Eddy Taillefer

Reactance domain MUSIC algorithm for electronically steerable parasitic array radiator

Conventional adaptive array antenna processing must observe signals on all of the array antenna elements. However, because the low-cost electronically steerable parasitic array radiator (ESPAR) antenna has only a single-port output, none of the signals on the antennas parasitic elements can be observed. A direct application of most of the algorithms for the conventional adaptive array antenna is impractical. In this paper, A technique of estimation of direction-of-arrivals (DoAs) is proposed for the ESPAR antenna. This technique is based on the modified MUltiple SIgnal Classification (MUSIC) algorithm. The correlation matrix used in the MUSIC algorithm is estimated from the signal received through the single-port output of the ESPAR antenna as it switches over a set of antenna patterns. Simulation results show that DoAs can be estimated by the reactance domain MUSIC algorithm for ESPAR antennas. Furthermore, the statistical performance on estimation error variance of the reactance domain MUSIC estimator is analyzed and compared with the Crame/spl acute/r-Rao lower bound. Analytic and empirical results show that high-resolution DoAs estimation can be achieved by using the reactance domain MUSIC algorithm for ESPAR antennas.

Reactance-domain ESPRIT algorithm for a hexagonally shaped seven-element ESPAR antenna

A direction-of-arrival (DoA) method that combines the reactance-domain (RD) technique and the ESPRIT algorithm is proposed for use with the 7-element electronically steerable parasitic array radiator (ESPAR) for the estimation of noncoherent sources. Simulations show that the method could resolve up to three incoming signals with an estimation performance that depends on the signals angle of arrival. Moreover, the method is compared with the Cramer-Rao lower bound (CRB) and the MUSIC asymptotic error variance, both modified for the RD technique. Numerical comparison between this lower bound and the MUSIC algorithm confirmed that the proposed method can achieve the CRB and provide high-precision DoA estimation with a level of performance that is sufficient for many DoA finding applications. The proposed method could be demonstrated by means of experiments on DOA estimation conducted in an anechoic chamber.

Enhanced Reactance-Domain ESPRIT Algorithm Employing Multiple Beams and Translational-Invariance Soft Selection for Direction-of-Arrival Estimation in the Full Azimuth

An enhanced reactance-domain estimation of signal parameters via rotational invariance techniques (RD-ESPRIT) algorithm is proposed for direction-of-arrival (DoA) estimation in the full-azimuth plane. Unlike the classical RD-ESPRIT algorithm, the proposed method employs a generalized RD correlation matrix combined with soft selection. The proposed algorithm is expected to allow estimating more than one signal DoA with improved estimation precision. The generalized RD correlation matrix is formed by utilizing a number of beam patterns greater than or equal to the number of array elements. The soft selection employed in the enhanced RD-ESPRIT consists of two steps. First, the estimates obtained by applying the generalized RD-ESPRIT to three translational-invariance configurations are gathered to form a set of DoA estimate candidates. Second, selection functions based on a modified MUSIC function are used to select the DoA estimates from among the estimate candidate set. The proposed algorithm is investigated through computer simulations with a seven-element electronically steerable parasitic array radiator (ESPAR) antenna. The simulation showed that the proposed algorithm can perform effective DoA estimation of up to four incoming signals in the full-azimuth plane with slightly improved DoA-estimation precision. So far, the classical RD-ESPRIT is not effective because it can estimate up to one signal DoA. Moreover, the proposed method showed robust estimation capability for up to two incoming signals. A robust estimation refers to the fact that a number of DoA estimates equal to the number of incoming signals can always be selected from trial to trial. A one-signal estimation experiment was conducted in an anechoic chamber with a fabricated seven-element ESPAR antenna. In general, the proposed algorithm showed as accurate estimation precision as the classical algorithm. In particular, using soft selection instead of hard selection increases the estimation precision, whereas augmenting the number of beam patterns brings an increase in the estimation precision only when used with hard selection.

Reactance-domain MUSIC for ESPAR antennas (experiment)

The electronically steerable parasitic array radiator (ESPAR) antenna offers low cost and low complexity relative to conventional array antennas. Because of the low complexity of the antenna there is only a single-port output for processing the signals impinging on the antenna elements. Since a reactance-domain MUSIC algorithm for ESPAR antennas has been proposed, the practical problem of estimating the direction of arrival of signals impinging toward an ESPAR antenna can be tackled. In this paper, two experimental methods of estimating the arrival signal angles are proposed. A method of solving the practical problem of calibrating the ESPAR antenna output signal model is also shown. The experimental results show that for one impinging signal the direction of arrival can be estimated with precision of 3 degrees.

Reactance domain MUSIC algorithm for ESPAR antennas

Conventional adaptive array antenna processing must observe signals on all of the array antenna elements. However, because the low-cost electronically steerable parasitic array radiator (ESPAR) antenna has only a single-port output, it is not possible to observe all of the signals on the antenna elements. A direct application of most of the algorithms for the conventional adaptive array antenna is impractical. In this paper, we propose a new technique of estimation for direction-of-arrivals (DoAs) for the ESPAR antenna. This technique is based on a modification of the MUSIC (multiple signal classification) algorithm. An M-dimension vector y of the output of the antenna is obtained by using the angular diversity provided by the ESPAR antenna reactances. Then theM byM correlation matrix of the y vector is employed to estimate the MUSIC spectrum. Simulation results show that DoAs can be estimated by the reactance domain MUSIC algorithm for ESPAR antennas.

Full Azimuth Direction-of-Arrival Estimation With Successive-Selection Technique

A method for full-azimuth direction-of-arrival (DoA) estimation of multiple signals with a hexagonal array is proposed. The DoA estimation is performed in two steps. In the first, a set of estimate candidates is constructed by gathering the estimates that are obtained from applying the low-computational-cost Unitary-ESPRIT algorithm to several translational invariances designed into a hexagonal array. In the second step, the DoA estimates are successively selected from the estimate candidate set by using a selection function. The proposed method removes the north-or-south signal membership ambiguity and the limitation on the number of estimable sources, problems common to any ESPRIT-based algorithm used with one translational invariance. Therefore, up to M-1 signal DoA estimations can be expected with an M- element hexagonal array in the full azimuth. The successive-selection approach is based on a selection function that uses an estimate of the signals spatial correlation matrix to successively select the DoA estimates. For each DoA estimate selection, the already estimated signal components are removed from the correlation matrix. Such an approach is shown to actually allow the selection of suitable estimates from among a set of estimate candidates. Finally, the methods DoA estimation and resolution capabilities are demonstrated by computer simulation and comparison with the Cramer-Rao bound.

A simple DoA estimator using adjacent pattern power ratio with switched beam antenna

A simple DoA estimator is proposed with a switched beam antenna. The estimator is implemented with an adjacent pattern power ratio algorithm. For a single source signal, the received signal powers are measured while the antenna switches over a set of measured directive beam patterns. The pattern that exhibits the maximum received signal power is chosen. Then, the ratio between the pattern adjacent to the chosen pattern and the chosen pattern, is used to find the DoA by using a lookup table or by performing a linear regression approximation. Compared with conventional DoA estimators with switched beam antenna, the proposed algorithm allows DoA estimation with low computational cost, without sacrificing much the estimation precision. Computer simulations and experiments in an anechoic chamber are carried out to verify the proposed algorithm with a switched beam antenna: the electronically steerable parasitic array radiator (ESPAR) antenna.

Exhaustive computation of exact duplications via super and non-nested local maximal repeats.

We propose and implement a method to obtain all duplicated sequences (repeats) from a chromosome or whole genome. Unlike existing approaches our method makes it possible to simultaneously identify and classify repeats into super, local, and non-nested local maximal repeats. Computation verification demonstrates that maximal repeats for a genome of several gigabases can be identified in a reasonable time, enabling us to identified these maximal repeats for any sequenced genome. The algorithm used for the identification relies on enhanced suffix array data structure to achieve practical space and time efficiency, to identify and classify the maximal repeats, and to perform further post-processing on the identified duplicated sequences. The simplicity and effectiveness of the implementation makes the method readily extendible to more sophisticated computations. Maxmers can be exhaustively accounted for in few minutes for genome sequences of dozen megabases in length and in less than a day or two for genome sequences of few gigabases in length. One application of duplicated sequence identification is to the study of duplicated sequence length distributions, which our found to exhibit for large lengths a persistent power-law behavior. Variation of estimated exponents of this power law are studied among different species and successive assembly release versions of the same species. This makes the characterization of the power-law regime of sequenced genomes via maximal repeats identification and classification, an important task for the derivation of models that would help us to elucidate sequence duplication and genome evolution.

Direction-of-arrival estimation using adjacent pattern power ratio with switched beam antenna

An adjacent pattern power ratio algorithm is proposed for DoA estimation with a switched beam antenna. For a single source signal, the received signal powers are measured while the antenna switches over a set of directive beam patterns. The pattern that exhibits the maximum received signal power is chosen. Then, the ratio between the pattern adjacent to the chose pattern and the chose pattern, is used to find the DoA by using a lookup table or by performing a linear regression approximation. Compared with conventional DoA estimators, the proposed algorithm allows DoA estimation with low computational cost, without sacrificing the estimation precision.

Algebraic length distribution of sequence duplications in whole genomes

The field of comparative genomics relies upon inference of neutrality or selection from sequence conservation. Recent studies of exactly-conserved sequences have revealed an anomalous, algebraic distribution of conserved sequence lengths that is inconsistent with standard models of neutral evolution based solely on local mutation. It has been proposed that linkage contributes to the shape of this anomalous distribution. Here we identify, for a variety of species, all ‘maximal’ repeats, direct or reverse-complement, within a chromosomal or whole-genome sequence of a single genome. For a set of maximal repeats of a given nucleotide length L, we report that the number of elements in the set F(L) typically exhibits an algebraic tail. We propose a method based on a cost function that allows us to analyze this distribution and estimate the range over what the distribution is most likely to be well-approximated a power law. We find that the range is proportional to the genome size and that although the power-law exponent differs between species, it falls chiefly within a relatively narrow range of values. A sharp cut-off in the power-law regime is observed for some genomes that turns out to coincide with a peak in contig lengths and therefore can be attributed to artifacts of genome assembly, leading to a prediction that the extent of the power-law regime will increase as assemblies are improved. The typical algebraic behavior of length-frequency distribution is the most remarkable observation emerging from our analysis. The algebraic form of the empirical distribution of duplication lengths characterized here suggests that recombination events might as a general rule involve transfer of chunks of sequence with an algebraic length distribution. It also places strong constraints on any model of genome evolution. The observation of an algebraic distribution of exactly-duplicated sequence lengths within a genome is a direct demonstration of the net impact of linkage on genome evolution, and is consistent with the proposal that linkage contributes to the anomalous distribution of strongly-conserved sequence lengths.