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Two-dimensional (2D) wavelength-time coding schemes have recently been studied for optical code-division multiple access. In this paper, we propose a new family of 2D codes, which use "synchronized" quadratic congruence sequences for wavelength hopping and (n,w,2,2) optical orthogonal codes for time spreading. The new 2D codes provide larger (asymptotically optimal) code cardinality than other 2D codes by relaxing the maximum cross-correlation function from one to two. Our study shows that the heavier code weight supported by our 2D codes results in better code performance than some of previously proposed 2D codes (of the maximum cross-correlation functions of one and two). The new codes potentially support more subscribers and heavier bursty asynchronous traffic with gradual performance degradation as traffic load increases. [ABSTRACT FROM AUTHOR]

To provide differential quality-of-service in optical code-division multiple access, variable-weight codes were proposed and analyzed under a conventional assumption of identical power in every optical pulses (i.e., same chip power). To account for power limit of some laser sources, we assume the use of same optical power in each bit duration (i.e., same bit power) in this paper. For illustration, we focus our study on double-weight codes under both same-chip-power and same-bit-power assumptions. A new and better approximate performance-analytical model for double-weight codes is developed and validated with computer simulation. We show that heavy-weight codes do not always perform better than light-weight codes under the same-bit-power assumption, contrary to previous findings under the same-chip-power assumption. [ABSTRACT FROM AUTHOR]