ON SPATIAL SMOOTHING TECHNIQUES FOR BEAMFORMING IN THE PRESENCE OF CORRELATED ARRIVALS

Conventional spatial smoothing techniques suffer from performance degradation in the presence of highly correlated (coherent) sources. This paper proposes a new method, called hybrid spatial smoothing, to decorrelate highly correlated sources and derives an analytical expression to show the decorrelation effect of the new technique for a linear equispaced array. The new technique produces a Toeplitz correlation matrix which is not only able to create deep null in the direction of the correlated and uncorrelated interference as well but improve the signal to noise ratio (SNR). The paper derives expressions for both the hybrid output signal to noise ratio (SNRHP) and the redundancy averaging (structured) output signal to noise ratio (SNRST) in case of correlated arrivals and compare between the two expressions for some special cases. The paper also illustrates how the output SNR for both methods is affected by the number of array sensors, the magnitude of correlation between the desired signal and unwanted interference, and the level of the uncorrelated internal noise power. Computer plots are provided to compare between the two methods.