Random Access Techniques for Data Transmission over Packet Switched Radio Networks.

We study the behavior of a population of data terminals which use packet-switching to communicate with a central station over a multiple-access radio channel. In order to reduce the interference among conflicting packets, we introduce Carrier Sense Multiple Access CSMA as a method for multiplexing the terminal traffic in the packet radio environment. In this access mode, a terminal will inhibit its transmission when it senses the carrier of any other transmission. This method is effective when the propagation delay is small compared to the packet transmission time. However, the performance of CSMA is highly dependent on the sensing ability of each terminal unfortunately, many situations exist in which some terminals are hidden from others either because they are out-of-sight or out-of-range. The existence of hidden terminals significantly degrades the performance of CSMA. To eliminate the hidden terminal problem, we consider a natural extension of CSMA, namely, the Busy Tone Multiple Access BTMA. BTMA with hidden terminals performs almost as well as CSMA without hidden terminals. A second alternative for multiplexing the terminals on a packet radio channel is to use reservation techniques. Here we study the Split-channel Reservation Multiple Access mode as one implementation of such reservation techniques. These many access modes are compared with regard to throughput and delay. Author