Radio Resource Allocation for Physical-layer Security in OFDMA Based HetNets with Unknown Mode of Adversary

Consider an orthogonal frequency division multiple access (OFDMA)-based heterogeneous cellular network (HetNet) in which a macrocell is underlaid with several small cells overheard by eavesdropper and jamming by jammer. In this paper, our goal is to design a transmission strategy, such that the achievable secrecy rate is maximized subject to the individual transmit power constraints for the macrocell base station (MBS) and each small-cell base station (SBS) and a constraint for the interference caused by SBSs to the macrocell user equipments (MUEs). There exists an adversary which can choose between two functional modes: eavesdropping the transmission between the legitimate parties or jamming it, but not both at the same time. We assume that the mode of adversary on each sub-carrier is unknown. To solve this non-convex problem, we employ an iterative approach in which sub-carriers and transmit powers of each base stations are alternatively assigned and optimized at every step. To handle the non-convexity of the power allocation, we adopt the successive convex approximation (SCA) approach by exploiting arithmetic-geometric mean (AGM) and logarithmic and difference-of-two-concave-functions (D. C.) approximations to transform problem into a sequence of convex subproblems. Simulation results demonstrate the close-to-optimal performance of the proposed schemes.