Error probabilities of coherent optical heterodyne FSK-CDMA signals in a noncoherent detection system degraded by laser phase noise

An error probability analysis is performed for noncoherent detection of optical heterodyne frequency-shift keying (FSK) direct sequence spread-spectrum code-division multiple access (CDMA) signals corrupted by laser phase noise, receiver noise, and multiuser noise. Receiver noise is included in the analysis as an additive white Gaussian process. The multiuser noise is also modeled as a Gaussian process. An FSK-CDMA system with low, moderate, and high user bit rates as compared with the laser linewidth is analyzed over different spreading code lengths for increasing numbers of users. The low bit rate system performs poorly even when the spreading code is long and the number of simultaneous users is very small. On the other hand, a high bit rate system which uses a spreading code with 2¹¹ chips can support up to 75 users if the maximum allowed possibility of bit error is 10^-6