In a cellular telephone network, handoff is the transition for any given user of signal transmission from one base station to a geographically adjacent base station as the user moves around. In an ideal cellular telephone network, each end user's telephone set or modem (thesubscriber's hardware) is always within range of a base station. The region coveredby each base station is known as its cell. The size and shape of each cell in anetwork depends on the nature of the terrain in the region, the number of base stations,and the transmit/receive range of each base station. In theory, the cells in anetwork overlap; for much of the time, a subscriber's hardware is within range of morethan one base station. The network must decide, from moment to moment, which basestation will handle the signals to and from each and every subscriber's hardware.
Each time a mobile or portable cellular subscriber passes from one cellinto another, the network automatically switches coverage responsibility from one basestation to another. Each base-station transition, as well as the switching processor sequence itself, is called handoff. In a properly functioning network, handoffoccurs smoothly, without gaps in communications and without confusion about which basestation should be dealing with the subscriber. Subscribers to a network need not doanything to make handoff take place, nor should they have to think about the process orabout which base station is dealing with the signals at any given moment.