Wireless data communications based on multi-mode vortex waves

Abstract

A method of wireless data communication based on multi-mode vortex waves is provided. The method includes: performing, at a transmitter side, a method of wireless data transmission for dynamically directly and focusing, for each vortex wave of a multi-mode vortex waves incident on a surface of a reconfigurable metasurface, the vortex wave to a predetermined one of a set of predefined receiver positions corresponding to a dynamically selected phase distribution state of a predefined set of phase distribution states based on an encryption key at the transmitter side that dynamically changes over time, the multi-mode vortex waves generated based on a plurality of data streams derived from an original series of data bits; and performing, at a receiver side, a method of wireless data reception, for receiving a plurality of signals of the multi-mode vortex waves focused at a plurality of receiver positions, respectively, of the set of predefined receiver positions that dynamically changes amongst the set of predefined receiver positions over time and determining the original series of data bits based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions and an encryption key at the receiver side. There are also provided a method of wireless data transmission based on multi-mode vortex waves and a method of wireless data reception based on multi-mode vortex waves. There are also provided a corresponding transmitter system, a corresponding receiver system and a corresponding wireless data communication system including the transmitter system and the receiver system.

Description

WIRELESS DATA COMMUNICATION BASED ON MULTI-MODE VORTEX WAVESCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore Patent Application No.10202403858W filed on 9 December 2024, the content of which being hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] The present invention generally relates to a method of wireless data communication based on multi-mode vortex waves, a corresponding method of wireless data transmission based on multi-mode vortex waves and a corresponding method of wireless data reception based on multi-mode vortex waves, as well as a wireless data communication system for wireless data communication based on multi-mode vortex waves, a corresponding transmitter system for wireless data transmission based on multi-mode vortex waves and a corresponding receiver system for wireless data reception based on multi-mode vortex waves.BACKGROUND

[0003] Multi-mode vortex waves (Orbital Angular Momentum (0AM) vortex waves, which may simply be referred to OAM waves) offer a unique structure compared to traditional plane waves, as they carry information through a helical phase front. This characteristic allows for multiple vortex modes (which may also be referred to as OAM modes) to coexist in the same transmission channel, effectively enhancing spectral efficiency. OAM waves exhibit orthogonality across different OAM modes, making them particularly valuable for multiplexing data streams within the same frequency band. However, OAM waves also have limitations, such as beam divergence over long distances, which requires careful management to maintain communication quality. The potential of OAM lies in its ability to support high-capacity wireless transmission without additional bandwidth, but there remain challenges such as signal degradation due to crosstalk between OAM modes.

[0004] A programmable metasurface (PMS) (which may also be referred to as a reconfigurable metasurface or a reconfigurable intelligent surface (RIS)) has been introduced as a groundbreaking technology capable of shaping the propagation environment of electromagnetic waves. An RIS comprises a planar array of passive reflective or transmissiveelements (RIS elements), which can dynamically control wavefronts by adjusting phase, amplitude, and polarization. RIS applications span beyond traditional beamforming; they also enable environmental control in complex wireless settings, offering solutions for issues like non-line-of-sight transmission, signal blockage, and spatial multiplexing. In various scenarios, an RIS has been employed to improve the performance of MIMO systems by optimizing energy efficiency and spectral efficiency, particularly in dense environments where direct links are compromised.

[0005] Conventional non-programmable metasurfaces play a crucial role in shaping and controlling electromagnetic waves, particularly OAM waves. Unlike dynamic RIS, which can adjust their properties in real time, conventional metasurfaces are typically passive and fixed in their design. These structures can manipulate wavefronts by adjusting the phase and amplitude of reflected or transmitted waves Conventional non-programmable metasurfaces have been extensively used for generating and controlling OAM beams, particularly in the context of beamforming and multiplexing. For example, conventional non-programmable metasurfaces can generate multiple OAM modes by encoding the geometric phase of incoming waves, enabling multiplexed data streams to be transmitted simultaneously. However, because conventional non-programmable metasurfaces lack dynamic reconfigurability, they are generally limited to predefined functionalities.

[0006] Several studies have demonstrated the use of metasurfaces to generate OAM beams with high efficiency. One approach involves using ultrathin, dual-polarized Huygens' metasurfaces to create mixed-OAM modes, which are suitable for millimeter-wave (mmWave) communications in 5G networks. These metasurfaces generate OAM beams with varying phase shifts to achieve high-gain antennas capable of multiplexing different OAM modes. However, these metasurfaces are static and cannot dynamically adjust the properties of OAM beams in real-time. This limitation has prompted researchers to explore new designs that incorporate programmable metasurfaces to allow dynamic beam manipulation.

[0007] In terms of secure communication, RIS-assisted MIMO systems have gained traction as a means to bolster physical layer security. These systems employ RIS to dynamically adjust beam patterns, ensuring that signal energy is directed toward legitimate users while minimizing the potential for eavesdropping. By optimizing the phase shifts across the RIS elements, MIMO systems can create highly directive beams that are difficult for unauthorized parties to intercept. This approach has been shown to significantly enhance secrecy rates in multi-user environments, particularly when combined with other security techniques, such asartificial noise injection or cooperative jamming. By incorporating RIS into MIMO systems, researchers have achieved improved spectral efficiency and security, making these systems highly suitable for future wireless networks such as 6G.

[0008] For example, the rapid expansion of internet of things (IoT) networks and the proliferation of connected devices have significantly increased the demand for wireless communication systems, particularly emphasizing data security, transmission efficiency, and reliability. Conventional cryptographic approaches, though effective, often involve high computational complexity and power consumption, making them less suitable for resource-constrained IoT environments. Consequently, physical-layer security (PLS) strategies have emerged as viable alternatives by leveraging inherent properties of wireless channels to achieve secure communication with reduced computational overhead. Notably, PLS techniques such as beamforming, cooperative relays, directional modulation, and spread spectrum techniques have been extensively investigated in recent literature.

[0009] Among the promising technologies enhancing PLS, programmable metasurfaces (PMS) stand out as planar artificial materials engineered to dynamically control electromagnetic (EM) waves. Due to their ultra-thin structure, low insertion losses, and compatibility with existing communication systems, metasurfaces have garnered extensive attention in recent research. Advances in PMS have particularly transformed their potential by integrating active tuning components such as PIN diodes, varactor diodes, and micro-electro-mechanical systems. These methods enable PMS to flexibly manipulate EM wave characteristics in real-time, significantly enriching the techniques available for secure information transmission in wireless networks. This multidimensional flexibility is especially critical for IoT networks, which are inherently susceptible to various forms of intrusion and eavesdropping. Despite these advantages, the PMS-based communication systems pose notable challenges. They typically disrupt traditional communication protocol architectures, necessitating integrated joint design efforts at both transmitter and receiver ends. The increase in controllable degrees of freedom inherently escalates the complexity of system link design and computational requirements, potentially limiting overall information transmission efficiency.

[0010] A need therefore exists to provide a method of wireless data communication based on multi-mode vortex waves, as well as a corresponding method of wireless data transmission and a corresponding method of wireless data reception based on multi-mode vortex waves, that seeks to overcome, or at least ameliorate, one or more deficiencies in conventional wireless data communication, and more particularly, that enhances both spectral efficiency and wirelessdata communication security in an efficient and effective manner. It is against this background that the present invention has been developed.SUMMARY

[0011] According to a first aspect of the present invention, there is provided a method of wireless data transmission based on multi-mode vortex waves, the method comprising:generating multi-mode vortex waves based on a plurality of data streams derived from an original series of data bits, each vortex wave of the multi-mode vortex waves generated based on a corresponding data stream of the plurality of data streams;transmitting the multi-mode vortex waves to a reconfigurable metasurface; and dynamically controlling the reconfigurable metasurface to be at a dynamically selected one of a predefined set of phase distribution states based on an encryption key that dynamically changes over time, each phase distribution state being configured to direct and focus, for each vortex wave of the multi-mode vortex waves incident on a surface of the reconfigurable metasurface, the vortex wave to a predetermined one of a set of predefined receiver positions corresponding to the dynamically selected phase distribution state.

[0012] According to a second aspect of the present invention, there is provided a method of wireless data reception based on multi-mode vortex waves, the method comprising:receiving, from a reconfigurable metasurface, a plurality of signals of multi-mode vortex waves focused at a plurality of receiver positions, respectively, of a set of predefined receiver positions that dynamically changes amongst the set of predefined receiver positions over time, the multi-mode vortex waves generated at a transmitter side based on a plurality of data streams derived from an original series of data bits and each vortex wave of the multimode vortex waves generated based on a corresponding data stream of the plurality of data streams,dynamically determining an encryption key that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multi-mode vortex waves is received over time; anddetermining the original series of data bits based on the plurality of signals of the multimode vortex waves received at the plurality of receiver positions and the encryption key.

[0013] According to a third aspect of the present invention, there is provided a method of wireless data communication based on multi-mode vortex waves, the method comprising:performing, at a transmitter side, the method of wireless data transmission according to the above-mentioned first aspect of the present invention for dynamically directly and focusing, for each vortex wave of the multi-mode vortex waves incident on the surface of the reconfigurable metasurface, the vortex wave to the predetermined one of the set of predefined receiver positions corresponding to the dynamically selected phase distribution state of the predefined set of phase distribution states based on the encryption key at the transmitter side that dynamically changes over time, the multi-mode vortex waves generated based on the plurality of data streams derived from an original series of data bits; andperforming, at a receiver side, the method of wireless data reception according to the above-mentioned second aspect of the present invention, for receiving, from the reconfigurable metasurface, the plurality of signals of the multi-mode vortex waves focused at the plurality of receiver positions, respectively, of the set of predefined receiver positions that dynamically changes amongst the set of predefined receiver positions over time and determining the original series of data bits based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions and the encryption key at the receiver side.

[0014] According to a fourth aspect of the present invention, there is provided a transmitter system for wireless data transmission based on multi-mode vortex waves, the transmitter system comprising:a reconfigurable metasurface;a multi-mode vortex wave generator configured to:generate multi-mode vortex waves based on a plurality of data streams derived from an original series of data bits, each vortex wave of the multi-mode vortex waves generated based on a corresponding data stream of the plurality of data streams; andtransmit the multi-mode vortex waves to the reconfigurable metasurface; a reconfigurable metasurface controller communicatively coupled to the reconfigurable metasurface and configured to:dynamically control the reconfigurable metasurface to be at a dynamically selected one of a predefined set of phase distribution states based on an encryption key that dynamically changes over time, each phase distribution state being configured to direct and focus, for each vortex wave of the multi-mode vortex waves incident on a surface of the reconfigurable metasurface, the vortex wave to a predetermined one of a set of predefined receiver positions corresponding to the dynamically selected phase distribution state.

[0015] According to a fifth aspect of the present invention, there is provided a receiver system for wireless data reception based on multi-mode vortex waves, the receiver system comprising:a set of signal detectors positioned at a set of predefined receiver positions, respectively, for receiving, from a reconfigurable metasurface, a plurality of signals of multi-mode vortex waves focused at a plurality of signal detectors of the set of signal detectors at a plurality of receiver positions of the set of predefined receiver positions, respectively, that dynamically changes amongst the set of predefined receiver positions over time, the multi-mode vortex waves generated at a transmitter side based on a plurality of data streams derived from an original series of data bits and each vortex wave of the multi-mode vortex waves generated based on a corresponding data stream of the plurality of data streams;an encryption key determinator configured to dynamically determine an encryption key that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multimode vortex waves is received over time; andan original data determinator configured to determine the original series of data bits based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions and the encryption key.

[0016] According to a sixth aspect of the present invention, there is provided a wireless data communication system for wireless data communication based on multi-mode vortex waves, the wireless data communication system comprising: the transmitter system according to the above-mentioned fourth aspect of the present invention; and the receiver system according to the above-mentioned fifth aspect of the present invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments of the present invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:FIG. 1 depicts a schematic diagram of a method of wireless data transmission based on multi-mode vortex waves, according to various embodiments of the present invention;FIG. 2 depicts a schematic diagram of a method of wireless data reception based on multi-mode vortex waves, according to various embodiments of the present invention;FIG. 3 depicts a schematic diagram of a method of wireless data communication based on multi-mode vortex waves, according to various embodiments of the present invention;FIG. 4 depicts a schematic block diagram of a transmitter system for wireless data transmission based on multi-mode vortex waves, according to various embodiments of the present invention;FIG. 5 depicts a schematic block diagram of a receiver system for wireless data reception based on multi-mode vortex waves, according to various embodiments of the present invention;FIG. 6 depicts a schematic block diagram of a wireless data communication system for wireless data communication based on multi-mode vortex waves, according to various embodiments of the present invention;FIG. 7 depicts a schematic block diagram of a reconfigurable metasurface controller, according to various embodiments of the present invention;FIG. 8 depicts a schematic block diagram of a receiver processing system, according to various embodiments of the present invention;FIG. 9 illustrates a schematic drawing of a wireless data communication system or method for wireless data communication based on multi-mode vortex waves, according to various first example embodiments of the present invention;FIG. 10 depicts an example schematic block of a transmitter processing section or portion of the transmitter system, according to various first example embodiments of the present invention;FIG. 11 depicts example types or designs of the multi-mode vortex wave generator; FIG. 12 depicts an example schematic block of the receiver system, according to various first example embodiments of the present invention;FIG. 13 illustrates the time-domain frame structure of the data transmission, where OAM mode 1 and mode 2 are transmitted over time, according to various first example embodiments of the present invention;FIG. 14 visualizes example energy distribution patterns generated by the reconfigurable intelligence surface (RIS) (also referred to as reconfigurable metasurface or programmable metasurface (PMS)) for different OAM modes and secrecy masks;FIG. 15 depicts a schematic drawing of a wireless data communication system or method for wireless data communication based on multi-mode vortex waves, according to various second example embodiments of the present invention;FIG. 16 depicts an encryption key lookup table (Table I) (representing or corresponding to a codebook) for determining the encryption key (decoded spreading bits) based on the focal spots pattern (signal location pattern) detected, according to various second example embodiments of the present invention;FIG. 17 illustrates the BER performance of the secure dual-channel transmission under various channel conditions (for Bob and Eve), according to various second example embodiments of the present invention;FIG. 18 illustrates the full-wave calculations for revealing the performance of the reconfigurable transmissive programmable metasurface unit, according to various second example embodiments of the present invention, namely, the S-parameters versus frequency with dual y-axes: phase (left, deg) and insertion loss (right, dB).FIG. 19A shows a setup with multi-mode OAM source and PMS (PIN diodes included) for full-wave EM calculations;FIGs. 19B to 19D show different configurations of the setup for converting two OAM modes to different focal spots;FIG. 20 shows an example fabrication of the PMS, including one sub-block (top-left), unit structure (top-right), front side of the whole PMS (bottom-left) and back side with LEDs (bottom-right)FIG. 21 A depicts a schematic drawing of an example multi-mode vortex wave generator;FIGs. 21B and 21C show the helical wavefront of vortex wave mode mode l = +1 and l = +2, respectively;FIG. 22 depicts an example real-time communications experimental system constructed for validating the secure dual-channel transmission method according to various second example embodiments of the present invention;FIG. 23 depicts the crosstalk isolation measurement results for four detectors strategically arranged on the receiver side of the PMS;FIGs. 24A and 24B show the BER measurement results for different channels for focal spots at EDI and ED4 (FIG. 24A) and for focal spots at ED2 and ED3 (FIG. 24B); and FIG. 25 shows real-time constellation diagrams for the decrypted data.DETAILED DESCRIPTION

[0018] Various embodiments of the present invention provide a method of wireless data communication based on multi-mode vortex waves, a corresponding method of wireless data transmission based on multi-mode vortex waves and a corresponding method of wireless data reception based on multi-mode vortex waves. Furthermore, various embodiments of the present invention provide a wireless data communication system for wireless data communication based on multi-mode vortex waves, a corresponding transmitter system for wireless data transmission based on multi-mode vortex waves and a corresponding receiver system for wireless data reception based on multi-mode vortex waves.

[0019] As discussed in the background, multi-mode vortex waves (OAM waves) have been utilized to enhance spectral efficiency in wireless data communication such that multiple vortex modes (0AM modes) can coexist in the same transmission channel (multiplexing data streams within the same frequency band). However, in view that the rapid expansion of internet of things (IoT) networks and the proliferation of connected devices have significantly increased the requirements for wireless communication systems, particularly emphasizing data security, transmission efficiency, and reliability, there is a need to provide a method of wireless data communication that not only enhances spectral efficiency (or transmission efficiency), but also enhances communication security, in an efficient and effective manner. A need therefore exists to provide a method of wireless data communication based on multi-mode vortex waves, as well as a corresponding method of wireless data transmission and a corresponding method of wireless data reception based on multi-mode vortex waves, that seeks to overcome, or at least ameliorate, one or more deficiencies in conventional wireless data communication, and more particularly, that enhances both spectral efficiency and wireless data communication security in an efficient and effective manner.

[0020] FIG. 1 depicts a schematic diagram of a method 100 of wireless data transmission based on multi-mode vortex waves, according to various embodiments of the present invention. The method 100 comprises: generating (106) multi-mode vortex waves based on a plurality of data streams derived from an original series of data bits, each vortex wave of the multi-mode vortex waves generated based on a corresponding data stream of the plurality of data streams; transmitting (108) the multi-mode vortex waves to a reconfigurable metasurface; and dynamically controlling (at 110) the reconfigurable metasurface to be at a dynamically selected one of a predefined set of phase distribution states based on an encryption key (which may also be referred to as a secret key) that dynamically changes over time, each phase distribution statebeing configured to direct and focus, for each vortex wave of the multi-mode vortex waves incident on a surface of the reconfigurable metasurface, the vortex wave to a predetermined one of a set of predefined receiver positions corresponding to the dynamically selected phase distribution state.

[0021] In various embodiments, the encryption key is dynamically changeable amongst a predefined set of encryption codes, each encryption code for controlling the reconfigurable metasurface to be at a corresponding one of the predefined set of phase distribution states.

[0022] In various embodiments, for each encryption code of the predefined set of encryption codes, a mapping between the encryption code and the corresponding phase distribution states of the predefined set of phase distribution states is defined based on a metasurface phase distribution state codebook (e.g., a predefined metasurface phase distribution state codebook).

[0023] In various embodiments, the reconfigurable metasurface comprises a two-dimensional (2D) array of unit cells, each unit cell being dynamically controllable to be at a dynamically selected one of a plurality of wave propagation path states based on the encryption key for providing a corresponding degree of phase shift for the multi-mode vortex waves incident thereon for said dynamically controlling the reconfigurable metasurface to be at the dynamically selected one of the predefined set of phase distribution states based on the encryption key.

[0024] In various first embodiments, the original series of data bits comprises a series of data segments. For each data segment of the series of data segments, the plurality of data streams is derived from a first portion (a series of data bits) of the data segment, and the encryption key is derived from (e.g., set as) a second portion (a series of data bits) of the data segment.

[0025] In various second embodiments, the original series of data bits comprises a series of data segments. For each data segment of the series of data segments, the plurality of data streams is generated based on a plurality of portions, respectively, of the data segment and the encryption key. For example, each portion of the data segment may be one data bit or a series of data bits. In various second embodiments, each data stream may be generated based on a corresponding portion of the data segment and a corresponding portion of the encryption key.

[0026] In various second embodiments, for each data segment of the series of data segments, each data stream of the plurality of data streams is generated by spreading each data bit of the corresponding portion of the plurality of portions of the data segment based on theencryption key. For example, in the case of the corresponding portion of the data segment being one data bit, the one data bit may be spread to generate the corresponding data stream. In the case of the corresponding portion of the data segment being a series of data bits, each data bit of the series of data bits may be spread to generate the corresponding data stream.

[0027] FIG. 2 depicts a schematic diagram of a method 200 of wireless data reception based on multi-mode vortex waves, according to various embodiments of the present invention. The method 200 comprises: receiving (at 206), from a reconfigurable metasurface, a plurality of signals of multi-mode vortex waves focused at a plurality of receiver positions, respectively, of a set of predefined receiver positions that dynamically changes (i.e., the plurality of receiver positions (or the specific receiver positions) at which the plurality of signals of multi-mode vortex waves is received) amongst the set of predefined receiver positions over time, the multimode vortex waves generated at a transmitter side based on a plurality of data streams derived from an original series of data bits and each vortex wave of the multi-mode vortex waves generated based on a corresponding data stream of the plurality of data streams; dynamically determining (at 208) an encryption key (which may also be referred to as a secret key) that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multimode vortex waves is received over time, and determining (at 210) the original series of data bits based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions and the encryption key.

[0028] In various embodiments, the above-mentioned dynamically determining (at 208) the encryption key comprises: dynamically determining a signal location pattern (e.g., representing or indicating which receiver positions (or which receivers (or signal detectors)) received the plurality of signals of multi-mode vortex waves) that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multi-mode vortex waves is received over time; and dynamically determining the encryption key that dynamically changes over time based on the signal location pattern and a metasurface phase distribution state codebook (e.g., a predefined metasurface phase distribution state codebook predefined between the transmitter side and receiver side, or shared by the transmitter side). In this regard, the encryption key is dynamically changeable amongst a predefined set of encryption codes, the signal location pattern is dynamically changeable amongst a predefined set of signal location patterns, and for each encryption code of the predefined set of encryption codes, a mapping between theencryption code and a corresponding signal location pattern of the predefined set of signal location patterns is defined based on the metasurface phase distribution state codebook, each signal location pattern corresponds to a phase distribution state of the reconfigurable metasurface.

[0029] In various first embodiments, the original series of data bits comprises a series of data segments. The above-mentioned determining (at 210) the original series of data bits comprises, for each data segment of the series of data segments: determining a plurality of data streams based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions that dynamically change over time; determining a first portion (a series of data bits) of the data segment based on the plurality of data streams, and determining a second portion (a series of data bits) of the data segment based on the encryption key.

[0030] In various second embodiments, the original series of data bits comprises a series of data segments. The above-mentioned determining (at 210) the original series of data bits comprises, for each data segment of the series of data segments: determining a plurality of data streams based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions that dynamically change over time; and determining a plurality of portions of the data segment based on the plurality of data streams, respectively, and the encryption key. For example, each portion of the data segment may be one data bit or a series of data bits. In various second embodiments, each portion of the data segment may be determined based on a corresponding data stream and a corresponding portion of the encryption key.

[0031] In various second embodiments, for each data segment of the series of data segments and for each portion of the plurality of portions of the data segment, each data bit of the portion of the data segment is determined by despreading the corresponding data stream of the plurality of data streams based on the encryption key. In various second embodiments, the corresponding data stream is despread by a corresponding portion of the encryption key. For example, in the case of the portion of the data segment being one data bit, the corresponding data stream may be despread to obtain the one data bit of the portion of the data segment. In the case of the portion of the data segment being a series of data bits, the corresponding data stream may be despread to obtain each data bit of the portion of the data segment.

[0032] FIG. 3 depicts a schematic diagram of a method 300 of wireless data communication based on multi-mode vortex waves, according to various embodiments of the present invention. The method 300 comprises: performing (306), at a transmitter side, the method 100 of wirelessdata transmission as described herein according to various embodiments of the present invention for dynamically directly and focusing, for each vortex wave of the multi-mode vortex waves incident on the surface of the reconfigurable metasurface, the vortex wave to the predetermined one of the set of predefined receiver positions corresponding to the dynamically selected phase distribution state of the predefined set of phase distribution states based on the encryption key at the transmitter side that dynamically changes over time, the multi-mode vortex waves generated based on the plurality of data streams derived from an original series of data bits; and performing (316), at a receiver side, the method 200 of wireless data reception as described herein according to various embodiments of the present invention for receiving the plurality of signals of the multi-mode vortex waves focused at the plurality of receiver positions, respectively, of the set of predefined receiver positions that dynamically changes amongst the set of predefined receiver positions over time and determining the original series of data bits based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions and the encryption key at the receiver side.

[0033] Accordingly, in various first embodiments and as described hereinbefore, the original series of data bits comprises a series of data segments. For the method 100 of wireless data transmission and for each data segment of the series of data segments, the plurality of data streams is derived from a first portion (a series of data bits) of the data segment, and the encryption key at the transmitter side is derived from (e g., set as) a second portion (a series of data bits) of the data segment, and for the method 200 of wireless data reception, the above-mentioned determining the original series of data bits comprises, for each data segment of the series of data segments: determining a plurality of data streams based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions that dynamically change over time; determining a first portion (a series of data bits) of the data segment based on the plurality of data streams, and determining a second portion (a series of data bits) of the data segment based on based on the encryption key at the receiver side.

[0034] Accordingly, in various second embodiments and as described hereinbefore, the original series of data bits comprises a series of data segments. For the method 100 of wireless data transmission and for each data segment of the series of data segments, the plurality of data streams is generated based on a plurality of portions, respectively, of the data segment and the encryption key at the transmitter side. For the method 200 of wireless data reception, the above-mentioned determining (at 210) the original series of data bits comprises for each data segment of the series of data segments: determining a plurality of data streams based on the plurality ofsignals of the multi-mode vortex waves received at the plurality of receiver positions that dynamically change overtime; and determining a plurality of portions of the data segment based on the plurality of data streams, respectively, and the encryption key at the receiver side.

[0035] Accordingly, in various second embodiments and as described hereinbefore, for the method 100 of wireless data transmission and for each data segment of the series of data segments, each data stream of the plurality of data streams is generated by spreading each data bit of the corresponding portion of the plurality of portions of the data segment based on the encryption key at the transmitter side. For the method 200 of wireless data reception, for each data segment of the series of data segments and for each portion of the plurality of portions of the data segment, each data bit of the portion of the data segment is determined by despreading the corresponding data stream of the plurality of data streams based on the encryption key.

[0036] FIG. 4 depicts a schematic block diagram of a transmitter system 400 for wireless data transmission based on multi-mode vortex waves according to various embodiments of the present invention, corresponding to the method 100 of wireless data transmission based on multi-mode vortex waves as described herein according to various embodiments of the present invention. The transmitter system 400 comprises: a reconfigurable metasurface 420; a multimode vortex wave generator 440 configured to: generate multi-mode vortex waves based on a plurality of data streams derived from an original series of data bits, each vortex wave of the multi-mode vortex waves generated based on a corresponding data stream of the plurality of data streams; and transmit the multi-mode vortex waves to the reconfigurable metasurface 420; and a reconfigurable metasurface controller 460 communicatively coupled to the reconfigurable metasurface 420 and configured to: dynamically control the reconfigurable metasurface 420 to be at a dynamically selected one of a predefined set of phase distribution states based on an encryption key that dynamically changes over time, each phase distribution state being configured to direct and focus, for each vortex wave of the multi-mode vortex waves incident on a surface of the reconfigurable metasurface 420, the vortex wave to a predetermined one of a set of predefined receiver positions (3D positions or locations) 430 corresponding to the dynamically selected phase distribution state.

[0037] FIG. 5 depicts a schematic block diagram of a receiver system 500 for wireless data reception based on multi-mode vortex waves according to various embodiments of the present invention, corresponding to the method 200 of wireless data reception based on multi-mode vortex waves as described herein according to various embodiments of the present invention. The receiver system 500 comprises: a set of signal detectors (or receivers) 510 positioned at aset of predefined receiver positions (3D positions or locations) 430, respectively, for receiving, from a reconfigurable metasurface 420, a plurality of signals of multi-mode vortex waves focused at a plurality of signal detectors of the set of signal detectors 510 at a plurality of receiver positions of the set of predefined receiver positions 430, respectively, that dynamically changes amongst the set of predefined receiver positions 430 over time, the multi-mode vortex waves generated at a transmitter side based on a plurality of data streams derived from an original series of data bits and each vortex wave of the multi-mode vortex waves generated based on a corresponding data stream of the plurality of data streams; an encryption key determinator 530 configured to dynamically determine an encryption key that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions 430 at which the plurality of signals of the multi-mode vortex waves is received over time; and an original data determinator 550 configured to determine the original series of data bits based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions and the encryption key.

[0038] FIG. 6 depicts a schematic block diagram of a wireless data communication system 600 for wireless data communication based on multi-mode vortex waves according to various embodiments of the present invention, corresponding to the method 300 of wireless data communication based on multi-mode vortex waves as described herein according to various embodiments of the present invention. The wireless data communication system 600 comprises the transmitter system 400 as described herein according to various embodiments of the present invention; and the receiver system 500 as described herein according to various embodiments of the present invention.

[0039] It will be understood by a person skilled in the art that the transmitter system 400 for wireless data transmission based on multi-mode vortex waves corresponds to the method 100 of wireless data transmission based on multi-mode vortex waves as described herein with reference to FIG. 1 according to various embodiments of the present invention, therefore, various operations, functions or steps configured to be performed by the transmitter system 400 may correspond to various operations, functions or steps of the method 100 of wireless data transmission as described hereinbefore according to various embodiments of the present invention, and thus need not be repeated with respect to the transmitter system 400 for clarity and conciseness. In other words, various embodiments described herein in context of methods (e.g., the method 100 of wireless data transmission) are analogously valid for the corresponding systems or devices (e g., the transmitter system 400 for wireless data transmission), and viceversa. Similarly, it will be understood by a person skilled in the art that the receiver system 500 for wireless data reception based on multi-mode vortex waves corresponds to the method 200 of wireless data reception based on multi-mode vortex waves as described herein with reference to FIG. 2 according to various embodiments of the present invention, therefore, various operations, functions or steps configured to be performed by the receiver system 500 may correspond to various operations, functions or steps of the method 200 of wireless data reception as described hereinbefore according to various embodiments of the present invention, and thus need not be repeated with respect to the receiver system 500 for clarity and conciseness. Similarly, it will be understood by a person skilled in the art that the wireless data communication system 600 for wireless data communication based on multi-mode vortex waves corresponds to the method 300 of wireless data communication based on multi-mode vortex waves as described herein with reference to FIG. 3 according to various embodiments of the present invention, therefore, various operations, functions or steps configured to be performed by the wireless data communication system 600 may correspond to various operations, functions or steps of the method 300 of wireless data communication as described hereinbefore according to various embodiments of the present invention, and thus need not be repeated with respect to the wireless data communication system 600 for clarity and conciseness.

[0040] It will be appreciated by a person skilled in the art that at least one processor may be communicatively coupled to at least one memory and configured to perform various functions or operations through set(s) of instructions (e.g., software modules) executable by the at least one processor to perform various functions or operations.

[0041] For example, FIG. 7 depicts a schematic block diagram of the reconfigurable metasurface controller 460 as described herein according to various embodiments of the present invention. The reconfigurable metasurface controller 460 comprises: at least one memory 462; and at least one processor 464 communicatively coupled to the at least one memory 462 and the reconfigurable metasurface 420 and configured to: dynamically control the reconfigurable metasurface 420 to be at a dynamically selected one of a predefined set of phase distribution states based on an encryption key that dynamically changes over time, each phase distribution state being configured to direct and focus, for each vortex wave of the multi-mode vortex waves incident on a surface of the reconfigurable metasurface 420, the vortex wave to a predetermined one of a set of predefined receiver positions 430 corresponding to the dynamically selected phase distribution state. Accordingly, as shown in FIG. 7, the reconfigurable metasurfacecontroller 460 may comprise: a reconfigurable metasurface controlling module (or a reconfigurable metasurface controlling circuit) 466 configured to dynamically control the reconfigurable metasurface 420 to be at a dynamically selected one of a predefined set of phase distribution states based on an encryption key that dynamically changes over time, each phase distribution state being configured to direct and focus, for each vortex wave of the multi-mode vortex waves incident on a surface of the reconfigurable metasurface 420, the vortex wave to a predetermined one of a set of predefined receiver positions 430 corresponding to the dynamically selected phase distribution state. For example, in various embodiments, the at least one memory 462 may have stored therein the reconfigurable metasurface controlling module 466, which are executable by the at least one processor 464 to perform the corresponding operations, functions or steps as described herein.

[0042] For example, FIG. 8 depicts a schematic block diagram of a receiver processing system 800 comprising the encryption key determinator 530 and the original data determinator 550 as described herein according to various embodiments of the present invention. The receiver processing system 800 comprises: at least one memory 862; and at least one processor 864 communicatively coupled to the at least one memory 862 and configured to: dynamically determine an encryption key that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions 430 at which the plurality of signals of the multi-mode vortex waves is received over time; and determine the original series of data bits based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions and the encryption key. Accordingly, as shown in FIG. 8, the receiver processing system 800 may comprise: the encryption key determinator (e.g., an encryption key determining module or circuit) 530 configured to dynamically determine an encryption key that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions 430 at which the plurality of signals of the multi-mode vortex waves is received over time; and the original data determinator (e.g., an original data determining module or circuit) 550 configured to determine the original series of data bits based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions and the encryption key. For example, in various embodiments, the at least one memory 862 may have stored therein the encryption key determining module 530 and the original data determining module 550, which are executable by the at least one processor 864 to perform the corresponding operations, functions or steps as described herein.

[0043] A computing system, a controller, a microcontroller or any other system providing a processing capability may be provided according to various embodiments in the present invention. Such a system may be taken to include one or more processors and one or more computer-readable storage mediums. For example, the reconfigurable metasurface controller 460 described hereinbefore may include at least one processor 464 and at least one computer-readable storage medium (or memory) 462 which are for example used in various processing carried out therein as described herein. A memory or computer-readable storage medium used in various embodiments may be a volatile memory, for example a DRAM (Dynamic Random Access Memory) or a non-volatile memory, for example a PROM (Programmable Read Only Memory), an EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), or a flash memory, e.g., a floating gate memory, a charge trapping memory, an MRAM (Magnetoresistive Random Access Memory) or a PCRAM (Phase Change Random Access Memory)

[0044] In various embodiments, a “circuit” may be understood as any kind of a logic implementing entity, which may be special purpose circuitry or a processor executing software stored in a memory, firmware, or any combination thereof. Thus, in an embodiment, a “circuit” may be a hard-wired logic circuit or a programmable logic circuit such as a programmable processor, e.g., a microprocessor (e.g., a Complex Instruction Set Computer (CISC) processor or a Reduced Instruction Set Computer (RISC) processor). A “circuit” may also be a processor executing software, e.g., any kind of computer program, e.g., a computer program using a virtual machine code, e.g., Java. Any other kind of implementation of various functions or operations may also be understood as a “circuit” in accordance with various other embodiments. Similarly, a “module” may be a portion of a system according to various embodiments in the present invention and may encompass a “circuit” as above, or may be understood to be any kind of a logic-implementing entity therefrom.

[0045] Some portions of the present disclosure may be explicitly or implicitly presented in terms of algorithms and functional or symbolic representations of operations on data within a computer memory. These algorithmic descriptions and functional or symbolic representations are the means used by those skilled in the data processing arts to convey most effectively the substance of their work to others skilled in the art. An algorithm may be, and generally, conceived to be a self-consistent sequence of steps leading to a desired result.

[0046] The present specification also discloses a system (e g, which may also be embodied as one or more devices or apparatuses), such as the reconfigurable metasurface controller 460 (or a reconfigurable metasurface controlling system) or the receiver processing system 800, forperforming various operations, functions or steps of various methods described herein. Such a system may be specially constructed for the required purposes or may comprise a general purpose computer system selectively activated or reconfigured by a computer program stored in the computer system. In general, various algorithms that may be presented herein are not limited to being implemented or executed by any particular computer system. Alternatively, the construction of more specialized computer system to perform various operations, functions or steps of various methods described herein may be provided as desired or as appropriate without going beyond the scope of the present invention.

[0047] In addition, the present specification also at least implicitly discloses computer program(s) or software / functional module(s), in that it would be apparent to a person skilled in the art that various operations, functions or steps of various methods described herein may be put into effect by computer code The computer program(s) is not intended to be limited to any particular programming language and implementation thereof, and it will be appreciated by a person skilled in the art that a variety of programming languages and coding thereof may be used to implement the computer program(s). Moreover, the computer program(s) is not intended to be limited to any particular control flow as there are a variety of programming languages which can use different control flows. It will be appreciated by a person skilled in the art that a computer program may be stored on any computer-readable storage medium (non-transitory computer-readable storage medium), such as but not limited to, a magnetic disk, an optical disk or a memory chip. For example, a computer program stored on a computer-readable storage medium may be loaded and executed on a computer system to implement various operations, functions or steps of various methods described herein according to various embodiments of the present invention.

[0048] Accordingly, in various embodiments, there is provided a computer program product, embodied in one or more computer-readable storage mediums (non-transitory computer-readable storage medium), comprising instructions (e.g., the reconfigurable metasurface controlling module 466) executable by one or more computer processors to dynamically control the reconfigurable metasurface 420 as described herein according to various embodiments of the present invention. Accordingly, various computer programs or software modules described herein may be stored in a computer program product receivable by a system therein, such as the reconfigurable metasurface controller 460, for execution by at least one processor 464 of the reconfigurable metasurface controller 460 to perform various operations, functions or steps of various methods described herein according to variousembodiments of the present invention. In various embodiments, there is also provided a computer program product, embodied in one or more computer-readable storage mediums (non-transitory computer-readable storage medium), comprising instructions (e.g., the encryption key determining module 530 and the original data determining module 550) executable by one or more computer processors to dynamically control the reconfigurable metasurface 420 as described herein according to various embodiments of the present invention

[0049] It will be appreciated by a person skilled in the art that various modules described herein (e.g., the reconfigurable metasurface controlling module 466, the encryption key determining module 530 and / or the original data determining module 550) may be software module(s) realized by computer program(s) or set(s) of instructions executable by a computer processor to perform various functions or operations. Various modules described herein (e.g., the reconfigurable metasurface controlling module 466, the encryption key determining module 530 and / or the original data determining module 550) may also be implemented as hardware module(s) being functional hardware unit(s) designed to perform various functions or operations. More particularly, in the hardware sense, a module is a functional hardware unit designed for use with other components or modules. For example, a module may be implemented using discrete electronic components, or it can form a portion of an entire electronic circuit such as an Application Specific Integrated Circuit (ASIC) or a Field Programmable Gate Array (FPGA). For example, in the case of the reconfigurable metasurface controlling module 466 being implemented as a FPGA, the memory 462 (e.g., a non-volatile memory such as a flash memory) may store a configuration file for programming or configuring the FPGA (e g., corresponding to the processor 464) to dynamically control the reconfigurable metasurface 420 as described herein according to various embodiments of the present invention. Accordingly, the programmed or configured FPGA comprises the reconfigurable metasurface controlling module (as a circuit) 466 configured to dynamically control the reconfigurable metasurface 420 as described herein according to various embodiments of the present invention. Numerous other possibilities exist. It will also be appreciated by a person skilled in the art that a combination of hardware and software modules may be implemented. Furthermore, various operations, functions or steps of various methods described herein may be performed in parallel rather than sequentially as desired or as appropriate (e.g., as long as it does not render the method(s) inoperable or unsatisfactory for its intended purpose).

[0050] It will be understood by a person skilled in the art multi-mode vortex wave generators are known in the art and thus need not be described herein for clarity andconciseness. Furthermore, it will be understood by a person skilled in the art that the present invention is not limited to any specific type or configuration of multi-mode vortex wave generator as long as the multi-mode vortex wave generator is capable of, or operable to, generating and transmitting multi-mode vortex waves based on data streams.

[0051] It will be appreciated by a person skilled in the art that the terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0052] Any reference to an element or a feature herein using a designation such as “first”, “second” and so forth does not limit the quantity or order of such elements or features, unless stated or the context requires otherwise. For example, such designations may be used herein as a convenient way of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not necessarily mean that only two elements can be employed, or that the first element must precede the second element, unless stated or the context requires otherwise. In addition, a phrase referring to “at least one of’ a list of items refers to any single item therein or any combination of two or more items therein.

[0053] In order that the present invention may be readily understood and put into practical effect, various example embodiments of the present invention will be described hereinafter by way of examples only and not limitations. It will be appreciated by a person skilled in the art that the present invention may, however, be embodied in various different forms or configurations and should not be construed as limited to the example embodiments set forth hereinafter. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0054] In various first example embodiments of the present invention, a method of wireless data communication based on multi-mode vortex waves will be described with respect to a covert communication method for transmitting and receiving indexing bits using 3D Orbital Angular Momentum (0AM) beam patterns and a reconfigurable metasurface.

[0055] Various first example embodiments relate to the field of 0AM electromagnetic wave transmission, Reconfigurable Intelligent Surface (RlS)-assisted wireless communication, and secure communication technologies. In particular, according to various first example embodiments of the present invention, a unique secure communication method is introduced based on RIS-aided space-division index modulation, leveraging 0AM vortex waves as an information transmission medium. The synergistic relationship between 0AM and RIS (which may also be referred to as a reconfigurable metasurface) plays a dual role, namely, enhancing the multiplexing capability of the RIS system to improve spectral efficiency and utilizing RIS’s advanced beamforming abilities to disentangle spatially overlapped 0AM vortex waves. These disentangled vortex waves are directed towards distinct reception positions or locations (e.g., points), thereby reducing the complexity of demodulation at the receiver through efficient space-division techniques.

[0056] FIG. 9 illustrates a schematic drawing of a wireless data communication system 900 for wireless data communication based on multi-mode vortex waves, as well as a corresponding method of wireless data communication, according to various first example embodiments of the present invention. In particular, in various first example embodiments of the present invention, there is provided a unique secure communication system (e g., transmission system) that significantly enhances spectral efficiency while reducing computational complexity, leveraging multi-mode vortex beams (0AM waves) and a reconfigurable metasurface (which may also be referred to as a RIS). The secure communication system is designed to provide high-capacity, space-division secure communication by exploiting the unique properties of vortex waves (0AM waves) and a RIS for signal modulation, multiplexing, and secure transmission.

[0057] In the transmitter system 910 (or the corresponding method of wireless data transmission) according to various first example embodiments, the original series of data bits comprises a series of data segments, and for each data segment of the series of data segments, the plurality of data streams is derived from a first portion of the data segment and the encryption key is derived from (e g., set as) a second portion of the data segment. Therefore, at each data segment, data is divided into two parts (or two portions or sets) at the transmitter side. The first part (or first portion or set) of data bits comprises a series of data bits that are encoded into multiple 0AM modes, which are transmitted simultaneously and at the same frequency through a coaxial transmitter. Accordingly, it will be appreciated by a person skilled in the art that the first part or portion of the data segment is not limited to any specific number of databits, which may be configured or set as desired or as appropriate. These 0AM waves (or 0AM beams) propagate through free space, each representing different data streams, and are then manipulated by the RIS 914 (reconfigurable metasurface). The RIS 914 acts as a dynamic relay, focusing the different 0AM waves (or 0AM beams) into distinct spatial points (positions or locations in the 3D space) Each OAM mode is thus concentrated in a separate spatial location. In various example embodiments, at each time slot, each OAM mode is directed to one spatial location, allowing for spatial multiplexing without the need for additional frequency resources. Accordingly, multi-mode OAM waves are generated based on a plurality of data streams derived from an original series of data bits, each OAM wave of the multi-mode OAM waves is generated based on a corresponding data stream of the plurality of data streams, and the multimode OAM waves are transmitted to the RIS 914.

[0058] The second part (or second portion or set) of the data bits is processed by a RIS controller 916 (which may also be referred to as an index mapper or a pattern mapper), which modifies the RF phase distribution of the RIS 914. This results in controlled changes to the spatial energy focal points of the different OAM beams. Basically, the RIS 914 is dynamically controlled to dynamically adjust the focal points of different OAM beams, creating a pattern of energy distributions across the receiving area over time that encodes the second part of the original data (secure data bits, which may be referred to as an encryption key) being transmitted. Accordingly, the RIS 914 is dynamically controlled to be at a dynamically selected one of a predefined set of phase distribution states based on an encryption key that dynamically changes over time, each phase distribution state being configured to direct and focus, for each OAM wave of the multi-mode OAM waves incident on a surface of the RIS 914, the OAM wave to a predetermined one of a set of predefined receiver positions corresponding to the dynamically selected phase distribution state. Accordingly, it will be appreciated by a person skilled in the art that the second part or portion of the data segment is not limited to any specific number of data bits, which may be configured or set as desired or as appropriate, such as based on the desired or configured number of phase distribution states of the RIS 914 (e.g., 4 phase distribution states require a second portion with 2 data bits or 16 phase distribution states require a second portion with 4 data bits).

[0059] In various first example embodiments, the encryption key is dynamically changeable amongst a predefined set of encryption codes, each encryption code for controlling the RIS 914 to be at a corresponding one of the predefined set of phase distribution states. Furthermore, for each encryption code of the predefined set of encryption codes, a mappingbetween the encryption code and the corresponding phase distribution states of the predefined set of phase distribution states is defined based on a covert codebook (e.g., a predefined metasurface phase distribution state codebook).

[0060] At the receiver side, in the receiver system 950 (or the corresponding method of wireless data reception) according to various first example embodiments, multiple signal detectors (e.g., antennas) are strategically placed at different spatial positions to capture the signals from the focused 0AM beams. These signal detectors are able to receive the first part of data bits (or the first portion or set of data bits) from the incoming 0AM signals for demodulation directly. Additionally, based on the spatial energy distribution and the changes in the focal points over time created by the RIS 914, the receiver system 950 can infer or decode the encryption key (i.e., the secure data bits (the second part or portion of the data segment) (e.g., based on a predefined covert codebook) used by the RIS controller 916 at the transmitter side for controlling the RIS 914 to encode the encryption key. Accordingly, a plurality of signals of multi-mode 0AM waves focused at a plurality of receiver positions, respectively, of a set of predefined receiver positions is received from the RIS 914 that dynamically changes (i.e., the plurality of receiver positions (or the specific receiver positions) at which the plurality of signals of multi-mode 0AM waves is received) amongst the set of predefined receiver positions over time. Furthermore, an encryption key (i.e., the secure data bits) is dynamically determined that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multimode 0AM waves is received over time. The original series of data bits may then be determined based on the plurality of signals of the multi-mode 0AM waves received at the plurality of receiver positions and the encryption key. In various first example embodiments, determining the original series of data bits comprising, for each data segment of the series of data segments: determining a plurality of data streams based on the plurality of signals of the multi-mode 0AM waves received at the plurality of receiver positions that dynamically change over time; determining a first portion of the data segment based on the plurality of data streams; and determining a second portion of the data segment based on the encryption key. In various first example embodiments, the first and second portions of each data segment are concatenated and adjacent data segments are concatenated.

[0061] In various first example embodiments, the above-mentioned dynamically determining the encryption key comprises: dynamically determining a signal location pattern (e g., representing or indicating which receiver positions (or which receivers (or signaldetectors)) received the plurality of signals of multi-mode 0AM waves) that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multi-mode 0AM waves is received over time; and dynamically determining the encryption key that dynamically changes overtime based on the signal location pattern and a covert codebook (e.g., a predefined metasurface phase distribution state codebook predefined between the transmitter side and receiver side, or shared by the transmitter side). In this regard, the encryption key is dynamically changeable amongst a predefined set of encryption codes, the signal location pattern is dynamically changeable amongst a predefined set of signal location patterns, and for each encryption code of the predefined set of encryption codes, a mapping between the encryption code and a corresponding signal location pattern of the predefined set of signal location patterns is defined based on the covert codebook, each signal location pattern corresponds to a phase distribution state of the RIS 914.

[0062] Accordingly, this dual-layer data transmission method (dual-stream transmission process) not only enhances the system’s communication capacity by allowing simultaneous transmission of multiple data streams using 0AM modes, but it also reduces the complexity of demodulation at the receiver. Moreover, the dynamic manipulation of energy focal points provides an additional layer of security, as the covert codebook is embedded in the RIS phase control, making it difficult for unauthorized parties to intercept the data. Accordingly, the wireless data communication system 900, as well as a corresponding method of wireless data communication, according to various first example embodiments of the present invention advantageously achieves both high spectral efficiency and secure transmission through a unique combination of 0AM vortex waves (or vortex beams) and RIS technology, providing a flexible and efficient solution for modem wireless communication systems.Wireless Data Transmission Using Multi-Mode Vortex Waves (0AM Beams) and RIS

[0063] The transmitter system 910 (or the corresponding method of wireless data transmission) will now be described in further detail according to various first example embodiments of the present invention. As described hereinbefore, a key aspect of the transmitter system 910 is its dual-stream transmission mechanism, which uniquely combines the use of multi-mode 0AM waves with RIS 914 to enhance both spectral efficiency and communication security.

[0064] FIG. 10 depicts an example schematic block of a transmitter processing section or portion 920 of the transmitter system 910 according to various first example embodiments of the present invention. As shown in FIG. 10, the transmitter processing section 920 comprises a digital information encoder 1004 and a bit splitter 1008. The bit splitter 1008 is configured to, for each data segment of the series of data segments of the original series of data bits (data input stream), divide the data segment into two distinct parts or portions, namely, one part or portion (corresponding to the above-mentioned first part or portion) for 0AM multiplexing and the other part or portion (corresponding to the above-mentioned second part or portion) for spacedivision index mapping, which is used to control the RIS 914.OAM-based Multiplexing Transmission from the Same Direction Angle

[0065] The first part or portion of each data segment of the original series of data bits is encoded onto multiple 0AM modes, which are orthogonal to each other. 0AM waves possess a helical phase structure, allowing different 0AM modes to be transmitted simultaneously at the same frequency. This property enables the system to transmit multiple data streams using the same spectral resource, significantly increasing the spectral efficiency. Unlike traditional transmission methods that would require multiple spatially distributed transmitters, the coaxial 0AM transmitter used here emits all the 0AM beams from a single point. Since all the 0AM beams originate from the same spatial position relative to the RIS 914, this eliminates the spatial dispersion issue encountered in conventional communication systems where signals are transmitted from different angles. By concentrating the 0AM modes into a single spatial direction, the system optimizes the use of spatial resources and simplifies the design of the transmitting apparatus.

[0066] The RIS 914 is strategically positioned in the path of these 0AM beams. One of the key challenges in traditional MIMO systems is the need to spatially separate signals transmitted from multiple antennas to avoid interference. In contrast, in the transmitter system 910, the orthogonality of the 0AM modes ensures that they can be transmitted through the same RIS 914 without overlapping or interfering with each other. This allows the transmitter system 910 to fully utilize the spatial and frequency resources without requiring additional complexity in transmitter placement or beam steering.RIS-based Covert Transmission

[0067] The second part or portion of each data segment of the original series of data bits is transmitted by modulating the phase distribution of the RIS 914 itself. For example, the RIS 914 comprises an array of numerous sub -wavelength elements (transmissive or reflective RIS elements), each capable of dynamically adjusting the phase of incoming 0AM beams By controlling the phase shifts across the RIS 914, the transmission system 910 can create spatial energy focal points, where the 0AM beams converge at specific locations. These focal points change dynamically over time, based on a predefined covert codebook. The codebook basically defines, or corresponds to, predetermined phase configurations (predefined set of phase distribution states) of the RIS 914, controlled by the RIS controller (or referred to as patterns mapper) 916, which are used to control how the 0AM beams are focused in space according to the covert codebook For example, the RIS 914 may comprise a 2D array of unit cells, each unit cell being dynamically controllable to be at a dynamically selected one of a plurality of wave propagation path states based on the encryption key for providing a corresponding degree of phase shift for the multi-mode 0AM waves incident thereon for dynamically controlling the RIS 914 to be at the dynamically selected one of the predefined set of phase distribution states based on the encryption key.

[0068] These changing focal points over time represent an additional, independent data stream, separate from the OAM-modulated data. This data stream is thus transmitted securely because only the legitimate receiver, which has prior knowledge of the covert codebook, can decode the information. The dynamic nature of the RIS 914 ensures that the focal points shift over time, making it difficult for any potential eavesdroppers to intercept the full transmission. This unique use of dynamic RIS phase manipulation in conjunction with 0AM beam multiplexing constitutes a breakthrough in secure communication systems, providing both high spectral efficiency and enhanced security in an efficient and effective manner.Covert Codebooks and Dynamic RIS Phase Control

[0069] A key aspect of the secure transmission method according to various first example embodiments of the present invention is the use of a covert codebook, implemented through the control of the RIS phase distribution. The RIS 914 is communicatively coupled to a RIS controller (patterns mapper) 916 (e g., based on FPGA orMCU technology) which dynamically adjusts the phase of each RIS element in the RIS 914 to form desired beam patterns. The 0AM beams, when they pass through the RIS 914, are first “de-helicalized”, meaning that the RIS914 processes the unique helical phase structures of the different 0AM modes of the multimode vortex waves, separating them spatially by focusing their energy at distinct locations.

[0070] The spatial focusing process is governed by secrecy masks, which are phase distributions calculated based on the relative geometric positions of the transmitter, receiver, and R1S 914. For example, the method or algorithm for calculating the secrecy masks can follow established techniques, such as that described in Algorithm I in International patent application no. PCT / SG2025 / 050086 (WO / 2025 / 174324) entitled “Multi-Target Spot Beamforming Using Reconfigurable Intelligent Surface”, the contents of which are hereby incorporated by reference in their entirety for all purposes, where the variables depend on the specific spatial configuration of the system. For example, PCT / SG2025 / 050086 describes a method and a system for controlling a RIS for multi-target spot beamforming at a plurality of target beam focus positions, which may be applied herein for controlling / adjusting the phase shifts across the RIS 914 (the phase of each RIS element in the RIS 914) to form desired beam patterns, that is, for directing and focusing the 0AM beams at specific locations, thereby creating spatial energy focal points. As the secrecy masks are altered, the spatial energy focal points of the 0AM beams change accordingly. This dynamic shifting of focal points makes the system highly secure, as an eavesdropper would need to know the exact phase distribution of the RIS 914 at any given moment to intercept the transmission.

[0071] In various first example embodiments, the covert codebook may be pre-defined between the transmitter side and the receiver side before the communication begins. This means that both the transmitting and receiving sides are aware of the codebook (or a sequence of codebooks) that will be used during the communication, ensuring that the information remains secure throughout the transmission. Because the covert codebook is known only to the legitimate communicating parties, the transmitter system 910 (or the corresponding method of wireless data transmission) advantageously introduces an additional layer of security that is independent of the 0AM multiplexing.

[0072] The ability of the RIS 914 to dynamically change its phase distribution in real time adds a level of flexibility to the system. Unlike traditional fixed meta-surfaces, which have static phase profiles, the RIS 914 in this invention can adapt to different transmission conditions, such as changes in the spatial configuration of the users or variations in the communication environment This adaptability ensures that the system remains robust even in dynamic or adversarial environments, where security is a top or key concern. Through the predefined covertcodebook, the dynamic control of the RIS phase distribution can further enhance the security of the wireless data communication system 900.

[0073] FIG. 11 depicts various possible types or designs of the multi-mode vortex wave generator 918, such as multiple ring antennas 918-1 or array antennas 918-2 that generate distinct 0AM modes (mode 1, mode 2, and so on), as illustrative examples only and without limitations. As described hereinbefore, it will be understood by a person skilled in the art that the present invention is not limited to any specific type or configuration of multi-mode vortex wave generator 918 as long as the multi-mode vortex wave generator is capable of, or operable to, generating and transmitting multi-mode vortex waves based on data streams.Receiver Structure and Time-Domain Frame Structure

[0074] FIG. 12 depicts an example schematic block of the receiver system 950 according to various first example embodiments of the present invention. The receiver system 950 is configured to demodulate the transmitted data and decode the secure information from the dynamic focal points created by the RIS 914. As shown in FIG. 12, a 3D energy detector array is positioned at a 3D space receiving area where the RIS 914 focuses the energy of the different 0AM modes. Therefore, multiple antennas placed at different spatial locations to capture the 0AM modes after they have passed through the RIS 914. These antennas are spatially separated to ensure that each one receives only the energy from a specific 0AM mode, minimizing the interference between the multiplexed data streams. The receiver system 950 demodulates the first data stream from the received signals while simultaneously extracting the encryption key (secret / covert bits / key) (based on a codebook known by both the transmitter and receiver sides) based on the energy distribution pattern created by the RIS 914. Accordingly, the receiver system 950 dynamically determines the encryption key that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multi-mode 0AM waves is received over time.

[0075] For example, each antenna may be connected to the receiver processing system 950 via an RF transmission line, and the received signals are processed to extract the information encoded in the 0AM beams. Because each 0AM mode is focused onto a different spatial location, the receiver can demodulate the data from each mode independently, with little to no cross-mode interference. This separation of 0AM modes at the receiver side is one of the key advantages of using 0AM multiplexing in combination with RIS.

[0076] As shown in FIG. 12, the receiver system 950 comprises a de-multiplexing block 1204 and a de-coding block 1208. The de-multiplexing block 1204 is configured to separate or de-multiplex the composite received signal (the plurality of signals of multi-mode 0AM waves received) into the parallel data streams that were multiplexed at the transmitter side. For example, using known multiplexing 0AM patterns together with the estimated channel state, the de-multiplexing block 1204 may perform stream separation and interference suppression (such as linear combining or equalization), and output a set of de-multiplexed baseband symbol sequences, each corresponding to one logical secure sub-channel and ready for symbol demapping and decoding. Accordingly, the de-multiplexing block 1204 may be configured to, for each data segment of the series of data segments, determine a plurality of data streams based on the plurality of signals of the multi-mode 0AM waves received at the plurality of receiver positions that dynamically change over time. The de-coding block 1208 is configured to determine or recover, for each data segment of the series of data segments, the original data bits from the de-multiplexed symbols. For each data stream, the de-coding block 1208 may perform symbol demapping (e.g., QAM / PSK demodulation), de-interleaving, and forward -errorcorrection (FEC) decoding. Accordingly, the de-coding block 1208 may be configured to, for each data segment of the series of data segments, determine a first portion (a series of data bits) of the data segment based on the plurality of data streams.

[0077] In addition to demodulating the data from the 0AM modes, the receiver processing system 950 also decodes the secure data stream transmitted via the dynamic shifting / changing of the RIS focal points. Based on the spatial locations of the energy focal points, the receiver processing system 950 identifies the current state of the secrecy masks and retrieves the corresponding data bits (encryption or secret key) from the secure transmission. Since the covert codebook is known only to the communicating parties, an eavesdropper would not be able to decode the secure data, even if they intercepted the signals.

[0078] As shown in FIG. 12, the receiver system 950 further comprises a location detection block 1212, an index de-mapping block 1216, a secrecy mask removing block 1220 and a secrecy mask codebook checking block 1224. The location detection block 1212 is configured to identify which detectors / receivers have been actively used (i.e., received the plurality of signals of the multi-mode 0AM waves) in each symbol period. These receiver locations are energy focal locations of different 0AM modes, depending on the specific index-modulation design. For example, by comparing the received energy / likelihood on all candidate receiver positions and applying a suitable detector (e g., thresholding orML / MAP decision), the locationdetection block 1212 outputs the set of active receiver locations for every symbol. These detected receiver locations thus form the raw observation of the index pattern that carries the secrecy mask (i.e., the encryption key or secure bits). Accordingly, the location detection block 1212 may dynamically determine a signal location pattern (e.g., representing or indicating which receiver positions (or which receivers (or signal detectors)) received the plurality of signals of multi-mode OAM waves) that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multi-mode OAM waves is received over time. The index demapping block 1216 is configured to convert the detected active locations into their corresponding binary index bits (i.e., the encryption key or secure bits). Using the publicly known index mapping rule (e.g., a look-up table that assigns each activation pattern to a bit vector), the index de-mapping block 1216 transforms each location pattern into a sequence of index bits. The output therefore contains both the payload-related index bits introduced by the secrecy mask at the transmitter side. Accordingly, the index de-mapping block 1216 may dynamically determine the encryption key (corresponding to the second portion of each data segment) that dynamically changes over time based on the signal location pattern and a covert codebook predefined between the transmitter side and receiver side, or shared by the transmitter side. The secrecy mask removing block 1220 may cancel an intentional scrambling that may have been applied to the index bits for security. For example, based on the secret key or shared randomness between the legitimate transmitter and receiver, the secrecy mask removing block 1220 reconstructs the mask sequence and applies the inverse operation (e g., XOR with the same mask, inverse permutation, or subtraction in a finite field) to the received index bits. After this operation, the original index-modulated information bits are recovered, while an eavesdropper without the correct mask cannot obtain a meaningful bit sequence. The secrecy mask codebook checking block 1224 verifies whether the recovered secrecy mask (encryption key) is consistent with the pre-shared covert codebook. For example, it compares the decoded mask index (encryption key) with valid entries in the codebook and generates a pass / fail decision or a reliability metric. Only if a valid / matching codeword is found, the corresponding mask index (encryption key) is accepted and forwarded; otherwise the frame is regarded as invalid or suspicious. This step provides an additional layer of authentication and spoofing / jamming detection at the physical layer.

[0079] The receiver system 950 further comprises a binary symbol integration block 1228 configured to assemble all recovered binary information into the original data stream. Forexample, the binary symbol integration block 1228 may be configured to concatenate the first and second portions of each data segment as well as concatenating adjacent data segments. The final output is a continuous, correctly ordered binary sequence that may, for example, be delivered to higher-layer decryption and data processing.

[0080] FIG. 13 illustrates the time-domain frame structure of the data transmission, where OAM mode 1 and mode 2 are transmitted over time, according to various first example embodiments of the present invention. In each time slot, the transmitter system 910 transmits multiplexed data using different OAM modes while simultaneously transmitting secure data by dynamically changing the RIS phase patterns. The receiver processing system 950 decodes both the data bits from the OAM beams and the covert information from the index de-mapper 1216. This dual-layer transmission structure not only ensures high spectral efficiency but also maintains robust security. The ability to transmit multiple data streams using OAM multiplexing, combined with the secure transmission of the covert codebooks, represents a significant advancement in wireless communication technology.

[0081] For illustration purposes, FIG. 14 visualizes example energy distribution patterns generated by the RIS 914 for different OAM modes and secrecy masks. The focused energy beams align with specific energy detector locations (ED1, ED2, ED3, ED4...), enabling the receiver system 950 to distinguish between different modes and extract both streams of information It will be appreciated by a person skilled in the art that FIG. 14 merely shows an illustrative example of energy distribution patterns generated and that other energy distribution patterns may be obtained by varying the secrecy masks of the RIS 914 and the energy detector locations.

[0082] Accordingly, the combination of OAM multiplexing, dynamic RIS phase control, and the use of covert codebook according to various first example embodiments of the present invention provides a powerful solution for secure, high-capacity communication. In this regard, the wireless data transmission method, the dynamic control of the RIS 914 and the wireless data reception method according to various first example embodiments of the present invention advantageously make the wireless data communication method (or the corresponding wireless data communication system 900) both secure and spectrally efficient.

[0083] In various second example embodiments of the present invention, a method of wireless data communication based on multi-mode vortex waves will be described with respect to enhanced information security via wave-field selectivity and structured wavefront manipulation.

[0084] In various second example embodiments, a secure wireless transmission method, as well as a corresponding transmitter system, is provided that enables the co-existence of spatial field modulation (SFM) and digital bandpass modulation (DBM), utilizing multi-mode vortex waves and a programmable metasurface (PMS). Distinct from conventional joint modulation schemes, the method or approach according to various second example embodiments establishes two logically independent transmission channels — SFM and DBM — thereby eliminating the need for joint signal design or time synchronization. Specifically, the orthogonality of vortex wave modes is exploited to construct a high-capacity multi-mode DBM channel, in which each mode carries modulated symbols independently As the composite waveform passes through the PMS, energy from different vortex modes is spatially focused onto distinct positions, dynamically determined by the PMS configuration. This spatial mapping forms a unique lookup table that encodes additional information in the electromagnetic (EM) field distribution, effectively enabling a second, concurrent SFM channel. To enhance physical-layer security, the DBM channel transmits encrypted symbols transformed via dynamic symbol-domain mapping, while the corresponding mapping relations — or key information — are carried by the SFM channel. This lightweight dual-channel encryption strategy provides strong confidentiality without requiring complex joint decoding. To validate the feasibility of the wireless transmission method, an example proof-of-concept prototype system was designed and implemented, and experimental demonstrations were conducted under real-world wireless communication conditions. The experimental results confirm the effectiveness of the co-existent DBM-SFM design in achieving reliable and secure transmission. The wireless data communication method, as well as the corresponding transmitter system or architecture, offers a scalable, low-complexity, and secure transmission solution for future IoT networks, especially in scenarios demanding both spectral efficiency and physical-layer confidentiality.

[0085] In particular, according to various second example embodiments of the present invention, a unique wavefield selectivity secure wireless transmission framework is provided that synergistically combines structured waves and PMS-based dynamic spatial modulation. Unlike joint index modulation systems requiring complex joint decoding and synchronization, the wireless data transmission method allows the coexistence of two logically independent yet physically integrated channels: a digital band-pass modulation (DBM) channel utilizing multimode vortex waves to enhance transmission efficiency, and a spatial field modulation (SFM) channel leveraging PMS for secure key distribution through dynamic spatial mappings.Vortex waves carrying OAM have garnered attention for their intrinsic orthogonality between different modes, allowing multi-mode transmissions within the same frequency band and significantly enhancing spectral efficiency. Unlike prior applications that vortex waves are just a subset of multi-input multi-output (MIMO) systems, their primary advantage lies in improving information transmission rate via mode multiplexing with notably simpler implementation complexity. Hence, according to various second example embodiments, vortex waves specifically serve as excitation sources feeding the PMS, effectively improving the information transmission efficiency of co-frequency channels, even under low-rank line-of-sight (LoS) propagation conditions, i.e., between the data source and the PMS.

[0086] Moreover, a key unique aspect of the approach according to various second example embodiments of the present invention lies in adopting a co-existence dual-channel architecture that fundamentally differs from traditional joint modulation methods: vortex waves facilitate high-efficiency data transmission through orthogonal mode multiplexing, while PMS, with its powerful programmable space-time modulation capabilities, constructs a secure channel for encryption key distribution. Unlike joint modulation systems, the co-existence model establishes two distinct and independent channels, removing the necessity for joint channel design and time synchronization. Specifically, benefiting from the intrinsic orthogonality among different vortex wave modes, multi-mode vortex waves are employed to independently transmit DBM data, thereby constituting the highly efficient multiplexing DBM channels. After passing through the PMS, energy from these distinct vortex modes is dynamically concentrated at separate spatial positions determined by the PMS. This unique spatial focusing forms a dynamically controlled spatial mapping lookup table, thereby establishing the secure SFM channel. This clear separation of roles significantly enhances system security, as unauthorized access requires simultaneous interception and decoding across both vortex modes and spatial domains.

[0087] To demonstrate the wave-field selectivity of the secure dual-channel transmission method according to various second example embodiments of the present invention, a proof-of-concept prototype was designed and implemented and experimental demonstrations were performed under realistic wireless communication environments. The experimental results substantiate the system’s validity, evidencing reliable information transmission and substantial resilience against potential eavesdropping attacks

[0088] In summary, key contributions of the wireless data communication according to various second example embodiments of the present invention are as follows.

[0089] Firstly, a unique co-existence dual-channel wireless transmission architecture is provided, significantly differing from traditional joint index modulation systems by eliminating the need for joint channel design and synchronization, which greatly reduces the system complexity.

[0090] Next, the multi-mode orthogonality of vortex waves is effectively utilized to independently construct the DBM channels, significantly enhancing spectral efficiency and information transmission efficiency, even under low-rank LoS channels.

[0091] Furthermore, a PMS-based high selectivity wavefield modulation technique is developed which dynamically mapping vortex mode energies onto spatially distinct positions. Importantly, a direct spatial matched filter is introduced to detect and demodulate the PMS-transmitted encryption key, eliminating the need for traditional coherent detection. This significantly reduces receiver demodulation complexity while maintaining robust and secure key transmission.

[0092] Moreover, to demonstrate in practice, a proof-of-concept prototype is designed and experimentally validated, demonstrating the practical feasibility, robustness, and security enhancement provided by the dual-channel transmission approach according to various second example embodiments of the present invention under realistic wireless communication scenarios.System Architecture

[0093] FIG. 15 illustrates a schematic drawing of a wireless data communication system 1500 for wireless data communication based on multi-mode vortex waves, as well as a corresponding method of wireless data communication, according to various second example embodiments of the present invention, with a dual-channel transmission architecture. In particular, FIG. 15 shows a system architecture for the PMS-assisted dual-channel (DBM and SFM) secure wireless transmission.

[0094] As shown in FIG. 15, a physical -layer secure wireless communication system 1500 is provided employing a dual-channel transmission framework. One is the DBM channel based on multi-mode vortex waves multiplexing, while the other is the SFM channel based on PMS-driven wave-field selective mapping for encryption key (spreading code) distribution. The transmitter system 1510 comprises a data encoder, a multi-mode vortex wave generator 1518, and a dynamically controlled PMS 1514. The receiver system 1550 comprises distributed spatial detectors (e g, ED 1, ED 2, ED 3 and ED 4), analog-to-digital converters (ADCs), DBMdemodulators, wave-field mapping codeword detectors, and despreading modules. The high-capacity communications and physical -lay er security arise from the joint exploitation of multimode vortex orthogonality and the multi-dimensional spatial control provided by PMS 1514.Data Encryption and Multiplexing for DBM Channel

[0095] Let b = [b1, b2,...,bK]Trepresent the sequence of user data bits. For secure transmission, each bit bnis spread using a dedicated, mode-dependent key (spreading code) cn=[cn,i>cn,2> — >CU, L]T, with L the spreading factor. Each bit is processed independently — no need for large joint codebooks as in joint index modulation. The encoded signal sequence for the 77-th channel is,sn ~ n "cn—[bncn,l’ ■■■> bnCn^](Equation 1) where bnis the original user data bit, cnis the spreading orthogonal bias group for the 7?-th vortex channel. Accordingly, in various second example embodiments, the original series of data bits comprises a series of data segments. For each data segment of the series of data segments, the plurality of data streams is generated based on a plurality of portions, respectively, of the data segment and the encryption key (spreading code). For example, each portion of the data segment may be one data bit or a series of data bits. For illustration purposes, in this example, each portion of the data segment is one data bit. In addition, for each data segment of the series of data segments, each data stream of the plurality of data streams is generated by spreading each data bit of the corresponding portion of the plurality of portions of the data segment based on the encryption key. For example, in the case of the corresponding portion of the data segment being one data bit, the one data bit may be spread to generate the corresponding data stream. In the case of the corresponding portion of the data segment being a series of data bits, each data bit of the series of data bits may be spread to generate the corresponding data stream. In various second example embodiments, each portion of the data segment corresponds to a corresponding vortex mode n. In various second example embodiments, each data bit of each portion is spread by a corresponding portion of the encryption key. That is, each data stream may be generated based on a corresponding portion of the data segment and a corresponding portion of the encryption key. In this regard, each portion of the encryption key corresponds to a corresponding vortex mode n. The security level of the system is closely associated with the sequence length of cn, which directly affects the complexity of potential eavesdropping and decryption attempts. In various second exampleembodiments, to reinforce transmission security, cnis periodically refreshed, and thus, dynamically changes In this regard, cnmay be independently generated across different vortex channels. The secret key information represented by cnis delivered through the SFM channel.

[0096] Then, each spread chip sn lis mapped to vortex mode £n(different bits or the corresponding different spread chips can be mapped to the same vortex mode) and corresponding waveform pnt). The multiplexed baseband transmit spread signals for all N vortex channels are combined as,N L- Tnii)n=l 1=1(Equation 2) where, i / i£n(t) ’sthe pre-PMS vortex waveform for mode £n,andZis the delay for the / -th chip in the / -th vortex channel. Each vortex channel is orthogonal in the spatial domain, so the interception of one vortex mode reveals nothing about others. To reduce the computational complexity, different from traditional index modulations, there is no multidimensional joint codebook design for the baseband signal.

[0097] In high-frequency near-field communications, non-LoS (NLoS) scattering paths are generally sparse and weak, with the LoS link being dominant. Hence, without loss of generality, the LoS channel model is adopted to characterize the propagation path from the signal source to the PMS. Under the influence of additive white Gaussian noise, the multi-mode multiplexed vortex signal arriving at each unit of the PMS can be expressed as,N Lyu,vW) = I ~Tn,l)+ wPMs(0n=l 1=1(Equation 3) where / i£ji(t) is the free-space channel for mode £n, wPMS(t) is the white noise. Suppose that there are reconfigurable units on the PMS 1514, due to the wavefront reconstruction capability, vortex waves carrying different 0AM modes are directed toward separate spatial positions, effectively forming three-dimensional (3D) focal spots and enabling spatial separation for multiplexing, i.e.,u vyn(t) = z s hu.v(t) ®(l£v)yu,v(t) +WPMs(0u=l v=l(Equation 4)where hnu,v(t) is the channel response from the u, v-th reconfigurable unit to the n-th 3D spatial focal spot. <t>(u, v) is the wavefront manipulation factor on of the u, v-th unit, and its calculation method will be described in detail later below.

[0098] Upon impinging on the PMS 1514, the vortex-multiplexed wavefront is spatially demultiplexed and transformed. For each ( / / , / ), the energy of each vortex mode £nis redirected and focused at spatial position pn (determined by the codebook. It is worth noting that each vortex waveform is transformed into a spatially separated spot beam after the PMS 1514, hence, the intended user data can only be detected at the correct location, which enhances the antieavesdropping capability. An eavesdropper must physically access the correct focal spot and time slot. Moreover, there is no need for multidimensional codebook remapping for different vortex modes - the demultiplexing is achieved by PMS physics.

[0099] Since each DBM symbol duration is significantly shorter than that of each SFM symbol, the DBM transmission can be reasonably modelled as undergoing conventional fastfading channels. This allows for the application of various well-established channel coding techniques. Moreover, each DBM data stream sn (can be received and demodulated using a single coherent detector, yielding an encrypted extended codeword sequence. The subsequent decryption and recovery of the original data rely on the secret key information conveyed through the SFM channel. This separation of encrypted payload and key transmission not only enhances security but also enables a low-complexity receiver design.

[0100] Accordingly, multi-mode vortex waves are generated based on a plurality of data streams derived from an original series of data bits, each vortex wave of the multi-mode vortex waves generated based on a corresponding data stream of the plurality of data streams. The multi-mode vortex waves is transmitted to the PMS 1514; and the PMS 1514 is dynamically controlled to be at a dynamically selected one of a predefined set of phase distribution states based on an encryption key that dynamically changes over time, each phase distribution state being configured to direct and focus, for each vortex wave of the multi-mode vortex waves incident on a surface of the PMS 1514, the vortex wave to a predetermined one of a set of predefined receiver positions corresponding to the dynamically selected phase distribution state.SFM Channel: Independent Encryption Key Transmission via Wave-Field Selectivity

[0101] The key (spreading code) information is transmitted through the PMS-based SFM channel. For each mode £n, and each chip / , the PMS 1514 spatially encodes cn (by directingthe energy to spatial position pn t. At the receiver, for each vortex mode £n, there are Q spatially distributed power detectors (e.g., and q2,...) positioned to correspond to all possible focus positions of the PMS 1514 Define the spatial mapping function as,„, i=+1^SFMCAUO=)„ ' _ 1<4 / 2 ■cn,l - (Equation 5)

[0102] Thus, the signal spatially encoded by PMS 1514 for the encryption key transmission is,N L■^SFMCOn=l 1=1(Equation 6) where <5Pn i(t) is an impulse indicating which spatial position is energized for bit cn l.

[0103] At the receiver side, for SFM symbol (encryption key) detection, each possible focal spot q G q, q2is equipped with a power detector. The received SFM symbol at the detector q can be written as,rSFMW = ^SFMW *XSFM(0 +WSFM(£)(Equation 7)where is the spatial mapping coefficient from the PMS 1514 to the detector q. Tn this regard, power detectors are usually modelled as an integrator, and such integral operation may be expressed as,|rs™(£)|dtTn,l(Equation 8) where Tntis the detection interval and A denotes the window width. The SFM bit sequence cni is detected asynchronously and independently from DBM timing. This is basically a codebook lookup: given the observed spatial pattern, find the pattern (and hence code) that was sent by the PMS 1514. Since the legitimate receiver knows the one-to-one mapping between PMS focusing patterns and code bits (or chips), it can immediately map p to the corresponding code bits cn i= fc~1(P^'). For a simple example, deciding the code bit from the measured power can be assumed as,4-1 pd7i) pf'tz)Cn'll -1 P^2) pQqi)rn,lrn,l(Equation 9)

[0104] If two focal points are used for each vortex mode (point for code bit “+1” and point q1for code bitand if energy is detected at focal spotthe receiver infers the spreading code bit was “+1” for that symbol. To clarify, an encryption key lookup table I (representing or corresponding to a codebook) shown in FIG. 16 yields the decoded spreading bits based on the focal spots pattern (signal location pattern) detected. It is worth noting that for each vortex mode, the receiver arranges these kinds of two power detectors at different focal spots.

[0105] Accordingly, a plurality of signals of multi-mode vortex waves focused at a plurality of receiver positions, respectively, of a set of predefined receiver positions is received from the PMS 1514 that dynamically changes (i.e., the plurality of receiver positions (or the specific receiver positions) at which the plurality of signals of multi-mode vortex waves is received) amongst the set of predefined receiver positions over time. Furthermore, an encryption key is dynamically determined that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multi-mode vortex waves is received over time. In this regard, dynamically determining the encryption key comprises: dynamically determining a signal location pattern (e g., representing or indicating which receiver positions (or which receivers (or signal detectors)) received the plurality of signals of multi-mode vortex waves) that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multimode vortex waves is received over time; and dynamically determining the encryption key that dynamically changes over time based on the signal location pattern and a covert codebook (e g., a codebook predefined between the transmitter side and receiver side, or shared by the transmitter side). In this regard, the encryption key is dynamically changeable amongst a predefined set of encryption codes, the signal location pattern is dynamically changeable amongst a predefined set of signal location patterns, and for each encryption code of the predefined set of encryption codes, a mapping between the encryption code and a corresponding signal location pattern of the predefined set of signal location patterns is defined based on the covert codebook, each signal location pattern corresponds to a phase distribution state of the PMS 1514.

[0106] Thereafter, having obtained the sampled data chips sn t(from DBM channel) and the corresponding key bits £n t(from SFM channel), the original data bncan be reconstructed by,1 Lbn ~ ’ $n,l ’ ^n.l1 = 1(Equation 10) Accordingly, the original series of data bits is determined based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions and the encryption key. In particular, for each data segment of the series of data segments of the original series of data bits, a plurality of data streams is determined based on the plurality of signals of the multimode vortex waves received at the plurality of receiver positions that dynamically change over time; and a plurality of portions of the data segment is determined based on the plurality of data streams, respectively, and the encryption key. Furthermore, for each data segment of the series of data segments and for each portion of the plurality of portions of the data segment, each data bit of the portion of the data segment is determined by despreading the corresponding data stream of the plurality of data streams based on the encryption key. In various second example embodiments, the corresponding data stream is despread by a corresponding portion of the encryption key.

[0107] Importantly, the DBM data channel and the SFM code channel can operate asynchronously - the data symbols snare modulated and transmitted continuously, while the code sequence cnis embedded in the changing spatial wave-field patterns. The two channels are processed independently: the data demodulator only needs to know which baseband modulation was used (provided by the DBM channel), and the secure code demodulator only observes the spatial energy distribution (independent of the specific data symbol value).

[0108] Since this index was chosen based on the secret code, the receiver basically reads the code from the spatial wavefield signature. This method is vastly simpler than jointly decoding data and index as in classical index modulation; the receiver perfoPMS a straightforward energy comparison across V outputs (which can be done with low-complexity power detectors). There is no need for maximum-likelihood multi-dimensional detection or iterative search — reducing complexity, especially for loT devices with limited processing power.Multi-Mode Vortex De-Multiplexing and Spot Beams Transform Aided By PMSThe PMS-based spatial modulation mechanism and secure key distribution method will now be described according to various second example embodiments of the present invention.

[0109] A key challenge in this transmission system lies in the dynamic, rapid reconstruction of the phase states across the entire meta-surface. In this regard, in a simple single-transmitter single-receiver scenario, it is straightforward to determine the phase shift that each element of a PMS must impart to redirect an incident vortex beam towards a given receiver. According to Huygens’ principle, each point on the meta-surface can be treated as a secondary radiation source. By carefully tuning the phase of each element, the outgoing waves from the PMS can constructively interfere at the desired receiver location, effectively focusing the beam there. This is possible because an abrupt phase discontinuity introduced by a metasurface allows one to shape wavefronts and steer energy in non-specular directions (anomalous reflection / refraction) beyond what conventional optics achieve.

[0110] Mathematically, for a transmitter located at uT£ji= (£n,y£n, z£n) emitting an vortex wave of mode £n, the required phase compensation at the (u, v)-th PMS element (position uu v= _xu v,yu v,zu v')') to focus the beam is,2TT. - f yup< Pu,v = — r -UT,£„ + tan1—A1\xu v(Equation 11) where is the wavelength. Suppose that the PMS is located at the x-y plane, and z-axis is the transmission direction. By aligning these element-wise phases, the outgoing wavefront can be bent or focused as required, and in a single-user case, this formula directly yields the desired phase profile.

[0111] However, when multiple vortex beams (with different mode indices £n) need to be served simultaneously (each destined for a different receiver), the phase design on the PMS becomes much more complex. A naive approach might attempt to superimpose the individual phase patterns for each beam on the same PMS, but this linear addition of phase patterns is insufficient - the requirements for different beams generally conflict and cannot all be met exactly by a single static phase profile. In other words, a single metasurface cannot perfectly satisfy the phase focal conditions for multiple distinct transmitter-receiver pairs at once if we only add their phases together This is a key challenge for multi-stream vortex-based loT or wireless systems, where different vortex modes from one transmitter must be directed todifferent spatial nodes. Simply summing phase gradients would lead to imperfect focusing and interference between beams.

[0112] To overcome this, a holography-inspired wavefront shaping method is employed according to various second example embodiments of the present invention. Rather than treating the multi-beam phase design as a simple superposition, the problem is approached in two stages (analogous to optical holography): recording and reconstruction. The strategy is to have the R1S capture a composite interference pattern generated by all transmitter and receiver waves (recording), and later use that pattern to quickly reconstruct the desired beams (reconstruction):

[0113] 1) Recording Phase: All vortex “reference waves ” (the 0AM beams of different modes Lngroup emanating from the transmitter) and the corresponding “object waves” (the focused beams toward each receiving node) are allowed to simultaneously illuminate the PMS, where they interfere with each other. Each metasurface element thus experiences an interference pattern resulting from the superposition of one reference wave and one object wave per transmitter-receiver pair. This interference pattern is essentially a hologram: a complex fringe pattern encoding the phase differences between the reference and object waves. The resulting pattern at the (u, v) element can be thought of as Tu v, a complex transmission coefficient that the PMS needs to “record”. In practice, the vector sum of all these interference contributions is stored in the PMS’s configurable elements (e.g. by setting a corresponding impedance or resonance state per element). During this recording stage, the phases and amplitudes of the meta-atoms are not yet being used to shape the beam; they are effectively just capturing the needed weights.

[0114] 2) Reconstruction Phase: Once the interference patterns Tuvare obtained and stored, the transmitter can re-illuminate the PMS with the same set of vortex reference beams (i.e. the same modes £ngroup as used during recording). The PMS now uses the recorded complex weights Tuvas multiplicative filters on the incoming reference waves. According to the holographic principle, this will reconstruct the obj ect waves corresponding to each reference wave. In other words, the PMS effectively performs the transformation it learned: each vortex mode Lnis “de-spiraled” and steered so that it focuses onto the intended receiver node. The previously stored interference pattern ensures that the outgoing waves from all PMS elements add up coherently at the target nodes. This holographic reconstruction enables the different vortex beams to be directed to different 3D locations simultaneously, achieving spatial division multiplexing via distinct focused spots.

[0115] Overall, this holographic approach allows the PMS to handle multi-pair transmission by recording a composite hologram for all transmitter - receiver pairs and then rapidly reconstructing the desired multi-beam wavefront when needed. It is not merely a linear superposition of phases, but a vector sum of complex patterns that captures the cross-terms between reference and object waves for each pair.

[0116] To formalize the above process, the positions of the vortex transmitters are denoted as and the positions of the power detector are denoted as uR q, and assuming each vortex mode £nis assigned to a unique detector q for simplicity. The complex field of an incident vortex wave (used as a “reference” in holography) at the (a, v) PMS element is modelled as h^Ref£n- hor LoS propagation, this can be expressed as,u vf’ReU W 'nVVRet, L X exp(;0u,v)47i|uu,p- uTAJ(Equation 12) where / ?Ref,£nis a complex amplitude factor accounting for the transmitter’s radiation pattern and power for mode Ln, |uu v— uT;£ji| is the distance from the / / -th transmitter to the (w, V) PMS element.

[0117] Then, assume that each detector will see a “spot beam” (object wave) from the PMS after reflection / transmission. If the -th detector at uR qis the target for the / / -th 0AM mode, the PMS should form a beam that converges at that special focus area. To ensure all contributions from the PMS add up in phase at the receiver, one must account for the different path lengths from each PMS element to the detector. LetAdq,u,v ~—1—(Equation 13) be the excess distance that the wave from element (u, v) travels compared to some reference distance (here we use zq, the distance from the PMS plane to the detector along the z-axis, as a baseline). The obj ect wave field contributed by the (w, v)-th element towards receiver q can then be written as, / ? Obj,q^Obj.q exp4TT|UU / 1;- URJ(Equation 14) where j?obj,<? isanamplitude factor related to how efficiently the PMS element radiates toward detector q. In this expression, it can be seen that each element introduces a phaseexpu vj such that if £dq u vis exactly compensated (i.e. this phase cancels the extrapropagation distance), the wave from element (u, v) will arrive in phase with waves from other elements at the detector. Thus,qrepresents a spherical wave (object wave) converging at the detector, originating from each PMS element.

[0118] During the recording stage, the reference waveand object wave(for the corresponding transmitter - receiver pair) interfere at the PMS element. The holographic interference pattern is essentially the complex ratio of the object field to the reference field at that element, which can be denoted as 7^v. Thisis the complex weight that the PMS needs to apply at element (M, V) to transform the incident vortex mode-£„ wave into a beam focused at detector q. From PFobj = T X WRef, the following is obtained,TU. V _ W ^Oub’vj,qwWVVRef, Ln(Equation 15)

[0119] Substituting the expressions above forqand yields an explicit form for the holographic transmission coefficient as,rpu.v / ? Obj,q |uu,v—| f.27T / i x, _1[yu,v\\ « - [7 - ~ jx exP U T (IUu,v - uT,£n| - MqiUiV) -]£ntan M — / 'Rcf,£„|ui;,i;— uR,q | \71\xu,v / / (Equation 16)

[0120] One practical issue with higher-order 0AM beams is their tendency to diverge rapidly in free space, which can severely limit the achievable distance for reliable communication. To counteract this energy divergence characteristic of vortex beams, the design can incorporate an additional Bessel beam phase mask on the PMS. Bessel beams have a more collimated profile and can maintain a tight core over a longer distance compared to ordinary vortex (Laguerre - Gaussian) beams. The Bessel phase mask essentially adds a conical phase distribution (like that of an axicon lens) to each PMS element, which converts a diverging helical beam into a Bessel-like beam with lower divergence. The phase mask is given by,2TT^Bessel = — (|u„,r| sina)(Equation 17) where |uuv| —+ y^vis the radial distance of the PMS element from the center of the surface, and is a a fixed angle related to the desired cone angle of the Bessel beam. In terms of wave-vector components, tan a = kp / kz, where kpand kzare the transverse and longitudinalcomponents of the wave vector for the resulting beam. By adding <pB'esselto the phase profile of each element, the RIS generates a high-order Bessel vortex beam that preserves the 0AM content but does not spread out as quickly. This helps maintain beam intensity over longer ranges and alleviates the short-distance limitation of 0AM beams.

[0121] In the multi-vortex multi -receiver scenario, the final phase to be programmed on each PMS element must simultaneously accommodate all the vortex modes (and their target detectors). The holographic multiplexing approach achieves this by vectorially superimposing the individual holographic patterns for each mode Specifically, suppose there are 0AM modes ranging from £inito(inclusive) that need to be served. For each mode £n, a complex pattern is derived as above. The Bessel phase factor exp(j<pBevssel) is also to be applied. The phase characteristics of any PMS unit can be obtained by talcing the phase of the vector-weighted summation of different holographic patterns, which can be expressed as,(Equation 18) where arg[-] denotes extracting the phase angle of the complex number in brackets. That is, all the complex field contributions at element (m, n) are added together, and the angle of this resultant complex sum is used as the phase shift for that element. The amplitude of the sum could in principle be used to adjust the amplitude response of the element if the RIS supports amplitude tuning, but typically PMS elements mainly tune phases, the amplitude variations may be less crucial or fixed.Numerical Calculation and Simulation ResultsReliability of Data Stream Transmission

[0122] The physical -lay er secure wireless communication system 1500 features a dualchannel transmission framework that integrates two distinct and complementary mechanisms for both high-throughput data delivery and robust physical-layer security. At the transmitter side, the system 1500 comprises the data encoder, the multi-mode vortex Wave generator 1518, and the programmable PMS 1514. User data bits are individually spread using a dedicated, mode-dependent key (spreading code) for each vortex channel. Multiple vortex modes (N channels) can be generated and multiplexed in parallel, taking advantage of the spatialorthogonality among vortex channels, which greatly increases the secure transmission capacity. A dynamically controlled PMS 1514 applies flexible wavefront manipulation, enabling three-dimensional spatial mapping for different vortex channels. This process both spatially separates the different vortex channels and, crucially, delivers the current encryption keys (spreading codes) via precisely directed EM energy.

[0123] Subsequently, the entire transmission process was numerically simulated, and the bit error rates (BER) under different channel conditions were evaluated using Monte Carlo methods, as illustrated in FIG. 17. In particular, FIG. 17 illustrates the BER performance of the secure dual-channel transmission under various channel conditions (for Bob and Eve). The multiplexed vortex waveforms are radiated through the PMS 1514 and propagate toward the receiving area. Each vortex mode with normal PSK-modulated symbols is directed to a distinct spatial location, with the channel modelled as LoS plus additive noise. Simultaneously, the PMS 1514 focuses energy onto specific spatial positions according to the current key bits cn l(spreading codes), embedding the key information directly in the spatial wave-field. Each key bit is mapped to a specific focal spot. This implies that the receiver must be equipped with a 3D multi-antenna architecture, which inherently mitigates the risk of eavesdropping.

[0124] The receiver array comprises two main processing chains: 1) At the correct spatial location for each vortex channel, a single coherent detector receives the corresponding data chip. The detector demodulates the data stream according to the normal PSK principle, recovering an encrypted codeword sequence per channel; 2) For each vortex mode, spatially distributed detectors (e.g., at locations q\, qi) monitor the potential focus points. The encryption key bit cn iis inferred via a simple threshold or lookup rule This 3D spatial beam focusing mechanism not only enhances security but also effectively reduces inter-channel interference.

[0125] As illustrated by the circles line in FIG. 17, only receivers at the correct locations (in space and time) can access both the data and the key. An eavesdropper (Eve) must be physically present at the targeted spatial position and at the correct timing window to intercept both channels. Hence, this encryption scheme provides strong physical-layer security. In the absence of beam separation and convergence provided by the PMS 1514, even if Eve circumvents the system to access the encrypted data from the opposite side of the PMS 1514 and attempts to infer the secret information through extensive learning and estimation, the inability to separate the multiplexed vortex channels results in severe inter-channel interference. This, in turn, significantly degrades the quality of the demodulated signal and leads to a sharpdeterioration in bit error performance (flat BER). This assumption has been simulated by the squares curve in FIG. 17.

[0126] Moreover, as for the DBM channel (blue-triangles curve), the BER decreases rapidly as E / No increases. This is typical of a well-designed, noise-limited communication link. Under sufficient signal-to-noise ratio (SNR) conditions, the DBM channel can flexibly accommodate high-order modulation schemes, thereby enabling the transmission of data streams with enhanced spectral efficiency. The SFM channel (green-diamonds curve) also benefits from increasing SNR, with BER dropping quickly. At high SNR, SFM channel BER is comparable or even better than the DBM channel. This validates that the spatial mapping (via PMS and distributed detectors) is robust and does not degrade the overall system reliability for the legitimate receiver.Effectiveness of EM Field Manipulation

[0127] Since key bits are spatially mapped and detected only at intended positions, Eve -who cannot access all spatial foci - cannot reconstruct the keys. This implies that the spatial selectivity enabled by the PMS’s EM field manipulation plays a critical role in system performance. Generally speaking, any focal spot can be arranged at different distances or directions, as needed by the communication scenarios, as shown in FIG. 14. The nearly orthogonal nature of 0AM modes, combined with the spatial separation introduced by the PMS 1514, implies that receivers placed at these focal spots can pick up their intended signals with little interference from the other mode’s signal. This ability to split and direct multiplexed beams is fundamental to the multi-channel secure communication scheme according to various second example embodiments of the present invention. These results in FIG. 14 demonstrate the principle of low-interference spatial separation: by mapping each vortex mode to a different focal point in space, the energy of each data stream is localized at its designated receiver position.

[0128] To substantiate the simulation predictions, a unique transmissive programmable metasurface unit is devised according to various second example embodiments of the present invention that embodies the concept of a programmable wavefield splitter. Departing from traditional designs that rely on equivalent circuit approximations, the approach according to various second example embodiments of the present invention enables the unit to directly capture incident electromagnetic waves and transform them into well-controlled traveling waves. Operating at 10 GHz, each element supports four discrete phase states, thereby realizing2-bit quantized wavefront control. By dynamically switching the states of the integrated PIN diodes, the transmission phase can be precisely reconfigured while maintaining nearly constant amplitude, ensuring both efficiency and fidelity. Full-wave calculations, presented in FIG. 18, reveal the outstanding performance of this reconfigurable design. In particular, FIG. 18 shows the S-parameters versus frequency with dual y-axes: phase (left, deg) and insertion loss (right, dB). As shown from the righty-axis, the insertion loss remains consistently below 1 dB for all states - superior to most reported transmissive implementations - while the left y-axis demonstrates near-perfect 90° phase separation across the four states. Together, these results confirm that the metasurface unit achieves accurate 2-bit phase reconstruction of the incident wavefront, paving the way toward scalable, programmable, and energy-efficient meta-surface architectures.

[0129] Furthermore, full-wave EM calculations were also conducted under the CST Studio environment. The setup (depicted in FIG. 19A) is divided into two stages to manage complexity:

[0130] 1) 0AM Source Module: First, the multi-mode 0AM transmitter in free space is calculated to capture its radiated field patterns. The near-field radiation from the dual-ring antenna (for each mode) is computed and saved as an equivalent source file. This step allowed us to represent the complicated field of the vortex waves without repeatedly meshing the antenna geometry.

[0131] 2) Near-field finite element EM calculation: Next, a model of the PMS panel was placed in the CST environment. The pre-computed 0AM source module is imported as the excitation source illuminating the PMS (positioned similarly to the real experiment). The PMS is modelled with its array of unit cells, where each unit’s tunable phase response could be toggled between discrete states (the on / off states of the PIN diode are represented by equivalent circuit models). By adjusting the phase-quantized states of each PMS unit in the CST, the dynamic phase pattern updates are emulated on the whole PMS panel.

[0132] Using this approach, a series of full-wave simulations was performed to see how two simultaneous vortex waves (modes I = +1 and I = +2) can be manipulated by the metasurface. The goal was to convert the incoming vortex waves into two concentrated beams focusing at the desired focal spots in 3D space. Following the aforementioned beam-focusing strategy, the tailored phase distributions were imposed across the PMS panel to achieve the desired spatial focusing effect.

[0133] FIG. 19B shows a configuration where the PMS focuses both vortex waves along the central normal direction (the transmission direction) (one focal point farther from the PMS, one closer, forming an axial distribution). FIG. 19C shows another configuration where the two focal spots are off to the sides of the PMS normal (beside the propagation axis) (forming a lateral side-by-side distribution). The EM field intensity plots clearly illustrate that the PMS can simultaneously concentrate two different vortex modes onto two separate focal spots. Each vortex wave, carrying independent information, is steered to a distinct location with minimal overlap. This confirms the PMS is capable of precise 3D beamforming control even for multiple incident vortex modes. FIG. 19D shows another configuration where the two 0AM modes are converted to focal spots randomly.Implementation and ExperimentsThe experimental prototype setup and validation process will now be described, and an extensive analysis of experimental results and system performance metrics are provided.PMS Fabrication from a Hardware Perspective

[0134] It is well known that the larger the electrical aperture of a meta-surface, the stronger its capability for wavefront manipulation. However, manufacturing a very large PMS as one piece is impractical due to panel size limits and PCB soldering constraints. To overcome this, a modular assembly approach is used according to various second example embodiments of the present invention: the full PMS is composed of smaller sub-panel “tiles” that can be easily fabricated and then assembled like building blocks. Each sub-block contains a 10 X 10 array of unit cells with an element spacing of about two-thirds of a wavelength between adjacent units. By tiling these sub-blocks and connecting them to a central controller, arbitrarily large PMS arrays in various shapes can be constructed. The concept is analogous to tiling a wall with individual tiles - multiple small PMS boards are joined to form one large aperture, as shown in FIG. 20. In particular, FIG. 20 shows an example fabrication of the PMS, including one subblock (top-left), unit structure (top-right), front side of the whole PMS (bottom-left) and back side with LEDs (bottom-right). Each sub-block has its own cable connection to the control system, allowing independent control. This way, large-scale PMS arrays can be built by mixing and matching modules, achieving high beamforming gain without the need for a single huge PCB.

[0135] To drive the PMS modules, we developed an integrated control system capable of managing two PMS boards (a total of 200 units) simultaneously with a single microcontroller. Using this scheme, the control board can support two RIS panels of 100 units each (total 200 units) with plenty of outputs to spare. In our prototype, we integrated four 10x10 RIS boards; two boards (2x 100 units = 200 units) are handled by one control system (one MCU + one latch board), and the other two boards by a second, identical control system. This modular control architecture is scalable to even larger configurations simply by adding more latch rows or parallel lines as needed. Example fabrication detail and programming logic can found in Zhao, et al., “2-Bit RIS prototyping enhancing rapid-response spacetime wavefront manipulation for wireless communication: Experimental studies,” IEEE Open J. the Commun. Soc., vol 5, pp.4885-4901, August 2024, the contents of which are hereby incorporated by reference in their entirety for all purposesMulti-Mode Vortex Waves Transmitter

[0136] Moreover, to validate the PMS in a complete wireless link, an innovative multimode vortex waves transmitter was designed. Traditional methods for generating vortex waves often use a uniform circular array (UCA) of antennas, where each antenna element needs a dedicated RF feed and phase shifter to impose the required phase twisting. This can become hardware-intensive and power-hungry, especially if each element is driven by its own RF chain. Instead, according to various second example embodiments, a more compact approach: a nested multi-layer UCAs structure that produces multiple vortex waves with a single feed per mode. As shown in FIG. 21A, the multi-mode vortex wave generator or transmitter comprises two concentric circular patch antenna arrays (an inner ring and an outer ring) fabricated on a double-sided Rogers 5880 PCB. Each ring has 8 patch radiators uniformly spaced in a circle For each vortex mode (corresponding to one ring), a carefully designed microstrip delay-line network distributes power from one input port to all 8 patches while providing progressive phase delays. Basically, the feed network acts as a passive power splitter with unequal path lengths: the varying lengths of the microstrip lines introduce the phase gradient around the ring needed to create the helical wavefront of a radiation beam. By tuning the line lengths and impedance match, each ring’ s network ensures that the patches radiate in-phase progression, generating a vortex wave carrying a specific topological charge.

[0137] Each ring’s feed network is implemented on one side of the PCB (front side for the inner ring, back side for the outer ring) and is excited by its own SMA connector. Thus, ModeI = +1 (for example) is generated by feeding the inner 8-element ring via Port 1, and Mode 1 = +2 by feeding the outer 8-element ring via Port 2. This multi-port, multi-mode design allows two independent RF signals (carrying different data) to create two 0AM beams simultaneously using a single integrated antenna structure. The prototype operates at a center frequency of 10 GHz with a measured bandwidth over 200 MHz, which is sufficient to carry typical communication baseband signals. FIGs. 21B and 21C illustrate the characteristic spiral phase fronts of the radiated waves for mode I = + 1 and I = +2, respectively. In the experimental setup, this dual-mode 0AM antenna was driven with two separate software-defined radios (SDRs) feeding the two SMA ports. Each port injects a modulated signal corresponding to a distinct data stream The Tx antenna then emits two coexistent vortex waves (nearly orthogonal in mode) on the same frequency, which are then directed toward the PMS panel for further manipulation.Testbed Setup

[0138] A real-time communications experimental system was constructed as shown in FIG.22 to validate the secure dual-channel transmission method according to various second example embodiments of the present invention. The testbed utilizes a PMS comprised of 400 independently programmable unit cells (arranged as a 20x20 array across a 400x400 mm panel). The PMS is assembled from four smaller sub-panels (each 10x10 units), with each pair of panels driven by a D-latch circuit board and controlled by an MCU. The MCU interfaces with a host computer via a serial link, receiving phase configuration instructions in real time. This hardware setup enables precise, on-the-fly control of the PMS phase pattern, which is crucial for data modulation through the SFM channel. In our design, each element provides 2-bit quantized phase shifting, and the entire array operates in transmissive mode. It is worth noting that the co-existent spatial field and band-pass modulation strategy demonstrated here is not limited to this transmissive meta-surface; the same principles apply to reflective or hybrid transmissive-reflective designs as well. This means the secure dual-channel approach can be adapted to many practical deployment scenarios, e.g., using wall-mounted reflective panels or transparent meta-surface windows, without loss of generality.

[0139] For baseband signal processing, we employ SDRPXIe platform from the Queentest company (M4x series) in conjunction with a host computer. This SDR platform provides 2 synchronous arbitrary waveform generating (AWG) channels, allowing us to transmit two separate data streams simultaneously. In the experiment, each AWG output i s up-converted andamplified before feeding one port of the dual-port multimode 0AM transmitter antenna. Thus, the AWG channels effectively create 2 synchronized band-pass data streams sharing the same frequency band, each launching a distinct vortex mode. Each data stream is modulated independently, carrying its own unique encryption information sequences. As mentioned above, the DBM channel carries sensitive highspeed multiplexing data streams, and the PMS-driven SFM channel transmits the encryption key for the DBM channel with spot beams wave-field selective keying modulation.

[0140] During the experiment, the two vortex waves are radiated from the transmitter toward the PMS, which is located 1.0 m away and oriented perpendicular to the beam direction. The PMS is pre-configured with phase patterns (beamforming codebooks) that transform the incident waves into desired focused spot beams in the 3D space on the opposite side of the PMS. In essence, the PMS in this demo acts like a real-time lens that can form multiple focal points for the incoming co-frequency beams. Thanks to the 2-bit phase shifting capacity of each PMS unit, the array can simultaneously focus both modes 1 = +1 and 1 = +2 0AM beams to different target locations in space. An eavesdropping receiver off the focal point will receive a much weaker or distorted signal, which somehow also enhances physical-layer security.

[0141] To monitor and ensure the PMS is functioning correctly, each element’s PIN diode is equipped with an LED indicator. These LEDs light up according to the element’s state, as shown in FIG. 20, providing an immediate visual confirmation that the PMS is applying the correct phase pattern at any given time. On the receiving end, multiple dipole antennas were set up that act as the energy detectors, which are mounted on a movable wooden frame, allowing precise positioning in the 3D region where the focused beams form, as shown in FIG. 22. Each dipole antenna is aligned to the polarization of the transmitted signal (single linear polarization in our case) to maximize reception. The received RF signals at these antennas are then down-converted to base-band and fed into the broadband intermediate frequency analog-to-digital (AD) signal acquisition card (ADQ7WB-PCle). The AD card simultaneously captures both data streams for further digital filtering and demodulation. Coherent demodulation and real-time signal analysis were performed on the host computer, including plotting constellation diagrams and measuring the BER for each channel. Furthermore, the recovered DBM signal undergoes a despreading process using the secret key conveyed through the SFM link, enabling the extraction of the final confidential data This operation ensures that only authorized receivers with access to the SFM key can successfully decode the transmitted information. All of thisprocessing is done in real-time, demonstrating that the system can support live secure communication with immediate feedback on performance.Wave-Field Selectivity

[0142] As illustrated in FIG 22, four dipole detectors were strategically arranged on the receiver side of the PMS. Two detectors are positioned along an axis perpendicular to the PMS plane at distances of 0.3 m and 0.9 m, respectively, facilitating the evaluation of the system’s focusing capability along the propagation direction. The remaining two detectors are placed symmetrically along an axis parallel to the PMS surface, separated by 0.6 m, with each located at an equal distance of 0.6 m from the PMS. As previously discussed, the successful detection of the key -bearing SFM channel is critically dependent on the PMS’ s ability to accurately focus electromagnetic energy into distinct spatial focal spots. Specifically, the quality of energy detectors’ demodulation of the secure key streams, as well as the interference between DBM data streams, is directly related to the degree of spatial isolation between these focal spots. To quantify this interference, a comprehensive measurement of power crosstalk between different focal spots were conducted.

[0143] During our experiments, targeted measurements at maximum transmission power were performed. As illustrated in FIG. 23, based on the spatial arrangement of four detectors, two detectors were arbitrarily selected for each measurement scenario. Two OAM channels were independently activated, and the crosstalk isolation at two focal spots was recorded. Specifically: (a) All detectors were active, but only OAM mode 1= +1 was transmitted; (b) All detectors were active, with only OAM mode I = +2 transmitted. Through these measurements, we compared the received power at each detector’ s designated focal spot against unintended interference power at the alternate focal spot.

[0144] The resulting values were normalized and organized into matrices presented in FIG.23. Each crosstalk matrix displays diagonal elements representing the desired signal power (normalized to 0 dB), measured at detectors placed at their intended focal spots. The off-diagonal elements represent undesired signal leakage or crosstalk received at detectors positioned at unintended focal spots, relative to the expected signals. The measurement outcomes consistently demonstrated crosstalk suppression exceeding 15 dB at all receiver focal spots, indicating that each detector receives other channel signals at least 15 dB weaker than its own. This significant spatial isolation dramatically mitigates interference, affirming the PMS’sefficacy in wave-field selectivity and thus creating effectively orthogonal communication channels.

[0145] From a communication standpoint, a crosstalk reduction of >15 dB equates to interference power being roughly 3% of the intended signal power, negligible enough to have minimal impact on coherent demodulation. Crucially, from a secure communication perspective, this high level of isolation implies that legitimate receivers positioned at their focal points can reliably decode the key information directly from the SFM channel due to extremely low interference levels, significantly enhancing decoding accuracy and reliability. Conversely, the wave-field selectivity provided by the PMS ensures that any unintended third-party receiver experiences a complex superposition of both channel signals without adequate isolation, substantially hindering the interception and decoding of transmitted information. Thus, the intrinsic interference isolation and spatial selectivity offered by the PMS deliver an additional robust layer of physical-layer security, complementing conventional cryptographic techniques and further solidifying the security posture of the co-existence dual-channel transmission.Reflections on the Performance and Significance ofBER

[0146] To rigorously evaluate the real-time communications performance under various signal and interference conditions, a series of measurements were conducted following a step-by-step procedure. This procedure ensured that we captured the impact of both noise and cochannel interference on each channel’s BER, thereby reflecting the real-world operating performance of the secure co-existence dual-channel link.

[0147] Noise Floor Measurement: First, we measured the average noise power at each receiver with no signal transmitted. This established the baseline noise floor (thermal and background noise) in the system Knowing the noise floor is essential for accurate SNR calculation.

[0148] Single-Stream Power Calibration: We then activated one transmitter at a time (only one 0AM channel on) and incrementally adjusted its output power. At each power level, the received signal strength at the corresponding receiver were measured. This allowed the mapping of transmit power to received SNR for each channel.

[0149] Data Collection and BER Calculation: For each SNR point (across a range of low to high SNRs), we collected a large sample of received bits from the demodulated output of each AD channel. We then computed the BER by comparing the received bit sequence to the knowntransmitted sequence. By doing so for each channel at each SNR (with both channels active), we built the BER vs. SNR curves under the dual-channel secure transmission condition.

[0150] Following the above procedure, comprehensive BER performance curves were obtained for both transmitted 0AM modes, as presented in FIGs. 24A and 24B. A critical observation from these results is that the measured BER inherently includes the impact of mutual interference between the channels. This is important for multi-mode multiplexing because it ensures that any degradation in one channel’s performance due to the other’s presence is taken into account. In our experiments, the interference from the co-channel signal manifested as a slight penalty in required SNR to achieve the same BER, but thanks to the PMS’s beam isolation, this penalty was relatively small (consistent with the high isolation we quantified before). The BER curves still trend downward with SNR and reach the low levels needed for reliable communication

[0151] From the experimental BER curves of the two modes DBM channels, it can be clearly seen that both independently modulated data streams achieve stable real-time communication links, which is also verified by the clean and distinguishable constellation diagrams, as shown in FIG. 25. Normally, as the SNR increases, the BER of each stream decreases correspondingly, which is the expected behavior for a well-functioning link. Crucially, both DBM multiplexing channels’ BERs drop below the FEC limit of 3.8 × 10-3, denoted by the horizontal dashed line in FIGs. 24A and 24B. Crossing this threshold means that standard forward error correction coding (such as LDPC or Turbo codes) can be employed to correct any remaining errors, yielding a effectively error-free connection. In practice, this demonstrates that even without sophisticated interference cancellation algorithms, the system can rely on FEC to clean up errors due to noise and the small amount of inter-channel interference, thereby ensuring reliable data transmission on both channels.

[0152] Another notable observation is that at higher SNR values, the BER curves do not continue to drop indefinitely but instead flatten out, approaching an error floor. This behavior indicates that there are limiting factors other than noise affecting the error rate. This flattening may be attributed primarily to energy leakage and residual interference between the two channels, caused by practical imperfections. In a perfect system with ideal components and calibration, focusing two 0AM beams would result in zero interference outside the focal spots. In reality, however, factors like slight misalignment of the PMS panels, non-ideal phase quantization (since we use 2-bit phase control, not continuous), and manufacturing tolerances of the PMS units mean that each focused beam still leaks a tiny amount of power toward theother receiver. This leakage acts as a constant interference floor - no matter how high the SNR gets (by increasing signal power), the other channel’s leaked signal plus any other static interference in the environment sets a lower bound on the error probability. In the measurements, such an error floor can indeed be seen, indicating a small but non-zero crosstalk between channels.

[0153] Fortunately, this residual interference is minor, so its effect on system performance is negligible in a practical sense. Moreover, modern channel coding techniques are very adept at handling a small percentage of errors; the use of strong channel coding can effectively correct the errors caused by this interference, allowing the system to approach error-free performance despite the error floor. In terms of security, the presence of crosstalk for legitimate receivers implies that an eavesdropper, which would likely see a much higher interference level, would be even less able to decode the signal - any eavesdropper positioned in between or off to the side of the focal spots would encounter both channels overlapping with insufficient separation, resulting in a high effective BER that prevents data recovery. Thus, the small crosstalk observed is essentially an artifact of hardware limits, but it also means that outside the intended spots, the interference is even more pronounced, naturally helping obscure the communication from prying ears.

[0154] Accordingly, a secure wireless transmission architecture enhanced by PMS-based wave-field selectivity and structured wave-based spectrum orthogonality is provided according to various second example embodiments of the present invention. This unique approach uniquely integrates two logically independent yet physically co-existent channels, markedly distinguishing it from conventional joint modulation methodologies. By leveraging the inherent orthogonality of multimode vortex waves and advanced programmable beamforming through a programmable wave-domain meta-surface router, our architecture significantly enhances secure wireless communication capabilities. The experimental results demonstrate the programmable wave-domain meta-surface splitter’s exceptional ability to focus electromagnetic energy precisely into defined spatial focal spots, achieving remarkable spatial isolation and crosstalk suppression exceeding 15 dB. This high degree of isolation substantially reduces interference between concurrently transmitted data streams, thereby greatly improving data integrity and communication reliability. Additionally, the PMS-induced wave-field selectivity fundamentally strengthens communication security; legitimate receivers positioned accurately at the designed focal spots enjoy clear, interference-minimized signals, while potential eavesdroppers receive significantly degraded and unintelligible transmissions.

[0155] Through comprehensive experimental validations conducted in realistic indoor environments, the practical feasibility and robustness of the wireless data transmission system according to various second example embodiments of the present invention have been established. This method further broadens the application potential of structured beams and presents significant potential for deployment in intricate and dynamic communication scenarios. By integrating advanced wave-manipulation techniques with sophisticated modulation strategies, the approach according to various example embodiments of the present invention constitutes a substantial advancement toward secure, high-capacity wireless communication systems. For example, the system design according to various second example embodiments of the present invention is of particular relevance to secure communication in loT environments characterized by high user density and stringent power constraints.

[0156] While embodiments of the invention have been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

1. CLAIMS1. A method of wireless data transmission based on multi-mode vortex waves, the method comprising:3.generating multi-mode vortex waves based on a plurality of data streams derived from an original series of data bits, each vortex wave of the multi-mode vortex waves generated based on a corresponding data stream of the plurality of data streams;4.transmitting the multi-mode vortex waves to a reconfigurable metasurface; and dynamically controlling the reconfigurable metasurface to be at a dynamically selected one of a predefined set of phase distribution states based on an encryption key that dynamically changes over time, each phase distribution state being configured to direct and focus, for each vortex wave of the multi-mode vortex waves incident on a surface of the reconfigurable metasurface, the vortex wave to a predetermined one of a set of predefined receiver positions corresponding to the dynamically selected phase distribution state.

2. The method according to claim 1, wherein the encryption key is dynamically changeable amongst a predefined set of encryption codes, each encryption code for controlling the reconfigurable metasurface to be at a corresponding one of the predefined set of phase distribution states.

3. The method according to claim 2, wherein for each encryption code of the predefined set of encryption codes, a mapping between the encryption code and the corresponding phase distribution states of the predefined set of phase distribution states is defined based on a metasurface phase distribution state codebook4. The method according to any one of claims 1 to 3, wherein the reconfigurable metasurface comprises a two-dimensional (2D) array of unit cells, each unit cell being dynamically controllable to be at a dynamically selected one of a plurality of wave propagation path states based on the encryption key for providing a corresponding degree of phase shift for the multi-mode vortex waves incident thereon for said dynamically controlling the reconfigurable metasurface to be at the dynamically selected one of the predefined set of phase distribution states based on the encryption key.

5. The method according to any one of claims 1 to 4, wherein8.the original series of data bits comprises a series of data segments, and9.for each data segment of the series of data segments,10.the plurality of data streams is derived from a first portion of the data segment, and11.the encryption key is derived from a second portion of the data segment.

6. The method according to any one of claims 1 to 4, wherein13.the original series of data bits comprises a series of data segments, and14.for each data segment of the series of data segments, the plurality of data streams is generated based on a plurality of portions, respectively, of the data segment and the encryption key.

7. The method according to claim 6, wherein for each data segment of the series of data segments, each data stream of the plurality of data streams is generated by spreading each data bit of the corresponding portion of the plurality of portions of the data segment based on the encryption key.

8. A method of wireless data reception based on multi-mode vortex waves, the method comprising:17.receiving, from a reconfigurable metasurface, a plurality of signals of multi-mode vortex waves focused at a plurality of receiver positions, respectively, of a set of predefined receiver positions that dynamically changes amongst the set of predefined receiver positions over time, the multi-mode vortex waves generated at a transmitter side based on a plurality of data streams derived from an original series of data bits and each vortex wave of the multimode vortex waves generated based on a corresponding data stream of the plurality of data streams;18.dynamically determining an encryption key that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multi-mode vortex waves is received over time; and19.determining the original series of data bits based on the plurality of signals of the multimode vortex waves received at the plurality of receiver positions and the encryption key.

9. The method according to claim 8, wherein said dynamically determining the encryption key comprises:20.dynamically determining a signal location pattern that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multi-mode vortex waves is received over time; and21.dynamically determining the encryption key that dynamically changes over time based on the signal location pattern and a metasurface phase distribution state codebook, wherein the encryption key is dynamically changeable amongst a predefined set of encryption codes,22.the signal location pattern is dynamically changeable amongst a predefined set of signal location patterns, and23.for each encryption code of the predefined set of encryption codes, a mapping between the encryption code and a corresponding signal location pattern of the predefined set of signal location patterns is defined based on the metasurface phase distribution state codebook, each signal location pattern corresponds to a phase distribution state of the reconfigurable metasurface.

10. The method according to claim 8 or 9, wherein25.the original series of data bits comprises a series of data segments, and26.said determining the original series of data bits comprises, for each data segment of the series of data segments:27.determining a plurality of data streams based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions that dynamically change over time;28.determining a first portion of the data segment based on the plurality of data streams, and29.determining a second portion of the data segment based on the encryption key.

11. The method according to claim 8 or 9, wherein31.the original series of data bits comprises a series of data segments, and said determining the original series of data bits comprises, for each data segment of the series of data segments:32.determining a plurality of data streams based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions that dynamically change over time; and33.determining a plurality of portions of the data segment based on the plurality of data streams, respectively, and the encryption key.

12. The method according to claim 11, wherein for each data segment of the series of data segments and for each portion of the plurality of portions of the data segment, each data bit of the portion of the data segment is determined by despreading the corresponding data stream of the plurality of data streams based on the encryption key.

13. A method of wireless data communication based on multi-mode vortex waves, the method comprising:36.performing, at a transmitter side, the method of wireless data transmission according to any one of claims 1 to 4 for dynamically directly and focusing, for each vortex wave of the multi-mode vortex waves incident on the surface of the reconfigurable metasurface, the vortex wave to the predetermined one of the set of predefined receiver positions corresponding to the dynamically selected phase distribution state of the predefined set of phase distribution states based on the encryption key at the transmitter side that dynamically changes over time, the multi-mode vortex waves generated based on the plurality of data streams derived from an original series of data bits; and37.performing, at a receiver side, the method of wireless data reception according to any one of claim 8 or 9, for receiving, from the reconfigurable metasurface, the plurality of signals of the multi-mode vortex waves focused at the plurality of receiver positions, respectively, of the set of predefined receiver positions that dynamically changes amongst the set of predefined receiver positions over time and determining the original series of data bits based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions and the encryption key at the receiver side.

14. The method according to claim 13, wherein39.the original series of data bits comprises a series of data segments, for the method of wireless data transmission and for each data segment of the series of data segments, the plurality of data streams is derived from a first portion of the data segment, and the encryption key at the transmitter side is derived from a second portion of the data segment, and40.for the method of wireless data reception, said determining the original series of data bits comprises, for each data segment of the series of data segments:41.determining a plurality of data streams based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions that dynamically change over time;42.determining a first portion of the data segment based on the plurality of data streams, and43.determining a second portion of the data segment based on based on the encryption key at the receiver side.

15. The method according to claim 13, wherein45.the original series of data bits comprises a series of data segments,46.for the method of wireless data transmission and for each data segment of the series of data segments, the plurality of data streams is generated based on a plurality of portions, respectively, of the data segment and the encryption key at the transmitter side, and47.for the method of wireless data reception, said determining the original series of data bits comprises, for each data segment of the series of data segments:48.determining a plurality of data streams based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions that dynamically change over time; and49.determining a plurality of portions of the data segment based on the plurality of data streams, respectively, and the encryption key at the receiver side.

16. The method according to claim 15, wherein51.for the method of wireless data transmission and for each data segment of the series of data segments, each data stream of the plurality of data streams is generated by spreading each data bit of the corresponding portion of the plurality of portions of the data segment based on the encryption key at the transmitter side, and for the method of wireless data reception, for each data segment of the series of data segments and for each portion of the plurality of portions of the data segment, each data bit of the portion of the data segment is determined by despreading the corresponding data stream of the plurality of data streams based on the encryption key at the receiver side.

17. A transmitter system for wireless data transmission based on multi-mode vortex waves, the transmitter system comprising:53.a reconfigurable metasurface;54.a multi-mode vortex wave generator configured to:55.generate multi-mode vortex waves based on a plurality of data streams derived from an original series of data bits, each vortex wave of the multi-mode vortex waves generated based on a corresponding data stream of the plurality of data streams; and56.transmit the multi-mode vortex waves to the reconfigurable metasurface; a reconfigurable metasurface controller communicatively coupled to the reconfigurable metasurface and configured to:57.dynamically control the reconfigurable metasurface to be at a dynamically selected one of a predefined set of phase distribution states based on an encryption key that dynamically changes over time, each phase distribution state being configured to direct and focus, for each vortex wave of the multi-mode vortex waves incident on a surface of the reconfigurable metasurface, the vortex wave to a predetermined one of a set of predefined receiver positions corresponding to the dynamically selected phase distribution state.

18. The transmitter system according to claim 17, wherein the encryption key is dynamically changeable amongst a predefined set of encryption codes, each encryption code for controlling the reconfigurable metasurface to be at a corresponding one of the predefined set of phase distribution states.

19. The transmitter system according to claim 18, wherein for each encryption code of the predefined set of encryption codes, a mapping between the encryption code and the corresponding phase distribution states of the predefined set of phase distribution states is defined based on a metasurface phase distribution state codebook.

20. The transmitter system according to any one of claims 17 to 19, wherein the reconfigurable metasurface comprises a two-dimensional (2D) array of unit cells, each unit cell being dynamically controllable to be at a dynamically selected one of a plurality of wave propagation path states based on the encryption key for providing a corresponding degree of phase shift for the multi-mode vortex waves incident thereon for said dynamically controlling the reconfigurable metasurface to be at the dynamically selected one of the predefined set of phase distribution states based on the encryption key.

21. The transmitter system according to any one of claims 17 to 20, wherein61.the original series of data bits comprises a series of data segments, and62.for each data segment of the series of data segments,63.the plurality of data streams is derived from a first portion of the data segment, and64.the encryption key is derived from a second portion of the data segment.

22. The transmitter system according to any one of claims 17 to 20,66.the original series of data bits comprises a series of data segments, and67.for each data segment of the series of data segments, the plurality of data streams is generated based on a plurality of portions, respectively, of the data segment and the encryption key.

23. The transmitter system according to claim 22, wherein for each data segment of the series of data segments, each data stream of the plurality of data streams is generated by spreading each data bit of the corresponding portion of the plurality of portions of the data segment based on the encryption key.

24. A receiver system for wireless data reception based on multi-mode vortex waves, the receiver system comprising:70.a set of signal detectors positioned at a set of predefined receiver positions, respectively, for receiving, from a reconfigurable metasurface, a plurality of signals of multi-mode vortex waves focused at a plurality of signal detectors of the set of signal detectors at a plurality of receiver positions of the set of predefined receiver positions, respectively, that dynamically changes amongst the set of predefined receiver positions over time, the multi-mode vortex waves generated at a transmitter side based on a plurality of data streams derived from an original series of data bits and each vortex wave of the multi-mode vortex waves generated based on a corresponding data stream of the plurality of data streams;71.an encryption key determinator configured to dynamically determine an encryption key that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multimode vortex waves is received over time; and72.an original data determinator configured to determine the original series of data bits based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions and the encryption key25. The receiver system according to claim 24, wherein said dynamically determine the encryption key comprises:74.dynamically determining a signal location pattern that dynamically changes over time based on the dynamic changes in the plurality of receiver positions of the set of predefined receiver positions at which the plurality of signals of the multi-mode vortex waves is received over time; and75.dynamically determining the encryption key that dynamically changes over time based on the signal location pattern and a metasurface phase distribution state codebook, wherein the encryption key is dynamically changeable amongst a predefined set of encryption codes,76.the signal location pattern is dynamically changeable amongst a predefined set of signal location patterns, and77.for each encryption code of the predefined set of encryption codes, a mapping between the encryption code and a corresponding signal location pattern of the predefined set of signal location patterns is defined based on the metasurface phase distribution state codebook, each signal location pattern corresponds to a phase distribution state of the reconfigurable metasurface.

26. The receiver system according to claim 24 or 25, wherein79.the original series of data bits comprises a series of data segments, and80.said determine the original series of data bits comprises, for each data segment of the series of data segments: determining a plurality of data streams based on the plurality of signals of the multimode vortex waves received at the plurality of receiver positions that dynamically change over time;81.determining a first portion of the data segment based on the plurality of data streams, and82.determining a second portion of the data segment based on the encryption key.

27. The receiver system according to claim 24 or 25, wherein84.the original series of data bits comprises a series of data segments, and85.said determine the original series of data bits comprises, for each data segment of the series of data segments:86.determining a plurality of data streams based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions that dynamically change over time; and87.determining a plurality of portions of the data segment based on the plurality of data streams, respectively, and the encryption key.

28. The receiver system according to claim 27, wherein for each data segment of the series of data segments and for each portion of the plurality of portions of the data segment, each data bit of the portion of the data segment is determined by despreading the corresponding data stream of the plurality of data streams based on the encryption key.

29. A wireless data communication system for wireless data communication based on multimode vortex waves, the wireless data communication system comprising:90.the transmitter system according to any one of claims 17 to 20; and91.the receiver system according to any one of claims 24 to 25.

30. The wireless data communication system according to claim 29, wherein93.the original series of data bits comprises a series of data segments,94.for the transmitter system and for each data segment of the series of data segments, the plurality of data streams is derived from a first portion of the data segment, and the encryption key at the transmitter side is derived from a second portion of the data segment, and for the receiver system, said determine the original series of data bits comprises, for each data segment of the series of data segments:95.determining a plurality of data streams based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions that dynamically change over time;96.determining a first portion of the data segment based on the plurality of data streams, and97.determining a second portion of the data segment based on based on the encryption key at the receiver side.

31. The wireless data communication system according to claim 29, wherein99.the original series of data bits comprises a series of data segments,100.for the transmitter system and for each data segment of the series of data segments, the plurality of data streams is generated based on a plurality of portions, respectively, of the data segment and the encryption key at the transmitter side, and101.for the receiver system, said determine the original series of data bits comprises, for each data segment of the series of data segments:102.determining a plurality of data streams based on the plurality of signals of the multi-mode vortex waves received at the plurality of receiver positions that dynamically change over time; and103.determining a plurality of portions of the data segment based on the plurality of data streams, respectively, and the encryption key at the receiver side.

32. The wireless data communication system according to claim 31, wherein105.for the transmitter system and for each data segment of the series of data segments, each data stream of the plurality of data streams is generated by spreading each data bit of the corresponding portion of the plurality of portions of the data segment based on the encryption key at the transmitter side, and106.for the receiver system, for each data segment of the series of data segments and for each portion of the plurality of portions of the data segment, each data bit of the portion of the data segment is determined by despreading the corresponding data stream of the plurality of data streams based on the encryption key at the receiver side.

Images