This paper presents a general analytical framework to evaluate the secrecy performance of transmit antenna selection (TAS) systems without requiring the identical average signal-to-noise ratios (SNRs) from different transmit antennas. Closed-form expressions of secrecy outage probability are derived in a multiple-input multiple-output (MIMO) wiretap channel. Moreover, a novel TAS scheme based on the limited feedback from both the receiver and the eavesdropper is proposed and analysed. With the additional consideration of the eavesdropper's channel, security is shown to be enhanced although the instantaneous channel state information (CSI) keeps unknown to the transmitter. Finally, numerical results substantiate the aforementioned analysis.
This paper presents a general analytical framework to evaluate the secrecy performance of transmit antenna selection (TAS) systems without requiring the identical average signal-to-noise ratios (SNRs) from different transmit antennas. Closed-form expressions of secrecy outage probability are derived in a multiple-input multiple-output (MIMO) wiretap channel. Moreover, a novel TAS scheme based on the limited feedback from both the receiver and the eavesdropper is proposed and analysed. With the additional consideration of the eavesdropper's channel, security is shown to be enhanced although the instantaneous channel state information (CSI) keeps unknown to the transmitter. Finally, numerical results substantiate the aforementioned analysis.
We propose and analyze transmit antenna selection (TAS) to enhance physical layer security in a wiretap channel with multiple antennas at the transmitter, the receiver, and the eavesdropper. We consider the practical scenario of passive eavesdropping, where the transmitter does not have any channel state information (CSI) of the eavesdropper's channel. In the main channel between the transmitter and the receiver, we select a single antenna at the transmitter that maximizes the instantaneous signal-to-noise ratio (SNR) at the receiver. At the receiver and the eavesdropper, we consider two combining techniques: 1) maximal-ratio combining (MRC) and 2) selection combining (SC). For non-identical Rayleigh fading between the main channel and the eavesdropper's channel, we first derive new closed-form expressions for the exact and asymptotic secrecy outage probabilities. The asymptotic results accurately reveal the secrecy diversity order and the secrecy array gain. Next, we derive new closed-form expressions for the probability of positive secrecy and characterize the ε-outage secrecy capacity. We show that, under TAS/MRC and TAS/SC protocols, the secrecy outage probability approaches zero and the ε-outage secrecy capacity increases with increasing number of transmitter antennas.
This paper proposes a new transmit antenna selection (TAS) scheme which provides enhanced physical layer security in multiple-input multiple-output (MIMO) wiretap channels. The practical passive eavesdropping scenario we consider is where channel state information (CSI) from the eavesdropper is not available at the transmitter. Our new scheme is carried out in two steps. First, the transmitter selects the two strongest antennas based on the feedback from the receiver, which maximizes the instantaneous signal-to-noise ratio (SNR) of the transmitter-receiver channel. Second, the Alamouti scheme is employed at the selected antennas in order to perform data transmission. At the receiver and the eavesdropper, maximal-ratio combining is applied in order to exploit the multiple antennas. We derive a new closed-form expression for the secrecy outage probability in non-identical Rayleigh fading, and using this result, we then present the probability of non-zero secrecy capacity in closed form and the ε-outage secrecy capacity in numerical form. We demonstrate that our proposed TAS-Alamouti scheme offers lower secrecy outage probability than a single TAS scheme when the SNR of the transmitter-receiver channel is above a specific value.
In this paper, we investigate the secrecy performance for a multiple-input multiple-output (MIMO) wiretap channel in the presence of a multiantenna eavesdropper. In particular, the legitimate transmitter uses transmit antenna selection (TAS) to transmit on a single antenna with the largest signal-to-noise ratio (SNR) while both the legitimate receiver and the eavesdropper adopt maximal ratio combining (MRC) for reception. We derive exact closed-form expressions for the probabilities of achieving positive secrecy rate and secrecy outage in the case of imperfect feedback due to feedback delay and/or feedback error. Furthermore, we derive the asymptotic secrecy outage probability at high SNR, which accurately reveals the secrecy diversity loss due to imperfect feedback. Simulation results are provided to verify our analytical results and illustrate the impact of imperfect feedback on the secrecy performance of such a wiretap system.
We propose and analyze transmit antenna selection (TAS) to enhance physical layer security in a wiretap channel with NAantennas at the transmitter, NBantennas at the receiver, and NEantennas at the eavesdropper. We focus on the practical scenario where the transmitter does not have any channel state information (CSI) of the eavesdropper's channel. The transmitter selects a single antenna that maximizes the instantaneous signal-to-noise ratio (SNR) at the receiver. The receiver and the eavesdropper employ either maximal-ratio combining (MRC) or selection combining (SC) to combine the received signals. For the proposed protocols, we derive new closed-form expressions for the probability of non-zero secrecy capacity. We consider Nakagami-m fading with non-identical fading parameters of the main channel, mB, and of the eavesdropper's channel, mE. Next, we derive new closed-form expressions for the exact secrecy outage probability, based on which the ε-outage secrecy capacity is characterized. Based on the exact expressions, we derive the asymptotic secrecy outage probability which accurately reveals the secrecy diversity order and the secrecy array gain. We confirm that the proposed protocols achieve identical secrecy diversity orders of NANBmB. An interesting conclusion is reached that this diversity order is independent of NEand mE. Furthermore, we prove that under the proposed protocols, the secrecy outage probability and the ε-outage secrecy capacity improve with increasing NA.
In this paper, we propose an effective method with low feedback overhead and low signal processing cost for security enhancement in multi-input multi-output (MIMO) wiretap channels. Based on transmit antenna selection (TAS) protocol, the transmitter selects two antennas that maximizes and minimizes the instantaneous signal-noise-ratio (SNR) at the receiver, respectively. Then, the transmitter uses the antenna with maximum SNR (strongest-antenna) to transmit valid data, and uses the antenna with minimum SNR (weakest-antenna) to transmit jamming, simultaneously. We derive new closed-form expressions for the exact probability density functions (PDFs) of receivers' SNR, based on which the secrecy outage probability and the probability of non-zero secrecy capacity are characterized. We demonstrate that our proposed TAS-Jamming protocol offers higher secure performance than other existing TAS protocols when the SNR of transmitter-receiver channel is below a specific value. The numerical simulation results verify our analysis.