On the Teletraffic Capacity of Optical CDMA

The capacity of an optical code-division multi-access (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 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 (BER) 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 on 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.