Myriota Pty Ltd

University of South Australia

Robert George McKilliam

Alexander James Grant

David Victor Lawrie Haley

William George Cowley

Andre Pollok

Gottfried Lechner

Ingmar Rudiger Land

John Lawrence Buetefuer

Linda Mary Davis

Marc Pierre Denis Lavenant

Sorin Adrian Barbulescu

Ricky Rocco Luppino

Ho Leung Chan

Ying Chen

Andrew Beck

Andre Polok

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.

Multi-access communication system

A method for determining a terminal ID from a message received from a terminal in a communication system avoids sending the terminal ID in the clear. In this system each terminal ID has an associated encryption key. A transmitted message comprises at least a Message Authentication Code (MAC), a n-bit hash, and encrypted message text. At least the terminal key and a nonce is used to generate the MAC, and neither the terminal ID or the terminal key are included in the transmitted message. An authentication broker stores the set of all (terminal ID, terminal key) pairs for the plurality of terminals in the communication system. The set of all terminal keys is grouped into at least two partitions, and on receipt of a message the authentication broker identifies the partition that includes the terminal key of the terminal that transmitted the received message using the n-bit hash (the search partition). The authentication broker then searches the search partition for the terminal key that authenticates the MAC to identify the terminal ID. In some embodiments the nonce is not included in the message but is known or obtainable by the terminal and the authentication broker. A partitioning function generates the &#xab;-bit hash from at least the nonce and a terminal key. In some embodiments the nonce is included in the received message and a partitioning function generates the n-bit hash by using the nonce to select n bits from the terminal ID. In some embodiments the partitions are arranged into hierarchical groups such as tree, and each node has a partition key, and the n-bit has is formed as the ordered set of MACs for the partition keys on the path from the root node to the leaf node partition that includes the terminal key.

Terminal identity protection method in a communication system

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.

Enhanced automatic identification system

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.

Multiuser communications system

A method for estimating the position of a terminal in a satellite communication at either the ground station or in the satellite is described. The method uses estimates of the time delay, Doppler and/or Doppler Rate of signals transmitted from the terminal to the satellite together with an estimate of the satellite position. The method can be used with both synchronised terminals and unsynchronised terminals provided they have a stable time or frequency reference as well as with low earth orbit satellites both with and without on-board global position and timing references. Additionally the method can also use estimates of the time delay, Doppler or Doppler rate of beacon signals received by either the satellite or terminals. These beacon signals may include GPS L1 signals. In contrast to standard GPS receivers, the method does not require the terminal to store GPS ephemeris data or to operate continuously.

Position estimation in a low earth orbit satellite communications system

A method and system for generating extended satellite ephemeris data for a satellite for use by a terminal apparatus is described. Historical orbital parameter data (e.g. from historical TLEs) are used to build a predictor for future values of the orbital parameters. The orbital parameter prediction model is then stored on the terminal apparatus (or an existing model can be updated), and at a desired epoch the pre-stored orbital parameter predictor is used to produce estimates of the orbital parameters for the satellite for that epoch (ie synthetic or predicted TLEs). These predicted orbital parameters (predicted TLE) are then used as input to a standard orbit predictor to produce an estimate of the satellite's location, for example to determine satellite pass times. This method allows generation satellite ephemeris data which is valid out to a year or more as compared to the normal validity of ephemeris data of a few hours or days.

System and method for generating extended satellite ephemeris data

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.

Communication system and method

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.

Multicarrier communications system

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.

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. Satellite induced Doppler effects can be utilized be further increase slot re-use and to improve allocation of slots so that the receiver sees an approximately uniform distribution of frequencies over the frequency band to improve system throughput. The approaches described herein greatly reduce or eliminate the probability of failure at the receiver, which has numerous implementation advantages such as reduced cost, complexity, and power consumption.

Channel allocation in a communication system

A method for estimating a time offset of a transmitted signal which comprises pilot symbols and data symbols, the method comprising: receiving the transmitted signal to produce a received signal; and processing an optimizing function of the received signal at a finite number of possible time offsets to produce an estimator of the time offset.

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Adelaide, Australia

Robert George McKilliam