passive geo-location of an rf transmitter · passive geo-location of an rf transmitter this work is...

Patrick Boudreau & Justin Rice

Group 105

October 15, 2014

Passive Geo-location of an RF Transmitter

This work is sponsored under Air Force Contract #FA8721-05-C-0002. Opinions, interpretations, conclusions and recommendations are those of the author and

are not necessarily endorsed by the United States Government.

Two Receiver TDOA- 2

PLB JDR 10/15/2014

Problem

Receiver 1

Receiver 2

Tx


PLB JDR 10/15/2014

System Concept: Block Diagram

Control

Center

GPS

Disciplined

Oscillator

Receiver 1

FPGA

Card

Clock

source

for ADC

Antenna

Control

Center

GPS

Disciplined

Oscillator

Receiver 2

FPG

Card

Clock

source

for ADC

Signal

Generator

Transmitter

Antenna Antenna

Com

munic

atio

n

Lin

k


PLB JDR 10/15/2014

Time Synchronization

GPS disciplined

oscillator 1Hz output

Trigger

225 MHz

Clock

Count since last

1 Hz signal


PLB JDR 10/15/2014

-20 -10 0 10 20-30

-20

-10

0

10

20

30

distance (km)

dis

tan

ce (

km

)

Two Receiver TDOA

Rx

Hyperbola

-25 -20 -15 -10 -5 0 5 10 15 20 25-30

-20

-10

0

10

20

30

distance (km)

dis

tance (

km

)

Two Reciever TDOA

Rx

TDOA Hyperbola

-25 -20 -15 -10 -5 0 5 10 15 20 25-30

-20

-10

0

10

20

30

distance (km)

dis

tance (

km

)

Two Reciever TDOA

Rx

TDOA Hyperbola

Geo-location Technique: Time Difference of Arrival


PLB JDR 10/15/2014


-20 -10 0 10 20-30

-20

-10

0

10

20

30

distance (km)

dis

tan

ce (

km

)

Two Receiver TDOA

Rx

Hyperbola

-20 -10 0 10 20-30

-20

-10

0

10

20

30

distance (km)

dis

tan

ce (

km

)

Two Receiver TDOA

Rx

Hyperbola


PLB JDR 10/15/2014


-20 -10 0 10 20-30

-20

-10

0

10

20

30

distance (km)

dis

tan

ce (

km

)

Two Receiver TDOA

Rx

Hyperbola


PLB JDR 10/15/2014


1.0 km

d1

d2

Receiver 1 at (-0.5, 0)

Receiver 2 at (0.5, 0)

Transmitter at (75, 100)

(All in kilometers)

So d1 = 125.3 km

So d2 = 124.7 km

Time signal travels along:

d1 is 415.7 ns

d2 is 417.7 ns

TDOA = 2.0 ns Receiver 1 Receiver 2

Transmitter


PLB JDR 10/15/2014

How Precise?

• The target should be located to within 1.5° in both azimuth and elevation, from the view

of receiver one 70% of the time

• This requirement corresponds to a timing error of within ±60 ns


PLB JDR 10/15/2014

Testing Outline

Step Result

Test GPS units outside of system

Test GPS units in the system in the lab

Test GPS units in the system in the field


PLB JDR 10/15/2014


• 1 Hz disciplined output

• 2hr 16 min capture time

• 11 captures GPS

Antenna

GPS

Antenna

Window

Oscilloscope

Ch 1 Ch 4 10 ft

10 ft

4 ft

4 ft

N

2 ft

GPS

Disciplined

Oscillator

GPS

Disciplined

Oscillator


PLB JDR 10/15/2014


0 0.5 1 1.5 2 2.5-60

-40

-20

0

20

40

60

80

Time (Hours) since 11:00 AM

Tim

e D

iffe

ren

ce (

ns)

Time Series Plot of Time Difference


PLB JDR 10/15/2014


Total

Runs

Mean

(ns)

Standard

deviation

(ns)

Percentage of

time differences

within ±60 ns

Percentage of

time differences

within ±40 ns

Percentages of

time differences

within ±30 ns

11 11.0 34.0 90.5% 73.5% 61.6%

These tests show that the requirement was exceeded. The times are within ±60 ns

over 70% of the time


PLB JDR 10/15/2014

Testing Outline

Step Result

Test GPS units outside of system Success

Test GPS units in the system in the lab



PLB JDR 10/15/2014


GPS disciplined

oscillator 1Hz output

Trigger

225 MHz

Clock

Count since last

1 Hz signal


PLB JDR 10/15/2014

Lab Test

Signal

Generator

Power

Divider

• -15 dBm

• 2.4 GHz

• 1 ms pulse repetition interval

• 100 μs pulse width

Control

Center

GPS

Disciplined

Oscillator

Receiver 2

FPGA

Card

Clock

source

for ADC

Control

Center

GPS

Disciplined

Oscillator

Receiver 1

FPGA

Card

Clock

source

for ADC


PLB JDR 10/15/2014

Lab Test: Zero Time Difference of Arrival

• 3 ft cable to power divider, 6 ft cable

to both receiver

• 86% within ±60 ns of the mean

• 105 ns mean

• Expected TDOA: 0 ns

• Actual (with offset): 105 ns

0 2 4 6 8 10 12 14 16-50

0

50

100

150

200

250

300

Time Elapsed (hours)

TD

OA

Valu

e (

nan

oseco

nd

s)

TDOA of Two Receivers with 6ft Cables Over 16 Hours


PLB JDR 10/15/2014

Lab Test: Cable Delay


to one receiver and 150 ft to the

other


• -96 ns mean

• Expected TDOA: -180 ns

• Actual (with offset): -201 ns 0 2 4 6 8 10 12 14 16

-300

-250

-200

-150

-100

-50

0

50

100


TD

OA

Valu

e (

nan

oseco

nd

s)

TDOA of Two Receivers with 150 ft of Cables to One Receiver Over 16 Hours


PLB JDR 10/15/2014

Lab Test: Cable Delay

• Cable delay, according to data sheet

should be 1.2 ns/ft

• Estimated cable delay was 1.8 ns/ft

0 50 100 150 200 250-350

-300

-250

-200

-150

-100

-50

0

50

100

150

Length of Cable to Receiver (ft)

Mean

Tim

e D

iffe

ren

ce (

ns)

Mean Time Difference vs Length of Cable to Receiver


PLB JDR 10/15/2014

Testing Outline

Step Result


Test GPS units in the system in the lab Success



PLB JDR 10/15/2014

Field Test

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2.2

-2.1

-2

-1.9

-1.8

-1.7

-1.6

-1.5

-1.4

-1.3

-1.2x 10

5


TD

OA

Valu

e (

nan

oseco

nd

s)

TDOA of Two Receivers Seperated by 50 m, Transmitter 26 m from Each Receiver

0 2 4 6 8 10 12 14 16-50

0

50

100

150

200

250

300


TD

OA

Valu

e (

nan

oseco

nd

s)



PLB JDR 10/15/2014

Testing Outline

Step Result


Test GPS units in the system in the lab Success

Test GPS units in the system in the field Failure


PLB JDR 10/15/2014

Lab Test: System After Startup


to both receivers


• Stabilized to a mean of 60 ns

0 5 10 15 20-150

-100

-50

0

50

100

150

200


TD

OA

Valu

e (

nan

oseco

nd

s)



PLB JDR 10/15/2014

Testing Outline

Step Result


Test GPS units in the system in the lab ???

Test GPS units in the system in the field Failure


PLB JDR 10/15/2014

Summary

• GPS disciplined oscillator’s time error small enough to meet the 1.5° requirement 70%

of the time

• System Testing

– Offset discovered but source still unknown

• Offset independent of cables

• Startup conditions affect the offset

– Field Test

• More lab testing required before further field testing can be conducted

• Results acquired useful to Group 105


PLB JDR 10/15/2014

Future Work

Lab testing: Is offset in GPS disciplined oscillator or the rest of Receiver Hardware?

- Input 1 Hz signal from signal generator into both receivers instead of GPS disciplined oscillator output

GPS Disciplined Oscillator

- Analyze satellite data – Signal to noise ratio and number of satellites over time

- Test other 1 Hz disciplined outputs

Other Receiver Hardware

- Test 1 Hz signal input to FPGA card. Test 1 Hz signal at every connection in the FPGA that it passes through

- Lock the signal generator to the GPS disciplined oscillator 10 MHz disciplined clock output as stable reference for the pulse repetition interval

- Test all connections in system


PLB JDR 10/15/2014

Acknowledgements

John Meklenburg 105

Ted Clancy WPI

Ryan Lewis 105

Dan Rabideau 105

Jeffrey Blanco 105

Rory Fagan 105

Matt Campbell 105

Robert Devine 86

David Scott TOIL


PLB JDR 10/15/2014

Thank You

Questions?

passive geo-location of an rf transmitter · passive geo-location of an rf transmitter this work is...

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