本論文將研究渦輪碼的實現，並以德州儀器公司所出產的TMSC6711DSK完成硬體製作。實現渦輪解碼器(turbo decoder)時，必須考慮各種硬體實現會面臨到的問題。開始將討論對數化最大事後機率(Log-MAP)、最大對數化最大事後機率(Max-Log-MAP)及軟輸入/軟輸出維特比演算法(SOVA)三種最廣泛用來做為渦輪解碼器的演算法，各種演算法的差異與優劣將被比較與分析，以做為選擇適當的疊代解碼器演算法之依據。接著討論一個改良過的SOVA解碼方式，發現在某些情形下此方法的確比傳統的SOVA演算法得到更佳的位元錯誤率(BER)。
為了設計一個定點數(fixed-point)計算之渦輪解碼器，量化(quantization)的效應也是應該考量的重要因素之一。然而，我們將透過理論探究與模擬去找出適當的量化處理方法。由於之前都是假設在已知通道訊息與完美同步的情形下，進行各種分析與討論。因此，最後也考慮訊號雜訊比量測(SNR estimate)與時間偏移(timing offset)的問題，希望可以找出適合於硬體實現的方法。

This thesis intends to study and implement turbo codes with the TMS320C6711 processor. When implementing the decoder of turbo code, we shall consider various problems related to our hardware implementation. We start with a discussion on the most popular turbo decoding algorithms: Log-MAP, Max-Log-MAP and SOVA algorithms. We then select those decoding algorithms that may be suitable for an iterative decoder. A modified SOVA decoding scheme is proposed to give improved performance in BER. It will be compared with the conventional SOVA algorithm.
We discuss the effect of quantization and give a suitable design for our fixed-point design of turbo decoders. The previous method for decoding turbo codes is analyzed under the assumption of perfect channel information and synchronization. Thus, we give consideration to the problems of SNR estimate and timing offset in the end.

[1] Woodard, J. P. Hanzo, L. “ Comparative study of turbo decoding techniques: an overview ”, IEEE Transaction on Vehicular Technology, VOL. 49, NO. 6, November 2000.

[2] Sang-Sic Yoon, Hyung-Chul Park, and Kwyro Lee. “ A High Performance Serially Mixed SOVA Decoder for Turbo Codes ”, IEICE Trans. Commun., VOL. E85-B, NO.1 January 2002.

[3] Jinghu Chen, Marc P. C. Fossorier, Member, IEEE, Shu Lin, and Chengqi Xu. “ Bi-Directional SOVA Decoding for Turbo-Codes ”, IEEE Communications Letters, VOL. 4, NO 12, December 2000.

[4] Peter H.Y. Wu. “On the complexity of Turbo Decoding Algorithms”, IEEE 2001.

[5] G. Montorsi, Member, IEEE, and S. Benedetto. “ Design of Fixed-Point Iterative Decoders for Concatenated Codes with Interleaver ”, IEEE Journal on Selected Area in Communications, VOL. 19, NO.5,May 2001.

[6] Todd A. Summers and Stephen G. Wilson. “ SNR Mismatch and Online Estimation in Turbo Decoding”, IEEE Transactions on Communications, VOL. 46, NO. 4, April 1998.

[7] A. Ramesh, A. Chockalingam and L. B. Milstein. “SNR Estimation in Generalized Fading Channel and its Application to Turbo Decoding”, IEEE 2001.

[8] Alexander Worm, Peter Hoeher and Norbert When. “Turbo-Decoding Without SNR Estimation”, IEEE Communications letter, VOL. 4, NO. 6, June 2000.

[9] Curt Schurgers, Francky Catthoor, and Marc Engels. “Memory Optimization of MAP Turbo Decoder Algorithms”, IEEE Transactions on Very Large Scale Integration(VLSI) Systems, VOL. 9, NO. 2, April 2001.

[10] Fathi Raouafi , adodo Dingninou, Claude Berrou. “Saving Memory in Turbo-Decoders Using the Max-Log-MAP algorithm”, IEEE

[11] Bartosz Mielczarek, Arne Svensson. “Improved MAP Decoders for Turbo Codes with Non-perfect Timing and Phase Synchronization”, VTC ’99.

[12] B. Mielczarek and A. Svensson. “Imfluence of the Phase and Timing Offset on the BCJR Algorithm Performance”, IEEE.

[13] Bartosz Mielczarek, Arne Svensson. “Timing and Phase Synchronization with Turbo Codes”, IEEE.

[14] Bartosz Mielczarek, Arne Svensson. “Post-Decoding Timing Synchronization of Turbo Codes on AWGN Channels”, VTC2000.

[15] Lijun Lu and Stephen G.. Wilson. “Synchronization of Turbo Coded Modulation Systems at Low SNR”, 1998 IEEE.

[16] J. Hagenauer and P. Hoeher, “A Viterbi Algorithm with Soft-decision Outputs and its Applications,” IEEE Globecom, pp. 1680-1686, 1989.

[17] L. R. Bahl, J. Cocke, F. Jelinek, and J. Raviv, “Optimal decoding of Linear Codes for Minimizing Symbol Error Rate,” IEEE Trans. Inform. Theory, pp. 284-287, Mar. 1974.

[18] A. Viterbi, “Approaching the Shannon Limit : Theorist’s dream and practitioner’s Challenge,” in Proc. Int Conf. Millimeter Wave and Far Infrared science and Technology, 1996, pp.1-11.

[19] B. Mielczarek and A. Svensson. “Timing Error Recovery in Turbo-Coded Systems on AWGN Channels,” IEEE Transactions on Communications, VOL. 50, NO. 10, October 2002.

[20] Lance C. Perez, Jan Seghers, and Daniel J. Costello, Jr, “A Distance Spectrum Interpretation of Turbo Codes,” IEEE Transactions on Information Theory, VOL. 42, NO 6, November 1996.

[21] Sergio Benedetto and Guido Montorsi, “Design of parallel Concatenated Convolutional Codes,” IEEE Transactions on Communications, VOL. 44, NO 5, May 1996.

[22] William J. Ebel. “Turbo Code Implementation on the C6x”.

[23] “TMS320C62x/C67x CPU and Instruction Set”, Texas Instruments, Reference Guide, Mar. 1998.

[24] “TMS320C6000 Peripherals”, Texas Instruments, Reference Guide, April. 1999.

[25] “TMS320C6711, TMS320C6711B Floating-Point Digital Signal Processors”, Texas Instruments, Revised Datasheet: SPRS088B, Sep. 2001.

[26] Carlos A.P.N. Solis. “Setting Up TMS320C6201 Interrupts in C”, Texas Instruments, DSP Application report: SPHA001.

[27] “Physical Layer Standard for cdma2000 Spread Spectrum Systems”, 3GPP2 C.S0002-A-1, September 12, 2000.