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In traditional generalized precoding-aided spatial modulation (GPSM), the mappings of the receive antenna combination index and the constellation symbol are performed independently. In this letter, we propose a joint GPSM and rotating symbol modulation for physical-layer security in wireless communications, which rotates conventional amplitude/phase modulation symbols according to the receive antenna combination index that is unknown to the eavesdropper. Both theoretical and numerical results for the bit error rate and secrecy rate indicate that the eavesdropper can neither successfully recover the spatial information bits nor symbol information bits, which validate that the proposed scheme can significantly enhance the physical-layer security of the considered communication system.

Omnidirectional or the phased-array antenna is usually adopted in the time-reversal literature, but it cannot focus the power of the transmitted signals in both time- and space-domains. In this letter, we propose the hybridization of time reversal and frequency diverse array (FDA), which transmits the signal with a small frequency offset across the array to generate both angle- and range-dependent beampattern, for temporal focusing. The time-reversal FDA channel is modeled in multipath scenarios. For the given parameters with 12 transmit elements spaced by half-wavelength, carrier frequency $1\,$ GHz, and frequency offset $1\,$ kHz, the peak of time-reversal FDA focusing is $18.7\%$ higher than that of a standard FDA. Both theoretic analysis and simulation results verify that, while maintaining FDA angular-time periodicity, the FDA range periodicity is eliminated and the energy is focused at the target position by the use of time-reversal processing.

In this paper, we investigate frequency diverse array (FDA) antenna for physical-layer security and analyze the system performance (i.e., average secrecy capacity and secrecy outage performance) over independent but not necessarily identical distributed Rayleigh fading channels. A single-antenna multiple-channel receiver structure is proposed to address the time-variance property of FDA antenna. The transmitter allocates part of its power to send artificial noise (AN) so as to ensure the security of communications, such that the channels other than the desired receiver’s are degraded. Specifically, we derive the closed-form expressions for average secrecy capacity, probability of nonzero secrecy capacity, and secrecy outage probability, respectively. The correctness of the proposed analysis is corroborated via simulations. Furthermore, the corresponding asymptotic expressions for average secrecy capacity and secrecy outage probability in high signal-to-interference-plus-noise ratio (SINR) regime are also provided, respectively, to have deep insights into the performance of the considered system. Numerical results show that the FDA communications significantly outperforms the phased-array (PA) scheme in range dimension for secure communication.

In this letter, we propose frequency diverse array (FDA) antenna for secure communication and study the secrecy capacity over Nakagami- ${m}$ fading channels. The closed form approximate expression for the average secrecy capacity of artificial noise-aided FDA secure communication is derived. The correctness of the proposed analysis is verified by numerical results. It is shown that the proposed FDA scheme significantly enhances the communication security and outperforms conventional phased-array communications in the range dimension. Moreover, the impacts of fading severity parameters and power allocation factor on the system secrecy performance are also analyzed.

To alleviate the spectrum congestion crisis, we design a dual-function radar-communication (DFRC) with frequency diverse array multiple-input multiple-output (FDA-MIMO) radar. A set of orthogonal waveforms are used to implement the primary radar operation, and we propose an information embedding scheme for the secondary communication function, which is carried out by embedding the information into the frequency increments of FDA-MIMO radar as part of phase of the transmit steering vector. The communication receiver detects the phase of the received signal and uses it to decode the embedded binary sequence. The probability of error is analyzed in terms of the bit error rate (BER). In addition, the Cramer-Rao bounds (CRBs) for angle and range respectively are derived to examine the effect of information embedding in radar emission on the performance lower bounds of the FDA-MIMO radar. Simulation examples are provided to demonstrate the effectiveness of the proposed information embedding technique.

Inspired by the frequency diverse array (FDA) producing range and angle dependent beampattern due to the employment of frequency increments across the array elements, this paper proposes a direction-dependent communications using 2-bit phase control across a two-element FDA antenna. The produced directional pattern projects the phase modulation signal as a constellation, which offers physical-layer security for wireless communications. This is because the transmitted symbols can be purposely distorted in other positions, but they could be successfully decoded at the intended range and angle position. The effectiveness of the proposed method is verified by numerical results.