Abstract: A method and apparatus are provided for easily and accurately calibrating an antenna array in a multipath environment. A calibration table containing spatial signature data together with corresponding location data is used to calibrate the antenna array, i.e. to determine the array response in various directions. The calibration table includes a set of calibrated signal covariances R1, . . . , RN together with a set of N corresponding geographical locations. From this data, a set of array calibration vectors {a(&thgr;)} is determined, where each vector a(&thgr;) characterizes the complex signal response of the antenna array in the direction &thgr;. Once the array calibration vectors are determined, this information can be used for direction finding, beamforming, and other enhancements to the performance of the communication system.

Abstract: A method and apparatus for wireless location finding determines a set of likely locations from a signal covariance matrix R, a set of array calibration vectors {a(.theta.)}, and a set of calibrated signal covariance matrices {R.sub.k } corresponding to calibrated locations. From these quantities, an angular energy distribution function B(.theta.) is calculated from R and a(.theta.), and compared to a set of calibrated angular energy distribution functions B.sub.1 (.theta.), . . . , B.sub.N (.theta.) corresponding to the set of calibrated signal covariance matrices R.sub.1, . . . , R.sub.N. The function B(.theta.) is then compared with each of the calibrated functions B.sub.1 (.theta.), . . . , B.sub.N (.theta.) to determine those calibrated functions that most closely match the calculated function B(.theta.). From these calculations a set of likely locations is then determined.

Abstract: A method and apparatus improves the accuracy of a wireless location finding system based on the use of multipath signal signatures. A location finding apparatus measures an array covariance matrix R of a signal. The covariance matrix is compared to a database of signatures comprising calibrated signal subspaces. The comparison is based on calculating the projection of R onto each calibrated subspace. From these calculations a set of likely locations is then determined.

Abstract: A method for determining a geographical location from a measured wireless signal signature comprises calculating from the measured wireless signal signature a multi-dimensional signature vector, wherein each component of the vector measures a degree of coincidence between the measured wireless signal signature and a calibrated signal signature stored in a calibration table. The method also includes matching the signature vector with vectors in a set of multi-dimensional calibrated vectors. The matching uses a procedure comprising searching a hierarchical tree structure and eliminating nodes that cannot contain the best match vector. Within the remaining nodes, the search eliminates individual vectors that cannot be the best match vector, and selects one or more vectors in the set of multi-dimensional calibrated vectors, where the matched vectors correspond to calibrated geographical locations.

Abstract: A system and method is provided for processing a calibration table used in a wireless location finding system. The initial calibration table data comprises points partitioned into routes followed by moving vehicles, where each point comprises a wireless signal signature and corresponding geographical location. The method comprises calculating, for each point, a list of neighboring points; and generating, for each route, a plurality of geographical bins covering all points in the route. Each bin has a bin location and a bin signature derived from those of the points within the bin. The resulting calibration table, which contains fewer redundant data points than the original calibration table data, may be used in a location finding system for quickly identifying the location of wireless transmitters in real time.

Abstract: A method for improving the accuracy of signal signature determinations in wireless location finding systems advantageously uses transmitter velocity estimates to accurately and reliably determine in real time a present signal covariance matrix for a transmitter. In a preferred embodiment of the invention, a method for determining a likely location of a transmitter in a wireless transmitter location finding system comprises coherently measuring transmitter signals received at an antenna array, and calculating a current signal covariance matrix from the measured transmitter signals. The method further comprises calculating an average covariance matrix by forming a linear combination of the current signal covariance matrix with past average covariance matrices.

Abstract: A method and apparatus reduces the ambiguities in the determination of cellular telephone locations in a location finding system based on the use of multipath signals. A location finding base station determines a signal signature from a subspace of an array covariance matrix. The signature is compared to a database of calibrated signal signatures and corresponding locations, and a set of likely locations whose calibrated signatures best match the measured signature is selected. A subset of most likely locations is selected from among the likely locations by comparing a function which represents how closely the measured signature matches the set of calibrated signatures with functions which represent how closely each likely signature matches the set of calibrated signatures. The locations corresponding to the best matching function are selected.