## 3 Motivation
### Motivation for Balanced Energy Efficiency  
Most existing clustering algorithms focus on maintaining the number of sensors that are still alive to extend the longevity, ignoring the distribution of the sensors. The coverage of a network is highly determined by the sensor distribution and it is crucial in most systems, like wildlife monitoring or battlefield sensing. Most existing work assumes that a sensor's sensing range is the \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Algorithm** & **Cluster Structure** & **Distributed** & **Node Density** & **CH Rotation** & **Data Fusion** & **TTC** & **Energy Aware** & **Cluster Size** & **Sensing** & **Simulation** & **Compared with** \\ \hline LEACH & Voronoi & Yes & No & Yes & Yes & Yes & No & None & MATLAB & Direct MTE, Static \\ \hline HEED & Voronoi & Yes & Yes & Yes & Yes & Yes & Yes & Energy & MATLAB & LEACH \\ \hline DWERIC & Voronoi & Yes & Yes & Yes & Yes & Yes & Yes & Location Energy & NS2 & IEEED \\ \hline PEGASS & Chain & Yes & No & Yes & Yes & No & Yes & No & Location & MATLAB & Direct LEACH \\ \hline CCS & Chain & No & No & Yes & Yes & No & Yes & No & Location Energy & MATLAB & PEGASS \\ \hline
5-WEB & Spectrum & No & No & No & No & No & Yes & No & Location Energy & MATLAB & Direct \\ \hline BEE(M) & Voronoi & Yes & Yes & Yes & Yes & Yes & Yes & Yes & Energy & MATLAB & LEACH HEED \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of 6 Existing Clustering Algorithms and BEE(M). \begin{table}
\begin{tabular}{c l} \hline \hline
**Survey** & **Major Contributions** \\ \hline \multirow{4}{*}{[PERSON] [24] 2007} & 1. Earlier clustering work before LEACH mainly addresses node failure problem. \\  & 2. Clustering algorithms after LEACH start to focus more on energy efficiency. \\  & 3. Multihop intra-cluster topology is rare. \\  & 4. Multihop inter-cluster communication is well applied. \\ \hline \multirow{4}{*}{[PERSON] [26]} & 1. Energy efficiency/maxing lifetime is the dominate objective for clustering. \\  & 2. No reviewed clustering algorithm can operate in a heterogeneous network. \\  & 3. Multihop intra-cluster communication is rarely supported. \\  & 4. Multihop inter-cluster communication is well applied. \\  & 5. The CH is only in charge of data aggregation and transmission. \\  & 6. Device mobility is hardly concerned in existing solutions. \\  & 7. Distributed implementation is the mainstream in clustering. \\ \hline [PERSON] [25, 27] & 1. Algorithms have small deliver delays tend to have low energy efficiency. \\  & 2012 & 2. Distributed implementation is the mainstream in clustering. \\  & 2015 & 3. Tree and train based implementations have lower scalability than grid based ones. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summaries for Selected Existing Survey Papers on Clustering for WSNs. same as its communication range. Therefore, the sensing coverage area is the same as communication area. Once the network is still connected, the network coverage is also guaranteed. This can simplify the connectivity problem and the coverage problem into one. However, this assumption is not true in reality. A sensor or an IoT device can have short distance communication and also long communication abilities. Even for classic clustering algorithms like LEACH and HEED, they only discussed communication connectivity problem, ignoring the fact that the network coverage could change during the network operations. To expose the network coverage problem in current work, three communication schemes are examined: direct routing, general LEACH and HEED. The experiment settings are the same as in HEED, shown in Table 9 in Section 6 Experimental Construction. In HEED, each CH is set to use a single hop to communicate with the BS. The number of nodes still alive after each round in the network is shown in Figure 2. LEACH and HEED performed significantly better than the direct transmission approach. However, the comparison between LEACH and HEED requires careful analysis. The first node died earlier in HEED than that in LEACH.