Abstract: A multiuser communication system comprises multiple transmitters and a multiuser receiver that detects multiple transmissions via iterative soft interference cancellation. An initial acquisition module and single user decoder module are also described. The multiuser receiver acquires and subtracts known users in the residual signal before acquiring new users in the residual signal, which is performed iteratively until no new users are detected or a stopping criterion is met. To aid receiver acquisition, the transmitters insert discrete tones into the transmitted signals. These allow the multiuser receiver to obtain initial estimates of the frequency, time, gain, and/or phase offset for each user. To improve the quality of cancellation the receiver refines estimates of gain, time, frequency and phase offsets for each user after each iteration, and calculates time varying SINR estimates for each user. The multiuser receiver may be satellite based, may be a distributed receiver, or process users in parallel.

Abstract: A method of scheduling wake up times for terminals in a satellite communication system using satellite ephemeris data in order to extend battery life of terminals is described. The terminal periodically evaluates the stored ephemeris data to determine whether it is valid, recently valid, or invalid. When the ephemeris data is valid the terminal can schedule wake up times to either transmit or receive updated ephemeris data. For recently valid ephemeris data the terminal calculates BB possible satellite pass windows and schedules wake up time. For invalid data the terminal wakes and listens periodically with a period that is less than the expected satellite pass duration. It may repeat this process several times before sleeping for an amount of time less than the expected satellite pass duration and repeating. Additional gateway beacons may be used to provide ephemeris data, and satellites may also provide information on beacon locations.

Abstract: A communication system is disclosed. In an embodiment, the communication system includes a user node for receiving data from a remote application program, the data including message data for communication to a central application program operatively associated with the remote application program; plurality of geographically distributed gateway nodes; one or more access nodes for receiving the message data from the user node via a first communications interface, and communicating the message data via a second communications interface to one or more of the plurality of geographically distributed gateway nodes; and a hub for communicating with the one or more of the plurality of geographically distributed gateway nodes to receive the message data for communication to the central application.

Abstract: A communication system is disclosed. In an embodiment, the communication system includes a user node for receiving data from a remote application program, the data including message data for communication to a central application program operatively associated with the remote application program; plurality of geographically distributed gateway nodes; one or more access nodes for receiving the message data from the user node via a first communications interface, and communicating the message data via a second communications interface to one or more of the plurality of geographically distributed gateway nodes; and a hub for communicating with the one or more of the plurality of geographically distributed gateway nodes to receive the message data for communication to the central application.

Abstract: Methods and apparatus for communication between terminals and an access node in a multiuser multicarrier communications network are described. The access node may be a satellite access node. Terminals are configured to perform initial estimation and tracking of channel offsets and to estimate channel offsets for future packets to be transmitted by the terminal. In some embodiments the channel offsets comprise mobility related channel offsets due to the relative movement between the access node and the plurality of terminals. Transmissions from the terminals to the access node are pre-compensated for the channel offsets, so that the aggregate signal received by the access node occupies a bandwidth greater or equal to the maximum signal bandwidth of any individual terminal. Terminal transmissions may overlap in frequency and time on the ground, but arrive orthogonally at the access node.

Abstract: Methods and systems are described which provide solutions for determining how to allocate terminals to slots in order to maximize communication system performance in the case where there is no feedback channel between a multiuser satellite receiver and terminals within the field of view. Terminals operate independently of each other and choose transmission slots based upon the geographic position of the terminal. Terminals can be programmed with a slot selector to choose slots according to some deterministic or non deterministic function of the current position. A slot plan database may be used to assist in efficient slot selection. Regular and irregular grid based allocation methods are described, that reduce the likelihood that too many terminals transmit using the same slot within the field of view.

Abstract: A multiple access slotted wireless communication system comprising a plurality of terminals and a multi-access receiver is described. The multi-access receiver can decode multiple transmissions in each slot of a frame from terminals in its field of view. Each terminal has an active state for transmitting and an inactive state. After receiving acknowledgement of a successful transmission by the terminal, the terminal enters the inactive state for at least a transmission delay time. This may be the remaining time that the terminal is in the field of view of the multi-access receiver. This may be achieved by the terminal using a probability of transmission to determine whether or not to transmit in the next frame. The terminal may also be configured to select the slot in a frame, and this may be based upon information such as which slots were acknowledged. The receiver may use compression to transmit acknowledgement messages.

Abstract: A multiple access slotted wireless communication system comprising a plurality of terminals and a multi-access receiver is described. The multi-access receiver can decode multiple transmissions in each slot of a frame from terminals in its field of view. Each terminal has an active state for transmitting and an inactive state. After receiving acknowledgement of a successful transmission by the terminal, the terminal enters the inactive state for at least a transmission delay time. This may be the remaining time that the terminal is in the field of view of the multi-access receiver. This may be achieved by the terminal using a probability of transmission to determine whether or not to transmit in the next frame. The terminal may also be configured to select the slot in a frame, and this may be based upon information such as which slots were acknowledged. The receiver may use compression to transmit acknowledgement messages.

Abstract: Methods and apparatus for use in communication systems using recursive modulation schemes with a Low Density Generator Matrix code (including an irregular repeat accumulate (IRA) code) are described that have reduced complexity and thus reduced cost compared to prior art systems. A communication system is described in which the transmitter concatenates a low density generator matrix code with an accumulator followed by a recursive modulator in order to eliminate the use of an interleaver, and in which the receiver combines the decoder for the accumulator and the soft demodulator into a single joint decoder in order reduce the number of components and complexity. Another variation is also described in which the transmitter is further simplified by eliminated the accumulator altogether, and in which the receiver is further simplified by replacing the joint decoder with a soft demodulator prior to the LDGM soft decoder.

Abstract: The invention relates to method and apparatus for improving the performance of communication systems using Run Length Limited (RLL) messages such as the existing Automatic Identification System (AIS). A binary data sequence is Forward Error Correction (FEC) coded and then the sequence is compensated, for example by bit-erasure, so that either bit-stuffing is not required, or a bit stuffer will not be activated to ensure that the coded sequence meets the RLL requirement. Various embodiments are described to handle different architectures or input points for the FEC encoder and bit erasure module. The bit erasure module may also add dummy bits to ensure a RLL compliant CRC or to selectively add bits to a reserve buffer to compensate for later bit stuffing in a header. Additional RLL training sequences may also be added to assist in, receiver acquisition.

Abstract: A multiuser communication system comprises multiple transmitters and a multiuser receiver that detects multiple transmissions via iterative soft interference cancellation. An initial acquisition module and single user decoder module are also described. The multiuser receiver acquires and subtracts known users in the residual signal before acquiring new users in the residual signal, which is performed iteratively until no new users are detected or a stopping criterion is met. To aid receiver acquisition, the transmitters insert discrete tones into the transmitted signals. These allow the multiuser receiver to obtain initial estimates of the frequency, time, gain, and/or phase offset for each user. To improve the quality of cancellation the receiver refines estimates of gain, time, frequency and phase offsets for each user after each iteration, and calculates time varying SINR estimates for each user. The multiuser receiver may be satellite based, may be a distributed receiver, or process users in parallel.

Abstract: Methods and apparatus are described for improving receiver performance in a multicarrier communication network in which an encoded symbol is transmitted over a transmission channel in the communications system. A model of the transmission channel is estimated, said model characterising an effect of intercarrier interference on at least one carrier in the multicarrier system. The received symbol is decoded using the estimated model to remove a predicted effect of intercarrier interference. A pre-processor is also described for operation in conjunction with a communications receiver in the network. The pre-processor includes a channel estimator operable to estimate at least one feature of the communication channel based on a received signal. The pre-processor modifies the received signal dependent on the at least one estimated feature and provides the modified signal to the communications receiver.

Abstract: Methods and apparatus for use in communication systems using recursive modulation schemes with a Low Density Generator Matrix code (including an irregular repeat accumulate (IRA) code) are described that have reduced complexity and thus reduced cost compared to prior art systems. A communication system is described in which the transmitter concatenates a low density generator matrix code with an accumulator followed by a recursive modulator in order to eliminate the use of an interleaver, and in which the receiver combines the decoder for the accumulator and the soft demodulator into a single joint decoder in order reduce the number of components and complexity. Another variation is also described in which the transmitter is further simplified by eliminated the accumulator altogether, and in which the receiver is further simplified by replacing the joint decoder with a soft demodulator prior to the LDGM soft decoder.

Abstract: A communication system is disclosed. In an embodiment, the communication system includes a user node for receiving data from a remote application program, the data including message data for communication to a central application program operatively associated with the remote application program; plurality of geographically distributed gateway nodes; one or more access nodes for receiving the message data from the user node via a first communications interface, and communicating the message data via a second communications interface to one or more of the plurality of geographically distributed gateway nodes; and a hub for communicating with the one or more of the plurality of geographically distributed gateway nodes to receive the message data for communication to the central application.

Abstract: Methods and systems are described which provide solutions for determining how to allocate terminals to slots in order to maximise communication system performance in the case where there is no feedback channel between a multiuser satellite receiver and terminals within the field of view. Terminals operate independently of each other and choose transmission slots based upon the geographic position of the terminal. Terminals can be programmed with a slot selector to choose slots according to some deterministic or non deterministic function of the current position. A slot plan database may be used to assist in efficient slot selection. Regular and irregular grid based allocation methods are described, that reduce the likelihood that too many terminals transmit using the same slot within the field of view.

Abstract: A multiple access slotted wireless communication system comprising a plurality of terminals and a multi-access receiver is described. The multi-access receiver can decode multiple transmissions in each slot of a frame from terminals in its field of view. Each terminal has an active state for transmitting and an inactive state. After receiving acknowledgement of a successful transmission by the terminal, the terminal enters the inactive state for at least a transmission delay time. This may be the remaining time that the terminal is in the field of view of the multi-access receiver. This may be achieved by the terminal using a probability of transmission to determine whether or not to transmit in the next frame. The terminal may also be configured to select the slot in a frame, and this may be based upon information such as which slots were acknowledged. The receiver may use compression to transmit acknowledgement messages.

Abstract: Described herein is a method and system for estimating a time-varying multipath communication channel. The system comprises a receiver for receiving a signal comprising a data packet transmitted over the multipath communication channel. The system also comprises a frequency-domain channel estimator that generates a frequency-domain channel estimate based on the received signal. The system further comprises a time-domain channel modeller that receives the frequency-domain channel estimate and generates an estimate of parameters in a time-domain model of the multipath communication channel. The model characterizes the multipath communication channel as a delay line with a plurality of taps, each tap having tap parameters defining a delay, a Doppler and a gain for the tap. The tap parameters are constant over the data packet.

Abstract: Methods and apparatus are described for processing data in a wireless communication network. Iterative estimation techniques are used to enable tracking of time-varying communication channels. A signal is transmitted over a channel in the network, the signal comprising a sequence of symbols carried on a plurality of sub-carriers. Boot-up estimator estimates, in a time domain, parameters of a model of the channel based on the received signal. A domain converter transforms at least one of the estimated parameters from the time domain to provide at least one transformed parameter in a second domain. An equalizer and decoder determine estimates of symbols from the received signal using the at least one transformed parameter, and tracking estimator updates the estimated model parameters during reception of the signal using at least one estimated symbol.

Abstract: Methods and apparatus are described for improving receiver performance in a multicarrier communication network in which an encoded symbol is transmitted over a transmission channel in the communications system. A model of the transmission channel is estimated, said model characterising an effect of intercarrier interference on at least one carrier in the multicarrier system. The received symbol is decoded using the estimated model to remove a predicted effect of intercarrier interference. A pre-processor is also described for operation in conjunction with a communications receiver in the network. The pre-processor includes a channel estimator operable to estimate at least one feature of the communication channel based on a received signal. The pre-processor modifies the received signal dependent on the at least one estimated feature and provides the modified signal to the communications receiver.

Abstract: A method and system are described for estimating an environment surrounding a wireless communication system, the environment including at least one inflector that inflects transmitted signals. An observation generator receives an input signal transmitted from a transmitter to a receiver via a wireless communication channel and also receives system state information pertaining to at least one of the receiver, the transmitter and the inflector. An observation processor uses observations from the observation generator to estimate at least one property of the inflector based on the received input signal and the system state information.