ABSTRACT The real‐time reconfigurable characteristics of meta‐surface antennas can be used to separate multi‐stream signals under the condition of single radio frequency (RF). However, with the increase of the symbol rate and the number of antenna arrays in the future, it will face the problem that the state switch rate of the electromagnetic unit is not enough to reach the upper limit of array effective degrees of freedom (DOF) of the meta‐surface antenna. To solve this problem, a theory of asynchronous control meta‐surface antenna is proposed in this paper. By designing the starting time of different element state switching, different electromagnetic element states are staggered to improve the array effective DOF of the meta‐surface antenna. Then, an electromagnetic unit state design algorithm of asynchronous control meta‐surface antenna based on the minimum condition number of equivalent channel matrix is proposed. We improve the sparrow search algorithm to solve the condition number minimization problem in order to obtain the better multi‐stream signal separation performance. The simulation results show that compared with the synchronous control meta‐surface antenna, theory proposed in this paper can improve the effective DOF of array under the condition of limited switch rate, and can effectively reduce the receiving bit error rate and improve spectral efficiency when separating multi‐stream signals.

An array’s degree of freedom (DoF) determines the number of jamming incidents that can be managed and the antijamming performance. Conventional arrays can improve the DoF only by increasing the number of antennas. On the other hand, when the received signal is digitized, high-power jamming will reduce the number of bits used to represent the desired signal, further increasing the difficulty of back-end antijamming based on digital signal processing. In this paper, we propose a joint radio frequency (RF) front-end and digital back-end antijamming scheme based on a metasurface antenna array. The metasurface antennas can rapidly switch patterns when receiving signals, so that a single channel can be equivalent to multiple channels and increase the DoF. We use independent component analysis to estimate the channel and then optimize the array parameters under the minimum signal-to-jamming ratio constraint of each antenna. The proposed scheme works well under high-power jamming conditions by suppressing jamming at the RF front end and using a low-precision analog-to-digital converter. Simulation results show that the proposed scheme reduces the bit error rate of the received signals by one order of magnitude compared with the conventional array.

Abstract The propagation of electromagnetic waves will produce multi‐path fading of wireless channel, which degrades communication performance substantially. If multi‐path can be separated, better signal transmission and reception strategies can be designed to weaken or eliminate fading and improve signal transmission performance. However, it is challenging for communication nodes with limited number of antennas. A general multi‐path separation and measurement framework based on single dynamic metasurface antenna is established which rapidly changes patterns within a single pilot symbol period so that equivalent multi‐dimensional received signals can be obtained. Based on the framework, a multi‐path channel estimation scheme is proposed. Specifically, the parameter estimation problem is formulated and present the algorithm based on atomic norm minimisation to estimate parameters including angle of arrival and complex gain of each propagation path. Simulation results illustrate that single dynamic metasurface antenna can approach the capability of a conventional multi‐antenna array, and even using single dynamic metasurface antenna with 1‐bit coding can estimate angle of arrivals and complex gains of multi‐path components accurately.

Existing studies on the secret key generation based on physical layer wireless fading channel are largely open under active attacks. In this paper, we discuss how the man-in-the- middle (MITM) attacker, who acts as a transparent relay, attacks the training phase in wireless communication to improve the information leaked rate. We prove that the MITM attacker can intercept all of the channel information when all of the paths pass through the attacker. We present the closed-form solution of information leakage rate and achieve the optimal attack effect when the transmitter can directly communicate with receiver besides the paths by way of attacker. The results show that the MITM attack can cause new challenges for physical-layer security since it leads to higher information leakage rate. Numerical results are presented to further demonstrate the potent threat of MITM attack.