CHANNEL COST OF MOBILITY

We analyze, for mobile users in regular cellular arrays, the probability that a call is blocked from accessing a channel (when originating or when attempting to hand off during an active user's sojourn). This probability, p, is studied here as a function of the originating call load, in Erlangs per cell, with the number of channels and user mobility treated as parameters. Using simulation, we demonstrate that a simple ad hoc Erlang-B formula, based on an equivalent traffic load, gives an excellent approximation to p. The approximation is good regardless of the nature of the user motion or whether the cellular arrays are linear or planar. By the ''cost of mobility,'' we mean the additional channels (in percent) that are needed to meet a required p because the user is mobile. Using the ad hoc formula, we show that the cost of mobility is generally minor, becoming appreciable only for high mobility coupled with low traffic loads. Two of the high-mobility examples consider 105-kmph user movement with only 200 m traversed per cell. Calls are assumed to have a one-minute mean holding time, and the value of p is required to be 1%. For a traffic load of 50 Erlangs per cell, about 10% more channels are needed with mobility than when there is no mobility. In the second example, with only 3 Erlangs per cell, the extra channels needed increase to 25%.