| In the realm of wireless communications, voice communication has always been one of the most dominant services for the very simple reason that speech is the most desirable means of communication between people. Due to a limited frequency spectrum, voice communication systems need to incorporate speech coding techniques to save bandwidth. Conventional methods like Pulse Code Modulation (PCM), Delta Modulation (DM) etc. are not suitable as their bandwidth occupancy is comparatively high. Speech coders like Code-Excited Linear Prediction (CELP) on the other hand, make an attractive choice because they offer high quality speech at low to medium bit rates (4.8--16 kbps). However, in the presence of transmission environment like the frequency selective Rayleigh fading channel, the received speech quality is often inferior. This can be attributed to fading, intersymbol interference (ISI), noise etc. that cause transmission errors. (Abstract shortened by UMI.)... |
