Mobile Communication Standards - … Channels (TCH): ... BCCH (Broadcast Control Channel) and SCH ... Mobile Communication Standards

MOBILE COMMUNICATION

STANDARDS By

Pradip Paudyal

GSM (GLOBAL SYSTEM FOR MOBILE)

2 G, digital standard

Wide range of services through the use of ISDN

GSM Services and Features

Teleservices: standard mobile telephony

Data services: Packet switched traffic; Computer

to computer communication

GSM SERVICES AND FEATURES

User Services are categorized as:

Telephone Services: emergency calling, facsimile,

videotext and teletext.

Barrier Services/ Data Services: Limited to layer

1, 2, 3 of OSI model, support packet switched

protocol, data rates from 300bps to 9.6 Kbps.


Supplementary ISDN Services: digital in nature

Call diversion

Caller identification

Closed user group

Short massaging services

SMS call broadcast


Features

Subscriber Identity Module; Memory devices

stores the information such as subscriber identity

number, network, country, privacy keys .

On the air privacy: Cryptography key known only

for carrier and changes with time for the user;

GSM SYSTEM ARCHITECTURE

GSM SYSTEM ARCHITECTURE CONT..

BSS (Base Station Subsystem)

Also known as radio subsystem, provides and

manages radio interface for transmission path.

Contains many BS, BSC and MS

NSS (Network Switching Subsystem)

Manage switching function of the system

Allow the MSC to communicate with other

network such as PSTN and ISDN.

GSM SYSTEM ARCHITECTURE CONT…

NSS handles the switching of GSM call between

external networks and BSCs

NSS is responsible for managing and providing

access to databases.

MSC control the traffic among BSCs


Contains three databases called;

Home Location Register (HLR):

Contains subscriber information and location information of user.

Each subscriber is assigned a unique IMSI (International Mobile Subscriber Identity) number to identify the each home user.

Visitor Location Register (VLR):

Temporary store the IMSI and customer information for each roaming subscriber who is visiting particular coverage area of MSC.

VLR are linked between several adjoining MSCs in particular geographical region.


Authentication Center (AuC):

Strongly protected database which handles the

authentication and encryption keys for every

single subscriber in HLR and VLR.

Contains a register called EIR (Equipment

Identity Register).


OSS (Operation Support Subsystem)

Support the operation and maintenance of GSM

Allows the system engineer to monitor, diagnose

and troubleshoot of all aspect of GSM system.

Support one or more OMC (Operation and

Maintenance Center)


Three main function of OSS are:

To maintain all telecommunication hardware

and network operation with a particular market.

Manage all charging and billing procedure

Manage all mobile equipment in the system

INTERFACES USED IN GSM

INTERFACES USED IN GSM CONT…

Interface which connect BTS and BSC called Abis

interface.

Abis interface carries traffic and maintenance

data.

BSCs are physically connected through

dedicated/leased line or microwave link to the

MSC

A interface uses an SS7 protocol

A interface allows service provider to use base

station and switching equipment made by

different manufacturer.

GSM RADIO SUBSYSTEM

Use two band of 25 MHz.

890-915 MHz band is used for reverse link.

935-960 MHz band is used for forward link.

It use FDD, TDMA and FHMA.

Available band is divided in to 200 KHz sub-

channel called ARFCN (Absolute Radio

Frequency Channel Number)

ARFCN denotes forward and reverse channel

pairs which are separated by 45 MHz and shared

by 8 time slots.

0.3 GMSK Modulation

GSM RADIO SUBSYSTEM

GSM FRAME STRUCTURE

GSM RADIO SUBSYSTEM

SIGNAL PROCESSING

Several successive operations have to be

performed to convert a speech signal into a radio

signal and back.

SIGNAL PROCESSING

The following operations take place on the

transmitting side:

• Source coding: Converts the analogue speech

signal into a digital equivalent.

• Channel coding: Adds extra bits to the data flow.

This way redundancy is introduced into the data

flow, increasing its rate by adding information

calculated from the source data, in order to allow

detection or even correction of bit errors that

might be introduced during transmission.

SIGNAL PROCESSING

• Interleaving:

Changes sequence of data stream

Reduces loss sequential data (Burst Error →

Random Error)

Improves ability to reconstruct original data

1 2 3 4 5 6 7 8 9 10 11 12

13 14 15 16 17 18 19 20 21 22 23 24

25 26 27 28 29 30 31 32 33 34 35 36

37 38 39 40 41 42 43 44 45 46 47 48

49 50 51 52 53 54 55 56 57 58 59 60

Data Input

Data

Output

Block Interleaver Input Data : 1, 2, 3, 4, . . . . . . 59, 60

Block Interleaver Output Data : 1, 13, 25, 37, . . . . . . 48, 60

SIGNAL PROCESSING

• Ciphering: Modifies the contents of these blocks through a secret code known only by the mobile station and the base station.

• Burst formatting: Adds synchronization and equalization information to the ciphered data. Part of this is the addition of a training sequence.

• Modulation: Transforms the binary signal into an analogue signal at the right frequency. Thereby the signal can be transmitted as radio waves.

The receiver side performs the reverse operations as follows:

• Demodulation: Transforms the radio signal received at the antenna into a binary signal.

SIGNAL PROCESSING

• Deciphering: Modifies the bits by reversing the ciphering code.

• De-interleaving: Puts the bits of the different bursts back in order to rebuild the original code words.

• Channel decoding: Tries to reconstruct the source information from the output of the demodulator, using the added coding bits to detect or correct possible errors, caused between the coding and the decoding.

• Source decoding: Converts the digitally decoded source information into an analogue signal to produce the speech.

GSM CHANNELS

Channels

Traffic Channels (TCH): may be full rate or half rate

When transmitted at full rate user data is contained within one time slot per frame; but for half rate same time slot but in alternative frame

Full rate TCH

Full Rate Speech Channel (TCH/FS): 13 Kbps from the source and after channel coding 22.8 Kbps.

Full Rate Data Channel for 9600 Bps



Half rate TCH

Half Rate Speech Channel: 6.5 Kbps from the speech coder and after channel coding 11.4 Kbps



GSM CONTROL CHANNEL

Control Channels:

For signaling and synchronization commands

Broadcast Channel (BCH)

Forward link and in TS0 of certain frame

Broadcast Control Channel (BCCH): Used to

broadcast certain information such as cell and

network identity, operating characteristics of cell, list

of channel that are currently being used

Frequency Correction Channel (FCCH): TS0 on

every 10 frames, frequency synchronization of user to

system

Synchronization Channel (SCH): to identify

serving base station

GSM CONTROL CHANNEL

Common Control Channel (CCCH): If

channel is not used by BCH or if idle

Paging Channel (PCH): Provides paging signal

from BS to MS, transmits IMSI number of user along

with request for acknowledgement from the mobile

unit on RACH, to broadcast text message e.g. SMS

Random Access Channel (RACH): Reverse link

channel, to ACK page from PCH and to originate

mobile call. (slotted ALOHA )

Access Grant Channel (AGCH): used by BS to

provide forward link communication to mobile and

carries data which instruct mobile to operate on

particular channel.

GSM CONTROL CHANNEL

Dedicated Control Channel (DCCH)

Stand Alone Dedicated Control Channel (SDCCH):

carries the signaling data just before TCH assignment by

BS, to remain in connection when BS and MSC verify the

subscriber unit and allocate resource for mobile. E.g.

temporary channel

Slow Associated Control Channel (SACCH):

Associated with TCH/SDCCH, on forward link used to send

slow (13th frame)but regularly changing control

information e.g. transmit power level and timing, on

reverse link received signal strength and quality of TCH

and BCH strength from neighboring cell.

Fast Associated Control Channel (FACCH): Carries

urgent message e.g. hand-off request, by stealing time slot

from TCH.

EXAMPLE OF GSM CALL

First MS must be synchronize with near by BS as it monitors BCH.

By receiving FCCH (frequency Correction Channel), BCCH (Broadcast Control Channel) and SCH (Synchronization Channel) message the subscriber would be locked on system and appropriate BCH.

First user dial the number and press send button

MS will transmit a burst of RACH (Random Access Channel) data using same ARFCN as locked with BS.

BS responds with AGCH; which assign a new channel for SDCCH (Stand-alone Dedicated Control Channel ) connection.

Once tuned to SDCCH, MS waits for SACCH (Slow Associated Control Channel) which gives power level and timing command.

EXAMPLE OF GSM CALL

Then MS is able to transmit normal burst

message.

SDCCH send message between MS and BS;

making care of validation and authentication.

After few second MS is commanded by BS via

SDCCH to retune to a new ARFCN and new TS

for TCH assignment.

Then speech data is transferred on forward and

reverse link.

ABOUT IS-95 CDMA

IS-95 is specified as:

Reverse Link: 824-849 MHz

Forward Link: 869-894 MHz

Forward and reverse is separated by 45 MHz

Maximum user data rate is 9.6 Kbps

Forward IS-95B Channel Structure

Pilot Channel (Walsh Code 0)

- The Pilot is “structural beacon” which does not contain a

character stream

- Allows Mobile to Acquire the System

- Reference Signal for System Acquiring, Timing, Coherent

Modulation

- Provides Mobile with Signal Strength Comparison during

handoffs

- Transmitted Constantly

- Non-Modulated Spread Spectrum Signal (Transmit Short PN

Code)

- Has Unique PN Offset(512) for each Cell or Sector

- Approximately 20% of radiated BTS power is in the pilot


Sync Channel (Walsh Code 32)

- Used by Mobile to Synchronize with System

- Carries a data stream of system identification and

Parameter information used by MS during system

acquisition

- Pilot PN Offset

- System Time

- Long PN Code

- System ID

-Network ID

- Paging Channel Data Rate

- Tx at 1200 bps


Paging Channel (Walsh Code 1 up to 7)

- Used by Base Station to :

-Page Mobile Information

-Transmit Overhead

-MS Control

-Assign Mobile to Traffic Channel

- Provides Mobile with:

-System parameter Message

- Neighbor List Message

-Access Parameter Message

-CDMA Channel List Message

- Tx at 9600 or 4800 bps


Reverse IS-95B Channel Structure

Access Channel

- Used by Mobiles not yet in a call to transmit :

-Registration Requests

-Call Setup Requests

-Page Responses

-Order Responses

- other Signaling information

- Be really just a public Long Code Offset unique to the BTS Sector

- Be Paired to Paging Channel (Each Paging Channel can have up

32 access channels)

- Tx at 4800 bps, 20ms frame length



Traffic Channel - Be used by individual users during their actual calls to transmit traffic to the BTS

- Be really just a user-specific public or private Long Code Mask

- there are many reverse Traffic channels as there are CDMA phones in the world

- 64-ary Orthogonal Modulator : For Non-coherent detection

- Data Burst Randomizer : For Power Control and Variable Rate Transmission

SUMMARY OF POWER CONTROL

All types of power control work together to minimizes power

consumption at the mobile stations and BS, and increases the overall

capacity of the system

FER FER

Mobile BTS BSC

Signal Strength

Measurement

Setpoint

or

Adjust Fwd.

power

Reverse Outer

Loop Power

Control

Reverse Closed Loop

Power Control

Forward Link Power Control

Reverse Open Loop

Power Control

FORWARD QUICK POWER CONTROL

Received the Frame

Quality Information

from the Forward Link

Eb/Nt>Eb/No?

Outer-loop

Algorithm

Up Power

Control Bit

Down Power

Control Bit

Puncture to

Power Control

Subchannel

Power Control

Command

Measurement

Power Control

Command

Measurement

Demodulate and

measure Eb/Nt

Outer Loop Correction

Closed-loop Control

Mobile Station

Base Station

Eb/No

No

Yes

DECT DECT (Digital European Cordless Telephone)

standardized by ETSI (ETS 300.175-x) for cordless telephones

standard describes air interface between base-station and mobile phone

DECT has been renamed for international marketing reasons into „Digital Enhanced Cordless Telecommunication“

Characteristics frequency: 1880-1990 MHz

channels: 120 full duplex

duplex mechanism: TDD (Time Division Duplex) with 10 ms frame length

multiplexing scheme: FDMA with 10 carrier frequencies, TDMA with 2x 12 slots

modulation: digital, Gaussian Minimum Shift Key (GMSK)

power: 10 mW average (max. 250 mW)

range: ca 50 m in buildings, 300 m open space

DECT SYSTEM ARCHITECTURE REFERENCE

MODEL

global

network

local

network

local

network

FT

FT

PT PA

PT PA

VDB

HDB

D1

D2

D3 D4

PA - Portable Application

PT - Portable radio

Transmission

FT - Fixed radio

Transmission

HDB - Home Data Base

VDB - Visitor Data Base

physical layer

medium access control

data link

control

data link

control

network

layer

OSI layer 1

OSI layer 2

OSI layer 3

U-Plane C-Plane signaling,

interworking

application

processes

DECT REFERENCE MODEL

close to the OSI

reference model

management plane

over all layers

several services in

C(ontrol)- and U(ser)-

plane

man

agem

en

t

DECT LAYERS I Physical layer

modulation/demodulation

generation of the physical channel structure with a guaranteed throughput

controlling of radio transmission

channel assignment on request of the MAC layer

detection of incoming signals

sender/receiver synchronization

collecting status information for the management plane

MAC layer

maintaining basic services, activating/deactivating physical channels

multiplexing of logical channels

e.g., C: signaling, I: user data, P: paging, Q: broadcast

segmentation/reassembly

error control/error correction

DECT LAYERS II

Data link control layer

creation and keeping up reliable connections between

the mobile terminal and basestation

two DLC protocols for the control plane (C-Plane)

several services specified for the user plane (U-Plane)

null-service: offers unmodified MAC services

frame relay: simple packet transmission

frame switching: time-bounded packet transmission

error correcting transmission: uses FEC, for delay critical,

time-bounded services

bandwidth adaptive transmission

„Escape“ service: for further enhancements of the standard

DECT LAYERS III

Network layer

similar to ISDN (Q.931) and GSM (04.08)

offers services to request, check, reserve, control, and release resources at the basestation and mobile terminal

resources necessary for a wireless connection

necessary for the connection of the DECT system to the fixed network

main tasks call control: setup, release, negotiation, control

call independent services: call forwarding, accounting, call redirecting

mobility management: identity management, authentication, management of the location register

DECT: For detailed Ref: T.S.R

Thank You……………………..????????????????

Documents

Mobile Communication Standards - … Channels (TCH): ... BCCH (Broadcast Control Channel) and SCH ... Mobile Communication Standards