Multipath mitigation technique using null-steering beamformer for positioning system

A multipath signal mitigation technique using a null steering beamformer is proposed. In the wireless communications, multipath signals cause the measurement errors of positioning parameters and reduce the wireless positioning accuracy. If a line of sight (LOS) signal exists, the multipath signals would have longer time delay than LOS signal. Therefore, the time delay values of received signals are ill-estimated by superposition of multipath signals. An angle of arrival (AOA) can be estimated from the reverse link using array antennas. However, the AOA measurements include not only the direction of LOS signal but also that of multipath signal. To remove the multipath signals, we use a null steering beamformer. The null steering beamformer can be used to cancel a signal from a known direction by producing a null in the undesired direction and to steer a beam to the desired direction. By repeating the null-steering beamforming for every incident angle, we can obtain the signal at each direction. With correlator, the time delay value for each direction can be estimated and the AOA of the LOS signal can be selected. The computer simulation results show that the proposed technique can reduce the delay estimation errors and angle estimation errors caused by multipath propagation.