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Wireless Communications with Programmable Metasurface: Transceiver Design and Experimental Results

Wankai Tang, Xiang Li, Jun Yan Dai, Shi Jin, Yong Zeng, Qiang Cheng, Tie Jun Cui

arXiv:1811.08119v2eess.SP

TL;DR

Conventional wireless transceiver architectures face challenges in future systems requiring wide bandwidth, high processing capability, and low power consumption. This paper develops and experimentally evaluates a programmable-metasurface transmitter for over-the-air QPSK, achieving reliable operation and comparable BER performance to a conventional architecture with a 5 dB transmit-power increase.

  • Problem

    Conventional transceiver architectures face challenges in wireless systems requiring ultra-wide bandwidth, high processing capability, low power consumption, and more flexible hardware.

  • Method

    The paper designs a programmable-metasurface transmitter that directly modulates the reflected carrier phase through electrically controlled reflection coefficients, eliminating mixers and filters.

  • Results

    With a 5 dB transmit-power increase, the metasurface-based system achieves the same BER performance as the conventional system, while QPSK measurements show clear, stable constellations and smooth video transmission without channel coding.

  • Takeaways & Limitations

    The demonstrated architecture offers a low-cost, low-complexity transmitter approach with potential for wireless communication applications and reduced hardware constraints.

Abstract

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Metasurfaces have drawn significant attentions due to their superior capability in tailoring electromagnetic waves with a wide frequency range, from microwave to visible light. Recently, programmable metasurfaces have demonstrated the ability of manipulating the amplitude or phase of electromagnetic waves in a programmable manner in real time, which renders them especially appealing in the applications of wireless communications. To practically demonstrate the feasibility of programmable metasurfaces in future communication systems, in this paper, we design and realize a novel metasurface-based wireless communication system. By exploiting the dynamically controllable property of programmable metasurface, we firstly introduce the fundamental principle of the metasurface-based wireless communication system design. We then present the design, implementation and experimental evaluation of the proposed metasurface-based wireless communication system with a prototype, which realizes single carrier quadrature phase shift keying (QPSK) transmission over the air. In the developed prototype, the phase of the reflected electromagnetic wave of programmable metasurface is directly manipulated in real time according to the baseband control signal, which achieves 2.048 Mbps data transfer rate with video streaming transmission over the air. Experimental result is provided to compare the performance of the proposed metasurface-based architecture against the conventional one. With the slight increase of the transmit power by 5 dB, the same bit error rate (BER) performance can be achieved as the conventional system in the absence of channel coding. Such a result is encouraging considering that the metasurface-based system has the advantages of low hardware cost and simple structure, thus leading to a promising new architecture for wireless communications.

I. INTRODUCTION

The paper proposes a wireless communication architecture built entirely on a programmable metasurface to address hardware challenges in future systems. It introduces the metasurface concept, unit-cell implementation, and planned over-the-air QPSK demonstration.

  • Future wireless systems require more flexible hardware architectures as conventional transceivers face bandwidth, processing, and power challenges.
  • The proposed transmitter uses a reflection-type programmable metasurface to manipulate reflected-wave phase electrically, reducing hardware cost, energy consumption, and structural complexity.
  • Programmable metasurfaces dynamically adjust electromagnetic-wave amplitude, phase, polarization, or orbital angular momentum, unlike fixed analog metasurfaces.
  • Each unit cell uses varactor-diode biasing to tune capacitance and thereby dynamically control its reflection coefficient.
  • The paper realizes single-carrier QPSK transmission over the air with a fabricated programmable metasurface prototype.

III. METASURFACE-BASED WIRELESS COMMUNICATION

The proposed system uses a programmable reflection coefficient to modulate an incident carrier directly, replacing mixer- and filter-based up-conversion. Its architecture covers the metasurface block diagram, transmitter and receiver design, and source-data mapping.

  • The section presents the proposed system’s fundamental principle, transmitter design, frame structure, and receiver design.
  • A. Fundamental Principle: The incident single-tone carrier is multiplied by the programmable reflection coefficient, producing a reflected wave carrying modulated information.
  • A. Fundamental Principle: The reflected-wave spectrum is shifted near the carrier frequency and shaped by the spectrum of the programmable reflectivity.
  • A. Fundamental Principle: This passive metasurface-based up-conversion eliminates mixers and filters while offering low complexity, cost, power consumption, and heat dissipation.
  • A. Fundamental Principle: System design maps source data to the time-varying reflection coefficient according to the desired modulation method and the metasurface’s reflection characteristics.

B. Transmitter Design

The transmitter maps source bits to programmable metasurface reflection coefficients, using four phase states to implement single-carrier QPSK modulation. Each QPSK symbol selects one of four complex reflection coefficients for a specified symbol duration.

  • Source bits are mapped to the metasurface reflection-coefficient control signal to modulate and emit the reflected wave.
  • Each message symbol selects one of four possible complex reflection coefficients, Γn, for duration T.
  • Adjacent QPSK symbols have a 90-degree phase difference while sharing identical amplitude.
  • P1, P2, P3, and P4 encode ‘00’, ‘01’, ‘11’, and ‘10’, respectively.For example, the bit sequence ‘00100111’ produces the coefficient sequence ‘P1P4P2P3’.

MAPPING BETWEEN REFLECTION COEFFICIENT AND TRANSMISSION BITS

The transmitter converts QPSK symbols into voltage-controlled reflection states, using measured voltage–phase characteristics to drive the programmable metasurface. Its processing chain forms frames and applies the resulting control sequence to modulate the incident carrier.

  • The 128-unit-cell metasurface can in principle control each cell independently to generate complex reflected waves and support multiple beams or MIMO.
  • The measured control-voltage-to-reflected-phase relationship is nonlinear because varactor capacitance approaches saturation at larger voltages.As voltage increases, the reflected-wave phase also tends to become unchanged.
  • Four voltage levels, V1 through V4, represent QPSK states ‘00’, ‘01’, ‘11’, and ‘10’, respectively.
  • The transmitter streams bits, maps data and pilots to QPSK points, forms a physical frame, and converts Γn into voltage-control signals.
  • The metasurface is controlled according to the voltage sequence so the arriving incident wave is transmitted as an information-modulated reflection.

C. Frame Structure Design

The proposed single-carrier frame combines synchronization, pilot, and data subframes to organize transmission. Its structure supports 36,864 bits per frame, with transmission rate governed mainly by the control-signal update rate.

  • Each frame contains one synchronization subframe, one pilot subframe, and nine data subframes.
  • The synchronization subframe contains a 420-length synchronization sequence.
  • The pilot and each data subframe contain 2048 symbols plus 160 cyclic-prefix symbols.
  • 36864 bits can be transmitted per frame, while transmission rate is mainly determined by the control-signal update rate.

D. Receiver Design

The receiver retains a conventional quadrature-sampling zero-IF architecture for synchronization, channel processing, demodulation, and bit recovery. Because the metasurface covers only 0 to 255 degrees, extended Barker coding is used for frame synchronization.

  • The conventional zero-IF receiver performs timing and carrier synchronization, channel estimation, equalization, and QPSK demodulation from baseband IQ signals.
  • The metasurface’s 0-to-255-degree phase-control range prevents use of a conventional 360-degree-dependent synchronization sequence such as Zadoff–Chu.
  • An extended Barker code provides frame synchronization instead, using two voltage states that create a 180-degree carrier-phase change.
  • The receiver uses cyclic prefixes for joint maximum-likelihood carrier-frequency-offset estimation and correction.
  • After synchronization, processing removes the cyclic prefix, estimates and equalizes the channel, demodulates QPSK, and recovers the bit stream.

IV. PROTOTYPE SETUP

The prototype combines a programmable metasurface, control circuitry, PXIe modules, and software-defined radios to implement the proposed single-carrier QPSK system.

  • The prototype setup employs a programmable metasurface, control circuit board, commercial PXIe modules, and software-defined radio platforms.These components implement the programmable metasurface-based single-carrier QPSK wireless communication system.
  • The metasurface is a reflection-type, phase-programmable surface centered at 4 GHz and controlled through an external voltage signal.Its phase profile is controlled across the surface by the input control voltage.
  • The control circuit board amplifies the input control voltage and distributes it to the metasurface’s unit cells.
  • The transmitter hardware architecture is documented in Fig. 8 as part of the implemented prototype system.

FEATURES OF HARDWARE MODULES

The hardware modules generate, distribute, convert, and synchronize control signals while SDR hardware supplies the carrier and performs receiver downconversion.

  • The central controller provides configuration and instrument-control functions and reads a local video file as the transmitter’s information source.
  • The chassis provides the interface between the central controller and PXIe modules for control and data exchange.
  • The SDR generates the 4 GHz single-tone carrier for the metasurface transmitter and downmixes received RF signals for baseband processing.The receiver sends the resulting baseband signal to the host computer for synchronization and demodulation.
  • A high-precision crystal oscillator supplies a common clock source to all modules.
  • The assembled hardware implements the metasurface-based wireless communication prototype described in Fig. 8.
  • The PXIe controller, FPGA, and DAC generate the analog voltage sequence used for real-time metasurface programming.The controller forms the source bit stream, while the FPGA and DAC provide adjustable sampling and digital-to-analog conversion.

V. EXPERIMENTAL EVALUATION

The experiments evaluate the prototype in a realistic wireless environment using constellation visualization, video streaming, and BER measurements.

  • The experimental setup tests the feasibility and performance of the programmable metasurface-based single-carrier QPSK prototype over the air.Evaluation includes receiving constellations, video streaming, and BER measurements using pseudo-random information.
  • The indoor video-streaming experiment places the receiver 4 meters from the metasurface transmitter.The recovered constellation and source video are displayed at the receiver.
  • The implemented prototype’s main parameters are summarized in Table III.
  • The prototype uses single-carrier QPSK wireless communication.

B. Measurement Results

Measurements show reliable QPSK transmission, while BER comparisons quantify the power gap to a conventional all-SDR system and reveal hardware-related limitations.

  • QPSK transmission: The equalized QPSK constellation is clear and stable, and video streams smoothly without channel coding.Higher transmission power produces denser constellation points, indicating improved BER performance.
  • Constellation measurements: The measured constellation points are non-square because the metasurface has non-uniform amplitude responses across phase states.The prototype can nevertheless operate reliably despite the uneven constellation distribution.
  • BER comparison: 5 dB higher transmit power enables the metasurface-based system to achieve the same BER performance as the conventional all-SDR-based system.The comparison varies SDR1 transmit power and evaluates both systems over the air.
  • Performance factors: Rectangular-window sampling leaks reflected-wave energy outside the effective frequency band, contributing to the BER performance gap.Feed-network imperfections and control-board noise are also identified as factors for future optimization.
  • Architectural implications: The authors identify simpler structure, lower cost, and easier large-scale implementation as advantages of the metasurface architecture.They also note that metasurface operating bands may span from microwave to visible light.
  • Activation comparison: The metasurface system’s SNR is measured with either all unit cells or only the left or right half activated.

VI. DISCUSSION AND FUTURE WORK

The proposed metasurface-based architecture reduces transmitter hardware complexity while opening several directions for modeling, receiver design, modulation, beam steering, and coverage enhancement.

  • The transmitter requires no filter, wideband mixer, or power amplifier, supporting a cost-effective wireless communication architecture.
  • The architecture can potentially generate multi-beams and complex radio signals because programmable metasurface unit cells can be controlled independently.
  • The research field remains at an early stage, with theoretical modeling, receiver design, high-order transmission, and coverage enhancement identified as open topics.
  • Theoretical modeling: Accurate analytical signal models remain important because the metasurface transmitter differs substantially from conventional architectures and has nonideal phase and varactor behavior.
  • Metasurface-based receiver: Programmable metasurfaces could support receiver functions including channel estimation, hybrid beamforming, and interference control.
  • High-order modulation and waveform design: Future work includes high-order modulation and waveform designs such as QAM, DMT, and OFDM to improve spectrum utilization.
  • Beam steering and coverage enhancement: Programmable metasurfaces can alter electromagnetic transmission paths for beam steering and coverage enhancement, including transforming some NLOS millimeter-wave channels into LOS channels.
  • The demonstrated 8×16-unit-cell QPSK prototype achieved performance comparable to the conventional architecture with less hardware complexity.
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