To improve the physical-layer security of mode-division multiplexing (MDM) systems, a simple security scheme named mapping-varied modulation (MVM) is proposed in this paper by combining cryptographic and information-theoretic security. Specifically, on top of the information-theoretic security provided by the less-conditioned wiretap channel due to the larger mode-dependent loss induced by fiber-bend tapping, the proposed MVM security method varies the mapping rules of the adopted constellations for the subchannels (one subchannel corresponds to one mode) by using the inherently time-varying random channel state information (CSI) of the MDM fiber, under the assumption that an eavesdropper does not know the exact instantaneous CSI of the legitimate link. To maximize the difference among the binary labels of the constellation points in the same position for each subchannel, a labeling optimization method is proposed as well. Numerical results demonstrate the effectiveness of the proposed MVM method via bit-error ratio performance and secrecy rate, showing a potential way to improve the security of the MDM link for high-speed data transmission.
To improve the physical-layer security of mode-division multiplexing (MDM) systems, a simple security scheme named mapping-varied modulation (MVM) is proposed in this paper by combining cryptographic and information-theoretic security. Specifically, on top of the information-theoretic security provided by the less-conditioned wiretap channel due to the larger mode-dependent loss induced by fiber-bend tapping, the proposed MVM security method varies the mapping rules of the adopted constellations for the subchannels (one subchannel corresponds to one mode) by using the inherently time-varying random channel state information (CSI) of the MDM fiber, under the assumption that an eavesdropper does not know the exact instantaneous CSI of the legitimate link. To maximize the difference among the binary labels of the constellation points in the same position for each subchannel, a labeling optimization method is proposed as well. Numerical results demonstrate the effectiveness of the proposed MVM method via bit-error ratio performance and secrecy rate, showing a potential way to improve the security of the MDM link for high-speed data transmission.
We propose a chaotic spatial symbol transforming encryption method for enhancing the physical layer security in fiber-optic systems based on space-division multiplexed (SDM) transmission. The designed 3-D chaotic sequences are used to scramble the real and imaginary part of quadrature amplitude modulation (QAM) symbols, permute the symbol-to-space mapping, and control iteration times between the two processes. The encrypted transmission of 200 Gb/s per mode polarization-division-multiplexed 16QAM signals has been simulated over 1000-km two-mode fiber. The results show that the eavesdropper cannot recover the original information with a part of the security keys or a part of the transmitted signals when the iteration times are beyond 5. We found the error spreading phenomenon can be combined with the mode-dependent loss (MDL) to realize the system security enhancement. When eavesdroppers coupled signals out from SDM waveguide by bending-induced fiber tapping, they need reduce the bend radius to receive more spatial leak modes. The bending-induced fiber tapping inherently causes MDL. Although the error spreading phenomenon leads to bit-error-rate increasing by 1.3 dB than conventional 16QAM transmission, it will be a promising solution to overcome the weakness that the huge amount of data can be compromised by taping out the portion of the signal in single-mode transmission.
Space-division multiplexed (SDM) fiber optic transmission systems can not only increase system capacity, but also achieve physical-layer security against fiber tapping attacks. In this paper, we examine the information-theoretic security of optical multiple-input-multiple-output (MIMO) SDM by evaluating the tradeoff between the achievable information rate and the confidentiality for different channel dynamics. In particular, we provide problem formulations for secure communication over these channels and study three types of secrecy capacities: 1) guaranteed capacity; 2) outage capacity; and 3) average capacity, each serving as a performance metric for a coding strategy tailored to a specific type of MIMO-SDM channel. We also assess the impact of key system parameters, such as the number of modes, the mode-dependent loss (MDL), and the signal-to-noise ratio (SNR), on the various secrecy capacities. Our results indicate that, with a proper design of channel codes that balance information rate and security, an SDM system has the potential of offering confidential data transmission at a rate that could be orders of magnitude higher than what can be achieved through other means of encryption. Moreover, we show that MDL, unavoidably induced by fiber tapping, can allow information-theoretic security even if the SNR of the eavesdropper's receiver is better than that of the legitimate receiver.
In this paper, a novel transmission strategy, referred to as mapping-varied spatial modulation, is proposed for physical layer security, where the transmitter varies mapping patterns for the radiated information and the antenna information of spatial modulation, based on the instantaneous pattern of legitimate channel quality information that is unknown to eavesdroppers. Therefore, eavesdroppers cannot successfully decode the confidential information and the transmission over the legitimate link is secured from the wire-tap of eavesdroppers, without relying on higher-layer encryption. An important virtue of the proposed transmission strategy is that the transmitter does not need to know eavesdroppers' channels states at all. To further demonstrate the advantage of this scheme, its secrecy rate was formulated for the purpose of facilitating the performance evaluation. Moreover, illustrative numerical results pertaining to the metrics of ergodic secrecy rate and secrecy outage probability not only substantiate the validity of the proposed transmission strategy, but also provide useful references for the system design with the mapping-varied spatial modulation, from the view of physical layer security.
In this paper, we propose a noisy and dynamic-index partitioned modulation (IPM) to secure a quadrature amplitude modulation (QAM) constellation transmission over a non-degraded wiretap channel. Unlike approaches that rely on multi-antenna systems or tight amplitude-phase tracking, IPM partitions QAM into multiple disjoint subsets that are separately indexed by a dynamic key, known at the transmitter (Alice) and the legitimate receiver (Bob), but not at the eavesdropper (Eve). The proposed IPM maps the information bits into multiple sequences, each one lying in a different partition of the QAM constellation space. This mapping is performed through a cross-bit labeling that we define to increase the confusion at the eavesdropper, while minimizing the bit error rate (BER) at the legitimate receiver. As the eavesdropper is not aware of the dynamic index pointing to the different partitions, the IPM creates larger Voronoï detection zones around Bob’s symbol compared to Eve. To induce further confusion at Eve, we inject random uniform noise into IPM symbols. The noise varies in a domain that is fully included in Bob’s larger detection zone, but it exceeds Eve’s detection zone. The performances of the noisy IPM scheme in terms of error rate and secrecy rate are analytically and numerically evaluated. Our results show that the IPM scheme creates on the Eavesdropper’s link an error floor, independently of its signal-to-noise ratio (SNR). However, the IPM scheme preserves the legitimate link, for which the BER decreases as the SNR increases. Indeed, the secrecy rate remains positive for all SNR values and achieves an asymptotical constant plateau value.
Orthogonal frequency division multiplexing (OFDM) systems have enjoyed widespread adoption as the physical layer standard for high data rate wired and wireless networks, due to their ability to efficiently cope with slowly varying dispersive channels. Therefore in searching for feasible implementations of physical layer security techniques, it is appropriate to analyze how existing information theoretic results can be applied to the OFDM structure This paper considers the information theoretic secrecy rates that are achievable in a wiretap OFDM channel when transmitting quadrature amplitude modulation (QAM) constellation symbols. The loss with respect to the secrecy rates obtained with Gaussian distributed inputs is evaluated for both nite constellation cardinalities and in the asymptotic approximation of arbitrarily high cardinality. Moving from the insight gained with this analysis, we propose bit-loading strategies to efficiently allocate the appropriate number of bits in each subchannel, by considering the twofold objective of minimizing the loss with respect to the Gaussian input secrecy capacity and minimizing the total bit load.
In this letter, a novel transmission scheme for spatial modulation (SM) is proposed to enhance the security of wiretap channel. In this scheme, partial channel state information (CSI) of the legitimate channel is exploited by the transmitter (Tx) to dynamically adapt the spatial and signal constellations mapping patterns that are unknown to Eve. Thus, Eve cannot successfully decode the confidential information over the wiretap channel. Further, an important virtue of the proposed transmission scheme, Tx does not need to know the full CSI of Eve and legitimate channels. To demonstrate the security guaranteed by the proposed scheme, bit error rate, secrecy rate, and secrecy outage probability are evaluated.