Patent GB-1144010-A (GB)
Title: Mobile telephone system
IPC: H04W84/02
Filed: 1967-05-05
Abstract: 1,144,010. Automatic exchange Systems. INTERNATIONAL STANDARD ELECTRIC CORP. 5 May, 1967 [26 May, 1966], No. 20924/67. Heading H4K. In a telephone exchange ordinary subscribers are connected to the final selector stages whilst a set of radio transceivers each connectible to any one of a plurality of mobile subscribers is connected to a group selector stage. In the cross-bar exchange shown n radio channel circuits 24a to 24n are connected through a cross-bar selector 20 to a group selector stage of the exchange. Each radio channel circuit is connected to a fixed transmitter 30 through an A.G.C. circuit 31 and to a plurality of diversely located fixed receivers 32a to 32n through a diversity selector 33 and noise suppressor 34. An allotter 40 including a relay chain (134, Fig. 6, not shown) selects from the idle radio channel circuits one to deal with the next call to a mobile subscriber, and causes it to transmit an availability frequency of 1500 cycles (modulated on to a carrier frequency individual to that channel). Those transceivers of the mobile subscribers that are free are automatically tuned (by stepping a carrier frequency selector switch until this availability frequency is detected) to this channel. When a fixed subscriber lifts his handset to initiate a call to a mobile subscriber a register at the exchange is seized and a test is made to see that the selector 20 is available and if available it is seized. The last three digits of the number of the wanted mobile subscriber are transmitted from the register to the Marker 35 in 2 out of 5 code over a multiple 42. In the Marker each digit is checked to see that it is in 2 out of 5 form and that radio channel circuit which has been preselected is seized. Each digit is changed from 2 out of 5 to pure (four bit) binary code and transmitted to the mobile transceivers, by frequency shift signalling. Each mobile receiver simultaneously responds by internally generating a frequency shiftrepresentation of its own number, and includes a comparator which compares the received and internally generated frequency shift signals. That mobile transceiver which detects a match transmits an " acknowledgement of receipt " frequency and the marker responds by completing the connection through the selector 20. When the preselected radio channel circuit is seized the allotter 40 immediately responds to allot another channel for the next call. Those mobile transceivers which did not detect a match automatically retune (after a predetermined delay) to the frequency of this next allotted channel. When a mobile subscriber lifts his handset for a call to a fixed subscriber the " acknowledgement of receipt " frequency is transmitted by the mobile station causing the preallotted channel to be seized. The mobile station internally generates the frequency shift representation of its own number and this is transmitted to the fixed station over the seized channel. This number is then retransmitted from the fixed station and the mobile station responds as for a call from a fixed subscriber. When the mobile station responds by again transmitting the " acknowledgement of receipt " frequency the fixed station returns a proceed to dial frequency. The subsequent dialling causes the " acknowledgement of receipt " frequency to be interrupted by shift to another frequency in accordance with the dialling pulses. Two mobile subscribers can be connected by employing two channels one to each subscriber. The internal generation of the mobile station numbers is effected by a counter which explores a diode matrix representation of that number. Reference has been directed by the Comptroller to Specification 1,010,299.