Summary: Chapter 1
Coherent Broadband DOA Estimation
Using Modal Space Processing
The problem of estimation of direction of arrival (DOA) of coherent broadband sources has
applications in wireless communication systems, especially systems with smart antennas .
DOA estimation and adaptive beamforming are the main issues in smart antenna systems.
However, in a complex multipath environment, received signal from different directions
may be correlated, which prevents the application of narrowband DOA estimation tech-
niques to estimate DOA of broadband sources. This chapter introduce a novel coherent
broadband DOA estimation technique based on modal decomposition of wavefields.
Wang and Kaveh  introduced the use of focusing matrices for the purpose of Coherent
Signal Subspace (CSS) processing for DOA estimation of farfield wideband sources. In this
method, the wideband array data are first decomposed into several narrowband compo-
nents. The focusing matrices are used for the alignment of the signal subspaces of narrow-
band components within the bandwidth of the signals, followed by the averaging of nar-
rowband array data covariance matrices into a single covariance matrix. Then, any signal
subspace direction finding procedure, such as MUSIC  or its variants, maximum likeli-
hood (ML), or minimum variance (MV), can be applied to this averaged covariance matrix