Patent GB-1239530-A (GB)
IPC: H04W72/06
Filed: 1970-01-22
Abstract: 1,239,530. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 22 Jan., 1970 [30 Jan., 1969], No. 3172/70. Heading H4K. In a radio-mobile system utilizing a fixed central exchange, one channel is preallotted for the transmission of an initial calling signal to or from the exchange although no carrier or tone is sent on this channel except during a calling period, whereby the system maintains radio silence so far as possible. Once the calling signal is recognized at the exchange, or at the called mobile set, the call is transferred to another channel. Separate predetermined channels may be used for the two possible directions of calling in which case different other channels are used for the continuation of the call. Fixed to mobile.-A register controller 4 in the exchange 1 (Fig. 1) causes telegraph transmitter 14 to transmit the wanted mobile's number in V.F. code over the predetermined calling channel. All inactive mobiles are tuned to this channel so that, if free, the wanted one (Fig. 2) via its receiver 21, control 32 and decoder 36 responds to the code by opening gate CA so as to start a counter 27, 24 which scans the communication channels by switching-in appropriate crystals. In addition, outgoing calls from this set are inhibited. During the transmission of the code by the transmitter 14, register controller 4 starts a counter 9R so as to hunt for a free channel for a terminating call and then to transmit the carrier and an R marking tone via the transmitter 6 allocated to this channel. The mobile set's counter 27, 24 eventually steps to this channel so that via a filter 29 tuned to the. tone R, the gate CA is closed to stop the counter and the controller 32 is effective to transmit a reply tone T1 via outgoing speech bus 34, 22. The exchange responds by replacing the R tone with ringing tone which is passed on to the handset circuit 38 of the mobile set. When the handset is lifted, an off-hook tone T2 is sent to cause the exchange to switch the calling trunk 2 through to the relevant radio channel 3. At hang-up, a tone T3 is sent to release the exchange equipment and via gate SA, the counter 27, 24 is restarted to restore the receiver 21 to the predetermined calling channel. Mobile to fixed.-Off-hook by the mobile subscriber causes controller 32 to open gate SD and so step counter 27, 24 to the predetermined outgoing calling channel over which carrier and off-hook tone T1 are sent. The exchange responds by transmitting carrier and O tone over a free channel for an outgoing call. This channel is hunted by the counter 27, 24 due to the opening of gate CD by the controller once an off-hook tone burst has been sent. The filter 30 " O," on detecting the O tone, stops the counter by inhibiting CD and via controller 32 transmits seizure tone (successively T1, T2, T1) over bus 22 and the allotted channel. The exchange stops the O tone and after receiving the subsequently transmitted identity of the caller reverts this identity to the mobile set. The latter's decoder 36 recognizes this and transmits a further T1 tone to which the exchange responds by sending dialling tone. The call then proceeds in the normal manner. Modification.-The same predetermined channel may be used for calling on terminating and originating calls in which case no distinction need be made between the speech channels, viz. " R " and " O " tone, used for these calls. Alternatively, separate calling channels may be used but no distinction is made for the speech channels. Preferably, the exchange is provided with diversity reception facilities.