Network control of speech bit rate for enhanced cellular CDMA performance

It is generally recognized today that variable rate speech coding is an increasingly important system component for high capacity cellular networks. By exploiting speech statistics to reduce the average bit rate, interference levels are reduced and system capacity is increased. We demonstrate that variable rate speech coding offers the possibility of an additional capacity enhancement through the use of network control of the user bit rate in response to changing traffic levels. We introduce the concept of network control of rate and propose a network-control method for CDMA systems, which is evaluated based on a performance measure called averaged speech quality and an M/M/∞//M queueing model applied to a cell under heavy traffic conditions. Simulation results demonstrate how network control of rate can achieve improved speech quality or increased capacity for a given quality objective