David Astely

The effects of local scattering on direction of arrival estimation with MUSIC

In wireless communication scenarios, multipath propagation may cause angular spreading as seen from a base station antenna array. Environments where most energy incident on the array is from scatterers local to the mobile transmitters are considered, and the effects on direction of arrival (DOA) estimation with the MUSIC algorithm are studied. Previous work has studied rapidly time-varying channels and concluded that local scattering has a minor effect on DOA estimation in such scenarios. In this work, a channel that is time-invariant during the observation period is considered, and under the assumption of small angular spread, an approximate distribution for the DOA estimates is derived. The results show that local scattering has a significant impact on DOA estimation in the time-invariant case. Numerical examples are included to illustrate the analysis and to demonstrate that the results may be used to formulate a simple estimator of angular spread. An extension to more general Rayleigh and Ricean fading channels is also included. In addition, results from processing experimental data collected in suburban environments are presented. Good agreement with the derived distributions is obtained.

Spatial signature estimation for uniform linear arrays with unknown receiver gains and phases

The problem of spatial signature estimation using a uniform linear array (ULA) with unknown receiver gain and phase responses is studied. Sufficient conditions for identifying the spatial signatures are derived, and a closed-form ESPRIT-like estimator is proposed. The performance of the method is investigated by means of simulations and on experimental data collected with an antenna array in a suburban environment. The results show that the absence of receiver calibration is not critical for uplink signal waveform estimation using a plane wave model.

Burst synchronization on unknown frequency selective channels with co-channel interference using an antenna array

In this work, burst oriented data transmission over unknown frequency selective channels is considered. The receiver is assumed to use multiple antennas and the problem of estimating the start position of a data packet in the presence of spatially correlated co-channel interference is addressed. Each burst is assumed to contain a known training sequence, and in the paper metrics for finding the position of this training sequence are studied. More specifically, we examine the advantages of taking the spatial correlation of the co-channel interference into account, as compared with treating it as spatially white. Simulations and experimental results for transmission of normal GSM bursts in interference limited scenarios are presented.

A blind frequency domain method for DS-CDMA synchronization using antenna arrays

A blind frequency domain method for estimating the propagation delays of DS-CDMA signals is presented. The algorithm is formulated using an antenna array, and uses the fact that the spatially and temporally correlated additive noise, consisting of both interfering users and thermal noise, will be asymptotically uncorrelated on the FFT frequency grid. The algorithm is computationally simple, and can be efficiently implemented using the FFT algorithm. Simulations illustrate that near-far resistance can be achieved using spatial diversity.

Measurements of spatial characteristics and polarization with a dual polarized antenna array

We consider antenna arrays equipped with cross-polarized antenna elements. The multipath propagation will affect both the spatial characteristics and the polarization of the received signals which will influence the performance of the system in terms of, for example, bit error rate or direction estimation. In this paper, we present results from field measurement data recorded at the 1800 MHz band, provided by Ericsson Radio Systems AB. The study is divided into two main parts. In the first part we introduce a diversity gain measure related to the BER of an MRC receiver. The polarization diversity introduced by the radio channel is studied, and compared to the spatial diversity. In the second part we use a parameterized model of the received polarized radio waves and illustrate the typical behavior of the estimated polarization parameters.

Structured spatio-temporal interference rejection with antenna arrays

We propose a structured, training sequence based method to find the parameters of a spatio-temporal co-channel interference (CCI) rejection filter. By exploiting the inherent structure of the CCI, it is shown that the number of parameters that are to be estimated can be made independent of the spatio-temporal filter order. It is further shown that by taking advantage of the desired users known protocol structure, the parameters can be estimated using a semi-blind technique. Simulation results indicate that by taking the structure into account, for short training sequences, considerable gains are achievable compared to an unstructured method.

Constrained complexity spatio-temporal interference rejection combining

Space-time processing for co-channel interference (CCI) rejection and equalization with antenna arrays may provide large gains over space-only processing, especially in interference limited scenarios. However, taking the temporal correlation of the noise and CCI process into account leads to sequence detection with higher complexity as compared to space-only processing that neglects this correlation. We propose the use of the generalized Viterbi algorithm for sequence detection with lower complexity. Special cases include the M-algorithm and the delayed decision feedback sequence estimator. A relevant comparison between spatial and spatio-temporal processing with sequence detectors of the same complexity may thus be performed. Numerical examples show substantial gains for spatio-temporal processing as compared to space-only processing also in this case when the optimality of the sequence detector is traded for interference rejection.