Towards Spectrally Efficient 2-D Optical CDMA Transmission with M-ary Symbols and Poisson Noise

The main objective of this paper is to achieve high normalized spectral efficiency (in bits per OCDMA chip) in optical CDMA network transmission. We design a time-wavelength M-ary transmission scheme that uses error-control coding and trellis coded modulation (TCM), optical M-ary intensity modulation and direct detection at the receiver. We use a probabilistic wavelength-time hopping approach, in order to transmit error-control coded and TCM modulated M-ary data directly through the optical channel without using optical spreading sequences. We present simulation results showing that the proposed OCDMA scheme is robust to Poisson and thermal noise. Hundreds of active users can be supported at target BER of 10^-9 and achieved spectral efficiency (1.37 bits per OCDMA chip) is almost twice larger that the best result previously reported.