Multi-access-interference mitigation using power control in optical-CDMA star networks

This paper investigates optical power control to enhance capacity of optical CDMA star coupled networks. We consider a network in which the nodes encode their optical signal by prime codes, and the resulting error rate performance is inspected with and without power control. Network impairments, such as fiber attenuation, star coupler loss, thermal noise and shot noise, are taken into account while inspecting the number of supported users. We use a well known centralized power control algorithm to adjust the laser power levels. In short range optical networks, as for instance Local Area Networks (LANs) and Metropolitan Area Networks (MANs), the thermal and shot noise levels can be very small compared to the signal level, thus, noise-free or multiple access interference (MAI) limited case is of interest. In our analysis, the star network is partitioned into access part and broadcasting part. We proof that in the MAI noise dominated scenario, the broadcasting part of the network is irrelevant with respect of the optimum power control problem. In this case, the users can apply a lookup table containing information about the access part of the network to set their optimum transmission power levels. We note that whenever a node is switched on or off, the other active nodes should update their power levels in order to maintain or upgrade their respective error rate limits.