Code acquisition in optical pulse CDMA utilizing coherent correlation demodulation

The performance of code acquisition based on an active optical correlation detector (OCD) used for optical pulse code division multiple access (CDMA) systems based on coherent correlation demodulation, is investigated. Passive matched filter acquisition used for most radio CDMA systems is not suitable for this system since the synchronization between the incoming optical pulse code and its local replica may have to be realized within a duration of several picoseconds or less. The parallel and serial implementations of the acquisition system under the same search algorithm are described; the effect of optical device noise, partial autocorrelation and multiuser interference on the acquisition is theoretically analysed and the numerical results are given for Gold codes. It is found that the acquisition time for a parallel search, due to the splitting penalty of the optical power, is not always shorter than that of a serial search, although optical amplification can improve the performance of the parallel system.