## 7 Performance Evaluation of the Recommended Stack Configurations in Alternative WHAN Scenarios  
In this section, we evaluate the performance of the default protocol stack configuration and the two recommended settings that have been introduced in the last section in alternative WHAN scenarios to cover a larger variety of possible network setups. First, we introduce two alternative network topologies that differ in size and layout from the basic test scenario and evaluate the performance of the default, Recommended-Compliant and Recommended-Unrestricted settings under these topologies. Second, we repeat these evaluations in all three introduced topologies with the transmit power level 2, corresponding to a transmission power of -28.7 dBm. For this transmission power, we measured a current consumption for the transmission state of \(I_{tx}=7.3\) mA. We demonstrate that in all topologies, independent of the transmission power level, an improvement can be achieved with the two recommended protocol stack configurations. We introduce the dumbbell topology (where nodes in the central zone are likely to suffer a greater degree of congestion than in the basic topology), as well as the square topology, where there exists a smaller node degree and, thus, a lower amount of end-to-end connectivity paths, in comparison with the basic topology. Figure 23 shows the layout of the dumbbell and square topologies and the assignment of roles to nodes for different traffic scales. The roles are the same as the ones defined for the basic topology in Section 4. Figure 22: Comparison of average energy efficiency between default, Recommended-Compliant and Recommended-Unrestricted stack configurations. We extracted the percentage improvement achieved by the recommended configurations over the default ZigBee stack configuration for different topologies and different traffic scales. For brevity, the obtained results are not presented in detail as in the evaluation section of the basic topology. The detailed results, including the figures for beta and kappa at a transmission power of -28.7 dBm, can be found in [42]. We present the improvement achieved for a given topology over high traffic scale in Tables 5 and 6 for a transmission power of -33.0 dBm and -28.7 dBm, respectively. Results confirm that the recommended settings are able to augment network performance without incurring any additional traffic overhead. As shown in Table 5, the overall PDR increases slightly in the alternative topologies, while the delay and energy efficiency improve noticeably. The lower performance improvement achieved by using the recommended configurations in the alternative topologies can be explained by the fact that in these scenarios, the network congestion is low, since the amount of nodes that generate traffic is almost halved compared to the basic topology. This results in a higher stability of the routes, less packets drops and lower one-hop delays. With the default protocol stack configuration, a high PDR is obtained. Still, the improvements provided by the recommended protocol stack settings are able to increase the overall PDR further. Less APL layer retransmissions and route repairs are necessary, causing a significant decrease in the average delay and an increase in the energy efficiency. Table 6 shows the improvement over the default communication protocol stack settings of the Recommended-Compliant (Compl.) and Recommended-Unrestricted (Unrestr.) configurations for the increased transmission power setting. As for the lower transmission power, the recommended configurations again improve network performance. There is a noticeable improvement of delay  
Figure 23: (**a**) Dumbbell and (**b**) square topologies, with roles as defined for the basic scenario. and energy efficiency, while the PDR stays almost the same. We observe that by incrementing the transmission power, the connectivity of the network changes dramatically, as the radio transmission range increases noticeably and so does the number of neighbors of the nodes.