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Achieving low-power and polarization-insensitive communication is a crucial and challenging task in the Internet of Everything. In this communication, we propose and demonstrate the implementation of two amplitude-reconfigurable metasurfaces, loaded with p-i-n diodes and operated around 5.8 GHz, to develop a novel polarization-insensitive backscatter communication (BC) system. Both communication transmitters using uniform and gradient metasurfaces are able to achieve high-efficiency polarization conversion and thus can cooperate with the receiver end to mitigate the interference generated by environmental carrier sources. To achieve the directional information transmission, we design a corner reflector metasurface and a gradient metasurface, which, respectively, enhances the gain in the backward and fixed scattering directions. Due to the advantages of polarization insensitivity and low energy consumption, this system promises great potential for future engineering applications in the Internet of Things, particularly for smart homes, wearable sensing, and other related areas.

This article proposes a reconfigurable intelligent surface (RIS) segmented symbiotic ambient backscatter system, which is composed of a primary source (S), a RIS, and a cooperative receiver (D) that decodes the signals from S and RIS with the aid of successive interference cancellation (SIC). For such, the RIS is segmented into two zones, namely, an EP zone and a BD zone, where the EP zone is used to enhance the received primary signal at D while the BD zone is utilized to backscatter RIS's signal to D. The coexistence outage probability (COP) is first developed, which is shown to be dominated by the minimum number of reflectors in the two zones for sufficiently high transmit signal-to-noise ratio (SNR). In contrast, the sum ergodic capacity (EC) can only be improved by increasing the transmit power and the number of reflectors in the EP zone at high transmit SNR. Finally, two algorithms are designed to minimize the number of reflectors in the two zones while achieving acceptable COP or sum EC.

This brief proposes a frequency domain model for injection-locked LC oscillators by introducing the impulse sensitivity function (ISF) and injection factor, analyzes the effect of the injection pulse width and injection position on oscillator performance based on this model, and derives an equation that can guide the design and optimization of oscillators. The model fills the gap in the field of frequency domain models for injection-locked LC oscillators. Based on the above model, a clock generator circuit structure operating at 14 GHz, combining a phase-locked loop with an injection-locked oscillator, is designed and measured based on a 65-nm cmos process. The circuit achieves better phase noise performance by optimizing the two parameters, which verifies the accuracy of the proposed model.

Achieving high-efficient and low-power communication is pivotal yet very challenging in the emerging technologies. Unlike conventional backscatter communication system, we propose and demonstrate an amplitude-reconfigurable metasurface loaded with PIN diodes to build a front-back scattering communication transmitter, which features the exclusive advantages of full-space secondary modulation of the ambient signals with high energy utilization efficiency. Meanwhile, this device can eliminate the interference originated from the ambient source by polarization conversion in the transmission channel. At a modulation rate of 800 kbps and a distance of 80 m, our system can achieve distortion-free transmission of a picture with size of 200 × 200 pixels. In addition, multiple amplitude-shift-keying modulation is also realized by segmenting the metasurface to further increase the communication rate. Due to the advantages of high spectral efficiency and low energy consumption, this system can be widely used in future engineering applications for the internet of things, especially for smart home, agriculture environmental monitoring, wearable sensing and others.

This article proposes a symbiotic backscatter non-orthogonal multiple access (backscatter-NOMA) system, where a backscatter device (BD) conveys its own information $c(n)$ to two users by riding on the NOMA downlink signal. Notably, different from the conventional backscatter-NOMA, the BD adaptively adjusts its reflection coefficient to guarantee the successful decoding of the NOMA downlink signal and the backscatter signal $c(n)$ at the two users, relying on the decoding requirement of $c(n)$ at the two users. To depict the overall transmission robustness of the concurrent NOMA downlink and the backscatter link, we introduce a metric of coexistence outage probability (COP) and develop its tight upper bound. Also, asymptotic analysis shows that, unlike the conventional backscatter-NOMA, the COP of the proposed symbiotic system obeys the scaling law of $\frac{\ln (P_{s})}{P_{s}}$, which eliminates the error floor of the conventional solution. In addition, for different decoding requirements of $c(n)$, it is shown that the optimal power allocations of the NOMA signal depend on different system parameters.