Adaftiive processing in the presence of near field Scatterers

In practical situations, it is necessary to have a flexible methodology for adaptive processing that can deal with the effects of mutual coupling between the various antenna elements, the coupling between the antennas and the platform and the effects of near-field scatterers. To merge the signal processing and the electro magnetics methodology with the goal to deploy it in a real system containing practical antenna elements, we propose to use a direct data domain approach for adaptive space-time processing which is quite amenable for real time processing [1, 2, 10, 11]. In this approach one adaptively minimizes the interference power while maintaining the gain of the antenna array along the direction of the signal. Not having to estimate a covariance matrix leads to an enormous savings in memory and computer processor time and makes it possible to carry out an adaptive process in real time. The advantage of this new method is that we can do the adaptive processing with a single snapshot of data (a snapshot is defined as the voltages induced in the antenna elements at a particular instance of time). As there is no need to form a covariance matrix, real time implementation is possible and one can deal with both noncoherent and coherent ( is . , the signal and the multi paths are in phase with either additive or destructive) signals whereas a conventional statistical based approach can deal with only the noncoherent case unless additional processing is carried out. It has been shown that a direct data domain method has a lower Cramer-Rao bound for the estimate of the parameter of interest than a stochastic model based methodology, i.e., the variance of the solution is smaller in the presence of noise for a direct data domain method over the conventional statistical approaches [3]. Let us illustrate the problem through an example and this will also provide a cursory overview of the technique.