Abstract: A remote unit which transmits and receives messages within a fleet of remote units on a single communications channel shared by a plurality of remote unit fleets is disclosed. Access to the channel is regulated by a central control station which transmits control signals on the channel. To obtain service, a remote unit transmits a request synchronized by one of the control signals. Upon receiving a grant of service from the central control station, the remote unit may transmit a message to its fleet. At the conclusion of the message, an end-of-transmission condition is indicated by the remote unit.

Abstract: A mobile radio system uses a predetermined number of control channels over which a hand-shake routine is performed to determine called station availability, before one of a limited number of talk channels (local and repeater) is assigned for communication between a calling and the called station. After locating an idle talk channel (local channels are searched first), the control channel to which the called station is predeterminedly assigned is attempted to be accessed. Transmission times on the control channel are a function of the called station's identification code, thus creating a logical ring. Provision is made for message based priorities, emergency numbers and high priority for stations having experienced a previous unsuccessful attempt to access a control channel.

Abstract: In satellite communication systems it is often necessary to relay the signal between terminal stations and the satellite through ground relay stations remote from the terminal stations. Normally, in systems using composite multi-carrier signals for transmission through the satellite, the composite multi-carrier signals are reduced to baseband in the ground relay station prior to retransmission. To reduce the amount of equipment and the cost of such a ground relay station, a method and apparatus for relaying the composite multi-carrier signal through the ground relay station without reducing it to baseband in the ground relay station is provided. Thus, with this arrangement, the composite multi-carrier nature of the signal is preserved throughout the ground relay station.

Abstract: This method relates to the control of the information stream in a cell constituted by several radio channels (C.sub.1) and (C.sub.2), each connecting terminal stations (T.sub.1l to T.sub.1m) and (T.sub.2l to T.sub.2n) to a main station (1) of the cell. In order to assign the ascendent path of a radio channel to a terminal station, the main station transmits in this channel a code signal S.sub.o, whereupon the terminal stations transmit calls to be used in call time windows each with an associated priority level. The main station transmits, in answer time windows, code signals dependent upon the received signals: a code signal S.sub.3 if the received signal is a distinct call, to give a terminal station the authorization to use the ascendent path, or a sequence of code signals S.sub.1 or S.sub.2 if the received signal contains, simultaneously, several calls, or does not contain any call. Dependent upon each code signal S.sub.1 or S.sub.

Abstract: A communications system and network wherein communications links between subscribers are established by retrodirective oscillating loops between each subscriber and a node station. Provision is also made for establishment of retrodirective oscillating loops between nodes so that remotely located subscribers can communicate. Information is transmitted between subscribers by using a mixing process in the node whereby information transmitted from one subscriber to a node is transferred to a carrier signal transmitted between nodes or between a second node and another subscriber. A sampling technique is also described for use in the node which greatly minimizes the amount of apparatus required to implement the mixing process.

Abstract: A digital communications satellite (12,44) receives signals from a plurality of narrow input spot-beams (14) of an uplink. It regenerates, multiplexes and routes the signals for transmission in a plurality of narrow output spot-beams (42) of a downlink. The uplink beams (14) each include a plurality of frequency re-use channels (18), while the downlink beams (42) each have only a single wide-band channel. The satellite (12,44) may multiplex the signals either before or after routing them. The spot-beams (14,42) may be fixed or scanning.

Abstract: In a satellite which asynchronously receives radio frequency signals from a lurality of beacons scattered at the surface of the earth, each signal received has a pure carrier wave portion followed by a phase modulated message carrying portion. The frequencies of the signals are not known within a predetermined frequency band. The satellite has a plurality of essentially identical processing units which each receive on their input all the signals present at any given instant in the input frequency band. Each processing unit has a phase locked loop which may be progressively tuned to the frequency of one of these input signals in response to a frequency estimate of this signal to which the operating frequency of the phase locked loop is preset. This frequency estimate is updated until the phase lock occurs on this input signal, ready for demodulation of the message part to begin. The estimate frequencies are derived from an input band frequency spectrum analyzer.

Abstract: Frequency division communication system wherein conventional transmitter-transceiver can be used as or repeater or local base station. No additional transmitter and receiver are required to adapt transceiver to function as interchannel repeater.

Abstract: Simulcast distortion in a receiver when using a same-frequency repeater is minimized by applying double modulation to a signal that is broadcast to the same-frequency repeater. A voice signal is applied without delay as AM on a carrier to a modulation index of up to 30%, and the same signal is also applied as FM on the same carrier with a time delay equal to the time delay in the same-frequency repeater. The same-frequency repeater detects the AM and applies the detected signal as FM on a carrier that is rebroadcast. Received FM signals are thus delayed by substantially the same amount whether they are received from the original broadcast or the same-frequency repeater.

Abstract: Arrangement for establishing communication between a first mobile radio station and a second mobile radio station through a repeater over a radio frequency channel selected from a plurality of such channels. In an idle mode, a mobile station searches the channels for a predetermined group signal identifying it as belonging to a particular group of mobile stations. When that predetermined group signal is received on a channel, the mobile station is enabled on that channel so that it can communicate with a call originating mobile station belonging to the same group. In a call originate mode, a mobile station searches for an idle or unused channel identified by the absence of a busy signal. When an idle channel is found, the call originating station transmits a busy signal. The repeater, hearing the busy signal, transmits an acquisition signal.

Abstract: An arrangement for the cellular operation of a repeater trunking system. In a repeater trunking system including a plurality of mobile stations communicating over a predetermined number of communication channels, each associated with a repeater, an arrangement for inhibiting attempted communication on channels not in a selected cell even though the mobile stations are capable of operation on the channels of non-selected cells.

Abstract: A communications system and network wherein communications links between subscribers are established by retrodirective oscillating loops between each subscriber and a node station. Provision is also made for establishment of links between nodes so that remotely located subscribers can communicate. Information is transmitted between subscribers by using a mixing process in the node whereby information transmitted from one subscriber to the node is transferred at the node to a carrier signal transmitted between the node and another subscriber.

Abstract: A method and apparatus employing spread spectrum techniques in a wide bandwidth communications system is disclosed. A plurality of transmitting stations are each equipped to provide a transmission signal representing a pseudo-random coded, phase modulated, message signal. The transmission signal is directed through a bandwidth which encompasses otherwise dedicated, relatively narrow bandwidth repeater channels, employed in connection with a communications satellite, to a generally fixed receiver station. At the receiving station, the incoming signal is (a) code acquired and tracked, (b) carrier acquired and tracked, (c) phase locked to the receiver local oscillator and (d) coherently demodulated to extract the desired data.

Abstract: A technique is disclosed for sharing a fixed number of identical transponders among a same or greater number of input and output signaling directions by rapidly scanning each transponder over appropriately defined group pairs of the input and output directions. The apparatus comprises n transponders having input and output terminals which are selectively and separately scanned over a plurality of m input and output signaling directions, respectively, by scanning means under the control of a controller. The scanning means can comprise separate m .times. n input and output matrix switches or a separate selectively changeable phase shifter at each antenna element which is connected to a summing and dividing means at the input and output terminal, respectively, of the associated transponder. An efficient TDMA slot assignment technique is also disclosed which covers nonuniform traffic requirements.

Abstract: Frequency bands in spot beams received by a satellite transponder are selectively routed to transmitted spot beams. The total band width from each spot beam receiver is divided among a plurality of independently adjustable variable bandpass filters, and the outputs from the selected bandpass filters at each receiver are combined at the spot beam transmitters so that each downlink spectrum is made up of a frequency multiplex of selected bands from each uplink spot beam.

Abstract: In one illustrated embodiment involving a railway communication system, about ten send-receive stations form a transmission section operating at one pair of frequencies in the range above one gigahertz, the stations being arranged at about one kilometer intervals along the route for radio communication with mobile stations moving therealong. A next succeeding similar transmission section operates at a different pair of send and receive frequencies above one gigahertz. All of the stations of a given transmission section may be in communication with a main station by means of a parallel cable connection. A central station then may communicate with mobile stations via the respective main stations. In another embodiment, the stations are implemented as microwave relay stations linked to a main station by the same antenna system used for communication with the mobile stations.

Abstract: The present invention discloses an FM microwave radio frequency repeater using the straight-through system for relaying signals of a plurality of channels having different carrier frequencies, each of the channels including an auxiliary channel. The system according to the invention is characterized in that the auxiliary channel has the signals thereof demodulated through frequency discrimination of a difference frequency signal obtained by mixing together two received microwaves.