Mahdi Nezafat

Estimation of the number of sources based on the eigenvectors of the covariance matrix

In this paper, we propose a method for estimating the number of sources based on the eigenvectors of the covariance matrix of a narrowband array. The proposed method provides the same detection sensitivity as AIC and MDL, but appears to be much more robust to signal and noise model perturbations. Unlike AIC and MDL that do not make use of the procedure used in calibrating the antenna array, the proposed method can use the calibrated antenna responses to take into account the existing nonidealities present in the antenna array, and hence outperforming AIC and MDL methods in practice.

Indoor Localization Using a Spatial Channel Signature Database

In this letter, we present preliminary results of a field measurement that was carried out in an office to study spatial characteristics of an indoor wireless channel for the purpose of localizing wireless transmitters using one receiver that is equipped with one antenna array. An induced spatial signature of multipath propagation and a spatial signature database are employed to associate the received signal with its transmission location

Statistical performance of subspace matching mobile localization using experimental data

In this paper, we present some statistical results on localization performance of subspace matching localization (SML), a technique for localizing non-cooperative transmitters in a microcellular environment Nezafat, M et al. (2004) using one (multiple) base-station(s) that is (are) equipped with an (multiple) antenna array(s). We use extensive experimental measurements obtained in Yokosuka, Japan. SML exploits the dissimilarities in spatial multipath propagation characteristics of distinct locations, as reflected in the received respective signal subspaces to localize a transmitter. The location detector utilizes a match of the received signal subspace with those in a database. The database can be constructed by measurement campaigns, or ray tracing based simulations. In this paper, we report the localization accuracy of SML using a database that is constructed using a measurement campaign and up to two base stations. Issues regarding the variations of signal subspace due to non-stationarities in the environment and tracking of mobile transmitters are also addressed briefly.

Localization of wireless terminals using subspace matching with ray-tracing-based simulations

This paper presents a method for localizing transmitters in a microcellular environment dominated by non-line-of-sight (NLOS) propagation, using one base station that is equipped with one antenna array. The proposed method takes advantage of the dissimilarities in multipath propagation characteristics of distinct locations in such an environment and site-specific ray tracing models to localize a transmitter. Studies of experimental data are provided to validate the proposed method.

Analysis of diversity, beamforming and hybrid diversity-beamforming systems

In this paper we compare Shannon capacities of diversity, beamforming, and hybrid diversity-beamforming systems for reverse and forward links. Our results show that the reverse link capacity of a diversity system is higher than that of a beamforming system, while the beamforming system can provide higher capacity than the diversity system in the forward link. A hybrid diversity-beamforming system can provide comparable capacity to the diversity system in the reverse fink and to the beamforming system in the forward link. We also compare outage capacities of these three systems and our results show that the diversity system provides higher outage capacity both in reverse and forward links. Estimation of forward link channel covariance matrix is of vital importance for sub-optimum design of forward link beamformer and is addressed in the last section of the paper. We propose two methods for estimating the forward link channel covariance matrix based on reverse link measurements for a frequency-division-duplex (FDD) system.

A new enhanced morphological filter and signal recovery

We present a new approach to noise reduction based on mathematical morphology. The proposed algorithm performs an adaptive, nonlinear, and recursive filtering. The results show that a deterministic or a stochastic signal corrupted by an additive noise of general nature is recovered using the new nonlinear filter. The new filter is able to remove a correlated noise, or a signal-dependent noise from the desired signal. This filter is also capable of recovering desired signals even in low signal-to-noise ratios and it is versatile enough to combat heavy tail Cauchy noise. We also provide the pertinent probability density function for the output of the main part of the new filter.

Estimation of the number of sources with DOA priors

In this paper, we present a technique for estimating the number of sources based on the eigenvectors of the covariance matrix of received signal at an antenna array when directions of arrival priors are obtained from the received signal, e.g. via a spectral estimation method such as MVDR. The proposed technique is designated the eigenvector order estimation technique (EOET). EOET outperforms AIC, MDL and GDE techniques in practice and provides comparable detection sensitivity as AIC, MDL, and GDE in simulation

A Robust MVDR Spectrum Estimation Technique

A major problem in applying Minimum Variance Distortionless Response (MVDR) beamformer, also known as Capon beamformer, in operational systems is the potential sensitivity to mismatch between actual and assumed models for the array response and/or the received signals used to derive the beamformer. Typical mismatches that have been addressed are DOA mismatch, sensor gain and phase perturbation, and sensor position perturbation. The subject of mutual coupling, for the most part, has been ignored in the development of algorithms for robust beamforming. In this paper, we present an extension of a previously developed robust MVDR beamformer that takes into account the mutual coupling between elements of the antenna array and the uncertainties in the array response and in the mutual coupling explicitly. We present several experimental results using measurements that were carried out in an anechoic chamber.

Study of buildings and antenna directivity effects on LMDS systems using a modified ray tracing algorithm

In this work we develop a computer-aided tool for propagation prediction of wireless channels based on a modified shooting and bouncing ray (SBR) method that is combined with GTD/UTD (geometrical theory of diffraction/uniform theory of diffraction). Our simulation results show that the new algorithm reduces the computation time while the accuracy of the algorithm is preserved. In this paper we also investigate the effects of receiver antenna height and antenna beamwidth on path loss and channel parameters for LMDS systems.