Delay spread profiles and receiver performance in a dense multipath environment

Delay spread in communication systems is due to the abundance of multipath reflections. The classical model of wide-sense stationary uncorrelated scatterers (WSSUS) is adopted for the derivation of the received power profile. It is found that there is a gain G(D) in the total received power relative to the direct ray received power in a free-space environment, that increases with transmitter-receiver distance D. The delay spread also increases with D. Using the derived power profile, the performance of a receiver that optimally combines the multipath rays, using side information about the sample channel impulse response, is analysed under Rayleigh statistics for both narrow and broadband signalling. An upper bound on the error rate indicates an improvement by a factor of e^-G(D) owing to the multipath diversity combined with spread spectrum transmission. The possible application of these results to indoor communications is discussed