# A Lifetime Maximization Relay Selection Scheme in Wireless Body Area Networks
## 6 Performance Evaluation
### Simulation Setup  
We have conducted simulations based on C++ platform. The WBAN in the simulation consists of one coordinator and 16 sensor nodes. Considering that sensor node executing a certain sensing task may not be always deployed at the same position but in a designated area, in order to show generality of sensor node deployment, we classify the human body into six parts in the simulations as shown in Figure 1, which contains head part, main body part, left/right arm part and left/right leg part. The range values of each part are measured from a male human body whose height is 175 cm. In the simulations, we deploy six sensor nodes in main body part and two sensor nodes for every other parts. Sensor nodes are randomly deployed in the parts where they belong. Considering the possible implanted sensors or sensor nodes deployed in the backside of human body, we set the ratio of implanted/back side sensors to the total sensor nodes in the network to 25%.  
The node distribution is decided based on the functionality each part contains referring to the general application scenarios for WBAN, where we sort that the main body part is responsible for tissue monitoring sensing like electrocardiogram (ECG) and capsule endoscope, positioning sensing, motion detection and drug delivery, arm parts for blood oxygen and glucose sensors, leg parts for lactic acid sensing, pressure sensing and, if possible, artificial support and head part for electroencephalogram (EEG) sensing. In addition, accelerator nodes can be deployed in all six parts. On the other hand, the main body part is physically more stable than other parts, so, in reality, functional sensor nodes that can be put either in the main body part or other parts are preferred to be deployed in the main body part. As a result, in the simulation scenario, we deploy more sensor nodes in the main body part since its physical stability and the fact that it contains more kinds of functional sensor nodes than other parts. The detailed information for node distribution and body parts are listed in Table 1.  
Each sensor node generates a fixed-size packet of \(k\) bits in one superframe. In the simulation, we set \(k\) as 1200 bits, which is a typical frame length in WBAN communication according to IEEE 802.15.6 [8]. In addition, we adopt 128 kbps as the transmission rate specified in the IEEE 802.15.6. Depending on this, slot length is set to 10 ms. One superframe contains 65 transmission slots and its duration is set to be 700 ms considering the beacon frame transmission slot, which is in the available range described in IEEE 802.15.6 as well.  
We adopt the parameter values in the Nordic nRF2401 low power single chip transceiver (Oslo, Skoyen, Norway), which is widely used in sensor node communication as the energy consumption parameters in Equations (1) and (2). The value of \(n\) is set to be 3.38 when the channel between transmitter and receiver is LOS (line-of-sight) and 5.9 when channel is NLOS (non-line-of-sight). The values of \(n\) are adopted from the measurement campaign in [29] and widely used in the WBAN-related literature [21; 27; 28; 30; 31]. That is, in Figure 1, the front side sensors get LOS channels with the coordinator while the back side or implanted sensors get NLOS channels with the coordinator. Mean value \(\mu\) for the energy storage distribution is set to 2 J, and we set a 50% offset from the mean value as the upper and lower bound (\(\Delta=1\) J) for the distribution.  
When the first sensor node in the WBAN runs out, the simulation stops. The simulation runs for 1000 times, and the averaged results are taken. The system parameters used in the simulation are summarized in Table 2.