KEYWORDS: Signal to noise ratio, Statistical analysis, Sensors, Error analysis, Interference (communication), Monte Carlo methods, Signal processing, Optical simulations, Phased arrays, Chemical elements
The output SINR achieved via Indirect Dominant Mode Rejection (IDMR) beamforming is substantially higher than the
achieved with other beamforming algorithms. IDMR is based on a parametric estimate of the covariance matrix which is
obtained using an estimate of the directions of the dominant sources and assuming that the array manifold is available. In
most applications the array manifold is not known precisely and performance of IDMR can be deteriorated. The focus of
this paper is to enable the IDMR beamformer to operate in a scenario of direction-independent steering vector mismatch. A
modified version of an algorithm introduced by Friedlander is employed to estimate the direction-independent mismatch.
Thereafter IDMR is implemented. Simulation analysis reveals that this technique enables IDMR to operate in a scenario
of direction-independent manifold mismatch.
In the adaptive beamforming problem it is usual that the covariance matrix is not know and an estimate from training samples is used. When the size of the training samples is limited the performance of the full rank Minimum Variance Distortionless Response (MVDR)
beamformer is deteriorated; and a low rank solution of the MVDR problem can yield a better performance. A new adaptive approach, Indirect Dominant Mode Rejection (IDMR), was introduced in previous work to solve the MVDR optimization problem. In the previous work the IDMR beamformer was used to extract the desired signal, while in this work we use the IDMR beamformer to estimate the power spectrum. We also introduce several modifications, which bring more robustness to the basic IDMR. These include root-music, forward/backward averaging of the sample covariance matrix and power window.
In this work we first analyze two methods of finding low rank solutions: Steering Independent Conjugate Gradient (SI-CG) and Steering Dependent Conjugate Gradient (SD-CG). These low-rank beamformers have a rank where the output SINR is maximized and a large drop in the output SINR can occur if the beamformer operates at an improper rank. Indirect Dominant Mode Rejection (IDMR) is proposed wherein one first employs a high-resolution spatial spectrum estimation technique to estimate the directions and powers of the dominant interferers. Subsequently, this information is used to construct an estimate of the signal-free (interference plus noise only) autocorrelation matrix (for a given look-direction.) In this process, any residual correlations between the interferers and the signal arriving from the look-direction due to finite sample averaging is effectively removed. Simulations reveal that IDMR yields a dramatic improvement in output SINR relative to CG and PCI/DMR, even when the latter operate at the optimal rank. In the case of correlated signals IDMR shows not to degrade the output SINR, different from CG and PCI/DMR.