L. I. Ponomarev, V. V. Parshikov, A. A. Vasin

One of the most important trends in the communication systems area during the last decade is a design of the principle of spectrum efficiency increase by using MIMO (multiple-input multiple-output) systems in multipath communication links. The MIMO system includes multiple antenna elements both at the transmitting end and at the receiving end of the wireless link. It is possible to reach mutual orthogonality of the channels in these systems by multibeam antenna diagram formation taking into account specifics of the wireless link and to transmit its information signal through each channel independently within the same frequency band. This article describes possibility of application of MIMO systems, including two transmitting and two receiving radiators, in relay lines. There is an opportunity of forming two independent eigen-channels, having energy channel matrix eigenvalues by way of channel gains in such a system. During modeling of multipath propagation it was supposed that along with a direct ray there are other two rays: a ground-reflected ray and a ray reflected from a tropospheric layer with high permittivity. Based on this model and the results of [3], we have analyzed the dependence of MIMO system spectrum efficiency on different transmission-line parameters such as mounting height of antenna above ground level, space between radiators of the antenna array, the reflected rays parameters. The simulation results permit to define the parameter space within which it is possible to increase spectrum efficiency of the relay line.