This letter studies the proactive eavesdropping in a suspicious decode-and-forward relay system, where the suspicious communication is divided into transmitter-to-relay (ST-SR) phase and relay-to-destination (SR-SD) phase with partial channel selection over N ≥ 2 orthogonal channels, and the monitor (E) can only jam/overhear the E-SR/SR-E link over M ≤ N sub-channels for practicality. Under this framework, with strict proof we first theoretically present the impact of jamming power and number of jamming channels selected by E on its eavesdropping success probability (ESP), and then reveal a fundamental trade-off: given jamming power (number of jamming channels), jamming with more channels (power) reduces the suspicious rate for E to overhear more clearly, but degrades the preconditions for successful eavesdropping. Results verify our obtained conclusions and show that the proposed jamming-assisted eavesdropping scheme with simple search method achieves pretty good performance compared with some intuitive schemes.
This letter studies the proactive eavesdropping in a suspicious decode-and-forward relay system, where the suspicious communication is divided into transmitter-to-relay (ST-SR) phase and relay-to-destination (SR-SD) phase with partial channel selection over N ≥ 2 orthogonal channels, and the monitor (E) can only jam/overhear the E-SR/SR-E link over M ≤ N sub-channels for practicality. Under this framework, with strict proof we first theoretically present the impact of jamming power and number of jamming channels selected by E on its eavesdropping success probability (ESP), and then reveal a fundamental trade-off: given jamming power (number of jamming channels), jamming with more channels (power) reduces the suspicious rate for E to overhear more clearly, but degrades the preconditions for successful eavesdropping. Results verify our obtained conclusions and show that the proposed jamming-assisted eavesdropping scheme with simple search method achieves pretty good performance compared with some intuitive schemes.
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.
This letter studies the Unmanned Aerial Vehicles (UAVs)-assisted proactive eavesdropping in the suspicious amplify-and-forward multi-relay system, where the suspicious transmitter based on opportunistic relaying protocol selects one best suspicious relay to communicate with the suspicious destination. In addition, we assume each UAV hovers over one specific relay for the purpose of jamming or eavesdropping, which is only valid for this relay due to the limited coverage of the UAVs and the dispersion between these relays. Moreover, the UAVs used for jamming cannot implement eavesdropping concurrently due to the half-duplex constraints. Under this setup, with detailed analysis and strict proof, we find an interesting trade-off in deciding the number of UAVs used for jamming: jamming with more UAVs helps decrease the suspicious rate to facilitate the eavesdropping by remaining UAVs, but is at the cost of degrading the precondition of successful eavesdropping. Numerical results verify this trade-off and show that with simple one-dimensional search, the proposed jamming-assisted strategy achieves significant gain compared to conventional passive eavesdropping.
This paper studies a legitimate proactive eavesdropping scenario where a central monitor covertly wiretaps the communications between suspicious users through a full-duplex multi-antenna relay. Specifically, the suspicious information is intercepted by the eavesdropping relay, and then encoded and forwarded to the central monitor. At the same time, the relay sends jamming signals to the suspect destination to reduce the quality of suspicious communication. To minimize the suspicious secrecy rate, the optimal forwarding and jamming beamforming vectors of the eavesdropping relay are first designed. Based on this optimized result, the best power allocation ratio is obtained. To this end, the optimal beamforming vectors and power allocation ratio are derived in closed-form. The simulation results verify the existence of the optimal forwarding power of the relay and show that the proposed scheme achieves better performance than the conventional schemes.
We investigate proactive eavesdropping with one half-duplex legitimate monitor (E) in unmanned aerial vehicle (UAV)-enabled suspicious relaying systems, which consist of a suspicious transmitter (ST), a suspicious UAV-based relay (SU) and a suspicious destination (SD). Under this setup, we propose two jamming-assisted eavesdropping strategies, namely, “Eavesdrop-Then-Jam” (ETJ) and “Jam-Then-Eavesdrop” (JTE), to maximize the eavesdropping throughput of E. Specifically, for ETJ, E first eavesdrops the suspicious signal of the ST in the ST-SU phase and then jams the SD in the SU-SD phase; for JTE, E first jams the SU in the ST-SU phase and then eavesdrops the suspicious signal of the SU in the SU-SD phase.However, in both strategies, as the jamming power of E (independent variable) changes, the SU can also adaptively adjust its deployment (dependent variable) to maximize the benefit of the suspicious system. Facing this challenge, we can only employ the undesirable exhaustive search over both the independent and dependent variables to achieve the optimal solution. To decrease the complexity, we further derive a tight approximation of the Lambert function and then develop easy-to-implement algorithms to find the sub-optimal solutions. Numerical results demonstrate the effectiveness of our proposed strategies compared to conventional passive eavesdropping.
This letter studies the proactive eavesdropping with one half-duplex legitimate monitor (E) over the wireless-powered multichannel suspicious system, where the suspicious transmitter (ST) proceeds energy harvesting from the power beacon and then communicates with the suspicious destination (SD) via N parallel channels. Under this setup, one jamming-assisted eavesdropping scheme is proposed to maximize the ergodic eavesdropping rate at E. Specifically, we first fix the number of jamming channels K at E, and then reveal that E should jam with maximum power over these K channels to force the ST to allocate more power over the other N - K channels, so as to maximally increase the perceived power at E over the corresponding N - K channels. Armed with this, to maximize the ergodic rate, the following work is only to find the optimal K with simple search. Moreover, one closed-form sub-optimal K is derived for practical implementation. Results present the great gain achieved by the proposed scheme compared to conventional passive eavesdropping and the effectiveness of the sub-optimal K.
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.