Importance

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Abstract

In a cellular radiotelephone system, a geographical area is divided into radio zones, each of which comprises a cell set, and a plurality of transponders which relay signals from portable units to the cell set, and from the cell set to the portable units. The use of transponders reduces the talk-back distance. This, in turn, results in a reduction of the power requirement of the portable units, which can therefore use smaller batteries and smaller transmitter components with a resulting reduction in size and weight. No hand-off takes place as the portable unit moves from transponder to transponder within the radio zone. Thus, the subdivision of the radio zone into transponder areas does not overburden the hand-off supervisory system. The number of channels assigned to a radio zone can be changed to suit conditions. In addition, however, the shapes and sizes of the radio zones can be varied with changes in user dispersion, to reduce the likelihood that all assigned channels in a given radio zone will be in use at the same time. The change in shape and size of a radio zone is carried out by breaking the communication link between a group of transponders and one cell set, and establishing a communication link between the same transponders and a different cell set. Hand-off occurs when a portable unit moves from one radio zone to another. The portable unit generates a hand-off request signal when the magnitude of the downlink voice signal falls below a preestablished level.

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First Claim