## 4 FWA Design Considerations, Challenges, and Solutions
### Envisaged 5G Deployment Spectrum
#### 4.1.4 Penetration Loss due to Vegetation (Tree Foliage Density)
The BF scheme is capable of alleviating inter-cell interference, in addition to enabling an improved signal coverage. Remarkably, the associated small wavelengths of mm-wave enable the design of small physical footprint,  
Figure 14: Effects of (**a**) low-e glass, (**b**) non-ideal LoS condition, and (**c**) tree foliage on high-frequency solution (adapted from [5]). large-antenna arrays such as massive MIMO. In massive MIMO, a large number of antennas are employed to support the concurrent transmission of single or several data streams to an individual user. This offers advantages such as high system reliability, high-density coverage, low-latency, high-data rates, and ultra-high-bandwidth connectivity to multiple devices for home and business applications [5, 12, 69, 85, 87, 89, 90, 91, 259, 264]. Furthermore, this implementation will indeed help in physically shaping the radio signal into a constricted beam that can be projected precisely to the intended targets (devices) in a confined small area. Moreover, this approach will not only aid in extending the range but also the penetration potential of mm-wave frequencies [5, 69, 264]. The input-output relationship for the transmit beamforming with receive combining system can be expressed as [299, 300]  
\[r=\mathbf{c}^{H}\mathbf{H}\mathbf{b}\mathbf{s}+\mathbf{c}^{H}\eta, \tag{4}\]  
where \(r\in\mathbbm{C}\) denotes the post-combining signal; \(s\in\mathbbm{C}\) is the information symbol; \(\mathbf{b}\in\mathbbm{C}^{N_{\mathrm{t}}\times 1}\), \(\mathbf{c}\in\mathbbm{C}^{N_{\mathrm{t}}\times 1}\) represent the beamforming; \((\cdot)^{H}\) represents the Hermitian transpose and combining vectors, respectively; and \(\eta\sim\mathcal{CN}(0,N_{0}\mathbf{I}_{N_{\mathrm{t}}})\) is the noise vector. As illustrated in Figure 15, implementation of multi-antenna schemes and BF can significantly enhance the system performance. For instance, to achieve a BER of \(10^{-3}\) for \(~{}2\times 1\) schemes without and with BF, \(E_{b}/N_{0}\) of about \(~{}24\) dB and \(~{}12\) dB are required, respectively. Similarly, at the same BER but for \(4\times 1\) scheme, about \(5\) dB is required. This implies that an increase in the antenna configuration with the BF technique offers further performance enhancement by compensating for the associated loss. In addition, the technique can help in addressing the coverage issues [5, 69, 264]. Noted that apart from the fact that a well-confined signal can offer an enhanced foliage penetration, it can also present a beam that can be considerably manipulated. Subsequently, the beam can be appropriately redirected (i.e., by bouncing it off of obstacles or surfaces) to the near LoS (nLoS) and NLOS targets [5, 69, 264]. This can significantly help in realizing a high-speed broadband service delivery at a relatively low cost. Furthermore, a method presented in [260], that is based on a passive repeater array to enhance the link budget in a NLoS path between the BS and the CPE for 5G FWA mm-wave system, can be adopted. Moreover, for seamless network connectivity, the link breakage issue can also be addressed by employing blockage averting schemes for mm-wave communications. For instance, an adaptive BF scheme can be implemented at the Tx. This will enable the Tx to swiftly search various beam directions to get around the obstacles and maintain acceptable channel quality [5, 69, 301, 302]. Figure 15: Multi–antenna schemes with and without transmit beamforming implementation. Furthermore, innovative RF assessment technology based on artificial intelligence (AI) can be employed by the operators for easy detection of the availability of 5G service in the concerned environment. Consequently, the scheme can help the operators in saving the related expenses of sending technicians to poor service areas. Furthermore, customers in the areas can be unsubscribed to prevent any dissatisfaction.