Integrated sensing and communication based on space-time-coding metasurfaces

Abstract

Programmable metasurfaces (PMs), also called reconfigurable intelligent surfaces (RISs), are planar structures capable of dynamically manipulating electromagnetic waves in real-time. Regarded as a key enabling technology for implementing smart wireless propagation environments, PMs/RISs also serve as an ideal supporting platform for integrated sensing and communication (ISAC). Here, we propose two ISAC schemes based on a special type of PMs/RISs: space-time-coding metasurfaces (STCMs). By leveraging space-time-coding strategies, STCMs simultaneously control the propagation at the fundamental (carrier) frequency for reliable wireless communication and generate spatially distributed harmonics for sensing. The proposed schemes seamlessly integrate both communication and sensing on a shared hardware platform, eliminating the need for additional sensors. For experimental validation, we implemented an ISAC system using a 2-bit STCM operating at microwave frequencies. Experimental results align with theoretical predictions, confirming the practical viability and effectiveness of the proposed ISAC schemes for applications in communication, imaging, radar, and sensing systems.

Fig. 1. Conceptual illustration of the proposed space-time-coding metasurface (STCM)-based integrated sensing and communication (ISAC) scheme.

in which an STCM controls the propagation direction of the fundamental-frequency wave for communication while generating spatially distributed harmonics for wireless sensing.

Fig. 2. Coding matrices and corresponding far-field scattering patterns of the proposed space-time-coding metasurface (STCM).

a, b Space-coding sequences for N = 16 and corresponding theoretical far-field patterns for the fundamental-frequency wave at ${\theta }_i=0^{\circ }$, respectively. c, d Optimized STC matrix for controlling the harmonics when N = 16 and L = 32, and corresponding far-field scattering patterns at ${\theta }_i=0^{\circ }$, respectively. e, f Optimized STC matrix for simultaneously controlling the fundamental-frequency wave and for generating multiple harmonics, and corresponding far-field scattering patterns, respectively.

Fig. 3. Space-time-coding metasurface (STCM)-based integrated sensing and communication (ISAC) system architecture.

a Adjustable partitioning scheme of the STCM, which is divided into two regions for sensing and communication. The size of the two regions can be flexibly adjusted based on the required needs. b Full-aperture scheme of the STCM without partitioning, which can utilize the entire STCM aperture by using STC matrices. c Architecture of the ISAC system, in which a USRP is used for signal modulation and demodulation, and the STCM establishes a reliable communication link by sensing the direction of the incoming wave in real-time and configuring the coding matrices.

Fig. 4. Experimental validation of 2-bit space-time-coding metasurface (STCM) prototype and measured far-field patterns for the full-aperture scheme.

a Measurement setup in an anechoic chamber. b Fabricated prototype of a 2-bit reflection-type STCM. c, Measured far-field scattering patterns of the fundamental-frequency wave for different STC matrices as detailed in Supplementary Fig. 4a. d–f, Measured far-field scattering patterns corresponding to three STC matrices for different parameters of the duty cycle and time shift, as detailed in Supplementary Fig. 4d–f.

Fig. 5. Measured far-field patterns for the adjustable partitioning scheme and direction of arrival (DOA) estimation results using the artificial neural network (ANN) model.

a Measured far-field patterns of the fundamental-frequency wave for different SC sequences. b, c Measured far-field harmonic scattering patterns for the reflected fundamental-frequency wave pointing to −15° and −30°, respectively. d Measured signal spectra received by antenna ANT2 (for θ_i=0°). e Distribution of the normalized harmonic amplitude for θ_i=−50° and θ_i=+20°, respectively. f Results and errors for DOA estimation by using the ANN model.

Fig. 6. Implementation and testing of the space-time-coding metasurface (STCM)-based integrated sensing and communication (ISAC) system.

a Experimental setup. b Received images corresponding to different angles of incidence when the STCM is not operational (upper panel) and operational (lower panel). c–f Measurement results for 10 positions of antenna ANT1. Demodulated constellation diagrams when the STCM is not operational and operational, respectively. e, f Measured error vector magnitudes (EVMs), and bit error ratios (BERs), respectively, when the STCM is not operational and operational, for different angles of incidence.