eLoran for e-Navigation - The Requisite Co-Primary Source

eLoran for e-Navigation -

The Requisite Co-Primary Source for Position, Navigation, Time, and Data

Gerard Offermans, Erik Johannessen, Stephen Bartlett,

Andrei Grebnev, & Charles Schue – UrsaNav, Inc.

ITM 2014, San Diego CA

January 27-29, 2014

EMEA OperationsBertem, Belgium

Corporate HeadquartersChesapeake, VA

Washington DC Metro AreaLeesburg, VA

Southeast RegionNorth Charleston, SC

Northeast RegionBedford, MA 2

The Problem

Vulnerabilities• Performance degradation

• Ionosphere & solar activities(natural)

• Unintentional & intentional(human factors)

• Signal blockage

• Spectrum competition

• Common signal use across GNSS

• Radio frequency interference

• System anomalies & failures

• Jamming

• Spoofing & Counterfeit Signals

• Proliferation of satellite systems

• Program funding delays

• Satellite launch problems

[Source: ctstechnologys.com/gps-jammers/]

Blocker

Disrupter

Waterproof

40 Watts

All Bands

1,000 m

Of the (16) CIKR sectors, (15) use GPS

timing.

GPS timing is deemed essential

for (10) of the sectors.

[Source: DHS]

http://www.ctstechnologys.com/gps-jammers/986809.html














The Problem

Source: Ministry of Land Transport and

Maritime Affairs of the Republic of Korea





Northeast RegionBedford, MA

eLoran Basics

Key characteristics

High power (250 kW)

Low frequency (100 kHz)

Pulse shaped signals allow

groundwave - skywave separation

Data channel to provide UTC

information, Differential corrections

and integrity information

Long range (>1,000 miles)

coverage

No common failure modes with

GNSS

Provides the same information as

GNSS (time, frequency, position,

heading and data)

10 ms

3 kmUTC Sync

Point






2013 Timing Trials Set-up

5

Monitor

Location

Distance from

Transmitter

USNO 118 miles

Leesburg 143 miles

Bedford 311 miles






Test Transmitter Set-Up in Wildwood, NJ

6

GPS Receiver

5071A Cesium

UTC synchronization

through GPS

eLoran

Broadcast

Legacy Loran Transmitter

360 kW

Preproduction NL Transmitter

60 kW






eLoran for Time and Frequency

eLoran receiver measures Time of Arrival (TOA) of the eLoran signal

TOA = TTOR – TTOT = PF + SF + ASF + ΔRx

where:

TOR - Time of Reception Measured

TOT - Time of Transmission UTC Message

PF - Primary Factor (propagation through air) By definition

SF - Secondary Factor (propagation over sea) By definition

ASF - Additional Secondary Factor Unknown

(propagation over land and elevated terrain)

ΔRx - Receiver and cable delays Unknown

7

TTOT

TTOR

PF SF ASF ΔRx

Known by UTC Message and Position One-time Calibration






Measurement Set-Up at USNO

8

eLoran

Broadcast

UN-152B eLoran

Timing ReceiverUSNO Master ClockTime Interval

Counter

22/11/2013 00:32:02, 56618.02224537,1.16192e-07

22/11/2013 00:33:02, 56618.02293981,1.15408e-07

22/11/2013 00:34:02, 56618.02363426,1.18039e-07

22/11/2013 00:35:02, 56618.02432870,1.17931e-07

…

eLoran vs. USNO

Master Clock






Measurement Set-Up in Bedford MA

9

eLoran

Broadcast

UN-152B eLoran

Timing ReceiverTime Interval

Counter

22/11/2013 00:32:02, 56618.02224537,1.16192e-07

22/11/2013 00:33:02, 56618.02293981,1.15408e-07

22/11/2013 00:34:02, 56618.02363426,1.18039e-07

22/11/2013 00:35:02, 56618.02432870,1.17931e-07

…

eLoran vs. Cesium or

eLoran vs. GPS

5071A Cesium

GPS Receiver






Timing Application: Electrical Power Grid

Frequency Data Recorder






GPS vs Cesium at Bedford, MA

11






Loran vs Cesium at Bedford, MA

12






Timing Application: Electrical Power Grid

0 500 1000 1500 200059.94

59.96

59.98

60

60.02

60.04

60.06

Time (s)

Fre

qu

en

cy(H

z)

Frequency Comparision of FDR with GPS vs with eLoran

Frequency-FDR with GPS

Frequency-FDR with eLoran

0 500 1000 1500 2000-50

-40

-30

-20

-10

0

10

Time (s)

Un

wra

p A

ng

le(r

ad

ian

)

Angle Comparision of FDR with GPS vs with eLoran

Angle-FDR with GPS

Angle-FDR with eLoran

40 60 80 100 120 14059.975

59.98

59.985

59.99

59.995

Time (s)

Fre

qu

en

cy(H

z)

Frequency Comparision of FDR with GPS vs with eLoran

Frequency-FDR with GPS

Frequency-FDR with eLoran

20 40 60 80 100 120 140-6

-4

-2

0

2

Time (s)

Un

wra

p A

ng

le(r

ad

ian

)

Angle Comparision of FDR with GPS vs with eLoran

Angle-FDR with GPS

Angle-FDR with eLoran

“That is great, now we can see the data from unit 905 and 913.

Could you tell me which unit is using eLoran now?”






Measurement Results: USNO

14

• eLoran 1PPS measured against USNO Master Clock

• 15-day continuous observation - 60 seconds observation interval

• Apparent diurnal behavior - Standard deviation: 29 ns

• 118 miles from transmitter – only coarse calibration performed






Measurement Results: Leesburg, VA

15

• eLoran 1PPS measured against Cesium (not disciplined)

• 15-day continuous observations - 120 seconds observation interval

• Apparent diurnal behavior - Standard deviation: 36 ns

• 143 miles from transmitter






Comparison of Leesburg and USNO data

16

• High correlation between phase differences at Leesburg and USNO

• Amplitude of phase changes higher at Leesburg

• Correlation indicates that differential corrections from USNO would benefit a

user at Leesburg ( ~ 25 miles)






eLoran in Europe

17

Transmitter

Location

Distance from

Bertem, Belgium

Lessay, France 480 km (298 mi)

Anthorn, UK 696 km (432 mi)






eLoran Timing in Europe

18

• eLoran 1PPS measured against Novatel OEM3 GPS Receiver

• 6-day continuous observation - 120 seconds observation interval

• Diurnal behavior present but less prominent, Standard deviation – 14 ns

• 480 km (298 miles) from transmitter at Lessay, France






UK GLA IOC dLoran System Configuration

19

Contract awarded 2013 for 7 differential Loran sites

General Lighthouse Authorities active in standardization efforts

System expansion in 2015 to cover south, west & Ireland






Typical Position Accuracies in Bertem, Belgium

Stand alone Loran-C offset 357.3 m, 7.1 m (95%) from surveyed position







GPS offset 0.6 m, 2.2m (95%) from surveyed position







Differential eLoran offset 2.4 m, 7.1 m (95%) from surveyed position






DLoran RSIM Implementation for eLoran

23






UN-154 differential eLoran RSIM 1U rack mount

Contains eLoran Receiver and Kontron CPU with dual power supplies and

solid state drive

24






Nautel NL-60 eLoran Transmitter

25






Possible Approach

• Government loans existing assets (i.e. land, buildings, antennas, site

equipment) under a 20 year lease

• Industry provides necessary equipment and services to fulfill a service-

level agreement

• Tiered service with mechanism for revenue recovery to reduce or

eliminate out-year costs to government

Phased Approach

• Initial phase resurrects 2008 era

• Rapid build out of CONUS high reliability timing network (dual coverage)

• Positioning and Navigation capabilities added later

Benefits

• Deferral of EC&R costs

• Fulfills backup PNT capabilities per NSPD-39

• Advances technology and creates employment

Next Steps: Co-Primary T+F Solution in U.S.?






Four Station (“Single”) Timing Coverage






Conclusions

eLoran system (transmitter and receiver) meets Statum-1

frequency standard and ETSI PRC mask requirements

eLoran system can provide UTC synchronization over large areas

eLoran UTC reception influenced by diurnal and seasonal

variations in ASF

ASF fluctuations can be compensated by use of differential

eLoran corrections

UTC Sync within 100 ns (unassisted) and within 50 ns (with

differential corrections)

United Kingdom and Republic of South Korea are moving forward

with eLoran; fulfilling a requirement for a resilient PNT system (co-

primary solution to GNSS)

United States …






GPS and eLoranCo-Primary Solutions

Documents

eLoran for e-Navigation - The Requisite Co-Primary Source