In this paper, we investigate multi-antenna covert communications, where the transmitter Alice equips multiple antennas, the legitimate receiver Bob and the eavesdropper Willie equips single antenna. Through analyzing the detection performance and the covert rate, we prove that a positive covert rate is achievable with a certain number of antennas in Alice. Numerical results are shown to illustrate the correctness of our results and the performance of MISO covert communication.
In this paper, we investigate multi-antenna covert communications, where the transmitter Alice equips multiple antennas, the legitimate receiver Bob and the eavesdropper Willie equips single antenna. Through analyzing the detection performance and the covert rate, we prove that a positive covert rate is achievable with a certain number of antennas in Alice. Numerical results are shown to illustrate the correctness of our results and the performance of MISO covert communication.
Covert communication conceals transmission of messages between Alice and Bob from an adversary, Willie, who tries to determine if a transmission took place or not. While covert communication in a basic, standard setting where all variables are known to Willie, results in the well-known square-root law, when a jammer is present and assists Alice by creating uncertainty in Willie's decoder, a strictly positive transmission rate is possible. In this work, we analyze the case where the jammer is equipped with multiple antennas. Specifically, we analyze the effect of multiple antennas at the jammer on Alice's transmission power and consequently on the transmission rate. We consider both the case where the channel knowledge of Willie is known as well as the case where it is unknown. We formulate several optimization problems for the transmission strategies of the jammer to maximize his assistance to Alice, in terms of maximizing Bob's received SNR and consequently the covert rate. When the channel information is known to the jammer, we show that under an achievable covertness scheme, the optimal strategy of the jammer is to perform beamforming towards a single direction with all his available power. This direction though, is not trivial, since it reflects a tradeoff point between minimizing the interference at Bob and maximizing the interference at Willie. When the channel knowledge is unknown, we show that the optimal strategy of the jammer is either to transmit isotropically to all directions or to the null-space of Bob, where this choice depends on certain channel conditions. This is in contrast to current schemes in the literature. Furthermore, we extend the optimization problems to the case where Bob is also equipped with multiple antennas, and provide insightful results, shown to be asymptotically optimal, accompanied by simulations.
In this paper, we consider a covert communication system with a multi-antenna full-duplex (FD) receiver to enhance covert performance. More precisely, the receiver Bob (i.e., multiple antennas) selects the best antenna to receive the covert message, and then it sends artificial noise (AN) to the warden Willie causing uncertainty by utilizing an antenna among the remaining antennas. In order to take full advantage of multi-antenna technology, we consider two cases: (1) Willie does not know which antenna Bob chooses to send AN, and Willie knows only part of the channel information. (2) Willie knows which antenna Bob chooses to send AN, and Willie knows all the channel information. Based on the analysis of the optimal detection threshold, we derive the minimum detection error probability of the two cases. Furthermore, given the pre-determined convert constraints, the closed-form expression of the maximum effective convert rate is derived. When the power of AN sent by Bob is greater than that of covert message sent by the sender Alice, surprised research results are shown: (1) the detection error rate of case 1 is higher than that of case 2. (2) the effective covert rate of case 1 is always lower than that of case 2. The simulation results show that the proposed scheme is more conducive to sending covert messages for Alice; in addition, the numerical results imply that the maximum effective covert rate of the system using the multi-antenna FD receiver is significantly higher than that of the traditional dual-antenna FD receiver system.
This paper investigates the joint physical layer security and covert communication in multi-input single-output (MISO) systems, aiming to enhance both the security and covertness of the system. In particular the base station, Alice, covertly transmits confidential information to the legitimate receiver, Bob, via multiple antennas, while avoiding detection by Willie, the detector, and eavesdropping by Eve. For the considered system, we analyze the covertness constraint with a noise uncertainty model at Willie's location and derive the closed-form expression for the system's average detection error probability. Next, we propose and solve the optimization problem to maximize the average security rate subject to the covertness constraint. Simulation results show that the multi-antenna at Alice with maximum ratio beamforming scheme can significantly improves the system's both security and covertness, and that the noise uncertainty at Willie's location and the nominal noise level have a substantial impact on the system's average security rate.
Covert communication conceals transmission of messages from Alice to Bob out of a watchful adversary, Willie, which tries to determine if a transmission took place or not. While covert communication in a basic, vanilla settings where all variables are known to Willie results in the well known square-root law, when a jammer is present and assists Alice by creating uncertainty in Willie's decoder, this transmission may have a positive rate.In this work, we analyze the case where the jammer is equipped with multiple antennas and obtain the optimal transmission strategy of the jammer in order to maximize his assistance to Alice, in terms of maximizing a ratio between Willie's and Bob's noise variance. We show that the optimal strategy of the jammer is to perform beamforming towards a single direction with all his available power. This direction though, is not trivial, since it reflects an optimal tradeoff point between minimizing the interference at Bob and maximizing the interference at Willie.
Covert communication aims to hide the existence of the transmissions to guarantee the security in wireless communications. In this letter, channel uncertainty is exploited to achieve covert communication in relay networks. The transmitter Alice sends messages to the legitimate receiver Bob with the help of a relay, while the warden Willie wants to detect the existence of the transmission. The channel uncertainty introduces confusions to degrade the performance of Willie's detection. We show that Alice can transmit O (n ) bits in n channel uses covertly with the help of relay and channel uncertainty. Numerical results are shown to illustrate the achievability and the performance of the considered scenario.
The fundamental limits of covert communication, where a message is sent from transmitter Alice to intended recipient Bob without detection by an attentive adversary warden Willie, has been considered extensively in recent years at the physical layer. The covert throughput depends critically on the warden's understanding of the characteristics of the radio environment and the type of receiver that he employs, and, as expected, the throughput increases when the warden has some uncertainty about the environment or some non-idealities in his receiver. In this paper, we consider the covert throughput when the adversary is only able to observe the medium access control (MAC) layer in a wireless communication system. In particular, given that the system has a rate ofλpackets per slot transmitted overnchannels by allowable system users, we study the allowable rateλaby covert users while maintaining covertness from an attentive warden observing the channel status in a slotted ALOHA system. We characterize performance for wardens with different abilities to discern the number of packets on a given channel, ranging from simple receivers that detect only whether there was a packet present to complicated receivers that can determine the number of packets involved in any collision, and also consider intended recipients Bob with varying abilities to perform multi-packet reception. In contrast to prior work in covert communications, the application considered motivates the consideration of results for finite (often small) observation vector lengthsnat the adversary. Numerical results are provided both to illustrate the tightness of our achievability regions for the packet transmission rate of the covert transmitters and to demonstrate the covert throughput of the system as a function ofλandn.