現今隨著科技的迅速發展下，無線通訊已成為行動通訊的一大熱門議題。對於資料傳輸而言，在雜訊嚴重與頻寬有限的無線衰減通道中傳輸，因此通道編碼在傳輸系統已成為不可或缺的應用。

本論文中，我們考慮二位元渦輪碼系統，利用刺穿機制改變其碼率，透過不同的調變方式後，再配合混合式自動再傳請求系統來做為傳送。在論文中除了利用渦輪更正碼外，還加入循環式錯誤更正碼，而我們所選用的為BCH碼。利用BCH碼在一區塊中加以更正，以確保資料的正確性，使得錯誤率可以有效的降低。因此，接收端在渦輪解碼器後，會經由可靠度指標來做為我們對資料的信賴程度。我們將此可靠度指標制定一門檻值，如果未達到我們所需的門檻，則接收端會要求補送或重送；否則，則以此資料為輸出。本論文另一項重點，利用我們所制定的可靠度門檻來減少請求及傳送的次數，達到降低傳輸與延遲的時間。經由電腦模擬驗證上述之架構在累加性高斯白雜訊通道效能，同時我們也加入瑞利衰減通道做分析，而在傳輸資料可分為bit-by-bit與區塊兩種方式做為我們的探討，由於在區塊瑞利衰減通道的錯誤率極為糟糕，因此在區塊瑞利衰減通道加入空時區塊碼來降低其錯誤率。最後在渦輪碼可適性調變中，透過不同調變、請求與傳輸次數之下，結合於混合式自動再傳請求系統，依不同使用者所需及通道環境下，可選擇最佳的調變與資料量。

In communication over wireless channels, which usually suffer from serious fading, forward error correction (FEC) and diversity techniques have become indispensable. In addition, automatic repeat request (ARQ) can be incorporated when a damaged codeword is beyond the capability of the FEC. The combined scheme of FEC and ARQ is called hybrid ARQ (HARQ).

In this thesis, we use the cascade of a cyclic error correction (CEC) code and a turbo code for the FEC. By puncturing, we can adjust the code rate of the turbo code. The code bits generated by the turbo code are transmitted in several rounds. We compute the reliability index (RI) at the turbo decoder output. When the RI shows that the received data bits are reliable enough, we accept them as the final decision; otherwise, a request is made to the transmitter to send the next round of complementary code bits. By the use of CEC codes, we can ensure that the received data packets have negligible packet error rates (PER’s) even when the bit error rates (BER’s) from turbo decoding are only medium small (e.g. in the order of one in a thousand). By the use of RI, we try to reduce the number of request for complementary (or even repeated) data retransmission and thus avoid long transmission delays. We also try a few different modulation schemes in our system, with a hope of achieving higher data transmission rate.

The performances of the techniques mentioned above are evaluated by computer simulation in additive white Gaussian noise (AWGN) channels and in Raleigh fading channels. Two types of Raleigh fading – bitwise and blockwise – are considered. Because the error rate is large in block Raleigh fading, we try to reduce it by space-time block codes (STBC). Finally, by different combinations of modulation schemes and number of requests in the turbo-coded adaptive modulation (TCAM) combined with HARQ, we can choose the optimum modulation and data rate depending on user’s demand and the channel condition.

[1] C. Berrou, A. Glavieux, and P. Thimtimajshima, “Near optimum error correcting coding and decoding: Turbo-codes,” in proc. ICC, vol. 2, pp.1064-1070, May 1993.
[2] J. Yuan, Turbo code principles and application. Kluwer Academic publishers, 2000.
[3] L. Hanzo, T.H. Liew and B.L. Yeap, Turbo coding, Turbo equalization and Space- time Coding for Transmission over fading channel. John Wiley and Sons, 2002.
[4] A. J. Goldsmith and S. -G. Chua, “Adaptive Coded Modulation for Fading Channels,” IEEE Trans. Commun. , Vol. 46, no. 5, pp. 595-602, May 1998.
[5] S. Ro, I. Hwang, D. Hong, C. Kang and M. Kang, “Adaptive Modulation and Coding of MIMO in Next Generation Mobile Systems,”in Proc. International Conference on Computational Sciences and its Application (ICCSA), Vol. 2668, pp. 445-454, Aug.2003.
[6] D. P. Agrawal and Q. Zeng, Introduction to Wireless and Mobile Systems Second Edition. Bill Stenquist Publisher, 2006.
[7] X. Peng, M. Song and J. Song, “Cross-layer Design for Adaptive Modulation and Coding with Hybrid ARQ,” in Proc. IEEE International Symposium On Microwave, Antenna, Propagation and EMC (MAPE) for Wireless Communications, pp. 138-141, Sept. 2007.
[8] D. F. Yuan and X. F. Song, “Turbo code performance over Rayleigh
fading channel using QPSK modulation,” in Proc. IEEE TENCON’02, Beijing, China , pp. 1056-1059, Oct. 2002.
[9] M.R.D. Rodrigues, I. Chatzgeorgiou, I.J. Wassell and R. Carrasco, ”
On the performance of turbo codes in quasi-static fading channels,” in Proc. IEEE Int. Symp. Inform. Theory(ISIT), Adeleide, Australia, pp. 622-626, Sept. 2005.
[10] S. Ryoo, S. Kim and D. S. Ahn, “Rate adaptation with hybrid ARQ based on cross layer information for satellite communication systems,” IEEE Int. Symp. on Consumer Electronics, pp. 165-168, Sept. 2004.
[11] L. Zhang and W. Heng, “Cross-layer adaptive modulation and coding design for space-time block coded MIMO-OFDM systems,” Computer Commun. , Vol. 32, pp. 540-545, 2009.
[12] Y. Zou, J. Dong and D. Li “A Novel HARQ and AMC Scheme Using Space-time Block Coding and Turbo Codes for Wireless Packet Data Transmission,” in Proc. IEEE ICCT’03, Vol. 2, pp. 1046-1050, Apr. 2003.
[13] R. Bose, Information Theory, Coding and Cryptography.McGraw-Hill, 2002.
[14] J. G. Proakis, Digital Communications 4th ed. McGraw-Hill, 2000.
[15] L. R. Bahl, J. Cocke, F. Jelinek, and J. Raviv, “Optimal decoding of linear codes for minimizing symbol error rate,” IEEE Trans. Inform. Theory, vol. IT-20, pp. 284-287, Mar. 1974.
[16] V. Franz and J. B. Anderson, “Concatenated decoding with a reduced-search BCJR Algorithm,‘‘ IEEE J. Select. Areas Commun. , vol. 16, no. 2, pp. 186-195, Feb. 1998.
[17] S.M.Alamouti ,”A simple transmit diversity technique for wireless
communications,” IEEE J. Select. Areas Commun. , Vol.16 ,no.8 , pp. 1451-1458, Oct. 1998.
[18] V. Tarokh, H. Jafarkhani, and A. R. Calderbank, “Space–time block
codes from orthogonal designs,＂IEEE Trans. Inform. Theory, vol. 45, no. 5, pp. 1456–1467, July 1999.
[19]S. Ghahramani, Fundamentals of probability with stochastic processes 3rd ed. Prentice-Hall, 2005.
[20] W. T. Kim, S. H. Lee, S. W. Song and E. K. Joo , ”Encoder Structure
of Turbo Code for HARQ System,” in Proc. IEEE Signal Processing Advances in Wireless Communication (SPAWC), pp. 31-35, Dec.2004.
[21] J. E. Hakegard and T. A. Myrvoll, “Evaluation of downlink IEEE802.16e communication at airports,” in Proc. IEEE Integrated Communications, Navigation and Surveillance (ICNS) , May 2008.
[22] M. N. Khan and S. Ghauri, “The WiMAX 802.16e Physical Layer Model,” in Proc. IET Int. Conf. , pp. 117-120, Jan. 2008.
[23] S. Gounai and T. Ohtsuki, “Performance Analysis of LDPC Code with Spatial Diversity,” in Proc. IEEE Veh. Technol. Conf.,pp.1918-1922, Sep. 2006.