# Capacity Bounds for Dense Massive MIMO in a Line-of-Sight Propagation Environment
## 2 Related Work  
In [19] the authors analyze the performance of the outage probability for the uplink of massive MIMO systems considering a uniform rectangular array (URA) and a pure random LoS scenario. They show that the outage probability increases logarithmically with the number of BS antennas due to the interference hardening effect.  
The authors of [24] study the user-interference in a single-cell multi-user pure LoS massive MIMO system. They demonstrate that the distribution of the interference term in the expression of the uplink signal-to-interference-plus-noise ratio (SINR) can be approximated as a Beta-mixture when pure LoS channels and element spacing of half-wavelength are considered.  
In [25], the authors assume a single-cell multi-user massive MIMO system with flat Rayleigh channels. They assess the distribution of the user-interference, which is modeled as a random variable, and the probability of outage for the downlink of the massive MIMO system adopting maximum ratio combining (MRC) precoding. They derive a distribution for the user-interference power and based on that they obtain an analytical outage probability equation.  
In [26], the authors demonstrate that in single-cell multi-user massive MIMO systems the free-space nonfading LoS channels becomes asymptotically orthogonal as the number of antennas increases, i.e., the channel offers asymptotic favorable propagation, which is the most desirable scenario in terms of maximizing the sum-capacity of such systems. They also demonstrate that when a finite number of antennas is considered, the channels are not mutually orthogonal. Additionally, they also introduce the distance from favorable propagation measure, which is used to measure how favorable the propagation offered by the channel is, i.e., it measures the gap between the sum-capacity and the maximum capacity that is achieved when the channel offers favorable propagation.  
In [27], the authors evaluate the impact of antenna element spacing of a uniform linear array (ULA) on the capacity of fixed point-to-point massive MIMO systems considering pure LoS channels. They demonstrate that the optimal spacing between antenna elements of ULAs, achieving full spatial multiplexing, can be reduced compared to the well-known element spacing criterion adopted in previous investigations.  
The authors of [28], show that switching from i.i.d. flat Rayleigh fading to uniformly random pure LoS propagation results in no significant loss in user throughput performance. They demonstrate that for massive MIMO systems to perform well in LoS conditions, it is sufficient to selectively drop a small number of users from service. They additionally provide an algorithm for deciding which users should be dropped.  
In [29], the authors study the potential of employing the Massive MIMO technology for communications with drones. They discuss the performance of the achievable uplink capacity in the case of pure LoS conditions. They determine the optimal antenna element spacing for ULAs and URAs that maximizes the ergodic rate achieved by a drone.  
All the aforementioned works did not consider the mobility of the devices and the influence of favorable propagation in their analysis. The focus of our work is on analyzing the impact of devices' mobility and favorable propagation on the ergodic sum-capacity and outage probability. Therefore, to the best of the authors' knowledge, there is no work that studied the ergodic sum-capacity and outage probability performance of massive MIMO systems under pure LoS and favourable propagation for a scenario with devices randomly moving around the cell.