This letter investigates the performance of a legitimate surveillance system, where a legitimate monitor aims to eavesdrop on a dubious decode-and-forward relaying communication link. In order to maximize the effective eavesdropping rate, two strategies are proposed, where the legitimate monitor adaptively acts as an eavesdropper, a jammer, or a helper. In addition, the corresponding optimal jamming beamformer and jamming power are presented. Numerical results demonstrate that the proposed strategies attain better performance compared with intuitive benchmark schemes. Moreover, it is revealed that the position of the legitimate monitor plays an important role on the eavesdropping performance for the two strategies.
This letter investigates the performance of a legitimate surveillance system, where a legitimate monitor aims to eavesdrop on a dubious decode-and-forward relaying communication link. In order to maximize the effective eavesdropping rate, two strategies are proposed, where the legitimate monitor adaptively acts as an eavesdropper, a jammer, or a helper. In addition, the corresponding optimal jamming beamformer and jamming power are presented. Numerical results demonstrate that the proposed strategies attain better performance compared with intuitive benchmark schemes. Moreover, it is revealed that the position of the legitimate monitor plays an important role on the eavesdropping performance for the two strategies.
This letter considers a legitimate surveillance scenario, where two suspicious nodes intend to exchange their information via one suspicious amplify-and-forward relay in two phases, the process of which is under the supervision of one legitimate monitor. To achieve the effective surveillance, one novel eavesdropping strategy is designed, in which the monitor proceeds passive eavesdropping in phase 1 and then implements passive eavesdropping or simultaneous assisting and jamming in general in phase 2. Under this setup, the monitor mainly aims to design the optimal structure of the transmit signal for each specific strategy in phase 2 and then optimize the corresponding beamformers and power allocation, in order to maximize the obtained sum eavesdropping rate subject to its power constraints. Simulation results verify that, compared to the conventional schemes, the proposed adaptive eavesdropping strategy achieves significant performance gains.
This article considers a proactive eavesdropping scenario, where two suspicious nodes exchange their information via one suspicious relay in two phases, the process of which is under the supervision of one legitimate monitor. Specifically, these two suspicious nodes broadcast their suspicious data in phase 1 and the relay forwards the amplified version of its received signal in phase 2, according to which two proactive eavesdropping strategies, i.e., “passive eavesdropping first” and “jamming first,” are designed. Using the former strategy, the monitor proceeds eavesdropping with a minimum-mean-squar-error (MMSE) receiver in phase 1 and implements eavesdropping or simultaneous assisting and jamming in phase 2. Using the latter strategy, the monitor implements jamming in phase 1 and performs eavesdropping in phase 2. For these strategies, we provide the detailed analysis and formulate the corresponding optimization problems of sum eavesdropping rate maximization subject to finite transmit power of the monitor, each of which is then solved by carefully designing the power allocation scheme or the assisting/jamming beamformer at the legitimate monitor. In addition, for the “passive eavesdropping first” strategy, we also consider a more advanced MMSE with a successive interference cancellation (SIC) receiver and concurrently exploit the time-sharing (TS) technique to further improve the eavesdropping rate. Finally, simulation results indicate that the “passive eavesdropping first” strategy is more preferable compared to the “jamming first” strategy, and the SIC and TS are preferable for promoting the more effective eavesdropping.
This paper considers wireless information surveillance systems, in which one suspicious communication link is intercepted by a legitimate monitor to prevent possible criminal or terrorist attacks from the link. To enhance the information surveillance performance, a novel proactive eavesdropping mechanism is proposed with the help of a cooperative relay. It is assumed that the relay operates in full-duplex (FD) mode to assist monitor for information relaying and jamming transmission simultaneously. Based on the proposed mechanism, the joint relay beamforming and power allocation scheme is further proposed and the closed form optimal solutions are derived. Simulation results show that the proposed proactive eavesdropping mechanism can achieve better surveillance performance than both proactive eavesdropping schemes without the help of cooperative relay and cooperative surveillance with pure information forwarding. Simulation results also reveal that the proposed power allocation scheme boosts surveillance performance significantly compared with those equal power allocation scheme.
Wireless information surveillance, by which suspicious wireless communications are closely monitored by legitimate agencies, is an integral part of national security. To enhance the information surveillance capability, we propose in this paper a new proactive eavesdropping approach via a spoofing relay, where the legitimate monitor operates in a full-duplex manner with simultaneous eavesdropping and spoofing relaying to vary the source transmission rate in favor of the eavesdropping performance. To this end, a power splitting receiver is proposed, where the signal received at each antenna of the legitimate monitor is split into two parts for information eavesdropping and spoofing relaying, respectively. We formulate an optimization problem to maximize the achievable eavesdropping rate by jointly optimizing the power splitting ratios and relay precoding matrix at the multiantenna monitor. Depending on the suspicious and eavesdropping channel conditions, the optimal solution corresponds to three possible spoofing relay strategies, namely constructive relaying, jamming, and simultaneous jamming and destructive relaying. Numerical results show that the proposed technique significantly improves the eavesdropping rate of the legitimate monitor as compared to the existing passive eavesdropping and jamming-assisted eavesdropping schemes.
In this paper, we consider a legitimate proactive eavesdropping scenario where a distant central monitor covertly wiretaps the communication between a pair of suspicious users via several multi-antenna full-duplex spoofing relays and a multi-antenna cooperative jammer. Assuming an adaptive transmission policy at the suspicious users, the spoofing relays not only intercept but also forward the manipulated information to control the data rate of the suspicious users in collaboration with the jammer. We provide a technique which jointly optimizes the receive combining vector at the central monitor, the precoders at the relays, and the transmit covariance matrix at the jammer for maximizing the eavesdropping rate. To reveal some fundamental properties of the optimal operation, we first study a single-relay system. It is shown that when the central monitor experiences a poor eavesdropping channel link, the spoofing relay and the jammer should transmit destructive signals and jamming signals, respectively. In this case, the suspicious users are forced to decrease their data rate, while the intercepted information can be successfully decoded by the central monitor. On the other hand, when the eavesdropping channel condition is favorable, the spoofing relay forwards constructive signals to further increase the data rate at the suspicious users in a way that more information can be intercepted from the suspicious users. We then formulate a general eavesdropping rate maximization problem for multiple relays and present a semi-definite relaxation approach. A low-complexity design is also proposed based on our analysis for the single-relay system. Simulation results verify the efficiency of the proposed solutions compared to other baseline schemes in various practical setups.
This letter studies the legitimate surveillance with one half-duplex legitimate monitor (E) over the suspicious multichannel relaying system, where the suspicious transmitter (ST) and relay (SR) implement the optimal power allocation over all orthogonal channels under a joint sum-power constraint to maximize the communication rate of the suspicious system. Under this setup and considering that SR operates in amplify-and-forward (AF) or decode-and-forward (DF) mode, E aims to i) determine the optimal set of sub-channels for jamming and ii) optimize its jamming power over these sub-channels in order to deliberately force ST and SR reallocating power to the unjammed sub-channels to the most, so as to increase the perceived power of E over the unjammed sub-channels and then maximize the eavesdropping rate. In particular, for the AF case, the formulated problem is non-convex, for which the slack variables are introduced and successive convex approximation is exploited. For the DF case, some insights are provided for the optimization process. Results present the considerable gain of the proposed strategy compared to intuitive schemes.