## 5 Conclusions  
As any radio channel, both narrowband and wideband characterization are required to determine the propagation properties of a near-ground scenario. From the wideband characterization the channel parameters obtained are power delay and angular profiles, RMS delay and angular spread, coherence bandwidth, and coherence distance. The path loss can be derived of both narrowband channelcharacterization. The narrowband model becomes a critical tool for the design of the wireless network in terms of system range and quality of service. In this paper, a narrowband radio channel model is proposed for a scenario with the radio link operating under near-ground conditions and using directional antennas, applied to a smart agriculture use case in bands planned for 5G-IoT. A comparison of the path loss results for different combinations of antenna heights, frequency bands and ground coverings demonstrated the influence of those elements:  
1. The difference between the free-space and measured path loss decreases as the transmitting frequency increases due to a larger obstruction of the FFZ. Because of this, the 868 MHz seems not to be an optimal solution just for minimizing path losses. 2. Lowering the height of the antennas produces a larger signal attenuation also explained by a larger obstruction of the FFZ. 3. The height of the ground covering (grass leaf length, p.e.) reduces the effective antenna height so increasing the obstruction of the FFZ. The path loss was determined to be dependent of the radio link range according to a three-slope log-distance model. The characteristics of the near-ground radio channel may be mainly explained in terms of Fresnel zones obstruction, and the proposed model reflects this fact. Actually, the main contribution of the approach here described is to enlighten that the distance between the transmitter and the receiver may be split into three zones limited by two critical points and the break or cross-over point. The QoS analysis performed for this case, derived from RSSI experimental values along a distance of 51 m, leads to state that the close ground scenario is more restrictive than an OLoS link, and it may require the use of more robust digital modulation schemes or error correction codes to equal the performance of LoS based networks. A near-ground setup can show up in a WSN even when the network configuration was not originally planned as such, p.e. in case of grass or crops growth occurs. Then, the network should be provided of any type of intelligence to prevent, correct or control such situation, so that a more proper modulation can be chosen, or data routing can be adapted to avoid those paths. An option would be to include software agents [36] dedicated to the mission of monitoring the radio channel obstruction. Even near-ground networks are increasingly used; many studies proposed in the literature lack generality and flexibility to be tested in a different scenario. The study and characterization of these systems admits a deep and extensive study to respond to the plausible influence of variables, such as the scenario, frequency bands, antenna radiation pattern and polarization, terrain roughness and profile, ground composition and dielectric properties or the fixed antenna height [15; 16; 17; 18; 19; 20; 21; 22]. Also missing is the application of techniques for increasing the capacity of the near-ground casuistry, such as diversity or MIMO. Only one work was found related to the analysis of MIMO to improve the effect of the diffraction topic [16]. Among other likely research lines, the design of ad-hoc antennas constitutes a goal for these systems, with a radiation pattern directive and with an elevation that minimizes the FFZ obstruction. The result of achieving a more accurate characterization, and standardization, of the near-ground systems would increase its use remarkably, broadening the variety of use cases, mainly in the short-term future of 5G-IoT. This work represents a key content in the PhD Thesis of the pre-doctoral student H.K.