# Interference-Robust Transmission in Wireless Sensor Networks
## 5 Performance Evaluation
Since DPLC does not provide noticeable performance improvement over the IEEE 802.15.4 baseline and DRACER, we hereafter consider the performances of the IEEE 802.15.4 baseline and DRACER for the clarity of description. It can be seen that DRACER can improve the performance of the IEEE 802.15.4 baseline by using a large payload size in the absence of interference and a small payload size in the presence of interference. However, there is no proposed strategy when to employ DRACER I and II and how to adjust the payload size together in the presence of interference and channel fading. It can also be seen that the proposed scheme can significantly improve the throughput performance by independently adjusting the transmission rate and the transmission time according to the interference characteristics and channel condition, respectively. It can be seen that GreenFrag provides poorer throughput performance than HiFrag, although GreenFrag is a combination of HiFrag and transmit power adaptation, where it uses a transmit power level of 0, \(-\)3, \(-\)7, \(-\)15 or \(-\)25 dBm. When GreenFrag confirms good transmission performance, it reduces the transmit power without consideration of the channel condition. This may cause a ping-pong effect, seriously deteriorating the throughput performance. In fact, GreenFrag may not work well unless the SNR is sufficiently high (e.g., \(>\)30 dB). Figure 7: Throughput according to the change of interference. (**a**) When \(L=300\) bytes; (**b**) When \(L=1000\) bytes. Figure 9 depicts the energy consumption (in uJoule/bit) according to the SNR when \(\rho=0\) and 0.2. The power consumption of GreenFrag is measured at various power levels [28]. It can be seen that the power consumption increases when the SNR decreases or the channel occupancy of the interference signal increases, which is mainly due to the increase of transmission failure. It can also be seen that the proposed scheme reduces the power consumption by adjusting the transmission rate and the transmission time. However, the gain in power consumption is somewhat marginal. It is mainly because the use of a larger payload size in the absence of interference may increase the data throughput and the average power consumption, as well. Figure 8: Throughput according to the SNR. (**a**) When \(\rho=0\); (**b**) When \(\rho=0.2\). Table 2 summarizes the transmission delay according to the SNR when \(\rho=0\) and 0.2, where \(T_{\text{period}}=983.04\,\text{ms}\), \(T_{\text{comm}}=0.5\)\(T_{\text{period}}\) and \(L_{\text{bulk}}=65\,\text{Kbytes}\). It can be seen that the transmission delay decreases when the SNR increases or the channel occupancy of the interference signal decreases, which is mainly due to the increase of the data throughput. It can also be seen that the proposed scheme and DRACER significantly outperform the other schemes, which is mainly due to the transmission rate adjustment. It can also be seen that the proposed scheme can reduce the transmission delay further than DRACER both in the absence and the presence of interference. This is mainly because the proposed scheme can adjust both the transmission rate and the payload size to maximize the data throughput in response to the change of operation environments. Figure 9: Energy consumption according to the SNR. (**a**) When \(\rho=0\); (**b**) When \(\rho=0.2\). Figure 10b,c depicts the throughput in the presence of the interference signal with \(\rho=0.2\) and a mobility of 3 km/h, as illustrated in Figure 10a, where the SNR slowly changes with a value of 35\(\sim\)40 dB, but the SINR changes from \(-20\) to 20 dB when the maximum transmission rate is limited to 2 Mbps and 250 Kbps, respectively. Figure 10b depicts the performance of the proposed scheme and DRACER since they outperform the other schemes. It can be seen that DRACER I outperforms DRACER II, which is mainly because it keeps the highest rate indifferently from the transmission failure.