In this paper, a secure communication system model for massive multiple-input multiple-output (MIMO) relay networks is investigated. Specifically, physical layer secure transmission is provisioned in multi-user relay networks by employing massive MIMO, linear precoder/detectors and artificial noise generation in the presence of a passive multi-antenna eavesdropper. In particular, the achievable asymptotic secrecy rate for infinitely many relay antennas is derived. The use of random artificial noise shaping matrices is advocated for massive MIMO relays for the sake of reducing the system implementation complexity. The effects of the numbers of antennas at the relay and the eavesdropper in achieving secure communication are investigated by comparing the corresponding achievable secrecy rates.
In this paper, a secure communication system model for massive multiple-input multiple-output (MIMO) relay networks is investigated. Specifically, physical layer secure transmission is provisioned in multi-user relay networks by employing massive MIMO, linear precoder/detectors and artificial noise generation in the presence of a passive multi-antenna eavesdropper. In particular, the achievable asymptotic secrecy rate for infinitely many relay antennas is derived. The use of random artificial noise shaping matrices is advocated for massive MIMO relays for the sake of reducing the system implementation complexity. The effects of the numbers of antennas at the relay and the eavesdropper in achieving secure communication are investigated by comparing the corresponding achievable secrecy rates.
In this paper, secure transmission strategies for the relay-assisted massive multiple-input multiple-output (MIMO) downlink are investigated by using artificial noise (AN) generation and by exploiting the excess degrees-of-freedom through the random and null-space based precoders. The achievable rate expressions are derived for the estimated channel state information, and hence, the detrimental effects of channel estimation errors in designing precoders are quantified. Specifically, the achievable secrecy rate at the relayed user nodes is derived in closed-form, and thereby, the performance gap between the random and null-space based precoders is investigated. Our performance analysis reveals that the AN generation by using random precoders can be employed to design secure physical layer transmission strategies for the relay-assisted massive MIMO downlink systems. The AN generation can be useful in the finite antenna regime for guaranteeing physical layer security in the base-station-to-relay hop of the relay-assisted massive MIMO downlink. Although the AN generated at the base-station propagates to the relay-to-user hop via amplify-and-forward operation at the relay, sophisticated security provisions are needed to secure the end-to-end transmission when the relay is equipped with finitely many antennas. Consequently, the performance gap between the random and null-space based precoders gradually diminishes in the limit of infinitely many base-station antennas. Nevertheless, the achievable secrecy rate steadily vanishes with an increasing number of antennas at the passive eavesdropper.
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.
In this paper, a secure communication model for cognitive multi-user massive multiple-input multiple-output (MIMO) systems with underlay spectrum sharing is investigated. A secondary (cognitive) multi-user massive MIMO system is underlaid within a primary (licensed) multi-user massive MIMO system. A passive multi-antenna eavesdropper is eavesdropping upon either the primary or secondary transmission. To this end, physical layer secure transmissions are provisioned for both primary and secondary systems by exploiting linear precoders and artificial noise (AN) generation. The excess degrees-of-freedom at the primary massive MIMO base-station are exploited to transmit the AN sequence by using random AN shaping matrices for the purpose of degrading the signal decodability at the eavesdropper. Achievable asymptotic secrecy rates for infinitely many base-station antennas are derived, and these secrecy rates are shown to be independent of the eavesdropper channels. Moreover, for infinitely many secondary base-station antennas, the secondary system becomes independent of the primary system allowing it to operate at its maximum transmission power without disturbing the primary system.
In this paper, we consider physical layer security provisioning in multicell massive multiple-input-multiple-output (MIMO) systems. Specifically, we consider secure downlink transmission in a multicell massive MIMO system with matched-filter precoding and artificial noise (AN) generation at the base station (BS) in the presence of a passive multiantenna 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 the following, in multicell 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 favorable performance/complexity tradeoff and are an attractive alternative to conventional AN shaping matrices.
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.
An overview over secure communication in massive multiple-input multiple-output (MIMO) systems is presented. A massive MIMO base-station serves multiple user nodes by provisioning physical layer security techniques to secure the confidential transmissions against an eavesdropper. The eavesdropper can either be passively eavesdropping upon the communication or can actively contaminate the channel estimates. The achievable secrecy rates for these settings are reviewed, and their asymptotic behavior is discussed. Finally, a detection scheme for active pilot contamination attacks is discussed.