In MIMO wireless channels, channel estimation can provide a source of randomness common to sender and receiver that may be used to generate secret keys. These keys can provide information theoretically secure communication. Alternatively, a known MIMO channel allows transmitting artificial noise in the null space of the main channel to secure communication. In this paper, we show that both methods can be combined to further enhance secrecy. Symbols encrypted at the transmitter simultaneously act as message for the intended receiver and as noise for any potential eavesdroppers. We derive expressions for the minimum-guaranteeable secrecy rate as a function of number of symbols encrypted. Given at least one symbol can be encrypted, our proposed method outperforms the standard artificial noise scheme in terms of both secrecy rate and power expenditure. We first analyze the system assuming keys can be instantaneously extracted from channel measurements. We then derive bounds for rates assuming the overhead time required for key generation produces a Gaussian channel-estimation error.
In MIMO wireless channels, channel estimation can provide a source of randomness common to sender and receiver that may be used to generate secret keys. These keys can provide information theoretically secure communication. Alternatively, a known MIMO channel allows transmitting artificial noise in the null space of the main channel to secure communication. In this paper, we show that both methods can be combined to further enhance secrecy. Symbols encrypted at the transmitter simultaneously act as message for the intended receiver and as noise for any potential eavesdroppers. We derive expressions for the minimum-guaranteeable secrecy rate as a function of number of symbols encrypted. Given at least one symbol can be encrypted, our proposed method outperforms the standard artificial noise scheme in terms of both secrecy rate and power expenditure. We first analyze the system assuming keys can be instantaneously extracted from channel measurements. We then derive bounds for rates assuming the overhead time required for key generation produces a Gaussian channel-estimation error.
This paper studies a secure communication over multiple-input multiple-output multi-antenna eavesdropper (MIMOME) channels which consist of legitimate parities, namely a transmitter and receiver, equipped with multi-antennas and a passive eavesdropper with multi-antennas. For securing the communication between the legitimate parties, we consider an artificial noise (AN) scheme in which the legitimate transmitter sends its secret messages and AN signal together. Meanwhile, it is assumed that the legitimate receiver has a full-duplex capability which enables it to capture the secret message from the transmitter and simultaneously generate a jamming signal to strengthen security. While there have been studies on similar setups, most of them focus on the design of the jamming signal with the assumption of full channel-state information (CSI) and/or system parameter optimization based on numerical evaluations. On the contrary, in this work, we instead introduce a tight lower bound on an achievable ergodic secrecy rate as a versatile analytic tool and derive a closed-form expressions for the bound. To confirm the analytic results, we carry out numerical evaluations of the ergodic secrecy rate which are compared with the proposed lower bound.
Security is one of the major issues in wireless communication system. In a wireless communication system as the transmission of information signal is over the air, eavesdroppers may have easy access to the transmitted data. The conventional network security mainly depends on cryptographic schemes. But as the security level increases, computational complexity will be high and cause complex key management problems. In this paper, the problem of secret communication between two nodes in the presence of a passive eavesdropper is considered. In general, nodes with multiple transmit antenna elements can ensure secure communication using directional antenna. In this paper, MIMO channel with multiple transmit antenna elements utilize fraction of the available power to produce „artificial noise‟ for the improvement of secure communication. The artificial noise is generated by the transmitter in such away that it degrades only the eavesdropper‟s channel. The various performance metrics such as bit error rate, channel capacity, optimal power allocation and secrecy rate were analyzed in the presence of non-colluding and colluding eavesdroppers. The obtained simulation results are compared with the existing work that does not use artificial noise. It is inferred from the results that the proposed work achieves improved secrecy rate than the existing work.
Recent research on the physical layer security of wireless systems focuses on artificial noise (AN) aided security. The main metric for analysis of such systems is the secrecy capacity of the system. Most of the AN schemes proposed in recent research are based on a hypothesis that the number of transmit antennas is larger than that of the receive antennas. Under this assumption, the system can utilize all eigensubchannels, equal to the number of the receive antennas, to send secret messages. The remaining null spaces are used for transmitting AN signals. These AN signals null out at the legitimate receivers and degrade illegitimate receiver's channels. However, this strategy can significantly impair the secrecy capacity of the system if the number of transmit antennas is constrained or even smaller than the number of receive antennas. Recently, a new strategy has been proposed, where messages are encoded in s (which is a variable) strongest eigen-subchannels based on ordered eigenvalues of Wishart matrices, while AN signals are generated in remaining spaces. This paper extends this strategy to Rician channels using the complex non-central Wishart distribution. A closed form expression for secrecy capacity of such system is computed using majorization theory. Performance of a MIMO communication system in Rician fading environment is simulated and effect of the Rician factor on secrecy capacity is studied. The same approach is then extended to decode and forward relay network. Secrecy capacity of the said network is computed, and the effect of AN is studied using the same methodology.
We consider secure downlink multiple-input–multiple-output (MIMO) communications between a transmitter and multiple users when there exists a passive eavesdropper. A downlink main channel between the transmitter and a user is estimated through uplink pilot symbols in a time-division duplex mode. On the other hand, to hinder an eavesdropper from estimating the eavesdropper channel between the transmitter and the eavesdropper, the transmitter does not send any pilot symbols. The main channel is hence available at the transmitter only, while the eavesdropper channel is unavailable at any node. Assuming these channel state information (CSI) conditions, we propose a MIMO transmission method using space–time line code (STLC) with artificial noise (AN) for enhancing the physical layer security. The STLC enables noncoherent detection at the receiver, i.e., a user, without CSI and achieves full spatial diversity. We derive the lower bound of the secrecy sum rate for the proposed STLC transmission method without AN, with AN, and with AN and imperfect CSI. Moreover, numerical results verify that the proposed STLC scheme outperforms the conventional eigen-beamforming and the precoding space-time block code in terms of secrecy sum rate regardless of the signal-to-noise ratio, the number of transmit antennas, and the CSI uncertainty.
At present, there has been a large amount of research on secrecy rate optimization. However, the reliability analysis of secure transmission is equally important although relatively less attention has been dedicated to. Therefore, this paper proposes a secure transmission method with artificial noise for the physical layer security issues in the transmission process of Multiple Input Multiple Output (MIMO) wireless communication systems. Firstly, we establish an artificial noise assisted MIMO systems model. Then, the channel state information (CSI) matrix is subjected to singular value decomposition to obtain the reasonable precoding and artificial noise matrices. Finally, the impact of artificial noise on the bit error rate performance of potential eavesdropper is analyzed, and based on the analysis, the problem of maximizing the system secrecy rate is established. The concave-convex procedure (CCCP) method is used to obtain the optimal power allocation, which significantly improves the security of MIMO systems. The simulation results show that using the null space of CSI matrix and artificial noise for signal encryption effectively improves the bit error rate of potential eavesdropping nodes. In addition, the secrecy rate obtained by the CCCP algorithm is consistent with the performance obtained by the particle swarm optimization algorithm, which verifies the effectiveness of the proposed algorithm.
An emerging area of interest in wireless security is the generation of secret encryption keys by leveraging the features of the physical propagation channel. The shared randomness of the wireless channel between two legitimate nodes in a communication network is exploited to provide strong secrecy. The secret keys are generated based on fluctuations or evolution of the wireless channel state. However, to the best of our knowledge, little work has been performed on algorithms to exploit the increased randomness available to wireless nodes equipped with MIMO antennas. In this paper, we present a practical key generation scheme for MIMO channels based on quantization performed on blind channel estimates. Our schemes generate random keys for transmitter and receiver by simultaneously quantizing the blind channel estimates. Our schemes are simulated for a realistic fading channel model, and performance metrics for error rate and efficiency are provided.