Novel Unmanned Aerial Vehicle-Based Line-of-Sight MIMO Configuration Independent of Transmitted Distance Using Millimeter Wave

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 × 4 MIMO transmission in an outdoor environment. The 4 × 4 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. INDEX TERMS Millimeter wave, unmanned aerial vehicle, line-of-sight multiple-input multiple-output, non-uniform antenna array, genetic algorithm.

Effectiveness of asymmetric line-of-sight MIMO transmission using millimeter-wave

“…In this study, we measured A-LoS-MIMO transmission in a real environment. For S-LoS-MIMO, previous studies have proven that the simulated and measured values are consistent [3]. Figure 3 of the circular array is set to 0.183 m. The transmission signal is a continuous wave of frequency 66.245 GHz.…”

“…In such applications, based on the transmission and reception distance, there is a large drop in the channel capacity. Therefore, the design of the antenna arrangement is important [3,4].…”

Non-uniform array design for robust LoS MIMO via convex optimization

“…By assuming fixed arrays consisting of non-uniformly spaced antennas at the Tx and/or Rx, reduced capacity fluctuations and, hence, improved performance can be achieved over a range of transmit distances. However, due to the complexity of the LoS MIMO array design problem, which is highly non-convex, most prior works rely on brute force exhaustive search (ES) [6], [7], stochastic optimization techniques, such as genetic algorithms (GAs) [8], [9], and on numerical results. Specifically, by applying ES and assuming identical antenna locations at the Tx and Rx, non-uniform linear arrays (NULAs) are derived for 4 × 4 systems to maximize the range of transmit distances over which capacity remains above a threshold [6] and the minimum capacity over a given range of transmit distances [7].…”

“…Specifically, by applying ES and assuming identical antenna locations at the Tx and Rx, non-uniform linear arrays (NULAs) are derived for 4 × 4 systems to maximize the range of transmit distances over which capacity remains above a threshold [6] and the minimum capacity over a given range of transmit distances [7]. In [8] a non-uniform planar array is obtained via a GA by maximizing the mean minus the standard deviation of the capacity over a range of distances. In [9], a NULA for a LoS massive MIMO system is obtained through a GA for maximizing the user sum rate.…”

“…[10] and [11] are tailored to the design of NULAs and cannot be applied in the design of arrays of arbitrary geometries. In all works, either identical Tx and Rx non-uniform configurations are considered for single user systems [6]- [8], [10] or a Tx NULA with single antenna Rx users is assumed [9], [11].…”