Low complexity cooperative jamming strategies in secure cellular network

We consider the K-user cellular network coexisting with a single helper node (HN) (or cooperative jammer) whose objective is to enhance the secrecy of the confidential data transmission. Due to the broadcast nature of the wireless medium, the information leakage to the undesired users is unavoidable when the base station (BS) transmits the private information to the intended mobile user (MU). In this paper, the unintended users are regarded as the potential eavesdroppers and called as the internal eavesdroppers. In [1], the proposed optimal transmission strategy for the helper maximizes the secrecy capacity of the intended user. However, its computational complexity geometrically increases as the number of the legitimate users or the network size grows. This property is inappropriate to the cellular network where dozens of users generally exist. To resolve such practical issue, we design the low complexity transmission strategies of the helper which are insensitive to the network size. In addition, as a part of an effort to develop the usability, we classify the helper´s cooperation according to whether the helper possesses the channel state information (CSI) about the downlink channel BS → MU_k for k ∈ K = {1, 2, ..., K} or not. We analyze the computational complexity of the proposed schemes and verify that their complexity dramatically decreases compared to the optimal transmission strategy in [1]. Also, through the simulation results, it is observed that the proposed transmission strategies provide the comparable secrecy rates to that of the optimal transmission.