Based On The Realization And Optimization Of The Dsp Evrc Vocoder

To meet the needs of the third mobile communication system for higher speechquality and greater system capacity, the CDMA systems employ variable rate speechcoding technologies, which select the encode rate dynamically according to the signalenergy and background noise. This method insures the speech quality as well as reduces,the average encode rate, so the system capacity is increased.In 1997, TIA has released the standard of IS-127, it is Service option 3 of IS-95 and the voice encoder/decoder standard of the third mobile communication, the core algorithm of this standard is Enhanced Variable Rate Codec, the shortened form is EVRC. The EVRC Vocoder is Varialbe Rate, the maximal encode rate is Skbps, its voice quality is closed to QCELP-13k, and has better ability of anti-disturbance. At the present time, EVRC is the best vocoder in the CDMA system when take into account both the voice quality and the encode rate.EVRC Vocoder is widely used in the Base Station of IS-95 and CDMA2000. Because our vocoder is mainly used in the Base Station, where the vocoder needs the excellent performance, so we select the TMS320C64xx , the most advanced DSPs of TI. The paper makes great efforts on the software optimization of EVRC vocoder. Based on the understanding of TMS320C64xx CPU structure, we do deeply-optimization on the loop which appear usually in voice signal processing, and this improve the utility ratio of CPU and the parallelity degree of CPU function cell. At the same time, we utilize the Bit-Exact test to test the fixed-point EVRC vocoder with the test vectors of TIA/EIA/IS-718, which improve the robustness of the vocoder.At last, our vocoder is compared with the vocoder Benchmark of Delphi company, with the result that the performance of our vocoder is better than Delphi's obviously, thus make the vocoder has applied value.