Analytical study of multiple access interference and beat noise in polarization-wavelength-time optical CDMA systems

The performance of a three-dimensional optical code-division multiple-access system based on polarization-wavelength-time codes is investigated. The unwanted effects of multiple access interference are first studied and an accurate enough expression is given for the upper bound of the bit error rate. The proposed expression is obtained by decomposing the three-dimensional polarization-wavelength-time codes into horizontally and vertically polarized two-dimensional wavelength-time codes that are assumed to be statistically independent. It is shown by Monte Carlo simulation that the assumption of independence gives accurate enough bit error rate, whenever the number of chips is much larger than the number of wavelengths. The impact of the beat noise is also studied by approximating its distribution as Gaussian. It is shown that beat noise in a network having three-dimensionally encoded signals is not as important as it is in a network having two-dimensionally encoded ones.