# BNS: A Framework for Wireless Body Area Network Realistic Simulations
## 4 Use Cases
### Analysis of Channel Access Mechanisms  
In the MAC layer of the WBAN standard, the use of the TDMA and CSMA/CA mechanisms are accepted, for data transmission at the scheduled intervals and random access, respectively. In this use case, a comparison of the performance of a WBAN using Time Division Multiple Access (TDMA) and CSMA/CA techniques is presented. For this comparison, a WBAN scenario with 12 health devices distributed in the human body was simulated. The positions of the nodes are represented in Figure 12 and in Table 3 the health devices and their data transmission rates are described. Figure 11: Temperature variation of the nodes. Node 1 acting as transmitter. (**a**) Using FRAR protocol; (**b**) using LAOR protocol; (**c**) using LATOR protocol. Figure 12: WBAN topology with 12 nodes. The application QoS requirements used in this scenario are of intelligent health applications [49; 50] and the dynamics of the application's data flow is based on the unconfirmed mode of the ISO/IEEE 11073 standard available in the Healthcare Application Layer of the proposed BNS framework. The nodes were in walking motion for 10 min of simulation. To simulate the mobility of the human body, the MoBAN proposed module was used, and the behavior of the channel was modeled using the Goswami wireless channel. In the PHY layer, the radios have a transmission power of \(-15\) dBm and the transmission rate used is the maximum allowed for a radio compatible with the standard NB-PHY, 1024 kb/s. In the MAC layer, the slot allocation time is used as a minimum value for IEEE 802.15.6 NB-PHY, which is 1 ms. Each node when joining the network requests 4 slots for transmission. As for the size of the superframe, 32 allocation slots were made available. Therefore, the time between beacons, i.e., the expected duration of a superframe is 92 ms. The metrics observed are the PDR of the application and the energy used to transmit a bit from the application (\(\upmu\)/bit). The results shown have a 95% confidence interval for ten simulation rounds. The results of the application PDR per node are represented in Figure 13. Figure 13a contains the results for the nodes positioned on the head, chest and upper limbs, whereas the results of Figure 13b are of the nodes in the waist and lower limbs. The PDR of lower limbs are inferior to those of the upper limbs, given the distance and the pendulum movement of the legs during walking, which increases the path loss when there is no line-of-sight to the hub. Another interesting fact is the synchronization of movements between the right arm/left leg and left arm/right leg, natural during the walking motion. This synchronized movement plays an important role in the wireless channel response, with nodes in the left leg having a better reception rate than the nodes in the right one, given the interference of nodes near the hub. Additionally, the TDMA scheduling and the pendulum movement cycle can influence the PDR, and proper transmission scheduling can take advantage of that periodic behavior [4]. The smaller interference of nodes in the right arm and a better transmission scheduling can be observed in Node 8, even though it is placed in an inferior limb, it has a high PDR. In this scenario we can highlight that the average PDR using TDMA is superior to using CSMA/CA, and considering the error margin, they have similar results. Another interesting fact is that for node 6, which is closer to the hub, CSMA/CA results are superior, therefore under good channel conditions CSMA/CA can improve the network throughput. The overall network PDR results were \(86.54\pm 2.58\%\) for TDMA, and \(83.86\pm 3.43\) for CSMA/CA.