On the Teletraffic Capacity of Optical CDMA

The capacity of an optical CDMA (OCDMA) network has traditionally been defined as the number of continuously transmitting circuits supported by the network. In this paper, we use teletraffic models to determine the teletraffic capacity of a circuit-switched OCDMA network where circuits carry bursty traffic. Our analysis is independent of the OCDMA implementation or spreading code. In conventional networks, e.g., a wavelength-routed-network (WRN), new circuits are blocked when all wavelengths are occupied. In OCDMA, when the number of codewords exceeds the number of network subscribers, new circuits need not be blocked. Instead, capacity is limited by multiple-access interference: when the number of actively transmitting circuits becomes excessive, the bit-error rate of all circuits on the network degrades, causing an outage. We find that through statistical multiplexing, the capacity of OCDMA exceeds that of a WRN, except when circuit activity is very high, while the constraints on outages are more stringent than those blocking. In such cases, we show how OCDMA with call admission control can be used to match or exceed the capacity of a WRN. Overall, our analysis shows that OCDMA is well suited to applications when conventional blocking is undesirable, and/or circuits carry bursty traffic.