In this paper, we propose an opportunistic user selection criterion to obtain a multiuser diversity gain for secure communication. At the same time, we also propose a strategy for utilizing a small base station in heterogeneous networks as a helper or a jammer adaptively. Our approach is to maximize the secrecy achievable rate based on an analytically derived lower bound instead of the original objective function due to its complexity. Based on a simple proposed user selection criterion considering both macro and small base stations, we propose two jamming strategies according to knowledge of eavesdropper's channel: adaptive jamming and probabilistic jamming strategies. Through simulations in two scenarios, it is shown that our proposed user selection and jamming schemes provide a good performance gain in terms of secrecy achievable rate.
In this paper, we propose an opportunistic user selection criterion to obtain a multiuser diversity gain for secure communication. At the same time, we also propose a strategy for utilizing a small base station in heterogeneous networks as a helper or a jammer adaptively. Our approach is to maximize the secrecy achievable rate based on an analytically derived lower bound instead of the original objective function due to its complexity. Based on a simple proposed user selection criterion considering both macro and small base stations, we propose two jamming strategies according to knowledge of eavesdropper's channel: adaptive jamming and probabilistic jamming strategies. Through simulations in two scenarios, it is shown that our proposed user selection and jamming schemes provide a good performance gain in terms of secrecy achievable rate.
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 → MUkfor 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.
In this paper, we investigate the physical layer security for heterogeneous networks (HetNets), where the confidential message transmitted to each legitimate user can be eavesdropped by multiple eavesdroppers. To enhance the secrecy performance, we introduce friendly jammers and full duplex users in our model. We propose a jammer selection scheme based on average user received jamming power. The jammers whose interference power on the scheduled users less than a threshold are selected to transmit independent artificial noise to confound the passive eavesdroppers. Furthermore, the scheduled users try to jam the eavesdroppers around using full duplex capacity. Using the tools from stochastic geometry, we derive the theoretical analyses of user connection probability and secrecy probability. In particular, the locations of selected jammers are modeled by a Poisson hole process instead of more popular homogeneous Poisson point process. Our analytical results show a good agreement with the simulations. The ergodic secrecy rate in our scheme outperforms that in the traditional HetNets.
In this article, we investigate the physical layer security for a wireless communication system consisting of a base station (BS) and a user (U) in the face of an eavesdropper (E). A friendly jammer is opportunistically selected from multiple jammers to create intentional interference upon E. However, the legitimate user U is not aware of the information transmitted by the jammer and thus cannot remove the interfering signal. In this context, we propose interference-limited opportunistic jammer selection (IL-OJS) scheme and interference-canceled opportunistic jammer selection (IC-OJS) scheme to reduce the damage of interference to U for improving physical layer security. Specifically, in the IL-OJS scheme, the selected jammer sets an interference threshold. When the interference to U is less than the threshold value, the selected jammer will work (i.e., emit artificial noise), and vice versa, it will stop jamming. By contrast, IC-OJS scheme utilizes a specially designed signal to eliminate interference received by U from the selected jammer. For comparison, we also present the conventional non-jammer (NJ) scheme as a benchmark. Exact and asymptotic closed-form secrecy outage probability expressions for NJ, IL-OJS, and IC-OJS schemes are derived over Nakagami-mfading channels. Numerical results show that the secrecy performance of proposed IL-OJS and IC-OJS schemes is better than that of NJ scheme. Additionally, the secrecy outage probability performance of IL-OJS and IC-OJS schemes can be improved by increasing the number of jammers.
In this paper, we investigate achievable secrecy sumrate in uplink multiuser networks where some base stations are compromised to operate as potential eavesdroppers. Due to the difficulty of analyzing the exact secrecy capacity region in multiuser networks, we focus on analyzing the secrecy sumrate scaling in terms of the number of transmitters based on multiuser diversity (MUD). We propose an opportunistic user scheduling scheme able to achieve optimal MUD gain in uplink multiuser networks whereNtransmitters (users), a single desired receiver (i.e., base station), andKpotential eavesdroppers (i.e., compromised base stations) are assumed. The proposed scheme enables multiuser transmissions in one scheduling time slot by employing orthogonal random beamforming at the receiver. In addition, the proposed scheme can fully exploit the degrees-of-freedom (DoF) gain when each transmitter is equipped with a single antenna, and base station and potential eavesdroppers are equipped withMantennas. The main results show that the proposed scheduling scheme achieves the optimal secrecy sum-rate scaling indicating that the achievable secrecy sum-rate scales asMlog (SNR log N) in a high signal-to-noise ratio (SNR) regime when a certain user scaling condition.
We investigate secure transmission for multiuser relay networks, where the undesired users who are not selected for data reception may overhear the source message as eavesdroppers. In this system, the secrecy performance may deteriorate as the number of users increases, since the number of eavesdroppers also increases. To address this issue, we consider a multiuser relay scheme with cooperative jamming (MUCJ). In this scheme, the desired user sends a jamming signal to the relay while the source sends its message to the relay, and then the relay amplifies and forwards the received signal to the desired user. Since the jamming can be subtracted only at the desired user, it acts as interference to prevent the eavesdroppers from intercepting the source message. We propose an optimal user selection scheme for the MUCJ, which is optimal in the sense of maximizing the secrecy rate. For the existing multiuser relay scheme (MURS) without cooperative jamming and the MUCJ, we derive the ergodic secrecy rates and analyze the asymptotic secrecy rate gains. We reveal that the ergodic secrecy rate can be increased as the number of users grows and much higher secrecy rate can be achieved by the MUCJ.
In this paper, we investigate secure communications uplink transmissions, where there are a base station (BS) with M receive antennas, K mobile users each with a single antenna, and an eavesdropper with N receive antennas. The closed-form expressions of the achievable ergodic secrecy sum rates (ESSRs) for a random k users selection scheme in the high and low signal-to-noise ratio regimes are presented. It is shown that the scaling behavior of ESSR with respect to the number served users k can be quite different under different system configurations, determined by the numbers of the BS antennas and that of the eavesdropper antennas. In order to achieve multiuser gain, two low-complexity user selection schemes are proposed under different assumptions on the eavesdropper's channel state information. The closed-form expressions of the achievable ESSRs and the multiuser secrecy gains of the two schemes are also presented in both low and high SNR regimes. observe that, as k increases, the multiuser secrecy gain increases, while the ESSR may decrease. Therefore, when N much larger than M, serving one user with the strongest channel (Time Division Multiple Address-like) is a favorable secrecy scheme, where the ESSR scales with √2 log K.