Abstract
Different applications of radio systems are based on the implementation of antenna arrays. Classically, radio di- rection finding operates with a multi channel receiving system connected to an array of receiving antennas. More recently, MIMO architectures have been proposed to increase the capacity of radio links by the use of antenna arrays at both the transmitter and receiver. The first part of this paper describes some novel experimental work carried out to examine the feasibility of ap- plying MIMO techniques for communications within the HF radio band. A detailed correlation analysis of a va- riety of different antenna array configurations is presented. The second section of the paper also deals with HF MIMO communications, focusing on the problem from a modelling point of view. The third part presents a sen- sitivity analysis of different antenna array structures for HF direction finding applications. The results demon- strate that when modelling errors, heterogeneous antenna arrays are more robust in comparison to homogeneous structures.
Highlights
A multiple input multiple output (MIMO) system utilises antenna arrays at the transmitterSignals received over HF (3-30 MHz) propagation paths through the ionosphere are prone to extensive fading as a consequence of multipath and multimode propagation
In order to assess this possibility and in order to gain some insight into the optimum design of HF MIMO systems, the characteristics of the digital HF channel have been explored in relation to this utilization
In order to realise increased channel capacity by means of a MIMO system, it is important that the signals received at each of the antenna elements of the receiver array from each of the elements of the transmitter array are adequately decorrelated
Summary
Direction finding techniques operate with synchronous acquisitions at the output of an array of sensors and the associated covariance matrix is the relevant information for the most popular high resolution algorithms (Capon, Music, Weighted Subspace Fitting). This work investigates the estimation of angular errors resulting from a perturbation on the steering-vector matrix. These uncertainties on the array response are due, for example, to imprecise positions of the sensors or to a default in the calibration of the electronic circuits connected to each of them. The expressions of the errors (limited to first order terms) are derived for two different structures of array. The first is the classical homogeneous array set up with identical sensors. The second is the heterogeneous structure (Erhel et al, 2004), set up with different sensors, that we proposed for HF applications in order to make the array sensitive to the incoming polarization. Statistics of the angular errors are computed for the two solutions and indicate a greater robustness of the second structure
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