PERFORMANCE OF PRMA - A PACKET VOICE PROTOCOL FOR CELLULAR-SYSTEMS

Future microcellular systems will require distributed network control. A packet-switched network is particularly suitable for this requirement. Moreover, packet switching naturally accommodates speech activity detection to improve capacity. Packet reservation multiple access (PRMA) is a Reservation-ALOHA protocol for packet speech transmission from wireless terminals to a base station. Because PRMA is a statistical multiplexer, the channel becomes congested when too many terminals are active. Voice packets require prompt delivery, and therefore PRMA responds to congestion by dropping packets delayed beyond a specified time limit. In this paper, equilibrium point analysis is used to evaluate system behavior. We derive the probability of packet dropping given the number of simultaneous conversations. We also establish conditions for system stability and efficiency. Numerical calculations based on the theory show close agreement with computer simulations. They also provide valuable guides to system design. For a particular example we find that speech activity detection permits 37 speech terminals to share a PRMA channel with 20 slots per frame, with a packet dropping probability of less than 1%.