Amitav Mukherjee

Robust Beamforming for Security in MIMO Wiretap Channels With Imperfect CSI

In this paper, we investigate methods for reducing the likelihood that a message transmitted between two multi-antenna nodes is intercepted by an undetected eavesdropper. In particular, we focus on the judicious transmission of artificial interference to mask the desired signal at the time it is broadcast. Unlike previous work that assumes some prior knowledge of the eavesdroppers channel and focuses on maximizing secrecy capacity, we consider the case where no information regarding the eavesdropper is available, and we use signal-to-interference-plus-noise-ratio (SINR) as our performance metric. Specifically, we focus on the problem of maximizing the amount of power available to broadcast a jamming signal intended to hide the desired signal from a potential eavesdropper, while maintaining a prespecified SINR at the desired receiver. The jamming signal is designed to be orthogonal to the information signal when it reaches the desired receiver, assuming both the receiver and the eavesdropper employ optimal beamformers and possess exact channel state information (CSI). In practice, the assumption of perfect CSI at the transmitter is often difficult to justify. Therefore, we also study the resulting performance degradation due to the presence of imperfect CSI, and we present robust beamforming schemes that recover a large fraction of the performance in the perfect CSI case. Numerical simulations verify our analytical performance predictions, and illustrate the benefit of the robust beamforming schemes.

Jamming Games in the MIMO Wiretap Channel With an Active Eavesdropper

This paper investigates reliable and covert transmission strategies in a multiple-input multiple-output (MIMO) wiretap channel with a transmitter, receiver and an adversarial wiretapper, each equipped with multiple antennas. In a departure from existing work, the wiretapper possesses a novel capability to act either as a passive eavesdropper or as an active jammer, under a half-duplex constraint. The transmitter therefore faces a choice between allocating all of its power for data, or broadcasting artificial interference along with the information signal in an attempt to jam the eavesdropper (assuming its instantaneous channel state is unknown). To examine the resulting trade-offs for the legitimate transmitter and the adversary, we model their interactions as a two-person zero-sum game with the ergodic MIMO secrecy rate as the payoff function. We first examine conditions for the existence of pure-strategy Nash equilibria (NE) and the structure of mixed-strategy NE for the strategic form of the game. We then derive equilibrium strategies for the extensive form of the game where players move sequentially under scenarios of perfect and imperfect information. Finally, numerical simulations are presented to examine the equilibrium outcomes of the various scenarios considered.

Detecting passive eavesdroppers in the MIMO wiretap channel

The MIMO wiretap channel comprises a passive eavesdropper that attempts to intercept communications between an authorized transmitter-receiver pair, with each node being equipped with multiple antennas. In a dynamic network, it is imperative that the presence of a passive eavesdropper be determined before the transmitter can deploy robust secrecy-encoding schemes as a countermeasure. This is a difficult task in general, since by definition the eavesdropper is passive and never transmits. In this work we adopt a method that allows the legitimate nodes to detect the passive eavesdropper from the local oscillator power that is inadvertently leaked from its RF front end. We examine the performance of non-coherent energy detection as well as optimal coherent detection schemes. We then show how the proposed detectors allow the legitimate nodes to increase the MIMO secrecy rate of the channel.

Utility of beamforming strategies for secrecy in multiuser MIMO wiretap channels

This paper examines linear beamforming methods for secure communications in a multiuser wiretap channel with a single transmitter, multiple legitimate receivers, and a single eavesdropper, where all nodes are equipped with multiple antennas. No information regarding the eavesdropper is presumed at the transmitter, and we examine both the broadcast MIMO downlink with independent information, and the multicast MIMO downlink with common information for all legitimate receivers. In both cases the information signal is transmitted with just enough power to guarantee a certain SINR at the desired receivers, while the remainder of the power is used to broadcast artificial noise. The artificial interference selectively degrades the passive eavesdroppers signal while remaining orthogonal to the desired receivers. We analyze the confidentiality provided by zero-forcing and optimal minimum-power beamforming designs for the broadcast channel, and optimal minimum-MSE beamformers for the multicast channel. Numerical simulations for the relative SINR and BER performance of the eavesdropper demonstrate the effectiveness of the proposed physical-layer security schemes.

Fixed-rate power allocation strategies for enhanced secrecy in MIMO wiretap channels

This paper studies the use of artificial interference in reducing the likelihood that a confidential message transmitted between two multi-antenna nodes is intercepted by a passive eavesdropper. A portion of the transmit power is used to broadcast the information signal with just enough power to guarantee a certain data rate for the intended receiver, and the remainder of the power is used to broadcast artificial noise in order to mask the desired signal from a potential eavesdropper. The interference is designed to be orthogonal to the multiple-stream information signal when it reaches the desired receiver. A modified water-filling algorithm is proposed that balances the required transmit power with the number of spatial dimensions available for jamming the eavesdropper. Numerical results verify the increase in secrecy capacity under the proposed transmission scheme.

A full-duplex active eavesdropper in mimo wiretap channels: Construction and countermeasures

We examine the design of a full-duplex active eaves-dropper in the 3-user MIMOME wiretap channel, where all nodes are equipped with multiple antennas. The adversary intends to optimize its transmit and receive sub-arrays and jamming signal parameters so as to minimize the MIMO secrecy rate of the main channel. The full-duplex operating mode of the adversary induces self-interference at its receive sub-array, which is factored into the adversarys optimization. We characterize the worst-case jamming covariance for arbitrary and Gaussian input signaling, and develop a numerical algorithm to compute the same. We then examine sub-optimal active eavesdropping schemes that comprise essentially an antenna subset selection problem for the adversary, followed by a brief discussion of a potential countermeasure where the transmitter allocates some of its spatial dimensions for jamming the eavesdropper. Numerical results are presented to verify the efficacy of the proposed adversarial optimization algorithms.

Securing multi-antenna two-way relay channels with analog network coding against eavesdroppers

This work investigates the vulnerability of analog network coding (ANC) to physical layer attacks from adversarial users, when all nodes are equipped with multiple antennas. Specifically, we examine the MIMO two way relay channel (TWRC) with two users trying to communicate with each other via a relay node in the presence of a passive eavesdropper. We propose a new performance metric, namely the secrecy sum rate of the MIMO TWRC, to quantify performance. We then consider secure transmission strategies for the scenarios of no eavesdropper channel state information at the transmitters (ECSIT) and complete ECSIT, respectively. Finally, numerical results are presented to illustrate the improvement in secrecy obtained with the proposed transmission schemes.

General Auction-Theoretic Strategies for Distributed Partner Selection in Cooperative Wireless Networks

It is unrealistic to assume that all nodes in an ad hoc wireless network would be willing to participate in cooperative communication, especially if their desired Quality-of-Service (QoS) is achievable via direct transmission. An incentive-based auction mechanism is presented to induce cooperative behavior in wireless networks with emphasis on users with asymmetrical channel fading conditions. A single-object second-price auction is studied for cooperative partner selection in single-carrier networks. In addition, a multiple-object bundled auction is analyzed for the selection of multiple simultaneous partners in a cooperative orthogonal frequency-division multiplexing (OFDM) setting. For both cases, we characterize equilibrium outage probability performance, seller revenue, and feedback bounds. The auction-based partner selection allows winning bidders to achieve their desired QoS while compensating the seller who assists them. At the local level sellers aim for revenue maximization, while connections are drawn to min-max fairness at the network level. The proposed strategies for partner selection in self-configuring cooperative wireless networks are shown to be robust under conditions of uncertainty in the number of users requesting cooperation, as well as minimal topology and channel link information available to individual users.

Energy-efficient device-to-device MIMO underlay network with interference constraints

Current interest is centered on non-orthogonal resource sharing between device-to-device (D2D) and cellular user equipments (C-UEs) that share the same frequency band, which then requires careful interference management techniques to avoid degrading the quality-of-service of the C-UEs. This work proposes an improved paradigm named device-to-multidevice (D2MD) communications, where a transmitting device communicates simultaneously with multiple receiving devices in an energy-efficient manner, and the underlay communication is augmented with the use of multiple transmit and receive antennas. Due to the difficulty of acquiring channel state information (CSI) of the C-UEs, we also present an enhanced D2MD scheme that does not require explicit feedback of CSI matrices from the C-UEs and/or D2MD receivers. Numerical simulations are presented to verify the efficacy of D2MD underlay transmission under a variety of CSI assumptions.

Optimal strategies for countering dual-threat jamming/eavesdropping-capable adversaries in MIMO channels

This paper investigates transmission strategies in a MIMO wiretap channel with a transmitter, receiver and wiretapper, each equipped with multiple antennas. In a departure from existing work, the wiretapper is able to act either as a passive eavesdropper or as an active jammer per channel use, under a half-duplex constraint. The transmitter therefore faces a choice between dynamically allocating all of its power for data; or broadcasting artificial noise along with the information signal in order to selectively degrade the eavesdroppers channel. We model the network as a zero-sum game in strategic form with the MIMO secrecy rate as the payoff function. We first carry out a detailed analysis of the various rate outcomes that result from the possible actions of the agents. We then discuss the conditions for equilibrium outcomes in the strategic form of the game. Finally, numerical simulations are presented to corroborate the analytical results.