Spread-spectrum techniques for fiber-fed microcellular networks

It is well known that for a specified radio capacity, the peak performance [such as the minimum bit error rate (BER) or probability of outage] of subc arrier multiplexing (SCM)-based fiber-fed microcellular systems is limited by the nonlinearity of the optical source. Conversely, for a specified perf ormance, the maximum radio capacity is restricted by the source nonlinearit y, It is the goal of this paper to examine the robustness of a code-divisio n multiple-access (CDMA)-based system in the presence of these nonlineariti es. This is done by comparing the error and outage probabilities of a CDMA- based system to that of a conventional SCM system, which utilizes frequency -division multiple access (FDMA), It is shown that a CDMA system can relax the bounds on the performance or capacity. However, this improvement is obt ained at the expense of large chunks of bandwidth, An alternative hybrid CD MA/FDMA approach is examined, wherein the inherent benefits of both CDMA an d FDMA techniques are utilized. Performance evaluation shows that the hybri d system achieves the same system requirements in a more spectrally efficie nt manner.