Design and performance analysis of a hybrid code -division /wavelength -division multiple access system based on ultrabroadband spectral encoding

A Hybrid code-division/wavelength multiple access system for local area networks is proposed and analyzed. The CDMA users use spectral phase encoding, which is a spread time (ST) scheme instead of the conventional spread spectrum (SS) CDMA. The concept of such a CDMA system and the basic structure of ultrashort pulse shaping for spectral coding will be introduced. The temporal and statistical behavior of pseudonoise bursts generated by spectrally phase-coded pulses and the evolution of these pulses into low intensity pseudonoise bursts as a function of the degree of phase coding will be reviewed. Examples will be given to show, in the absence of coding, what an ultrashort pulse train looks like after transmission due to dispersion effects of single mode fibers and the compensation procedure. New intensity profiles will be obtained accordingly. The hybrid CDMA/WDMA system model is then provided, and the signal-to-interference plus noise ratio (SIR) is computed. After a brief review of interference suppression, the bit error rate (BER), as a function of data rates, signal powers, numbers of CDMA and WDMA users, and receiver threshold, is calculated. The capacity and total throughput of the system at a pre-determined BER are obtained, first without any notching process to separate the CDMA and WDMA channels, then with a double notching method. It is shown when an m-sequence of length 512 is used for CDMA spectral phase coding, the system can accommodate tens of WDMA users and hundreds of CDMA users. The total throughput achieved when double notching is used is then around 900Gbps at a BER of 10−9 . An architecture for efficiently installing such a hybrid system is then proposed and the tradeoffs involved are analyzed. The possibilities of a single laser source, single fiber link and single pulse-shaping device are discussed. Their innovations significantly lower the cost of implementing a large CDMA-based LAN. A functional block diagram of the hybrid system is provided and a related work on implementation is described