# Spectrum Awareness for Cognitive Radios Supported by Radio Environment Maps: Zonal Approach +
## 5 Analysis of the Results
The following notation was applied for the calculated difference for each control point:  
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Zone** & **Point** & \multicolumn{8}{c}{**Difference between Interpolated and True Values [dB]**} & \multicolumn{2}{c}{**True**} \\
**ID** & **ID** & **IDW p1** & **IDW p2** & **IDW p3** & **IDW p4** & **IDW p5** & **IDW p6** & **Kriging** & **NN** & **[dB]** \\ \hline \multirow{6}{*}{\(1\)} & P3 & -5.6 & -4.6 & -2.7 & -3.1 & -1.1 & -2.7 & -7.6 & -4.9 & -77.9 \\ \cline{2-11}  & P5 & 0.1 & -3.6 & -10.1 & -2.1 & -15.2 & -10.9  
The results for the scenario with 26 control points are given in Table 3. It may be easily noticed that the biggest number of CEPs appeared for NN (12) and for Kriging (11), so these methods may be considered as promising for REM. For NN method 6, UEPs and 8 OEPs occurred while for Kriging 5 UEPs and 10 OEPs. As the smallest number of CEPs occurred for IDW p1 (3) and IDW p2 (4), these methods can be discarded in further analysis. For the remaining IDW methods the number of CEPs amounted from 7 to 9. The above comparison showed that there were three control points (P5, P17, P35) for which all the methods overestimated the signal level. On the other hand, for P37, all the methods underestimated the signal value. There were two control points for which only one method gave the correct signal value, namely IDW p1 for P18 and NN for P33, while for the remaining interpolation techniques, the signal level was underestimated. This suggests that the deployment of control points plays a very important role, especially in the case of areas which are diverse in terms of coverage. Additionally, for further analysis the control points were combined into four groups (zones) reflecting the distance of the sensors from the TX antenna, the direction to the TX  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Zone**} & **Point** & \multicolumn{8}{c}{**Difference between Interpolated and True Values [dB]**} & **True** \\ \cline{2-11}  & **ID** & \(IDW\)\(p\)1 & \(IDW\)\(p\)2 & \(IDW\)\(p\)3 & \(IDW\)\(p\)4 & \(IDW\)\(p\)5 & \(IDW\)\(p\)6 & _Kriging_ & _NN_ & **[dBm]** \\ \hline \multirow{8}{*}{\(1\)} & P3 & \(-\)11.1 & \(-\)10.6 & \(-\)9.6 & \(-\)11.7 & \(-\)11.6 & \(-\)13.6 & \(-\)9.5 & \(-\)21.6 & \(-\)77.9 \\ \cline{2-  
antenna, and the signal levels measured by the sensors. These zones are also presented in Figure 2.  
It is clearly visible in Table 3 that there were more UEPs in Zone 1 than in the other zones. It is worth noting that the sensors in Zone 1 were located closely to the TX antenna and therefore, the signal levels measured by these sensors were the highest. The two control sensors P33 and P37 measured the highest levels of the signal. However, in the interpolation process the measurement data from the remaining sensors placed in this zone was taken into account. As in the input data for the interpolation process, the signal levels were lower than for the two control sensors, and assuming that the interpolation methods flatten the results, it is obvious that the estimated levels for these control sensors were much lower than the measured levels. In Zone 2, there was only one control point, namely P18, with dominating UEP. For this point, nearly all the interpolation techniques, except for IDW p1, underestimated the signal level by approximately 10 dB. This effect can be explained in the following way. The signal levels measured for all the neighboring sensors in this zone were much lower than for P18, and as a result, the interpolated signal level was much lower than the level measured by the control sensor P18. In Zone 2, there was one control point P17 for which all the interpolating techniques overestimated the signal level by approximately 15 dB. The analysis revealed that the measurement points neighboring P17 (P3, P4, and P16) measured much higher signal levels. There were no points surrounding P17 that measured comparable or lower signal levels than P17.