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MICHAEL RICEBRIGHAM YOUNG UNIVERSITY

SPACE-TIME CODING FOR AERONAUTICAL

TELEMETRY

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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

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The Two-Antenna Problem

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The Two-Antenna Problem

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The Two-Antenna Problem

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The Two-Antenna Problem

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Demonstration

6 feet

5 feet

Aircraft Fuselage

carrier frequency = 2200 MHz

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Demonstration: Aircraft Turn

\mydocs\tier-1\stcdemo0.m

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Solution 1: Frequency Diversity

carrier f0

carrier f1

Requires 2× the bandwidth

Requires 2 receivers (possibly two receive antenna dishes)

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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 …

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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.

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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.

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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.

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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

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Abstract Model for Space-Time Coding

space-time

encoder

data

s0(t)

s1(t)

h0

h1space-time

demodulator +

decoder

r(t) = h0s0(t) + h1s1(t) + w(t)

data

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s(k-2) s(k-1) s(k) s(k+1) s(k+2) s(k+3)

s(k-2)

s(k-1)

s*(k-1)

s*(k-2)

Example: the 2 × 1 Alamouti Space-Time Code

space-time

encoder

inphase

quadrature

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s(k-2) s(k-1) s(k) s(k+1) s(k+2) s(k+3)s(k) s(k+1) s(k+2) s(k+3)

s(k)

s(k+1)

s*(k+1)

s*(k)

Example: the 2 × 1 Alamouti Space-Time Code

space-time

encoder

s(k-2)

s(k-1)

s*(k-1)

s*(k-2)

inphase

quadrature

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Why This Works ...

SNR with traditional signaling:

SNR with space-time coding:

0

210 NEhh b

0

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20 N

Ehh b

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Demonstration: Aircraft Turn With STC

\mydocs\tier-1\stcdemo.m

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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

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binary data

source

ARTM Tier-1

Space-Time Block

Encoder

FQPSK-JR Transmitter

FQPSK-JR Transmitter

PA

PA

to top antenna

to bottom antenna

STC transmitter

aircraft fuselage

S-band downconverter

DMO

100 Msamples/sec

70 MHz

5 Mbits/sec

to DVD

data

data

clock

clock

0h

1h

ts0

ts1

Experimental Configuration

LNA

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C-12 Beechcraft: Airborne Platform

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On-Board Transmit Equipment

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Space-Time Encoder

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The Signal Processing

ts0

ts1

0h

1h

000 tsh

111 tshDigital Signal ProcessingThe demodulator needs to estimate • The channel gains: h0, h1

• The propagation delays: t0, t1

• The frequency offset: Df

System Model

digital signal processingusing MATLAB

data

estimates

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0 5 10 150

0.5

1|h

0|

0 5 10 150

0.5

1

|h1|

time, seconds

Estimated Channel Gain Magnitudes

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0 5 10 150

50

100

150

200

250

300

350 ,

deg

rees

time, seconds

Estimated Channel Gain Phase Difference

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0 5 10 15-1

-0.5

0

0.5

1 /T

s

time, seconds

Estimated Channel Delay Difference

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0 5 10 15 20-70

-60

-50

-40

-30

-20

-10

time (sec)

|h0 +

h1| (

dB)

A Fade Using Traditional Signaling

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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 …

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Development Contract

Deseret Morning News 11 March 2005

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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

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Pilot Structure

D bitsLd samples

D bitsLd samples

data 0

data 0pilot 0 data 0 pilot 0

P bitsLp samples

D bitsLd samples

P bitsLp samples

D bitsLd samples

D bitsLd samples

data 1

data 1pilot 1 data 1 pilot 1

P bitsLp samples

D bitsLd samples

P bitsLp samples

Pilot bits are added to each transmitted waveform for estimating the frequency offset, the timing delays, and the (complex-valued) channel gains.

upper antenna

lower antenna

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STC Modulator Block Diagram

bit-levelSTC

encoder

MUXstored pilot bits

(A)

SOQPSK-TG

Modulator

RF(L-Band) PA RF A

RF BMUXstored pilot bits

(B)

clock 2 control

control

control

control

control

bit stream A

bit stream BSOQPSK-

TGModulator

RF(L-Band) PA

frequency locked (minimum)phase locked (preferred)

data

clock

buffer

input clock clock 2 IF/RF

input domain(TTL)

output domain

(RF)

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Prototype Transmitter

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Prototype Transmitter

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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

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downconvert&

resample

pilotdetector

frequency estimator

from ADC

timing&

channelestimator

Buffer

space-timedecoder(trellis)

derotated data

01 0h 1h

derotated pilots from Buffer

to channel/timing

estimatorto interpolators/

ST decoder

derotated data from Buffer

0

1

to output buffer

interpolator

interpolator

0 1 0h 1h

pilots

data

System Design

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A/DConverter

Sampling at 93.33 MHz

Resampling Filters

Pilot DetectorFrequency

OffsetEstimator

Timing & Channel Estimator

Detection Filters

BufferReindexer

Buffer Buffer

Buffer

Interpolator

Trellis Detector bits

Prototype Demodulator Hardware

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Resampling and Pilot Acquisition

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

A/DConverter

Sampling at 93.33 MHz

Resampling Filters

Pilot Detector

Reindexer

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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 0, 1, 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

Frequency Offset

Estimator

Timing & Channel Estimator

Detection Filters

Buffer

Buffer

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Timing and Channel Estimator

Signal Model for Pilot Symbols in Matrix-Vector Form

Maximum-Likelihood Estimator

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Timing Estimator

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Timing and Channel Estimator

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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

Trellis Detector bits

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Trellis 0

16 16 32 64 128 128 64 32 16

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Trellis 1

16 16 32 64 128 128 64 32 16

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Prototype Demodulator

IF input (70 MHz)

A/D Converter (93.3 Msamples/s)

FPGAs Vertex 2 Pro Clock and Data Output(10 Mbit/s)

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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

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Prototype Testing

QuasonixSTC

Transmitter

atten

Combiner

atten

atten

Noise+

InterferenceTest Set

TelemetryReceiver

BYUSTC

DemodBERT

Laptop PC

RF1485 MHz

RF1485 MHz

IF70 MHz

EAFB Telemetry Lab Configuration

FastBit FB2000

Channel MicrowaveIsolator LS3211

Hewlett-PackardStep Attenuator

HP8495B

Narda 4322-2

BERT

Fireberd 6000A

atten

atten

PasternackPE7017-40

Reach TechnologiesVBERT-50S-1-R

M/A Comm 5550i

Channel MicrowaveIsolator LS3211

PasternackPE7017-40

Hewlett-PackardStep Attenuator

HP8495B

Hewlett-PackardStep Attenuator

HP8495B

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BER Tests (EAFB Telemetry Lab)

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Flight Tests: Block Diagram

STCTransmitter

SOQPSKTransmitter

+

+÷

L-band isolator

L-band isolator

L-band isolator

L-band isolator

L-band isolator

3 dB

3dB

attenuator

attenuator

splitter

combiner

combiner

upper antenna

lower antenna

10 W

10 W

5 W

5 W

5 W

5 W

10 W

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Flight Tests: Transmit Antennas

Lower Telemetry Antenna(behind the antenna looking forward)

Upper Telemetry Antenna(looking across the fuselage)

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Flight Tests: Idealized Gain Patterns

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More on Space Time Coding for Aero-T/M

Michael Jensen, Michael Rice, and Adam Anderson, "Aeronautical Telemetry Using Multiple-Antenna Transmitters," IEEE Transactions on Aerospace and Electronic Systems, vol. 43, no. 1, pp. 262 - 272, January 2007.

Tom Nelson and Michael Rice, "MIMO Communications Using Offset Modulations," in Proceedings of the IEEE International Waveform Diversity and Design Conference, Lihue, HI, 23 - 27 January 2006.

Tom Nelson, Michael Rice, and Michael Jensen, "Experimental Results for Space-Time Coding Using ARTM Tier-1 Modulation," in Proceedings of the International Telemetering Conference, Las Vegas, NV, October 2005, pp. 90-100.

Tom Nelson, Michael Rice, and Michael Jensen, "Experimental Results with Space-Time Coding Using FQPSK," in Proceedings of the European Test and Telemetry Conference, Toulouse, France, June 2005.

Michael Jensen and Michael Rice, "Alamouti and Differential Transmit Diversity for Air-to-Ground Communications," in Proceedings of the IEEE/ACES International Conference on Wireless Communications and Applied Computational Electromagnetics, pp. 468 - 471, April 2005, Honolulu, Hawaii.

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More on Space Time Coding for Aero-T/M

Tom Nelson and Michael Rice, "Detection of SOQPSK in a Space-Time Coded System With Arrival Time Differences," in Proceedings of IEEE Military Communications Conference, Monterey, CA, November 2004.

Michael Jensen, Michael Rice, Tom Nelson and Adam Anderson, "Orthogonal Dual-Antenna Transmit Diversity for SOQPSK in Aeronautical Telemetry Channels," in Proceedings of the International Telemetering Conference, San Diego, CA, October 2004, pp. 337-344.

Michael Jensen, Michael Rice, and Adam Anderson, "Comparison of Alamouti and Differential Space-Time Codes for Aeronautical Telemetry Dual-Antenna Transmit Diversity," in Proceedings of the International Telemetering Conference, San Diego, CA, October 2004, pp. 345-354.

Tom Nelson and Michael Rice, "Space-Time Coded SOQPSK in the Presence of Differential Delays," in Proceedings of the International Telemetering Conference, San Diego, CA, October 2004, pp. 738 - 747.

Ron Crummett, Michael Jensen, and Michael Rice, "Transmit Diversity Scheme for Dual-Antenna Aeronautical Telemetry Systems," in Proceedings of the International Telemetering Conference, San Diego, CA, October 2002, pp. 113 - 121.