## 2 Literature Review  
Numerous studies on the evaluation of radio links in WSN are proposed in the literature. Some authors propose theoretical models [16; 17; 18] of the wireless channel, while others adopt experimental approaches [19]. In [18], the authors proposed a coexistence model of two standards (IEEE 802.15.4 and IEEE 802.11b/g), which exposes the interactions between these technologies. They analyzed the vulnerabilities low power IEEE 802.15.4 technology face compared to technologies such as 802.11b/g, which use a higher transmission power and work in the same frequency band. Their results show that, when IEEE 802.11b/g interference occurs, the throughput of IEEE 802.15.4 decreases drastically. Our experimental results presented below also highlight that the link quality in IEEE 802.15.4 standard is influenced by interference from other technologies. Experimental studies have demonstrated that there is a large transitional region (a geographical area) in the communication area of a wireless node, characterized by a significant level of unreliability and asymmetry. Therefore, in [16; 17], the authors derived the analytical expression of the packet reception rate distribution as a function of distance, as well as the location and extent of the transitional region. Their results show that the environment (path-loss exponent snf noise floor) and the hardware (hardware variance and output power) have an impact on the size of the transitional region. In this study, we used a single (and homogeneous) hardware platform. Nevertheless, our results show that, from one deployment area to another, the link quality can drastically change, due to the local environment and the precise node location. Because of the complexity of wireless sensor networks, the designers of communication protocols generally use simplifying assumptions when building their protocols. Thus, in most medium access control (MAC) or routing protocols, a common approach is to assume that the area covered by a signal emitted by a sensor \(S_{i}\) is a circle of radius \(R\), where \(R\) is the maximum communication range of node \(S_{i}\). This implies that a message transmitted by \(S_{i}\) is received by all nodes located at a distance less than or equal to \(R\) from \(S_{i}\). This implicitly assumes an isotropic communication area and symmetrical link between a couple of nodes. However, it is established that such assumptions are far from the reality [20]. Our experimental results show that asymmetric links are even more common when nodes are deployed at the ground level. In a comprehensive experimental study [14], the authors measured the quality of the radio link in two indoor and one outdoor environments. They tested the validity of several assumptions usually made in conceptual models used to theoretically evaluate communication protocols. These include the _stability_ assumption (i.e., the link quality in terms of packet reception ratio changes slowly compared to data rate), the _channel_ assumption (i.e., the link quality is the same on all frequency channels), the _spatial_ assumption (i.e., losses on different links are independent) and the _acknowledgment_ assumption (i.e., acknowledgment and packet delivery ratios are the same). Their results show that none of these assumptions holds. Focusing on outdoor deployments [15], the authors evaluated the link quality in three different environments: two tunnels (one with vehicular traffic and another without vehicular traffic) and a vineyard. Their study shows that the link quality in the tunnels is significantly different from other classical WSNs. Indeed, the authors observed that, in tunnels, links are generally stable and long-range compared to the vineyard deployment, with the tunnel behaving as a waveguide. While the experiments described in [14; 15] do not consider the scenario of ground-level deployment, an important conclusion, which we observed in our experiments as well, is the high dependence of the link quality on the deployment environment.