## 2 Indoor Scenario Simulation and Characterization
On the other hand, a failed communication could happen with intra-system interference in some case, although it is nearly the worst case possible: transmitting at maximum data rate and the interfering devices transmitting at highest power level (0 dBm). Under these conditions, the communication is viable only when the transmission power level is 0 dBm or \(-2\) dBm. Therefore, our simulation tool can help estimating the SNR value at each point of the scenario, allowing the designer making the correct decision in order to deploy the devices and configuring them in an energy-efficient way. In terms of SNR, the selected configuration could not be as suitable as some preliminary tested scenarios. Continuing with the examples shown in Figure 4 where three and four antennas are considered, the SNR levels are higher since more antennas suppose more intra-system noise. In Figure 10 the approximation of the range that can be covered until the \(-10\)dB SNR threshold is reached with the three different configurations is shown. In this figure it is considered that antenna 5 or 7 is emitting and that the rest of antennas are noise. As it is visible when the three antenna configuration is employed, the area where SNR is acceptable is larger than in other cases. Moreover, since more antennas are placed next to the 7 th antenna in the definitive configuration, the SNR area is smaller than when antenna #5 is transmitting. Note that in the real system the power received from at least one of the transmitters must be considered as valid information and not as noise/interference. In fact, according with the represented circles in some cases the noise level is too high to allow a correct data transmission. These variations in noise floor levels can be given by variations in the density of mobile transceivers (_i.e._, mobile users in the vicinity of the transmitter antennas within the scenario), which must be determined empirically. Nevertheless, as it is visible in Figure 9 and in the experimental results presented later on, the communication between devices is feasible in the finally chosen configuration. It is worth noting that a full description of the received levels in terms of desired transmit signals and potential interferers (which can be intra-system, inter-system or background interference) is obtained and computed. The use of 3D Ray Launching is an adequate tradeoff between computational complexity and precision, leading to error minimization and hence to an optimal network configuration in a lower time frame within the design process. Figure 4:0 Approach to the maximum emitting distance for three configurations of antennas according to \(-10\)dB SNR threshold considering that 5 th (**Left**) or 7 th (**Right**) antenna is emitting. As it is previously mentioned, the main propagation mechanism present in an indoor scenario with topological complexity is the multipath propagation, due to the strong presence of reflections, diffractions and refractions of the transmitted RF signals. The relevance of multipath propagation can be determined by estimating the values of all reflected components within the coherence bandwidth, given by the power delay profile and the delay spread. In Figure 11 the delay spread when antenna 3 is emitting is calculated, for a cut plane located at a height of 1 m. A larger time span can be seen in the center of the figure, due to the location of the antenna and consequently where higher power is observed. Therefore, the ricochets caused by the walls next to this point are more powerful and there are more probabilities for them to cross central points. Since the system under analysis is based on ZigBee technology, the consumption of the deployed motes becomes essential in radio planning strategies. As seen previously, the location of the mote within the scenario has a significant impact in terms of the received power, which itself has a great impact on the power consumption of the transmitting devices, as the link balance varies.