Space-Time Block Coding in Rayleigh and Rician Fading Channels Jari - - PowerPoint PPT Presentation

21.11.2007

Space-Time Block Coding in Rayleigh and Rician Fading Channels

Jari Tissari

21.11.2007 2

Introduction – space-time coding

• Signal propagation in multipath channels causes the received signal power to fade,

leading to severe degradation on signal quality

• Space-time coding, a combination of channel coding and transmit diversity, can be

used to reduce the harmful effect of signal fading

• The encoder takes a group of binary information symbols and maps them into

modulation symbols

• Encoded data is fed to a serial-to-parallel converter and transmitted simultaneously

by multiple antennas

• Different types of STCs: block and trellis codes, layered space-time codes

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Space-time block coding

• Space-time block codes are designed to achieve full transmit diversity using an

arbitrary number of transmit antennas

• The codes are constructed through orthogonal designs
• Decoding by maximum likelihood algorithms based only on simple linear processing –

no channel state information is required at the transmitter

• Example: The Alamouti code for two transmit antennas

Alamouti encoder

⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − =

∗ ∗ 1 2 2 1

x x x x X

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Performance simulations

• Alamouti code using different numbers of receive antennas
• Codes for two, three and four transmit antennas using different spectral efficiencies
• The above codes using two-antenna receive diversity
• Slow and flat Rayleigh/Rician fading channel
• Modulation: BPSK/QPSK/16-QAM

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Performance of the Alamouti Code

5 10 15 20 25 30 35 10

• 4

10

• 3

10

• 2

10

• 1

10 SNR, dB Pb BER performance of BPSK Alamouti scheme on Rayleigh fading channels Uncoded nR=1 nR=2 nR=4

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Performance of different codes at spectral efficiency 1 bps/Hz

5 10 15 20 25 30 35 10

• 4

10

• 3

10

• 2

10

• 1

10 SNR, dB Pb BER performance of codes attaining 1 bps/Hz No diversity Alamouti X

3 c

X

4 c

mR = η

• Alamouti, BPSK:

R=1, m=1

• Xc3, QPSK: R=1/2,

m=2

• Xc4, QPSK: R=1/2,

m=2

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Performance of different codes at spectral efficiency 2 bps/Hz

5 10 15 20 25 30 35 10

• 4

10

• 3

10

• 2

10

• 1

10 SNR, dB Pb BER performance of codes attaining 2 bps/Hz No diversity Alamouti X

3 c

X

4 c

• Alamouti, QPSK:

R=1, m=2

• Xc3, 16-QAM:

R=1/2, m=4

• Xc4, 16-QAM:

R=1/2, m=4

mR = η

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Performance of different codes at spectral efficiency 3 bps/Hz

5 10 15 20 25 30 35 40 10

• 4

10

• 3

10

• 2

10

• 1

10 SNR, dB Pb BER performance of codes attaining 3 bps/Hz No diversity Alamouti X

3 h

X

4 h

• Alamouti, 8-PSK:

R=1, m=3

• Xh3, 16-QAM:

R=3/4, m=4

• Xh4, 16-QAM:

R=3/4, m=4

mR = η

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Performance of STBCs using receive diversity

5 10 15 20 25 30 35 10

• 4

10

• 3

10

• 2

10

• 1

10 SNR, dB Pb BER performances at 1 bps/Hz using two receive antennas No diversity Alamouti X

3 c

X

4 c

mR = η

• Alamouti, BPSK:

R=1, m=1

• Xc3, QPSK: R=1/2,

m=2

• Xc4, QPSK: R=1/2,

m=2

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Code performance in Rician fading channels: two transmit antennas

2 4 6 8 10 12 14 16 18 20 10

• 4

10

• 3

10

• 2

10

• 1

10 SNR, dB Pb BER performance of BPSK Alamouti scheme on Rician fading channels K=-inf dB K=0 dB K=5 dB K=10 dB K=20 dB

• K=-inf dB: Rayleigh

fading channel

• K=20 dB: very strong

LOS component

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Code performance in Rician fading channels: three transmit antennas

2 4 6 8 10 12 14 16 18 20 10

• 4

10

• 3

10

• 2

10

• 1

10 SNR, dB Pb BER performance of X

3 c on Rician fading channels

K=-inf dB K=0 dB K=5 dB K=10 dB K=20 dB

• K=-inf dB: Rayleigh

fading channel

• K=20 dB: very strong

LOS component

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Code performance in Rician fading channels: four transmit antennas

2 4 6 8 10 12 14 16 18 20 10

• 4

10

• 3

10

• 2

10

• 1

10 SNR, dB Pb BER performance of X

4 c on Rician fading channels

K=-inf dB K=0 dB K=5 dB K=10 dB K=20 dB

• K=-inf dB: Rayleigh

fading channel

• K=20 dB: very strong

LOS component

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Simulation results / conclusions

• Even a basic STBC system offers a significant gain in performance
• The codes provide radically improved signal quality even in very harsh propagation

conditions

• The optimal code depends on the system environment: at low SNRs, using a spectral

efficiency >1 bps/Hz, the simplest code (Alamouti with two Tx antennas) is the

• ptimal choice
• Using receive diversity results in larger performance gain than using additional

transmit antennas

• When there is a strong line-of-sight component available, signal fading is negligible

and space-time coding will not provide any performance gain