MECLAB, EE, NCKU, Taiwan 1

An SDR-Based Architecture Ground Station for Small Satellite Tracking

Presenter: Y.F. TsaiAuthors: C. T. Tsai, Y. F. Tsai, J. C. Juang, and J. J. Miau

Department of Electrical EngineeringNational Cheng Kung University, Taiwan

MECLAB, EE, NCKU, Taiwan 2

Outline

Background

Motivation and objective

Conventional ground station

Ground station with software defined radio

Implementation

NLS4 Tracking Results

Conclusion

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Background

Recently, small satellites and constellations are developed for earth observation or communication network.As many small satellites will be released in a piggy-back launch, the closeness in spatial and spectral separation between different small satellites may render problems for ground stations in satellite tracking, especially in the early orbit phase.

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Spectral Problem

Sat Frequency Sat Frequency Sat Frequency

AO-51 435.1500 MHz AO-16 437.0260MHz CO-55 437.4000 MHz

CAPE1 435.2450 MHz AO-16 437.0510MHz Libertad-1 437.4050 MHz

AO-51 435.3000 MHz GeneSat-1 437.0750 MHz HO-59 437.4250 MHz

RS-22 435.3520 MHz LO-19 437.1250 MHz XI-V 437.4650 MHz

FO-29 435.7950 MHz SSETI-1 437.2500 MHz CO-57 437.4900 MHz

AO-27 436.7950 MHz HO-59 437.2750 MHz UWE-1 437.5050 MHz

SO-50 436.7950 MHz NCUBE-2 437.3050 MHz CO-52 437.5050 MHz

CO-55 436.8375 MHz CP4 437.3250 MHz SO-33 437.9100 MHz

CP3 436.8450 MHz XI-V 437.3450 MHz AAUSat-II 437.4250 MHz

CO-57 436.8475 MHz CO-56 437.3850 MHz COMPASS-1 437.2750 MHz

Cute-1.7+APDII 437.3850 MHz SEEDS 437.4850 MHz

Satellite frequency list in 435~438MHz:

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Spatial Problem

Example:CAPE-1, CP3, CP4 and AeroCube-2 were launched on April 17th, 2007.

The picture of CP4 taken by AeroCube-2 on April 17th, 2007

Positions of CAPE 1, CP3, CP4 and AeroCube-2 on May 17th, 2007

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Motivation and Objective

In the early orbit phase, all small satellites are close for several days, even one month. All satellite developers are eager to assess the status of satellites as early as possible.The problems (for a ground station to track multiple satellites) are - How to receive all the satellite signals simultaneously?→ Wide band and multi-channel

- How to improve BER?→ Interference cancellation

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Conventional Ground Station

Architecture– Antennas, Amateur radio, TNC modem, PC.

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Comparison

Conventional GS

GS with SDR

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GS with SDR Architecture

Architecture– Antennas, RF front end, A/D converter, PC

Software based

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Down Conversion

Use band pass sampling to down-convert the signal.Need filter to prevent from aliasing

( )

( )

⎧ ⎛ ⎞⎜ ⎟⎪

⎪ ⎝ ⎠= ⎨⎛ ⎞⎪⎜ ⎟⎪ ⎝ ⎠⎩

, , , .2

- , , , .2

: :

:

SRF S RF

IFS

S RF S RF

IF

RF

S

Frem F F if fix F is evenF

FF rem F F if fix F is odd

F Intermediate frequencyF Radio frequencyF Sampling frequency

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Fs Selection

Consideration: linearity (folded area), frequency resolution and available Fs.

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 59 600

5

10

15

20

25

30

Sampling Frequency

Inte

rmed

iate

Fre

quen

cy

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Frequency Estimation

Because of Doppler shift, the received frequency is not fixed.By Short-Time FFT, frequency information varying with time can be estimated.

The frequency information will be transmitted to the dynamic filter and Doppler shift calculator.

146 0.5 ( 2 16384)

16384 2.7307 6

S

s

F MHzFrequency resolution kHz NN N

Time resolution N T msM

= = ≤ = =

= × = =

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Co-Channel Interference

For separating multiple signals in the same frequency band, co-channel interference (CCI) cancellation methods are developed.

For general ground stations, SAIC (Single Antenna Interference Cancellation) is suitable.

Furthermore, MIMO (Multi-Input Multi-Output) can be implemented at ground stations with multi-antenna.

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CCI Cancellation

Several SAIC methods are proposed:– Cross-coupled phase-locked loop (CCPLL)– Phase-tracking circuit (PTC)– Joint Viterbi estimation based on the maximum likelihood

estimation (JMLSE)

The CCPLL and PTC methods typically outperform the JMLSE when the modulation parameters are dissimilar. Good performance for the PTC requires both dissimilar parameters and a prior knowledge of the co-channel signal amplitudes.JMLSE provides for a more robust estimation of the co-channel signals.

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SDR Implementation(1/4)

The receiver consists of ADLink PXI-3710 system controller and ADLink PXI-9820 A/D converter.Features:– 14-bit A/D resolution– Up to 60MS/s – 3dB bandwidth : about 30MHz

Receiver function blocks are built in MATLAB/Simulink

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SDR Implementation(2/4)

IC-910H U/V Band Transceiver Power Splitter

PXI-3710 with PXI-9820A/D converter

DC-Block

AG-25 LNA

AG-35 LNA

DC-Block PA

DC 12.35V

VHF Band Channel

UHF Band Channel

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SDR Implementation(3/4)

Receiver block diagram

12Ch2 Amplitude1

11Ch2 Data1

10Ch1 Amplitude1

9Ch1 Data1

8Recorder1

7Frequency1

6Ch2 Amplitude

5Ch2 Data

4Ch1 Amplitude

3Ch1 Data

2Recorder

1Frequency

M-FSK

M-FSKDemodulatorBaseband3

M-FSK

M-FSKDemodulatorBaseband2

M-FSK

M-FSKDemodulatorBaseband1

M-FSK

M-FSKDemodulator

Baseband

In1

Max_Peak

Second

Frequency_Dection(FFT)

In1

In2

Out1

Filter1

In1

In2

Out1

Filter

0

Display2

0

Display1

In1

Channel 1

Amplitude 2

Channel 2

Amplitude 2

CCI Separator1

In1

Channel 1

Amplitude 2

Channel 2

Amplitude 2

CCI Separator

1In1

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SDR Implementation(4/4)

PXI-3710 has several interface to connect with ground station devices.The SDR and conventional transceivers can be combined in PXI-3710 with ‘MATLAB ActiveX’component in Visual Basic.Transceiver calls the frequency information in MATLAB workspace and get the RF frequency.

144 ( )

438 ( )IF RF IF

IF RF IF

F F MHz F VHF

F F MHz F UHF

↓ ⇒ = +

↑ ⇒ = −

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NLS4

NLS4: Nanosatellite Launch Service 4Launch date: April 28th, 2008Launch vehicle:– Antrix Polar Satellite Launch Vehicle (PLSV-C9)

Satellites onboard:– AAUsat-2 (Denmark), CanX-2 (Canada), Cute-1.7+APD II

(Japan), COMPASS-1 (Germany), Delfi-C3 (Netherlands), SEEDS (Japan)

Inclination: 98 degreeAltitude: 630 km

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Result of VHF Band Receiving

Delfi-C3

Perhaps NOAA-15

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Result of UHF Band Receiving(1/2)

Sampling Frequency: 6MHz

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Result of UHF Band Receiving(2/2)

Sampling Frequency: 0.5MHz

Compass-1CUTE 1.7+APD II

AAUSat IIUnknown

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Compass-1 CW Signal Decoding

1 2 3 4 5 6 7 8 9

x 104

0.05

0.1

0.15

0.2

0.25

Time

1 2 3 4 5 6 7 8 9

x 104

-0.2

0

0.2

0.4

0.6

0.8

1

Time

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Decoding Result

After decoding the filtered IF signal in Morse code format, we got some results:

Compass-1:?mpass29000000?00000001602c?1508

Cute1.7+APDII:cute 87 c6 a? a? 48 17 cute 8????8624 ????12 1

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Conclusion

We have proposed a method to improve ground station capability with software defined radio. The benefit provided by the SDR receiver are:1.Multi-channel2.Wide frequency range3.CCI cancellation4.More accurate Doppler shift informationIn May 2008, the proposed SDR receiver has already received simultaneously several signals from cubesatslaunched by NLS4.

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Reference[1] http://polysat.calpoly.edu/CP4.php[2] Peter B. Kenington, RF and Baseband Techniques for Software Defined Radio, Boston,

Artech House, 2005[3] Jeffery H. Reed, Software Radio: A Modern Approach to Radio Engineering, Prentice Hall

PTR, 2002.[4] W. Etten, “Maximum Likelihood Receiver for Multiple Channel Transmission Systems,” IEEE

Trans. Commun., Vol. 24, No. 2, pp. 276–83, Feb. 1976.[5] Rodney G. Vaughan, “The Theory of Bandpass Sampling,” IEEE Trans. on Signal Processing,

Vol. 39, No. 9, September 1991.[6] Riccardo Raheli, Andreas Polydoros and Ching-Kae Tzou, “Per-Survivor Processing: A

General Approach to MLSE in Uncertain Environments,” IEEE Trans. on Communications, Vol. 43, No. 2/3/4, Feb/March/April 1995

[7] Akos, D.M. Stockmaster, M. Tsui, J.B.Y. Caschera, J., “Direct Bandpass Sampling of Multiple Distinct RF Signals,” IEEE Trans. Commun., Vol. 47, Issue 7, pp. 983-988, Jul 1999.

[8] Jon Hamkins, Ed Satorius, Gent Paparisto and Andreas Polydoros, “A Comparative Study of Co-Channel Interference Suppression Techniques,” Proc. 5th IMSC, pp. 327-332, June 1997.

[9] Mostafa et al., “Single Antenna Interference Cancellation (SAIC) for GSM Networks,” Proc. IEEE VTC, Orlando, FL, pp. 1089–93.

[10] http://en.wikipedia.org/wiki/Software-defined_radio[11] Charles R. Cahn. “Phase tracking and demodulation with delay,” IEEE Trans. Inform.

Theory, IT-20(1), pp:50-58, January 1974.

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Thanks for your attention!