Capacity enhancement in digital cellular systems using variable bitrate speech coding

In this paper, we consider the use of variable bitrate (VBR) speech coding to reduce co-channel interference and thus increase the capacity of cellular systems. We propose the so-called VBR-FEC scheme in which a variable-rate forward error-correcting code (FEC) is used in conjunction with a VBR speech coder. We then present an analysis of the enhancement in capacity that can be expected in the case of a CDMA system employing the proposed VBR-FEC scheme. Next, we present a design example using a specific VBR coder and a family of BCH codes for the FEC. Finally, we present a real-time statistical simulation platform that can be used to evaluate the impact on capacity of interference-reduction techniques, by studying their effect on received speech quality using listening tests. We use this platform to simulate the design example and present results of its performance