Multichannel direct communication based on a programmable topological plasmonic metasurface

Many emerging technologies, such as ultra-massive multiple-input multiple-output (UM-MIMO), terahertz (THz) communications are under active discussion as promising technologies to support the extremely high access rate and superior network capacity in the future sixth-generation (6G) mobile communication systems. However, such technologies are still facing many challenges for practical implementation. In particular, UM-MIMO and THz communication require extremely large number of radio frequency (RF) chains, and hence suffering from prohibitive hardware cost and complexity. In this article, we introduce a new paradigm to address the above issues, namely wireless communication enabled by programmable metasurfaces, by exploiting the powerful capability of metasurfaces in manipulating electromagnetic waves. We will first introduce the basic concept of programmable metasurfaces, followed by the promising paradigm shift in future wireless communication systems enabled by programmable metasurfaces. In particular, we propose two prospective paradigms of applying programmable metasurfaces in wireless transceivers: namely RF chain-free transmitter and space-down-conversion receiver, which both have great potential to simplify the architecture and reduce the hardware cost of future wireless transceivers. Furthermore, we present the design architectures, preliminary experimental results and main advantages of these new paradigms and discuss their potential opportunities and challenges toward ultra-massive 6G communications with low hardware complexity, low cost, and high energy efficiency.

The objectives of this study are to compare the effectiveness of bone‐ and air‐conduction radio communication while listening to natural auditory signals through air conduction and to assess the feasibility of using a mixed bone‐ and air‐conduction system for multichannel radio communication. There are many benefits to both air‐conducted and bone‐conducted systems, but little research on combining the two into one radio system. The goal of the study is to explore this possibility. The SATASK test developed at the U.S. Army Research Laboratory is used to observe human capabilities to distribute attention across multiple channel communication systems. This test consists of sentences structured as follows: NAME write the number NUMBER on the COLOR OBJECT. Five different multichannel communication systems (three three‐channel and two four‐channel systems) consisting of various combinations of air‐conducted earphones, bone‐conducted vibrators, and an array of loudspeakers are used for data collection. Each channel presents different sentences in different voices. Listeners are given a target name and they are to record the corresponding information associated with that name (selective attention) or they are to record information from all channels (divided attention). The results of the study will be discussed at the meeting.

Programmable metasurfaces show great application potential in many fields, so studying their radar cross-section reduction (RCSR) characteristics is very important. Metasurfaces based on polarization conversion and artificial magnetic conductors are widely used for RCSR, but they cannot scan beams. Programmable metasurfaces can dynamically steer beams in-band and reduce RCS by changing the phase of electromagnetic waves. But to meet practical needs, they must be stealthy both in-band and out-of-band. This paper presents a low-profile self-stealth programmable metasurface. Self-stealth describes the capability of the metasurface to achieve in-band and out-of-band RCSR through its intrinsic design, without requiring additional structures such as radomes or absorbing materials. The design principle is to achieve out-of-band RCS reduction without increasing the profile height or adding extra radio frequency components. The meta-atom has a positive-intrinsic-negative (PIN) diode to control the in-band ( f 0 ) x -polarization phase. Switching the PIN diode states gives 1-bit phase modulation. The in-band y -polarization uses a bridge design. Changing the size can get 1-bit phase, and the x - and y -polarizations can be adjusted separately. Also, the top layer has 4 cross-shaped dumbbells and 4 branch structures for out-of-band high ( fh 1 ) and low ( fl 1 ) frequencies. The middle layer has four 45° rotated cross-shaped dumbbells and 4 branch structures for out-of-band high ( fh 2 ) and low ( fl 2 ) frequencies. So, the meta-atom can modulate phase across 5 frequency bands ( fl 2 < fl 1 < f 0 < fh 2 < fh 1 ). The profile height is 0.065λ of the in-band center frequency, which is more conducive to conformal design. A 12 × 12 prototype was made. Simulation and measurement show that the metasurface reduces RCS in 5 bands and its in-band radiation can be used in communication transmission mode, which is good for programmable metasurface technology development.

Over the past two decades, an extensive research effort has been devoted to elastic metamaterials, structured artificial materials at subwavelength scales, for elastic wave manipulations in solids. Due to the extreme values of material parameters, negative and/or positive, they achieved, the applications can range from wave and/or vibration attenuations, wave guiding and imaging, enhanced sensing, to invisible cloaking. However, conventional passive metamaterials have limitations, i.e. they can only be operated in narrow frequency regions and their functions are usually locked into space or with minor tunabilities once fabricated, lacking real time reconfigurabilities. Those limitations strongly hinder them from practical usages. With the rapid development of smart materials and structures, more and more intelligent elements are being introduced into wave propagation, vibration and sound control systems. The piezoelectric shunting technique is one well known method that receives considerable attention. In this dissertation, by leveraging the circuit control concept, both analog and digital, we propose some circuit controlled active/adaptive/hybrid/programmable metamaterials and metasurfaces for unprecedent elastic wave manipulations. Analytical, numerically and experimentally approaches are combined throughout the dissertation to illustrate design concepts, characterize wave propagation properties, and valid the designs. Specifically, active elastic metamaterials with tunable stiffness in local resonators are first designed for tunable wave and/or vibration mitigations. We then extend this concept to achieve super broadband wave attenuations with frequency-dependent stiffness elements. By introducing the variable stiffness elements to the host medium, a hybrid metamaterial is developed for switched ON/OFF wave propagations and broadband negative refractions. Based on a developed approximate transformation method, an active metamaterial is designed and placed on a plate to achieve spatially varying effective mass densities for broadband elastic trajectory control. Finally, a programmable metasurface with ultrathin-thickness is demonstrated for broadband, real-time and multifunctional wavefront manipulations in a plate. The active, adaptive, hybrid, and programmable elastic metamaterials and/or metasurfaces are still in their infant stages. The examples presented in the dissertation are transformable to different length and time scales and could serve as efficient and powerful tools in exploring some unconventional wave phenomenon in solid structures, i.e. by using concepts in quantum mechanics, where passive approaches are significantly limited. The designs could also immediately open new possibilities in elastic wave control devices including, but not limited to structural health monitoring, stealth technology, active noise control, as well as medical instrumentation and imaging.

Programmable metasurfaces (PMs) are consisted of reconfigurable digital elements, and electromagnetic properties of the PMs can be manipulated by configuring digital states of these elements. This paper proposes to synthesize multiple beams, sum and difference beams based on a PM. Theoretical calculations validate the functions of the presented PM.

In this paper, we propose two dynamic error control schemes and apply them to the multichannel data communication system. The proposed schemes are based on the basic Stop-and-Wait ARQ and Selective Repeat ARQ protocols, The former and latter are used for the error controls in a round-trip time and among the multiple channels in a slot, respectively. The state of each channel is assumed as Markov chain with two states. The operations of the proposed schemes are described and their performances are evaluated through computer simulation. The numerical results show that the performances of the proposed schemes are improved remarkably comparing with the traditional scheme.

Free-Space Optical communication technology is a potential solution to the last mile or broadband access problem. Conventional free-space optical (FSO) communication is over a single link between two nodes. We explore multi-channel FSO communication system using compact (a maximum of a Sq.Ft) 2-dimensional antennas with multiple communication links between them to achieve very high aggregate bandwidths (100's of Gbps). But, close packaging of optical channels on the arrays causes inter-channel interference, reducing per channel capacity. We model the error due to inter-channel interference for such arrays and estimate the channel capacity. We address the multi-channel interference issue by both array design and by employing optical orthogonal codes (OOCs) for free-space optical communications and show that we can achieve multi Gbps bandwidths using such arrays. Possible applications for such multi-channel FSO systems can be in multi-hop broadband access networks or mesh networks and in back haul, connecting wireless base stations.

Programmable metasurfaces have shown exceptional potentials in wireless communications due to their capability to manipulate electromagnetic (EM) waves dynamically and flexibly. However, the large-scale application and flexible deployment of programmable metasurfaces still face challenges of high communication capacity requirements and stringent energy constraints. Here, we report an ambient-energy-driven space-time-coding metasurface to address these issues. On one hand, the metasurface can achieve efficient space-frequency-division multiplexing manipulations by dynamically controlling multiple frequencies and the spatial propagation directions of reflection EM waves. On the other hand, the shared-aperture ambient solar energy harvesting capability and low power consumption characteristic of the metasurface enable it to be self-powered without relying on any external power supply. To demonstrate these remarkable features, a four-channel wireless communication system prototype is built using the programmable metasurface. Experimental results confirm that four distinct images can be transmitted to four user terminals simultaneously, independently, and in real time with remarkably low energy consumption per bit. Such innovative metasurface provides a simple and effective approach for integrating ambient energy harvesting, multi-dimensional microwave manipulation, and direct information modulation on a single physical platform, which will advance the wireless communications in cost-effectiveness, enhanced capacity, energy efficiency, and environmental friendliness.

Relevance. The rapid development of the Internet of Things technology has led to an exponential increase in the number of different intelligent hardware connected to the Internet, which, in turn, has contributed to the emergence of a large amount of data to be transmitted over communication systems. Electromagnetic communication networks have insufficient potential to solve this problem, and optical information transmission systems via atmospheric channels are one of the real options for solving this problem. However, optical atmospheric communication systems are subject to the influence of atmospheric factors, i.e. due to absorption, scattering, and diffraction, the laser beam is weakened in power and broadens. In well-known works on the divergence of the beam, the question of the dependence of the maximum divergence of the beam on such indicators as the power of the laser source, the geometric length of the channel, and the wavelength of optical radiation is investigated. At the same time, in these works, one channel of the laser communication network is considered, and the question of choosing the diameter of the laser beam in all channels of the laser multichannel atmospheric network is not discussed. Purpose. The problem of optimal choice of the diameter of a laser beam in a multichannel atmospheric optical communication system of a distributed type is formulated, taking into account the divergence of the beam. The essence of the proposed solution, unlike well-known works that solve the optimization problem taking into account the influence of beam divergence, the solution to this goal covers both stationary and mobile versions of the network channels of the entire multichannel system. The task was solved by forming a single target functional and further optimizing it in order to identify the optimal relationship between the radius of the beam at the input of the channel receiver and the radius of the beam at the output of the radiator when applied to the atmospheric channel under consideration, taking into account the possibility of its broadening. It is shown that such an expansion of the diameter of the laser beam, according to the optimal law identified, makes it possible to achieve a maximum of the average intensity of the laser beam transmitted through the atmospheric channel to all receivers of the system. The conducted model studies of the proposed method for accounting for beam diameter broadening confirmed the possibility of obtaining an optimal ratio between the main indicators of a multichannel laser atmospheric network. Scientific novelty. A mathematical model for optimizing the choice of beam diameter in a multichannel laser atmospheric network has been developed. Theoretical and practical significance. Optimization of the proposed model made it possible to obtain an optimal ratio between the main indicators of a multi-channel laser atmospheric network of a distributed type, which can be used in the construction of such systems.

In this paper we model the base station of multi-channel mobile communication systems with finite user population discrete time queueing system. Using the method of Markov chain we derive the performance index such as probability of loss in one slot, the average throughput of the system, and the utilization ratio of channels. And through the numerical simulation, we discuss the effect of the model to the multi-channel mobile communication systems.

Metasurfaces have been extensively studied for generating electromagnetic waves carrying orbital angular momentum (OAM). In particular, programmable metasurfaces enable real‐time switching between multiple OAM modes in a digital manner. However, the current programmable metasurfaces are mostly based on reflective mode, which suffer from low efficiency as well as serious feed blockage. In this paper, a transmissive programmable metasurface is presented for the highly efficient generation of multimode convergent OAM beams. The proposed transmissive metasurface is composed of electronically reconfigurable units with 1‐bit phase resolution (0/π), which are obtained by integrating two PIN diodes in the radiating layer for current direction modulation. Through the antisymmetry configuration of the two PIN diodes, nearly uniform transmission magnitudes but inversed phase states in a wide band can be obtained. The simulation results show that the proposed reconfigurable unit can achieve good 1‐bit phase tuning, with minimum insertion loss of 0.2 dB and 2 dB transmission bandwidth of more than 10%. Through the dynamic modulation of the quantized code distributions on the metasurface, programmable multimode OAM beams can thus be constructed. Both simulated and measured results verify the effectiveness of the proposed design.

Low complexity and finer granularity quantization scheme for perturbation-based fiber nonlinearity compensation in coherent optical communication systems

Soliton transmission has been proposed for achieving a high-bit-rate long-distance optical fiber communication system.1 In the absence of fiber loss, distortionless pulses can be propagated along the fiber due to the balance between the frequency dispersion and self-phase modulation. However, in practical situations the pulse intensity decays because of fiber loss, resulting in a weaker self-phase modulation and hence the destruction of soliton. To solve this problem, loss compensation techniques using stimulated Raman scattering have been Introduced recently.2,3 In such a technique, cw pump waves are injected periodically into the fiber so that the signal pulses are amplified through the stimulated Raman scattering. It has been found that stable transmission of solitons over a long distance can be obtained using this amplification scheme. Nevertheless, the technique proposed so far is mainly focused on the soliton reconstruction for single-channel communication systems. An amplification scheme for multichannel systems is practically needed.

The application of inverse filter designs as a means of providing improved communication performance in acoustic environments is investigated. Tikhonov regularized inverse filters of channel transfer functions calculated in the frequency domain are used as a means of obtaining multi-channel filters. Three classifications of inverse filter structures have been considered using time-domain simulations. The performance of Tikhonov regularized inverse filters designed according to each of these classifications is compared with each other and against a filter design developed by Stojanovic [Stojanovic, M. (2005). "Retrofocusing techniques for high rate acoustic communications," J. Acoust. Soc. Am. 117, 1173-1185]. It is shown that the filter design developed by Stojanovic requires less regularization and outperforms the Tikhonov regularized inverse filter designs when communicating over a single channel. While the filter developed by Stojanovic is designed to use multiple transmitters to transmit to a single receiver, the filter was implemented in a multi-channel system and proposed to have a focusing similar to that obtained using time-reversal. It was found that for the scenario used in the simulation, the Tikhonov regularized inverse design for full multi-channel inversion achieved better focusing than the design by Stojanovic, where simulation results show 20 dB less cross-talk at the expense of around 2 dB loss in signal strength.

Amplitude‐phase programmable metasurfaces (APPMs) have attracted significant attention in recent years for their real‐time control of electromagnetic (EM) waves. However, existing APPMs often face challenges such as low energy efficiency, limited amplitude‐tuning range, and low phase‐modulation resolution. Additionally, achieving high‐precision amplitude and phase modulations simultaneously requires complex control circuits, thereby increasing the system cost and complexity. To address these challenges, an amplifying APPM (AAPPM) is proposed that achieves independent wide‐range amplitude tuning and high‐precision phase control through a novel and simplified architecture. Specifically, the designed AAPPM is embedded with gain‐tunable amplifiers, achieving over 5 dB EM‐energy amplification and ≈30 dB dynamic amplitude‐tuning range. Meanwhile, the AAPPM provides the 1‐bit phase modulations by controlling the states of integrated PIN diodes. With the introduction of time‐coding techniques, it can further achieve wide‐range and high‐precision phase controls of harmonics. To demonstrate its capability, a 6×6 AAPPM prototype is designed, simulated, and measured. The results indicate that AAPPM can achieve EM energy amplification, wide‐range dynamic amplitude control, and high‐precision phase modulation. By implementing various time‐coding strategies, the AAPPM facilitates flexible harmonic beam manipulations. With these distinctive features, the AAPPM shows great potential in wireless communication and radar systems.