Mode division multiplexing (MDM) using orbital angular momentum (OAM) is a recently developed physical layer transmission technique, which has obtained intensive interest among optics, ...millimeter-wave, and radio frequency due to its capability to enhance communication capacity while retaining an ultra-low receiver complexity. In this paper, the system model based on OAM-MDM is mathematically analyzed and it is theoretically concluded that such system architecture can bring a vast reduction in receiver complexity without capacity penalty compared with conventional line-of-sight multiple-inmultiple-out systems under the same physical constraint. Furthermore, a 4×4 OAM-MDM communication experiment adopting a pair of easily realized Cassegrain reflector antennas capable of multiplexing/demultiplexing four orthogonal OAM modes of l = -3, -2, +2, and +3 is carried out at a microwave frequency of 10 GHz. The experimental results show high spectral efficiency as well as low receiver complexity.
Based on metallic traveling-wave ring-slot structure, an easily realized four-orbital angular momentum (OAM)-mode antenna capable of generating four coaxially propagating waves with OAM modes of l = ...-3, -2, +2, and +3, respectively, is experimentally demonstrated at 10 GHz. The feeding network is simply implemented using two 90° hybrid couplers. A ring-focus double-reflector with a favorable focus-diameter-ratio is specially designed to gain a high directivity. The main characteristics of the antenna-such as S-parameters, directivity, and near-field radiation-are presented both in simulation and experiment. Employing a pair of four-OAM-mode antennas, the experiment shows that the near-field OAM-based radio communication channels are naturally isolated.
A plane spiral orbital angular momentum (OAM) waves-based 4 × 4 multiple-in-multiple-out (MIMO) communication system for line-of-sight channel is proposed and experimentally demonstrated in ...comparison with conventional MIMO. The transmitting OAM waves are propagating along the transverse direction; hence there is no singularity or divergence problem. Compared with the conventional MIMO, this system could achieve lower spatial correlations and a higher capacity gain while the OAM antennas as the elements of the transmitting array are sorted in an ordered sequence. The measured bit-error-rate performance clearly demonstrates the feasibility of the proposed system, and the causation of the improved performance is also detailedly discussed. This technology can be applied in near-field communications or short-range MIMO systems to realize higher capacity communications.
A generalized signal model for multiple orbital angular momentum (OAM) mode-based radio communication combined with a novel partial arc sampling receiving (PASR) scheme for compactly receiving is ...proposed and mathematically analyzed. Furthermore, a near-field line-of-sight PASR radio data link using four OAM modes is experimentally demonstrated to quadruple the spectral efficiency without adding signal processing complexity at the receiving end. Experiment results show that all the four OAM channels are recovered with bit-error rates below 3.8 × 10 -3 , indicating the robustness of the four-OAM-mode-PASR data link.
Descartes’ metaphysical doubts in the Third and Fifth Meditations present a scenario like this: it is possible that I (the Meditator) am so imperfect as to be deceived by my author (i.e., an ...omnipotent God/Deceiver) in the matters which I think I perceive clearly and distinctly. The metaphysical doubts attempt to cast doubt on beliefs based on present or recollected clear and distinct perceptions. This paper clarifies the intension of the metaphysical doubts by answering the question of how an omnipotent God/Deceiver might exercise a deceptive influence on clear and distinct perception. My analysis shows: (1) the memory interpretation and the retrospective interpretation to be implausible; (2) the incoherence interpretation to be ill-founded, though its conclusion is partly right, such that we should accept a weaker version of it; (3) the misrepresentation interpretation, the defective-origin interpretation, the truth-value variation interpretation and the radical interpretation to be plausible; (4) all of these credible interpretations to be compatible with each other as well.
The design of a radio communication system employing orbital angular momentum (OAM) mode multiplexing is described. Rotman lenses followed by circular antenna arrays are used to transmit and receive ...radio frequency beams carrying OAM. In our experiment, two 3 × 3 Rotman lenses are fabricated to feed the three-element circular arrays with certain phase gradients for OAM modes multiplexing and demultiplexing. The OAM-carrying beams of mode number l = +1, 0, and -1 are generated at 9.7 GHz, with each channel carrying an independent data stream of 40 Mbit s -1 quadrature phase shift keying signal in a bandwidth of 20 MHz. And all three channels are recovered with bit error rates below the forward error correction limit of 3.8 × 10 -3 .
This work presents and experimentally tests the framework used by our context-aware, distributed team of small Unmanned Aerial Systems (SUAS) capable of operating in real time, in an autonomous ...fashion, and under constrained communications. Our framework relies on a three-layered approach: (1) an operational layer, where fast temporal and narrow spatial decisions are made; (2) a tactical layer, where temporal and spatial decisions are made for a team of agents; and (3) a strategical layer, where slow temporal and wide spatial decisions are made for the team of agents. These three layers are coordinated by an ad hoc, software-defined communications network, which ensures sparse but timely delivery of messages amongst groups and teams of agents at each layer, even under constrained communications. Experimental results are presented for a team of 10 small unmanned aerial systems tasked with searching for and monitoring a person in an open area. At the operational layer, our use case presents an agent autonomously performing searching, detection, localization, classification, identification, tracking, and following of the person, while avoiding malicious collisions. At the tactical layer, our experimental use case presents the cooperative interaction of a group of multiple agents that enables the monitoring of the targeted person over wider spatial and temporal regions. At the strategic layer, our use case involves the detection of complex behaviors, i.e., the person being followed enters a car and runs away, or the person being followed exits the car and runs away, which require strategic responses to successfully accomplish the mission.
An orbital angular momentum (OAM) multiplexed radio data link with the novel partial arc sampling receiving (PASR) scheme is experimentally demonstrated. These four coaxially propagating OAM waves ...with modes of l = -6, -2, +2 and +6 are generated by a Cassegrain antenna based on the dual ring-slot radiators. Over 10 m free-space transmission, four identical horn antennas uniformly located at the π/2 arc with a fixed radius of 45 cm are used to capture the four overlapped OAM waves. The de-multiplexing is then performed by digital phase-shift (DPS) at digital baseband. Experiment results show that the bit-error rates (BER) can reach below the forward error correction limit of 3.8 × 10 -3 for all the four OAM channels. Multi-OAM-mode communications with the PASR scheme is capable of providing the receiving end with desired properties of compact size as well as easy realization.
Conventional security screening systems cannot operate in real time and often suffer from false alarms due to the profile-only imaging without further analysis on the object material properties. ...Reflectarrays were recently proposed as devices capable of performing real-time security screening using a single-frequency radar signal. This article presents first a physical optics (PO)-based simulation method to facilitate the design of a multireflectarray system. Then, an object material characterization method using geometrical optics (GO) is derived for such a system. The characterization process not only retrieves the complex relative permittivity of the object but also improves its profile reconstruction in terms of a more accurate thickness. Both simulations and experiments are carried out to verify the effectiveness and efficiency of the proposed methods. Primary results show great potentials for security screening, especially in scenarios where the inspection of human bodies for threat materials, such as narcotics and explosives, is required.
High-performance millimeter-wave (mm-wave) multiple-in-multiple-out (MIMO) radars have been using efficient multiplexing with increasingly complicated radar waveforms, where conventional hardware ...architectures suffer from inevitably high design complexity and cost. This article presents a new software-defined mm-wave multistatic imaging system which provides great efficiency and flexibility to generate and process complicated radar waveforms. A general system block diagram and its signal model are proposed to use space-time-coded orthogonal frequency-division multiplexing (OFDM) for simultaneous MIMO transmission at the same time and frequency. The space-time coding (STC) is designed based on the Hadamard matrix which allows simple decoupling and decoding for imaging processing. A radar prototype is designed to validate the proposed system architecture, which operates at 83.5 GHz with a frequency bandwidth of 4.8 GHz. The mm-wave front-end consists of a metal-printed 8-by-8 waveguide array with a small element-separation of 9 mm to form 64 virtual channels for three-dimensional imaging. Experimental results show good imaging performance, giving great potential to design future cost-effective high-performance mm-wave imaging with efficient multiplexing.
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