  Wireless communication systems, such as wireless sensor networks and RFIDs,
are increasingly adopted to transfer potential highly sensitive information.
Since the wireless medium has a sharing nature, adversaries have a chance to
eavesdrop confidential information from the communication systems. Adding
artificial noises caused by friendly jammers emerges as a feasible defensive
technique against adversaries. This paper studies the schedule strategies of
friendly jammers, which are randomly and redundantly deployed in a
circumscribed geographical area and can be unrechargeable or rechargeable, to
maximize the lifetime of the jammer networks and prevent the cracking of
jamming effect made by the eavesdroppers, under the constraints of geographical
area, energy consumption, transmission power, and threshold level. An
approximation algorithm as baseline is first proposed using the integer linear
programming model. To further reduce the computational complexity, a heuristic
algorithm based on the greedy strategy that less consumption leads to longer
lifetime is also proposed. Finally, extensive simulation results show that the
proposed algorithms are effective and efficient.
