# Interference-Robust Transmission in Wireless Sensor Networks
## 5 Performance Evaluation
It can be seen that the normalized throughput and the optimum transmission time are quite affected by the channel occupancy of the interference signal, but little by the transmission rate. Note that the data throughput and the optimum payload size depend on the transmission rate. This property makes it desirable to adjust the transmission time according to the interference condition and the transmission rate according to the channel condition. Figure 5: Energy consumption according to the payload size. Figure 6: Normalized throughput according to the transmission time. Figure 7 depicts the data throughput according to the channel occupancy of the interference signal when the SNR is 8 dB and the maximum Doppler frequency is 0.1 Hz, where the IEEE 802.15.4 baseline and DRACER use a fixed payload size of 300 or 1000 bytes, DPLC uses an initial payload size of 300 or 1000 bytes and adjusts it according to the performance and Seda, HiFrag and GreenFrag use their own frame structure proposed in their works, whereas the proposed scheme determines the initial payload size by estimating the average idle period of interference and then adjusts it according to the throughput performance. It can be seen that the IEEE 802.15.4 baseline provides very poor throughput performance even with the use of a large payload size (i.e., 300 or 1000 bytes) mainly due to the use of a low fixed transmission rate. It can also be seen that DRACER can improve the throughput performance by adjusting the transmission rate, but it may suffer from performance degradation with the use of a small fixed payload size in the absence of interference, which is mainly due to the transmission inefficiency, or with the use of a large fixed payload size in the presence of interference, which is mainly due to the increase of packet collision. We consider two DRACER schemes; DRACER I, which transmits packets at the highest rate regardless of transmission failure, and DRACER II, which adjusts the transmission rate in response to transmission failure. It was reported that these schemes are effective in an interference and a channel fading environment, respectively [22]. However, it can be seen that DRACER I and II make little difference on the transmission performance. This is mainly because they do not consider the effect of the payload size in the presence of interference, yielding inefficient use of white space. It can also be seen that DPLC can little improve the throughput performance even with the use of DRACER. This is mainly because it does not consider the effect of the transmission rate adjustment with a fixed step size of 10 bytes regardless of the transmission rate [23], yielding inefficient use of white space and slow adaptation of the payload size. It can also be seen that the proposed scheme significantly outperforms the other schemes by adjusting both the transmission rate and the transmission time in response to the change of interference and channel condition. It can also be seen that the PPR schemes (i.e., Seda, HiFrag and GreenFrag) may provide throughput improvement over the IEEE 802.15.4 baseline in the presence of co-channel interference. This is mainly because they partition the data packet into a number of small blocks and adapt the block size based on the transmission performance, which may provide robustness to co-channel interference. It can also be seen that they may outperform DPLC, which is mainly due to fast adaptation of the block size. However, PPR schemes may severely suffer from the presence of co-channel interference, mainly due to the frequent loss of recovery frames. It can also be seen that their performances are limited mainly due to the use of a low fixed transmission rate, fixed frame structure and small maximum payload size. It may not be easy for the PPR schemes to increase the maximum payload size and the transmission rate since the computational complexity may considerably increase as the number of blocks for the packet partitioning increases. Figure 8 depicts the throughput according to the SNR when \(\rho=0\) and 0.2.