Towards Near-Field Communications for 6G:Challenges and Opportunities

Extremely large-scale multiple-input multiple-output(XL-MIMO)and terahertz(THz)communications are pivotal candidate technologies for supporting the development of 6G mobile networks.However,these techniques invalidate the common assumptions of far-field plane waves and introduce many new properties.To accurately understand the performance of these new techniques,spherical wave modeling of near-field communications needs to be applied for future research.Hence,the investigation of near-field communication holds significant importance for the advancement of 6G,which brings many new and open research challenges in contrast to conventional far-field communication.In this paper,we first formulate a general model of the near-field channel and discuss the influence of spatial nonstationary properties on the near-field channel modeling.Subsequently,we discuss the challenges encountered in the near field in terms of beam training,localization,and transmission scheme design,respectively.Finally,we point out some promising research directions for near-field communications.

MmWave extra-large-scale MIMO based active user detection and channel estimation for high-speed railway communications

The current High-Speed Railway(HSR)communications increasingly fail to satisfy the massive access services of numerous user equipment brought by the increasing number of people traveling by HSRs.To this end,this paper investigates millimeter-Wave(mmWave)extra-large scale(XL)-MIMO-based massive Internet-of-Things(loT)access in near-field HSR communications,and proposes a block simultaneous orthogonal matching pursuit(B-SOMP)-based Active User Detection(AUD)and Channel Estimation(CE)scheme by exploiting the spatial block sparsity of the XLMIMO-based massive access channels.Specifically,we first model the uplink mmWave XL-MIMO channels,which exhibit the near-field propagation characteristics of electromagnetic signals and the spatial non-stationarity of mmWave XL-MIMO arrays.By exploiting the spatial block sparsity and common frequency-domain sparsity pattern of massive access channels,the joint AUD and CE problem can be then formulated as a Multiple Measurement Vectors Compressive Sensing(MIMV-CS)problem.Based on the designed sensing matrix,a B-SOMP algorithm is proposed to achieve joint AUD and CE.Finally,simulation results show that the proposed solution can obtain a better AUD and CE performance than the conventional CS-based scheme for massive IoT access in near-field HSR communications.

Web Services Invocation over Bluetooth

Over the last years, technology evolution is leading the way towards autonomous, ubiquitous and widespread interactions among small computing devices. To this aim, communication technologies that support dynamicity and mobility and work on inexpensive small devices have attracted much attention. The Bluetooth speci?cation particularly ?ts this idea, providing a free, versatile, and ?exible wireless network technology with low power consumption. On the other hand, as the degree of penetration of computational services has increased in everyday life, users’ habits have deeply changed, resulting into an increasing request for mobile and ubiquitous services. In a few years, most of the devices accessing the web services will be mobile. Therefore, we need solutions that encompass networking and application issues involved in realizing mobile and ubiquitous access to the services. In this paper, we analyze how Bluetooth can be used to design, develop, and deploy Web Services-based applications that run on mobile devices. We propose and evaluate a framework that allows the interaction with Web Services from mobile devices using Bluetooth as communication channel.

A Wireless Distributed Condition Monitoring System Based on Bluetooth Technology

Based on the discussion of bluetooth and network technology, this paper proposed an entire framework of a wireless distributed monitoring system by combining the characteristics of industry application. The feasibility of putting this kind of system in practice is discussed. The wireless distributed monitoring system can enhance the performance of condition monitoring more than the traditional one used now.

An efficient technique to retrieve information from a damaged near-field communication tag

Purpose-The purpose of this paper is to discuss a technique of restoring data from a broken/damaged near-field communication(NFC)tag whose coil is damaged and seems unrecoverable.Design/methodology/approach-This paper discusses a method to restore data from damaged NFC tags by designing a coil that matches the technical specification of NFC for restoring information.In this paper,an NFC tag with a broken antenna coil and its operational NFC chip is used for restoring data by making an external loop antenna for the same chip.Findings-If the NFC tag is damaged,the information stored on the tag can be lost and can cause serious inconvenience.This research provides an excellent mechanism for retrieving all the information accurately from a damaged NFC tag provided the NFC chip is not damaged.Research limitations/implications-One of the major limitations of this research is that the NFC chip remains intact without any damages.Data can only be recoverable if just the antenna of the NFC tag is damaged;any damage to the NFC chip would make it impossible for the data to be recoverable.Practical implications-The research is carried out with limited resources in an academic institute and hence cannot be compared to antenna designs of the industry.Furthermore,industry vendors are using aluminum to design the coil;however,in this study a copper coil is used for coil design since it is far less expensive than aluminum coil.Originality/value-NFC is a rather new short-range wireless technology and not much work is done in this field as far as antenna study is concerned.This study brings a technique to design a coil antenna for a damaged NFC tag to retrieve all the information without losing even a single bit of sensitive information.

BLE Mesh： A Practical Mesh Networking Development Framework for Public Safety Communications

Owing to advanced storage and communication capabilities today, smart devices have become the basic interface between individuals and their surrounding environment. In particular, massive devices connect to one other directly in a proximity area, thereby enabling abundant Proximity Services（Pro Se）, which can be classified into two categories： public safety communication and social discovery. However, two challenges impede the quick development and deployment of Pro Se applications. From the viewpoint of networking, no multi-hop connectivity functionality component can be directly operated on commercially off-the-shelf devices, and from the programming viewpoint, an easily reusable development framework is lacking for developers with minimal knowledge of the underlying communication technologies and connectivity. Considering these two issues, this paper makes a twofold contribution. First, a multi-hop mesh networking based on Bluetooth Low Energy（BLE） is implemented,in which a proactive routing mechanism with link-quality（i.e., received signal strength indication） assistance is designed. Second, a Pro Se development framework called BLE Mesh is designed and implemented, which can provide significant benefits for application developers, framework maintenance professionals, and end users. Rich application programming interfaces can help developers to build Pro Se apps easily and quickly. Dependency inversion principle and template method pattern allow modules in BLE Mesh to be loosely coupled and easy to maintain and update. Callback mechanism enables modules to work smoothly together and automation processes such as registration, node discovery, and messaging are employed to offer nearly zero-configuration for end users.Finally, based on the designed Pro Se development kit, a public safety communications app called Quote Send App is built to distribute emergency information in close area without Internet access. The process illustrates the easy usability of BLE Mesh to develop Pro Se apps.

An Extended Application form of Mobile Computing ── Augmented Reality

With the rapid developments of wireless communication and microelectronic technology, the bandwidth of wireless communication is becoming wider than ever, up to 100Gbps and the computer can be designed as small as a match with powerful computing and controlling capability. These rapid developments have extended the mobile computing. There are many application forms of mobile computing, such as mobile databases, mobile data management, wearable computing etc. A great branch of mobile computing, Augmented Reality (AR), which is the combination of mobile computing and wearable computers was discussed.

Focusing Ability Enhancement in Broadside Direction of Array:From UCA to UCCA

To meet the ever-increasing demand for the data rates of wireless communications,extremely large-scale antenna array(ELAA)has emerged as one of the candidate technologies for future 6G communications.The significantly increased number of antennas in ELAA gives rise to near-field communications,necessitating tailored beamforming techniques within the near-field regions to accommodate the spherical-wave propagation characteristics.Among various array geometries of ELAA,uniform circular array(UCA)has gained much attention for its distinct capability of maintaining uniform beam pattern across different azimuth angles.However,existing analysis of near-field UCA beamforming indicates that the near-field region severely declines in the broadside of UCA,where the system fails to benefit from near-field communications.To tackle this problem,the near-field beamforming technique of uniform concentric circular arrays(UCCAs)is investigated in this paper,which has the potential to enlarge the near-field region in the broadside direction.First,the analysis of beamforming gain in the 3D space with UCA and UCCA is provided.Then,the distinct beamforming characteristics that set UCCA apart from UCA are delineated,revealing the superiority of UCCA in extending the near-field region in broadside at the cost of slightly reduced near-field region in the coplane.Simulation results are provided to verify the effectiveness of the theoretical analysis of beamforming gain with UCCA and the enhanced focusing ability of UCCA in the broadside direction.

Multifunctional Semiconducting Fibers for Visual Detection of Sarin Gas

There is a growing need for protective instruments that can be used in extreme environments,including those encountered during exoplanet exploration,anti-terrorism activities,and in chemical plants.These instruments should have the ability to detect external threats visually and monitor internal physiological signals in real time for maximum safety.To address this need,multifunctional semiconducting fibers with visual detection ranging from yellow to red and near-field communication(NFC)capabilities have been developed for use in personal protective clothing.A composite conductive yarn with semiconducting fluorescent probe molecules is embroidered on the clothing,forming an NFC coil that allows for the visual monitoring of atmospheric safety through color changes.The fluorescence detection system was able to selectively detect diethyl chlorophosphate(DCP),a substitute for the toxic gas sarin,with a detection limit of 6.08 ppb,which is lower than the life-threatening concentration of sarin gas.Furthermore,an intelligent protective suit with the abovementioned dual functions was fabricated with good mechanical cycle stability and repeatability.Real-time physiological signals such as the temperature and humidity of the wearer could be read through the NFC conveniently.Such intelligent protective suits can quickly provide an early warning to the identified low-dose DCP and evaluate the health of wearer according to the changes in physiological signals.This study offers a smart,low-cost strategy for designing intelligent protective devices for extreme environments.

Public Bicycle Operating System Based on Space-Time Security and the Internet of Things

The bad behaviors of some users and the drawbacks of public bicycles have hindered the promotion of public bicycles. The current problems include low utilization rate, uneven distribution, high loss rate and insecure lock. However, there is few feasible research in this new field. To address these issues of public bicycles, we propose a public bicycle operating system（PBOS）. PBOS involves three key technologies： 1） To acquire a dynamic password and realize bicycle self-rescue, we devise an intelligent lock that utilizes the Internet of Things（IoT） to establish Bluetooth connection with user＇s mobile phone. 2） To avoid bicycle loss and improve the security of data transmission, we design a space-time security protocol to work between bicycle＇s intelligent lock, mobile app, and server. 3） To increase the average utilization rate and distribution, we present a cooperative game model for bicycle scheduling. Finally, we evaluate the performance and validate the theoretical properties of PBOS through extensive simulations.