# Challenges in Wireless System Integration as Enablers for Indoor Context Aware Environments
## 3 Wireless Sensor Network Radioelectric Analysis
#### Total Surface of Test Scenario: 216 \(m^{2}\)
This fact has also a direct impact in terms of overall interference values, which is a key point in system level analysis, as transmitted power from those nodes that are not in the established communication link contribute as intra-system or inter-system interference, leading to system performance degradation, as will be shown later on in Section 4. In the case of Context Aware scenarios, on-body transceivers corresponding to wearables can also be operating, independently or in a collaborative scheme with other transceivers. To take into  
Figure 4: Estimation of received power levels, for an operating frequency of 2.4 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. account these cases, a sub-network of wearable devices has also been implemented and simulated. The results are depicted in Figure 5. In this case, the 2D distributions of received power levels show that hot spot identification is more apparent in the case of a cut-plane height of 0.5 m. This condition is given by the fact that wearables have been located within the upper half of a conventional human body model (e.g., consideration of wrist-worn devices). An additional consequence of employing wearable transceivers is the existence of hot-spots in the vicinity of each wearable node. This fact is relevant in terms of potential interference generated by these nodes, which is time-dependent and will affect infrastructure nodes as well as other users (non-wearable as well as wearable nodes). Therefore, simplified received power estimations, considering average losses owing to transceiver typology (i.e., infrastructure, mobile, wearable) provides limited insight both in terms of received power level compared with required receiver sensitivity or overall interference. The previous results have been obtained by deploying a uniform set of transceivers within the scenario. In order to provide more realistic cases (mainly considering time dependent links, such as mobile terminals provided by users) non uniform distributions have also been considered. A test case with a total of 10 transceivers has been considered, in order to clearly visualize topological differences in relation with the different configurations. In this case, a higher level of spatial sparseness aids in the process of discriminating the different cases. The following transceivers have been used (obtained by random number generator outputs), forming a subset of elements from the initial complete set given by the uniform network of highest density:  
* Random Transceiver Set1: 15, 22, 36, 46, 59, 64, 68, 82, 88, 104. * Random Transceiver Set2: 5, 8, 29, 32, 43, 46, 65, 92, 98, 105. * Random Transceiver Set3: 21, 25, 26, 39, 55, 69, 78, 83, 98, 108. The results for the three random transceiver sets are depicted in Figure 6, for different cut plane heights (0.5 m and 2 m, respectively). As expected, variations in power distribution profiles are larger than in the uniform case. Even though the number of transceiver is the same, power distribution levels are considerably different, since both non-line of sight and line of sight schemes can be emphasized, given the relative distance between nodes for each of the transceiver sets. In the case of random distributions depicted, non-uniformity can give rise to high node concentration, leading to the location of hot-spots within the scenario. Two of these hot-spots can be identified in Figure 5, for a cut-plane height of 0.5 m, in which power distribution profiles are considerably different than in the uniform cases previously described. These hot-spots can strongly degrade system performance, as signal to  
Figure 5: Estimation of received power levels, for an operating frequency of 2.4 GHz, for the case of ad-hoc wearable transceiver configuration. noise ratios tend to decrease significantly as node density increases, with spatial power deviation in the order of 10-20 dB for distances within conventional transceiver link operation.