# Challenges in Wireless System Integration as Enablers for Indoor Context Aware Environments
## 3 Wireless Sensor Network Radioelectric Analysis
#### Total Surface of Test Scenario: 216 \(m^{2}\)
In order to gain insight on the effect of node density variation, linear received power level distributions have been compared and are shown in Figure 7. As it can be seen, average power levels exhibit a variation in the order of 20 dB between the low density cases (i.e., seven nodes/scenario)  
Figure 6: Estimation of received power levels, non-uniform distribution, for a frequency of 2.4 GHz, at bidimensional planes at a height of 0.5 m and 2 m, respectively. and the high density cases (108 nodes/scenario). In the vicinity of transmitter nodes, all power level profiles converge, given that nodes transmit at nominal output power. It is worth noting that the average received power level estimations can also be seen as the equivalent noise level (in terms of intra-system, i.e., users within the same network or inter-system if they are in different networks), which increase as the number of nodes increase. Therefore, in terms of coverage analysis, results improve as the number of nodes increases and in terms of system performance, the equivalent noise floor rise must be considered in order not to degrade potential communication links. Estimations have also been obtained for the case of using a frequency of 5.8 GHz. The change in frequency implies higher attenuation given the use of a smaller wavelength, which can be seen in the results presented in Figures 8-10 for the case of uniform network layout, with variable node density values. Power distribution is also different within the bi-dimensional planes, given the fact that wave/obstacle interaction is also modified within the ray launching scheme, given once again by the geometrical changes inherent to smaller operational wavelength. Figure 8: Estimation of received power levels, for a frequency of 5.8 GHz, for a scenario with 7 nodes and 27 nodes, at bi-dimensional planes at a height of 0.5 m and 2 m, respectively. Figure 9: Estimation of received power levels, for a frequency of 5.8 GHz, for a scenario with 54 nodes and 108 nodes, at bi-dimensional planes at a height of 0.5 m and 2 m, respectively. Non-uniform random distributions of transceivers have also been considered for the case of 5.8 GHz, depicted in Figure 11. As with the uniform cases, received power levels are lower, which modifies link balance levels as well potential interference values (intra-system interference contribution, mainly). Provided that due to lower transceiver count in the case of random node sets employed and higher path losses within the 5.8 GHz frequency band, hot-spot identification is also less defined. Figure 3:0 _Cont._  
Figure 3:1 Estimation of received power levels, for a frequency of 5.8 GHz, for the case of ad-hoc wearable transceiver configuration. In order to highlight the impact of frequency selection within the 2.4 GHz and 5.8 GHz frequency bands, different received power levels have been depicted in Figure 3:2 As expected, there is a power offset between both frequency bands, owing to inherently higher losses due to frequency increase in the range of 5 dB. The average power levels can be considered as interference level background when performing system level analysis. Therefore, frequency band selection must take into account not only coverage restrictions but also potential noise floor rise given by interference, which impacts on overall system performance. System performance is limited by coverage/capacity relation and hence, precise power level distribution estimations play a key role in QoS analysis. Another relevant parameter to consider is the impact of time-dependent elements, given by multipath propagation and which determine fast fading components. Figure 13 represents bi-dimensional distributions of delay spread (i.e., difference between first and last field component detected at a given transceiver location), considering different potential transceiver nodes.