Abstract: The present invention relates to a point-to-multipoint or broadcast TDMA or FDMA satellite arrangement wherein each up-link message unit is intended for reception at one or more geographically dispersed remote receiving sites within a wide service area. In one arrangement of a TDMA or FDMA satellite, the up-link message units are received and each message unit is directed to a transponder and to one or more down-link antenna ports for concurrent transmission to each of the destinations receiving sites for such message. An alternative TDMA satellite arrangement provides for each up-link message unit to be temporarily stored during the receiving frame period and then transmitted in accordance with a predetermined frame format during the appropriate time segments of the subsequent frame period to all of the destinational receiving sites. A technique for providing such predetermined frame format is also disclosed.

Abstract: The present invention relates to a satellite communication system comprising a plurality of limited scan spot beams which permits high transponder utilization efficiency by virtue of pooling the resources of each terrestrial footprint. In an embodiment of the invention, a satellite comprises a plurality of transponders, the signals from each transponder being directed via one or more associated scanning beams over a separate limited scanning beam region on the surface of a celestial body. In a preferred arrangement, each of the plurality of scanning spot beams is scanned linearly and parallel to the other scanning spot beams in a manner wherein each of the scanning beams covers a separate one of adjacent bands dividing the overall service region on the celestial body. By proper orientation of each of the scan regions or bands, nearly equal volumes of traffic can be served by each transponder.

Abstract: The present invention relates to a technique for increasing the rain margin at ground stations of a satellite communication system. In the present technique, spare TDMA time slots in each frame sequence are shared among all ground stations as required by stations experiencing a fade condition which exceed a predetermined power margin. Additional up-link power margin at a faded transmitter can be achieved by either increasing power transmission of a normal burst or by the use of spare time slots plus encoding and preamble field extension techniques for burst extension. Additional down-link power margin to a faded receiver is accomplished by either increased transmitter power transmission or by the use of burst extension and coding and field extension techniques. Apparatus for implementing framing, carrier and clock recovery and start of message detection using extended fields and coding techniques for other data at a transmitter and receiver and disclosed to overcome fade conditions.

Abstract: The present invention relates to a technique for increasing the rain margin of a satellite communication system which includes a satellite capable of transmitting multiple concurrent beams comprising time slot bursts in a TDMA mode. The present technique creates a small pool of TDMA time slots which are dedicated or formed at some instant of time by the rearrangement of traffic to permit the power normally transmitted in any portion of the multiple concurrent beams to be applied to one beam in a multiple fixed beam or limited scanning beam system or any portion of the beams which are directed at one ground station in a multiple unlimited scanning beam system for accessing a ground station experiencing, for example, a fade condition.

Abstract: The present invention relates to a technique for creating dedicated in-band, two-way, signaling channels between a master signaling ground station and each remote ground station of a satellite communication system using either an area coverage beam or a plurality of fixed and/or scanning spot beams. In the present technique, separate bursts of information within a superframe sequence are dedicated for only providing signaling information between the master signaling station and each ground station of the system. Each ground station, in turn, is dedicated a separate burst of information for transmitting only signaling information back to the master signaling station. Coarse ranging is performed by triangulation methods and then each ground station transmits a unique word within the predetermined time period of its dedicated signaling burst to the master signaling station.

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: The present invention provides a processor for interfacing a TDMA burst modem (40), which transmits and receives bursts of information at high data rates in assigned time slots, and slow speed terminal processing equipment. The present processor comprises circuitry (50) capable of detecting frame or superframe markers in a received sequence and regenerating such markers, after initiation, at the normal interval for such markers despite false alarms or missed marker signals. Other circuitry (53, 57 and 52, 62) causes a memory (48, 56) to directly output a burst of information during an assigned time slot to the modem (40) and directly store received information from modem (40) during a predetermined interval which is designed to start before and end after the expected arrival of an assigned burst. Slower processing equipment is then used to find and process the burst in the stored information.

Abstract: The present invention relates to method and apparatus for substantially reducing the effects of interference at a receiver between concurrently received first and second digital signals which use the same frequency spectrum. Interference between signals is effectively reduced by transmitting the first digital signal in an uncoded form while concurrently transmitting the second digital signal with both reduced capacity when compared with the first signal and in coded form using a forward error correcting code such as, for example, a block or convolutional code. At the receiver intercepting both digital signals, a suitable detection process is performed to decode the second signal and separate both signals. The present invention is applicable to the simultaneous satellite transmission of an area coverage beam and a plurality of spot coverage beams or to increase capacity on a radio channel.

Abstract: The present invention relates to method and apparatus for communicating with one or more receiver stations disposed within a blackout region located in the vicinity of and surrounding each spot beam coverage area, the blackout region being caused by interference between concurrently transmitted and overlapping global coverage and spot coverage antenna radiated beams using the same frequency band despite the application of global beam interference suppression techniques at the spot beam receiving areas. Access to the receiver stations within each blackout region is provided by selectively turning off the associated interfering spot beam during a predetermined interval of time while ensuring that the power level of the radiated global coverage beam is not suppressed within the accessed blackout region to permit the global coverage beam to communicate with these receiver stations.

Abstract: The present invention relates to method and apparatus for substantially cancelling interference between signals using the same frequency spectrum which are received via overlapping area coverage and spot coverage antenna beams. At the transmitter where the overlapping area and spot coverage beams are concurrently transmitted, a predetermined portion of the area coverage signal is coupled into each of the spot beam signals which will be overlapped at the associated spot beam receiver area by the area coverage beam. The predetermined portion coupled into each spot beam signal will have a magnitude and phase to substantially cancel the area coverage signal at the associated spot beam receiver area.

Abstract: The present invention relates to two novel approaches for implementing an approximation of the Viterbi decoding algorithm using analog processing techniques which offer the potential for decoding at higher rates than currently achievable with digital processing decoders. The first approach employs at least one tapped delay means having a plurality of taps to enable the provision of the inverted and noninverted received analog channel waveform while path metric operations are performed by selectively switching between corresponding inverting and noninverting provisions of the at least one delay means according to the contents of a decision-directed digital memory. The second approach employs sample-and-hold circuits to store and update the path metrics based upon previous maximum-likelihood decisions.