Abstract
Recently, the millimeter-wave band has been used in outdoor wireless communications to improve the frequency utilization efficiency. In this study, we propose a method to realize line-of-sight multiple-input multiple-output (LOS-MIMO) transmission independent of the transmitted distance using a two-dimensional (2-D) fixed antenna element arrangement, assuming millimeter-wave-band communication by small autonomous unmanned aerial vehicles. In conventional LOS-MIMO transmission with uniformly spaced antenna elements, the theoretical upper bound of the channel capacity is obtained, which decreases at a certain transmitted distance. Therefore, we focus on the fact that the propagation channel characteristics in pure LOS are geometrically determined by the transmitted distance, and consider the optimization of the arrangement of antenna elements. The element arrangement is fixed without using antenna selection from the viewpoint of system simplification. In addition, from the viewpoint of array size, we study the optimization corresponding to a 2-D element arrangement. The proposed method approximates the optimal arrangement from a vast number of 2-D element arrangements using a genetic algorithm. We evaluate the channel capacity characteristics of the proposed method by computer simulation and show that the characteristic degradation due to change in the transmitted distance in conventional LOS-MIMO transmission is improved. In addition, we evaluate a $4\times4$ MIMO transmission in an outdoor environment. The $4\times4$ MIMO propagation channel is also measured by an actual measurement equipment in the 66-GHz band and it is shown that the measured and calculated results agree with each other.
Highlights
With the diversification of wireless communications, such as the Internet of Things (IoT), the fifth generation mobile communication (5G) system is targeted to increase the capacity of mobile data by more than 1000 times in comparison with that of 4G [1]
Focusing on the geometrical relationship between the antenna element arrangement and the transmitted distance, we proposed a 2-D fixed element arrangement using genetic algorithm (GA)
We showed the effectiveness of the proposed method by evaluating the channel capacity characteristics with respect to transmitted distances
Summary
With the diversification of wireless communications, such as the Internet of Things (IoT), the fifth generation mobile communication (5G) system is targeted to increase the capacity of mobile data by more than 1000 times in comparison with that of 4G [1]. We use a genetic algorithm (GA) [20] that is effective in deriving the approximate optimal solution, and realize an arrangement with a small amount of channel capacity degradation with changes in transmitted distance using fixed elements.
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