## 2 Background for Location-Aware Beamforming in 5G Ultra-Dense Networks  
5G and B5G UDN in the current decade are expected to continue densification trend with the increase of base station or gNB and UE number per unit area in 2D and unit volume in 3D. However, network densification has fundamental limits which can be explained by the following analogy [56]: area spectral efficiency gain reaches saturation, when the number of wireless transceiver devices and spectrum reuse increase, likewise, semiconductor industry reaches a plateau of Moore's law, when chips computing power is no longer doubled every two years. For example, in [56] it is reported, that in the interference limited scenario network densification initially leads to SINR increase, however, after some finite gNB density is reached, potential throughput reach limit and can even decrease to zero, if pathloss exponent is below 2 and 3 for 2D and 3D cases respectively. Directional transmissions for multi-user (MU) mMIMO in mmWave are seen as one of the solutions to push fundamental densification limits as far as possible. Analysis of radio-frequency pollution (RFP) for UDN scenarios in [57] proves, that densification of gNB, working in omnidirectional mode, does not lead to exponential increase of RFP. As for gNB in multi-user BF mode, it supposes, that perceived by UE RFP level should be substantially lower, than theoretical maximum with omni gNB, because beams are usually activated by gNB to temporarily cover UE locations. Analytical approach in [57] appears to be capable for estimation not only RFP levels, but also upper and lower bounds of SINR, which varies both in time and space for UDN with gNB and UE, working in BF mode. Assessment of 5G network with mMIMO in [58] states, that spatial distribution of UE, served by gNB in BF mode, largely impact electromagnetic field (EMF) exposure in both azimuth \(\varphi\) and elevation \(\theta\) dimensions, and maximum power level is obtained for UE with focused beams. To tract analytically the uncertainty of UE spatial distribution, authors in [58] propose four scenarios of directional link establishment, defined by the probability, that UE at each time instant is positioned in the predefined \(\varphi\) and \(\theta\) direction. For investigation of the dependence of signal power levels on spatial user location authors in [58] introduce time averaging across beam orientations through predefined directions across AA broadside. Main conclusion in [58] is, that time-averaged maximum power levels in BF mode allows to reduce Inter-Site Distance (ISD) between gNB from the EMF exposure point of view and thus facilitates network densification. In spite of some analytical tractability, main drawback of approach in [58] is its inability to assess instantaneous power levels for mobile UE. One of the first scientific approach to assess pencil BF, using UE location knowledge, is presented in [59] and is supplied with an open-source simulator. The contribution of [59] is a LAB technique, which implements 3D traffic beam steering in azimuth and elevation planes according to UE position estimate with predefined uncertainty level. Besides dispelling the myth about increasing EMF exposure with pencil BF, it provides comprehensive mathematical and simulation model for LAB on the network level of abstraction with intra-sector and inter-sector interference evaluation, depending on the direction and HPBW toward each UE, tuned by gNB. SINR evaluation for multiple-beam system is performed according to approach in [60]. Despite pioneering contribution in LAB field of research, investigation [59] lacks accounting of the following factors: (a) traffic beams adaptation to UE mobility cases; and (b) trade-off between the time needed to adaptively steer the beam and positioning estimate relevance, which needs to be frequently updated for high-speed VUE. Approach of location-aware beamforming stems from challenges in alternative beam management (BM) procedures in mmWave UDN [61].