# Design and Analysis of High-Capacity MIMO System in Line-of-Sight Communication
## 1 Introduction
### Related Literature  
There are many emerging technologies in the field of new generation mobile communication. Terahertz (THz) communication has emerged as a possible alternative to accommodate a future 6G wireless network massive data load and increase network capacity. Air radio access networks (ARANs) support the global access infrastructure for seamless mobile communication systems [4]. When compared to the sub-6 GHz massive MIMO system, the aerospace terahertz MIMO channel has a unique delay-beam-doppler squint effect, and transmissions are mostly along the LoS direction [5]. Satellite communication frequency has been addressed mostly on the Ka frequency range (26 GHz-40 GHz), where more efforts are needed in the U and V higher frequency bands (40 GHz-75 GHz) [6]. The authors of [7] focused on satellite massive MIMO transmission and stated that a massive MIMO transmission scheme based on frequency reuse can boost the data rate of satellite communication systems. The authors in [8] first provided an overview of green transportation in automotive industry 5.0 and showed significance of backscatter communication and non-orthogonal multiple access (NOMA) for green transportation applications. A novel alternating optimization framework is proposed in [9] to enhance the energy efficiency of intelligent reflective surface (IRS)-assisted non-orthogonal multiple access beamforming (NOMA-BF) systems for 6G wireless communication networks. The authors in [10] provided an overview of an IRS-enhanced physical layer security (PLS) for unmanned aerial vehicle (UAV) communication. The IRS-assisted PLS is presented in UAV communications to improve the secrecy rate. Many studies on MIMO technology have been conducted in recent years, including capacity analysis, channel estimation, and channel modeling [11]. An effective solution, based on different antenna parameters to boost the massive MIMO channel capacity, is provided in [12]. Under low signal-to-noise ratio (SNR) situations, the authors in [13] derived a simple analytical expression for the MIMO channel capacity with Rayleigh fading. In [14], it the authors proved that MIMO channel capacity drops with the increase of K-factor, and increases with the increase of delay spread. The statistical comparison of curved and straight tunnels on channel performance is analyzed in [15]. Changes in K-factor over time, frequency, and location are investigated in [16]. The relationship between Rician channel and K-factor, as well as the effects of mobility and the carrier on K-factor is studied in [17]. Statistical parameters of the channel, such as root mean square delay spread (RMS-DS), K factor, and shadowing are studied in [18; 19]. The efficient method to approximate the MIMO channel model by sparse matrices with an equivalent Markov process is introduced and thoroughly analyzed in [20]. A shared aperture two-element MIMO antenna design for 5G standards is presented in [21], which uses the same radiating structure to cover both the sub-6 GHz and millimeter-wave bands. In [22], the analytic upper bound and lowerbound of the ergodic capacity are presented for distributed MIMO systems operating on Rayleigh/lognormal fading channels. The influence of positive definiteness of the matrix on channel correlation under realistic propagation conditions in MIMO wireless channels is studied in [23; 24]. The derivation and analysis of spatial correlations based on stochastic channel models for MIMO systems using polarized and isolated antenna arrays are studied in [25; 26]. The authors in [27] eliminated all numerical integrations required to compute far-field envelope cross-correlation in a MIMO system, deriving accurate and efficient analytical expressions for the frequency-domain cross-correlation Green's function. The authors in [28; 29] proposed research of a linearly polarized compact multi-band MIMO antenna system for small mobile terminals, and conducted an in-depth analysis of its antenna circuit.