Capacity of a low mobility spread spectrum system over a wireless local loop

This paper reports on a series of simulations designed to investigate the efficiency of a low mobility direct sequence, spread spectrum (DS-SS) cellular system operating over a 2.0 GHz wireless local loop (WLL). The WLL consists of a base station with omnidirectional antenna at roof-top height, or pole-mounted, transmitting to a receiver terminal which also uses an omnidirectional antenna. The receiver is always considered inside a building. The simulations and efficiency calculations were performed using wideband channel responses taken from experimental data at many locations worldwide representing both urban and suburban environments. The aim of the system is to provide data rates appropriate for voice communications for the maximum possible numbers of simultaneous users each with low mobility. The system modelled utilises a linear adaptive receiver structure to minimise the multiple access interference (MAI) experienced from other users. The performance of the system in terms of total efficiency is considered while maintaining a specific BER. The performance is compared to that of a similar system based on conventional matched filter DS-SS receiver. This paper will show that there is substantial gain to be achieved from using the adaptive receiver system in each of the propagation environments considered