In this paper, we investigate the secrecy performance of cognitive multi-input multi-output multiuser (MIMO-MU) wiretap networks over space-and-time correlated fading channels. Specifically, we propose a joint transmit antenna selection (TAS) and multiuser scheduling scheme to improve the security of the considered system. To thoroughly analyze the impact of the joint TAS and multiuser scheduling scheme and the channel correlation on the physical layer security, the new exact and asymptotic closed-form expressions for the secrecy outage probability of cognitive MIMO-MU wiretap networks are derived in two distinct scenarios, i.e., space-and-time correlated fading channels and independent-and-perfect fading channels. From the theoretical and simulation results, several important remarks are concluded as follows. 1) The channel space correlation does not affect the achievable secrecy diversity order in a high main-to-eavesdropper ratio (MER) regime. While it produces different impacts on the secrecy performance with different values of the MER in a low MER regime. 2) The channel time correlation on the main channel can reduce the achievable secrecy diversity order from$N_{\rm A}N_{\rm B}$to 1. 3) The joint TAS and multiuser scheduling scheme can achieve better performance than the traditional random scheduling scheme over space-and-time correlated fading channels.
In this paper, we investigate the secrecy performance of cognitive multi-input multi-output multiuser (MIMO-MU) wiretap networks over space-and-time correlated fading channels. Specifically, we propose a joint transmit antenna selection (TAS) and multiuser scheduling scheme to improve the security of the considered system. To thoroughly analyze the impact of the joint TAS and multiuser scheduling scheme and the channel correlation on the physical layer security, the new exact and asymptotic closed-form expressions for the secrecy outage probability of cognitive MIMO-MU wiretap networks are derived in two distinct scenarios, i.e., space-and-time correlated fading channels and independent-and-perfect fading channels. From the theoretical and simulation results, several important remarks are concluded as follows. 1) The channel space correlation does not affect the achievable secrecy diversity order in a high main-to-eavesdropper ratio (MER) regime. While it produces different impacts on the secrecy performance with different values of the MER in a low MER regime. 2) The channel time correlation on the main channel can reduce the achievable secrecy diversity order fromNANBto 1. 3) The joint TAS and multiuser scheduling scheme can achieve better performance than the traditional random scheduling scheme over space-and-time correlated fading channels.
I265 this paper, we investigate the secrecy performance of multi-input single-output and single-eavesdropper (MISOSE) cognitive radio (CR) networks over correlated fading channels. For the security enhancement, the transmit antenna selection (TAS) scheme is used to select the best transmit antenna at Alice based on the main channel. In order to analyze the impact of channel correlation coefficient, interference temperature threshold and antenna numbers on the secrecy performance, we firstly derive the exact closed-form expression of the secrecy outage probability (SOP) for the considered system taking into account the correlation between the main channel and wiretapping channel. Moreover, to extract more deep insights, the asymptotic expression of SOP in high main-to-eavesdropper ratio (MER) regime is also derived, which reveals that the channel correlation does not degrade the secrecy diversity order and even can strengthen the secrecy performance in high MER regime. Finally, numerical results are provided to demonstrate the correctness and accuracy of our analysis.
In this paper, we analyze the impact of the antenna correlation on the secrecy of multiple-input multiple-output (MIMO) wiretap channels with multiple eavesdroppers, where transmit antenna selection (TAS) and maximal-ratio combining (MRC) are employed at the transmitter, receiver and eavesdroppers, respectively. For the practical passive eavesdropping, we first develop new and closed general formulas for the secrecy outage probability and the probability of non-zero secrecy capacity to characterize the effect of spatial correlation, and results prove that the enhanced security performance can be achieved when multiple antennas are provided at the transmitter. We then explore how spatial correlation affects the asymptotic secrecy outage probability, and the secrecy diversity order is revealed. Based on these, the results show that when the average SNR of the main channel is relatively low, higher antenna correlation is more perfect to the secrecy. When the average SNR of the main channel is relatively high, higher antenna correlation is more destructive to the secrecy.
This paper presents a detailed secrecy outage performance analysis of correlated multi-antenna wiretap channels with three popular diversity combining schemes, namely maximal ratio combining, selection combining, and equal gain combining at the legitimate receiver. For single input multiple output wiretap channels, both exact and asymptotic expressions are derived for the secrecy outage probability (SOP) of these systems. The findings suggest that, compared with the scenario where all the channels are independent, correlation of the main channels alone increases the SOP by a factor of 1/ det(U), where det(U) is the determinant of correlation matrix U. In contrast, in the high signal-to-noise ratio regime at the legitimate receiver, correlation between the main channels and the eavesdropper channels has a positive effect on SOP. Moreover, for multiple input and multiple output wiretap channels, the SOP of two transmit antenna selection (TAS) schemes are analyzed for the considered correlated channel model. The SOP relationship of the both TAS schemes is quantified by the secrecy array gain. Finally, numerical simulations are conducted to corroborate the analytical results.
In this paper, we consider a multiuser downlink wiretap network consisting of one base station (BS) equipped with AA antennas, NB single-antenna legitimate users, and NE single-antenna eavesdroppers over Nakagami-m fading channels. In particular, we introduce a joint secure transmission scheme that adopts transmit antenna selection at the BS and explores threshold-based selection diversity scheduling over legitimate users to achieve a good secrecy performance while maintaining low implementation complexity. More specifically, in an effort to quantify the secrecy performance of the considered system, two practical scenarios are investigated, i.e.: in Scenario I, the eavesdropper's channel state information (CSI) is unavailable at the BS, and in Scenario II, the eavesdropper's CSI is available at the BS. For Scenario I, novel exact closed-form expressions for the secrecy outage probability are derived, which are valid for general networks with an arbitrary number of legitimate users, antenna configurations, number of eavesdroppers, and the switched threshold. For Scenario II, we take into account the ergodic secrecy rate as the principle performance metric, and derive novel exact closed-form expressions for the ergodic secrecy rate. In addition, we also provide simple and asymptotic expressions for secrecy outage probability and ergodic secrecy rate under two distinct cases, i.e.: in Case I, the legitimate user is located close to the BS, and in Case II, both the legitimate user and eavesdropper are located close to the BS. Our important findings reveal that the secrecy diversity order is AAmA and the slope of secrecy rate is one under Case I, while the secrecy diversity order and the slope of secrecy rate collapse to zero under Case II, where the secrecy performance floor occurs. Finally, when the switched threshold is carefully selected, the considered scheduling scheme outperforms other well-known existing schemes in terms of the secrecy performance and complexity tradeoff.
In this paper, we introduce transmit antenna selection/maximal-ratio combining (TAS/MRC) scheme in dual-hop randomize-and-forward (RaF) cognitive multiple-input multiple-output (MIMO) wiretap networks with outdated channel state information (CSI). In this network, the secondary transmitter adopts the TAS scheme to choose the antenna with the maximal received signal-to-noise ratio (SNR), while the secondary receiver and the eavesdropper adopt the MRC scheme to combine the received signals. To thoroughly assess the secrecy performance achieved by the TAS/MRC scheme and the impact of outdated CSI on the secrecy performance, we derive a new closed-form expression for the secrecy outage probability of dual-hop RaF cognitive MIMO wiretap networks. In order to achieve more insights on the application of TAS/MRC scheme, we further present tractable asymptotic secrecy outage probability at high SNR regimes under two distinct scenarios. From our analysis, several important concluding remarks are obtained as follows: 1) the RaF relaying strategy achieves better secrecy performance than that of the decode-and-forward relaying strategy for dual-hop cognitive MIMO wiretap networks; 2) outdated CSI decreases the secrecy diversity gain of the TAS/MRC scheme from NRmin (NA, NB) to (NR, NB) ; and 3) although TAS/MRC scheme cannot attain full secrecy diversity gain for the considered system with outdated CSI, it still can achieve an extra secrecy coding gain compared with the random antenna selection/MRC scheme.
In this paper, we investigate the secrecy performance of dual-hop randomize-and-forward (RaF) cognitive relay multi-channel wiretap networks over correlated fading channels, in which the eavesdropper can wiretap the information from source and relays simultaneously. Specifically, in order to enhance the secrecy performance, we introduce two cooperation diversity schemes: 1) traditional partial relay selection (TPRS), where an optimal relay is selected to receive-and-forward the information based on the channel quality between the source and relays and 2) decoding threshold-aided optimal relay selection (DTaORS), where an optimal relay is selected from the threshold-based relay set based on the channel quality between the relays and destination. For these criteria, we analyze the secrecy performance of two cooperation diversity schemes by deriving the exact and asymptotic expressions for the secrecy outage probability of cognitive relay wiretap networks over correlated fading channels. From the results, we conclude that: 1) even though the channel correlation does not influence the secrecy diversity order, it is beneficial to the secrecy coding gain in high main-to-eavesdropper ratio regime; 2) DTaORS with an appropriate decoding rate can achieve better secrecy performance than TPRS. However, affected by the multi-channel wiretap, both of DTaORS and TPRS can not increase the secrecy diversity order any more, which is always equal to 1; and 3) the secrecy performance with a RaF scheme is better than that with a decode-and-forward scheme in multi-channel wiretap scenario.