}
+@article{ref17,
+ title={A survey on sensor networks},
+ author={Akyildiz, Ian F and Su, Weilian and Sankarasubramaniam, Yogesh and Cayirci, Erdal},
+ journal={IEEE Communications magazine},
+ volume={40},
+ number={8},
+ pages={102--114},
+ year={2002},
+ publisher={IEEE}
+}
+
+@book{ref19,
+ title={Wireless sensor networks},
+ author={Akyildiz, Ian F and Vuran, Mehmet Can},
+ volume={4},
+ year={2010},
+ publisher={John Wiley \& Sons}
+}
+
+@article{ref22,
+ title={Energy efficiency in wireless sensor networks: A top-down survey},
+ author={Rault, Tifenn and Bouabdallah, Abdelmadjid and Challal, Yacine},
+ journal={Computer Networks},
+ volume={67},
+ pages={104--122},
+ year={2014},
+ publisher={Elsevier}
+}
\ No newline at end of file