Spectral efficiency limit of bipolar signaling in incoherent optical CDMA systems

A universal scheme is developed to reproduce the effect of bipolar signaling in a unipolar optical channel. Without any hardware modification, the electro-optic/opto-electronic (EOE) system proposed enables the transmission of any bipolar code sequence through the unipolar optical channel while maintaining the correlation properties of the codes. The bit error rate performance of the EDE system is shown to be identical to that of an optimal baseband bipolar phase shift keying code-division multiple access (CDMA) system. Hence, the maximum spectral efficiency of an incoherent optical CDMA system using bipolar codes is the same as that of an optimal bipolar baseband CDMA system.