+@inproceedings{ref156,
+ author = {F. Pedraza and A. L. Medaglia and A. Garcia},
+ title = {Efficient coverage algorithms for wireless sensor networks},
+ booktitle = {Proceedings of the 2006 Systems and Information Engineering Design Symposium},
+ pages = {78-83},
+ YEAR = {2006},
+}
+
+@book{ref157,
+ title={Handbook of sensor networks: algorithms and architectures},
+ author={Stojmenovic, Ivan},
+ volume={49},
+ year={2005},
+ publisher={John Wiley \& Sons}
+}
+
+@ARTICLE{ref158,
+author = {A. Varga},
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+journal = {Available: http://www.omnetpp.org},
+year = {2003},
+}
+
+@inproceedings{ref159,
+ title={Coverage and Lifetime Optimization in Heterogeneous Energy Wireless Sensor Networks},
+ author={Idrees, Ali Kadhum and Deschinkel, Karine and Salomon, Michel and Couturier, Rapha{\"e}l},
+ booktitle={ICN 2014, The Thirteenth International Conference on Networks},
+ pages={49--54},
+ year={2014}
+}
+
+@article{ref160,
+ title={Transforming Area Coverage to Target Coverage to Maintain Coverage and Connectivity for Wireless Sensor Networks},
+ author={Deng, Xiu and Yu, Jiguo and Yu, Dongxiao and Chen, Congcong},
+ journal={International Journal of Distributed Sensor Networks},
+ volume={2012},
+ year={2012},
+ publisher={Hindawi Publishing Corporation}
+}
