Communications: directive radio wave systems and devices (e.g. – Directive – Including antenna pattern plotting
Reexamination Certificate
1998-09-14
2001-05-15
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including antenna pattern plotting
C342S174000, C342S378000
Reexamination Certificate
active
06232918
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to methods for calibrating an antenna array. More particularly, it relates to methods for determining antenna array calibration vectors from location-finding data.
BACKGROUND OF THE INVENTION
Wireless radio communication systems, such as cellular telephone networks, sometimes make use of phased arrays of antennas to provide spatial diversity, direction-finding, and increased capacity. Normally, however, it is necessary to calibrate each antenna array in order to determine its response to signals originating from various different directions. Only after the array response is known is it possible to use the array. A common technique for calibrating an antenna array involves collecting test signals from transmitters having known angular locations relative to the array. Yet, for this technique to be effective it is required that the signal propagation from these locations to the array is free of multipath. Many wireless environments, however, are characterized by a significant amount of multipath. Consequently, the calibrated array response will be inaccurate, and appropriately compensating for the multipath errors can be an inconvenient and time-consuming task, if possible at all. Accordingly, it would be desirable to have an improved method for calibrating antenna arrays.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide a method and apparatus for easily and automatically calibrating an antenna array. Another object of the present invention is to provide a technique for determining the response of an antenna array used in a wireless communication system. In one aspect of the invention, a method is provided for calibrating an antenna array through the use of data provided by a calibration table containing spatial signature data together with corresponding location data. In the present invention, a method is provided to use this information to calibrate the antenna array, i.e. to determine the array response in various directions. In one embodiment of the invention, a calibration table includes a set of calibrated signal covariances R
1
, . . . , R
N
together with a set of N corresponding geographical locations. From this data, a set of array calibration vectors {a(&thgr;)} can be 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.
REFERENCES:
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Hilsenrath Oliver
Jayaraman Sriram
Wax Mati
Issing Gregory C.
Lumen Intellectual Property Services Inc.
US Wireless Corporation
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