Block subspace updating algorithms for tracking directions of coherent signals in SDMA mobile systems

In this paper we address the problem of estimating and tracking the directions-of-arrival (DOA) of multiple and possibly coherent signals impinging on the antenna array of a base station. The problems of coherency and time variation of DOAs have been treated independently in literature, and successful methods have been proposed for each case separately. In this paper a new approach is proposed tackling both problems simultaneously. To this end it is shown that a family of subspace tracking techniques can be properly extended by incorporating the idea of spatial smoothing. The resulting algorithms track efficiently the signal subspace and provide accurate estimates of the new DOAs each time a new burst of data is received.