In this paper, we study the secrecy performance of massive multiple-input multiple-output (MIMO) system for a scenario in which a number of BS antennas fail to send/receive any signals rendering them to be a source of additive distortion noise. The secrecy model studied here is based on multiple-input single-output single-eavesdropper (MISOSE) wiretap channel in which a single-antenna eavesdropper performs pilot contamination attack on a target user in order to increase the decodability of the confidential message intended to the target user. A lower bound of the achievable ergodic secrecy rate and a closed form expression for the maximum ratio (MR) precoder are derived. Results show that for the given MISOSE wiretap channel a positive secrecy rate is achievable even when a large number of antennas fail. The study also shows that massive MIMO systems with spatially correlated channels yield higher secrecy rate than with uncorrelated spatial channels albeit the earlier showed to be more impacted by BS antenna failure.
In this paper, we study the secrecy performance of massive multiple-input multiple-output (MIMO) system for a scenario in which a number of BS antennas fail to send/receive any signals rendering them to be a source of additive distortion noise. The secrecy model studied here is based on multiple-input single-output single-eavesdropper (MISOSE) wiretap channel in which a single-antenna eavesdropper performs pilot contamination attack on a target user in order to increase the decodability of the confidential message intended to the target user. A lower bound of the achievable ergodic secrecy rate and a closed form expression for the maximum ratio (MR) precoder are derived. Results show that for the given MISOSE wiretap channel a positive secrecy rate is achievable even when a large number of antennas fail. The study also shows that massive MIMO systems with spatially correlated channels yield higher secrecy rate than with uncorrelated spatial channels albeit the earlier showed to be more impacted by BS antenna failure.
The secrecy performance of forward link multi-user massive multiple-input multiple-output (MIMO) system is investigated in this paper. The base station (BS) equipped with a large number of transmit antennas sends mutually independent datas to multiple single-antenna legitimate users simultaneously. A passive multi-antenna eavesdropper is placed in the scenario to intercept the signals. We consider the case that the number of legitimate users and eavesdropper antennas increases proportionally with the number of BS antennas. Maximum ratio transmission (MRT) is used as linear precoder at the BS. Lower bounds on the ergodic achievable rate of legitimate users and upper bounds of the eavesdropper are derived. By minimizing the upper bounds on the achievable rates of the eavesdropper while satisfying the rate constraints of legitimate users, we present the corresponding optimal radiated power scaling (RPS) factor. In the limit of an infinite number of BS antennas, we prove that the optimal RPS factor converge to a different constant limit with that of the case in which the number of legitimate users and eavesdropper antennas is finite. We show that when the number of BS antennas grows large, the secrecy performance is mainly determined by the ratios between the number of BS antennas, legitimate users and eavesdropper antennas. A number of simulation results are presented to visualize the analysis.
In this paper, we study the problem of secure transmission in the downlink of a multi-cell massive multiple-input multiple-output (MIMO) system, where pilot contamination is considered due to non-orthogonal uplink training sequence. The channel state information (CSI) of the eavesdropper is assumed to be unavailable at the base station (BS) and hence, the BS cooperation and an artificial noise(AN) are investigated for secrecy enhancement. Based on regularized channel inversion (RCI), we derive a closed-form expression for ergodic secrecy sum rate in the large-system regime, in which the number of users per cell K, the number of antenna at BS N and the number of antenna at eavesdropper NEtend to infinity. Our analysis shows that the secrecy sum-rate saturates at high signal-to-noise ratio (SNR) with BSs cooperation and AN under pilot contamination.
In this paper, we investigate secure and reliable transmission strategies for multi-cell multi-user massive multiple-input multiple-output systems with a multi-antenna active eavesdropper. We consider a time-division duplex system where uplink training is required and an active eavesdropper can attack the training phase to cause pilot contamination at the transmitter. This forces the precoder used in the subsequent downlink transmission phase to implicitly beamform toward the eavesdropper, thus increasing its received signal power. Assuming matched filter precoding and artificial noise (AN) generation at the transmitter, we derive an asymptotic achievable secrecy rate when the number of transmit antennas approaches infinity. For the case of a single-antenna active eavesdropper, we obtain a closed-form expression for the optimal power allocation policy for the transmit signal and the AN, and find the minimum transmit power required to ensure reliable secure communication. Furthermore, we show that the transmit antenna correlation diversity of the intended users and the eavesdropper can be exploited in order to improve the secrecy rate. In fact, under certain orthogonality conditions of the channel covariance matrices, the secrecy rate loss introduced by the eavesdropper can be completely mitigated.
In this paper, we consider physical layer security provisioning in multi-cell massive multiple-input multiple-output (MIMO) systems. Specifically, we consider secure downlink transmission in a multi-cell massive MIMO system with matched-filter precoding and artificial noise (AN) generation at the base station (BS) in the presence of a passive multi-antenna eavesdropper. We investigate the resulting achievable ergodic secrecy rate and the secrecy outage probability for the cases of perfect training and pilot contamination. Thereby, we consider two different AN shaping matrices, namely, the conventional AN shaping matrix, where the AN is transmitted in the null space of the matrix formed by all user channels, and a random AN shaping matrix, which avoids the complexity associated with finding the null space of a large matrix. Our analytical and numerical results reveal that in multi-cell massive MIMO systems employing matched-filter precoding (1) AN generation is required to achieve a positive ergodic secrecy rate if the user and the eavesdropper experience the same path-loss, (2) even with AN generation secure transmission may not be possible if the number of eavesdropper antennas is too large and not enough power is allocated to channel estimation, (3) for a given fraction of power allocated to AN and a given number of users, in case of pilot contamination, the ergodic secrecy rate is not a monotonically increasing function of the number of BS antennas, and (4) random AN shaping matrices provide a favourable performance/complexity tradeoff and are an attractive alternative to conventional AN shaping matrices.
Multiuser multiple-input multiple-output (MIMO) wireless techniques have received tremendous attention as a way to achieve high spectral efficiency in current mobile communication systems such as Long Term Evolution (LTE) [1]. Due to the broadcast nature of the physical medium, wireless multiuser communications are very susceptible to eavesdropping, and it is critical to secure the transmitted information. In this work, consider the broadcast channel with confidential messages and external eavesdroppers (BCCE), where a multi-antenna base station [2] simultaneously communicates to multiple potentially malicious users, in the presence of randomly located external eavesdroppers. The secrecy capacity is measured in terms of outage probability and provides a complete characterization of the maximum transmission rate at which the eavesdropper is unable to decode any information. Using the proposed model, the secrecy rates is achieved with regularized channel inversion (RCI) precoding and analyzed by performing a large-system analysis where the number of users K and the number of transmit antennas N both grow to infinity in a fixed ratio. Finally an explicit expression for the probability of secrecy outage and the system performance is analyzed in the presence of both colluding and non-colluding eavesdroppers.
In this paper, a novel transmit antenna selection scheme for multiple input multiple output (MIMO) wiretap channels is proposed. This new scheme achieves higher secrecy performance by exploiting eavesdropper's channel state information. The key idea behind our proposal is to perform the antenna selection aiming to maximize the overall secrecy rate instead of maximizing the instantaneous signal-to-noise ratio of the main channel. In our analysis, we assume that the legitimate receiver and the eavesdropper employ a maximal-ratio combining technique to combine the received signals from the transmitter. Considering Nakagami-m fading channels, a closed-form expression for the secrecy outage probability is derived, which can be used as a quality of service metric. Further, an asymptotic analysis is carried out and the diversity/array gains are obtained. The ergodic secrecy rate is also investigated for the case of multiple input single output wiretap channels. Representative numerical examples are plotted and validated through Monte Carlo simulations. Insightful discussions are drawn from the proposed analysis.