Reconfigurable intelligent surfaces (RISs) comprised of tunable unit cells have recently drawn significant attention due to their superior capability in manipulating electromagnetic waves. In particular, RIS-assisted wireless communications have the great potential to achieve significant performance improvement and coverage enhancement in a cost-effective and energy-efficient manner, by properly programming the reflection coefficients of the unit cells of RISs. In this paper, free-space path loss models for RIS-assisted wireless communications are developed for different scenarios by studying the physics and electromagnetic nature of RISs. The proposed models, which are first validated through extensive simulation results, reveal the relationships between the free-space path loss of RIS-assisted wireless communications and the distances from the transmitter/receiver to the RIS, the size of the RIS, the near-field/far-field effects of the RIS, and the radiation patterns of antennas and unit cells. In addition, three fabricated RISs (metasurfaces) are utilized to further corroborate the theoretical findings through experimental measurements conducted in a microwave anechoic chamber. The measurement results match well with the modeling results, thus validating the proposed free-space path loss models for RIS, which may pave the way for further theoretical studies and practical applications in this field.

Large intelligent surface (LIS)-assisted wireless communications have drawn attention worldwide. With the use of low-cost LIS on building walls, signals can be reflected by the LIS and sent out along desired directions by controlling its phases, thereby providing supplementary links for wireless communication systems. In this study, we evaluate the performance of an LIS-assisted large-scale antenna system by formulating a tight approximation of the ergodic capacity and investigate the effect of the phase shifts on the ergodic capacity in different propagation scenarios. In particular, we propose an optimal phase shift design based on the ergodic capacity approximation and statistical channel state information. Furthermore, we derive the requirement on the quantization bits of the LIS to promise an acceptable capacity degradation. Numerical results show that using the proposed phase shift design can achieve the maximum ergodic capacity, and a 2-bit quantizer is sufficient to ensure capacity degradation of no more than 1 bit/s/Hz.

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Tailoring the electromagnetic responses by metasurface greatly expands one's capabilities to manipulate light in a controlled manner. Either amplitude or phase of the incident wave can be altered during the light–matter interaction, and thus opens the possibility of information modulation without conventional analog or digital circuits. A prototype of quadrature phase‐shift keying (QPSK) wireless communication based on time‐domain digital coding metasurface, whose reflection properties can be varied within different time slots by changing the biasing voltages of varactor diodes in specially designed meta‐atoms, is developed here. As the information is transformed into binary bit streams and mapped to pulse sequences of the biasing voltage, the baseband digital signal is directly modulated to the carrier wave through the digital coding metasurface. Compared to the earlier version of binary frequency‐shift keying architecture based on digital coding metasurface, the proposed QPSK system has a much higher data‐transmission rate for wireless communications. A proof‐of‐concept experiment is conducted to prove the real‐time transmission ability of this system, where a video is delivered between the transmitter and receiver with high accuracy and date rate. The presented work is promising in the development of next‐generation wireless communication technologies.