Calibration and direction of arrival estimation with a uniform circular array for mobile radio channels

By use of array antennas in mobile radio communications, a gain for the desired signal and more efficient rejection of interference can be achieved, either through diversity or beamforming techniques. Their use depends, basically, on the correlation coefficient between signals on the different array elements, that is influenced by the existence of direct line of sight (LOS). As yet, arrays are located only at the base station, but their use at the mobile station is also possible. In. this work, advanced direction of arrival (DOA) and delay estimation algorithms with a uniform circular array (UCA) located at the mobile station are analysed. These techniques demand a highly accurate calibration of the array to reduce the effects of both inter-element coupling and non-omni directional antenna pattern. On the basis of measurements in an anechoic room calibration is performed, and a unitary delay-DOA algorithm is adapted and implemented for circular arrays. The results obtained from a measurement campaign show that at a high percentage of locations the DOA of the first multipath component coincides with the direction towards the transmitter in azimuth. This result implies the use of array antennas also in mobile stations where enough space is available, e.g. on the roof of cars and trains.