In this paper, we propose a novel dual index pulse position modulation differential chaotic shift keying (DI-PPM-DCSK) system for wireless covert communication. Unlike conventional PPM schemes, at the transmitter, we propose to modulate index bits with the positions of both the reference and information-bearing signals, thereby incorporating more index bits into each symbol. Thus both energy efficiency and data rate can be improved. Besides, the information-bearing modulated signals are hidden with the artificial noise to enhance the covertness of communications. At the receiver, we propose to demodulate the information bits by calculating the coherence of adjacent symbols. Moreover, we derive analytical expressions for the bit error rate (BER) and covert performance of the system, which are validated through numerical simulations. The results demonstrate that the proposed system achieves superior data rate and BER performance compared to existing counterparts over fading channels. Furthermore, the covertness is validated with both theoretical analysis and simulation results.

In order to meet increasing demands of higher energy efficiency and better reliability performance for the multiuser Internet of things (IoT) secure communications, in this paper, we design a reliable and energy efficient superposition modulation (SM) and singular value decomposition (SVD) detection based multi-user orthogonal frequency division modulation-based differential chaos shift keying (SM-MU-OFDM-DCSK) transceiver for IoT devices. At the transmitter, we propose to superimpose and overlap the information-bearing chaotic signals for higher energy efficiency. Since the chaotic modulated signals of each user share identical reference chaotic signals, the transmitted superimposed signal matrices have the low-rank property. Then at the receiver, we apply the SVD-aided detection to recover these low-rank signals, which can suppress the noise to attain better reliability performance. Moreover, we prove that the proposed design can achieve the maximum likelihood detection performances. Furthermore, we derive the theoretical bit rate, energy efficiency and bit error rate expressions over additive white Gaussian noise (AWGN) channel. Simulation results are then provided to validate the theoretical derivations. Subsequently, the simulated performances over AWGN and fading channels are investigated to show that higher energy efficiency and better reliability performances than benchmark schemes can be achieved in industrial IoT scenarios.

Radio frequency watermarking systems embed the secret watermark bits into host bits for secure transmissions. However, malicious users may initiate falsifying attacks via broadcasting wireless channels. Meanwhile, the interferences of watermark signals to host signals will degrade the bit error rate (BER) performances. With the aim to enhance both the security and the reliability performances, we propose to utilize the Hash function to generate the unique digital digest of host signals for the integrity check. Then the lightweight encryption and spreading are conducted to compose the watermark signals. At the receiver, reverse operations are performed to recover both host signals and watermark signals. Then the retrieved digest is used to check the integrity and validity of host signals to combat falsifying attacks. Subsequently, we derive the bit error rate (BER) and the information leakage expressions. Simulation results are then provided to validate the proposed design.

In this paper, we design a novel orthogonal time frequency space modulation based differential chaos shift keying (OTFS-DCSK) transceiver for reliable information transmissions. In this design, we exploit the orthogonal time frequency space (OTFS) modulation which is a two-dimensional modulation designed in the delay-Doppler domain, to combat multiplicative channel fading. Besides, since the OTFS-DCSK signal matrix is rank-1, we propose to utilize a singular vector decomposition (SVD) aided detection at the receiver to suppress the additive white Gaussian noise (AWGN) to further enhance the reliability. Thanks to the diversity obtained from OTFS modulation and the noise-suppression achieved by the SVD aided detection, the proposed OTFS-DCSK transceiver significantly improves the reliability performance, particular in the high-mobility wireless communications over the dual-dispersive channels caused by multipath propagation effects and Doppler shift effects. Simulation results validate the proposed OTFS-DCSK system outperforms the benchmark systems over AWGN, multipath and dual-dispersive fading channels.