SUPRESSION OF LORAN-C NAVIGATION SIGNAL IN DIGITAL CAVE RADIOS (AN EXPERIMENTAL APPROACH)

SUPRESSION OF LORAN-C NAVIGATION SUPRESSION OF LORAN-C NAVIGATION SIGNAL IN DIGITAL CAVE RADIOS SIGNAL IN DIGITAL CAVE RADIOS (AN EXPERIMENTAL APPROACH)(AN EXPERIMENTAL APPROACH)

Mr. Antonio Muñoz

Group of Technologies in hostile Environments (GTE) Group of Technologies in hostile Environments (GTE)

University of Zaragoza (Spain)University of Zaragoza (Spain)

BCRA Cave Technology Symposium

Group of Technologies in Group of Technologies in hostile Environments (GTE) hostile Environments (GTE) http://gte.unizar.eshttp://gte.unizar.es 22


OutlineOutline

Loran-CLoran-C

Digital Radios (SDR)Digital Radios (SDR)

Supression algorithmSupression algorithm

Experimental resultsExperimental results

ConclusionsConclusions


Loran-C: introductionLoran-C: introductionRadionavigation signalRadionavigation signal

Position is computed by carefully estimating Position is computed by carefully estimating pulse arrival times pulse arrival times

Operated in chains identified by its GRI (Group Operated in chains identified by its GRI (Group Repetition Interval)Repetition Interval)

Stations power ranging from 11kW up to 1MWStations power ranging from 11kW up to 1MW

Signal propertiesSignal properties– Uses 20 kHz BandwidthUses 20 kHz Bandwidth– Estimated dynamic range: 100 dBEstimated dynamic range: 100 dB


Loran-C: why eliminate it?Loran-C: why eliminate it?User perspectiveUser perspective– Introduces a great deal of distortion in voice communicationIntroduces a great deal of distortion in voice communication– Disturbing noise in absence of communicationDisturbing noise in absence of communication– Contributes to battery dischargeContributes to battery discharge

Designers perspectiveDesigners perspective– Input dynamic rangeInput dynamic range– Dificulties AGC controlDificulties AGC control– Band has no other source of noise Band has no other source of noise

Loran-C perspectiveLoran-C perspective– Valuable position determinationValuable position determination– Helps to evaluate the electrode coupling/wiring problemsHelps to evaluate the electrode coupling/wiring problems


Loran-C: signal description (I)Loran-C: signal description (I)Built arround a deterministic pulse envelopeBuilt arround a deterministic pulse envelopeEach chain has a master and several slavesEach chain has a master and several slaves– Master: 9 equally spaced pulses (1 ms) except for the last (2 ms)Master: 9 equally spaced pulses (1 ms) except for the last (2 ms)– Slave: 8 equally spaced pulses (1 ms)Slave: 8 equally spaced pulses (1 ms)

Pulses have also phase coding to enhance chain identificationPulses have also phase coding to enhance chain identification

kHzffttEtx

usteAttEt

1002sin

in timeis where652

2


Loran-C: signal description (II)Loran-C: signal description (II)

Master burst

Slave burstsLoran-C

6731 Lessay


Loran-C: some mathLoran-C: some mathKnown factsKnown facts– GRI times are between 50 and 100 msGRI times are between 50 and 100 ms– Chains have from 3 to 5 stationsChains have from 3 to 5 stations– Pulse amplitude is reduced to Pulse amplitude is reduced to ~0.1% @ 400 us~0.1% @ 400 us– Received Loran-C signal >> received voice link signalReceived Loran-C signal >> received voice link signal

Pulse is “active” 400 us / 1 ms (40 %)Pulse is “active” 400 us / 1 ms (40 %)

In each GRI (50 ms) there are 25 (9 + 8 + 8) pulsesIn each GRI (50 ms) there are 25 (9 + 8 + 8) pulses– Channel is “used” 20% of the time (25 * 0.4 / 50) in worst caseChannel is “used” 20% of the time (25 * 0.4 / 50) in worst case

Pulses are like gaps in audio signalPulses are like gaps in audio signal– To reconstruct it perfectly To reconstruct it perfectly BWmax < 1250 Hz (FS = 1/400us) BWmax < 1250 Hz (FS = 1/400us)


SDR: topologySDR: topologySSB Modulation uses Weaver schemeSSB Modulation uses Weaver scheme– Simple implementationSimple implementation– Suitable for SDR systemsSuitable for SDR systems– Frequencies choosen to avoid in band auto generated Frequencies choosen to avoid in band auto generated

interferences (PWM armonics)interferences (PWM armonics)

IF

88450Hz 1500Hz


SDR: signals (I)SDR: signals (I)

0 1 2 3 4 5 6 7 8 9 10-5

-4

-3

-2

-1

0

1

2

3

4

5RF signal

Time [s]

Am

plitu

de [

v]


SDR: signals (II)SDR: signals (II)

1 1.2 1.4 1.6 1.8 2 2.2 2.4

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

IQ Channels

Time [s]

Am

plitu

de [

v]


Supression AlgorithmSupression AlgorithmWhere goes the algorithm?Where goes the algorithm?– RF RF Signal information is complete(!), processing Signal information is complete(!), processing

requirements HIGH (Power consumption)requirements HIGH (Power consumption)– IF IF Some signal information is lost, processing req. Some signal information is lost, processing req.

MEDIUMMEDIUM– BB BB Most of signal information is gone, processing Most of signal information is gone, processing

req. LOWreq. LOW

Separate mixing structure?Separate mixing structure?

Does it have to be accurate?Does it have to be accurate?

How Loran-C removal can be done?How Loran-C removal can be done?


Algorithm: implementationAlgorithm: implementationNo separate mixing structureNo separate mixing structure

Implemented in IF/BB (48/24 ksps)Implemented in IF/BB (48/24 ksps)

Must be simple (low resources)Must be simple (low resources)

No Loran-C synchronisation neededNo Loran-C synchronisation needed

Uses signal power to implement signal Uses signal power to implement signal detectiondetection


0 2 4 6 8 10 12 14

x 104

-140

-120

-100

-80

-60

-40

-20

0Original RF Spectrum

Frequency [Hz]

Mag

nitu

de [

dB]

Algorithm: signal processing (I)Algorithm: signal processing (I)Wideband signal is mixed in RF with 88.450 Wideband signal is mixed in RF with 88.450 Hz, “folding” the spectrum arround FmixHz, “folding” the spectrum arround Fmix

Fmix = 88540 Hz

0 0.5 1 1.5 2 2.5

x 104

-120

-100

-80

-60

-40

-20

0IQ Spectrum

Frequency [Hz]

Mag

nitu

de [

dB]


Algorithm: signal processing (II)Algorithm: signal processing (II)Phase & Quadrature signals are decimated to Phase & Quadrature signals are decimated to get desired IF/BB frequencyget desired IF/BB frequency

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

IQ Channels

Time [s]

Am

plitu

de [

v]

0 2000 4000 6000 8000 10000 12000-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0IQ Spectrum

Frequency [Hz]

Mag

nitu

de [

dB] Audio information

DCF77


Algorithm: signal processing (III)Algorithm: signal processing (III)High pass filter IQ signals (to remove audio information)High pass filter IQ signals (to remove audio information)Compute power of the filtered IQ signals and make two Compute power of the filtered IQ signals and make two averages, one fast and one slowaverages, one fast and one slow

0 0.5 1 1.5 2 2.5 3 3.5

x 105

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8Fast power avg.(red) and slow power avg.(black)

Samples

Pow

er

8.65 8.7 8.75 8.8 8.85 8.9

x 104

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Fast power avg.(red) and slow power avg.(black)

Samples

Pow

er


Algorithm: signal processing (IV)Algorithm: signal processing (IV)If fast average is n times greater than slow average, If fast average is n times greater than slow average, then blank signal starting at the point which fast then blank signal starting at the point which fast average was greater than slow averageaverage was greater than slow average

0 0.5 1 1.5 2 2.5

x 105

-1

-0.5

0

0.5

1Original I signal(blue) and filtered I signal (red)

Samples

Am

plitu

de [

V]

6.63 6.64 6.65 6.66 6.67 6.68 6.69 6.7 6.71

x 104

-1

-0.5

0

0.5

Original Q signal(blue) and filtered Q signal (red)

Samples

Am

plitu

de [

V]

Detail (zoomed version)


Algorithm: resourcesAlgorithm: resourcesAre very dependant of sampling speedAre very dependant of sampling speed

Case of BB sampled at 24 ksps:Case of BB sampled at 24 ksps:– Delay lines for I & Q channels (64 samples)Delay lines for I & Q channels (64 samples)– Compute IQ Power (2 multiplications + 1 add)Compute IQ Power (2 multiplications + 1 add)– Delay line for computed power (32 samples)Delay line for computed power (32 samples)– Fast and slow power averages (2 adds + 2 Fast and slow power averages (2 adds + 2

substractions)substractions)


Experimental ResultsExperimental ResultsSNR is enhanced, but improvement has a SNR is enhanced, but improvement has a strong dependance with relative signal strong dependance with relative signal amplitudes (Loran-C vs. Voice)amplitudes (Loran-C vs. Voice)

Proposed algorithm introduces little distortion Proposed algorithm introduces little distortion while eliminates some of the annoying noise.while eliminates some of the annoying noise.

As the human hearing has logarithmic As the human hearing has logarithmic behaviour with perceived power, algorithm has behaviour with perceived power, algorithm has to be very accurate to completely eliminate to be very accurate to completely eliminate Loran-C perception.Loran-C perception.

Audio samplesAudio samples


ConclusionsConclusions

This is our first approach to Loran-C This is our first approach to Loran-C supressionsupression

Pulse correlation combined with confort Pulse correlation combined with confort noise would greatly enhance the resultsnoise would greatly enhance the results

Use of other bandsUse of other bands


Thank you!!Thank you!!Antonio MuñozAntonio Muñoz

[email protected]@unizar.es

SUPRESSION OF LORAN-C NAVIGATION SUPRESSION OF LORAN-C NAVIGATION SIGNAL IN DIGITAL CAVE RADIOS SIGNAL IN DIGITAL CAVE RADIOS (AN EXPERIMENTAL APPROACH)(AN EXPERIMENTAL APPROACH)

Mr. Antonio Muñoz

Group of Technologies in hostile Environments (GTE) Group of Technologies in hostile Environments (GTE)

University of Zaragoza (Spain)University of Zaragoza (Spain)

BCRA Cave Technology Symposium

SUPRESSION OF LORAN-C NAVIGATION SIGNAL IN DIGITAL CAVE RADIOS (AN EXPERIMENTAL APPROACH)

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