## 6 Test-Beds  
From a communication point of view, the Smart Grid is characterized by a very complex and unsteady nature. Simulators deal with this concern by using realistic-enough propagation models and (in the case of TOSSIM along with its CPM) by incorporating some key features of the real environment, such as noise pattern. However, some phenomena are difficult to reproduce and are usually simplified or even neglected. For instance, shadowing deviation is simplified by a model based on a log-normal expression whereas the adjacent-channel interference effect is simply omitted. Therefore, the only way to ensure that those phenomena do not have a major impact on the network performance is by running a set of well-controlled test-beds which will be used, in addition, to validate the results obtained by both, analysis and computer simulation. Figure 12: Packet reception ratio of SENSED-SG _vs._ non-beacon ZigBee for three different scenarios. As in the simulation study, two representative scenarios are considered in the test-beds: an electrical substation (indoor) and the SG distribution segment (outdoor). Since in an electrical substation too many elements can interfere and thus affect the results, nodes are deployed in a controlled environment: the High Voltage AC/DC laboratory of the Heriot-Watt University (Edinburgh Campus)--depicted in Figure 13. There, the topology in Figure 10 is built inside a Faraday cage where the equipment (transformers and circuit breakers among others) is energized to simulate the normal functioning of power assets and the resulting electromagnetic noise. In particular, nodes 0, 6, 7, 8 and 9 are deployed in the laboratory, placing WSN nodes close to power assets and dispatching the same amount of information as in the simulation phase as a proof of concept. As in simulations, the sensing and reporting periods are left untouched, being 5 and 15 min respectively. The packet size is fixed to 15 bytes and the transmission power of the devices is set to its default value as well. Regarding the second test-bed, the same settings as in the previous experiment are employed (same values for the sensing and reporting frequencies, packet size and transmission power) and nodes 1, 2, 3, 4 and 5 of the topology illustrated in Figure 10 are deployed in a T&D segment as a demonstration of the proper operation of our proposal in an outdoor environment. The distance between two consecutive nodes is approximately 100 m (distance between transmission poles) and the only interfering phenomenon is the electromagnetic noise generated by the distribution segment itself. Nodes are deployed on the electrical towers and, as in the former test-bed, their readings periodically requested. The PRR and the delay are continuously monitored all along the experiments to detect any deviation from the simulation results. On the other hand, power consumption depends on the protocol stack and the use of hardware resources (mainly the microcontroller and the radio interface), which are thoroughly evaluated by the Avrora simulator. Avrora simulations have been proved to be of remarkable accuracy by many works [63, 77]; however, being one of the key points of the proposed system is its long-lasting feature, we have considered that a validation of the power consumption simulation results is of  
Figure 13: Experiment setting in Heriot-Watt High-Voltage Lab. paramount importance. To this aim, the power consumption of the seventh node has been examined for an entire week. This measurement has been carried out by periodically sampling the current drawn by the WSN node from a power source. After a week we obtained a value that is 99% equal to the one predicted by the simulations--being the actual power consumption slightly lower than expected. Therefore, we consider that, in general, simulated power consumption matches the reality and therefore, the solution here proposed is, as aforementioned, of long-lasting nature.