### Background and Related Work  
#### 1.1.1 Channel Models  
Channel modeling for fixed wireless access applications is discussed in [5; 6; 7], and the third generation partnership project (3 GPP) released a channel model for mmWave frequencies [8]. Outdoor radio channel measurements at mmWave frequencies are presented in [5], noting the sparsity of the outdoor radio channel. Building penetration loss measurements for fixed wireless access applications are presented in [6], with reported losses ranging from 9 dB to 17 dB. In [7], the authors performed outdoor measurements at 32 GHz and compared the measurement results to channel simulations. Channel models at mmWave frequencies for indoor environments are presented in [9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. An overview of research on indoor propagation at mmWave and sub-THz frequencies, including a living room scenario, is presented in [9]. Only a Line-of-Sight (LOS) link is considered, and a single reflection is measured. 60 GHz channel models for a public shopping mall and office environments are discussed in [10; 11; 12] presents the 60 GHz channel model for a ship hull. Path loss differences between mmWave and sub-6 GHz bands are limited, whereas delay and angular spread differ significantly [10]. Path loss (PL) and delay spread of the 60 GHz radio channel of a hospital environment are presented in [13], and are found to be lower than for other indoor environments such as an office room. The indoor radio channel for large office and laboratory environments is characterized in [14], reporting few multipath components at 60 GHz. The directional characterization of the 60 GHz office channel is discussed in [15; 16], concluding that scattering from smaller objects, including desktop displays, is characterized by specular reflections, and that channel clusters correspond to first-order and second-order reflections. Compared to indoor LOS channels, there is a larger variability in non-Line-of-Sight (NLOS) mmWave channel models [21]. PL exponent values for NLOS channel models for an office environment range from 2.7 to 5.4 [22; 23]. Angular characteristics of the mmWave channel in the azimuth plane are found to be more dependent on antenna position and the environment, whereas in the elevation plane, they depend on the height difference [24]. Passive reflectors can be used to enhance coverage for NLOS links [25; 26; 27]. A statistical channel model for a conference room is provided in [17], i.e., blockage probabilities are assigned to channel clusters. In [28], the spatio-temporal channel model at 60 GHz is compared to the characteristics of the 70 GHz channel model. Spatio-temporal characteristics at the two frequencies are similar and reveal only weak diffuse scattering. Spatial and temporal characteristics of the 60 GHz indoor radio channel are provided in [18; 19], confirming that only first-order and second-order reflections form relevant multipath components. In [29], the angular spread is simulated based on the 3 GPP standard for different antenna types, and 6 GHz results are compared to 60 GHz, showing that directional antennas significantly reduce the angular dispersion. In [20], an indoor radio channel model for an office environment at 73 GHz is provided, and the indoor radio channel for an office environment at 140 GHz is characterized in [30; 31; 32]. In [33; 34; 35], the influence of human activity on an indoor 60 GHz wireless link is investigated, reporting an attenuation exceeding 20 dB when a body blocks the communication path. Estimation of walking speed using Doppler shift of a 60 GHz indoor signal is presented in [36]. In [37], it is shown that furniture in a residential environment greatly impacts the channel. Indoor MIMO channel measurements in a lab at frequencies up to 30 GHz are presented in [38], concluding that the size of the antenna array influences the number of multipath components that are captured.