Reduction of optical beat interference in optical frequency-hopping CDMA networks using coherence multiplexing

In order to reduce the optical beat interference (OBI) in an optical frequency-hopping code division multiple access (FH-CDMA) network, we propose applying coherence multiplexing (CM) technique into the optical FH-CDMA network. Since the CM technique achieves multiplexing by using time delays exceeding the coherence time of the light sources, crosstalk between CM channels depends on a space of delay difference between CM channels. We analyze the ratio of crosstalk to signal as a function of the space, and find a channel space enough to neglect crosstalk from other CM channels. Using this channel space, we obtain the number of CM channels accommodated within one chip duration. Since the conventional FH-CDMA supports traffic by the code channels only, its capacity is limited by OBI as traffic increases. In addition to the code channel, the proposed network supports traffic by the CM channels. Since the addition of CM channels decreases the number of active code channels for uniform traffic, OBI is reduced. Numerical results show that the proposed network attains larger capacity than the conventional FH-CDMA.