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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

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 (AlS). 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.

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..

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..

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 (AlS). 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.

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..

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 (AlS). 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.

Circular statistics has found substantial application in science and engineering. One of the fundamental problems in circular statistics is that of estimating the mean direction of a circular random variable from a number of observations. The standard approach in the literature is called the sample circular mean and its asymptotic properties are well known. It can also be computed efficiently in a number of arithmetic operations that is linear in the number of observations. In this paper we consider an alternative estimator called the sample intrinsic mean that is based on minimizing squared arc length. We show how this estimator can be computed efficiently in a linear number of operations using an algorithm from algebraic number theory and we derive its asymptotic properties. In some scenarios the sample circular mean and the sample intrinsic mean are estimators of the same quantity and can therefore be compared. We show both theoretically and by simulation that in some of these scenarios the sample intrinsic mean is statistically more accurate than the sample circular mean. As such the results in this paper potentially have implications for the wide variety of fields in science, engineering and statistics that currently use the sample circular mean. Refereed/Peer-reviewed

The Coxeter lattices, which we denote $A_{n/m}$, are a family of lattices containing many of the important lattices in low dimensions. This includes $A_n$, $E_7$, $E_8$ and their duals $A_n^*$, $E_7^*$ and $E_8^*$. We consider the problem of finding a nearest point in a Coxeter lattice. We describe two new algorithms, one with worst case arithmetic complexity $O(n\log{n})$ and the other with worst case complexity O(n) where $n$ is the dimension of the lattice. We show that for the particular lattices $A_n$ and $A_n^*$ the algorithms reduce to simple nearest point algorithms that already exist in the literature., Comment: submitted to IEEE Transactions on Information Theory

Polynomial-phase signals have numerous applications including radar, sonar, geophysics, and radio communication. Many techniques for estimating the parameters of polynomial-phase signals have been described in the literature. Despite the significant interest, aliasing of polynomial-phase parameters has not been fully clarified. We address the problem of identifiability and aliasing in polynomial-phase signals. We fully describe the region in which aliasing does not occur for polynomial-phase signals of any order. We call this the identifiable region. We find that this region is the Voronoi region of a lattice generated by the coefficients of a set of polynomials known as the integer-valued polynomials. We show how aliasing can be resolved by solving the nearest lattice point problem. We discuss some of the consequences of these results on a popular estimator for polynomial-phase signals that is based on the discrete polynomial phase transform (DPPT). It is shown that the range of parameters suitable for the DPPT estimator is very small compared to the identifiable region.

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 (AlS). 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.

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.

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..

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.

We examine the problem of estimating the periods of interleaved periodic point processes. We are particularly interested in the case where times of arrival (TOAs) are either measured with noise or not measured at all. This can arise in communications surveillance, where communications signals of different bauds may lie within the same surveillance bandwidth, and likewise in Electronic Surveillance (ES), where pulses or scans from different radars are observed together. In [1], the authors developed a general asymptotic theory for the Bartlett point-process periodogram estimator of the period of a single periodic process. In this paper, we extend the model to multiple periodic processes, each with a distinct period. The TOAs are observed unlabelled and in time order, i.e., they are interleaved. The largest local maximizers of the periodogram are shown to be good estimators of the unknown periods, asymptotically, and central limit theorems are proved. Simulations highlight a number of practical problems, and some problems with outstanding solutions are suggested.

The Institute for Telecommunications Research (ITR) at the University of South Australia has led a consortium to design a Global Sensor Network (GSN) system for remote sensor data gathering and communication using low earth orbit (LEO) micro satellites, with Canadian-based COM DEV acting as Mission Prime. The program has covered a broad range of activities, including mission design, communication system design, advanced waveform and receiver design, demonstration system implementation and field trials. The research and development was supported by the Australian federal government's Australian Space Research Program.

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.

The Institute for Telecommunications Research has led a consortium to design a Global Sensor Network (GSN) system for remote sensor data gathering and communication using small low earth orbit satellites. The program has covered a broad range of activities, including mission design,communication system design, advanced waveform and receiver design, demonstration system implementation and field trials. The research and development was supported by the Australian federal government's Australian Space Research Program.The GSN provides a low cost mechanism to gather data from remote land based and marine sensors, delivering information to end users. The system also allows users to control and upgrade remotely deployed devices.This paper describes technologies developed that enable the GSN to provide multiuser communications with high spectral efficiency. It also presents results from aircraft and satellite field trials that demonstrate support for heavily loaded multiuser scenarios.

We consider least squares estimators of carrier phase and amplitude from a noisy communications signal. We focus on signaling constellations that have symbols evenly distributed on the complex unit circle, i.e., M-ary phase shift keying. We show, under reasonably mild conditions on the distribution of the noise, that the least squares estimator of carrier phase is strongly consistent and asymptotically normally distributed. However, the amplitude estimator is not consistent, but converges to a positive real number that is a function of the true carrier amplitude, the noise distribution and the size of the constellation. The results of Monte Carlo simulations are provided and these corroborate the theoretical results. Refereed/Peer-reviewed

The problem discussed in this paper is that of estimating the period of a sequence of periodic events when the measurements of the occurrence times are noisy and sparse. The problem is common to many signal processing applications, such as baud estimation from zero-crossings in telecommunications and in pulse repetition interval estimation in electronic support measures. Previous algorithms have been based on periodogram maximisation [1, 2], Euclidean algorithms [3-5], least-squares line search [6], lattice line search [7] and Gaussian maximum likelihood [8]. Until now, very little has been known about the asymptotic statistical properties of any such algorithm. In this paper, a new algorithm is proposed, based on a modified least-squares approach. Under very general properties, the estimators of the system parameters are shown to have excellent (theoretical) asymptotic statistical properties. These properties are illustrated using a number of simulations. Refereed/Peer-reviewed

We show that for those lattices of Voronoi's first kind with known obtuse superbasis, a vector of shortest nonzero Euclidean length can computed in polynomial time by computing a minimum cut in a graph. Refereed/Peer-reviewed

This paper focuses on the problem of code acquisition in multiuser CDMA systems in a near-far scenario. A new time offset estimator which iteratively cancels interference from correctly acquired users is proposed. Interference cancellation is accomplished by projecting the received signal into the null space of already acquired users. The proposed technique performs well under low SNR conditions in the presence of high multiple access interference. Analytical expressions for the missed detection probability of the proposed estimator are derived and these agree with the results of Monte-Carlo simulations. Refereed/Peer-reviewed

Estimating the coefficients of a noisy polynomial phase signal is important in many fields including radar, biology and radio communications. One approach to estimation attempts to perform polynomial regression on the phase of the signal. This is complicated by the fact that the phase is wrapped modulo 2π and therefore must be unwrapped before the regression can be performed. A recent approach suggested by the authors is to perform the unwrapping in a least squares manner. It was shown by Monte Carlo simulation that this produces a remarkably accurate estimator. In this paper we describe the asymptotic properties of this estimator, showing that it is strongly consistent and deriving its central limit theorem. We hypothesise that the estimator produces very near maximum likelihood performance. Refereed/Peer-reviewed

We consider block noncoherent detection of hexagonal quadrature amplitude modulation (QAM). We focus on hexagonal constellations generated from a Voronoi code. We find that these constellations are particularly well suited to noncoherent detection because they avoid most of the identifiability problems that occur with more traditional constellations. We describe a fast, approximate, noncoherent detection algorithm with statistical performance that is almost indistinguishable from an optimal, brute force approach, but with significantly smaller computational requirements. The performance is close to that of coherent detection when the block length is sufficiently large. Refereed/Peer-reviewed

Single frequency estimation is a long-studied problem with application domains including radar, sonar, telecommunications, astronomy and medicine. One method of estimation, called phase unwrapping, attempts to estimate the frequency by performing linear regression on the phase of the received signal. This procedure is complicated by the fact that the received phase is ‘wrapped’ modulo ???? and therefore must be ‘unwrapped’ before the regression can be performed. In this paper, we propose an estimator that performs phase unwrapping in the least squares sense. The estimator is shown to be strongly consistent and its asymptotic distribution is derived.We then show that the problem of computing the least squares phase unwrapping is related to a problem in algorithmic number theory known as the nearest lattice point problem. We derive a polynomial time algorithm that computes the least squares estimator. The results of various simulations are described for different values of sample size and SNR.

The lattice $A_n^*$ is an important lattice because of its covering properties in low dimensions. Clarkson \cite{Clarkson1999:Anstar} described an algorithm to compute the nearest lattice point in $A_n^*$ that requires $O(n\log{n})$ arithmetic operations. In this paper, we describe a new algorithm. While the complexity is still $O(n\log{n})$, it is significantly simpler to describe and verify. In practice, we find that the new algorithm also runs faster., Comment: 3 pages

It has been well known for at least twenty years[1] that computing the maximizer of the periodogram, in orderto estimate the unknown frequency in a noisy sinusoid, isproblematic. In particular, because the periodogram is highlynonlinear, a grid size of order o T−1 is needed to find themaximizer reliably, where T is the sample size, and that Newton'smethod may fail to find the zero of the first derivative ofthe periodogram closest to the maximizer of the periodogramcalculated, for example, using the FFT. In this paper, we showthat Newton's method does, in fact, work if it is applied to anappropriately chosen monotonic function of the periodogram.

The problem of estimating the period of a periodic point processis considered when the observations are sparse and noisy.There is a class of estimators that operate by maximizing anobjective function over an interval of possible periods, notablythe periodogram estimator of Fogel & Gavish [1] andthe line-search algorithms of Sidiropoulos et al. [2] and Clarkson[3]. For numerical calculation, the interval is sampled.However, it is not known how fine the sampling must be in orderto ensure statistically accurate results. In this paper, a newestimator is proposed which eliminates the need for sampling.For the proposed statistical model, it calculates a maximumlikelihoodestimate. It is shown that the expected arithmeticcomplexity of the algorithm is O(n3 logn) where n is the numberof observations. Numerical simulations demonstrate thesuperior statistical performance of the new estimator.

The lattice An* is an important lattice because of its covering properties in low dimensions. Two algorithms exist in the literature that compute the nearest point in the lattice AAn* in O(n log n) arithmetic operations. In this paper we describe a new algorithm that requires only O(n) operations. The new algorithm makes use of an approximate sorting procedure called a bucket sort. This is the fastest known nearest point algorithm for this lattice.

Ryan et al. [1] recently described two polynomial time algorithms for noncoherent detection of square QAM in block fading channels with additive white Gaussian noise (AWGN). The first algorithm is optimal with respect to the generalized likelihood ratio test (GLRT) and requires O(T 3) arithmetic computations, where T is the block length of the noncoherent receiver. The second algorithm requires only O(T 2 log T ) arithmetic computations but is statistically suboptimal. This paper derives a new algorithm that is optimal yet requires only O(T 2 log T ) arithmetic computations. The new algorithm has the geometric interpretation of finding the nearest codeword to a plane (2 dimensional subspace). The nearest codeword is found by testing codewords that are near a finite number of lines formed by the intersection of the plane and the nearest neighbour boundaries of the codewords.