# Vegetation Loss Measurements for Single Alley Trees in Millimeter-Wave Bands
## 1 Introduction  
Fixed wireless access is a promising technology for fast-speed internet access without the need for costly excavation to connect optical fibers. In general, in FWA, two points with fixed locations are connected in a wireless way, and the major considered frequency band is a millimeter-wave band (mmWave). Furthermore, in mmWave, there is a great amount of bandwidth, which allows high user throughput. Moreover, it is possible that in an FWA link, there may be no line of sight, and the presence of foliage is possible. There are examples where foliage is an important factor to consider in mmWave links. First, dedicated software for predicting path loss in a foliage-dominant environment is described in [1]. It utilizes the empirical model P.1812 with a physics-based radiative energy transfer. Second, the prediction of UAV link coverage is characterized in simulation-based work [2]. The probability of coverage was shown to be reduced for 28 and 60 GHz by up to 13% and 43%, respectively, if the attenuation of foliage and rain is taken into account. Therefore, the attenuation of foliage is an important impairment that must be considered in modern systems. In addition, many measurement campaigns have been carried out in different frequency bandwidths [3; 4; 5; 6; 7]. For instance, in [8], measurements were made for LoRa transmission at a frequency of 868 MHz in an artificial forest consisting of three thousand elm, ash, and plane trees. The path loss results presented showed a good fit with empirical models. Furthermore, the authors claim that the dispersion of the results increases with the distance between the transmitter and receiver, and for 50 m and 200 m, it is 12 dB and 18 dB, respectively. Other articles have investigated the effects of foliage in millimeter-wave bands. In [9; 10], the examination focused on the frequency of 28 GHz. Two different measurement scenarios were prepared and investigated, one for the parallel orientation of the measurement link to the tree alley and the other for the skew orientation. After the analysis of the measurements, it was found that two types of components could be distinguished in the receivingsignal: a well-defined directive component and extra diffusive components. Furthermore, the authors compared their results with various vegetative attenuation models, including the models in the document ITU-P833. Based on the measurement points, the appropriate coefficients were tuned and derived. In [10], the seasonal variability of vegetation for the path loss measurements was verified. The measurements were carried out during December when leaves barely covered the trees and in October when the leaves were lush. The authors of this paper also made some measurements of vegetation loss, described in [11], where two different scenarios were considered. In the first scenario, the attenuation of the London plane tree was verified, with the transmitter located at a height of 5 m and the receiver located at a height of 3.6 m. This is the typical scenario for cellular networks, where the base station is of greater height compared to the user equipment (UE). On the other hand, in another scenario (referred to as Scenario 3), the transmitter and receiver were placed at the same height of 2.6 m; therefore, parallel orientation was considered. Measurements were made in the vicinity of small trees in the park, namely, London plane trees. The average diameter of the corona was 1.4 m; however, the branches inside the corona were rather dense. This may be the reason why the attenuation of the foliage in that scenario was claimed to be 10 dB higher than for regular trees and nonhorizontal measurements [11]. It was somewhat surprising that the parallel scenario was the worst-case scenario. Thus, in this work, the parallel scenario, as is considered for fixed wireless links, is considered to be the main use case for further investigation. As new frequency bands are envisioned for future communication systems, including mmWaves, sub-terahertz, and terahertz, a new investigation is needed.