Optical CDMA with overlapping PPM

Direct-detection optical code-division multiple access (CDMA) systems employing overlapping pulse-position modulation (OPPM) schemes are proposed. A union upper bound on the bit error rate is derived taking into account the effect of both multiple-user interference and receiver shot noise. The photodiodes' dark currents are neglected in order to have some insights on the problem. Performance characteristics are then compared to the traditional on off keying (OOK) and pulse-position modulation (PPM) schemes. It is shown that under the constraints of both throughput and chip time, the OPPM system outperforms both traditional systems.