A performance analysis of optical overlapping PPM-CDMA communication systems

Direct-detection optical code-division multiple-access (CDMA) systems employing overlapping pulse-position modulation (OPPM) schemes are proposed. Both upper and lower hounds on the bit error rate (BER) are derived taking into account the effect of both multiple-user interference and receiver shot noise. The photodiodes' dark currents are neglected since their effect is minor. The throughput limitation of this system is evaluated as well. Performance characteristics are then compared to optical CDMA systems employing traditional ON-OFF keying (OOK) and pulse-position modulation (PPM) schemes. It is shown that under fixed data rate and chip time, OPPM-CDMA system superperforms both traditional systems. Moreover, it is shown that the throughput limitation of OPPM-CDMA is almost 6.7 times greater than that of OOK-CDMA.