推荐 | 《ZTE Communications》面向6G的近场通信与传感专题

Near-Field Communication and Sensing Towards 6G

Special Topic on Near-Field Communication and Sensing Towards 6G

Editorial

WEI Guo, CHEN Li, ZHAO Yajun

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

LIU Mengyu, ZHANG Yang, JIN Yasheng, ZHI Kangda, PAN Cunhua

XL-MIMO and 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 the 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 communication.

Link Budget and Enhanced Communication Distancefor Ambient Internet of Things

YANG Yibing, LIU Ming, XU Rongtao, WANG Gongpu, GONG Wei

Backscatter communication, a key technology for ambient IoT, will play an important role in connecting everything for B5G and 6G systems. One open challenge for backscatter communications is that the signals suffer a round-trip path loss so that the communication distance is short, which motivates our present work. In this paper, we first calculate communication distance upper bounds for both uplink and downlink by measuring the tag sensitivity and reflection coefficient. It is found that the activation voltage of the envelope detection diode of the downlink tag is the main factor limiting the backscatter communication distance. Based on this analysis, we then propose to implement an LNA module before the envelope detection at the tag to enhance the incident signal strength. Our experimental results on the hardware platform show that our method can increase the downlink communication range by nearly 20 m.

Impacts of Model Mismatch and Array Scale on Channel Estimation for XL-HRIS-Aided Systems

LU Zhizheng, HAN Yu, JIN Shi

XL-HRIS, an improved version of the RIS, can receive the incident signal and enhance communication performance. However, as the RIS size increases, the phase variations of the received signal across the whole array are non-negligible in the near-field region, and the channel model mismatch, which will decrease the estimation accuracy, must be considered. In this paper, the LB of the estimated parameter is studied and the impacts of the distance and SNR on LB are then evaluated. Moreover, the impacts of the array scale on LB and SE are also studied. Simulation results verify that even in extremely large-scale array systems with infinite SNR, channel model mismatch can still limit estimation accuracy. However, this impact decreases with increasing distance.

Degree of Freedom Analysis for Holographic MIMO Based on a Mutual-Coupling-Compliant Channel Model

SUN Yunqi, JIAN Mengnan, YANG Jun, ZHAO Yajun, CHEN Yijian

DOF is a key indicator for spatial multiplexing layers of a wireless channel. Traditionally, the channel of a MIMO half-wavelength dipole array has a DOF that equals the antenna number. However, recent studies suggest that the DOF could be less than the antenna number when strong mutual coupling is considered. We utilize a mutual-coupling-compliant channel model to investigate the DOF of the HMIMO channel and give an upper bound of the DOF with strong mutual coupling. Our numerical simulations demonstrate that a dense array can support more DOF per unit aperture as compared to a half-wavelength MIMO system.

Near-Field Beam Training for Holographic MIMO Communications: Typical Methods, Challenges and Future Directions 

SHEN Jiayu, YANG Jun, ZHU Chen, DENG Zhiji, HUANG Chongwen

HMIMO has become an emerging technology for achieving ultra-high frequency spectral efficiency and spatial resolution in future wireless systems. The increasing antenna aperture leads to a more significant characterization of the spherical wavefront in near-field communications in HMIMO scenarios. Beam training as a key technique for wireless communication is worth exploring in this near-field scenario. Compared with the widely researched far-field beam training, the increased dimensionality of the search space for near-field beam training poses a challenge to the complexity and accuracy of the proposed algorithm. In this paper, the authors introduce several typical near-field beam training methods: exhaustive beam training, hierarchical beam training, and multi-beam training, which includes equal interval multi-beam training and hash multi-beam training. The performances of these methods are compared through simulation analysis, and their effectiveness is verified on the hardware testbed as well. Additionally, we provide application scenarios, research challenges, and potential future research directions for near-field beam training.

Near-Field Wireless Power Transfer, Sensing and Communication with Bessel Beams

CAO Xinghan, YIN Huarui, YOU Changsheng

The Bessel beam, characterized by its unique non-diffracting properties, holds promising applications. In this paper, we provide a detailed introduction and investigation into the theory and research of the Bessel beam, with a special focus on its generation and applications in the near-field region. We provide an introduction to the concepts, properties, and foundational theories of the Bessel beam. Additionally, the current study on generating Bessel beams and their applications is categorized and discussed, and potential research challenges are proposed in this paper. This review serves as a solid foundation for researchers to understand the concept of the Bessel beam and explore its potential applications.

Review

Recent Advances in Video Coding for Machines Standard and Technologies 

ZHANG Qiang, MEI Junjun, GUAN Tao, SUN Zhewen, ZHANG Zixiang, YU Li 

In recent years, owing to the advancement of intelligent devices, a substantial volume of videos are provided to machines for analysis instead of humans. To improve the performance of video compression for machine vision analysis tasks, a VCM standard working group was established to promote standardization procedures. In this paper, we present recent advances of video coding for machine standards, and give a comprehensive introduction about the use cases, requirements, evaluation framework and corresponding metrics of the VCM standard. Then we present the existing methods, introducing the existing proposals by category and the research progress of the latest VCM conference. Finally, we give conclusions.

RIS-Assisted Cell Free MIMO: A Survey

ZHAO Yaqiong, KE Hongqin, XU Wei, YE Xinquan, CHEN Yijian

CF MIMO is a promising technique to enable the vision of ubiquitous wireless connectivity for next-generation network communications. Compared to traditional co-located massive MIMO, CF MIMO allows geographically distributed APs to serve all users on the same time-frequency resource with spatial multiplexing techniques, resulting in better performance in terms of both spectral efficiency and coverage enhancement. However, the performance gain is achieved at the expense of deploying more APs with high cost and power consumption. To address this issue, the recently proposed RIS technique stands out with its unique advantages of low cost, low energy consumption and programmability. In this paper, we provide an overview of RIS-assisted CF MIMO and its interaction with advanced optimization designs and novel applications. Particularly, recent studies on typical performance metrics such as EE and SE are surveyed. Besides, the application of RIS-assisted CF MIMO techniques in various future communication systems is also envisioned. Additionally, we briefly discuss the technical challenges and open problems for this area to inspire research direction and fully exploit its potential in meeting the demands of future wireless communication systems.

Research on Multi-Core Processor Analysis for WCET Estimation 

LUO Haoran, HU Shuisong, WANG Wenyong, TANG Yuke, ZHOU Junwei

Real-time system timing analysis is crucial for estimating the WCET of a program. To achieve this, static or dynamic analysis methods are used, along with targeted modeling of the actual hardware system. This literature review focuses on calculating WCET for multi-core processors, providing an overview of traditional methods used for static and dynamic analysis and highlighting the major challenges that arise from different program execution scenarios on multi-core platforms. This paper outlines the strengths and weaknesses of current methodologies and offers insights into prospective areas of research for multi-core analysis. By presenting a comprehensive analysis of the current state of research on multi-core processor analysis for WCET estimation, this review aims to serve as a valuable resource for researchers and practitioners in the field.

Research Paper

Filter Design of Wireless Base Station Power Supply

LI Wei, GUO Wei, WANG Zhida

The design of EMI filters needs to fulfill the EMI standards. Designing a filter is a time-consuming process for new engineers as well as for experienced engineers. This paper measured and compared the noise spectrum of the wireless base station power prototype with and without the original filter. The ideal IL of the original filter is obtained by combining calculation and simulation. It is pointed out that the effect of the original filter is not good. Based on the improved insertion-loss method, the source impedance model of the prototype is established by combining measurement and theory. A procedure for designing EMI filters for switch power supply will be presented. The filter design procedure makes it possible to design filters quickly and easily. Finally, the proposed filter design method is proved to be effective by the EMI measurement of the wireless base station power supply prototype.

Real-Time 4-Mode MDM Transmission Using Commercial 400G OTN Transceivers and All-Fiber Mode Multiplexers

REN Fang, LI Yidan, YE Bing, LIU Jianguo, CHEN Weizhang

Weakly-coupled MDM technique is considered a promising candidate to enhance the capacity of an optical transmission system, in which mode multiplexers/demultiplexers with low insertion loss and modal crosstalk are the key components. In this paper, a low-modal-crosstalk 4-mode MMUX/MDEMUX for the weakly-coupled triple-ring-core few-mode fiber (TRC-FMF) is designed and fabricated with side-polishing processing. The measurement results show that a pair of MMUX/MDEMUX and 25 km weakly-coupled TRC-FMF MDM link achieve low modal crosstalk of lower than −17.5 dB and insertion loss of lower than 11.56 dB for all the four modes. Based on the TRC-FMF and all-fiber MMUX/MDEMUX, an experiment for 25 km real-time 4-mode 3-λ WDM-MDM transmission is conducted using commercial 400G OTN transceivers. The experimental results prove weakly-coupled MDM techniques facilitate a smooth upgrade of the optical transmission system.

WEI Guo, ZHAO Yajun, CHEN Li. Special Topic on Near-Field Communication and Sensing Towards 6G. ZTE Communications[J], 2024, 22(1): 1-2 DOI:10.12142/ZTECOM.202401001