Capacity Analysis of Asynchronous Optical CDMA Systems Utilizing Wrapped OPPM: Multiple Access Interference Limited Case

In this paper the capacity of asynchronous incoherent optical CDMA (OCDMA) systems employing wrapped overlapping pulse position modulation (WOPPM) for two types of receiver structures is analyzed. The analysis is performed in the presence of multiple access interference as the main limiting factor. Throughput analysis for uncoded systems utilizing WOPPM is conducted and a lower bound on the capacity for two types of correlator based receiver structures is derived. Furthermore, for a fixed code and a fixed maximum number of symbols, a numerical solution for maximizing the capacity is presented. Moreover, to minimize the probability of error when the throughput and the number of users are fixed, a numerical solution is introduced. Finally, for two common design problems, algorithms are proposed for achieving the system parameters well close to the optimal settings. The results of our different analyses for uncoded systems using WOPPM have been compared with unwrapped OPPM. Our results have also been compared with on-off keying (OOK) and pulse position modulation (PPM). The results of this work show that, for a fixed throughput, the performance of WOPPM is significantly superior to OOK and PPM.