Half-rate GSM vocoder implementation on a dual mac digital signal processor

The Global System for Mobile (GSM) communications uses a 13 Kbps vocoder which expands to 22.8 Kbps after channel coding. To increase the user capacity the half-rate channel has a gross transfer rate of 11.4 Kbps. The vocoder for the half-rate channels operates at 5.6 Kbps. The computational requirements of a half-rate vocoder and other necessary services required design of an entirely new digital signal processing architecture geared towards l-D signal and speech processing. The architecture is characterized by Very Large Instruction Word (VLIW) and two multiply-accumulate (MAC) units. Other enhancements of the hardware allow an efficient implementation of the half-rate GSM vocoder. This paper describes the architecture and compares the vocoder performance with existing implementations