Optimal placement and power allocation for jammers in wireless mesh networks

Abstract

Wireless networks are gaining widespread use and popularity because of their progressive increase in affordability and convenience. Owing to the improved facilitation of communication and data transfer, wireless networks are being deployed in numerous modalities, ranging from wireless local area networks, to mesh and sensor networks. Wireless Mesh Networks (WMNs) have numerous applications in both civilian and military based environments. The main disadvantage of WMNs is its susceptibility to interference and eavesdroppers that are able to intercept, and listen in on the communication between devices in the networks. Eavesdroppers can act as non-lethal weapons to combatants at war and can have dire consequences if vital information is obtained by the adversaries. As a result of the emerging and prevalent use of WMNs in military domains, protecting information contained in networks is of utmost importance in this information driven age. This study proposes a novel physical-layer based security method that utilises jammers to generate additional interference for devices that are eavesdropping on wireless network communication. The most popular method for ensuring data confidentiality is through the use of cryptographic techniques; however, as a result of the decentralised nature and power limited network nodes of WMNs, the protection scheme precludes the use of any cryptographic techniques and is only physical-layer based. The scheme involves the intelligent placement of continuous jammers in order to achieve maximum protection and data confidentiality for WMNs with multiple eavesdroppers, sources and destinations. Furthermore, the scheme is optimised in terms of the transmitting power associated with each jammer, so that the energy expended by the jammers is kept at a minimum. The security method is modelled as a minimisation mixed integer non-linear problem, and is approximated as the sequential solution of two linear optimisation sub-problems relating to the placement, and power allocation of the wireless jammers. The proposed security model is subject to constraints which ensure that sufficient interference is generated for malicious devices that seek to obtain confidential information, while legitimate communication within the network is not affected. The placement of the jammers takes the form of a multiple demand multi-dimensional knapsack problem with a minimisation objective. The power allocation problem is modelled as a linear real-valued minimisation optimisation problem. The branch-and-cut method, and the simplex method are the algorithms used for solving the placement and power allocation problems respectively. In the effort to reduce the computation time associated with solving the linear integer jammer placement problem, an alternating control tree based heuristic is also developed. The performance of the proposed security method and heuristic are evaluated through appropriate simulations conducted on random network instances. The performance of the proposed security scheme is shown for a number of different scenarios with varying parameters. The branch-and-cut algorithm is used to solve various cases of the jammer placement sub-problem while altering parameters such as the grid size, the number of legitimate nodes, the number of malicious eavesdropping nodes and the locations of potential jammers. The heuristic is successfully applied to large networks, demonstrating the scalability of the implementation. The performance in terms of the solution provided and the computation time associated with use of the heuristic, in comparison to the branch-and-cut algorithm, is also shown. The heuristic can perform up to 60 times faster than the branchand- cut method depending on the particular network instance, while returning a solution that is within 10% of the optimal solution. The use of the heuristic proves to be imperative in real-life large network scenarios, where an acceptable solution needs to be obtained with a low execution time. It can therefore be concluded, that for small network scenarios, where optimality in terms of the number of jamming devices required to protect an area is critical, the branch-and-cut method should be implemented. However, in scenarios where the execution time is critical, the heuristic can be used to obtain a reasonable solution within a small time limit.