Secure Communications in OFDMA networks with active eavesdropper

In this paper, we formulate the resource allocation problem for secure communications in a single cell OFDMA network where a base station wants to communicate to the users which are spread over its coverage area while an adversary is present in the network. In our model, we assume that the adversary s an active attacker which is able to either eavesdrop on the information transmitted over the wireless link or jam the connection by sending an interference signal but is not able to both eavesdrop and jam at the same time. The attacker's aim is to choose between eavesdropping and jamming a subcarrier such that the secrecy rate over that subcarrier is minimized. Knowing this strategy, users should consider the minimum of secrecy data rate in both cases as their achievable secrecy rate over each subcarrier. We formulate our proposed resource allocation problem into an optimization problem whose objective is to maximize the total secrecy rate of all users over all subcarriers while it is required that the total transmit power of base station remains below a predefined threshold. To solve the proposed optimization problem, we use the dual Lagrange approach. Using simulations, we study the behavior and the efficiency of the proposed scheme.