## 3 Performance Evaluation
### On-Body Access Point Network Architecture  
Eight EDs were placed on a 170 cm, 70 kg male subject as shown in Figure 1. The host computer was carried in a backpack and connected to the AP via a USB cable. For both simulation and hardware experiments, the target RSSI (\(RSSI_{T}\)) was arbitrarily chosen to be \(-60\) dBm to support a large dynamic range of power consumption. The positioning of EDs and AP on the body along with link-cost notation is depicted in Figure 1.  
The experimental setup was used to implement the routing algorithm in real-time in response to the changing channel conditions using various values of \(M\). The subject walked around a room depicted in Figure 2, while the following procedure was carried out at a rate of 5 Hz:  
Figure 1: Experimental setup for network architecture with access point on the body. Note that only neighboring nodes network connections are depicted for clarity of presentation.  
1. The AP sends a synchronization beacon which includes routing and power control tables.
2. Each ED transmits its own RSSI table back to the AP, while simultaneously listening to other ED messages and storing the received power from each.
3. Once all EDs have transmitted their data, the AP transfers a table with the RSSI data from all devices to the host, see Table 1 for an example.
4. The host uses the RSSI table to compute the routes along with the required powers to meet the selected links using [PERSON]'s algorithm and the link costs depicted in Equations (1)-(3).
5. The host sends both routing and power tables back to the AP so that a new cycle may begin.  
\begin{table}
\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|} \cline{2-11} \multicolumn{1}{c|}{} & **AP** & **ED1** & **ED2** & **ED3** & **ED4** & **ED5** & **ED6** & **ED7** & **ED8** \\ \hline
**AP** & – & \(-60\) & \(-60\) & \(-60\) & \(-60\) & \(-60.5\) & \(-60.5\) & \(-60\) & \(-79.5\) \\
**ED1** & \(-66\) & – & \(-62\) & \(-75\) & \(-63.5\) & \(-69\) & \(-75.5\) & \(-73\) & \(-67.5\) \\
**ED2** & \(-72\) & \(-61.5\) & – & \(-80\) & \(-69\) & \(-70\) & \(-74\) & \(-75\) & \(-66\) \\
**ED3** & \(-77.5\) & \(-74.5\) & \(-80.5\) & – & \(-67.5\) & \(-70\) & \(-72.5\) & \(-70.5\) & \(-70\) \\
**ED4** & \(-39\) & \(-63\) & \(-69.5\) & \(-67\) & – & \(-82.5\) & \(-74.5\) & \(-69\) & \(-65.5\) \\
**ED5** & \(-67.5\) & \(-68\) & \(-71\) & \(-69.5\) & \(-84\) & – & \(-55.5\) & \(-51.5\) & \(-62\) \\
**ED6** & \(-67\) & \(-75\) & \(-75\) & \(-72.5\) & \(-75\) & \(-55.5\) & – & \(-44.5\) & \(-53\) \\
**ED7** & \(-46\) & \(-70\) & \(-77.5\) & \(-70.5\) & \(-69\) & \(-50.5\) & \(-45\) & – & \(-51.5\) \\
**ED8** & \(-78\) & \(-67.5\) & \(-66.5\) & \(-71\) & \(-66\) & \(-62\) & \(-54\) & \(-51.5\) & – \\ \hline \end{tabular}
\end{table}
Table 1: Sample RSSI Table at the AP.  
Figure 2: Experimental setup environment for network architecture with access point on the body.  
To minimize the number of control packets being transmitted, the EDs are not individually polled. The only control packet sent is the synchronization beacon, which also carries the routing and power tables. Once the EDs are synchronized, they transmit their data on a pre-defined schedule to avoid collisions. Each ED has a network ID. The time between synchronization packets is divided into time-slots, where each slot is used by a single ED. The time slot used depends on the network ID of each device. This avoids the need for scheduling during runtime.  
The routing table is a simple array which lists the destination for each ED packet. The ED does not need to know the entire route its packets will take, but only the next device in the path. Similarly, the power table lists the transmission power setting each device needs to use. The size of these tables is directly proportional to the number of devices in the network.