Most military applications of GPS require performing both jammer nulling and localization. While nulling can be achieved using adaptive gradient techniques applied to the input sampled data, high resolution direction of arrival estimation can precede using subspace and eigenstructure methods applied to the estimate of the covariance matrix. In this paper, we extract the jammer direction of arrival (DOA) information directly from the adaptive weights, in which case we assume interference nulling precedes interference localization. This high resolution DOA estimation approach based on available beamforming weight values leads to simplified receiver structure and allows a choice of IF or baseband processing as well as flexibility for analog, digital or mixed mode implementations.
Radio Frequency Identification (RFID) has recently attracted much attention in both the technical and business communities. It has found wide applications in, for example, toll collection, supply-chain management, access control, localization tracking, real-time monitoring, and object identification. Situations may arise where the movement directions of the tagged RFID items through a portal is of interest and must be determined. Doppler estimation may prove complicated or impractical to perform by RFID readers. Several alternative approaches, including the use of an array of sensors with arbitrary geometry, can be applied. In this paper, we consider direction-of-arrival (DOA) estimation techniques for application to near-field narrowband RFID problems. Particularly, we examine the use of a pair of RFID antennas to track moving RFID tagged items through a portal. With two antennas, the near-field DOA estimation problem can be simplified to a far-field problem, yielding a simple way for identifying the direction of the tag movement, where only one parameter, the angle, needs to be considered. In this case, tracking of the moving direction of the tag simply amounts to computing the spatial cross-correlation between the data samples received at the two antennas. It is pointed out that the radiation patterns of the reader and tag antennas, particularly their phase characteristics, have a significant effect on the performance of DOA estimation. Indoor experiments are conducted in the Radar Imaging and RFID Labs at Villanova University for validating the proposed technique for target movement direction estimations.