Evaluation: Baseline scenario

Figure 4: Baseline Scenario

Figure 5: Three other scenarios.

Figure 6: Measured 5 days apart

To test the hypothesis, we performed the following experiment. We use the same settings (802.11a, full transmit power, transmission rate fixed at 6Mbps) that we used in Section 4 and consider the same 75 link pairs as shown in Figure 2. To minimize the impact of environmental factors, the broadcast experiments designed to measure $BIR$ were performed just before the unicast experiments designed to measure $LIR$. The median values of $BIR$ and $LIR$ for each link pair are shown in Figure 3. We see that $BIR$ matches $LIR$ well in most cases. The CDF of the absolute error ($\vert LIR-BIR\vert$) is shown in Figure 4. The median of absolute error is zero, and the mean is 0.026. Given that $\vert LIR-BIR\vert$ can range from 0 to 1, the mean and the median are quite low. Thus, our methodology works quite well in this scenario.

These results bring up several interesting questions. First, does the methodology work for other scenarios? Second, note that we carried out the broadcast and the unicast experiments back-to-back. In reality, we must do all the broadcast experiments together, and then use the results to predict link interference. The question then becomes: if we do broadcast experiments separately, will $BIR$ obtained at some point in time still match $LIR$ observed at some later point? Third, is the model capable of telling us why two links interfere? We discuss these questions next.