Decoupled estimation of DOA and angular spread for a spatially distributedsource

In mobile communications, local scattering in the vicinity of the mobile re sults in angular spreading as seen from a base station antenna array. In th is paper, we consider the problem of estimating the parameters [direction-o f-arrival (DOA) and angular spread] of a spatially distributed source, usin g a uniform linear array (ULA), A two-step procedure enabling decoupling th e estimation of DOA from that of the angular spread is proposed. This metho d combines a covariance matching algorithm with the use of the extended inv ariance principle (EXIP). More exactly, the first step makes use of an unst ructured model for the part of the covariance matrix that depends on the an gular spread. Then, the solution is refined by invoking EXIP, Instead of a 2-D search, the proposed scheme requires two successive 1-D searches. Addit ionally, the DOA estimate is robust to mismodeling the spatial distribution of the scatterers. A statistical analysis is carried out, and a formula fo r the asymptotic variance of the estimates is derived. Numerical examples i llustrate the performance of the method.