10.1 Introduction

The problem of estimating the DOAs of sources by an array of sensors is very important. This information is used by different functions, such as sorting and routing of communications towards remote mobiles, handover management, or geographic localization of terminals.

A good model of the propagation between a source and a base station is crucial in the design of communication system employing antenna arrays. The point source model often used in the sensor array processing literature is useful for environments with open areas, where a direct transmission between the source and the base station exists. However, in many real applications, signal scattering phenomena may cause angular spreading of the source energy [1]. Indeed, for modern radio communications, the transmitted signal is often obstructed by objects such as buildings, vehicles, and trees, or reflected by, for example, rough sea surfaces. In such complex propagation environments, the distributed source model is more appropriate than the point source model [1 3].

Depending on the mobile environment, the base station mobile distance, and the base station height, angular spreads up to 10 are observed in practice [4, 5]. On the other hand, depending on the relationship between the channel coherency time and observation period, the scattered sources are viewed either as coherently distributed (CD) or incoherently distributed (ID). More precisely, for a CD source, the signal components arriving from different directions are modeled as the delayed and attenuated replicas of the same signal. For an ID source,...