Michael Rice Brigham Young University

1. Space-Time Coding for Aeronautical Telemetry Michael RiceBrigham Young University

2. Outline • The “Two Antenna” Problem • Space-Time Coding • An Experiment with Space-Time Coding and Tier-1 Modulations at EAFB • Prototype Transmitter • Prototype Demodulator • Flight Test Results

3. The Two-Antenna Problem 

4. The Two-Antenna Problem  

5. The Two-Antenna Problem   

6. The Two-Antenna Problem    

7. Demonstration Aircraft Fuselage 6 feet 5 feet carrier frequency = 2200 MHz

8. Demonstration: Aircraft Turn \mydocs\tier-1\stcdemo0.m

9. Solution 1: Frequency Diversity Requires 2× the bandwidth Requires 2 receivers (possibly two receive antenna dishes) carrier f0 carrier f1

10. Solution 2: Steerable Beam Think of the two antennas as a two-element antenna array Adjust the phases of the signals to steer the beam at the receive antenna Requires an uplink to tell the transmitter where the receiver is …

11. Solution 2: Steerable Beam Think of the two antennas as a two-element antenna array Adjust the phases of the signals to steer the beam at the receive antenna … or requires GPS output to be linked to the telemetry package.

12. Solution 3: Space-Time Coding The space-time code provides transmit diversity. Transmit two different signals from the two antennas. The signals are different from each other, but both are related to the data stream. The relationship is defined through a “space-time code.” The two signals posses a phase relationship that avoids destructive interference on average.

13. Solution 3: Space-Time Coding The space-time code provides transmit diversity. Transmit two different signals from the two antennas. The signals are different from each other, but both are related to the data stream. The relationship is defined through a “space-time code.” The two signals posses a phase relationship that avoids destructive interference on average. The ground-based receiver is much more complex.

14. Outline • The “Two Antenna” Problem • Space-Time Coding • An Experiment with Space-Time Coding and Tier-1 Modulations at EAFB • Prototype Transmitter • Prototype Demodulator • Flight Test Results

15. space-time encoder Abstract Model for Space-Time Coding s0(t) h0 data space-time demodulator + decoder data h1 s1(t) r(t) = h0s0(t) + h1s1(t) + w(t)

16. space-time encoder Example: the 2 × 1 Alamouti Space-Time Code s*(k-1) s(k-2) s(k-1) s*(k-2) s(k-2) s(k-1) s(k) s(k+1) s(k+2) s(k+3) quadrature inphase

17. s*(k-1) s(k-2) s(k-1) s*(k-2) space-time encoder Example: the 2 × 1 Alamouti Space-Time Code s*(k+1) s(k) s(k+1) s*(k) s(k) s(k+1) s(k+2) s(k+3) s(k-2) s(k-1) s(k) s(k+1) s(k+2) s(k+3) quadrature inphase

18. Why This Works ... SNR with traditional signaling: SNR with space-time coding:

19. Demonstration: Aircraft Turn With STC \mydocs\tier-1\stcdemo.m

20. Outline • The “Two Antenna” Problem • Space-Time Coding • An Experiment with Space-Time Coding and Tier-1 Modulations at EAFB • Prototype Transmitter • Prototype Demodulator • Flight Test Results

21. Experimental Configuration data 5 Mbits/sec ARTM Tier-1 Space-Time Block Encoder FQPSK-JR Transmitter PA to top antenna clock binary data source data FQPSK-JR Transmitter PA to bottom antenna clock 100 Msamples/sec STC transmitter DMO S-band downconverter LNA aircraft fuselage 70 MHz to DVD

22. C-12 Beechcraft: Airborne Platform

23. On-Board Transmit Equipment

24. Space-Time Encoder

25. The Signal Processing System Model • Digital Signal Processing • The demodulator needs to estimate • The channel gains: h0, h1 • The propagation delays: t0, t1 • The frequency offset: Df digitalsignal processing using MATLAB data estimates

26. Estimated Channel Gain Magnitudes

27. Estimated Channel Gain Phase Difference

28. Estimated Channel Delay Difference

29. A Fade Using Traditional Signaling

30. Experimental Results • No bit errors • Even during signal fade (using traditional two-antenna transmission) • We need to build a prototype receiver to see if this really works …

31. Development Contract Deseret Morning News 11 March 2005

32. Outline • The “Two Antenna” Problem • Space-Time Coding • An Experiment with Space-Time Coding and Tier-1 Modulations at EAFB • Prototype Transmitter • Prototype Demodulator • Flight Test Results

33. Pilot Structure Pilot bits are added to each transmitted waveform for estimating the frequency offset, the timing delays, and the (complex-valued) channel gains. data 0 data 0 pilot 0 data 0 pilot 0 upper antenna D bits Ld samples P bits Lp samples D bits Ld samples P bits Lp samples D bits Ld samples data 1 data 1 pilot 1 data 1 pilot 1 lower antenna D bits Ld samples P bits Lp samples D bits Ld samples P bits Lp samples D bits Ld samples

34. STC Modulator Block Diagram output domain (RF) input domain (TTL) input clock clock 2 IF/RF control clock 2 control clock control control bit stream A buffer bit-level STC encoder SOQPSK-TG Modulator RF (L-Band) PA MUX RF A stored pilot bits (A) data frequency locked (minimum) phase locked (preferred) control bit stream B SOQPSK-TG Modulator RF (L-Band) PA MUX RF B stored pilot bits (B)

35. Prototype Transmitter

36. Prototype Transmitter

37. Outline • The “Two Antenna” Problem • Space-Time Coding • An Experiment with Space-Time Coding and Tier-1 Modulations at EAFB • Prototype Transmitter • Prototype Demodulator • Flight Test Results

38. System Design derotated data downconvert & resample pilot detector Buffer frequency estimator to channel/timing estimator from ADC pilots to interpolators/ ST decoder data timing & channel estimator derotated pilots from Buffer interpolator space-time decoder (trellis) derotated data from Buffer to output buffer interpolator

39. Prototype Demodulator Hardware Buffer Detection Filters Buffer Resampling Filters A/D Converter Sampling at 93.33 MHz Timing & Channel Estimator Buffer Pilot Detector Interpolator Frequency Offset Estimator Reindexer Buffer Trellis Detector bits

40. Resampling and Pilot Acquisition A/D Converter Sampling at 93.33 MHz • IF to Complex Baseband • 70 MHz IF signal • 93.3 MHz ADC • Resample • Post aliasing DDC is 46.67 Msps • Resample to 4 samples/bit = 41.6 Msps • Pilot Detection (middle 96 bits) • 96 bits → ~66.6 kHz bandwidth • Detect Pilot #0 and Pilot #1 • Frequency-domain fast correlation • Cover a 200 KHz bandwidth • Single 1024-point forward FFT • Six 1024-point inverse FFT’s • Implements the overlap-and-add fast correlation algorithm Resampling Filters Pilot Detector Reindexer

41. Frequency and Channel Estimations • Data-aided ML frequency offset estimation • STC decoding demands RMSEE of ~10 Hertz! • Coarse estimation and “bracketing” followed by fine estimation • Received signal derotated based on estimate • Joint Estimation of t0, t1, h0, and h1 • Maximum Likelihood (ML) estimate of the delays and channel gains • Calculate the channel gains h0 and h1 for the given delay estimates • Minimize object function using a “discrete” simplex algorithm Buffer Detection Filters Timing & Channel Estimator Frequency Offset Estimator Buffer

42. Timing and Channel Estimator Signal Model for Pilot Symbols in Matrix-Vector Form Maximum-Likelihood Estimator

43. Timing Estimator

44. Timing and Channel Estimator

45. Interpolation and Detection • Interpolation • Piece-wise parabolic Farrow filter • Outputs 1 sample/bit • Least Squares trellis detector • Detector based on a reduced complexity model of the Tier 1 waveforms • Model is the 8 waveform XTCQM common model for SOQPSK-TG and FQPSK-JR • Trellis accounts for the memory in the signal due to the modulation and the STC Buffer Buffer Interpolator bits Trellis Detector

46. Trellis 0 64 16 16 32 64 128 32 16 128

47. Trellis 1 64 16 16 32 64 128 32 16 128

48. Prototype Demodulator Clock and Data Output (10 Mbit/s) FPGAs Vertex 2 Pro IF input (70 MHz) A/D Converter (93.3 Msamples/s)

49. Outline • The “Two Antenna” Problem • Space-Time Coding • An Experiment with Space-Time Coding and Tier-1 Modulations at EAFB • Prototype Transmitter • Prototype Demodulator • Flight Test Results

50. Prototype Testing EAFB Telemetry Lab Configuration Hewlett-Packard Step Attenuator HP8495B Reach Technologies VBERT-50S-1-R Channel Microwave Isolator LS3211 Pasternack PE7017-40 Quasonix STC Transmitter BERT atten atten Combiner RF 1485 MHz atten atten atten Hewlett-Packard Step Attenuator HP8495B Channel Microwave Isolator LS3211 Pasternack PE7017-40 Hewlett-Packard Step Attenuator HP8495B Narda 4322-2 Noise + Interference Test Set Telemetry Receiver BYU STC Demod BERT RF 1485 MHz IF 70 MHz FastBit FB2000 M/A Comm 5550i Fireberd 6000A Laptop PC