Performance comparison of number- and coherent-state optical CDMA in lossy direct-detection photon channels

The performance of optical code-division multiple-access (CDMA) communication systems utilizing number-state light field is evaluated. Lossy direct detection optical channels are assumed. Both on-off keying (OOK) and pulse-position modulation (PPM) schemes are investigated. For OOK, the exact bit error rate is evaluated taking into account the effect of both multiple-user interference and transmission loss. Upper and lower bounds on the bit error probability for PPM-CDMA systems are derived under the above considerations. The effect of both background and thermal noise is neglected in the analysis. A comparison between the performance of the number- and coherent-state OOK/PPM-CDMA networks is also presented. The results demonstrate that the number-state system requires less than half the energy consumed by the coherent-state one in order to attain the same performance.<>