modeling and simulation of turbo encoder and decoder for...
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Modeling and Simulation of Modeling and Simulation of Turbo Encoder and Decoder for Turbo Encoder and Decoder for Wireless Communication Wireless Communication SystemsSystems
Sayantan Choudhury
Problem StatementProblem Statement
• Implementation of a turbo encoder and decoder
- Maximum A Posteriori (MAP) algorithm- Sliding window implementation
• Performance metrics : - Bit Error Rate (BER)- Signal to Noise Ratio (SNR)
• For a fixed BER, SNR requirement is reduced (Coding Gain)
Turbo EncoderTurbo Encoder
D D D
Interleaver
D D D
Information Sequencedk
Encoder 1
Encoder 2Zk
Xk
Yk
Turbo DecoderTurbo Decoder
DecoderDEC 1
Inter-Leaving
DecoderDEC2
Deinter-leaving
Deinter-leaving
Feedback Loop
Decoded Output
Zk
xk
yk
dk
Le2 (dk)
L2 (dk)
L1(dk)L2 (dk)
ImplementationImplementation
• SDF model of computation
• Use MAP algorithm for decoding – Advantage : Higher coding gain at low SNR – Disadvantage : More computationally and memory
intensive
• Enhancements– Sliding window
– MAX* approximation
Performance EvaluationPerformance Evaluation
Performance Factors and TradeoffsPerformance Factors and Tradeoffs
• Selection of algorithm• Constraint length and number of
iterations• Interleaver design • Trellis termination • Puncturing• Frame size
ConclusionsConclusions
• Successful implementation of Turbo Encoder and Decoder
• Written mainly in C• Works with TMS320C67 DSK• Well designed code should be very easy
to port to Advanced Design Systems (ADS)