# Patient Mobility Support for Indoor Non-Directed Optical Body Area Networks
## 5 Experiments and Results
### Results and Discussion  
Figure 11 shows the experiment results of the proposed mobility scenarios expressed in terms of BER. The average transmission distance is the vertical distance measured from the chest of the patient  
Figure 10: Experiments: (**a**) Mobility scenario 1. (**b**) Mobility scenario 2. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline Room dimensions (x, y, z) & 5 m \(\times\) 5 m \(\times\) 3 m \\ Number of LEDs & 2 \\ Optical output power of each LED & 20 mW \\ Reflection coefficient & 0.8 \\ Physical area of the photodetector & 1.0 cm\({}^{2}\) \\ Field of view (FOV) & 70\({}^{\circ}\) \\ Semi angle at half power & 50\({}^{\circ}\) \\ Responsivity & 1 A/W \\ Speed of the patient & 0.5 m/s \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Experiment parameters. to the PD at the ceiling. We performed several experiments by varying distances at a range of 0 to 200 cm. For a relatively short distance of up to 120 cm, the system achieved error-free transmission. The performance of the first mobility scenario achieved a BER value of 1.6 \(\times\) 10\({}^{-6}\) at 125 cm. The performance of the second scenario achieved a BER value of 0.1 \(\times\) 10\({}^{-4}\). The system performance was degraded when the distance between the transmitter and receiver increased. The performance was significantly affected if the transmission distance was greater than 1.5 m. This was because the ambient light from the environment interfered with the received signal. The ambient light was the indoor artificial lights for illumination purposes. Since the experiment was performed in a typical indoor lighting environment to emulate practical working conditions, the received signal cannot be identified easily due to the wideband ambient light. To analyze the effect of ambient light, we measured the light intensity at an accuracy level of \(\pm\)0.5 lux with a sampling period of 1 s. The measured light intensities were 1000 and 200 lux at distances of 25 cm and 200 cm, respectively. The transmission distance can be increased by increasing the output power of the LED or dimming the environment. From the above two scenarios, it is clearly seen that the coordinator at the shoulder (scenario 1) shows a reliable data transmission with efficient patient mobility and hence it is found to be an optimum position for the coordinator on the patient body. As part of further evaluation, we continued to perform experiments for the third scenario to analyze the effect of transmit diversity. Figure 11 shows the BER performance of transmit diversity. In this diversity technique, the transmission was carried out with two transmitters and a single receiver. The monitoring ECG data was transmitted from the transmitters fixed at the shoulder and wrist part of the patient body. The BER value at a distance of 120 cm was found to be 1.2 \(\times\) 10\({}^{-6}\). Thus, the performance of the transmit diversity outperforms mobility scenarios 1 and 2. From the results, it is apparent that the average system performance was improved. Hence, the diversity improved the overall system performances, particularly at large distances. The performance mainly depends upon the distance between the transmitter and receiver, the reflectivity of the wall surfaces, the responsivity of the receiver, the orientation of the coordinator, and indoor ambient light sources. In the proposed work, it should be noted that we employed the adaptive threshold method to extract the received signals more precisely. It is aimed at excluding false data in the reconstructed signal. In addition, the threshold selection was strongly dependent on the ambient noise in the indoor environment. We have developed this mobility model for a single patient analysis. This  
Figure 11: Performance analysis: BER versus transmission distance. idea can be further extended for the multiple-patient mobility, considering advanced interference mitigation techniques.