Code IODFj = 310

indicates that for one or several satellites from the Message Type j the error уi2,UDRE is

sharply risen. Relationship of IODF2, IODF3, IODF4 and IODF5 and satellite numbers

is given in Section 7.7 below.

Table 18. Message Types 2-5 – fast corrections


IODFj 2 0–3 1

IODP 2 0–3 1

For 13 satellites (or 12 satellites in Message type 5):



45


Fast correction (FCi) 12 256,000 m 0,125 m

UDREIi 4 (see Table 19) (see Table 19)

7.7 Integrity parameters of fast and long-term corrections (Message Type 6)

This Message contains range accuracy data – UDRE. Apart from this, Message

Type 6 contains information permitting to define the integrity of all data. When a new

satellite becomes available, Message Type 6 reflects this information.

The value of UDREIi indicating the integrity of fast and long-term corrections

delivered to the user is defined on the basis of Root-mean-square residual errors for i-

th satellite (σi,UDRE) as Table 19 shows.

Dispersion (σ2i,UDRE) of the residual errors file of the satellite (satellite clock

and ephemeris) is defined by pseudorange error after the user has applied fast and

long-term corrections (not taking into account ionosphere corrections). Residual error

is used by the user when assessing integrity parameters, in particular in horizontal

and vertical protection levels evaluations.

Table 19. Evaluation of UDREIi

UDREIi i2,UDRE

0 0,0520 m2

1 0,0924 m2

2 0,1444 m2

3 0,2830 m2

4 0,4678 m2

5 0,8315 m2

6 1,2992 m2

7 1,8709 m2

8 2,5465 m2

9 3,3260 m2

10 5,1968 m2

11 20,7870 m2

12 230,9661 m2

13 2 078,695 m2

14 Not monitored

15 Do not use



46

Timeliness of UDREIi delivery provides the reliability of navigation for the

user. Therefore these parameters in addition to the Message Type 6 are also

transmitted with fast corrections (in Messages Type 2-5 and 24).

Figure 17 shows Type 6 Message format comprising integrity parameters.


250 Bits - 1 second

UDREI parameters for 51 satellites (by 4 Bitsт)


8-Bit Preamble

24-Bits parityBlock of parameters: IODF2, IODF3, IODF4, IODF5 (by 2 Bits)

IODF (2 Bits)

Figure 17. Type 6 Message format

Preamble, message identifier and parity field are defined above (Sections 6.2,

6.3, 6.7).

UDREIi definition is given above.

IODFj, apart from standard synchronization functions when changing data in

the channel (for this purpose sequential values of IODF equal to 0, 1 and 2 are used

in the manner described in Annex B “Basic integrity principles”), may also be used

for urgent informing the user about the failure of integrity included into the respective

group: for this purpose the value of IODF equal to 3 is used. The following

relationship is taken:

IODF2 = 3 – the failure of integrity for satellites 1 … 13,



IODF5 = 3 – the failure of integrity for satellites 40 … 51.

The satellite in which integrity is failed is defined after UDREIi parameters

have been received and analyzed completely from Message Type 6.

Table 20 shows Type 6 integrity message content.



47

Table 20. Type 6 integrity message content


IODF2 2 0–3 1

IODF3 2 0–3 1

IODF4 2 0–3 1

IODF5 2 0–3 1

UDREIi 4 (See Table 19) (See Table 19)

7.8 Ionosphere Grid Point Masks Message Type 18

Message Type 18 simultaneously with Message Type 26 (see Section 7.9),

permits calculating ionosphere propagation delay (at L1) of a navigation satellite and

its accuracy.

Corrections to user equipment pseudoranges (corrections compensating

navigation signal delays in ionosphere) according to the SBAS standard are

transmitted as two parameters: vertical delay and conditional digital codes-indicators

GIVEIi, unambiguously connected with dispersion of vertical ionosphere delay

assessments (see Table 23). These parameters are defined in Ionospheric Grid Point

locations and give the assessment of L1 (1575,42 MHz) vertical ionosphere delay for

the case of signal vertical pass through this location. Using these data the user shall,

according to the methodology described in SDCM ICD, interpolate SBAS message

vertical delay from nearest grid points to the slant delay for the line of sight of

operating satellite.

Aggregate of points on the Earth surface for which zenith (vertical)

ionosphere delays are calculated is designated as IGP – Ionospheric Grid Point.

IGP parameters are defined as follows. The predicated IGPs are contained in

11 bands (numbered 0 to 10):

Bands 0 – 8 are vertical bands on a Mercator projection map, covering the

Equator and middle latitudes;

Bands 9 – 10 are horizontal bands on a Mercator projection map, higher south

and north polar latitudes.



48

IGP location coordinates are indicated in Table 18. General spacing of 1808

IGP points for all 11 IGP bands is showed in Figure 18.

Figure 18. Predefined Global IGP Grid

For each indicated IGP point, IGP Band Mask in Message Type 18

defines if there are data about respective point delay in Message Types 26.

Coordination rule:

0 – no data;

1 – data exist.

The number of IGP Band Mask is equal to the maximum number of IGP points

within one band and, according to Table 21, is equal to 201 bits.

Table 21. Ionospheric mask bands

Coordinates of IGP points

Bits in Mask Longitu

de Latitudes for all band points:

1 2 3

Band 0



49




1 2 3

180 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N,

85N

1–28

175 W 55S, 50S, 45S, ..., 45N, 50N, 55N 29–51

170 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 52–78

165 W 55S, 50S, 45S, ..., 45N, 50N, 55N 79–101

160 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 102–128

155 W 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151

150 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178

145 W 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201

Band 1

140 W 85S, 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N,

75N

1–28

135 W 55S, 50S, 45S, ..., 45N, 50N, 55N 29–51

130 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 52–78

125 W 55S, 50S, 45S, ..., 45N, 50N, 55N 79–101

120 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 102–128

115 W 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151

110 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178

105 W 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201

Band 2

100 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27

95 W 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50

90 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N,

85N

51–78

85 W 55S, 50S, 45S, ..., 45N, 50N, 55N 79–101

80 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 102–128

75 W 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151

70 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178

65 W 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201

Band 3

60 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27

55 W 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50

50 W 85S, 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N,

75N

51–78

45 W 55S, 50S, 45S, ..., 45N, 50N, 55N 79–101

40 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 102–128

35 W 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151

30 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178



50




1 2 3

25 W 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201

Band 4

20 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27

15 W 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50

10 W 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 51–77

5 W 55S, 50S, 45S, ..., 45N, 50N, 55N 78–100

0 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N,

85N

101–128

5 E 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151

10 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178

15 E 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201

Band 5

20 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27

25 E 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50

30 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 51–77

35 E 55S, 50S, 45S, ..., 45N, 50N, 55N 78–100

40 E 85S, 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N,

75N

101–128

45 E 55S, 50S, 45S, ..., 45N, 50N, 55N 129–151

50 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 152–178

55 E 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201

Band 6

60 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27

65 E 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50

70 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 51–77

75 E 55S, 50S, 45S, ..., 45N, 50N, 55N 78–100

80 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 101–127

85 E 55S, 50S, 45S, ..., 45N, 50N, 55N 128–150

90 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N,

85N

151–178

95 E 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201

Band 7

100 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27

105 E 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50

110 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 51–77

115 E 55S, 50S, 45S, ..., 45N, 50N, 55N 78–100

120 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 101–127

125 E 55S, 50S, 45S, ..., 45N, 50N, 55N 128–150



51




1 2 3

130 E 85S, 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N,

75N

151–178

135 E 55S, 50S, 45S, ..., 45N, 50N, 55N 179–201

Band 8

140 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 1–27

145 E 55S, 50S, 45S, ..., 45N, 50N, 55N 28–50

150 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 51–77

155 E 55S, 50S, 45S, ..., 45N, 50N, 55N 78–100

160 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 101–127

165 E 55S, 50S, 45S, ..., 45N, 50N, 55N 128–150

170 E 75S, 65S, 55S, 50S, 45S, ..., 45N, 50N, 55N, 65N, 75N 151–177

175 E 55S, 50S, 45S, ..., 45N, 50N, 55N 178–200

1 2 3

Band 9

60 N 180W, 175W, 170W, …, 165E, 170E, 175E 1–72

65 N 180W, 170W, 160W, …, 150E, 160E, 170E 73–108

70 N 180W, 170W, 160W, …, 150E, 160E, 170E 109–144

75 N 180W, 170W, 160W, …, 150E, 160E, 170E 145–180

85 N 180W, 150W, 120W, … , 90E, 120E, 150E 181–192

Band 10

60 S 180W, 175W, 170W, …, 165E, 170E, 175E 1–72

65 S 180W, 170W, 160W, …, 150E, 160E, 170E 73–108

70 S 180W, 170W, 160W, …, 150E, 160E, 170E 109–144

75 S 180W, 170W, 160W, …, 150E, 160E, 170E 145–180

85 S 170W, 140W, 110W, …, 100E, 130E, 160E 181–192

In Message Types 26 data routing (affixment of transmitted delays to grid

points) is effected by indicating in a message the following features:

A band number, for which delays are transmitted. IGP points locations in bands

are defined in Table 21;

a block ID comprising 15 points inside a band. All initial sequence comprising

201 points is divided by groups of 15 sequential points called the block;



52

Transmission of delays for point inside the block strictly in such sequence in

which their respective «1» follow in IGP Band Mask (this identification scheme is

identical to the identification scheme described above – see Section 7.2).

Type 18 Message Format comprising IGP Band Mask data is given in Figure

19.

Preamble, message identifier and parity field are defined above (6.2, 6.3, 6.7).

250 Bits - 1 second

8-bit Preamble

24 Bits Parity

NO.of bands (4 Bits)

Band number (4 Bits)

IODI (2 Bits)

Spare Bit

201-bit Mask Field

6-Bit Message Type Identifier

Figure 19. Type 18 Message Format –IGP Band Mask.

Table 22 shows bits network of Message Type 18.

Table 22. Message Type 18 – IGP field

Parameter

No. of

Bits

Effective

Range Resolution

Number of bands being broadcast 4 0–11 1

Band Number 4 0–10 1

Issue of Data - Ionosphere (IODIk) 2 0–3 1

For 201 band points the following is transmitted:

IGP Mask 1 0 or 1 1

Spare 1 — —

7.9 Ionospheric Delay Corrections Messages Type 26

The Type 26 Ionospheric Delay Corrections Message provides the users with:

Vertical Pseudorange delay relative to an L1 signal (in meters);

Their accuracy 2

,i GIVE at geographically defined IGPs identified by band

number and IGP number in Table 21. The evaluation of the 2

,i GIVE is transmitted in



53

the form of 4-bit block ID GIVEIi unambiguously corrected with dispersion value (in

meters), as showed in Table 23.

Table 23. Evaluation of GIVEIi

GIVEIi 2

,i GIVEI Meters2

:

0 0,0084

1 0,0333

2 0,0749

3 0,1331

4 0,2079

5 0,2994

6 0,4075

7 0,5322

8 0,6735

9 0,8315

10 1,1974

11 1,8709

12 3,3260

13 20,787

14 187,0826

15 Not monitored

The data content of this message is given in Table 24 with a format presented

in Figure 20.


250 Bits - 1 second

Repeat for 14 more grid points

IGP Vertical delay (9 Bits)

Block ID (4 Bits)

Band Number (4 Bits)

IODI 24 Bits Parity

S – Spare (7 Bits)

2 15141312111098765

43 S

GIVEI (4 Bits)


8-Bit Preamble

1

Figure 20. Type 26 Ionosphere Delay Corrections Message Format

Preamble, message type identifier and parity field are defined above (Section

6.2, 6.3, 6.7).



54

Table 24. Ionospheric Delay Model Parameters for Message Type 26

Parameter

No. of

Bits Effective Range Resolution

Band Number 4 0–10 1

Block ID 4 0–13 1

For each of 15 grid points:

IGP Vertical Delay

Estimate

9 0–63,875 m 0,125 m

Grid Ionospheric Vertical

Error Indicator (GIVEIi)

4 (see Table 23) (see Table 23)

IODIk 2 0–3 1

Spare 7 — —

7.10 Degradation parameters (Messages Type 7 and 10)

Message Type 7 comprises information about fast corrections ageing time and

fast and long-term corrections change factor.

Message Type 10 transmits a set of additional data to be used for navigation

accuracy definition.

Degradation parameters define SDCM corrections ageing rate and required for

definition of validity period of transmitted data. Degradation parameters are

transmitted in two messages:

- Fast corrections degradation parameters are transmitted in Message Type 7;

- For all the others (ionosphere, long-term corrections) Message Type 10 is

used.

Figure 21 shows Type 7 message format.



55


250 Bits - 1 secondIODP (2 Bits)

51 4-Bit UDRE degradation factor indicators

1tSpare (2 Bits)

8-Bit Preamble

24- Bits Parity6-Bit Message Type Identifier

(4 Bits)

Figure 21. Type 7 Fast Correction Degradation Factor Message Format


6.2, 6.3, 6.7).

Specific data of Message Type 7 comprise:

a) System latency time (t1) – time interval between the start of correction

degradation (the time for which the correction is calculated) and the time of data

uplinking to SDCM channel (repeating delay is assumed zero);

b) Fast correction degradation factor indicators (aii) which are

unambiguously connected with corrections change rate (with degradation factor) and

defined according to Table 25.

Table 25. Fast corrections degradation factor

Fast Corrections Degradation

Factor Indicator iai

Fast Corrections Degradation Factor

ia , м/с2

ia

0 0,00000

1 0,00005

2 0,00009

3 0,00012

4 0,00015

5 0,00020

6 0,00030

7 0,00045

8 0,00060

9 0,00090



56

Fast Corrections Degradation

Factor Indicator iai

Fast Corrections Degradation Factor

ia , м/с2

ia

10 0,00150

11 0,00210

12 0,00270

13 0,00330

14 0,00460

15 0,00580

Table 26 shows Type 7 message contents.

Table 26. Fast Correction Degradation Factor

Parameter

No. of

Bits

Effective

Range Resolution

System latency (tl) 4 0–15 s 1 s

IODP 2 0–3 1

Spare 2 — —

For each of 51 satellites (according to PRN mask):

Degradation Factor Indicator

(aii) 4 (see Table 25) (see Table 25)

Figure 22 shows Type 10 message format comprising degradation parameters

of long-term corrections and ionosphere delays.

250 Bits - 1 second

8-Bit Preamble

24- Bits Parity


Brrc(10 Bits)

Cltc_lsb(10 Bits)

Cltc_v1(10 Bits)

Iltc_v1(9 Bits)

Cltc_v0(10 Bits)

Iltc_v0(9 Bits)

Cgeo_lsb(10 Bits)

Cgeo_v(10 Bits)

Igeo(9 Bits

Cer(6 Bits)

Ciono_step(10 Bits)

Iiono(9 Bits)

Ciono_ramp(10 Bits)

RSSUDRE(1 Bits)RSSiono(1

Bits)

Empty bits (81 Bits)

Figure 22. Type 10 Long-term Correction Degradation Factor Message Format



57


6.2, 6.3, 6.7).

Table 27 shows specific parameters transmitted in Message Type 10.

Table 27. Type 10 Degradation Factors

Parameter No. of Bits Effective Range Resolution

Brrc 10 0–2,046 m 0,002 m

Cltc_lsb 10 0–2,046 m 0,002 m

Cltc_v1 10 0–0,05115 m/sec 0,00005 m/sec

Iltc_v1 9 0–511 sec 1 sec

Cltc_v0 10 0–2,046 m 0,002 m

Iltc_v0 9 0–511 m 1 с

Cgeo_lsb 10 0–0,5115 m 0,0005 m

Cgeo_v 10 0–0,05115 m/sec 0,00005 m/ sec

Igeo 9 0–511 sec 1 sec

Cer 6 0–31,5 m 0,5 m

Ciono_step 10 0–1,023 m 0,001 m

Iiono 9 0–511 sec 1 sec

Ciono ramp 10 0–0,005115 m/ sec 0,000005 m/ sec

RSSUDRE 1 0 or 1 1

RSSiono 1 0 or 1 1

Ccovariance 7 0–12,7 0,1

Spare 81 — —

Where:

rrcB – parameter defining noise and approximation error ranges when

calculating correction to range rate of change.

_ltc lsbC – maximum approximation error defined by definition of transmitted

orbit and time data.

_ltc vlC – is the velocity error bound on the maximum range rate difference of

missed messages due to clock and orbit rate differences derived from Message Type

10

_ltc lsbI –long-term corrections update interval when rate code is equal to «1».



58

_ 0ltc vC – parameter defining discrepancy limits between two sequential long-

term corrections for satellites with rate code equal to «0».

_ 0ltc vI – minimum update interval for long-term messages when rate code is

equal to «0».

_GEO lsbC – not used in SDCM.

_GEO vC – not used in SDCM.

GEOI – not used in SDCM.

erC – residual error range connected with data use outside time interval.

_iono stepC – range of differences between sequential delays in ionosphere grid.

ionoI – minimum update interval for messages with ionosphere corrections.

_iono rampC – ionosphere corrections rate of change.

UDRERSS – indication of Root Mean Square addition for differences of fast and

long-term corrections.

The following code rule is used:

0 – correction differences are added linearly;

1 – correction differences squares are added under square root.

ionoRSS – indication of Root Mean Square addition for differences of ionosphere

corrections.

The following code rule is used:

0 – correction differences are added linearly;

1 – correction differences squares are added under square root.

covC – parameter used for compensation of discretization when Message Type

28 is applied.

Comments:

1. Parameters ai and tl, required for application of parameter are to be selected

from Message Type 7.

2. If Message Type 28 is not transmitted parameter covC is not applied.



59

7.11 SDCM Network Time/UTC/GLONASS Time Offset Parameters

Message Type 12

Message Type 12 comprises offset between GLONASS and GPS time scales.

Figure 23 shows Type 12 message format.

Figure 23. Type 12 Time Parameters Message Format


6.2, 6.3, 6.7).

Table 28 shows Type 12 message contents.

Table 28. SDCM Network Time/UTC Parameters

Parameter

No. Of


1SNTA 24 7,45 10–9

sec/sec 2–50

sec/sec

0SNTA 32 1 sec 2–30

sec

t0t 8 0–602 112 sec 4 096 sec

tWN 8 0–255 weeks 1 weeks

LSDT 8 128 sec 1 sec

LSFWN 8 0–255 weeks 1 weeks

DN 8 1–7 days 1 days

250 Bits - 1 second

8-Bit Preamble

24- Bits Parity


A1SNT

(24 Bits)

A0SNT

(32 Bits)

t0t (8 Бит)

WNt (8 Bits)

∆tLS (8 Bits)

WNLSF (8 Bits)

DN (8

Bits)

∆tLSF (8

Bits)

IUTS (3 Bits)

TOW (20 Бит)

WN (10

Bits)

IGLO (1 Bits)

δaGLONASS (32 Bits)

Spare (42 Bits)

DtLSF (8 Bits)



60

LSFDt 8 128 sec 1 sec

UTC standard Identifier 3 BIPM, NIST, USNO —

GPS Time-of-Week (TOW) 20 0–604 799 sec 1 sec

GPS Week Number (WN) 10 0–1 023 weeks 1 weeks

GLONASS Indicator 1 0 or1 1

GPS-GLONASS time offset

ai,GLONASS

32 2 10–30

sec 1 sec

Spare 42 — —

Parameters given in Table 25 are defined as follows:

1) UTC standard Identifier – indicates reference source of UTC as

defined in Table 29.

Table 29. UTC standard Identifier

UTC Identifier UTC standard

0 UTC as operated by the Communications Research

Laboratory (CRL), Tokyo, Japan

1 UTC as operated by the National Institute of Standards and

Technology (NIST), USA

2 UTC as operated by the U.S. Naval Observatory

3 UTC as operated by the International Bureau of Weights and

Measures (BIPM)

4 UTC as operated by the European Laboratory

5 UTC as operated by the TBD

6 Not reserved

7 UTC not provided

2) Time count in Time-of-Week (TOW): the number of seconds passed from

transition from previous to current GPS-week.

3) GLONASS Indicator: shows if GLONASS time parameters are transmitted

or not.

Code rule:

0 – GLONASS time parameters are not transmitted;

1 – GLONASS time parameters are transmitted.



61

4) Correction ai,GLONASS to GLONASS system time offset relative to GPS

system time: parameter indicating correction to offset between GLONASS and GPS

system time.

5) Parameters A1SNT, A0SNT, t0t, WNt, tLS, WNLSF, DN and tLSF are defined

according to UTC standard.

7.12 SDCM Service Message Type 27

Type 27 messages may be transmitted to increase the σUDRE values in selected

areas. This provides the user with the opportunity of more precise definition of

navigation service quality or the extent of location reliability of position vector. This

message may content the information about integral quality of all SDCM system.

The format of Message Type 27 is given in Figure 24 and Table 30.

250 Bits - 1 second

8-Bit Preamble

24- Bits Parity


IODS (3 Bits)

Number of service messages (3 Bits)

Service Message Number (3 Bits)

Number of regions (3 Bits)

Priority Code (2 Bits)

UDRE Indicator – inside (4 Bits)

UDRE Indicator - outside 4 Bits)

Spare (15 Bits)

Region 1

(35 Bits

Region 2

(35 Bits)

Region 3

(35 Bits)

Region4

(35 Bits)

Region5

(35 Bits)

Coordinate1 latitude (8

Bits)

Coordinate 2 latitude

(8 Bits)

Region data (35 Bits)

Coordinate2 longitude

(9 Bits)

Coordinate1 longitude

(9 Bits)

Region shape (1 Bit)

Figure 24. Service Message Type 27


6.2, 6.3, 6.7).

Table 30. Type 27 Service Message Parameters

Parameter No. of

Bits

Effective

Range Resolution

Issue of Data, Service (IODS) 3 0–7 1

Number of service messages 3 1–8 1

Service message number 3 1–8 1

Number of regions 3 0–5 1

Priority code 2 0–3 1



62

Parameter No. of

Bits

Effective

Range Resolution

UDRE Indicator - Inside 4 0–15 1

UDRE Indicator - Outside 4 0–15 1

For each of up to 5 regions:

Coordinate 1 (latitude) 8 90 1

Coordinate 1 (longitude) 9 180 1

Coordinate 1 (latitude) 8 90 1

Coordinate 1 (longitude) 9 180 1

Region Shape 1 — —

Spare 15 — —

The above parameters of Message Type 27 are defined as follows:

A. Issue of Data, Service (IODS): identification of data service from

different Messages Type 27;

B. Number of service messages: number of transmitted Messages Type 27

(value is transmitted with an offset to minus 1; the first transmitted message is zero);

C. Number of service message: message ID which defines present Message

Type 27 in the transmitted sequence of Message Type 27 (from 1 to quantity of

service messages coded with an offset to minus 1);

D. Number of regions: number of service regions for which coordinates are

transmitted in present Message Type 27;

E. Inside UDRE Indicator is a conventional code defining (according to

Table 28) the degradation factor ( UDRE) of regional parameter UDRE. This

conventional code is applicable only when positioning on the territory of regions

coordinates of which are defined in present Message Type 27;

F. Priority code: a code for definition of message priority in positions

belonging to two overlapping regions. Message with higher code has higher priority.

If priority codes are equal, message with lower UDRE has higher priority;

G. Outside indicator UDRE is a conventional code defining (according to

Table 31) the degradation factor ( UDRE) of regional parameter UDRE. This



63

conventional code is applicable only when positioning outside the territory of regions

defined in all current Message Type 27;

Table 31 – UDRE Indicator Evaluation

UDRE Indicator UDRE

0 1

1 1,1

2 1,25

3 1,5

4 2

5 3

6 4

7 5

8 6

9 8

10 10

11 20

12 30

13 40

14 50

15 100

H. Multifunctional coordinate 1 (latitude, longitude) {coordinate 2 (latitude,

longitude)}: latitude and longitude of angular point 1 {point 2} of region territory.

Used for definition of region borders which can be square and triangular;

I. Coding of Region Shape: 0 denotes a triangular region, 1 denotes a square

region.

Region borders are defined according to the rules:

- coordinate 3 has always the latitude of coordinate 1 and longitude of

coordinate 2;

- for definition of square region form coordinate 4 is required which has

always the latitude of coordinate 2 and longitude of coordinate 1;

- region border is formed by linking coordinates as 1-2-3-1 (triangle) or 1-2-3-

4-1 (square). The segments of border have either constant latitude or longitude, or



64

constant slant in latitude degrees into longitude degrees. Latitude or longitude

variation along any segment of border between two coordinates is less than 180о.

7.13 Clock-ephemeris Covariance Matrix Message Type 28

Message Type 28 may be broadcast to provide the relative covariance matrix

for clock and ephemeris errors. Message Type 28 provides increased availability

inside and increased integrity outside the service area of SDCM Wide Area

Differential System.

Elements of covariance matrix are used taking into account a user position for

definition of degradation factor ( UDRE) required for calculation of User

Differential Range Error (UDRE).

For compression of transmitted data in SBAS format clock-ephemeris

covariance matrix (С) is transmitted as a set of decomposition matrices: SF

coefficient of scale factor (SFi,j;),i,j = 1…4 and triangular matrix (Е4х4) of Cholesky

factorization:

C = (E∙SF)т ∙ E∙SF.

Cholesky factorization elements (Eij) are the elements of upper triangular

matrix (4х4) which together with scale factor matrix SF4х4 minimize digital data

content to be transmitted.

Figure 25 and Table 32 present the contents of the of Type 28 message

representing the Cholesky factor of the clock-ephemeris covariance matrix for two

PRN codes.



65


250 Bits - 1 secondIODP

Scale Exponent

1,1E 2,2E 2,3E3,3E 4,4E 1,2E 1,4E 2,4E 3,4EFirst satellite

PRN Mask Number24- Bits Parity


8-Bit Preamble

E Second satellite

Figure 25. Type 28 Clock-ephemeris Covariance Matrix Message Format.

Table 32. Type 28 Clock-ephemeris Covariance Matrix Message Parameters

Parameter

No. Of

Bits

Effective

Range Resolution

IODP 2 0–3 1

For each of two satellites:

PRN Mask No. 6 0–51 1

Scale exponent 3 0–7 1

E1,1 9 0–511 1

Е2,2 9 0–511 1

Е3,3 9 0–511 1

Е4,4 9 0–511 1

Е1,2 10 512 1

Е1,3 10 512 1

Е1,4 10 512 1

Е2,3 10 512 1

Е2,4 10 512 1

Е3,4 10 512 1


6.2, 6.3, 6.7).



66

7.14 Null Message Type 63 and Internal Test Message Type 62

The null Message Type 63 is used as a filter message if no other message is

available for broadcast for the one-second time slot. The Internal Test Message Type

62 is used for internal testing purposes. The user will continue to use the GEO

broadcast and ranging capabilities.



67

8 Annex А. Definitions of basic a priory and a posteriori parameters

for navigation user equipment accuracy assessment taking into account

SDCM data

The following parameters are assumed a priori for user positioning accuracy

assessment:

HAL (Horizontal Alert Limit) – horizontal circle radius (with the center

in the actual user position) meeting integrity requirement: all altitude

positioning reports are within the circle with probability of 1-10-7

[1/hour];1

VAL (Vertical Alert Limit) – half length of vertical distance (in the

actual user position) meeting integrity requirement: all altitude positioning

reports are within the interval {- VAL, + VAL } with probability of 1-10-

7 [1/hour];

1

For navigation user equipment accuracy evaluation taking into account

SDCM data the following a posteriori parameters called the protection levels

are evaluated according positioning results:

HPLSDCM (Horizontal Protection Level) – Horizontal Protection Level.

Equal to distribution model dispersion of horizontal positioning true error

taking into account SDCM data within confidence interval «6 » (expectancy

of hitting – more than 1-10-7

);

VPLSDCM (Vertical Protection Level) – Vertical Protection Level. Equal

to distribution model dispersion of vertical positioning true error taking into

account SDCM data within confidence interval «6 » (expectancy of hitting –

more than 1-10-7

);

Navigation user equipment accuracy taking into account SDCM data

meets integrity requirements (more than 1-10-7

) provided that the following

conditions are met:

1 Given probability is defined by integrity requirements. Here the probability of failure in

GPS /GLONASS/SDCM system is a priory less than 10-4

[1/hour].



68

HAL ≥ HPLSDCM;

VAL ≥ VPLSDCM .



69

9 Annex B. Basic integrity principles

B.1 Integrity of GLONASS/GPS/SDCM navigation field

B.1.1 Monitoring and integrity maintenance of GLONASS navigation field

and integrity monitoring of GPS navigation field are important features defining the

user positioning quality. GNSS radionavigation field integrity is a final product of

complex interaction of various factors which can be classified as follows:

- errors of monitoring navigation satellites by GNSS ground facilities and

generating data for uplinking to navigation satellites defined by ground facilities

accuracy;

- errors of generating radionavigation signal onboard GLONASS and GPS

satellites;

- residual error of atmosphere effects along navigation signal propagation path.

For GNSS users the errors of first two groups are indistinguishable and appear

as a general error of a range signal. When SDCM system is used the general error of

range signal is range ambiguity (residual discrepancy) generated after the application

of long-term and fast corrections and after the definition of error of atmosphere

effects. Such discrepancy is defined as a variation of centered normal distribution of

measured range difference (normally distributed value) and estimated (geometrical)

difference for each signal source, and designated as UDRE. For the user UDRE

defines the upper limit of pseudorange assessment error and therefore is a criterion of

GNSS field integrity assessment.

B.1.2 For integrity assessment dual frequency user receiver can use only

UDRE parameter because this parameter includes the errors of first two groups (see

Section 7), troposphere errors, and residual ionosphere error is small in dual

frequency measurements.

For integrity assessment single frequency user receiver also requires UIRE

parameter. UIRE is a residual error for taking into account ionosphere effects on the

basis of ionosphere delays map data for SDCM signal. The map is a set of grid



70

vertical delays introduced by ionosphere into a navigation signal and, additionally,

GIVE codes unambiguously connected with dispersion of such delays. Basing on

GIVE and its own position, the user defines UIRE parameter, the analogue of GIVE

but for a user position, for example between grid nodes of delays map.

B.1.3 There is the finite probability of non-receiving a regular SDCM

message by a SDCM receiver. In this case for continuing navigation SDCM

transmits message degradation parameters. Said parameters are used in a number of

mathematical models describing additional residual error from long-time and fast

differential corrections appearing as a result of using aged but valid SDCM data. Said

models are used for modification of UDRE and UIRE variations if necessary.

B.1.4 Above parameters UDRE and UIRE vare used by a receiver for

navigation solution error assessment. Navigation solution error is calculated by

projecting pseudorange errors into a user coordinate area. Horizontal Protection Level

(HPL) defines the border of user horizontal positioning error with the probability

obtained from integrity requirements. The same algorithm is assumed for VPL and

Vertical Protection Level. If estimated value of HPL or VPL exceeds HAL or VAL

alert limit, SDCM integrity is not enough for support of this navigation solution.

B.1.5 Clock-ephemeris residual errors ( GIVE)

Clock residual error is described by zero mean and normal distribution.

Ephemeris residual error depends on a user position. At accurate differential

correction the residual error for any user within service area is included in UDRE.

B.1.6 Vertical ionosphere error ( GIVE)

Residual ionosphere error is presented by normal distribution with zero mean.

The errors are the functions of measurement noise of ionosphere map and ionosphere

spatial decorrelation.

B.1.7 Errors of navigation user equipment

Total error due to multipath and receiver contribution is restricted as presented

in Annex C. This error can be divided into the multipath and receiver contribution in



71

accordance with Section C 9, here a standard multipath model may be used. The

receiver contribution may be obtained from the accuracy requirements (Annex C) and

extrapolated to typical signal conditions. In particular, it may be assumed that the

following expression is true for navigation user equipment: 2

air = 2

receiver + 2

multypath,

where receiver is assumed to be defined by RMSpr_air, and multypath is defined in Annex

В.

B.1.8 Troposphere model error

A receiver uses the model for troposphere effects correction. The user assess

the residual error of the model ( tropo) according to the formula (E.5) presented in

Annex E .

B.2 SDCM data integrity

B.2.1 Digital data synchronization in the structure of messages transmitted

by SDCM geostationary satellites

Correct use of received SDCM digital data in navigation user equipment

consist in selecting complete set of messages for each operational satellite out from

received digital data flow, and in appropriate application of selected messages that

must belong to the same data validity interval.

SDCM messages delivery must take into account the asynchronous manner of

data transmission and reception. Moreover, the order of transmitted digital data in

SDCM channel is not constant and may vary if necessary in order to quickly correct

current errors of navigation satellites. Main mission of SDCM channel is to provide

transmission of digital data within data update intervals defined by the SBAS

standard. The user must be provided with all necessary information for identification

and affixment of received data, i.e. for “synchronization” of received digital data with

the number of navigation satellite for which it is generated, and with the time to

which these digital data belong.

Digital data identification and synchronization methods defined by the

standard, also consider restrictions from data transmission channel. Digital data



72

format described herein provides digital data identification and synchronization for

the user under the following channel restrictions:

а) finite capacity for data transmission in the SBAS standard.

Comments. The SBAS standard permits the transmission of data flow with the

rate of 250 bits/sec for no more than 51 satellites;

б) SDCM assumes SBAS standard extension with maintenance of succession

for navigation user equipment in force.

Comments. For servicing prospective expanded orbital constellation of

navigation satellites under conditions of restricted channel capacity (see above) data

flow “compression” is required, for the sake of which non-relevant digital data (for

antipode satellites) are excluded from transmitted messages. Digital data are

transmitted only for those navigation satellites which are visible for users of present

SDCM satellite – these are the SDCM messages of the SBAS standard necessary for

the user. Here decoding and application algorithm of digital data is not changed

which guarantees return succession (applicability) of current version of the Standard

for actual navigation user equipment.

SBAS standard extension consists in the necessity of transition to the dynamic

model of the mask which now defines not only the list of satellites from all

navigation systems but exactly those satellites for which digital data are transmitted

via present SDCM satellite (for no more than 51 satellites);

в) asynchronous manner of digital data update in a channel.

Comments. Digital data reception in a channel is not synchronized with

transmission, messages in the channel may comprise both new (updated) digital data

and digital data from previous update cycle. It is worth reminding that for the user

digital data are mutually compatible and correct only when they belong to the same

update cycle.

Validity of considering these restrictions follows from the analysis of SBAS

standard parameters, the analysis of total number of satellites in GPS, GLONASS,

Galileo, WAAS, EGNOS and SDCM systems. Considering declared redundancy the

number of satellites will make up 100 (which significantly exceeds SDCM channel



73

capacity on the basis of the SBAS standard – channel can transmit digital data only

for 51 satellites), at the same time the total number of satellites in visibility field will

not exceed 43. Moreover, return compatibility is possible: the provisions of present

document are entirely applicable for existing navigation user equipment widely used,

which operate using GPS/WAAS systems on the basis of previous version of the

SBAS standard.

Considering the above channel restrictions the following principles of digital

data synchronization are used in present document (in the order of descending

priority to be observed by users when decoding digital data):

1) beginning of each message is to be defined by the field “Preamble” (see

Section 6.2);

2) content and rules of digital data decoding “Data fields” are to be defined by

the field «Message type identifier» (see Section 6.3);

3) control of reliability of received digital data is effected with use of control

sum (see Section 6.7);

4) Digital data synchronization in accordance with satellites numbers is

effected using one of the following methods:

4.1) By direct indication a number of satellite PRN in a message for which

digital data are intended;

4.2) If there is no data for 4.1 – digital data belonging to specific satellite is

effected via position code PRN Mask (Message Type 1 – see Section 7.2). The

following rule is used: digital data blocks in decoded message follow exactly in the

same order (and comprise digital data for satellites with same numbers), in which

numbers of bits of PRN Mask with code 1 follow (the number of bit in PRN Mask is

numerically equal to the number of satellite). Satellites numbers with the code of

PRN Mask equal to 0, are not presented in transmitted digital data and not considered

in the sequence of digital data blocks.

Comment. For instance, 210-bits code of PRN Mask equal to 1001 1000 1100

0010 0000…0000, in decoded message defines availability of digital data for the

satellites having numbers PRN = 1, 4, 5, 9, 10 and 15, and defines the following



74

blocks sequence in this message (digital data for the satellite number N): digital data

1, digital data 4, digital data 5, digital data 9, digital data 10, digital data 15.

5) Digital data time synchronization is effected by selection out from received

data file those data which have the identical code in the field «data identifier».

Mutually compatible digital data have the identical code in the field Issue of

Data. The length of field Issue of Data (no more than 2 bits) provides data division by

the feature «new – old» for not less that two sequential digital data updates in the

SBAS channel (see Section 6.3).

B.2.2 Separation of compatible data from different messages

SBAS standard does not have user requirements for synchronous data reception

and transmission. Therefore, during the time of receiving messages by the user in the

SBAS channel periodical digital data update may occur, in this case received

messages will relate to different time and become incompatible. For correct use all

digital data must be preliminary checked by the user for compatibility. Compatible

data have the same code value in the field Issue of Data. The following Issue of Data

are used in present document: (IOD – Issue of Data):

GPS clocks Issue of Data (GPS IOD Clock – IODCk) – GPS satellite time, k –

satellite number;

GPS ephemeris IOD (GPS IOD Ephemeris – IODEk) – GPS satellites

ephemeris, k – satellite number;

GLONASS Data (IODGk) – GLONASS IOD identifies clocks and ephemeris

of GLONASS satellites, k – satellite number;

IOD PRN Mask (IODP) – identifies data about satellites used. Identifies the

current list of satellites used;

IODFj – identifies data about fast corrections, j - message number (2-5);

Additional functions IODFj: see Section 7.6;

IODI – ionosphere IOD– identifies aggregate of points for which ionosphere

delay is calculated;



75

IODS – service IOD– identifies Service Message Type 27.

Figure B.1 shows the correlation diagram provided for compatibility check of

received SDCM messages by the user.

GPS EphemerisLong-term changes

(25)

Fast changes

(2-5,24)

GPS ClocksField of used satellites

(1)

GLONASS Data

Integrity information (6)

Ionospheric corrections

(26)

Ionospheric Mask

(18)

Covariance Matrix

(28)

Service Messages

(27)

Navigation data of

SDCM satellite (9)

Degradation parameters

(7)

IODE

IODPIODC

IODG

IODP

IODP IODP

IODS

IODI

IODP

Figure B.1– Message Correlation Diagram

Before use of digital data message types indicated in the Figure must be

checked for compatibility by the user with application of IODs presented.



76

10 Annex C. Tables of SDCM message formats

Each SDCM message is coded in accordance with established message format

defined in Tables C.1 – C.16. All parameters defined in these Tables with digit,

comprise digit bit transmitted in the most significant bit.

Table C.1 – Message Type 0. Do not use for safety applications

Parameter

No. Of

Bits

Effective

Range Resolution


Table C.2 – Message Type 1. PRN Mask assignments

Parameter

No. Of

Bits

Effective

Range Resolution

For each of 210 numbers

of PRN-code

Mask value 1 0 or 1 1

IODP 2 0–3 1

Comment. All parameters are defined in Section 7.2.

Table C.3 – Message Type 2–5. Fast corrections

Parameter

No. Of

Bits

Effective

Range Resolution

IODFj 2 0–3 1

IODP 2 0–3 1

For 13 points


For 13 points


Comments:

1. Parameters IODFj and FCi are defined in Section 0.

2. Parameter IODP is defined in Section 7.2.

3. Parameter UDREIi is defined in Section 7.7.



77

Table C.4 – Message Type 6. Integrity information

Parameter

No. Of


IODF2 2 0–3 1

IODF3 2 0–3 1

IODF4 2 0–3 1

IODF5 2 0–3 1

For 51 satellites (defined by the number of PRN Mask)


Comments:

1. Parameters IODFj are defined in Section 0.


Table C.5 – Message Type 7. Fast correction degradation factor

Parameter

No. Of

Bits

Effective

Range Resolution

System delay (tlat) 4 0–15 sec 1 sec

IODP 2 0–3 1


For 51 satellites (defined by the number of PRN Mask)

Degradation indicator (aii) 4 (See Table D.4) (See Table D.4)

Comments:

1. Parameters tlat and aii are defined in Annex D

2. Parameter IODP is defined in Section 7.2

Table C.6 – Message Type 9. GEO navigation message

Parameter

No. Of


Not reserved 8 –– ––

t0,GEO 13 0–86 384 sec 16 sec

URA 4 (See Table C.7) (See Table C.7)

XG 30 42 949 673 m 0,08 m

YG 30 42 949 673 m 0,08 m

ZG 25 6 710 886,4 m 0,4 m

17 40,96 m/sec 0,000625 m/sec

17 40,96 m/sec 0,000625 m/sec

18 524,288 m/sec 0,004 m/sec

10 0,0064 m/sec2 0,0000125 m/sec

2

10 0,0064 m/sec2 0,0000125 m/sec

2

10 0,032 m/sec2 0,0000625 m/sec

2

aGf0 12 0,9537 10-6

sec 231

sec

aGf1 8 1,1642 10-10

sec/sec

240

sec/sec

Comment: All parameters are defined in Section 7.3

GX

GY

GZ

GX

GY

GZ



78

Table C.7 – User range measurement accuracy

URA

Accuracy

(rms)

0 2 m

1 2,8 m

2 4 m

3 5,7 m

4 8 m

5 11,3 m

6 16 m

7 32 m

8 64 m

9 128 m

10 256 m

11 512 m

12 1 024 m

13 2 048 m

14 4 096 m

15 "Do not use"

Table C.8 – Message Type 10. Degradation parameters

Parameter No. Of Bits

Effective

Range Resolution

Brrc 10 0–2,046 m 0,002 m

Cltc_lsb 10 0–2,046 m 0,002 m

Cltc_v1 10 0–0,05115 m/s 0,00005 м/s

Iltc_v1 9 0–511 s 1 s

Cltc_v0 10 0–2,046 m 0,002 m

Iltc_v0 9 0–511 s 1 s

Cgeo_lsb 10 0–0,5115 m 0,0005 m

Cgeo_v 10 0–0,05115 m/s 0,00005 m/s

Igeo 9 0–511 s 1 s

Cer 6 0–31,5 m 0,5 m

Ciono_step 10 0–1,023 m 0,001 m

Iiono 9 0–511 s 1 s

Ciono ramp 10 0–0,005115 m/s 0,000005 m/s

RSSUDRE 1 0 or 1 1

RSSiono 1 0 or 1 1

Ccovariance 7 0–12,7 0,1


Comment: All parameters are defined in Section 7.10.



79

Table C.9 – Message Type 12. SDCM network time /UTC offset parameters

Parameter

No. Of


A1SNT 24 7,45 10–9

sec/sec 2–50

sec/sec

A0SNT 32 1 sec 2–30

sec

t0t 8 0–602 112 sec 4 096 sec

WNt 8 0–255 weeks 1 weeks

tLS 8 128 sec 1 sec

WNLSF 8 0–255 weeks 1 weeks

DN 8 1–7 hours 1 hours

tLSF 8 128 sec 1 sec

UTC standard identifier 3 (See Table 25) (See Table 25)

Time in GPS week (TOW) 20 0–604 799 sec 1 sec

Number of GPS week

(WN)

10 0–1 023 weeks 1 weeks

GLONASS indicator 1 0 or 1 1

ai, GLONASS (comment 2) 32 1 sec 2–30

sec

Reserved 42 — —

Comment:

1. All parameters are defined in Section 7.11.

2. To be applied only when the information about GPS/GLONASS time offset

correction is transmitted in Message Type 12.

Table C.10 – Message Type 17. GEO satellite almanacs

Parameter

No. Of

Bits

Effective

Range Resolution

For each of three satellites


Number of PRN-code 8 0–210 1

Operability and status 8 — —

Not used 49 — —

Not used 11 — —

Comment: All parameters are defined in Section 7.4.

Table C.11 – Message Type 18. Ionospheric grid point masks

Parameter

No. Of

Bits

Effective

Range Resolution

Number of IGP bands 4 0–11 1

IGP band ID 4 0–10 1



80

Parameter

No. Of

Bits

Effective

Range Resolution

Feature of ionosphere data package

(IODIk)

2 0–3 1

For 201 points of IGP

IGP Mask 1 0 or 1 1


Comment: All parameters are defined in Section 0.

Table C.12 – Message Type 24. Mixed fast corrections/

long-term satellite error corrections

Parameter

No. Of


For six points


For six points


IODP 2 0–3 1

Fast correction IOD 2 0–3 1

IODFj 2 0–3 1


Half Message Type 25 106 — —

Comment:

1. Parameters " Fast correction type identifier ", IODFj and FCi are defined in Section 8.5.

2. Parameter IODP is defined in Section 7.2


Table C.13 – Message Type 25. Long-term satellite error corrections

(Half Message for VELOCITY CODE = 0)

Parameter

No. Of

Bits

Effective

Range Resolution

Velocity Code = 0 1 0 1

For two satellites

PRN Mask number 6 0–51 1

Feature of data package (IODi) 8 0–255 1

xi 9 ±32 m 0,125 m

yi 9 ±32 m 0,125 m

zi 9 ±32 m 0,125 m

ai,f0 10 ±2–22

sec 2–31

sec

IODP 2 0–3 1




81

Parameter

No. Of

Bits

Effective

Range Resolution

Comments:

1. Parameters " PRN Mask number " and IODP are defined in Section 7.2.

2. All other parameters are defined in Section 7.5.

Table C.14 – Message Type 25. Long-term satellite error corrections

(Half Message for VELOCITY CODE = 1)

Parameter

No. Of

Bits

Effective

Range Resolution

For one satellite

Velocity Code = 1 1 1 1


Feature of data package (IODi) 8 0–255 1

xi 11 ±128 m 0,125 m

yi 11 ±128 m 0,125 m

zi 11 ±128m 0,125 m

ai,f0 11 ±2–21

sec 2–31

sec

8 ±0,0625 m/sec 2–11

m/sec

8 ±0,0625 m/sec 2–11

m/sec

8 ±0,0625 m/sec 2–11

m/sec

ai,f1 8 ±2–32

sec/sec 2–39

sec/sec

Time-of-Day Applicability (ti,LT) 13 0–86 384 sec 16 sec

IODP 2 0–3 1

Comments:

1. Parameters " PRN Mask number " and IODP are defined in Section 7.2.

2. All other parameters are defined in Section 7.5.

Table C.15 – Message Type 26. Ionosphere delay corrections

Parameter

No. Of


IGP band identifier 4 0–10 1

IGP block identifier 4 0–13 1

For each of 15 grid points

IGP vertical delay evaluation 9 0–63,875 m 0,125 m

Grid ionosphere vertical error

indicator (GIVEIi)

4 (See Table 23) (See Table 23)

IODIk 2 0–3 1


Comment: All other parameters are defined in Section 7.

ixδ

iyδ

izδ



82

Table C.16 – Message Type 27. SDCM Service Message

Parameter

No. Of

Bits

Effective

Range Resolution

Feature of service data (IODS) 3 0–7 1

Number of service data 3 1–8 1

Service data number 3 1–8 1

Number of regions 3 0–5 1

Priority code 2 0–3 1

Inside index UDRE 4 0–15 1

Outside index UDRE 4 0–15 1

For each of five regions

Coordinate 1 latitude 8 90 1

Coordinate 1 longitude 9 180 1

Coordinate 2 latitude 8 90 1

Coordinate 2 longitude 9 180 1

Shape of region 1 — —


Comment: All other parameters are defined in Section 7.12

Table C.17 – Message Type 63. Null message

Parameter

No. Of

Bits

Effective

Range Resolution


Table C.18 – Message Type 28. Clock-Ephemeris Covariance Matrix Message


Effective

Range Resolution

IODP 2 0–3 1

For two satellites


Scale Exponent 3 0–7 1

E1,1 9 0–511 1

Е2,2 9 0–511 1

Е3,3 9 0–511 1

Е4,4 9 0–511 1

Е1,2 10 512 1

Е1,3 10 512 1

Е1,4 10 512 1

Е2,3 10 512 1

Е2,4 10 512 1

Е3,4 10 512 1



83


Effective

Range Resolution

Comments:

1. Parameters including PRN mask number and IOD are defined in Section

7.2.

2. All other parameters are defined in Section 7.13



84

11 Annex D. Recommendations on SDCM data use in the navigation

algorithm GLONASS/GPS/SDCM

D.1 General provisions

D.1.1 Required data and transmission intervals

SDCM transmits data required for the functions supported by the system, as

showed in Table D.1. If SDCM data transmitted by the system are not required for

specific function, these data are used for other functions. Maximum transmission

intervals of all data via each type of messages are defined in Table D.1.

D.1.2 Control of SDCM radiofrequencies

SDCM controls SDCM satellite parameters indicated in Table D.2 and

undertake provided actions.

Comment: SDCM can transmit zero messages (Type 63) in each transmission

interval for which there is no any other data to be transmitted.

D.1.3 Message "Do not use"

SDCM transmits the message "Do not use" (Type 0) when it is necessary to

inform users than transmitted SDCM data should not be used.

D.1.4 Almanac

SDCM transmits the almanac of SDCM satellites (defined in Section 7.4) in

which satellites coordinates are defined with the error of less than 150 km. In unused

cells of the almanac in the Message Type 17 zero number of PRN-code is indicated.

Words " health " and "status " indicate the status of a satellite and service provider as

defined in Section 7.2.



85

Table D.1 – Data transmission intervals and provided functions

Data type

Maximum

transmissi

on

intervals

Status of

GEO

SDCM

Status of

GNSS

satellites

Standard

differential

corrections

Accurate

differential

corrections

Respe

ctive

messa

ge

types

Clock-ephemeris

covariation matrix 120 sec 28

SDCM in test

mode

6 sec 0

PRN Mask 120 sec R R R 1

UDREI 6 sec R*

R R 2–6,

24

Fast corrections 60 sec R* R R 2–5,

24

Long-term

corrections

120 sec R* R R 24, 25

GEO navigation

data

120 sec R 9

Fast corrections

degradation

120 sec R* R R 7

Degradation

parameters

120 sec R 10

Ionosphere grid

mask

300 sec R 18

Ionosphere

corrections,

GIVEI

300 sec R 26

Time data 300 sec R

(see

Comment

3)

R

(see Comment

3)

R

(see

Comment

3)

12

Almanac 300 sec R R R 17

Service level 300 sec 27

Comments:

1. "R" indicates that present information is transmitted for provision of present function.

2. "R*" indicates special coding as defined in 4.

3. Messages Type 12 are required only for GLONASS satellite data.

D.2 Status of GNSS satellites

If SDCM provides satellite status data, they correspond to the requirements of

present section.

D.2.1 Characteristics of satellite status functions



86

Under any reliable combinations of valid information the probability of

horizontal error exceeding HPLSDCM (as defined in Annex I) within more than 8 sec,

shall not exceed 10–7

for any hour provided that the user has zero delay.

Comment: Valid information means the information validity period of which is

not expired in accordance with Table D.1.

D.2.2 PRN Mask and feature of PRN data set (IODP)

SDCM transmits parameters "PRN Mask" and IODP (Message Type 1). The

values of PRN Mask indicate whether data on each GNSS satellite provided or not.

IODP changes when PRN Mask changes. Change of IODP in Message Type 1 take

place before IODP change in any other message. In Messages Type 2–5, 7, 24 and 25

IODP is determined in the same manner as IODP transmitted in Message Type 1 for

PRN Mask, used for indication of satellites for which information is provided in

present message.

When PRN Mask is changed, SDCM repeats Message Type 1 a few times

before transmission to other messages, in order to guarantee reception of a new Mask

by the user.

D.2.3 Integrity data

If SDCM does not provide the required accuracy of differential correction, fast

corrections, long-term corrections and fast corrections degradation parameters for all

visible satellites indicated in the PRN Mask are transmitted in zero coding.

If SDCM does not provide the required accuracy of differential correction and

if the pseudorange error exceeds 150 m, it means that the satellite is not healthy

(feature “Do not use”).


if the pseudorange error can not be defined, SDCM reports that for given satellite

there is “No monitoring”.


if no features “Do not use” and “No monitoring” are assigned to the satellite, SDCM

transmits URDEIi 13.

Parameter IODFj in Messages Type 2 5, 6 or 24 is defined equal to 3.



87

D.3 Differential correction

If SDCM provide the required accuracy of differential correction, SDCM

meets the requirements contained in this Section, in addition to the information about

SDCM satellites status (Section 7.4).

D.3.1 Differential correction characteristics

Under any combinations of valid data the probability of horizontal error

exceeding HPLСДКМ (as defined in Annex I) within more than 8 sec, does not exceeds

10-7

for any hour, provided that the user has zero delay.

Comment: under valid data the following is assumed: data validity period of

which is not expired in accordance with Table D.1.

D.3.2 Long-term corrections

SDCM defines and transmits long-term corrections for each visible GNSS

satellite (see Comment) indicated in the PRN Mask (PRN Mask is equal to "1"), apart

from SDCM satellites. For each GLONASS satellite SDCM, before definition of

long-term corrections, transforms satellites coordinates into WGS-84 as indicated in

Section 7.5. For each GPS satellite IOD feature transmitted by it coincide

simultaneously with GPS IODE and 8 lower bits of IODC which correspond to clock-

ephemeris data used for calculation of corrections (Section 7.5). When a GPS satellite

transmits new ephemeris SDCM continues using aged ephemeris for long-term and

fast corrections definition within, at least, 2 minutes but no more than 4 minutes. For

each GLONASS satellite SDCM calculates and transmits IOD including delay and

action time, as indicated in Section 7.5.

Comment: Satellites visibility is defined on the basis of reference stations

coordinates and takeoff angle mask (5°).

D.3.3 Fast corrections

SDCM defines fast corrections for each GNSS visible satellite indicated in the

PRN Mask (PRN Mask is equal to "1"). If IODF 3, each time when any data of a

fast correction are changed in Messages Type j (j = 2, 3, 4 or 5), IODFj feature is

changed in the order of "0, 1, 2, 0, ...".



88

Comment: In case of irregular operation IODFj feature may be equal to 3 (see

Section 0).

D.3.4 Time data

If the data are provided for GLONASS, SDCM transmits a time message

(Message Type 12) including GLONASS time offset as defined in Table D.8.

D.3.5 Integrity data

For each satellite for which corrections are applied SDCM transmits integrity

data (UDREIi and additionally the data of Message Type 27 or 28 for calculation of

UDRE) in the manner that provides meeting integrity requirements contained in

Annex B. If fast and long-term corrections exceed the limits of their code intervals,

SDCM indicates that the satellite is unhealthy (“Do not use”). If 2

i, UDRE parameter is

not defined SDCM indicates that there is “No monitoring” for the satellite.

If Message Type 6 is used for transmission of 2

i, UDRE than:

Feature IODFj coincide with IODFj for fast corrections assumed in Message

Type j for which 2i,UDRE is applied; or IODFj is equal to 3 if

2i,UDRE is applied to all

reliable fast corrections assumed in Message Type j the validity period of which is

not expired.

D.3.6 Degradation parameters

SDCM transmits degradation parameters (Message Type 7) for indication of

validity period of fast corrections and meeting integrity requirements presented in

Section 7.10.

D.4 Differential correction

SDCM provides differential correction in accordance with requirements

contained in this Section.

D.4.1 Differential correction characteristics

When GNSS errors occur and under any reliable combinations of SDCM data,

when the user is assumed to have zero delay, SDCM data application provides the



89

probability of exceeding admissible thresholds of positioning error of less than 2

10-7

within any time interval after SDCM alarm activation (less than 10 second).

Exceeding of admissible threshold is defined as horizontal error exceeding of

HPLSDCM (as defined in Annex I). When exceeding of admissible threshold is

detected a final alarm message is repeated three times (transmitted in Messages Type

2–5 и 6, 24, 26 or 27).

Altogether SDCM alert occurs for times in 4 seconds.

Comments:

А). Under valid data the following is assumed: data validity period of which is

not expired in accordance with Table D.1. This requirement includes failures of

GLONASS, GPS and SDCM.

B). Sequential messages can be transmitted with standard update rate.

D.4.2 Ionosphere grid point model Mask (IGP Mask)

SDCM transmits IGP and IODIk Mask (up to 11 Messages Type 18

corresponding to 11 IGP diapasons). IGP values indicate if data are provided for each

IGP. If the 9-th diapason of IGP is used, IGP values for points located to the north

from 55 N in the diapasons 0–8 are set to "0". If the 10-th diapason of IGP is used,

IGP values for points located to the south from 55 S in the diapasons 0–8 are set to

"0". IODIk feature is changed when IGP Mask values are changed in k-th diapason.

New IGP Mask is transmitted in Message Type 18 before a reference to it in

corresponding Message Type 26 occurs. IODIk feature in Message Type 26 is equal

to IODIk feature transmitted in the message for IGP Mask (Message Type 18) which

is used for indication of IGP points by which data are transmitted in the message.

D.4.3 Ionosphere corrections

SDCM transmits Ionosphere corrections for IGP points indicated in IGP Mask

(IGP Mask values are equal to “1”).

D.4.4 Ionosphere data integrity



90

For each IGP provided with ionosphere corrections SDCM transmits GIVEI

data in such manner which provides meeting integrity requirements of D.3.5. If

ionosphere correction of parameter 2

i,GIVE exceed code interval SDCM indicates that

IGP is unhealthy (indicated in correction data). If parameter 2

i,GIVE can not be

defined, SDCM indicates that there is “Mo monitoring” for present IGP (indicated at

coding GIVEI).

D.4.5 Degradation parameters

SDCM transmits degradation parameters (Message Type 10) in such manner

which provides meeting integrity requirements of Table C.8.

D.5 Additional functions

D.5.1 Time data

If UTC time parameters are transmitted they are defined as showed in Table

C.9. (Message Type 12).

D.5.2 Service indication

If service data are transmitted they are defined as showed in Table C.15

(Message Type 27), and Messages Type 28 are not transmitted. IODS parameter in

all Messages Type 27 is increased by one when any change of data occurs in Message

Type 27.

D.5.3 Clock-ephemeris covariation matrix

If covariation matrix data are transmitted they are transmitted for all controlled

satellites as defined in Table C.16 (Message Type 28), and Messages Type 27 are not

transmitted.

D.6 Monitoring

D.6.1 SDCM radiofrequency monitoring

SDCM continuously monitors SDCM satellites parameters indicated in Table

D.2 and undertakes indicated actions.

D.6.2 Data monitoring



91

SDCM monitors satellite signal in order to detect conditions which may cause

incorrect function of differential processing in Navigation user equipment, using

tracking characteristics.

D.6.2.1 SDCM monitors all operational GNSS data which may be used by any

user within service area.

D.6.2.2 SDCM gives up an alarm within 10 sec if any combination of valid

data and signals in space radiated by GNSS is out of defined thresholds.

Comment. Monitoring covers all failure cases including the failures of

basic orbital system(s) of satellites of SDCM.

Table D.2 – SDCM radiofrequency monitoring

Parameter Threshold Required action

Signal/noise ratio

of received signal

Less than 34 dBHz

More than 55 dBHz

Cease reception of onboard repeater

Swith off telecommand system (switch to

redundant set)

Carrier frequency

stability

Frequency drift from

nominal more than 6,0

kHz

Swith off telecommand system (switch to

redundant set)

Reliability

Control of

uplinked

information

Invalid data are

detected

Cease data transmission within 2 sec

D.6.3 Robustness to failures of basic orbital system(s)

When a failure occurs at a satellite of the basic orbital system(s) SDCM

continues normal operation using available tracked signals of healthy satellites.

D.7 Recommended receiver parameters

Comments:

1. Parameters referred to in this Section are defined in Section 8.

2. Requirements of this Section are not mandatory for equipment which

includes additional navigation sensors (for example, for a receiver interconnected

with inertial sensors).



92

D.7.1 GNSS receiver using SDCM signals

If not defined specially, a GNSS receive capable to receive SDCM signals

process simultaneously SDCM signals and GLONASS and GPS signals. Pseudorange

measurements for each satellite are smoothed using carrier measurements and

smoothing filter which has post-initialization offset of less than 0,1 m for 200 sec

relative to the stable status of filter response defined in Section 8.4, provided that the

drift between the code phase and integrated carrier phase makes up to 0,01m/sec.

D.7.2 Conditions of data use

Reception of Message Type 0 from SDCM satellite cause ceasing operations

with this satellite and all data received from it during at least 1 minute. For GPS

satellites a receiver applies long-term corrections only when IOD coincides with

IODЕ and 8 lower-order bits of IODС. For GLONASS satellites a receiver applies

long-term corrections only when GLONASS ephemeris reception time (tr) is within

the following IOD validity time:

LT r LTt L V t t L

Comments: This requirement does not assume that a receiver cease tracking

SDCM satellite.

D.7.2.1 Receiver uses integrity or correcting data only when IODP for this

information coincides with IODP for PRN Mask.

D.7.2.2 Receiver uses ionosphere data provided by SDCM (assessment of

IGP and GIVEIi vertical delay) only when IODIk connected with these data in

Message Type 26 coincides with IODIk, connected with respective mask of IGP

diapason transmitted Message Type 18.

D.7.2.3 Receiver uses the latest received integrity data for which: IODFj is

equal to 3 or IODFj coincides with IODFj connected with applied fast corrections (if

any transmitted).

D.7.2.4 Receiver uses any regional degradation to parameters 2

i,UDRE as

defined by service Message Type 27. If Message Type 27 with new IODS contains

higher UDRE for a user position, this higher UDRE is to be applied without delay.



93

Lower UDRE in a new Message Type 27 is not used until a complete message set

has not been received with a new IODS.

D.7.2.5 Receiver uses satellite degradation to parameters i,UDRE2 as defined

by Message Type 28 about Clock-Ephemeris Covariation Matrix. Parameter UDRE

received from Message Type 28 is to be applied without delay.

D.7.2.6 For GPS satellites a receiver applies long-term corrections only when

IOD coincides with IODE and 8 lower-order bits of IODC.

D.7.2.7 Receiver does not use transmitted parameter of data if it is expired.

Table D.3 shows data validity intervals.

D.7.2.8 Receiver does not use a fast correction if t for respective correction

to range rate (RRC) exceeds a validity interval for fast corrections of if RRC age

exceeds 8 t.

D.7.2.9 RRC calculation is renewed if for given satellite the features “Do not

use” and “No monitoring” are assigned.

D.7.2.10 Receiver uses only satellites with elevation angle not less than 5 .

D.7.2.11 Receiver uses signals of given satellite if received UDREIi is less

than 12.

Table D.3 – Data validity intervals

Data

Respective

message types Validity period

Clock-Ephemeris Covariation

Matrix 28 360

SDCM in the test mode 0 No

PRN Mask 1 600 sec

UDREI 2–6, 24 18 sec

Fast corrections 2–5, 24 See Table D.4

Long-term corrections 24, 25 360 sec

Degradation of fast corrections 7 360 sec

Degradation parameters 10 360 sec

Ionosphere grid mask 18 1 200 sec

Ionosphere corrections, GIVEI 26 600 sec

Time 12 86 400 sec

GLONASS time offset 12 600 sec

Almanac 17 No

Service level 27 86 400 sec

Comment. Validity intervals are counted from the message reception time.



94

Table D.4 – Definition of fast corrections validity interval

Degradation factor of fast

corrections (aii)

Validity interval of fast

corrections

0 180 sec

1 180 sec

2 153 sec

3 135 sec

4 135 sec

5 117 sec

6 99 sec

7 81 sec

8 63 sec

9 45 sec

10 45 sec

11 27 sec

12 27 sec

13 27 sec

14 18 sec

15 18 sec

D.7.2.12 SDCM satellites status

D.7.2.12.1 Definition of GEO satellite status. Receiver decodes Message

Type 9 and defines status of SDCM satellite.

D.7.2.12.2 SDCM satellites identification. Receiver identifies SDCM

satellites.

D.7.2.12.3 SDCM satellites status. Receiver excludes the satellites from

navigation solution if SDCM gave up the "Do not use". If integrity data provided by

SDCM are used, the receiver has no need to exclude GPS satellites on the basis of

unhealthiness feature provided by GPS or GLONASS satellites on the basis of

unhealthiness feature provided by GLONASS.

Comments:

1. If a satellite is indicated as unhealthy by GLONASS or GPS, SDCM can not

generate clock and ephemeris corrections which allow to the user to use the satellite.

2. If SDCM indicated a satellite by the feature “No monitoring” and it is used

in navigation solution, SDCM provides no integrity data.

D.7.2.13 Differential functions realized in the receiver



95

D.7.2.13.1 Range measurement accuracy of the basic orbital system(s). Root

Mean Square (1 ) of onboard error total contribution into the error of corrected

pseudorange for a GPS satellite under the minimum received power and the worst

interference conditions shall not exceed 0,4 m without taking into account multipath

effects, troposphere and ionosphere residual errors.

Root Mean Square (1 ) of onboard error total contribution into the error of

corrected pseudorange for a GLONASS satellite under the minimum received power

and the worst interference conditions shall not exceed 0,8 m without taking into

account multipath effects, troposphere and ionosphere residual errors.

D.7.2.13.2. Receiver calculates and applies long-term corrections, fast

corrections, corrections to the range rate (single frequency receiver additionally

applies transmitted ionosphere corrections). For GLONASS satellites ionosphere

corrections received from SDCM are multiplied by a squared ratio of GLONASS and

GPS frequencies (fGLONASS/fGPS)2.

D.7.2.13.3 Receiver applies technique of least squares for navigation solution.

D.7.2.13.4 Receiver applies troposphere model the average residual error of

which ( ) is less than 0,15 m and standard deviation (1 ) is less than 0,07 m.

Recommendations for troposphere delay calculation are given in Annex E.

D.7.2.13.5 Receiver calculates and applies horizontal and vertical protection

levels as defined in Section 8.4. Here parameter tropo is defined as follows:

2

i

10,12 м,

0, 002 sin (θ )

where iθ – elevation angle of i-th satellite.

In addition, parameter air meets the condition of normal distribution with zero

mean, and the standard deviation equal to air restricts the distribution error for

residual pseudorange errors in navigation user equipment as follows:

ny

yyf x dx Q для всех 0

σσ , and

y

n

yyf x dx Q для всех 0

σσ,



96

where

fn(x) – the function of probability density of residual pseudorange errors.

2t

2

x

1e dt.

2πQ x

Comment. Standard multipath attenuation for navigation user equipment can

be used for restricting multipath error.

D. 7.2.14 Error in the form of continuous wave (CW)

D.7.2.14.1 GPS and SDCM receivers

D.7.2.14.1.1 GPS and SDCM receivers correspond to the required

characteristics over disturbing signals in the form of continuous wave the power of

which at antenna input is equal to interference threshold indicated in Table D.5, and

presented in figure D.1, and the useful signal level of which at antenna input is equal

to –164,5 dBW.

Figure D.1 – Threshold of interference in the form of continuous wave (CW)

for GPS and SDCM receivers



97

D.7.2.14.2 GLONASS receivers

D.7.2.14.2.1 GLONASS receivers correspond to the required characteristics

over disturbing signals in the form of continuous wave the power of which at antenna

input is equal to interference threshold indicated in Table D.6, and presented in figure

D.2, and the useful signal level of which at antenna input is equal to –165,5 dBW.

Figure D.2 – Threshold of interference in the form of continuous wave (CW)

for GLONASS receivers

Table D.5 –Threshold of interference in the form of continuous wave (CW) for

GLONASS receivers

Interference frequencies fi (MHz) Interference thresholds for receivers (dBW)

fi 1315 –4,5

1 315 <fi 1 525 Linearly decrease from –4,5 to –42

1 525 <fi 1 565,42 Linearly decrease from –42 to –150,5

1 565,42 <fi 1 585,42 –150,5



98


1 585,42 <fi 1 610 Linearly decrease from –150,5 to –60

1 610 <fi 1 618 Linearly decrease from –60 to –42

1 618 <fi 2 000 Linearly decrease from –42 to –8,5

1 610 <fi 1 626,5 Linearly decrease from –60 to –22

1 626,5 <fi 2 000 Linearly decrease from –22 to –8,5

fi> 2 000 –8,5

Table D.6 – Threshold of interference in the form of continuous wave (CW) for

GLONASS receivers


fi 1 315 –4,5

1 315 <fi 1 562,15625 Linearly decreases from –4,5 to –42

1 562,15625 <fi 1 583,6525 Linearly decreases from –42 to –80


1 592,9525 <fi 1 609,36 –149




1 635,15625 <fI 2 000 Linearly decreases from –42 to –8,5

1 626,15625 <fi 2 000 Linearly decreases from –22 to –8,5

fi> 2 000 –8,5

D.7.2.15 Noise-type interference with restricted spectrum

D.7.2.15.1 GPS and SDCM receivers

D.7.2.15.1.1 After transition in the navigation solution mode GPS and SDCM

receivers correspond to the required characteristics over the noise-type disturbing

signals in the bandwidth of 1575,42 MHz Bwi/2 with the power levels at antenna



99

input equal to interference threshold indicated in Table D.7 and presented in figure

D.3, and the useful signal level at antenna input equal to –164,5 dBW.

Figure D.3 – Relation of interference threshold from a bandwidth for GPS and

SDCM receivers

Comment: Bwi – equivalent bandwidth of noise-type disturbing signal.

Table D.7 – Noise-type interference thresholds for GPS and SDCM receivers

Interference bandwidth Interference threshold (dBW)

0 Hz <Bwi 700 Hz –150,5

700 Hz <Bwi 10 kHz –150,5 + 6 log10(BW/700)

10 kHz <Bwi 100 kHz –143,5 + 3 log10(BW/10000)

100 кГц <Bwi 1 MHz –140,5

1 MHz <Bwi 20 MHz Linearly increases from –140,5 to –127,5*



40 MHz <Bwi –119,5 *

* Interference threshold does not exceed–140,5 dBW / MHz in the bandwidth of

1575,42 10 MHz.



100

D.7.2.15.2 GLONASS receiver

D.7.2.15.2.1 After transition in the navigation solution mode GLONASS

receivers correspond to the required characteristics over the noise-type disturbing

signals in the bandwidth of fk Bwi/2 with the power levels at antenna input equal to

interference threshold indicated in Table D.8, and the useful signal level at antenna

input equal to –165,5 dBW.

Comment: fk is the central frequency of the GLONASS channel equal to

fk = 1602 MHz + k 0,6525 MHz, where k may vary from–7 to +6, and Bwi –

equivalent bandwidth of the noise-type disturbing signal.

D.7.2.15.2.2 Pulse interference. After transition in the navigation solution

mode the receiver correspond to the required characteristics over the pulse disturbing

signal having the parameters of Table C.9 in which interference threshold at antenna

input are indicated.

D.7.2.15.2.3 SDCM receivers do not provide incorrect data over an

interference including the interference with the level exceeding the value defined in

Sections D.10 and D.11.

Table D.8 – Noise-type interference thresholds for GLONASS receivers

Interference bandwidth Interference threshold (dBW)

0 Hz <Bwi 1 kHz –149

1 kHz <Bwi 10 kHz Linearly increases from –149 to –143

10 kHz <Bwi 0,5 MHz –143

0,5 MHz <Bwi 10 MHz Linearly increases from –143 to –130

10 MHz <BwI –130

Table D.9 – Pulse interference thresholds

GPS and SDCM GLONASS

Frequency band 1575,42 10 MHz 1592,9525–1609,36

MHz

Interference threshold (Pulse peak power) –10 dBW –10 dBW

Pulse duration 125 microsec, 1

millisec *

1 millisec

Off-duty factor 10 % 10 %

* For GPS receiver without SDCM.



101

D.8 GNSS antenna for reception of GLONASS/GPS/SDCM signals

D.8.1 Antenna visibility field

GNSS antenna has required performance when the reception of GNSS signals

is provided within 0 - 360 in azimuth direction and 0 - 90 in elevation direction

relative to the horizontal user plane.

D.8.2 Antenna gain

Minimum antenna gain for indicated elevation angles shall not be less than one

indicated in Table D.10. Maximum antenna gain shall not exceed +7 dBi for

elevation angles more than 5 .

Table D.10 – Minimum antenna gain of GLONASS/GPS/SDCM

Elevation (о)

Minimum antenna gain

(dBi)

0 –7,5

5 –4,5

10 –3

15–90 –2

D.8.3 Antenna polarization

GNSS Antenna has circular right-hand polarization (clockwise in the direction

of propagation).



102

12 Annex E. Recommendations on the troposphere model

Troposphere delay of navigation signal propagation is calculated as follows:

)()( iwethydtropo Elmddt (E.1)

where dhyd, dwet – parameters depending on a receiver altitude and five

metrological parameters: pressure P, temperature T, pressure of saturated water vapor

e, temperature – altitude response and water evaporation gradient . Here each of

these five parameters depends on receiver geographic latitude and current day of

the year D, starting from the 1-st of January:

(E.2)

where:

Dmin = 28 for northern latitudes and Dmin = 211 for southern latitudes,

mean and seasonal parameter variation,

(E.3)

(E.4)

For definition of each of these five meteorological parameters for a receiver

latitude interpolation is used for data presented in Table E.1. Meteorological

parameters for northern and southern hemispheres are identical.



103

Table E.1 – Meteorological parameters for calculation of the troposphere delay.

Parameters dhyd and dwet are calculated as follows:

(E.5)

(E.6)

where

g = 9.80665 m/sec2 ,

H – receiver altitude above sea level,



104

(E.7)

(E.8)

k1 = 77.604 K/mbar,

k2 = 382000 K2/mbar,

Rd = 287.054 Dj/kg/K,

gm = 9.784 m/sec2.

The function of troposphere correction m(El) is calculated as follows:

(E.9)

The correction is valid for elevations not less than 5°.

Root mean square of troposphere delay error is calculated as follows tropoi, :

)(12.0, itropoi Elm (E.10)



105

13 Annex F. Transmission sequence of SDCM messages.

Table F.1 shows a sequence diagram of SDCM messages transmission order.

Messages in this sequence diagram are partitioned into 6 second fragments

(row in the Table) following each other. Total duration of the sequence – 264 sec.

Table F.1 – Transmission sequence of SDCM messages.

Time of digital

data transmission

(sec)

Digital data content

(types of transmitted messages)

1-6 C 1 C 2 C 3 C 4 C 5 C 25

7-12 C 18 C 2 C 3 C 4 C 5 C 25

13-18 C 7 C 2 C 3 C 4 C 5 C 25

19-24 C 18 C 2 C 3 C 4 C 5 C 25

25-30 C 10 C 2 C 3 C 4 C 5 C 25

31-36 C 18 C 2 C 3 C 4 C 5 C 25

37-42 C 9 C 2 C 3 C 4 C 5 C 25

43-48 C 18 C 2 C 3 C 4 C 5 C 25

49-54 C 17 C 2 C 3 C 4 C 5 C 25

55-60 C 18 C 2 C 3 C 4 C 5 C 25

61-66 C 1 C 2 C 3 C 4 C 5 C 25

67-72 C 18 C 2 C 3 C 4 C 5 C 25

73-78 C 27(28) C 2 C 3 C 4 C 5 C 25

79-84 C 26 C 2 C 3 C 4 C 5 C 25

85-90 C 7 C 2 C 3 C 4 C 5 C 25

91-96 C 26 C 2 C 3 C 4 C 5 C 25

97-102 C 10 C 2 C 3 C 4 C 5 C 25

103-108 C 26 C 2 C 3 C 4 C 5 C 25

109-114 C 9 C 2 C 3 C 4 C 5 C 25

115-120 C 26 C 2 C 3 C 4 C 5 C 25

121-126 C 1 C 2 C 3 C 4 C 5 C 25

127-132 C 26 C 2 C 3 C 4 C 5 C 25

133-138 C 6 C 2 C 3 C 4 C 5 C 25

139-144 C 26 C 2 C 3 C 4 C 5 C 25

145-150 C 7 C 2 C 3 C 4 C 5 C 25

151-156 C 26 C 2 C 3 C 4 C 5 C 25

157-162 C 10 C 2 C 3 C 4 C 5 C 25

163-168 C 26 C 2 C 3 C 4 C 5 C 25

169-174 C 12 C 2 C 3 C 4 C 5 C 25

175-180 C 26 C 2 C 3 C 4 C 5 C 25

181-186 C 1 C 2 C 3 C 4 C 5 C 25

187-192 C 26 C 2 C 3 C 4 C 5 C 25

193-198 C 27(28) C 2 C 3 C 4 C 5 C 25



106

199-204 C 26 C 2 C 3 C 4 C 5 C 25

205-210 C 7 C 2 C 3 C 4 C 5 C 25

211-216 C 26 C 2 C 3 C 4 C 5 C 25

217-222 C 10 C 2 C 3 C 4 C 5 C 25

223-228 C 26 C 2 C 3 C 4 C 5 C 25

229-234 C 9 C 2 C 3 C 4 C 5 C 25

235-240 C 26 C 2 C 3 C 4 C 5 C 25

241-246 C 1 C 2 C 3 C 4 C 5 C 25

247-252 C 26 C 2 C 3 C 4 C 5 C 25

253-258 C 10 C 2 C 3 C 4 C 5 C 25

259-264 C 26 C 2 C 3 C 4 C 5 C 25

The above sequence provides meeting SBAS requirements for correction data

update time.

Table F.2 shows SBAS requirements for maximum data update time (3-rd

column) and SDCM data update time (4-th column) corresponding to the sequence

diagram presented in Table F.1.

Table F.2 – Maximum data update time.

Data type Messages

SBAS

(sec)

SDCM

(sec)

Data field of used satellites

(PRN Mask) C 1 120 60

UDREI C 2-6, 24 6 6

Fast corrections C 2-5, 24 12 6

Slow corrections C 25, 24 120 75

Ionosphere grid point C 18 300 265

Ionosphere delay data C 26 300 265

UTC time C 12 300 265

Fast corrections degradation C 7 120 80

SDCM navigation message С 9 120 120

SDCM satellite status C 17 300 265

Degradation parameters C 10 120 80

Service region C 27(28) 300 120



107

14 Annex G. Transmission sequence of SDCM messages when changing

data field of used satellites (change of PRN mask)

Figure G.1 shows a sequence diagram of SDCM messages when changing data

field of used satellites, i.e. when changing PRN Mask.

Change is organized in three phases.

Phase 1 – before changing PRN Mask 4 Messages Type 1 are transmitted

sequentially which contain a new data field of used satellites (PRN Mask).

Phase 2 – preparation for using a new data field of PRN Mask. Slow

corrections are transmitted for a new data field of PRN Mask – 13 Messages Type 25

are to be transmitted. Total duration of Phase 2 is 22 sec. During this phase the user

uses an old field of PRN Mask.

Phase 3 – use of a new field of PRN Mask. At the beginning of Phase 3

Messages Type 1 is repeated, then fast corrections follow corresponding to а new

data field.

Figure G.1 shows digital data transmission process when changing PRN Mask.

Figure G.1 –Sequence diagram of SDCM messages when changing data field

of used satellites



108

15 Annex I. Definitions of SDCM data application protocols

In this Section parameters definitions are given which are used in the

GLONASS/GPS navigation algorithm taking into account SDCM information. These

parameters are used to obtain a navigation solution and assess its reliability

(protection levels).

I.1 Long-term corrections

I.1.1 GPS time correction.

Time correction for i-th GPS satellite is carried out as follows:

,]δΔt)t[(tt SV,iL1SV,iSV,i

where:

t– GPS current time;

tSV,i–GPS satellite onboard time at the time of message transmission;

( tSV,i)L1 – correction to onboard time (PRN-code phase);

tSV,i – correcting of correction to onboard time.

I.1.2 Onboard clock error assessment ( tSV,i) for i-th GPS satellite for any

time kt for GPS system time and in current day:

).t(taδaδΔtδ LTi,kf1i,f0i,iSV,

I.1.3 GLONASS time correction

Time correction for i-th GLONASS satellite is carried out as follows:

SV,i n b n b SV,i b ,t t τ t γ t t t δ t ,SV i

where:

t – GLONASS current time;

tSV,i – GLONASS satellite onboard time at the time of message transmission;

tb, n(tb), n(tb) – GLONASS time parameters;

tSV,i – code phase offset correction.



109

Code phase offset correction tSV,i for i-th GLONASS satellite in the

GLONASS system time is carried out as follows:

tSV,i = ai,f0 + ai,f1 (t – ti,LT),

where (t – ti,LT) is corrected at transition to a new day. If the range rate = 0,

than ai,f1 = 0.

Code phase offset correction tSV,i for i-th GLONASS satellite in the GPS

system time is defined considering GPS and GLONASS time offset:

tSV,i = ai,f0 + ai,f1 (t – ti,LT) + τ(GPS)+ ai,GLONASS ,

where:

t – GPS current time;

τ(GPS) – fractional part of a second in GPS time scale offset relatively

GLONASS time scale transmitted as a part of GLONASS satellites ephemeris

information;

ai,GLONASS – correction to GPS time scale offset relatively GLONASS time

scale transmitted by SDCM in Message 12.

I.1.4 Satellite coordinates correction

GPS uses WGS-84 coordinate system and GLONASS uses PZ-90.02.

Transition matrices from one to the other coordinate system are as follows:

90.02-PZ84WGS18,0

08,0

36,0

And back transition:

84-WGS90.02-PZ18,0

08,0

36,0

A specific feature of the transition is that the coordinate systems WGS-84 and

PZ-90.02 are parallel to each other and have only linear offset of coordinate origin. It

means that differential corrections to coordinates do not depend on the system used.

This conclusion is also valid for rate corrections.



110

Vector for i-th satellite of GLONASS and GPS systems corrected in SDCM

system is defined as follows for the time t:

,tt

zδ

yδ

xδ

zδ

yδ

xδ

z

y

x

z

y

x

LTi,

i

i

i

i

i

i

i

i

i

correctedi

i

i

where:

(t – ti,LT) – is corrected at transition to a new day;

[xiyizi]T – position vector of a GLONASS or GPS satellite.

If the range rate = 0, than:

.0 ;0 ;0 i

zi

yi

x

I.1.5 Corrections to pseudoranges

Corrections to pseudoranges also do not depend on the coordinate system used.

Corrected pseudorange at the time t for i-th satellite спутника is defined as

follows:

,TCIC)t(tRRCFCPRPR iii,0fiiicorrectedi,

where:

PRi – measured pseudorange after application of corrections to the satellite

onboard time;

FCi – fast correction;

RRCi– correction to the range rate;

ICi – ionosphere correction;

TCi – troposphere correction (negative value considering troposphere delay);

ti,0f – time of applicability of the most recent fast corrections which is the

beginning of the second époque of SDCM time coinciding with the time of

transmission of the first symbol of the message block to a SDCM satellite.



111

I.1.6 Corrections to pseudorange rate (RRC)

RRC for i-th satellite is defined as follows:

,tt

FCFCRRC

ousi,0f_previi,0f

previousi,currenti,

i

where:

FCi,current – the latest fast correction;

FCi,previous – the previous fast correction;

ti,0f – time of applicability of the most recent fast correction FCi,current;

ti,0f_previous – time of applicability of the FCi,previous.

I.2 Transmitted ionosphere corrections

I.2.1 Coordinates of ionosphere pierce point (IPP)

IPP coordinates are defined as the coordinates of crosspoint of the receiver-

satellite line with the ellipsoid having constant altitude of 350 km over WGS-84

ellipsoid. These coordinates are defined in latitude ( pp) and longitude ( pp) of WGS-

84.

I.2.2 Ionosphere corrections

Ionosphere correction i-th satellite is defined as follows:

i pp vppIC F τ , Fpp =

12 2

e i

e I

R cosθ1 ;

R h

where:

Fpp – deflection factor;

vpp – interpolated assessment of the vertical ionosphere delay

Re – 6 378,1363 km;

i – elevation of i- th satellite;

hI – 350 km.

Comment – For GLONASS satellites ionosphere correction (ICi) must be

multiplied by the squared ratio of GLONASS and GPS frequencies ( ГЛОНАСС/ GPS)2.



112

I.2.3 Interpolated assessment of the vertical ionosphere delay

When four points are used for interpolation, interpolated assessment of the

vertical ionosphere delay at the latitude pp and longitude pp is equal to:

where:

vk – transmitted values of a vertical delay of a grid-point model for k-th IGP

angle as showed in the Figure I.1.

W1 = xpp ypp;

W2 = (1-xpp )ypp;

W3 = (1-xpp )(1-ypp);

W4 = xpp (1-ypp).

Figure I.1 –IGP numerating condition (for four IGP)

x

y

v2

1

1

2

2

pp= pp- 1

pp= pp- 1

vpp( pp, pp)USER'S IPP

v1

v3 v4

4

1k

,vkkvpp τWτ



113

For IPP points between N85° and S85°:

pp 1

pp

2 1

λ λx ,

λ λ

pp 1

pp

2 1

,y

where:

1 – IGP longitude to the west of IPP;

2 – IGP longitude to the east of IPP;

1 –IGP latitude to the south of IPP;

2 – IGP latitude to the north of IPP.

Comment – If 1 and 2 cross 180о longitude when calculating xpp is considered

the difference in longitude values.

For IPP points located to the north of N85о or to the south of S85

о:

pp 1

ppy10 ,

pp 1

ppy10 ,

pp 3

pp pp pp

λ λx (1 2y ) y ,

90

where

1 – longitude of the second IGP located to the east of present IPP;

2 – longitude of the second IGP located to the west of present IPP;

3 – longitude of a nearest IGP located to the west of IPP;

4 – longitude of a nearest IGP located to the east of IPP.

When three points are used for interpolation, interpolated assessment of the

vertical ionosphere delay is as follows:

For points between 75оS and 75

оN:

vpp vk

3

kk 1

τ W τ ,

где:

W1 = ypp;

W2 = 1 – xpp – ypp;

W3 = xpp.



114

xpp and ypp is calculated as for 4-points interpolation, only that 1 and 1 are

always longitude and latitude of IGP2 and 2 and 2 – others longitude and latitude.

IGP2 is always a vertex of triangle (defined by the three points) opposite to the

hypotenuse; IGP1 has the same longitude as IGP2 and IGP3 has the same latitude as

IGP2 (example is showed in the Figure I.2).

x

y

v1

1

1

2

2

pp= pp- 1

pp= pp- 1

vpp( pp, pp)USER'S IPP

v2 v3

Figure I.2 –IGP numerating condition (three IGP points)

Three-points interpolation is not provided for points located to the north of

75оN and to the south of 75

оS.

I.2.4 Selection of ionosphere grid points (IGP)

Algorithm for selection of ionosphere grid points is given below:

a) For IPP between N60° and S60°:

1) If four IGP points defining around IPP a mesh 5 x 5о are set at "1" in the IGP

Mask, they are selected; otherwise,

2) If any three IGP points defining around IPP a triangle 5 x 5о are set at "1" in

the IGP Mask, they are selected; otherwise,



115

3) If four IGP points defining around IPP a mesh 10 x 10о are set at "1" in the

IGP Mask, they are selected; otherwise,

4) If any three IGP points defining around IPP a triangle 10 x 10о are set at "1"

in the IGP Mask, they are selected; otherwise,

5) Ionosphere correction is unavailable.

б) For IPP points between N60° and N75° or between S60° and S75°:

1) If four IGP points defining around IPP a mesh of size 5о latitude x 10

о

longitude are set at "1" in the IGP Mask, they are selected; otherwise,

2) If any three IGP points defining around IPP a triangle 5о of size 5

о latitude x

10о longitude are set at "1" in the IGP Mask, they are selected; otherwise,

3) If any four IGP points defining around IPP a mesh 10 x 10о are set at "1" in

the IGP Mask, they are selected; otherwise,

4) If any three IGP points defining around IPP a triangle 10 x 10о are set at "1"

in the IGP Mask, they are selected; otherwise,


в) For IPP points between N75° and N85° or between S75° and S85°:

1) If two IGP points nearest to 75° or two IGP points nearest to 85° (partitioned

by 30о longitude if diapason 9 or 10 is used, in other cases partitioned by 90

о) are set

at "1" in the IGP Mask, a mesh 10 x 10° is formed by linear interpolation between

IGP points at 85° for generation of virtual IGP points at longitudes equal to

longitudes of IGP points at 75°; otherwise,


г) For IPP to the north of N85°:

1) If four IGP points at N85° and longitudes W180о, W90

о, 0

о and E90

о are set

at "1" in the IGP Mask, they are selected; otherwise,


д) For IPP южнее S85°:

1) If four IGP points at S85° and longitudes W140о, W50

о, E40

о and E130

о are

set at "1" in the IGP Mask, they are selected; otherwise,




116

Comment: This selection algorithm is based only on the data contained in the

mask not taking into account in monitoring of selected points is effected or they are

not used. In any of selected points is identified by "Do not use" feature, ionosphere

correction is unavailable. If four IGP points are selected and one of them is identified

by "No monitoring" feature, 3-points interpolation is used provided that IPP point lies

inside the triangular area for which there are three corrections.

I.3 Protection levels

Horizontal Protection Level (HPL) and Vertical Protection Level (VPL) which

are measures of reliability of navigation solution, are defined as follows:

majorHSDCM dKHPL ,

VVSDCM dKVPL ,

where:

2

v

N2 2

v,i ii 1

d s σ – dispersion of distribution model including true error

distribution along the vertical axis;

22 2 2 2

x y x y 2

major xy

d d d dd d

2 2,

where:

2

x

N2 2

x,i ii 1

d s σ – dispersion of distribution model including true error distribution

along the x axis;

2

y

N2 2

y,i ii 1

d s σ – dispersion of distribution model including true error distribution

along the y axis;

xy

N2

x,i y, i ii 1

d s s σ – covariation of distribution models along the x and y axes,

where:

sx,i – partial x derivative of the position error relative to the pseudorange error

of the i-th satellite;



117

sy,i – partial y derivative of the position error relative to the pseudorange error

of the i-th satellite;

sV,i – – partial vertical derivative of the position error relative to the

pseudorange error of the i-th satellite;

2 2 2 2 2

i i,flt i,UIRE i,air i,tropoσ σ σ σ σ .

Dispersions (2

i,flt и 2

i,UIRE) are defined in Annexes I.3.2 and I.3.3. Parameters

(2

i,air and 2

i,tropo) are defined by onboard components (Section C.9).

x and y axes lie in the local horizontal plain and v axe is the local vertical.

For general case of least-squares method projection matrix S looks as follows:

x,1 x,2 x,N

y,1 y,2 y,N T 1 T

v,1 v,2 v,N

t,1 t,2 t,N

S S ... S

S S ... SS G W G G W,

S S ... S

S S ... S

where:

i-th column of the matrix G;

2

1

2

2

i i i i i i

2

1G cos El cos Az cos El sin Az sin El 1

0 0

0 0

0 0 N

W

,

where:

Eli – elevation of i-th range source (in degrees);

Azi – azimuth of i- th range source measured unticlockwise from the x axis (in

degrees);

wi – weighting factor corresponding to the i-th satellite.

Comment:

1 For easy reading the index i in the projection matrix is omitted.

2 For getting solution by the least-squares method without weighting factors

weighting matrix is set as unitary (wi = 1).

I.3.1 Definition of protection level coefficient K

Values of coefficient K are defined as follows:



118

6,0K H

5,33KV .

I.3.2 Definition of error model for fast and long-term corrections

If fast corrections and long-term corrections/range parameters of SDCM and

degradation parameters are applied, then:

flt

UDRE fc rrc ltc er UDRE

UDRE fc rrc ltc er UDRE

if RSS Message Type

if RSS Message Type

2

2

2 2 2 2 2

0 10

1 10

( )

, ( )

where:

If Message Type 27 is used, UDRE – index of a specific region;

If Message Type 28 is used, UDRE – index of a specific satellite;

If no message is used, UDRE = 1.

If fast corrections and long-term corrections/range parameters of SDCM are

not applied, then degradation parameters are not used:

22

, , 8i flt i UDRE UDRE m.

If fast corrections and long-term corrections/range parameters of SDCM are

not applied relative to a satellite or if relative to the satellite Message Type 28 is not

received with ephemeris covariation but valid Message Type 28 is received for

another satellite,:

22 2

, 60i flt м.

I.3.3 Fast corrections degradation

Degradation parameter for fast corrections looks as follows:

2

u lat

fc

t t tε a

2 ,

where:

t – current time;

tu – (reference time UDREIi): if IODFj 3, then this is the time of beginning of

1-second SDCM time époch which coincides with the transmission beginning of the



119

message block comprising the UDREIi data (Messages Type 2 5 or 24) which

coincide with IODFj of the used fast correction. If IODFj = 3, then this is the time of

beginning of 1-second SNT époch which coincides with the transmission beginning

of the message comprising the fast correction for the i-th satellite;

tlat – system delay (as defined in Section.054).

Comment – For UDRE parameters transmitted in Messages Type 2–5 and 24,

tu is equal to the affixment time of fast corrections as they are transmitted in the same

messages. For UDRE parameters transmitted in Message Type 6 and if IODF = 3, tu

is also equal to the affixment time of fast corrections (tof). For UDRE parameters

transmitted in Message Type 6 when IODF 3, tu is defined as the time of first bit

transmission of Message Type 6 to a SDCM satellite.

I.3.4 Corrections degradation to the range rate of change

If 0RRC , then 0rrc .

If 0RRC and 3IODF , then degradation parameter for fast corrections

looks as follows:

If 0RRC and 3IODF , then degradation parameter for the range rate of

change data looks as follows:

where:



120

t – current time;

IODFcurrent – parameter IODF corresponding to the latest fast correction;

IODFprevious – parameter IODF corresponding to the previous fast correction

∆t–ti,0f – ti,0f_previous;

Ifc – fast corrections validity interval for the user.

I.3.5 Degradation of long-time corrections of GLONASS and GPS satellites

For the range rate equal to 1 degradation parameter of a long-time correction of

the i- th satellite looks as follows:

ltc ltc_lsb ltc_v1 i,LT i,LT ltc_v1ε C C max(0, t t, t t I ).

For the range rate equal to 0 degradation parameter of a long-time correction is

defined as follows:

ltcltc ltc_v0

ltc_v0

t tε C ,

I

where:

t – current time;

tltc – the time of first bit transmission of a long-term correction message to

SDCM;

[x] – largest integer less than x.

Residual error degradation:

er

er

neither fast nor long term corrections

have timed out for precision approach

Cif fast or long term corrections

have timed out for precision approach

0,

,

Degradation factor UDRE is calculated on the basis of Message Type 28 data.

T

UDRE cδ I C I ε ,

where:



121

x

y

z

i

iI

i

1 ,

x

y

z

i

i

i

единичный вектор от пользователя до спутника в кадре координат ECEF WGS 84;

С = RT

R;

C = Ccovariance SF;

SF = 2scale exponent–5

;

R = E SF;

1,1 1,2 1,3 1,4

2,2 2,3 2,4

3,3 3,4

4,4

E E E E

0 E E E

0 0 E E

0 0 0 E

E

.

I.3.6 Definition of error model for ionosphere correction

Transmitted ionosphere corrections. If SDCM ionosphere corrections are

applied, looks as follows:

,

Where the same weighting factors are used for ionosphere pierce points (Wn)

and grid points selected for ionosphere correction. For each grid point the following

is valid:

ionogrid

GIVE iono iono

GIVE iono iono

if RSS Message Type

if RSS Message Type

2

2

2 2

0 10

1 10

( )

, ( )

,

ionoiono iono_step iono_ramp iono

iono

t tε C C (t t )

I ,

where:

2

UIREσ

UIRE pp UIVE

2 2 2σσ F

2

UIVE UIVE

4 32 2 2

n n,ionogridn n,ionogridn 1 n 1

σ W σ или σ W σ ,. .



122

t – current time;

tiono – the time of first bit transmission of a long-term correction message to

SDCM;

[х] – largest integer less than x.

Comment – For GLONASS and GPS satellites GIVE and IONO are multiplied

by the squared ration of GLONASS and GPS frequencies ( GLONASS / GPS)2.

I.3.7 Ionosphere corrections

If SDCM ionosphere corrections are not applied, 2

UIREσ looks as follows:

2

2 2ionoUIRE pp vert

Tσ MAX , F τ

5,

where:

Tiono– ionosphere delay according to an assessment results for a selected model;

pp

vert pp

pp

9m, 0 20

τ 4, 5m, 20 55;

6 m, 55

pp – ionosphere pierce point latitude.

I.3.8 GLONASS time

Degradation parameter of a long-time correction of the i- th satellite looks as

follows:

,][ clock_clock_ockGLONASS_cl GLONASSGLONASS t-tC

where:

t – current time;

clock_GLONASSt – the transmission time of synchronization message first bit

(Message Type 12) to GEO;

[x] – largest integer less than x.

Comments:



123

1. For satellites not included in GLONASS,

_ 0GLONASS clock .

2. sec/00833,0clock_ smCGLONASS .



124

16 Annnex J. Additional materials and data

J.1 SDCM Coverage and Service area

J.1.1 It is necessary to distinguish the terms «SDCM Coverage» and «SDCM

Service area within SDCM Coverage».

SDCM Coverage is defined by the area in which the user receives a signal from

a SDCM GEO satellite of receives the same SDCM data via ground-based

communication channels.

SDCM Service area within SDCM Coverage is defined by the borders of one

or several, possibly not crossing, areas within which a service provider (i.e.

“organization operating SDCM”) provides access to SDCM functions for navigation

operation being realized by navigation user equipment.

For most operations global SDCM data are sufficient, i.e. correcting data and

integrity data delivered via ground links or via geostationary satellites. Service area

of such operations coincides with the SDCM coverage. Other operations will require

additional local data distributed by SDCM ground facilities only in those local areas

for which these data are valid. In general service areas for different navigation

operations may not coincide and they are defined by a service provider by deploying

SDCM ground facilities in those areas where they will be in demand. However, in

any case a system service area covers all SDCM service areas within admissible

operations effected by navigation user equipment.

The information below concerning service and coverage areas pertains to the

SDCM service area and permissible system coverage area.

Figure J.1 shows service and coverage areas for five SBAS systems:

- Wide Area Augmentation System WAAS;

- European Geostationary Navigation Overlay Service EGNOS;

- Japanese Multi-functional Satellite Augmentation System MSAS;

- Indian GPS Aided Geo Augmented Navigation GAGAN;



125

- Russian Satellite Augmentation System SDCM.

Figure J.1 – Service areas of SBAS.

Currently all the systems – WAAS, EGNOS, MSAS, GAGAN transmit wide

area corrections only for GPS satellites.

J.1.2 Enhanced C/A codes of SDCM

Currently the issue of enhancing the quantity of codes to be used (by systems

of SDCM type, for example) is considered. Enhancement extent is from 19 to 39 (see

Table J.1).

Table J.1– Permissible С/А codes (enhanced table)

PRN G2 delay (chips) First 10 chips

120 145 0671

121 175 0536

122 52 1510

123 21 1545

124 237 0160

125 235 0701

126 886 0013



126

127 657 1060

128 634 0245

129 762 0527

130 355 1436

131 1 012 1226

132 176 1257

133 603 0046

134 130 1071

135 359 0561

136 595 1037

137 68 0770

138 386 1327

139 797 1472

140 456 0124

141 499 0366

142 883 0133

143 307 0465

144 127 0717

145 211 0217

146 121 1742

147 118 1422

148 163 1442

149 628 0523

150 853 0736

151 484 1635

152 289 0136

153 811 0273

154 202 1026

155 1021 0003

156 463 1670

157 568 0624

158 904 0235



127

17 References

1. Minimum Operational Performance Standards for Global Positioning System /

Wide Area Augmentation System Airborne Equipment - Document NO. RTCA/DO-

229D, Washington, 2006.

2. International standards and recommended practice /Annex 10 to the

Convention on the International Civil Aviation – International Civil Aviation

Organization, Edition 6, July 2006.

3. Wide Area Augmentation System (SBAS), Federal Aviation Administration

Specification, FAA-E-2892B – U.S. Department of transportation, September 1999.

4. Minimum Operational Performance Standards for Airborne Supplemental

Navigation Equipment Using Global Positioning System (GPS) - Document NO.

RTCA/DO-208, Washington, 1991.

5. Software Considerations in Airborne Systems and Equipment Certification -

Document NO. RTCA/DO-178B, Washington, 1992.



128

18 Changes registration list

Version Date of change Changes Signature

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INTERFACE CONTROL DOCUMENT - sdcm.ru · PDF fileSYSTEM OF DIFFERENTIAL CORRECTION AND MONITORING INTERFACE CONTROL DOCUMENT Radiosignals and digital data structure of GLONASS Wide