Analysis of Coherent Random-Carrier CDMA and Hybrid WDMA/CDMA Multiplexing for High-Capacity Optical Networks.

Abstract

In this paper we provide an accurate analysis of the performance of a random-carrier (RC) code-division multiple-access (CDMA) scheme recently introduced for use in high-capacity optical networks. According to this scheme coherent optical techniques are employed to exploit the huge bandwidth of single-mode optical fibers and are coupled with spread-spectrum direct-sequence modulation in order to mitigate the interference from other signals due to the frequeng overlap caused by the instability of the carrier frequency of the laser, or to the mistakes in the frequency coordination and assignment. The average bit error probability of this multiplexing scheme is evaluated by using the characteristic function of the other-user interference at the output of the matched optical filter. Both phase noise and thermal noise (AWGN) are taken into account in the computation. Both synchronous and asynchronous systems are analyzed in this context. The analysis is valid for any spreading gain and any number of interfering users and makes very limited use of approximations. The performance evaluation of RC CDMA establishes the potential advantage in employing hybrids of WDMA (wavelength- division multiple-access) and CDMA multiplexing to combat inter- carrier interference in dense WDMA systems.