A SUBCARRIER MULTIPLEXED CDM OPTICAL LOCAL-AREA-NETWORK, THEORY AND EXPERIMENT

In this paper, a hybrid scheme is proposed for the purpose of suppress ing the effects of external modulation and/or laser nonlinearities in subcarrier multiplexing (SCM) fiber optic communications systems. Hybr id CDMA/FDMA combines two schemes in such a way that the resulting hyb rid network is robust against interference and is much more spectrally efficient than a CDMA system. Several possible architectures are intr oduced for the hybrid CDMA/FDMA subcarrier fiber optic local area netw ork (LAN). The networks utilize CDMA and SCM, an asynchronous multiple access scheme. Direct sequence spread spectrum multiple access (DS/SS MA), the most common form of CDMA is employed. It is shown that by usi ng the code sequence sets for which the shift-and-add property holds, intermodulation products (IMP's) and harmonics have a similar interfer ence-like effect as nonmatching sequences do. Owing to the fact that s hift-and-add property holds for conventional spreading sequences, supp ression of nonlinear distortions is examined, An average error probabi lity performance evaluation of the selected configuration is presented for a transceiver pair. In analysis of the system, we assume the inte rference term arising from other users is Gaussian distributed. The re sults are compared to that obtained by exact evaluation of interferenc e distribution using Gauss quadrature rule integration (GQR) method. W e compare the performance of this scheme for two different code sequen ce lengths. We also present some preliminary experimental results on t he proposed LAN implementation as well as its measured transmission pe rformance. The results show promise.