Analysis of a CDMA downlink in multi-path fading channels

This paper deals with the performance analysis of a CDMA downlink in multi-path fading channels. An approximate expression for the demodulated signal-to-noise ratio is developed for a conventional RAKE receiver. The expression includes an orthogonality factor that quantifies the performance gain of using orthogonal spreading codes in the presence of a time-dispersive channel. A comparison with simulation results shows that the accuracy of the expression is high in various combinations of desired signal, orthogonal and non-orthogonal intra-cell interference, and AWGN. The numerical results also show that not only the strength of individual rays but also their relative phases and delays determine the value of the orthogonality factor.