# Enhanced Distributed Dynamic Skyline Query for Wireless Sensor Networks
## 4 Performance Evaluation
### Efficiency  
The efficiency of the proposed approach is measured based on three parameters--energy consumption, latency and accuracy. These performance metrics and scalability of the proposed model is directly affected by the query range, which varies based on the average number of sectors indicated by \(\alpha\). With the increase of \(\alpha\), the number of messages that are generated due to three fundamental operations such as _Tree Propagation_, _Regular Update_ and _Triggered Query_ increases exponentially. Thus, in a model such as skyline query, it is an utmost challenge to minimize the energy consumption and latency while maximizing the accuracy. This experiment was conducted in a 90 m \(\times\) 90 m rectangular field, in which 180 nodes were randomly and independently disseminated. The data distribution used in this experiment was uniform. The query rate varied from 0.1 to 0.5 queries per sector per second and the simulation was run for 60 min. The _Skyline Query_ overhead is comparatively high due to its three phase query calculation. Figure 12(a)-c presents the average energy consumption (J) per node, latency (s) and accuracy (accuracy was defined as the percentage of skyline queries that were correctly resolved) as a function of the query rate per sector per second. In this experiment, the query range was varied in four different ways as shown in Figure 13. In order to show the scalability of the system, \(\alpha\) has been varied exponentially up to 36, where 36 is the total number of sectors in a 90 m \(\times\) 90 m (Table 4) rectangular field. From Figure 12(a),b, it is noted that the overhead in terms of energy consumption and latency grows radically as \(\alpha\) increases. It is also to be noted that the data in Figure 12(a) are presented in logarithmic scale in order to reduce the wide range to a more manageable size. However, the accuracy of the query response was very high (see Figure 12(c)) and close to 100%. Packet loss due to interference causes some minor inaccuracy.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Setting** \\ \hline Field Size (\(F\)) & 60 \(\times\) 60 m\({}^{2}\), 90 \(\times\) 90 m\({}^{2}\), 120 \(\times\) 120 m\({}^{2}\), 150 \(\times\) 150 m\({}^{2}\) \\ \hline Number of Nodes (\(N\)) & 80 (3600 m\({}^{2}\)), 180 (8100 m\({}^{2}\)), 320 (14,400 m\({}^{2}\)), \\  & 500 (22,500 m\({}^{2}\)) \\ \hline Number of Sectors/Field Size (\(S\)/\(F\)) & 16/(60 \(\times\) 60 m\({}^{2}\)), 36/(90 \(\times\) 90 m\({}^{2}\)), 64/(120 \(\times\) 120 m\({}^{2}\)), \\  & 100/(150 \(\times\) 150 m\({}^{2}\)) \\ \hline Member Node Density (\(f_{m}\)) & 1 node/56.25 m\({}^{2}\) \\ \hline Sector Head Node (SH) Density (\(f_{SH}\)) & 1 node/225 m\({}^{2}\) \\ \hline Radio Range (member node) & \(\sim\)8 m \\ \hline Radio Range (SH) & \(\sim\)20 m \\ \hline Transmission Power & 0 dBm (\(SH\)), \(-\)5 dBm (_member node_) \\ \hline Power Consumption in Sending and & 57.42 mW (\(SH\)), 46.2 mW (_member node_) \\ Receiving Messages & 0.02 m/Joule \\ \hline Data Rate, Modulation Type, Bits Per Symbol, & 250 Kbps, PSK, 4, 20 MHz, 194 MHz, \(-\)100 dBm, \\ Bandwidth, Noise Bandwidth, Noise & \(-\)95 dBm \\ Floor, Sensitivity & \(-\)95 dBm \\ \hline pathLossExponent & 2.4 \\ \hline Initial Average Path Loss (\(PL(d_{0})\)) & 55 \\ \hline Reference Distance (\(d_{0}\)) & 1.0 m \\ \hline Gaussian Zero-Mean Random Variable (\(X_{\text{a}}\)) & 4.0 \\ \hline Routing Protocol & SBD [15] \\ \hline MAC Protocol, Maximum Transmission Retries & SMAC [32], 2 \\ \hline SMAC Acknowledgment, Synchronization, RTS, CTS & 11, 11, 13, 13 bytes \\ Packet Size & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Simulation Parameters.