Mohit K. Prasad

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.

Evolutionary Algorithm for the Design of Stack Filters Specified using Selection Probabilities

Evolutionary algorithms are applied to the design of a class of nonlinear discrete-time filters: the positive Boolean function defining a stack filter is derived from its properties (specified in terms of selection probabilities). For window size 9, best results for this computationally intractable problem were obtained using a tree representation for each stack filter.