Channel based optimum bandwidth for spread spectrum land cellular radio

The mobile cellular service is driven by requirements for quality of service, most of which is measurable in terms of bit or frame error rates, and capacity-the number of active calls per unit area. In the time varying mobile environment the ratio of the average received energy per information bit to the noise spectral density (E_b/N₀ ) needs to be high enough to overcome fades, but such a trend also increases the transmitted interference to other units, and thus reduces the capacity. Spread spectrum transmission, where the signal is spread over a broad band and the different calls are differentiated by their coded spreading, is a way of increasing the capacity and enhancing some service related features. An optimum is observed for the bandwidth of such systems, which is derived from the nature of the mobile channel, and is a trade off between the statistical ensemble encapsulated within the time resolution window, the diversity gain and the code strength