CHANNEL COST OF MOBILITY

We analyze, for mobile users in regular cellular arrays, the probabili ty that a call is blocked from accessing a channel (when originating o r when attempting to hand off during an active user's sojourn). This p robability, p, is studied here as a function of the originating call l oad, in Erlangs per cell, with the number of channels and user mobilit y treated as parameters. Using simulation, we demonstrate that a simpl e 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 li near or planar. By the ''cost of mobility,'' we mean the additional ch annels (in percent) that are needed to meet a required p because the u ser is mobile. Using the ad hoc formula, we show that the cost of mobi lity is generally minor, becoming appreciable only for high mobility c oupled with low traffic loads. Two of the high-mobility examples consi der 105-kmph user movement with only 200 m traversed per cell. Calls a re 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 mobi lity. In the second example, with only 3 Erlangs per cell, the extra c hannels needed increase to 25%.