Packet Switching in Radio Channels : Part IV - Stability Considerations and Dynamic Control in Carrier Sense Multiple Access

Absmct-In two companion papers a method for multiplexing a population of terminals communicating with a central station over a packet-switched radio channel was introduced; this method is known as Carrier Sense Multiple Access (CSMA). CSMA, as with ALOHA multi-access broadcast channels, has the unfortunate property that the throughput falls to zero as the channel load increases beyond a critical value. The dynamic behavior and stability o f slotted ALOHA channels have been studied extensively and have led to a definition of stability. In this paper, similar techniques are used to analyze CSMA, which is shown to have a behavior not unlike that of ALOHA. However, contrary to ALOHA channels where steady-state performance is badly degraded when true stability is to be guaranteed, hence requiring dynamic control , we find that CSMA'provides excellent stable performance even with as large a population as 1000 terminals. Furthermore, we study a simple adaptive retransmission control procedure which provides a significantly improved channel performance which is insensitive to the population size.