Broadband signal subspace processing for range estimation

The problem of broadband range and bearing estimation is considered. Coherent focusing of the data covariance matrix over multiple frequency bins for 2-D MUSIC estimation is studied and compared to incoherent summing of the MUSIC cost function over frequency bins. Coherent focusing provides improved performance over incoherent processing in the far-field bearing-only estimation problem, but introduces instabilities when applied to the near-field range and bearing estimation problem. The cost function response in the range parameter is not highly peaked, so initial focusing using even a slightly incorrect range estimate prevents convergence of the range estimate to the true range value. Incoherent processing, on the other hand, is less computationally complex, and achieves the Cramer-Rao lower bound at high SNR.