# Energy-Efficient Spatial Query-Centric Geographic Routing Protocol in Wireless Sensor Networks
## 3 QTGrid Routing Protocol
### CH and PCH Election
#### 3.2.2 PCH Election
Second, CH nodes were selected based on several metrics, such as distance from the candidate node to the grid center and adjacent CHs and residual energy. Third, the next-hop routing node was selected depending on the residual energy of the candidate node and its distance to the sink node. Lastly, a lossless data aggregation algorithm and a flexible spatial query algorithm were adopted to reduce the transmission of redundant data and meet the application requirements, respectively. Extensive simulations were conducted on QTGrid and three related protocols (GeoGrid, QTBDC, and GCCR) in terms of performance in network lifetime and spatial query. The simulation results revealed that compared with the three other protocols, QTGrid had a longer network lifetime and higher spatial query efficiency and was thus more suitable for large-scale WSN spatial query application scenarios. Conceptualization, Y.F. ; Formal analysis, X.J. ; Investigation, Y.X. ; Methodology, M.Z. ; Project administration, X.J. and M.Z. ; Software, X.W. and Y.F. ; Supervision, X.J. ; Writing-original draft, X.W. ; Writing-review & editing, X.W. This work was partially supported by the National High-tech R&D Program of China (863 Program) (2015 AA123901), National Natural Science Foundation of China (NSFC) (41771420 and 41601422), the Priority Academic Program Development of Jiangsu Higher Education Institutions. The authors would like to thank the editors and the anonymous reviewers for their constructive comments and suggestions, which greatly helped to improve the quality of the manuscript. The authors declare no conflict of interest. ## References

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