Patent GB-1502255-A (GB)
Title: Network radio systems
IPC: H04B/
Filed: 1971-09-15
Abstract: 1502255 Relaying SIEMENS AG 15 Sept 1971 [30 Dec 1970] 43079/71 Heading H4L A network radio system employs a number of transmitter/receiver stations each constructed to compare a call sign contained in a received signal with its own call sign and, if non-coincidence is detected, to relay the received signal in modified form or, if coincidence is detected, to effect the connection back to the original calling station via any relay stations used in the search procedure. The stations, which operate on the frequencyhopping technique, each have the basic form illustrated in Fig. 2. An antenna 31, which may be omni-directional or a combination of several differently-oriented directional antennae, is selectively connected via a switch 21 to a receiver 22 or transmitter 23. Output from receiver 22 is recorded in a store 24 and from here can be fed to the transmitter 23. A PBX telephone exchange with separate lines and a distribution cabinet can be connected at respective terminals 29, 30. In this case, and where the station is to act purely as a relay, an intermediate store 32 can be provided to record the receiver output and supply the transmitter input with a modulating signal. In operation (Fig. 3). in which each station has the basic construction described, station 317 wishes to communicate with station 331. Each station in the network has its characteristic frequencyhopping sequence, while a further sequence is reserved as a common channel to establish connections between stations, and other purposes. The origin station 317 transmits a call signal which embodies a starting pulse, representing a time datum, and two marker pulses (Fig. 4, not shown). One of the latter identifies the origin station as station 317, while the other identifies the destination station as station 331. Stations not transmitting at this time are switched to receive and effect the frequency-hopping sequence of the common channel. Thus, for instance, two such stations 311, 322 receive the call signal from station 317 and record it. During the next hopping interval, each of these stations 311, 322 relays the signal in modified form. The modification involves substitution of the origin station marker 317 by the relay station marker 311, 322 respectively. The destination station marker 331 and starting pulse remain unaltered. The signals transmitted from stations 311, 322 are, for instance, received by stations 328 and 331. The former, not recognizing the marker 331, relays the signal, as already described for stations 311, 322, to a further station 328 and so on. However, station 331 recognizes that it is the destination station. It receives, almost simultaneously, the two signals from stations 311, 322 which differ only by their respective markers. Based on some suitable criterion (alternative criteria are described), station 331 selects one of the two stations 311, 322 to use in developing the link to the origin station 317. Station 331 then transmits a signal which causes other stations (such as 323) to cease relay operations; subsequently, station 331 sets itself to its own frequency-hopping sequence, and via any station(s)-in this example, the selected one of stations 311, 322-which was used in the search procedure, becomes synchronized with station 317 (which sets itself to the frequency-hopping sequence of station 322) and message reception commences. Each time the speech button at one or other end station 317, 331 is released, the link is reset for transmission in the reverse direction, via the relay station(s). Enciphering may be used. The link can be broken if one station sends a disconnect signal which renders the transmitter of the destination station inoperative and switches its receiver to the service channel.