This letter generalizes the precoding-aided spatial modulation (PSM) to a multiuser (MU) downlink scenario. With precoding vectors elaborately designed, a proposed MU-PSM scheme has the capability to resist a multiple antenna eavesdropper. Specifically, signal precoding matrices (SPMs) are designed to cancel the MU interference and modulate partial information bits on the indices of receive antennas. To improve physical layer security, scrambling on SPMs is conceived to construct a fast-varying precoding matrix, which contributes to the degradation at Eve's blind estimation and detection. Moreover, issues of detection algorithms and a lower bound of secrecy rate are addressed to verify security enhancement in the proposed scheme.
This letter generalizes the precoding-aided spatial modulation (PSM) to a multiuser (MU) downlink scenario. With precoding vectors elaborately designed, a proposed MU-PSM scheme has the capability to resist a multiple antenna eavesdropper. Specifically, signal precoding matrices (SPMs) are designed to cancel the MU interference and modulate partial information bits on the indices of receive antennas. To improve physical layer security, scrambling on SPMs is conceived to construct a fast-varying precoding matrix, which contributes to the degradation at Eve's blind estimation and detection. Moreover, issues of detection algorithms and a lower bound of secrecy rate are addressed to verify security enhancement in the proposed scheme.
In this letter, the precoding-aided spatial modulation (PSM) is generalized to a secret PSM (SPSM) scheme, which has the capability to resist malicious eavesdropping from an eavesdropper that is unknown to the transmitter. We design a time-varying precoder for the SPSM so that it can retain all the PSM's advantages at the desired receiver while producing time-varying interference to the eavesdropper. The secrecy capacity of our proposed SPSM is studied, and the optimal power allocation between signal and interference transmission is investigated. Our studies and performance results demonstrate that our SPSM can significantly improve the secrecy performance of the PSM, particularly in a high-signal-to-noise-ratio region. Furthermore, the SPSM is capable of achieving a nonzero secrecy rate even when the eavesdropper has more antennas than the desired receiver.
We investigate signaling and linear precoding designs for secure downlink communications in a multiuser MIMO (MU-MIMO) network. The network is tapped by an external eavesdropper (Eve) who is equipped with a large number of antennas. In addition to the transmission of several (unicast) information signals to downlink users (Bobs), the transmitter (Alice) generates friendly jamming (FJ), aiming to prevent Eve from decoding Alice’s signals. To mitigate both multiuser interference (MUI) and FJ on Bobs, MU-MIMO systems often rely on zero-forcing (ZF) precoders. A condition for the application of such precoders is that the network must beunderloaded, i.e., Alice has more antennas than all Bobs combined. Foroverloadedscenarios, ZF-based precoding cannot guarantee nullification of both MUI and FJ at legitimate receivers. Accordingly, we propose a combined signaling-and-precoding scheme that can also be applied to an overloaded MU-MIMO network. In an underloaded scenario, our technique is shown to impose a more stringent antenna requirement on Eve than a classical ZF-based precoding, i.e., Eve must utilize more antennas if she is to successfully eavesdrop on Alice’s transmissions. Although our scheme is comparable to antenna selection (AS) approaches in terms of Eve’s antenna requirement, it incurs much less delay and complexity by avoiding frequent on/off switching of the RF chains at Bobs. For underloaded scenarios, we provide security analysis that establishes the conditions under which our scheme is superior to the ZF scheme. Using computer simulations, we validate the advantages of our design and contrast it with ZF and AS schemes in terms of the symbol error rate, the EVM, and the achievable rate in both underloaded and overloaded scenarios.
In this paper we investigate the physical layer security for downlink MU-MIMO systems where the transmitter and the eavesdropper are equipped with multiple antennas, while the legitimate users have single antenna. This is a more challenging topic because the eavesdropper appears to be more powerful than the legitimate users. We propose a transmission scheme able to enhance secure transmission for legitimate users, by intentionally applying different beamforming matrices to pilot signals and data signals. The beamforming matrix for data signals is constructed in a way that legitimate users can derive the channel matrix experienced by data signals based on pilot signals, whereas the eavesdropper fails to obtain the channel matrix experienced by data signals even with the aid of pilot signals. Therefore coherent detection at the eavesdropper is impossible and the signal-plus-interference-to-noise (SINR) of the eavesdropper is significantly degraded. In addition, the proposed beamforming design is formulated as an optimization problem to maximize the minimum SINR. We theoretically prove that with this formulation, the resultant optimal SINR is not affected by the proposed format of beamforming matrix for data signals. Numerical results show that, the proposed beamforming design outperforms the conventional beamforming design in terms of ergodic secrecy sum rate. Furthermore, with suitable beamforming designs, the ergodic secrecy sum rate achieved will not be noticeably affected by the number of antennas at the eavesdropper, although it is significantly degraded with conventional beamforming design.
Existing secure strategies based on precoding-aided spatial modulation (PSM) ensure the secrecy communication by introducing time-varying interference with extra power towards the eavesdropper, which, however, reduces the energy efficiency. In this paper, we propose two novel schemes to enhance the secrecy performance based on PSM. The first scheme utilizes the random antenna selection (RAS) technique, namely RAS- PSM, to generate zero-forcing (ZF) precoding matrices with randomly activated transmit antennas. It ensures efficient transmission to the legitimate user, while confusing the eavesdropper via the turbulence of RAS without extra power consumption. The second scheme, called hybrid secret PSM (HS-PSM), is an enhanced version of RAS-PSM by introducing the time-varying artificial noise into RAS-PSM. The resulting secrecy rates by the two proposed schemes are theoretically analyzed and evaluated via Monte Carlo simulations as well, whose results demonstrate that RAS-PSM achieves a higher secrecy rate than the existing schemes and HS- PSM is capable of further improving the secrecy performance especially at high signal-to-noise ratio (SNR).
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.
We consider the physical layer security (PLS) problem in multi-user non-orthogonal multiple access (NOMA) enabled multiple-input multiple-output (MIMO) visible light communication systems intercepted by a passive eavesdropper (Eve). We propose a novel transmit precoding scheme based on receive spatial modulation (RSM) to degrade the signal-to-interference-noise ratio (SINR) of Eve by exploiting only the slow-fading characteristics of the visible light channel of the legitimate users (Bobs). The proposed PLS precoder is reinforced with secret parameter exchange with Bobs and a CSI acquisition model is proposed to reduce the PLS algorithm's computational load substantially at the transmitter. The closed-form expressions for the achievable secrecy rates and their upper and lower bounds are derived. Via Monte Carlo simulations, we confirm that Bobs can successfully decode their information in various user configurations while Eve's received SINR is significantly worsened by the jamming signal induced by the proposed precoder with secret key exchange. It is also shown that Eve's bit error rate (BER) is increased to the 0.5-level for almost any position in the considered indoor environment. Finally, we corroborate the derived secrecy expressions by computer simulations and show that the proposed scheme provides PLS for Bobs.