Author:

Abstract:

The technique of using multiple antennas or an antenna array, is well-known to provide spatial diversity in a wireless communication system. Exploiting the phase information of the received signals from all elements of the antenna array enables the detection of the direction of arrival of the incoming signals. Radio direction finding is widely used in navigation, auto-piloting, tracking wildlife, discovering interfering or co-located transmitters. Beamforming is a specific example of utilization of spatial diversity. Beamforming increases the total system capacity and spectral efficiency. Throughout the research of this Ph.D., several aspects of electronic beamforming and direction finding are tackled. First, a compact architecture for real-time direction of arrival (DoA) estimation, tracking and beamforming is presented. The architecture is tailored to the use of low cost, off-the-shelf, readily available components. A proof of concept prototype, including a 1×2 planar array, an analog front end, and an FPGA based embedded system, is built and measured. Additionally, the influence of the non-ideal front end and propagation effects are taken into account in the direction finding and beamforming. In general, the actual beam direction differs from the beam direction of the array factor. This is an issue coming up especially when studying beam steering in small and medium sized arrays. Also, (artificially created) propagation imbalance, for example due to the amplitude response variance on receiving elements, can be also considered as a source information for direction finding. A prototype is designed and assembled to study two-antenna microwave passive direction finding systems with an additional scatterer in between the elements. Second, a complete communication system with sixteen antenna elements, software defined radio, and beam tracking capabilities for up to four users is designed, built and measured according to results of the previous study. A key feature is that all digital beamforming and advanced DoA tracking algorithms are integrated into one segment – the multiple users beam tracker. Experimental results regarding system performance, responding time and efficiency illustrate the effectiveness of the concept. Additionally, a hardware implementation of a MUSIC based DoA estimator is integrated into the Multiple Users Beam Tracker to improve the response performance. The hardware accelerated multiple users beam tracking system (MUBTS) is tested and its performance is also evaluated against the original one. Third, a compressive DoA estimation algorithm is investigated on three sparse arrays, namely the nested array, the coprime array, and the sparse ruler array. The algorithm exploits the second order moments properties of the covariance matrix structure of a non-uniform linear array to gain extra degrees of freedom and detect more sources of DoA than antenna elements physically present. Crucial is that this study is based on real measurements conducted on a real demonstrator platform. The results show clearly that the sparse ruler algorithm has a better performance.