Abstract: A technique for enhancing the signal-to-noise performance of a digital communication link without affecting its power flux density. An information data stream has its original signaling rate selectively reduced prior to transmission, to enhance signal-to-noise performance. Then the reduced signaling rate information signal is combined with a pseudorandom data sequence at the original signaling rate, to provide a randomized data sequence to be transmitted at the original signaling rate, thereby maintaining power flux density levels below those permitted by regulatory limits.

Abstract: A technique for reducing power requirements in a communication transponder by converting signals in multiple uplink channels carried in frequency division multiplexed (FDM) form on multiple uplink beams, to a lesser number of downlink beams that operate in time division multiplexing (TDM) but at a bandwidth different from and preferably greater than the bandwidth of the uplink channels. Because the TDM downlinks can utilize amplifiers operating at or near peak power, whereas conventional FDM downlinks must operate with amplifiers backed off to minimize intermodulation products, use of the TDM downlinks effects significant power savings.

Abstract: A modulation channelization, demodulation and error-control system based on orthogonal bipolar spreading vectors is provided that permits a variable information rate to be transmitted without inducing envelope fluctuations and which permits multiple access without requiring the transmitter amplifier to support the combined information rate of all users. The modulation system uses the Hadamard matrix vectors to form communication channels. The information rate on any channel may be doubled by using half the vector length to transmit information. The vector that is not orthogonal-in-the-half to the rate-doubled vector is deactivated. Similarly, higher information rates may be provided through truncation of the transmission vector and the elimination of the resultant non-orthogonal vectors. The system provides biorthogonal coding in addition to multirate communication.

Abstract: A modulation channelization and demodulation system based on orthogonal bipolar spreading vectors is provided that permits a variable information rate to be transmitted without inducing envelope fluctuations and permits multiple access without requiring the transmitter amplifiers to support the combined information rate of all users. The modulation system uses the vectors of a Hadamard matrix to form communication channels. The information rate on any channel may be doubled by using half the vector length to transmit information. The vector that is not non-orthogonal-in-the-half to the rate-doubled vector is preferably deactivated. In the same fashion, higher information rates may be provided through truncation of the transmission vector and the elimination of the resultant non-orthogonal vectors. A multi-channel receiver including a Fast Hadamard Transform structure comprised of controllable modified logic cells for performing the multi-rate communication of the present invention is illustrated.

Abstract: A decoder of a data signal subjected to phase shifting keying (PSK) modulation uses a plurality of phase locked loops (801-1 to 801-n) having an inner decoder for short block codes, at least one of which is adapted to apply excess processing power to process a selected burst of the data signal, such as processing the burst with multiple initial phase/frequency error estimates. A selection circuit identifies the burst and supplies to said one of said plurality of phase-locked loops (801-1 to 801-n) for re-processing the bust with excess processing power. An outer Reed-Solomon block decoder (319) may be used to correct errors in the codewords from the phase locked loops and may be used in the selection of the burst by the selection circuit.

Abstract: A downlink beam frame signal processing system (100) for a communication satellite includes a packet switch (608) that routes self addressed uplink data to a memory (804). The memory (804) stores queues for at least a first and a second downlink beam hop locations (302, 304). The processing system (100) also includes a power amplifier (108) that amplifies a waveform formed using the uplink data. A power gating circuit (1200) coupled to the power amplifier (108) includes a power gate input (1216) responsive to a power gating signal to remove RF power from at least a portion of the waveform before transmission.

Abstract: A method and apparatus for scheduling, in real-time, the order in which data packets from multiple uplink channels are organized in a downlink channel of a satellite communications network. The satellite includes uplink and downlink channels for conveying data packets over channels between user terminals, ground stations and other user terminals. Queues in the satellite collect data packets from uplinks and output the data packets to the downlink using a bandwidth that is dynamically allocated. A scheduler allocates the bandwidth to at least one queue and continuously changes the amount of bandwidth allocated to each active queue while the queue is buffering data packets between the uplinks and downlink. The scheduler allocates bandwidth based upon a priority-class packet service schedule calculated based upon traffic parameters associated with each active queue.

Abstract: A frame signal (100) for communicating payloads (104, 110) of data includes a first payload field (104) and a first header field (102) with a first frame type indicator (120). The frame signal (100) also includes a second payload field (110) and a second header field (108) smaller than the first header field (102) that includes a second frame type indicator (128). The first payload field (104), first header field (102), second payload field (110), and the second header field (108) are encapsulated in a single frame (100) to provide multiple payload delivery with reduced overhead compared to individually transmitted single payload frames.

Abstract: A downlink frame processing system (200) includes a packet switch (608) routing self addressed uplink data (706) from an input port to an output port, a memory (804) coupled to the output port, and a downlink scheduler (802) coupled to the memory (804). The memory (804) includes storage for at least two downlink beam hop locations (302, 304). The downlink scheduler (802) processes from one of a plurality of segments at least one scheduling entry (1312) that includes, for example, a header field (1316) defining at least one of a payload and frame type (1404) for at least one of a payload and frame (1200) to be transmitted, and payload data pointers (1502, 1504, 1506) into the memory (804).

Abstract: A decision directed phase locked loop (DD-PLL) is efficiently implemented in a communication receiver. The phase locked loop includes an enhanced block decoder inside a phase detector which takes in the baseband complex samples and the current channel phase estimate (or the tracked phase) and generates a feedback phase error term. A loop filter filters the phase error terms and a phase accumulator updates the tracked phase estimate on each iteration of the loop.

Abstract: A power gating module (200) for a downlink beam frame signal (402) includes a power amplifier (210) for amplifying for transmission frame signals that include at least a first header signal (418), a first payload signal (420), a second header signal (424), and a second payload signal (426). The power gating module (200) further includes a power gating circuit (300) coupled to the power amplifier (210). The power gating circuit (300) includes a power gate input (318) and is responsive to a power gating signal to remove power from at least one of the first header signal (418) and first payload signal (420) in combination, and the second header signal (424) and second payload signal (426) in combination before amplification by the power amplifier (210).

Abstract: A data routing subsystem (200) for a communication satellite includes an inbound module (602) that accepts demodulated uplink data. The inbound module (602) includes a routing table (702) that stores queue tags (714) specifying downlink beam hop locations (302, 304) for the uplink data. The subsystem (200) also includes a self addressed packet switch (608) having an input port coupled to the inbound module (602), and an outbound module (610) coupled to an output port of the switch (608). A memory (804) in the outbound module (610) stores the uplink data in accordance with the downlink beam hop locations (302, 304). A multiple beam array antenna (116–122) is coupled to the outbound module (610). The multiple beam array antenna (116-122) includes a first feed element (116) assigned to a first downlink beam hop location (302) and a second feed element (118) assigned to a second downlink beam hop location (304).

Abstract: A side-fed dual reflector antenna system (10) of the present invention overcomes the size cost and complexity limitations associated with conventional single and multiple reflector antenna systems. The antenna system (10) includes a feed array (18) including separate feeds for generating separate respective antenna beams, a subreflector (20) for reflecting the separate respective antenna beams generated by the separate feeds of the feed array (18), and a reflector (22) having a shaped reflecting surface for reflecting the separate respective antenna beams received from the subreflector (20) toward a terrestrial target (16) to produce substantially contiguous flat beams, each of which provides substantially uniform coverage within a predetermined coverage area on the terrestrial target.

Abstract: The present invention provides a highly accurate synchronization method for a satellite communication system (100). The system maintains a downlink symbol counter at an earth terminal and determines a downlink symbol count representative of the time of arrival of a burst transmitted from the earth terminal to a satellite (106, 206). The earth terminal adjusts the downlink symbol counter to correspond to the downlink symbol count (136, 220) upon arrival of a predetermined reference point in a downlink frame. A timing error may initially be determined by launching an entry order wire from the earth terminal to the satellite (116). The timing error may be transmitted to the earth terminal using a correction code which indicates the transmission is early, late, absent, or no change is required (134, 218). The terminal may make additional periodic timing adjustments based on the length of the propagation path between the earth terminal and the satellite (108, 208).

Abstract: A side-fed dual reflector antenna system (10) of the present invention overcomes the size cost and complexity limitations associated with conventional single and multiple reflector antenna systems. The antenna system (10) includes a feed array (18) including separate feeds for generating separate respective antenna beams, a subreflector (20) for reflecting the separate respective antenna beams generated by the separate feeds of the feed array (18), and a reflector (22) having a shaped reflecting surface for reflecting the separate respective antenna beams received from the subreflector (20) toward a terrestrial target (16) to produce substantially contiguous flat beams, each of which provides substantially uniform coverage within a predetermined coverage area on the terrestrial target.

Abstract: A modulation channelization, demodulation and error-control system based on orthogonal bipolar spreading vectors is provided that permits a variable information rate to be transmitted without inducing envelope fluctuations and which permits multiple access without requiring the transmitter amplifier to support the combined information rate of all users. The modulation system uses the Hadamard matrix vectors to form communication channels. The information rate on any channel may be doubled by using half the vector length to transmit information. The vector that is not orthogonal-in-the-half to the rate-doubled vector is deactivated. Similarly, higher information rates may be provided through truncation of the transmission vector and the elimination of the resultant non-orthogonal vectors. The system provides biorthogonal coding in addition to multirate communication.

Abstract: Satellite communication systems are provided that employ highly inclined, highly elliptical orbits. The satellite communication systems have a satellite constellation phased to provide a ground trace with respect to the earth that is repeated by each of the satellites in the constellation such that the satellites appear to follow one another over similar paths over the earth. Due to the path of the ground trace provided, ground stations can employ a single axis tracking device since the satellites appear to move along similar overlapping paths in opposing directions relative to a user on the ground during communication control handoffs.

Abstract: A modulation channelization and demodulation system based on orthogonal bipolar spreading vectors is provided that permits a variable information rate to be transmitted without inducing envelope fluctuations and permits multiple access without requiring the transmitter amplifiers to support the combined information rate of all users. The modulation system uses the vectors of a Hadamard matrix to form communication channels. The information rate on any channel may be doubled by using half the vector length to transmit information. The vector that is not non-orthogonal-in-the-half to the rate-doubled vector is preferably deactivated. In the same fashion, higher information rates may be provided through truncation of the transmission vector and the elimination of the resultant non-orthogonal vectors. A multi-channel receiver including a Fast Hadamard Transform structure comprised of controllable modified logic cells for performing the multi-rate communication of the present invention is illustrated.

Abstract: The present invention provides a method for reducing power consumption in a satellite downlink transmitter (100). The method includes the steps of defining a frame structure for use on a downlink, and further defining a traffic body (218, 220, 222) and an overhead body (212, 214, 216) in the frame structure (202, 204, 206). The method further determines the amount of time required to transmit the traffic body (“the traffic transmit time”) and the amount of time required to transmit the overhead body (“the overhead transmit time”). Subsequently, the method activates a transmitter for the overhead transmit time to transmit the overhead body (212, 214, 216) including the synchronization information. Thus, a ground station may acquire synchronization and lock onto the downlink. The method then, however, selectively deactivates the transmitter for the traffic transmit time.

Abstract: A demodulator demodulates a modulated signal waveform in a data communication system. A phase tracking loop tracks the phase of said modulated signal waveform and having an inner block decoder configured to decode a set of vector pairs of the modulated signal waveform at a decode rate to generate associated codewords and phase estimates. A group of data symbols consisting of the first data symbols of the modulated signal waveform are run backwards through the phase tracking loop. An outer block decoder receives the associated codewords generated by said inner block decoder and utilizes and corrects only codewords associated with symbols after and including the group of data symbols consisting of the first data symbols of the modulated signal waveform.