**Imanol Picallo 1, Hicham Klaina 2, Peio Lopez-Iturri 1,3, Erik Aguirre 1,3, Mikel Celaya-Echarri 4, Leyre Azpilicueta 4, Alejandro Eguizábal 1, Francisco Falcone 1,3 and Ana Alejos 2,\***


Received: 29 July 2019; Accepted: 18 October 2019; Published: 23 October 2019

**Abstract:** In this paper we consider the D2D (Device-to-Device) communication taking place between Wireless Sensor Networks (WSN) elements operating in vegetation environments in order to achieve the radio channel characterization at 2.4 GHz, focusing on the radio links blocked by oak and pine trees modelled from specimens found in a real recreation area located within forest environments. In order to fit and validate a radio channel model for this type of scenarios, both measurements and simulations by means of an in-house developed 3D Ray Launching algorithm have been performed, offering as outcomes the path loss and multipath information of the scenarios under study for forest immersed isolated trees and non-isolated trees. The specific forests, composed of thick in-leaf trees, are called Orgi Forest and Chandebrito, located respectively in Navarre and Galicia, Spain. A geometrical and dielectric model of the trees were created and introduced in the simulation software. We concluded that the scattering produced by the tree can be divided into two zones with different dominant propagation mechanisms: an obstructed line of sight (OLoS) zone far from the tree fitting a log-distance model, and a diffraction zone around the edge of the tree. 2D planes of delay spread value are also presented which similarly reflects the proposed two-zone model.

**Keywords:** device-to-device; internet of things; wireless sensor networks; vegetation; ray launching; 5G; radio channel model; scattering; log-distance
