| Now, Turbo code has been applied to the real commucation systems, and how to implement the Turbo encoder and decoder with hardware effectively has become a research hot spot. This thesis aims at implementing a Turbo decoder with short-decode-latency, little resource, high working clock frequency, and designs a configurable Turbo decoder which can be applied both in LTE baseband system and WiMAX baseband system.On the base of analysing the decoding algorithms of MAP, Log_MAP and Max_Log_MAP, the radix-4 Log_MAP and Max_Log_MAP algorithms are derived to adapt LTE and WiMAX baseband system separately. The enhanced Max_Log_MAP decoding algorithm of radix-4 is chosen as the decoding algorithm of this decoder's design, through comparing the computing complexity and performance. This thesis adopts parallel sub-block decoding and sliding window decoding, and designs the simulating platform of Turbo decoder of LTE and CTC decoder of WiMAX respectively using C language. Based on many simulations with the key parameters such as the block number, the length of sliding window, the width of data and so on which influence the performance of the decoder in AWGN channel, an optimum scheme of the configurable Turbo decoder is proposed.In the hardware implementation based on FPGA, the decoding delay has been reduced availably when parallel sub-block decoding, sliding window decoding and ping-pong operating structure had been adopted. The higher working clock can be used in the system when pipelining structure had been adopted. And the resource consumed has been decreased effectively when sliding window decoding had been adopted. The configurable Turbo decoder has been implemented on the FPGA chip (Stratix II GX EP2SGX90FF1508C3) of Altera company, and the performance testing is fulfilled in the baseband system of LTE and WiMAX respectively. The studies of this thesis provide the foundation of designing a Turbo decoder with better performance in the wireless baseband system in the future. |
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