## 7 Simulation Results
### Simulation Results  
Figures 11 and 12 show the simulation results for the following three cases: without the proposed protocols, with the original PS-Request protocol, and with the revised PS-Request protocol. The Signal-to-Interference Ratio (SIR), denoted as \(P_{interface}\)/\(P_{interface}\). \(P_{interface}\) is the average received signal power of the interferee system, and \(P_{interface}\) is the average received interference power from the interferer system. The case without the proposed protocols is evaluated for the following six conditions: without interference (\(P_{interface}=0\) [W], which is equivalent to \(P_{interface}\)/\(P_{interface}=\infty\) [dB]), \(P_{interface}\)/\(P_{interface}=12\) [dB], \(P_{interface}\)/\(P_{interface}=9\) [dB], \(P_{interface}\)/\(P_{interface}=6\) [dB], \(P_{interface}\)/\(P_{interface}=3\) [dB], \(P_{interface}\)/\(P_{interface}=0\) [dB]. If a WiFi AP can transmit a revised PS-Request frame within a WiFi zone, there will be no mutual interference in the following WiMAX Tx ON period equal to the PSM duration of the WiFi system. That is, \(P_{interface}\)/\(P_{interface}=\infty\) [dB]. Figure 11 shows the throughput of a WiMAX system _vs._ the received _Eb_/_N\({}_{0}\)_ under interference from a WiFi system sharing the same frequency band. Cases with the proposed PS-Request protocols perform better than the case without the proposed protocols. The performance of the revised PS-Request protocol does not depend on the interference power received from the WiFi system but the received _Eb_/_N\({}_{0}\)_ of the WiMAX system, differing from the original PS-Request protocol. The revised PS-Request protocol has about 50% more throughput than the original PS-Request protocol for \(P_{WiMAX}\)/\(P_{WiFi}=0\) or 3 [dB] and \(E_{b}\)/\(N_{0}=12\) [dB] at which the throughput for the case without the proposed protocols is zero. Protecting the transmission of WiFi STAs beyond the end of the WiFi zone, as shown in Figure 10, improves performance. For smaller or zero interference environments corresponding to large \(P_{WiMAX}\)/\(P_{WiFi}\), the proposed PS-Request protocols may have worse performance, such as smaller throughput, because the allowed transmission interval for the WiFi system cannot be used to transmit data by the WiMAX system. However, for larger interference environments, corresponding to small \(P_{WiMAX}\)/\(P_{WiFi}\), the proposed PS-Request protocols can have better performance, such as relatively higher throughput. For the worst case of \(P_{WiMAX}\) = \(P_{WiFi}\) corresponding to \(P_{WiMAX}\)/\(P_{WiFi}=0\) [dB] at which the WiMAX throughput, the WiFi throughput and the sum of two throughputs for the case without the proposed protocols are zero, the revised PS-Request protocol has about 50% more WiMAX throughput than the original PS-Request protocol does. Figure 12 shows the throughput of a WiFi system _vs._ the received _Eb_/_N\({}_{0}\)_ under the interference from a WiMAX system sharing the same frequency band. The two proposed PS-Request protocols also perform better than the case without the proposed protocols. The performance of the revised PS-Request protocol outperforms the original PS-Request protocol. This also results from avoiding the overlap of the transmission time of the WiFi system and WiMAX system. The performance of the revised PS-Request protocol depends on the received _Eb_/_N\({}_{0}\)_ of the WiFi system, rather than on the interference power received from the WiMAX system. For smaller or zero interference environments, corresponding to large \(P_{WiFi}\)/\(P_{WiMAX}\), the proposed PS-Request protocols have worse performance, such as smaller throughput, because the allowed transmission interval for the WiMAX system cannot be used to transmit data by the WiFi system. However, for larger interference environments, corresponding to small \(P_{WiFi}\)/\(P_{WiMAX}\), the proposed PS-Request protocols can have better performance, such as relatively higher throughput.