Far-field Communication Research Articles

User Clustering for Coexistence Between Near-Field and Far-Field Communications

User Clustering for Coexistence Between Near-Field and Far-Field Communications

Parametric Channel Estimation With Short Pilots in RIS-Assisted Near- and Far-Field Communications

Parametric Channel Estimation With Short Pilots in RIS-Assisted Near- and Far-Field Communications

Physical Layer Security of the MIMO-NOMA Systems under Near-Field Scenario

In this paper, we propose a secure transmission framework for near-field MIMO-NOMA systems. This architecture integrates beamforming mechanisms for both transmission and reception, allowing the base station to send encrypted information to authorized users, effectively countering eavesdropping attempts in a near-field environment. To optimize the secrecy communication capability in the near field, a two-phase alternating optimization algorithm is introduced. In the first phase, the semidefinite relaxation (SDR) method is used to relax constraints in the problem and convert it into a semidefinite programming (SDP) problem. In the second phase, the successive convex approximation (SCA) algorithm is employed to transform the original non-convex problem into a convex optimization problem, obtaining a locally optimal solution through multiple iterations. Simulation results validate that the proposed near-field communication strategy exhibits superior secrecy communication capabilities under various parameter settings compared to far-field communication strategies.

Large-Scale Intelligent Surfaces Enabled Unified Near-Field and Far-Field Communications: Codebook Design and Beam Training

Large-Scale Intelligent Surfaces Enabled Unified Near-Field and Far-Field Communications: Codebook Design and Beam Training

Task Offloading Optimization for UAV-Aided NOMA Networks With Coexistence of Near-Field and Far-Field Communications

Task Offloading Optimization for UAV-Aided NOMA Networks With Coexistence of Near-Field and Far-Field Communications

Mixed Near- and Far-Field Communications for Extremely Large-Scale Array: An Interference Perspective

Mixed Near- and Far-Field Communications for Extremely Large-Scale Array: An Interference Perspective

NOMA-Based Coexistence of Near-Field and Far-Field Massive MIMO Communications

This letter considers a legacy massive multiple-input multiple-output (MIMO) network, in which spatial beams have been preconfigured for near-field users, and proposes to use the non-orthogonal multiple access (NOMA) principle to serve additional far-field users by exploiting the spatial beams preconfigured for the legacy near-field users. Our results reveal that the coexistence between near-field and far-field communications can be effectively supported via NOMA, and that the performance of NOMA-assisted massive MIMO can be efficiently improved by increasing the number of antennas at the base station.

Recent Advances in Batteryless NFC Sensors for Chemical Sensing and Biosensing.

This article reviews the recent advances in the field of batteryless near-field communication (NFC) sensors for chemical sensing and biosensing. The commercial availability of low-cost commercial NFC integrated circuits (ICs) and their massive integration in smartphones, used as readers and cloud interfaces, have aroused great interest in new batteryless NFC sensors. The fact that coil antennas are not importantly affected by the body compared with other wireless sensors based on far-field communications makes this technology suitable for future wearable point-of-care testing (PoCT) devices. This review first compares energy harvesting based on NFC to other energy-harvesting technologies. Next, some practical recommendations for designing and tuning NFC-based tags are described. Power transfer is key because in most cases, the energy harvested has to be stable for several seconds and not contaminated by undesired signals. For this reason, the effect of the dimensions of the coils and the conductivity on the wireless power transfer is thoroughly discussed. In the last part of the review, the state of the art in NFC-based chemical and biosensors is presented. NFC-based tags (or sensor tags) are mainly based on commercial or custom NFC ICs, which are used to harvest the energy from the RF field generated by the smartphone to power the electronics. Low-consumption colorimeters and potentiostats can be integrated into these NFC tags, opening the door to the integration of chemical sensors and biosensors, which can be harvested and read from a smartphone. The smartphone is also used to upload the acquired information to the cloud to facilitate the internet of medical things (IoMT) paradigm. Finally, several chipless sensors recently proposed in the literature as a low-cost alternative for chemical applications are discussed.

MSCNN-LSTM Model for Predicting Return Loss of the UHF Antenna in HF-UHF RFID Tag Antenna

High-frequency (HF) and ultrahigh-frequency (UHF) dual-band radio frequency identification (RFID) tags with both near-field and far-field communication can meet different application scenarios. However, it is time-consuming to calculate the return loss of a UHF antenna in a dual-band tag antenna using electromagnetic (EM) simulators. To overcome this, the present work proposes a model of a multi-scale convolutional neural network stacked with long and short-term memory (MSCNN-LSTM) for predicting the return loss of UHF antennas instead of EM simulators. In the proposed MSCNN-LSTM, the MSCNN has three branches, which include three convolution layers with different kernel sizes and numbers. Therefore, MSCNN can extract fine-grain localized information of the antenna and overall features. The LSTM can effectively learn the EM characteristics of different structures of the antenna to improve the prediction accuracy of the model. Experimental results show that the mean absolute error (0.0073), mean square error (0.00032), and root mean square error (0.01814) of the MSCNN-LSTM are better than those of other prediction methods. In predicting the return loss of 100 UHF antennas, compared with the simulation time of 4800 s for High Frequency Structure Simulator (HFSS), MSCNN-LSTM takes only 0.927519 s under the premise of ensuring prediction accuracy, significantly reducing the calculation time, which provides a basis for the rapid design of HF-UHF RFID tag antenna. Then MSCNN-LSTM is used to determine the dimensions of the UHF antenna quickly. The return loss of the designed dual-band RFID tag antenna is and at 13.56 and 915 MHz, respectively, achieving the desired goal.

On the Study of Reconfigurable Intelligent Surfaces in the Near-Field Region

As reconfigurable intelligent surface (RIS) is expected to be implemented with a large aperture in terms of wavelengths, using a RIS to perform near-field rather than conventional far-field communications might gain some benefits. The electric fields in the near-field region from the near-field focusing and conventional far-field RISs are simulated and compared to assess and validate the benefits. Two metrics of benefit distance and near-field gain are defined to characterize the electric fields in the near-field region. The cumulative distribution function (CDF) related to the near-field gain is calculated to describe the benefits in the area of interest where the total scan patterns from the near-field focusing and conventional far-field RISs are plotted. For demonstration, the benefit distance, near-field gain, and CDFs are presented and calculated for near-field focusing RISs with assigned focal distances of 80 and 300 mm. It is concluded that the benefit distance is a critical factor affecting the CDF directly. The effects of the size of a RIS and phase quantization of elements on the benefit distance, near-field gain, and CDF are also discussed. Moreover, the maximum focal distance of a near-field focusing RIS with a certain size is derived and specified. Finally, the electric fields of three prototypes (e.g., conventional far-field RIS, near-field focusing RISs with assigned focal distances of 500 and 1500 mm) at 26 GHz are measured and compared, where the benefit distances and near-field gains are experimentally observed.

Frequency Reconfigurable Smart Antenna With Integrated Electroactive Polymer for Far-Field Communication

For the first time, the ionic polymer metal composite (IPMC) actuator is integrated with a radio frequency identification (RFID) tag antenna for achieving frequency reconfiguration in the ultrahigh-frequency (UHF) band. Here, the IPMC movable flap serves as an actuator that can effectively tune the tag resonant frequency. By applying a two-layer-crenelated structure and employing a surface patterned electrode for restraining back relaxation, the deflection of the IPMC actuator can be significantly improved. The IPMC actuator can move in two directions, enabling two-degree frequency tuning. Numerical and experimental data confirm that the tip displacement of the IPMC actuator can be enhanced up to 266% with the use of the two-layer-crenelated structure. The IPMC actuator allows the resonant frequency of the tag antenna to be tuned back by as much as 35 MHz, after deviating due to placing on an unintended object. UHF RFID application is also performed using a portable commercial RFID reader. Good frequency reconfiguration and broad tuning range, along with far read distances, have been achieved with our tunable UHF RFID tag antenna.

CMOS THz-ID: A 1.6-mm² Package-Less Identification Tag Using Asymmetric Cryptography and 260-GHz Far-Field Backscatter Communication

This article presents an ultra-small, high-security identification tag that is entirely built in a CMOS chip without external components. The usage of backscatter communications at 260 GHz enables full integration of a 2 × 2 patch antenna array. For chip compactness and minimum interference caused by direct wave reflection, the backscatter signal is frequency-shifted by 2 MHz and radiated with cross polarization from the same antenna array. Such a configuration also, for the first time for RF tags, enables beamsteering for enhanced link budget. For authentication and secure wireless data transmission, the tag also integrates a compact elliptic-curve-cryptography (ECC) dedicated processor, which is based on a narrow-strong private identification protocol. The presented tag has a peak power consumption of 21 μW and can be powered by a chip-wide array of photodiodes and a DC-DC converter. Using a low-cost 65-nm bulk CMOS technology, the terahertz (THz) ID chip has an area of only 1.6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and demonstrates the measured downlink speed of 100 kb/s and the upload speed of 2 kb/s across 5-cm distance from the reader. The tag-reader authentication/communication protocol is fully demonstrated using external tag power and partially demonstrated using the tag-integrated photo-voltaic powering. The tag size is the smallest among all prior radio-frequency identifications (RFIDs) using far-field communications.

Near-Field HF-RFID and CMA-Based Circularly Polarized Far-Field UHF-RFID Integrated Tag Antenna

This research proposes an integrated high-frequency (HF) and ultrahigh-frequency (UHF) passive radio frequency identification (RFID) tag antenna for near-field (13.56 MHz) and far-field (920–925 MHz) communication. This tag antenna is advantageous for the applications with lossy material in the near-field communication and mitigates polarization loss in the far-field communications. The HF-RFID tag antenna is of square spiral structure, and the circularly polarized UHF-RFID structure consists of a square loop radiator with cascading loop feeding and shorted stub. The structure of HF-RFID tag antenna situated inside the circularly polarized UHF-RFID tag can avoid the significant effect of the near-field magnetic coupling from the square loop. The UHF-RFID tag antenna is realized by using characteristic mode analysis for wideband circular polarization. The HF-RFID structure is conjugate-matched with NXP NT3H2111 chip, and the UHF-RFID structure is conjugate-matched with NXP G2X chip. Simulations were carried out, and an antenna prototype was fabricated. The experimental results reveal that the radiation pattern of UHF-RFID tag antenna is bidirectional with a gain of 0.31 dBic. The impedance bandwidth covers the frequency range of 903–944 MHz, and the axial ratio in boresight direction at 922.5 MHz is 1.67 dB, with the axial ratio bandwidth over 863–938 MHz. The maximum near-field and far-field reading ranges are 4.9 cm and 8.7 m. The proposed integrated dual-band passive tag antenna is operationally ideal for HF-RFID and UHF-RFID applications.

A High-Resolution Wireless Power Transfer and Data Communication System for Studying Gastric Slow Waves.

We present a wireless recording system designed for high-resolution mapping of gastric slow-wave signals. The system is composed of an implantable unit (IU), a wearable unit (WU), and a stationary unit (SU) connected to a computer. Two independent wireless data communication links consisting of IU-WU and IU-SU were developed based on near-field and far-field communication, respectively. Furthermore, the WU is capable to wirelessly recharge the IU's battery through an inductive link. For the IU-WU near-field communication, a differential pulse position data encoding algorithm with only 6.25% duty cycle, with load shift keying (LSK) modulation is developed to guarantee continuous power transmission and high data transfer rate, simultaneously. The IU sends the encoded data to the WU, and the WU can either store the data locally on a memory card or transmit them to the SU for real-time monitoring. In addition, the IU-SU far-field data communication was developed based on a RF transceiver in which the IU transmits the data directly to the SU. The benchtop validation of the system demonstrated successful IU-WU and WU-SU data transmission, while sample signals were recorded successfully at IU through saline solution and received by SU.

IoT-Linked Integrated NFC and Dual Band UHF/2.45 GHz RFID Reader Antenna Scheme

This research proposes a system board of integrated antenna scheme of near-field communication (NFC) and dual band ultra-high frequency (UHF, 920–925 MHz)/2.45 GHz radio frequency identification (RFID) reader antennas for Internet of Things (IoT) applications. The integrated antenna scheme is capable of simultaneous execution of NFC and UHF RFID functions whereby the NFC and UHF RFID modules, which are serially connected to a microcontroller with Wi-Fi module (NodeMCU), read the universal identification (UID) of NFC and UHF RFID tags. The data are then forwarded to a cloud server via Internet of Things (IoT) and are viewable on smartphones using Blynk mobile application via IoT. To realize the optimal antenna design, simulations were carried out using CST Studio Suite. Prototype antennas were subsequently fabricated and integrated into the system board for IoT-linked near- and far-field communication. The simulation and measured results are in good agreement. The NFC reader antenna resonates at 13.56 MHz, and the dual band UHF/2.45 GHz RFID reader antenna achieves the 920–925 MHz and microwave (MW) bands with high isolation. The novelty of the proposed integrated NFC and UHF RFID antenna scheme lies in the use of cloud technology to store real-time and archival data, in place of traditional servers. The integrated antenna scheme could achieve the NFC, UHF, and MW frequency bands, rendering it ideal for IoT applications.

Seamless exploitation of cell‐phone antennas for near‐field WPT by a frequency‐diplexing approach

This paper introduces a novel solution for portable devices to exploit their existing communication antennas for bi-directional near-field wireless re-charging, without compromising their far-field properties. To demonstrate the concept, the radio-frequencies (RF) 900/1800 MHz and 433 MHz are adopted for the far-field communication and for the near-field wireless recharging, respectively. First, a pair of faced, dual-band, printed monopoles is characterized as a two-port network over the bands of interest at several distances. Then, each antenna is fed by a frequency-selective three-port network, designed to simultaneously ensure data communication at the higher frequencies and wireless re-charging at the lower one. In this way, the combined far-field and near-field operations of the resulting four-port network can be optimized. A proof-of-concept prototype has been characterized, showing ports isolation higher than 20 dB and RF-to-RF power transfer efficiency between 15% and 40% for variable faced antennas distance. When a rectifier is connected to the receiving power port, the measured RF-to-dc link efficiency varies between 9% and 20%, with portable devices located 1 and 2 centimeters apart, and the transmitted power is 10 dBm. The simultaneous high frequency communication is verified with slightly reduced performance.

Graphene nanoribbon antenna modeling based on MoM-GEC method for electromagnetic nanocommunications in the terahertz range

In this paper, we present a graphene nanoribbon (GNR)-based terahertz antenna array modeling using the MoM-GEC method (the moments method combined with the generalized equivalent circuit). The quantum mechanical conductivity of graphene is used to introduce the graphene’s effect in the mathematical formulation. The GNR is excited by a gap source with unit voltage localized in its center. The antenna structure is shielded in a rectangular waveguide with electric boundary walls. The proposed formulation is firstly validated and it yields efficient and accurate solutions. The obtained input impedance, current density distribution, and radiated electric field are presented to discuss the antenna performance in cases of single and antennas array. It is demonstrated that all results verify the boundary conditions and behave correctly corresponding to the physical laws. Furthermore, we showed that the antenna array leads to enhance the far-field communications for lower distances compared to conventional antenna.

Radio Frequency Identification Upon Near Field Communication and Far Field Communication For Next Generation Wireless Network Infrastructures

The electromagnetic field that outlines the RFID antenna can be divided up into two portions – Near-field and Far-field. Near Field Communication (NFC) and Far-Field communication (FFC) both are the most emerging wireless short-range communication technologies, both are based on existing standards of the Radio Frequency Identification (RFID) network framework. In collaboration with NFC-efficient next generation smartphones it authorizes automatic application frameworks for contact less connections, in different exceptional utilities for future generation smartphone payment and over-the air ticketing. The principle aim of current study is to explain basic characteristics and benefits of the wireless short- range technologies like (RFID, NFC, and FFC) and analogy between them to classify modes of operation and to present various illustrations. NFC mechanism, applications and FFC with possible future or Next Generation scenarios will be analyzed. Finally, this study provides the fundamental security concerns; challenges and present conflicts will be investigated in order to achieve the efficiency in Next Generation Network Infrastructures.

Wearable textile antennas

Owing to the rapid progress in fabrication technologies of conductive fibrous materials and the increasing demand for wireless communications in smart clothing systems, the potential application of wearable textile antennas in this field continues to increase. This article reviews a variety of wearable textile antennas in order to provide background information and application ideas for designing such antennas. The various materials used in the construction of wearable textile antennas, their fabrication methods, as well as the antenna types and their application fields are summarised. Owing to the high conductivity of metals, various metal composite yarns (MCYs) and fabrics have been used in the production of textile antennas. For inductively coupled near-field communication within smart clothing systems, woven or embroidered multiturn loop antennas are suggested. For far-field communication, a variety of broadband textile antennas were developed to counterbalance the detuning caused by the presence of a human body. Embroidered-folded dipole array antennas, metal-coated fabric patched bowtie and spiral antennas, a microstrip patch antenna array and a coplanar antenna made of metal-coated fabric patches and a ground plane, are the antennas that cover a broad spectrum and thus are capable of operating on the body.

Sex recognition in surface and cave dwelling male Atlantic mollies Poecilia mexicana (Poeciliidae, Teleostei)

Abstract Animals colonizing lightless subterranean habitats can no longer rely on visual signals to find mating partners. In the present study, we investigated the ability of males to recognize females in two surface and a cave dwelling population of a livebearing fish, Poecilia mexicana. In surface populations males discriminated between sexes with visual plus non-visual cues available and with visual stimuli only. In the cave form the ability to discriminate with solely visual stimuli is lacking. In all three populations, males did not recognize females in darkness (infrared observations), suggesting that sex recognition via far-field communication is lacking in surface and cave dwelling P.mexicana. Different preferences in large and small males to stay near a female or a male stimulus fish probably reflect differences concerning a trade-off between sexual and aggressive behaviour.