+}
+
+@article{ref236,
+ title={Localization and coverage for high density sensor networks},
+ author={Bahi, Jacques M and Makhoul, Abdallah and Mostefaoui, Ahmed},
+ journal={Computer Communications},
+ volume={31},
+ number={4},
+ pages={770--781},
+ year={2008},
+ publisher={Elsevier}
+}
+
+@article{ref237,
+ title={Hilbert mobile beacon for localisation and coverage in sensor networks},
+ author={Bahi, Jacques M and Makhoul, Abdallah and Mostefaoui, Ahmed},
+ journal={International Journal of Systems Science},
+ volume={39},
+ number={11},
+ pages={1081--1094},
+ year={2008},
+ publisher={Taylor \& Francis}
+}