| LTE (Long Term Evolution) is the project name of a new high performance air interface for cellular mobile communication systems. It is the last step toward the 4th generation (4G) of radio technologies designed to increase the capacity and speed of mobile telephone networks. The LTE specification provides downlink peak rates of at least 100 Mbps, encompassing voice, high-speed data and multimedia services. Such high data rate makes it challenging for channel coding design. The error correction coding for LTE should involve both the characteristics of low decoding complexity and good performance. In this thesis the tail-biting convolutional code (TBCC) and turbo code in LTE system are analyzed for their encoding structures and decoding performance.In the first part of the thesis, the convolutional code and Viterbi algorithm are introduced, based on that three types of decoding algorithms for TBCC are analyzed for their advantages and shortcomings. Then, a Bidirectional-Extended Circular Viterbi Algorithm (BE-CVA) is presented to improve the performance of the Circular Viterbi Algorithm (CVA). Computer simulation shows that this algorithm can efficiently reduce the computational complexity of decoding while improve the bit error ratio (BER). Encoding structure and basic decoding algorithm of Turbo code are investigated in the second part of the thesis. The effects of parameters, such as the interleaving depth, number of iteration and interleaver types on the BER performance are simulated thereafter. Based on the Max-Log-MAP algorithm, a new Two-step Enhanced Max-Log-MAP algorithm is presented. This proposed algorithm owns a similar computational complexity as the Max-Log-MAP while has a performance comparable to the Log-MAP algorithm. Finally, the common stopping criterions for Turbo code are analyzed, and a joint CRC-MR stopping rule is proposed. Computer simulation shows this new criterion does reduce the average number of iteration and decoding delay without BER performance degradation. |
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