Dual-function radar andcommunication (DRC) system has been recently recognized as a promising approach to solve the spectrum scarcity problem. However, when the target exists within a crowded area where pathloss dominating, the performance of radar may be severely degraded. To tackle this issue, this article proposes for the first time the deployment of an intelligent reflecting surface (IRS) to help the DRC system to enhance the radar detection performance. The IRS can configure the environment around the radar by adaptively adjusting the phases of its reflecting units to strengthen the signal quality toward specific directions, mostly the target direction, and completely null-out transmissions in other directions, mostly the directions toward the communication system. Specifically, in this article, we investigate the joint optimization of the IRS passive phase-shift matrix (PSM) and precoding matrix of the radar-aided basestation for the DRC system. The optimization is carried-out through maximizing the signal-to-noise ratio (SNR) at the radar receiver under both sensing and communication constraints, which turns out to be a nonconvex problem. In order to circumvent this challenging problem, an alternation optimization approach is employed to decouple the optimization variables and split this intractable problem into two subproblems. However, it is still challenging to obtain the optimal PSM due to the high power of the objective function and the unit-modulus constraints. To solve this problem, a majorization–minimization algorithm is conceived to transform the nonconvex problem to an easy to solve quadratic constraint quadratic programming problem. Simulation resultsdemonstrate that the IRS can help improving the performance of the DRC system in terms of the received SNR, and the proposed algorithm shows fast convergence.

A major challenge in designing a spectral co-existence between radar and communication systems is how to simultaneously provide efficient utilization of the shared spectrum while maintaining a reliable performance for both systems. Due to its flexibility in using linear independent waveforms and superiority in terms of target detection and estimation, the collocated multiple-input-multiple-output (MIMO) radars provide a paramount capability in realizing spectrum sharing with communication systems. In this paper, we consider the use of joint transmit and receive beamformers for both the MIMO radar and MIMO communication systems. Specifically, we design a two-tier alternating optimization spectrum sharing framework that is based on interference alignment (IA) approach. The effectiveness of spectrum sharing between radar and communication systems is guaranteed by mitigating the mutual interference signals in the shared spectral band. Subsequently, motivated by the excellent performance provided by IA in different wireless network scenarios, we propose a spectrum sharing framework that consists of a main iterative algorithm with two subalgorithms included within its operation. The first subalgorithm is used to maximize the signal-to-interference-plus-noise ratio of the radar system, whereas the second one is utilized to maximize the average sum-rate of the communication system. The main iterative algorithm is proposed to jointly optimize the transmit and receive beamforming filters of both systems by performing alternating optimization between the two subalgorithms. The convergences of the proposed algorithm and its subalgorithms are numerically verified. Simulation results are provided to confirm the superiority of the proposed framework for both systems.

This paper concerns the problem of authenticating the transmitter without a secret key. In comparison with traditional cryptographic-based authentication mechanisms, the Physical-Layer Authentication (PLA) has the following advantages: high security, low complexity, and high compatibility, since it exploits intrinsic and unique features of the physical layer to authenticate the transmitter rather than using a secret key. The prior channel-based PLA schemes use a quantization algorithm to deal with multiple channel-based features for simplicity. However, there are two main limitations in the prior schemes: performance loss due to quantization error and the difficulty of obtaining the optimal thresholds in closed-form. In this paper, we propose two multiple Channel Impulse Response (CIR) based PLA schemes to effectively overcome the aforementioned limitations of the prior schemes. The first scheme uses multiple CIRs to realize the PLA, which is named as the Multiple CIRs PLA (MCP) scheme. The MCP scheme has better authentication performance than the prior schemes, since it avoids to use a quantization algorithm. The second scheme further improves the authentication performance by exploiting the channel correlation coefficient, which is named as the Enhanced Multiple CIRs PLA (EMCP) scheme. We provide rigorous performance analysis of two proposed schemes. We implemented the proposed schemes and conducted extensive performance comparisons through simulations. Our experimental results show that the closed-form expressions of the theoretical results of the proposed schemes perfectly match the corresponding simulation results. The EMCP scheme has the best authentication performance and the MCP scheme is the second one, whereas the prior scheme is the worst one. As the SNR or the channel correlation coefficient declines, the performance gap among various schemes gradually increases.

This paper addresses the issue of deceptive jamming against synthetic aperture radar (SAR) by using 1-bit sampling and time-varying threshold (TVT). With 1-bit intercepted SAR signal, the multipliers involved in a convolution is replaced by xnor gates, which considerably simplify the jamming signal generation. Moreover, the TVT is used for 1-bit quantization before retransmission to retain the relative amplitude information of the jamming signal. As a result, the proposed deceptive jamming schemes are superior to their conventional counterpart in terms of realization. Effects of harmonics and oversampling are analyzed to evaluate the performance degradations caused by the 1-bit sampling and TVT. Simulation results are provided to confirm the validity of the proposed schemes.

This paper studies the physical-layer security (PLS) improvement in wireless communication systems, where a hybrid reconfigurable intelligent surfaces (RISs) is deployed between the transmitter and legitimate receiver to enhance the communication security. To achieve a tradeoff between the secrecy capacity and power consumption, the element on-off mechanism is considered firstly to represent the connection relationship between the RIS elements and power amplifier. To address this non-convex problem, two-stage cyclic iterative technique is utilized to the considered optimization problem by iteratively optimizing the transmit beamformingreflection coeffcient and amplifcation coeffcient. Simulation results demonstrate that the proposed algorithm can effectively improve the performance gains compared with existing solutions.