# Implementation of Context Aware e-Health Environments Based on Social Sensor Networks
## 4 Characterization and Impact of Wireless Channel Behavior
Real antennas have been considered for simulation, taking into account their radiation diagram pattern, polarization, transceivers gain, and transmitted power. The simulation parameters are shown in Table 2.  
Figure 9 shows simulation results for Transmitters 1 and 2. It shows the bi-dimensional planes of received power for the receiver antenna height (1 m). It should be pointed out that Transmitter 1 was collocated on the table and the Transmitter 2 was on-body, specifically in the chest. The radio channel complexity in both planes can be observed. On the one hand, in the case of Transmitter 1, there is a higher influence of the surface of the table in the received values, and, on the other hand, in the case of Transmitter 2, a great impact of the person is observed due to the scattering originated for the position of the antenna in the chest of the person. In addition, the influence of walls and furniture in the environment is also represented. Due to the use of transceiver elements employing Bluetooth communication, intra-system interference is not a relevant issue in the present case, due to inherent interference control in channel access of transmitters within the network. In any case, it is compulsory to meet with receiver sensitivity levels in order to guarantee adequate service as a function of transmission bit rate. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Parameters in the Ray Launching Simulation**} \\ \hline Frequency & 2.43 GHz \\ Transmitter power & 0 dBm \\ Antenna gain & \(-1\) dBi \\ Horizontal plane angle resolution (\(\Delta\Phi\)) & \(1^{\circ}\) \\ Vertical plane angle resolution (\(\Delta\Theta\)) & \(1^{\circ}\) \\ Reflections & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation transmitter antenna characteristics. Figure 9: Bi-dimensional planes of Received Power (dBm) for the receiver antenna height (1 m) for two different transmitting cases, Transmitters 1 and 2. As can be seen in Figure 9, the impact of multipath propagation in the environment is highly important. In order to represent this effect, the Power Delay Profiles (PDPs) in the receiver point for two different positions of the person have been depicted. Figure 10 represents the PDPs for Position 1 (green person in Figure 8) and Position 2 (black person in Figure 8) for both positions of the transmitter, above the table and on-body. It can be seen that multipath behavior is absolutely vital in this type of environment. Furthermore, not only does the position of the antenna (on-body or above a surface) have a great impact in electromagnetic propagation, but also the distance between transceivers: in the case of Position 2, there are higher values of multipath received values. The delay spread can be a good indicator of the propagation dispersion when the complexity of the scenario is elevated. In Figure 11, a Delay Spread map is depicted for the case of Transmitters 1 and 2. Higher delays are visible nearby the transmitter antenna. This is due to the fact that higher values of power are received in these points and the contribution of the reflections is higher. Nevertheless, there are some critical points such as corners or around some obstacles where the delay spread could be elevated depending on the morphology of the environment. This is the reason why the Delay Spread and Power distribution changes completely when the position of the transmitter antenna changes. The impact of delay spread variation to end-user operation is given by the fact that larger fast fading losses can decrease overall received signal levels, with values below sensitivity thresholds and hence with large error rates. Moreover, reception of multiple propagation components increases bit error rate, given mainly by Inter Symbol Interference. In the case of Bluetooth transmitters, effective transmission bit rates are low compared to operation bandwidth, implying that conventional channel equalization techniques can be employed to mitigate potential information degradation.