GB1268030A - A mobile apparatus for a radiomobile telecommunications system integrated with the public telephone network - Google Patents

Abstract

1,268,030. Automatic exchange systems. SOC. ITALIANA TELECOMUNICAZIONI SIEMENS S.p.A. 13 Jan., 1971 [4 Feb., 1970], No. 1598/71. Heading H4K. In a system having mobile subscribers connected via radio channels to the public telephone network, each subscriber set includes a coding matrix whose columns are sequentially read-out automatically so as to cause a two-out-of-six tone generator to transmit the set's identity whenever the set goes off-hook at the beginning of a call or whenever its call detector responds to an incoming calling signal at the beginning of a call. A wanted subscriber's number is setup, prior to going off-hook, on another matrix whose columns are read-out in a similar way after the set identity code has been sent. If two or four or six &c. successive digits are the same, a special repetition code is transmitted instead of the normal digit code for the second, fourth &c. digit, a set of comparator gates being provided for this purpose. A number may comprise up to ten digits. All numbers (wanted or own) are prefixed and suffixed by respectively " start message " and " end message " two-tone codes. The two-out-of-six generator comprises two frequency selective circuits which are energized by weighted 2-out-of-6 codes derived from the markings in the matrix columns. A single channel is used for signalling to and from the mobiles. Each mobile's speech transceiver normally rests on the channel to which it was tuned during the last call so that this channel becomes first choice on subsequent calls. If a " channel occupied " signal, e.g. the carrier, ceases, e.g. due to fading, during a call, the set is cleared down after a predetermined time. It is also cleared, if a free channel cannot be found, on hanging up the telephone instrument and on receipt of an " end-call " signal from the exchange. Detailed logic circuitry for performing all the functions mentioned above is given in the Specification.