Code tracking in optical pulse CDMA through coherent correlation demodulation

The code tracking performance of a noncoherent digital delay-locked loop (DLL) for use in coherent optical pulse CDMA systems is investigated. Tracking is fundamental to the overall performance of such systems since the incoming pulse code sequence and its local replica at the receiver have to maintain synchronism to within the chip duration that may be several pico-seconds for an optical implementation. After describing the tracking loop, the steady-state probability density function (PDF) of the tracking jitter is theoretically analyzed in the presence of multiuser interference and optical device noise, and numerical results of its variance are discussed.