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IEEE Communications Letters

Best Antenna Placement for Eavesdroppers: Distributed or Co-Located?

Jue Wang, Jemin Lee, Tony Q. S. Quek

Published Jun 9, 2016• 7 citations
Publisher

Abstract

In this letter, we investigate the best antenna placement for eavesdroppers (Eves), who intend to wiretap information from the legitimate transmitter (Alice). Two configurations of co-located or distributed antennas (CA or DA) are compared to find the most harmful eavesdropper setting, which achieves higher average eavesdropping rate, i.e., the long-term leakage rate to Eves averaged over channel fading and random locations. For K → ∞, where K is the number of available antennas for Eves, we prove that without a guard zone (i.e., a geometric zone around Alice where Eves cannot be located in), DA Eves are more harmful, while with a nonzero guard zone, CA Eve is superior. For the finite-K case, we derive upper/lower bounds for the average eavesdropping rate. The bounds are then used to find a DA region, in which the DA Eves definitely outperform CA Eve. It is shown that this region depends on the value of K, the radius of the guard zone, and the jamming at Alice.

DOI
10.1109/lcomm.2016.2578927

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In this letter, we investigate the best antenna placement for eavesdroppers (Eves), who intend to wiretap information from the legitimate transmitter (Alice). Two configurations of co-located or distributed antennas (CA or DA) are compared to find the most harmful eavesdropper setting, which achieves higher average eavesdropping rate, i.e., the long-term leakage rate to Eves averaged over channel fading and random locations. For K → ∞, where K is the number of available antennas for Eves, we prove that without a guard zone (i.e., a geometric zone around Alice where Eves cannot be located in), DA Eves are more harmful, while with a nonzero guard zone, CA Eve is superior. For the finite-K case, we derive upper/lower bounds for the average eavesdropping rate. The bounds are then used to find a DA region, in which the DA Eves definitely outperform CA Eve. It is shown that this region depends on the value of K, the radius of the guard zone, and the jamming at Alice.
In this paper, we investigate the secure communication in the massive MIMO uplink, where a legitimate single antenna transmitter (Alice) communicates with a legitimate receiver implemented with massive antenna array, in the presence of multiple eavesdroppers (Eves). Considering co-located or distributed antenna (CA or DA) placement of the eavesdropping nodes, we first respectively derive analytical expressions or approximations of the average eavesdropping rate. Based on that, the most harmful eavesdropping antenna configuration is investigated by comparing the CA and DA cases. After determining the worst case, artificial noise-aided jamming is performed at Alice to degrade Eve's receive SNR and maximize the average secrecy rate. Simulation results show that the worst-case design can be efficient even when Alice does not know the exact number of eavesdropping antennas.
This paper presents secrecy analyses of a full-duplex MIMOME network which consists of two full-duplex multi-antenna users (Alice and Bob) and an arbitrarily located multi-antenna eavesdropper (Eve). The paper assumes that Eve's channel state information (CSI) is completely unknown to Alice and Bob except for a small radius of secured zone. The first part of this paper aims to optimize the powers of jamming noises from both users. To handle Eve's CSI being unknown to users, the focus is placed on Eve at the most harmful location, and the large matrix theory is applied to yield a hardened secrecy rate to work on. The performance gain of the power optimization in terms of maximum tolerable number of antennas on Eve is shown to be significant. The second part of this paper shows two analyses of anti-eavesdropping channel estimation (ANECE) that can better handle Eve with any number of antennas. One analysis assumes that Eve has a prior statistical knowledge of its CSI, which yields lower and upper bounds on secure degrees of freedom of the system as functions of the number (N) of antennas on Eve and the size (K) of information packet. The second analysis assumes that Eve does not have any prior knowledge of its CSI but performs blind detection of information, which yields an approximate secrecy rate for the case of K being larger than N.
This article considers a two-way multiple-input multiple-output (MIMO) Rayleigh block fading wiretap channel with two full-duplex nodes (Alice and Bob) exchanging messages simultaneously and wiretapped by a $ {N}_{ {e}}$ -antennas eavesdropper (Eve). The channel state remains unchanged over a coherence interval T and is unknown to all terminals, including Alice, Bob, and Eve, at the beginning of the coherence interval. We first show the expression of the optimal signal waveform for Alice and Bob, which maximizes the sum secrecy rate, should be the products of independent random diagonal matrices and isotropically distributed unitary matrices. Then, conditioned on large T and small $ {N}_{ {e}}$ , the upper-bound for the secure degree of freedom (s.d.o.f.) of the two-way wiretap channel is derived, and a constant-norm-signaling (CNS) scheme is presented to achieve this theoretical bound. Finally, we formulate an optimization problem of the s.d.o.f. achieved by the CNS scheme for general cases with arbitrary T and $ {N}_{ {e}}$ , and solve this problem by exploring the monotonicity of the achievable s.d.o.f.. Our result shows that the optimal s.d.o.f. can be independent of coherence time T and becomes the product of the numbers of legitimate nodes's transmitter antennas (NLNTA) for large $ {N}_{ {e}}$ and small NLNTA.
This paper presents a number of fundamental properties of full-duplex radio for secure wireless communication under some simple and practical conditions. In particular, we consider the fields of secrecy capacity of a wireless channel between two single-antenna radios (Alice and Bob) against an unknown number of single-antenna eavesdroppers (Eves) from unknown locations, where Alice and Bob have zero knowledge (except a model) of the large-scale-fading channel-state-information of Eves. These properties show how the secrecy capacity is distributed in terms of the location of any Eve, how the optimal jamming power applied by the full-duplex radio varies with various parameters, and how bad or good the worst cases are. In particular, these properties show how the quality of self-interference cancelation/suppression affects various aspects of the fields of secrecy capacity. The cases of colluding Eves and non-colluding Eves are treated separately and yet coherently. For non-colluding Eves, asymptotically constant fields of secrecy capacity are revealed. For each of the two cases, we also treat subcases with or without small-scale fading.
In this paper, for the conventional MISO wiretap channel, we take into account the locations' random nature regarding those eavesdroppers and the ambient interferers in the wireless networks. For the convenience of mathematical analysis, these location distributions are modeled as Poisson point processes (PPPs). We assume that the transmitter Alice has no channel state information (CSI) about the other nodes except that it knows the statistical CSI of links about the legitimate user Bob and those eavesdroppers. In order to improve the security of Bob, we further set up a protected zone (PZ) to prevent excessive eavesdroppers from overhearing confidential signals. We investigate the probabilities of connection outage and secrecy outage to derive the closed form expression of secrecy transmission rate. Afterwards, we formulate an secrecy rate maximization problem and solve it to determine the optimized beamforming vector. The numerical results reveal the superiority of the proposed beamforming optimization over the relevant eigen beamforming design in [1].
We consider secure communications over MIMO wiretap channels, in the presence of a passive eavesdropper with an unlimited number of antennas. In this scenario, we characterize the performance of the artificial noise scheme proposed by Goel et al., and show that non-zero secrecy capacity is available even when the eavesdropper has more antennas than the transmitter. Our results are derived based on the fraction of the transmission power used for artificial noise and the ratio of the channel noise variances of the eavesdropper and the intended receiver. Finally, we investigate the attack option for the eavesdropper to drive the secrecy rate to zero by increasing the number of antennas.