An Experimental Investigation into the Feasibility of MIMO Techniques within the HF Band

MIMO research so far has primarily focussed on the VHF-SHF frequency bands with an aim to increase the data rates achieved over a limited spectrum. MIMO requires a rich scattering environment in order to create parallel spatial data pipes between antennas at the transmitter and the receiver. The HF band is also affected by the multipath effects through reflections in the different layers of the ionosphere and hence is a suitable candidate for MIMO. A 255 km radio link was established between Durham and Leicester in UK to make measurements using different types of antenna arrays in the HF band. Both spaced and collocated antenna arrays were used in various campaigns over the period of two years between September 2007 and August 2009. The correlation between the signals from antennas in a spaced array was found to depend not only on the separation distance but also on the orientation of the antennas in the array. The correlation between the antenna elements in the collocated arrays was dependent on the polarization and the far field patterns (both magnitude and phase). The capacity estimates derived from the channel matrix obtained using the Fourier transform of the received signal verified the correlation coefficient results. NEC-2 software was used to analyze the response of the antennas in the array. It was determined that antenna modelling could be used to design small, collocated antenna arrays for HF-MIMO application. This research may act as the foundation stone on which the future endeavours into the application of MIMO techniques in the HF band could be built.