“…A large number of studies have been devoted to detecting and recovering coverage holes [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. However, most existing approaches [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ] are based on an assumption that the sensing range of a sensor node is like a disk (as shown in Figure 1 a) with the centre of the disk as a sensor.…”