In this paper we study and evaluate the performance of a spectral-phase encoded optical CDMA (SPE-OCDMA) system using advanced receiver structures based on second harmonic generation (SHG) effect imposed in a Thick or Thin crystal. This receiver structure is employed as the nonlinear pre-processor prior to the conventional low-speed photodetector. In our performance evaluation amplified spontaneous emission (ASE) of the optical amplifiers, receiver front end thermal noise and photodetector shot noise which are effective in low power conditions, and multiple access interference (MAI) noise which is the dominant source of noise in high power conditions in any coherent OCDMA communications system have been considered. We begin by studying the statistical behavior of Thick crystals in an optically amplified digital lightwave communication system in the context of a SPE-OCDMA communication system. The error probability for Thick crystal receiver structure is evaluated using Saddle-Point approximation. Furthermore, we obtain a closed form approximation for the probability density function (pdf) of the decision variable in SPE-OCDMA systems with Thin crystal SHG receiver. In this analysis, to obtain approximate probability density function, we employ Gram-Charlier expansion based on the corresponding first order moments of the decision variable. The first three moments are obtained in a closed form approximation and consequently a closed form expression for the error probability is obtained by integrating the approximated pdf of the decision variables for transmitting bit "1" and "0" in Thin crystal receiver structure. The precision of the approximation is verified by the Monte-Carlo simulation. Finally the performance of SPE-OCDMA network for both Thin and Thick SHG crystals are analytically evaluated and discussed for different number of interfering users and different code-lengths and different speed of the conventional photodetectors. We deduce that the performance of Thin SHG crystal receiver is more sensitive to the transmitted power level especially in low power conditions. It is concluded that in low power conditions where ASE, thermal and shot noises are the dominant noise sources, Thick SHG crystal receiver outperforms the Thin crystal receiver. However, in high power conditions where MAI noise is the most effective noise term, Thin SHG crystal receiver structure outperforms the Thick crystal receiver.

In this paper we present and investigate a digital design and implementational details of a wireless optical CDMA (OCDMA) system based on generalized optical orthogonal codes (OOCs). A detailed digital implementation analysis and transmitter/receiver architectures in the context of the above design are fully studied. We analyze various subsystems for a wireless OCDMA system including detector and receiver structure, acquisition, and tracking blocks as well as evaluating their performance in a typical wireless OCDMA communication system. By analyzing two main parts of the system, namely, chip-level detector and OCDMA receiver blocks we evaluate the performance of the overall system. Analytical and simulation results are presented to depict system performance. Results on the design and implementation of such systems in this paper indicate the viability and the importance of OOC based wireless OCDMA technology to satisfy certain applications need in a wider communication system worldwide. Finally we describe an experimental prototype where we highlight the main aspects of the implementation of the system.

In this paper we study and present an in-depth analysis on the operability and the viability of a typical wireless optical CDMA (OCDMA) local area network. Three receiver structures for OCDMA systems, using optical orthogonal codes (OOC) with minimum auto and cross-correlations as signature sequence, namely, correlation, correlation with hard-limiter, and chip-level detection are studied and proposed for such a network. For the synchronization circuit design the performance of two algorithms for OOC based OCDMA networks, namely, simple serial-search and multiple-shift in the context of wireless OCDMA LAN are studied. Furthermore, we study a synchronization method based on matched filtering and show that it presents a much better performance in our wireless OCDMA system. The effect of sampling rate and its performance on tracking circuit is analyzed. Bit-error-rate (BER) analysis is performed by photon counting methodology. Multi-user interference (MUI), ambient light, and photodetector dark current are considered in our analysis. Our analysis strongly indicates the viability and practicality of such systems in certain important wireless optical communications systems.