Performance analysis of chip-asynchronous coherent time-spreading optical CDMA system

Multiple-access interference(MAI) and beat noise(BN) in chip-asynchronous coherent time-spreading OCDMA system are evaluated by the aperiodic cross-correlation function of up-sampled sequence. Relationship between the mean intensity of aperiodic cross-correlation and MAI and BN is deduced, and then the relationship between BER and mean intensity of aperiodic cross-correlation is discussed. For 127-long gold sequence, mean BER performance of chip-asynchronous coherent time-spreading OCDMA is derived and compared with that of the chip-synchronous system. It can be shown that the chip-synchronous assumption provides a performance upper limit. For realistic asynchronous coherent time-spreading OCDMA system, BER will reduce by about one order of magnitude.