A Simplified Approach to the Performance Evaluation of FDMA/CDMA Systems

This work shows it is possible to apply for the performance evaluation of FDMA-CDMA cellular mobile systems a simple analytical approximated method, previously successfully proposed by two of the authors with reference to FDMA-TDMA systems. The distinctive feature of the methodology we describe is that it allows for an immediate determination of both the indexes traditionally employed to define system performance, i.e., average bit error probability and outage probability at a very low computational cost. The hypothesis required to apply the proposed approximation is that the examined spread spectrum system be characterized by a bandwidth occupancy lower than the coherence bandwidth of the transmission channel. This could be the case of a wireless DS-CDMA system envisioned to provide voice service and exploiting a processing gain of the order of a hundred. We apply our methodology to determine the performance improvements introduced increasing the protection of the transmitted information through error correcting codes and interleaving, in different operating conditions as regards the functioning of the power control loops. A comparison is also satisfyingly carried out with some other approximated analytical methods found in literature. We strongly point out that the corresponding results are achieved at a much more modest computational cost than in traditional approaches.