Whitened Matched Filter Research Articles

Assessing detector performance, with application to Pareto coherent multilook radar detection

A necessary and sufficient condition is established, which can be used to compare the performance of two radar detection schemes. This means that the performance of detectors can be measured relative to a benchmark detector. In the context of coherent multilook detection in a Pareto clutter environment, the whitening matched filter (WMF) detector, which is optimal for Gaussian clutter, has been observed to perform very well as a suboptimal detector. Based upon this, variations of the WMF are constructed and analysed.

Validity of whitening-matched filter approximation to the Pareto coherent detector

It has been observed that the coherent multilook detector for targets embedded within Pareto intensity clutter can be approximated by the Gaussian optimal detector, or whitening-matched filter, in a number of real data sets. These correspond to clutter returns obtained from the Defence Science and Technology Organisation's Ingara radar, operating in X-band, at high grazing angles and in a circular spotlight mode. This study will establish conditions under which this can be explained mathematically. The key to this is to apply Stein's method from probability theory to establish rules of thumb to determine the validity of the approximation.

Sampling-balanced imaging system utilizing whitening matched filter

Imaging systems designed for point target detection and 3D reconstruction must be filtered in order to maximize signal-to-noise ratio and minimize position expectation error. An optimal whitening matched filter (WMF) is derived based on expected spatial target distribution and system colored noise. The expected noise is derived as a weighted combination of clutter aliasing, target aliasing, and detector noise. Further optimization of system performance is achieved by modification of the optical point spread function (PSF), so a sampling-balanced operation is achieved where all noise components are comparable. The improved performance of the optimized system is calculated and compared to the performance of other systems using other known linear postfilters with various optical PSF widths. It is shown that the WMF in a sampling-balanced system is a robust configuration that needs only minor modifications when scenario parameters are varied.

Cochannel interference mitigation using whitening receiver designs in bandlimited microcellular wireless systems

The problem of cochannel interference (CCI) suppression using a noise-plus-interference whitening matched filter (WMF) is addressed. Binary phase-shift keying modulated transmission over a Nakagami-m fading channel is considered in a bandlimited microcellular wireless system. It is shown that the signal-to-interference-plus-noise ratio (SINR) of the WMF can not exceed that of the conventional matched filter (CMF) receiver for synchronous CCI, but in the asynchronous channel, CCI whitening can be used to improve receiver performance. The SINR-maximizing filter (SINRMF) in an asynchronous channel is derived and shown to be composed of a WMF followed by a discrete time filter. The SINRs of the WMF and SINRMF receivers are analytically evaluated for a standard raised-cosine (RC) and a Beaulieu-Tan-Damen pulse. It is shown that for the RC pulse, the WMF can achieve a SINR gain as large as 1.76 dB over the CMF receiver provided that the transmission is free of intersymbol interference (ISI). The SINR of the ISI-impaired system is also evaluated and the conditions under which this system can achieve close to ISI-free SINR are studied. The SINR is evaluated for the SINRMF and it is shown that this filter can restore much of the SINR loss incurred due to ISI introduced by the WMF.

Asymptotic Equivalence Between the UML and the Extended SLN Symbol Timing Estimation on an Additive Colored Gaussian Noise Channel

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> It has recently been reported that the unconditional maximum likelihood (UML) symbol-timing estimation is asymptotically equivalent to the square-law nonlinearity (SLN) on an additive white Gaussian noise (AWGN) channel. By introducing a whitened matched filter (WMF), we propose an extended SLN and prove the asymptotical equivalence between the UML and the extended SLN on an additive colored Gaussian noise. Simulation results show the same behavior asymptotically when a mixture of an AWGN and a flicker noise is adopted as a noise source. </para>

Vector subspace detection in compound-Gaussian clutter. Part I: survey and new results

Deals with the problem of detecting subspace random signals against correlated non-Gaussian clutter exploiting different degrees of knowledge on target and clutter statistical characteristics. The clutter process is modeled by the compound-Gaussian distribution. In the first part of the paper, the optimum Neyman-Pearson (NP) detector, the generalized likelihood ratio test (GLRT), and a constant false-alarm rate (CFAR) detector are sequentially derived both for the Gaussian and the compound-Gaussian scenarios. Different interpretations of the various detectors are provided to highlight the relationships and the differences among them. In particular, we show how the GLRT detector may be recast into an estimator-correlator form and into another form, namely a generalized whitening-matched filter (GWMF), which is the GLRT detector against Gaussian disturbance, compared with a data-dependent threshold. In the second part of this paper, the proposed detectors are tested against both simulated data and measured high resolution sea clutter data to investigate the dependence of their performance on the various clutter and signal parameters.

Low-Complexity Iterative Receiver for Space-Time Coded Signals over Frequency Selective Channels

We propose a low-complexity turbo-detector scheme for frequency selective multiple-input multiple-output channels. The detection part of the receiver is based on a List-type MAP equalizer which is a state-reduction algorithm of the MAP algorithm using per-survivor technique. This alternative achieves a good tradeoff between performance and complexity provided a small amount of the channel is neglected. In order to induce the good performance of this equalizer, we propose to use a whitened matched filter (WMF) which leads to a white-noise "minimum phase" channel model. Simulation results show that the use of the WMF yields significant improvement, particularly over severe channels. Thanks to the iterative turbo processing (detection and decoding are iterated several times), the performance loss due to the use of the suboptimum List-type equalizer is recovered.

Clairvoyant and adaptive signal detection in non-Gaussian clutter: a data-dependent threshold interpretation

This paper addresses the problem of signal detection in correlated non-Gaussian clutter modeled as a spherically invariant random process. The optimum strategy to detect a constant signal, with either known or unknown complex amplitude, embedded in correlated Gaussian clutter is given by comparing the whitening-matched filter output with a fixed threshold. When the clutter is non-Gaussian, the performance of the matched filter sensibly degrades. The optimum strategy is the classical whitening-matched filter output compared with a data-dependent threshold. This interpretation provides a deeper insight into the structure of the optimum detector and allows us to single out a family of suboptimum detectors based on a polynomial approximation of the data-dependent threshold. They are easy to implement and have performance that is really close to the optimal. The adaptive implementation of the polynomial detectors is also investigated, and their performance is analyzed by means of Monte Carlo simulation for various clutter scenarios.

Optimal sequence estimation for convolutionally coded signals with binary digital modulation in ISI channels

Decoding convolutional codes with binary digital modulation in intersymbol interference (ISI) channels is studied. The receiver structure is a whitened matched filter (WMF) whose transfer function is determined by the ISI channel. Decoding of the output sequence can be performed in two steps or one step. The two-step decoding first decodes the ISI corrupted coded sequence back to the ISI free coded sequence which is then decoded back to the uncoded message sequence. For one-step decoding, the entire encoder-channel-receiver system is modeled as a new encoder with combined memory length of the memory lengths of the original encoder and the channel, and followed by a weighted summation mapping from the binary symbols to real number symbols. The weighting coefficients are determined by the channel characteristic. In both two-step and one-step decoding, the Viterbi algorithm (VA) is used to perform the maximum likelihood decoding. Decoding error probability and complexity of both methods are analyzed, simulated and compared.

Sequential decoding of convolutional codes in channels with intersymbol interference

Sequential sequence estimation for communications channels with convolutionally coded input sequences and intersymbol interference (ISI) is proposed. The receiver consists of a whitened matched filter (WMF) and a vector sequential decoder. The metric of the vector sequential algorithm (SA) is derived. Analytical results for error probability and computational complexity of the sequential decoder are presented. The error probability is found to be dominated by the minimum Euclidean distance between the possible output sequences and the computational distribution is Pareto, typical of a sequential decoder. The computational cut-off code rate R/sub comp/ and its lower bound R/sub comp/' are also derived. Numerical simulation results of the error probability and the computational complexity are presented. Comparing with the Viterbi algorithm (VA) reveals that the SA essentially has the same error performance as that of the VA while its average computational complexity is one to two orders of magnitude less than that of the VA.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Simplified parallel recision feedback equalisation for CCITT V.32/V.32 bis coded modems

A simplified parallel decsion feedback equaliser (SPDFE) with the 32/64/128 AMPM CCITT trellis code is considered. The SPDEF detector consists of a whitened matched filter (WMF) and a reduced parallel decision feedback equaliser incorporated in the Viterbi decoder. The bit error rate simulation results show substantial improvement over the conventional detector with a linear equaliser and a separate Viterbi algorithm (LE &amp; VA), although the implemation complexity remain the same.