Implementation And Protection Of G.729 Vocoder In SCDMA System

Synchronous CDMA ( SCDMA ) system is a wireless communication system using smart antenna, synchronous CDMA, SWAP?( Synchronous wireless access protocol) and it is implemented on software radio architecture. Due to many practical problems, the voice quality of the system is not so ideal as what it had been thought to be, it works unsteadily usually when channel error occurs, which absolutely hindered the marketing process of the system.To improve the voice quality, this thesis start with replacing the present QCELP vocoder with a new one. After analysis and comparison among candidate vocoders that can be used in SCDMA, ITU-T G729A, which is the simplified version of G.729 algorithm, proved itself the optimum one. Therefore, the main purpose of this thesis is to implement G729A algorithm on TMS320C54x in real time and design an effective protect scheme to enhance its error robustness.ITU-T provided a C source code for G729A implementation on DSPs of 16-bit fixed point. However, owing to the heavy load of computation, such C code can not work in real time on C54x after compilation. Chapter 3 focuses on translating the C code into assembly code. The implementation and optimization involves issues of assignment of variables and memories, pass of function parameters, addressing modes, control of nested repetition, use of AR registers, pipeline conflicts, and so on. A performance test for the assembly code is given at the end of chapter 3 and the result shows that the assembly code is tens of times efficient in comparison with the original C code.It is highly important to enhance the error robustness of G.729 vocoder. On the subjective sensitivity analysis of G.729 vocoder bits using PESQ algorithm, the problem is concentrated on how to protect those subjectively important bits by using the additional 1.6kbps channel bandwidth in SCDMA. Referring to the self-guard mechanism of G.729, characteristics of RS coding and SCDMA channel, a scheme using RS(7,5) coding with CRC and block interleaving is put forward and its effectiveness is verified by both PESQ algorithm and subjective test at the end of chapter 4.