Patent GB-1248058-A (GB)
Title: Improvements in or relating to mobile radio telephone systems
Inventor: DASKALAKIS ANDREW
IPC: H04W88/02
Filed: 1968-10-10
Abstract: 1,248,058. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. 10 Oct., 1968 [12 Oct., 1967], No. 48044/68. Heading H4K. A radio telephone system used over an extended vehicle route, in which the route is divided into zones covered by fixed transceiver units each having several operating channel frequencies, each frequency being used over an associated group of adjacent zones less than the total number of zones and in which each mobile transceiver has means for determining the zone in which the transceiver is located and means for selecting a frequency channel available in that zone and in the next zone to be entered along the route for use. As described, the route is divided up into eight zones A to H and each frequency channel is used over a group of up to three adjacent zones, not used for the next two zones then used again for a further group of zones. Thus the same frequency can be used for different calls in different groups of zones. The transceiver unit for a zone comprises one transceiver TX-RC for each channel frequency used in that zone. Channel 1 frequency is used for each of zones A to C and the transceivers at those zones and associated with that channel frequency are connected to a common channel switch CH1. Similarly, channel 2 frequency is used for zones B, C and D, channel 3 frequency is used for zones C, D and E &c. Each channel switch normally receives idle tone from a common source and causes an idle signal to be transmitted from the associated transceivers. If a mobile is involved in a call, a carrier signal is received from the mobile and the appropriate channel switch such as CH1 responds by selecting the transceiver receiving the best signal and ceasing to pass idle tone to its transceivers. Each mobile includes a zone mark detector, a pick-up of which co-operates inductively with fixed zone marker circuits to generate two successive frequency tones each time the mobile crosses from one zone to another. The order of these tones is reversed if the mobile crosses in the other direction. The tones are converted to pulses on corresponding lines and the first pulse is stretched or delayed to coincide with the second pulse and both pulses are applied as inputs to an array of AND gates, one for each possible combination of tones, i.e. one for each zone boundary for each direction of travel. As a boundary is crossed one AND gate responds and pulses via diodes, lines corresponding to channels not to be used for new calls, i ,e. channels not available in both the zone entered and the next zone. These pulses set bi-stables which open circuit corresponding inputs of the transceiver which is of the type which homes on to a channel on which an idle signal is being received. The transceiver is arranged to ignore the open circuited channels and thus select a free one of the remaining channels for use in the next call. The pulses to the bi-stables are also applied to a comparator which simultaneously receives from the transceiver an indication of the channels in use. If a pulse is received on a line associated with a channel in use this indicates that the channel is not available in the next zone and a visual or audible signal warns the user that the call if not soon terminated will be cut off. For a call to a mobile every fixed transceiver not in use transmits in coded form the designation of the wanted mobile on its channel and the mobile receives this on the channel to which it is tuned. The mobile returns a carrier signal on that channel and the corresponding channel switch responds and frees the other channels for further use.