AN-Aided Secure Beamforming Design for Correlated MISO Wiretap Channels

AN-Aided Secure Beam forming Design for Correlated MISO Wiretap Channels

Abstract: An artificial-noise (AN)-aided beam former for reducing secrecy loss due to the correlation between the main and wiretap channels is designed in this paper. We consider slow fading multiple-input-single-output (MISO) wiretap channels with a passive single-antenna eavesdropper, where the source has accurate main channel information and statistical wiretap channel information. By exploiting the channel correlation, the power of the AN in the null space of the main channel can be placed more reasonably instead of using a simple uniform distribution. Then, an efficient algorithm for power allocation between the information-bearing signal and the AN is developed. Simulation results show that the secrecy rate under the transmit power and secrecy outage constraint is improved.

Existing system: This paper focuses on AN-aided beam forming design based on channel correlation. Despite the secrecy loss, the correlation suggests some useful information, which can be used to help design an improved beam former.

Compared to the existing AN-aided beam forming schemes, our model,

considering the channel correlation, describes the statistical distribution of the wiretap channel more precisely. Therefore, the power of the AN in the null space of the main channel is placed more reasonably instead of using a simple uniform distribution. Then, an efficient algorithm for power allocation between the information-bearing signal and the AN is developed. Based on this, the achievable secrecy rate under the transmit power.

Proposed system: Shows the relationship between the power correlation coefficient Ď and the achievable secrecy rate Rs, where some parameters in the simulations are set as follows: the number of antennas at Alice is Ns = 16; the required secrecy outage probability is 15%; the variances of h and g, related to the path loss as a function of distance, are set. In the simulations, two cases, for which the total transmit power P = 20 and 30 dB, are presented. The blue and green curves represent our proposed AN-aided beam forming scheme based on correlation. The difference is that the former and the latter employ the bound method and a brute-force search for power allocation between the information-bearing signal and the AN, respectively. In contrast, the traditional scheme in which AN is uniformly distributed in the null space of the main channel is presented in red. Note that these curves correspond to both analytical and simulation methods simultaneously since these two methods have the same results.

Advantages: We observe that Rs continuously decreases as Ď increases for all curves.

Moreover, the secrecy rate gap between the proposed and traditional schemes decreases because with Ď increasing, the difference between the main and wiretap channels definitely diminish. For both schemes, as a result, less AN in the null space of h and more confidential information are projected to the direction of g.

We also observe that a higher P can help reduce the secrecy loss due to the correlation. Compared to the traditional scheme, our proposed scheme achieves a higher Rs, which means that AN is placed more reasonably in our proposed scheme. The blue curve is very close to the green one, which indicates that the bound method with much lower computational complexity works almost as well as a brute-force search.

Disadvantages: We consider a multiple-input single-output single-antenna eavesdropper (MISOSE) system over slow-fading channels, where an Ns-antenna source (Alice) sends confidential messages to a single-antenna destination (Bob) with the transmission overheard by a passive single-antenna eavesdropper (Eve).

We assume that the transmitter side is independent, whereas the receiver side is correlated. This situation occurs in scenarios where the transmitted antenna spacing at Alice is sufficiently large and Eve is near Bob. Additionally, Alice has accurate CSI of the Alice-Bob link, denoted by h 2 CNsĂ—1, and statistical CSI of the AliceEve link, denoted by g.

Modules: Artificial – noise: IN physical layer (PHY) security, artificial-noise (AN)-aided Beam forming techniques are typically utilized to strengthen the secrecy of wiretap channels.

Beam forming aims to enhance the signal quality at the destination while limiting the signal strength at the eavesdropper; AN inserted into the transmitted signal helps to degrade the reception at the eavesdropper. However, when the main and wiretap channels are strongly correlated, the secrecy enhancement due to the techniques is substantially weakened, resulting in significant secrecy loss. In this situation, we consider slow-fading correlated multiple input- single-output (MISO) wiretap channels with a passive single-antenna eavesdropper. Under the assumption that the source has accurate main and statistical wiretap channel state information (CSI), we study the secrecy outage constrained secrecy rate maximization by optimizing the AN-aided beam former. AN-aided beam forming techniques have achieved considerable success in improving secrecy.

Slow-fading channel: From the perspective of the average effect, this scheme is also applied to slowfading channels. In, A was utilized to degrade the signal quality at the eavesdropper and was placed only in the null space of the main channel with an isotropic distribution to avoid jamming the reception at the destination. The authors in proved that AN in the null space of the main channel must be

symmetrical to maximize the secrecy when the main and wiretap channels are independent of each other. When the desired signal was transmitted in the direction of the main channel and AN was uniformly generated in the null space of the main channel, the authors in derived a closed-form expression for power allocation for minimizing the secrecy outage probability. Nevertheless, the scheme that full AN power is placed only in the null space of the main channel is not optimal because when a part of AN power is placed in the direction of the main channel, it is still possible that the net secrecy rate increases despite interference with the destination.

The authors in showed that the optimal AN is always orthogonal to the information-bearing signal for the maximum secrecy rate under the secrecy outage constraint and derived the optimal power allocation between the information bearing signal and the A without any approximation.

Beam former: However, some scenarios exist in which the main and wiretap channels are statistically correlated, and the related research on correlation is in its infancy. The correlation between the main and wiretap channels is harmful to the transmission security, and excessively large signal power provides less benefit. To reduce the secrecy loss due to the correlation, the channel fluctuation between time slots, antennas, users and relays is often exploited, based on which opportunistic selection can be implemented in a centralized or distributed manner through dedicated feedback links. In these strategies, the channel correlation information is not fully utilized as a resource to help improve the secrecy; thus, room for secrecy improvement still exists. This paper focuses on AN-aided beam forming design based on channel correlation. Despite the secrecy loss, the correlation suggests some useful information, which can be used to help design an improved beam former. Compared to the existing AN-aided beam forming schemes, our model, considering the channel correlation, describes the statistical distribution of the wiretap channel more precisely.