The eavesdropping attack is a serious security threat to a wireless sensor network (WSN) since the eavesdropping attack is\r\na prerequisite for other attacks. Conventional WSNs consist of wireless nodes equipped with omnidirectional antennas, which\r\nbroadcast radio signals in all directions and are consequently prone to the eavesdropping attacks. Different from omnidirectional\r\nantennas, directional antennas radiate radio signals on desired directions and potentially reduce the possibility of the eavesdropping\r\nattacks. In this paper, we propose a model to analyze the eavesdropping probability in both single-hopWSNs and multihopWSNs\r\nwith omnidirectional antennas and directional antennas.We verify the correctness of our analytical model by conducting extensive\r\nsimulations.We have found that using directional antennas in either single-hopWSNs or multihopWSNs can significantly reduce\r\nthe eavesdropping probability.The reason of the improved security ofWSNswith directional antennas lies in (i) the smaller exposure\r\nregion of a directional antenna and (ii) the fewer hops to route a packet due to the longer transmission range of a directional antenna.\r\nOur results have also shown that the security improvement factor heavily depends on the node density, the antenna beamwidth,\r\nand the signal path loss factor.
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