適應性多重位元率語音編碼器之渦輪碼通道編碼

Turbo Channel Coding for AMR Speech Codec

曾偉誌(Wei-Chih Tzeng)

指導教授 ： 簡福榮

國立臺北科技大學/電資學院/電機工程系研究所/碩士(2007年)

摘要

適應性多位元率（Adaptive Multi-rate，AMR）語音編碼是由歐洲電信標準組織在1997年10月為全球行動通訊系統（Global System for Mobile Communication， GSM）所制定的語音編碼器，AMR語音編碼器可藉由分析通道的狀況，在語音編碼率與通道編碼率之間做適應性的調整，有效的降低位元的錯誤率，因此，在1999年的4月更被3GPP（3rd Generation Partnership Project）指定為第三代寬頻分碼多重存取（Wideband Code Division Multiple Access，WCDMA）的語音編碼器。
本論文以三種通道錯誤保護編解碼組合︰迴旋碼編碼（Convolutional Coding）配合上硬決策維特比演算法解碼、迴旋碼編碼配合上軟決策維特比演算法解碼、渦輪碼編碼（Turbo Coding）配合上對數最大事後機率演算法（Log-Maximum A Posteriori，Log-MAP）解碼。再各別以均勻錯誤保護（Equal Error Protection，EEP）和非均勻錯誤保護（Unequal Error Protection，UEP）的方式，對AMR語音編碼器所編出的位元流做通道保護編碼，比較各個不同的編碼方法在不同的訊雜比環境下的效能表現。主觀與客觀實驗中，在同樣的通道錯誤保護編解碼的條件下，皆以非均勻通道保護的方式在低SNR的環境中有較佳的表現，其中又以使用渦輪碼編碼配合上指數最大事後機率演算法解碼效果最好。

關鍵字

適應性多重位元率語音編碼器 ； 通道編碼 ； 渦輪碼

並列摘要

European Telecommunication Standards Institute (ETSI) initiated a standardization program in October 1997 to develop an Adaptive Multi-Rate (AMR) speech codec for Global System for Mobile Communication (GSM). Depending on channel conditions, the AMR codec offers substantial improvement in error robustness by adapting bit rates between speech and channel coding. In April 1999, the Third Generation Partnership Project (3GPP) adopted the AMR codec as the mandatory speech codec for the third generation WCDMA (Wideband Code Division Multiple Access) system.
Three different channel coding schemes are incorporated with the AMR codec and compared in this thesis. The first scheme encodes the bitstream with the convolutional code and decodes it back using the hard-decision Viterbi algorithm. The second scheme encodes the bitstream with the same convolutional code but decodes it back by a soft-decision Viterbi algorithm. The last one exploits the turbo code to encode the bitstream and decodes it back by using the log-maximum a posteriori (log-MAP) algorithm. Both unequal error protection (UEP) and equal error protection (EEP) strategies are also included for comparison. The experimental results show that the performance of the UEP is better than that of the EEP in low signal-to-noise ratio (SNR) environment, and the third scheme that exploits turbo code performs best among all of the three channel coding schemes.

並列關鍵字

Adaptive Multi-Rate(AMR) ； Channel Coding ； Turbo Code

參考文獻

[1] F. Hillebrand, GSM and UMTS : the creation of global mobile communication, Wiley, 2002.

[3] S. A. Spanias, “Speech coding: A tutorial review,” Proceedings of the IEEE, vol. 82, no. 10, pp. 1541-1582, Oct. 1994.

[8] TS 26.101, “Adaptive Multi-Rate (AMR) speech codec frame structure”, June 2002.

[10] J. G. Proakis and M. Salehi, Contemporary Communication System using MATLAB, Boston: PWS Pub, 1998.

[13] A. J. Viterbi, “Error bounds for convolutional codes and an asymptotically optimum decoding algorithm,” IEEE Trans. Inform. Theory, vol. 13, no. 2, pp. 260-269, April 1967.