# Secure Inter-Frame Space Communications for Wireless LANs
## 4 Performance Evaluation  
As shown in Section 3, a radar signal consists of a train of pulses that typically have a short pulse width and narrow frequency band. That is, a transmitted radar signal is a simple sinusoidal wave modulated by On-Off keying or OOK. In this case, the important design aspect is to control the timings of pulses and bursts. To test several different types of radar signal pulses, it is important to set the signal parameters, such as PRF, pulse width, and burst period, as input parameters so that the simulator can change them easily. Figure 4 shows the block diagram of the radar transmitter. With the input signal parameters set by a user, the signal power, frequency, and phase are computed and then fed into the sinusoidal generator. On the other hand, the timings of the pulse train are computed with counters, burst counter, and pulse counter. The pulse ON signal enables the sinusoidal wave generator to output the radar signal pulses. The channel is assumed static throughout a burst and generated independently for each burst. The impulse response of the channel is composed of complex samples with randomly distributed phase and Rayleigh distributed magnitude with the average power decaying exponentially. In the simulation model, the WLAN data sender and receiver, which have the proposed radar detector and secure inter-frame space communications system at 5 GHz, are modeled in the C programming language. Figure 4: Block diagram of the radar transmitter. A periodic interference detection algorithm has been designed and implemented. The designed algorithm utilizes the periodic property of the interferences. To do this, the periodic interference detector first measures the received signal power averaged over a moving window. The decision is saved in a shift register to cover a period of interference detection. The count of the decisions is compared with a threshold again. The final decision is delayed to see if the received signal is a valid packet. The detection of the periodic interference is with PHY, while the decision bit stream is passed to the MAC layer. The MAC layer transforms the one-bit stream into a 32-bit time stamp driven by signal detection activation. The transformed time stamps are stored and the upper layer fetches this information to search the periodic interference patterns. Finally, WLAN factors are considered to decide the presence of the periodic interferences. Periodic interference detection is not only a power detection problem, but also a network problem in the WLAN stations. The nodes and access point should cooperate together to detect the periodic interferences. Figure 5 demonstrates the improved detection performance of the proposed detection scheme, and Figure 6 shows the improved maximum user datagram protocol (UDP) throughput. The simulation model was built on the bit- and cycle-accurate C simulator which is the same model used for the implemented commercial chipset and was certified through standard Wi-Fi certification process. In Figures 5 and 6, \"PRO\" and \"CON\" refer to the proposed scheme and conventional scheme, respectively. Ten thousand radar samples were used for this test. \"W\" and \"P\" refer to pulse width and periodicity of radar signals, respectively. As a result, shorter pulse width and periodicity result in performance degradation due to the limited resolution of the detector. However, the proposed scheme outperformed for test scenarios. In Figure 6, W50-P2000 was much better than W50-P500 because short periodicity increased the interfered duration. However, all the cases of the proposed scheme outperformed when compared with the conventional scheme. In conventional WLAN systems, once a periodic interference signal is detected within the basic service set either by an access point or station, they must follow the rule to escape the channel and search another clearer channel. The channel search can also be done by all stations as well as access points. The searched results are gathered at the access point.