Adaptive control for random access traffic in mobile radio systems

An adaptive random access control method is developed for the idle-signal-casting multiple-access (ICMA) or other random-access protocols. Its purpose is to prevent channel breakdown by controlling permission probabilities of user terminal´s transmission according to the load of a random-access channel. In ICMA, a base station broadcasts an `idle´ or `busy´ signal to prevent collisions of random access signals from terminals. Two kinds of control parameters related to permission probabilities are used. Probability q is referred to by all user terminals attempting transmission, and probability p is referred to if a user terminal must wait for the end of another´s transmission. The values of these parameters are determined according to the channel occupancy factor measured at a base station, and the base station broadcasts them to user terminals with `idle´ or `busy´ signals. This method can prevent channel breakdown and greatly improve channel performance under heavy-traffic conditions. Results of evaluating the method by computer simulation are discussed