An asymptotically optimum receiver designed for detecting coherent pulse trains in compound-Gaussian clutter is introduced and assessed. The proposed receiver assumes knowledge of the structure of the clutter covariance matrix, but does not require that of its amplitude probability density function (apdf). Performance is analytically evaluated, showing that the loss, as measured with respect to the corresponding optimum structure, is kept within a few dBs even for a relatively small number of integrated pulses and that it largely outperforms the matched-filter detector under all instances of practical interest. Interestingly, the proposed detector achieves constant false alarm rate (CFAR), regardless of the clutter envelope distribution and, consequently, its power. >

http://lops.perso.enseeiht.fr/papers/Conte_IEEE_TAES_1995.pdf

Asymptotically optimum radar detection in compound-Gaussian clutter

Complex elliptically symmetric (CES) distributions have been widely used in various engineering applications for which non-Gaussian models are needed. In this overview, circular CES distributions are surveyed, some new results are derived and their applications e.g., in radar and array signal processing are discussed and illustrated with theoretical examples, simulations and analysis of real radar data. The maximum likelihood (ML) estimator of the scatter matrix parameter is derived and general conditions for its existence and uniqueness, and for convergence of the iterative fixed point algorithm are established. Specific ML-estimators for several CES distributions that are widely used in the signal processing literature are discussed in depth, including the complex t -distribution, K-distribution, the generalized Gaussian distribution and the closely related angular central Gaussian distribution. A generalization of ML-estimators, the M-estimators of the scatter matrix, are also discussed and asymptotic analysis is provided. Applications of CES distributions and the adaptive signal processors based on ML- and M-estimators of the scatter matrix are illustrated in radar detection problems and in array signal processing applications for Direction-of-Arrival (DOA) estimation and beamforming. Furthermore, experimental validation of the usefulness of CES distributions for modelling real radar data is given.

Complex Elliptically Symmetric Distributions: Survey, New Results and Applications

A novel class of probability distributions resulting from a compound Poisson process is found to correlate well with amplitude distributions of radar clutter returns spatially sampled from composite terrain. This class of distributions, derived from assumptions of random scattering phase and Poisson spatial distribution of elementary scattering sources, is specified by several physical and statistical parameters in its complete generality. These parameters are: 1) the number of scatterer types; 2) the average radar scattering cross section and the cross-sectional distribution of each different scatterer type; 3) the occurrence probability or the average scatterer size and spatial density; 4) the radar resolution area; and 5) the average background radiation as well as the radar internal noise power. Excellent fits of the theoretical clutter distributions to the measurement data are obtained by assuming a Rayleigh amplitude distribution for the elementary scatterer return for high grazing angle cases and a more general K -distribution for low grazing angle cases.

Amplitude distribution of composite terrain radar clutter and the &#954;-Distribution

A relatively narrow beam of either RF or optical electromagnetic radiation is scanned over a relatively wide azimuthal range. The return signal is processed to detect the range and velocity of each point of reflection. Individual targets are identified by clustering analysis (102) and are tracked (106) in a Cartesian coordinate system using a Kalman filter. The threat to the vehicle for a given target is assessed (116) from estimates of the relative distance, velocity, and size of each target, and one or more vehicular devices are controlled (120) responsive to the assessment of threat so as to enhance the safety of the vehicle occupant. In a preferred embodiment, a quantized linear frequency modulated continuous wave RF signal is transmitted from and received by a multi-beam antenna having an azimuthal range of at least +/- 100 degrees and an individual beam width of approximately 10 degrees.

Predictive collision sensing system

A method for forming an adaptive phased array transmission beam pattern at a base station without any knowledge of array geometry or mobile feedback is described. The approach is immune to the problems which plague methods which attempt to identify received angles of arrival from the mobile and map this information to an optimum transmit beam pattern. In addition, this approach does not suffer the capacity penalty and mobile handset complexity increase associated with mobile feedback. Estimates of the receive vector propagation channels are used to estimate transmit vector channel covariance matrices which form objectives and constraints in quadratic optimization problems leading to optimum beam former solutions for the single user case, and multiple user case. The new invention in capable of substantial frequency re-use capacity improvement in a multiple user cellular network.

Method and apparatus for adaptive transmission beam forming in a wireless communication system

Weibull-distributed ground clutter of cultivated land was measured using an L-band long-range air-route surveillance radar (ARSR) having a 3.0 ?s pulsewidth and a 1.23° beamwidth at very low grazing angles between 0.21° and 0.32°. It is shown that the shape parameter of the Weibull distribution varied from c = 1.507 to c = 2.0, corresponding to the Rayleigh distribution.

Weibull-Distributed Ground Clutter

Sea clutter was measured using and L-band long-range air-route surveillance radar (a.r.s.r.) at very low grazing angles between 0.13° and 0.25°. From the stored data of six scans, it is shown that the sea-clutter amplitude statistics obey a log-Weibull distribution.

Log-Weibull distributed sea clutter

The apparatus comprises a digital filter with cascaded digital delays or memories (311-1 -311-(N-1)), weighting multipliers (331-1 -331-N) applying weights to the output signals from the memories and adder (380) for combining the weighted signals. A region discriminator (360) discriminates between different return signal regions and the weighting coefficients are correspondinglv switched by a control signal generator (350) and a weighting coefficient generator (340). The filter characteristics are thereby switched for individual regions so that the optimum characteristics can be obtained for the stationary clutter region, moving clutter region, clear region, etc, thereby providing suppression of undesired signals which is adapted for each region.

Adaptive radar signal processing apparatus

Weibull-Distributed sea clutter

A coherent sidelobe canceller configured as a linear array antenna system having a digital open-loop configuration comprising signal receiver means having (N+1) channels (N is an integer more than one) comprising a main antenna, N auxiliary antennas, and (N+1) signal receiver circuits connected to (N+1) antennas including said main antenna with a one-to-one relationship, to produce radar video signals; analog-to-digital converter means, each channel being connected to corresponding one of said signal receiving means to convert said radar video signals to digital signals; memory means connected to said analog-to-digital converting means to store said digital signals therein; weighting coefficient calculating means connected to all (N+1) channels of said analog-to-digital converting means to perform statistical calculation processing with respect to time series digital signals, thus calculating weighting coefficients based on statistical characteristic of an input signal; multiplier means having (N+1) channels, each channel being connected to corresponding one of said memory means and said weighting coefficient calculating means to start readout operation from said memory means upon completion of the weighting coefficient calculation, thereby to multiply a weighting coefficient, calculated by said weight coefficient calculation circuit, by digital signals thus read and; adder means for summing output signals from said multiplier means, thereby enabling to suppress interference signal based on real time processing.

Eiichi Kiuchi

Papers

Weibull-Distributed Ground Clutter

Log-Weibull distributed sea clutter

Adaptive radar signal processing apparatus

Weibull-Distributed sea clutter

Coherent sidelobe canceller for radar