A DECODE AND FORWARD COOPERATION SCHEME WITH SOFT RELAYING IN WIRELESS COMMUNICATION

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A DECODE AND FORWARD COOPERATION SCHEME WITH SOFT
RELAYINGIN WIRELESS COMMUNICATION

• Presenter Tuyen Bui
• Supervisor Prof. Yuan
• UNSW
• 10/07/07

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OVERVIEW

• INTRODUCTION
• SYSTEM DESCRIPTION
• SOFT RELAYING CODING
• SOFT RELAYING RECEIVER
• RESULTS
• CONCLUSION

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INTRODUCTION
Conventional transmission
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INTRODUCTION

• Cooperation communication
• A ? D bad
• A ? B and B ? D good
• Cooperation schemes
• AF (Amplify and Forward)
• DF (Decode and Forward)

Cooperative transmission of relay system
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INTRODUCTION

• Several transmission schemes for DF provide
  promising achievements
• Results are based on successful decoding at the
  relay
• ? no longer true in practical communications
• performance for conventional DF significantly
  degraded
• ? Soft relaying technique

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OVERVIEW

• INTRODUCTION
• SYSTEM DESCRIPTION
• SOFT RELAYING CODING
• SOFT RELAYING RECEIVER
• RESULTS
• CONCLUSION

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SYSTEM DESCRIPTION

• S and R work in a half-duplex manner
• Channels are block Rayleigh fading channels
• asd, asr, ard N(0,1) independent and constant
  in a time slot
• nsd, nsr, nrd N(0, ?2) AWGN noise

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SYSTEM DESCRIPTION
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SYSTEM DESCRIPTION

• S Encodes, BPSK modulates its information bits

R (CRC) Distributed Turbo Coding Soft relaying
Coding
D (Flag bit) Distributed Turbo Coding
Receiver Soft relaying Receiver
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SYSTEM DESCRIPTION

• Soft relaying coding
• Aim Forwards soft LLR to D when R fails in
  recovering information from S (DF cannot help)
• How Quantizer Digitalize analog LLR
• Superposition Encoding protect the
  forwarded information in a bandwidth saving way

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SYSTEM DESCRIPTION

• Soft relaying receiver
• Aim Use all available information to decode the
  original data of S
• How Superposition decoder Extract information
  from R
• Modified MAP Decoder Decode the
  received signal from S with extra information
  from R

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OVERVIEW

• INTRODUCTION
• SYSTEM DESCRIPTION
• SOFT RELAYING CODING
• SOFT RELAYING RECEIVER
• RESULTS
• CONCLUSION

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SOFT RELAYING CODING

• MAP Decoder
• Calculate soft LLR of each message bit
• Ly approximately has a symmetric Gaussian
  distribution with
• The condition pdf of Lyi
• The pdf of Lyi

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SOFT RELAYING CODING

• MAP Decoder
• Where ??Ly dependent on the input SNR of the
  decoder

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SOFT RELAYING CODING

• Quantizer
• Consider scalar quantizers with fixed-rate index
  K2
• Quantize soft LLR Ly ? map each bit to a
  binary sequence of length K
• Focus on the bin-boundary design
• Criterion design

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SOFT RELAYING CODING

• Quantizer
• The condition entropy

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SOFT RELAYING CODING

• Quantizer
• The condition entropy
• Where

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SOFT RELAYING CODING

• Quantizer
• The condition entropy
• Where

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SOFT RELAYING CODING

• Quantizer
• is a function of ud and ?Ly
• ud is obtained by

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SOFT RELAYING CODING

• Superposition Encoder
• Take as input K quantized sequences to produce a
  superimposed signal, forwarded to D
• The superimposed output provides an error
  protected transmission in a bandwidth saving way

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OVERVIEW

• INTRODUCTION
• SYSTEM DESCRIPTION
• SOFT RELAYING TECHNIQUE
• SOFT RELAYING RECEIVER
• RESULTS
• CONCLUSION

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SOFT RELAYING RECEIVER

• Superposition decoder
• Extract side information provided by R
• Use a low complexity decoder
• Soft information exchanging

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SOFT RELAYING RECEIVER

• Modified MAP decoder
• Calculate soft LLRs for information bit
  with the help of soft information provided by the
  relay
• The branch metric must be calculated by taking
  into account the constrain

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SOFT RELAYING RECEIVER

• Modified MAP decoder
• Calculate soft LLRs for information bit
  with the help of soft information provided by the
  relay
• The branch metric must be calculated by taking
  into account the constrain

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SOFT RELAYING RECEIVER

• Modified MAP decoder
• Calculate soft LLRs for information bit
  with the help of soft information provided by the
  relay
• The branch metric must be calculated by taking
  into account the constrain

Obtained due to quantization and superposition
process
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SOFT RELAYING RECEIVER

• Modified MAP decoder
• Markcov chain
• where

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OVERVIEW

• INTRODUCTION
• SYSTEM DESCRIPTION
• SOFT RELAYING TECHNIQUE
• SOFT RELAYING RECEIVER
• RESULTS
• CONCLUSION

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Results-SNRsdSNRrdSNR, SNRsr-5dB
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Results-SNRsdSNRrdSNR, SNRsr10dB
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OVERVIEW

• INTRODUCTION
• SYSTEM MODEL
• SOFT RELAYING TECHNIQUE
• SOFT RELAYING RECEIVER
• RESULTS
• CONCLUSION

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CONCLUSION

• A soft relaying DF scheme exploiting the benefits
  of superposition is presented.
• Some principles of the quantizer design, the
  superposition process and the modified MAP
  decoder are provided.
• The scheme effectively improves the inter-user
  outage performance in wireless communication.
• Performance analysis can be obtained.