A deterministic least-squares approach to space-time adaptive processing (STAP)

A direct data domain (D-3) least-squares space-time adaptive processing (ST AP) approach is presented for adaptively enhancing signals in a nonhomogene ous environment. The nonhomogeneous environment may consist of nonstationar y clutter and could include blinking jammers. The D-3 approach is applied t o data collected by an antenna array utilizing space and in time (Doppler) diversity. Conventional STAP generally utilizes statistical methodologies b ased on estimating a covariance matrix of the interference using data from secondary range cells. As the results are derived from ensemble averages, o ne filter (optimum in a probabilistic sense) is obtained for the operationa l environment, assumed to be wide sense stationary. However, for highly tra nsient and inhomogeneous environments the conventional statistical methodol ogy is difficult to apply Hence, the D-3 method is presented as it analyzes the data in space and time over each range cell separately. The D-3 method is deterministic in approach. From an operational standpoint, an optimum m ethod could be a combination of these two diverse methodologies. This paper represents several new D-3 approaches. One is based on the computation of a generalized eigenvalue for the signal strength and the others are based o n the solution of a set of block Hankel matrix equations. Since the matrix of the system of equations to be solved has a block Hankel structure, the c onjugate gradient method and the fast Fourier transform (FFT) can be utiliz ed for efficient solution of the adaptive problem. illustrative examples pr esented in this paper use measured data from the multichannel airborne rada r measurements (MCARM) database to detect a Sabreliner in the presence of u rban, land, and sea clutter. An added advantage for the D-3 method in solvi ng real-life problems is that simultaneously many realizations can be obtai ned for the same solution for the signal of interest (SOI), The degree of v ariability amongst the different results can provide a confidence level of the processed results. The D-3 method may also be used for mobile communica tions.