Implementation And Performance Researching Of G.729D In SCDMA System

The ITU-T Recommedation G.729D is the low-rate extending standard of Recommendation G729.It has improvements on the basis of G729 in many aspects such as the structure of codebook,quantization of gain,post-processing.The algorithm that improved has low(6.4kbps) encoding rate,small delay and good speech quality.The main research work of this paper is the implementation of G.729D vocoder in C54X DSP and analysis of the performance of the vocoder in SCDMA system.The last part of the paper is the research of the robust of G729D vocoder,that is,improving the performance by channel coding.The paper has been divided in six chapters:In chapter 1,the background of the research and the present vocoder in SCDMA Wireless Local Loop(WLL) system is introduced.The following is the analysis of problems that exsist in G.729 vocoder and the performance improvement that bring by G729D. In chapter2,the concept of SCDMA Wireless Local Loop(WLL) system is introduced,the key techniques of SCDMA is discussed.In chapter 3,the priciple of G729D encoder/decoder is described in detail.G729D is the successive vertion of G.729,the later is subscibed by ITU-T in the year 1996,and it is 4th generation recommendation for the coding of speech at 8kbps using Conjugate-Structure Algorithm -Code-Excited Linear-Prediction(CS-ACELP). G.729D is the low-rate extending standard of Recommendation G.729.It has improvement on the basis of G.729 in many aspects such as the structure of codebook,quantization of gain,post-processing. The character of digital signal processor(DSP) C54X is intruduced in chapter 4 at the first.Then we descirbed the opimization of memory during the implementaion of G.729D algorithm and point out the issue that we should pay attention to in the optimization of the code.At last,the clock cycles that needed by the assembly code is caculated when running the code in SCDMA system.The result proved that the assembly coding is successful. In chapter 5,the algorithm for speech evaluating,PESQ,is introduced at first,then we described the emulation of G.729D in SCDMA system using PESQ.We can get the performance by the emulation.The encoding rate of G.729D vocoder is 6.4kbps and the voice channel rate of SCDMA Wireless Local Loop is 9.6kbps,so we have 3.2kbps for channel encoding.But it is not enough to protect all the 64 encoding bits,also it's not needed to protect all of them.For this reason ,we should find out the sensitive bits of the 64 encoding rate.The 64 bits is divided in 3 groups by theoretical analysis and experiment. In the last chapter,the principle of BCH is introduced at first,as follow is the simulation of G.729D vocoder with BCH channel encoding.The result of the simulation indicates that the performance of the vocoder is highly improved.