This work proposes the use of a unitary modulation scheme to enhance physical layer secrecy in multi-antenna wireless systems. The proposed scheme takes advantage of having only channel state information at the transmitter (CSIT) but not at the receiver and the eavesdropper. With CSIT, the transmitter can first take the LQ or singular value decomposition of the channel matrix and then replace its unitary component by an information-bearing unitary matrix symbol. When the SNR is sufficiently high, the legitimate receiver is able to extract the unitary matrix by exploiting the uniqueness of the matrix decomposition. But the eavesdropper is incapable of doing so due to the ambiguity caused by the unknown unitary rotation on its channel, which ensures zero information leakage to the eavesdropper when the channels are independent. A detection scheme based on the chordal distance is proposed, and the achievable secrecy rate is derived and shown to depend only on the mutual information of the main channel. The simulation results demonstrate the effectiveness and secrecy advantages of our proposed unitary modulation scheme.
This work proposes the use of a unitary modulation scheme to enhance physical layer secrecy in multi-antenna wireless systems. The proposed scheme takes advantage of having only channel state information at the transmitter (CSIT) but not at the receiver and the eavesdropper. With CSIT, the transmitter can first take the LQ or singular value decomposition of the channel matrix and then replace its unitary component by an information-bearing unitary matrix symbol. When the SNR is sufficiently high, the legitimate receiver is able to extract the unitary matrix by exploiting the uniqueness of the matrix decomposition. But the eavesdropper is incapable of doing so due to the ambiguity caused by the unknown unitary rotation on its channel, which ensures zero information leakage to the eavesdropper when the channels are independent. A detection scheme based on the chordal distance is proposed, and the achievable secrecy rate is derived and shown to depend only on the mutual information of the main channel. The simulation results demonstrate the effectiveness and secrecy advantages of our proposed unitary modulation scheme.
du Abstract-This work proposes the use of a unitary modulation scheme to enhance physical layer secrecy in multi-antenna wire less systems. The proposed scheme takes advantage of having only channel state information at the transmitter (CSIT) but not at the receiver and the eavesdropper. With CSIT, the transmitter can first take the LQ or singular value decomposition of the channel matrix and then replace its unitary component by an information bearing unitary matrix symbol. When the SNR is sufficiently high, the legitimate receiver is able to extract the unitary matrix by exploiting the uniqueness of the matrix decomposition. But the eavesdropper is incapable of doing so due to the ambiguity caused by the unknown unitary rotation on its channel, which ensures zero information leakage to the eavesdropper when the channels are independent. A detection scheme based on the chordal distance is proposed, and the achievable secrecy rate is derived and shown to depend only on the mutual information of the main channel. The simulation results demonstrate the effectiveness and secrecy advantages of our proposed unitary modulation scheme.
This work examines the advantages of having only channel state information at the transmitter (CSIT), and not at the receiver and the eavesdropper, when achieving secrecy in fading wiretap channels. The key idea is that, with only CSIT, the transmitter can pre-compensate for the amplitude and phase distortions on the main channel. This allows the receiver to decode coherently even without knowledge of the CSI, while leaving the eavesdropper confused by the unknown variations of its own channel. When the channel is reciprocal, this CSI assumption can be achieved in practice through reverse training, i.e., by having the receiver emit the training signal so that the transmitter can estimate the channel by itself. Two secrecy-enhancing transmission schemes are proposed to exploit the CSIT. The truncated channel inversion scheme is used when the receiver and the eavesdropper have no CSI available, and the truncated phase compensation scheme is adopted when they can practically measure the SNR. The achievable secrecy rates of these schemes are derived for both single-antenna and multi-antenna wireless fading scenarios. Numerical results show significant improvements in secrecy rate compared to the case with full CSI at all terminals.
We investigate the secure degrees of freedom (SDoF) of the multiple-input multiple-output (MIMO) wiretap channel with intersymbol interference (ISI) in the presence of a multi-antenna cooperative jammer. We focus on the practically relevant setting with no channel state information at the transmitters (CSIT). More specifically, the legitimate transmitter and the cooperative jammer only have statistical knowledge of the channel in terms of the effective number of ISI channel taps, i.e., channel impulse response (CIR) lengths, toward the legitimate receiver and the eavesdropper. Our main contribution is to show that in the absence of CSIT, positive SDoF can be achieved by carefully exploiting: 1) the heterogeneity of the CIR lengths toward both receivers and 2) the relative number of antennas at the four terminals. To achieve secrecy, we propose a scheme in which the transmitter strategically sends a mixture of information and artificial noise symbols in a way that exploits the heterogeneity of CIR lengths. Additionally, the cooperative jammer transmits artificial noise symbols in a way that completely masks all the information symbols that are received at the eavesdropping node. Under the proposed scheme, positive SDoF can be achieved, even when the number of antennas at the legitimate receiver is less than the number of antennas at the eavesdropper.
With the rapid development of wireless communications, security becomes extremely important. In many applications, each transmitter desires to send independent and confidential message to its intended receiver while ensuring mutual information-theoretic secrecy. In this dissertation, I study strategies for enhanced secrecy in wireless communication systems with limited rate feedback and transmitter cooperation. The two-user Gaussian channel model is considered under different scenarios. The transmitters both require channel state information (CSI), which is quantized at the receiver and fed back through the sum-rate-limited feedback channels. The quantization errors reduce the beamforming gain from the direct transmitter, and cause interference leakage from the cross transmitter. In the first scenario, I introduce the wiretap channel model where one receiver is a known eavesdropper, and a second transmitter is used to send a cooperative jamming signal to degrade the eavesdropper's channel. I consider two cases, one where no information about the eavesdroppers is available, and one where statistical CSI is available. With no information about the eavesdroppers, I show how to choose the allocation of feedback bits to the transmitters in order to maximize the amount of jamming power available to interfere with the eavesdroppers, subject to maintaining the lower bound on the rate at a minimum quality-of-service level. For the case of statistical CSI, I derive an approximate lower bound on the average secrecy rate, and optimize the bound to find a suitable bit allocation and the transmit power allocated to the transmitters. In the second scenario, I consider the interference channel model where the two transmitters are amenable to cooperation for improving the overall secrecy performance of the system. I derive an approximation for the average secrecy rate of each link, and optimize the sum secrecy rate over the transmit power and feedback bits allocated to the transmitters. Interestingly, increasing the transmit power beyond a certain point decreases the secrecy performance. When the transmitters have the same number of antennas, I derive the results in closed form. Simulations validate the theoretical analysis and demonstrate the significant performance gains that result from the use of optimal transmit power control and intelligent feedback bit allocation.
Conventional beamforming transmission techniques can enhance physical layer secrecy performance while requiring the full channel state information (CSI) of legitimate users and even that of eavesdroppers at the transmitter. However, providing full CSI of legitimate users at the transmitter can be challenging in practice. Thus, it is of considerable interest to enhance secrecy performance with partial CSI of legitimate users at the transmitter. Random unitary beamforming (RUB) is a low‐complexity multiple antennas transmission scheme requiring limited CSI. In this study, the authors investigate the secrecy performance of RUB transmission over multiple‐input single‐output single‐eavesdropper and multiuser multiple‐input multiple‐output single‐eavesdropper channels. They also propose a novel RUB‐based artificial noise (AN) method for multiple antennas communication system. They derive the closed‐form expressions of the exact and the asymptotic ergodic secrecy rate and the secrecy outage probability for these transmission scenarios. Numerical results are presented to illustrate the trade‐off between performance and complexity of the resulting physical layer security design. They show that the deployment of RUB and RUB‐based AN offers an attractive solution for enhancing the security of wireless transmission systems.
In this paper, we present a new secrecy-enhancing scheme for the spatial modulation (SM) system, by considering imperfect channel state information (CSI). In the proposed scheme, two antennas are activated at the same time. One of the activated antennas transmits information symbols along with artificial noise (AN) optimized under the imperfect CSI condition. On the other hand, the other activated antenna transmits another AN sequence. Because the AN are generated by exploiting the imperfect CSI of the legitimate channel, they can only be canceled at the legitimate receiver, while the passive eavesdropper will suffer from interference. We derive the secrecy rate of the proposed scheme in order to estimate the performance. The numerical results demonstrated in this paper verify that the proposed scheme can achieve a better secrecy rate compared to the conventional scheme at the same effective data rate.