Abstract
Problem statement : In this study we propose a method to improve the performance of Maximum A-Posteriori Probability Algorithm, which is used in turbo decoder. Previously the performance of turbo decoder is improved by means of scaling the channel reliability value. Approach : A modification in MAP algorithm proposed in this study, which achieves further improvement in forward error correction by means of scaling the extrinsic information in both decoders without introducing any complexity. The encoder is modified with a new puncturing matrix, which yields Unequal Error Protection (UEP). This modified MAP algorithm is analyzed with the traditional turbo code system Equal Error Protectio n (EEP) and also with Unequal Error Protection (UEP) both in AWGN channel and fading channel. Result: MAP and modified MAP achieve coding gain of 0.6 dB over EEP in AWGN channel. The MAP and modified MAP achieve coding gain of 0.4 dB and 0.9dB over EEP respectively in Rayleigh fadi ng channel. Modified MAP in UEP class 1 and class 2 gained 0.8 dB and 0.6 dB respectively in AW GN channel where as in fading channel class 1 and 2 gained 0.4 dB and 0.6 dB respectively. Conclusion/Recommendations: The modified MAP algorithm improves the Bit Error Rate (BER) performance in EEP as well as UEP both in AWGN and fading channels. We propose modified MAP error correction algorithm with UEP for broad band communication.
Highlights
Unequal Error Protection (UEP) Turbo Code[1,2] is development of traditional Turbo code in practical application
This study introduces an implementation of UEP Turbo Codes by designing a new puncturing matrix scheme
For the decoding of traditional Turbo Codes, the Bit Error Rate (BER) have nothing to do with the position of information symbol, and these codes are called the Equal Error Protection (EEP) Turbo Codes
Summary
UEP Turbo Code[1,2] is development of traditional Turbo code in practical application. Suppose Cmax= 3, the unequal error protection turbo codes increase the redundant information in C1 and C2 classes. The operation principles of the unequal error protection turbo codes encoder are as follows: According the structure of frame to design the puncturing matrix. Firstly: we must accord the importance of each part of information and equation (3) to confirm the partial rate of Ci class and Hamming weight of puncturing matrix P1, P2. We need to design the structure of puncturing matrix P1 and P2, to confirm the protection situation of the information bits to be encoded. In class 1 gained 0.4 dB and class 2 gained 0.6 dB at 1.2 dB over EEP in fading channel
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