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    Signal Detection and Channel Estimation in OTFS
    NAIKOTI Ashwitha, CHOCKALINGAM Ananthanarayanan
    ZTE Communications    2021, 19 (4): 16-33.   DOI: 10.12142/ZTECOM.202104003
    Abstract253)   HTML8)    PDF (2749KB)(494)       Save

    Orthogonal time frequency space (OTFS) modulation is a recently proposed modulation scheme that exhibits robust performance in high-Doppler environments. It is a two-dimensional modulation scheme where information symbols are multiplexed in the delay-Doppler (DD) domain. Also, the channel is viewed in the DD domain where the channel response is sparse and time-invariant for a long time. This simplifies channel estimation in the DD domain. This paper presents an overview of the state-of-the-art approaches in OTFS signal detection and DD channel estimation. We classify the signal detection approaches into three categories, namely, low-complexity linear detection, approximate maximum a posteriori (MAP) detection, and deep neural network (DNN) based detection. Similarly, we classify the DD channel estimation approaches into three categories, namely, separate pilot approach, embedded pilot approach, and superimposed pilot approach. We compile and present an overview of some of the key algorithms under these categories and illustrate their performance and complexity attributes.

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    Payload Encoding Representation from Transformer for Encrypted Traffic Classification
    HE Hongye, YANG Zhiguo, CHEN Xiangning
    ZTE Communications    2021, 19 (4): 90-97.   DOI: 10.12142/ZTECOM.202104010
    Abstract173)   HTML23)    PDF (965KB)(209)       Save

    Traffic identification becomes more important, yet more challenging as related encryption techniques are rapidly developing nowadays. Unlike recent deep learning methods that apply image processing to solve such encrypted traffic problems, in this paper, we propose a method named Payload Encoding Representation from Transformer (PERT) to perform automatic traffic feature extraction using a state-of-the-art dynamic word embedding technique. By implementing traffic classification experiments on a public encrypted traffic data set and our captured Android HTTPS traffic, we prove the proposed method can achieve an obvious better effectiveness than other compared baselines. To the best of our knowledge, this is the first time the encrypted traffic classification with the dynamic word embedding has been addressed.

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    Recent Developments of Transmissive Reconfigurable Intelligent Surfaces: A Review
    TANG Junwen, XU Shenheng, YANG Fan, LI Maokun
    ZTE Communications    2022, 20 (1): 21-27.   DOI: 10.12142/ZTECOM.202201004
    Abstract145)   HTML12)    PDF (1869KB)(257)       Save

    Reconfigurable intelligent surface (RIS) is considered as one of the key technologies for the next-generation mobile communication systems. The transmissive RIS is able to achieve dynamic beamforming capability while transmitting an in-band RF signal through its aperture, and has promising prospects in various practical application scenarios. This paper reviews some of the latest developments of the transmissive RIS. The approaches for transmissive RIS designs are classified and described briefly. Numerous designs with different phase resolutions, such as 1-bit, 2-bit or continuous 360° phase shifts, are presented, with detailed discussions on their operating mechanisms and transmission performances. The design solutions for various transmissive RIS elements are summarized and compared.

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    A Survey on Low Complexity Detectors for OTFS Systems
    ZHANG Zhengquan, LIU Heng, WANG Qianli, FAN Pingzhi
    ZTE Communications    2021, 19 (4): 3-15.   DOI: 10.12142/ZTECOM.202104002
    Abstract135)   HTML11)    PDF (1427KB)(263)       Save

    The newly emerging orthogonal time frequency space (OTFS) modulation can obtain delay-Doppler diversity gain to significantly improve the system performance in high mobility wireless communication scenarios such as vehicle-to-everything (V2X), high-speed railway and unmanned aerial vehicles (UAV), by employing inverse symplectic finite Fourier transform (ISFFT) and symplectic finite Fourier transform (SFFT). However, OTFS modulation will dramatically increase system complexity, especially at the receiver side. Thus, designing low complexity OTFS receiver is a key issue for OTFS modulation to be adopted by new-generation wireless communication systems. In this paper, we review low complexity OTFS detectors and provide some insights on future researches. We firstly present the OTFS system model and basic principles, followed by an overview of OTFS detector structures, classifications and comparative discussion. We also survey the principles of OTFS detection algorithms. Furthermore, we discuss the design of hybrid OTFS and orthogonal frequency division multiplexing (OFDM) detectors in single user and multi-user multi-waveform communication systems. Finally, we address the main challenges in designing low complexity OTFS detectors and identify some future research directions.

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    Dual‑Polarized RIS‑Based STBC Transmission with Polarization Coupling Analysis
    ZHOU Mingyong, CHEN Xiangyu, TANG Wankai, KE Jun Chen, JIN Shi, CHENG Qiang, CUI Tie Jun
    ZTE Communications    2022, 20 (1): 63-75.   DOI: 10.12142/ZTECOM.202201009
    Abstract131)   HTML18)    PDF (1409KB)(225)       Save

    The rapid development of the reconfigurable intelligent surface (RIS) technology has given rise to a new paradigm of wireless transmitters. At present, most research works on RIS-based transmitters focus on single-polarized RISs. In this paper, we propose a dual-polarized RIS-based transmitter, which realizes 4-transmit space-time block coding (STBC) transmission by properly partitioning RIS’s unit cells and utilizing the degree of freedom of polarization. The proposed scheme is evaluated through a prototype system that utilizes a fabricated dual-polarized phase-adjustable RIS. In particular, the polarization coupling phenomenon in each unit cell of the employed dual-polarized RIS is modeled and analyzed. The experimental results are in good agreement with the theoretical modeling and analysis results, and an initial research effort is made on characterizing the polarization coupling property in the dual-polarized RIS.

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    Recent Progress in Research and Development of Reconfigurable Intelligent Surface
    YUAN Yifei, GU Qi, WANG Anna, WU Dan, LI Ya
    ZTE Communications    2022, 20 (1): 3-13.   DOI: 10.12142/ZTECOM.202201002
    Abstract125)   HTML21)    PDF (2269KB)(325)       Save

    We aim to provide a comprehensive overview of the progress in research and development of the reconfigurable intelligent surface (RIS) over the last 2–3 years in this paper, especially when the RIS is used as relays in next-generation mobile networks. Major areas of research in academia are outlined, including fundamental performance, channel estimation, joint optimization with antenna precoding at base stations, propagation channel modeling and meta-material devices of RIS elements. Development in industry is surveyed from the aspects of performance potentials and issues, realistic joint optimization algorithms, control mechanisms, field trials and related activities in standardization development organizations (SDOs). Our views on how to carry out the engineering-aspect study on RIS for 6G systems are also presented, which cover the realistic performance, the comparison with other topological improvements, approaches for channel modeling, factors for designing control mechanisms and the timeline for RIS standardization.

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    General Introduction of Non-Terrestrial Networks for New Radio
    HAN Jiren, GAO Yin
    ZTE Communications    2022, 20 (S1): 72-78.   DOI: 10.12142/ZTECOM.2022S1010
    Abstract125)   HTML11)    PDF (1266KB)(87)       Save

    In the new radio (NR) access technology, non-terrestrial networks (NTN) are introduced to meet the requirement of anywhere and anytime connections from the world market. With the introduction of NTN, the NR system is able to offer the wide-area coverage and ensure the service availability for users. In this paper, the general aspects of NTN are introduced, including the NTN architecture overview, the impact of NTN on next-generation radio access network (NG-RAN) interface functions, mobility scenarios and other NTN related issues. The current progress in 3GPP Release 17 is also provided.

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    Message Passing Based Detection for Orthogonal Time Frequency Space Modulation
    YUAN Zhengdao, LIU Fei, GUO Qinghua, WANG Zhongyong
    ZTE Communications    2021, 19 (4): 34-44.   DOI: 10.12142/ZTECOM.202104004
    Abstract119)   HTML5)    PDF (2103KB)(171)       Save

    The orthogonal time frequency space (OTFS) modulation has emerged as a promising modulation scheme for wireless communications in high-mobility scenarios. An efficient detector is of paramount importance to harvesting the time and frequency diversities promised by OTFS. Recently, some message passing based detectors have been developed by exploiting the features of the OTFS channel matrices. In this paper, we provide an overview of some recent message passing based OTFS detectors, compare their performance, and shed some light on potential research on the design of message passing based OTFS receivers.

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    End-to-End Chinese Entity Recognition Based on BERT-BiLSTM-ATT-CRF
    LI Daiyi, TU Yaofeng, ZHOU Xiangsheng, ZHANG Yangming, MA Zongmin
    ZTE Communications    2022, 20 (S1): 27-35.   DOI: 10.12142/ZTECOM.2022S1005
    Abstract109)   HTML10)    PDF (436KB)(93)       Save

    Traditional named entity recognition methods need professional domain knowledge and a large amount of human participation to extract features, as well as the Chinese named entity recognition method based on a neural network model, which brings the problem that vector representation is too singular in the process of character vector representation. To solve the above problem, we propose a Chinese named entity recognition method based on the BERT-BiLSTM-ATT-CRF model. Firstly, we use the bidirectional encoder representations from transformers (BERT) pre-training language model to obtain the semantic vector of the word according to the context information of the word; Secondly, the word vectors trained by BERT are input into the bidirectional long-term and short-term memory network embedded with attention mechanism (BiLSTM-ATT) to capture the most important semantic information in the sentence; Finally, the conditional random field (CRF) is used to learn the dependence between adjacent tags to obtain the global optimal sentence level tag sequence. The experimental results show that the proposed model achieves state-of-the-art performance on both Microsoft Research Asia (MSRA) corpus and people’s daily corpus, with F1 values of 94.77% and 95.97% respectively.

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    SVM for Constellation Shaped 8QAM PON System
    LI Zhongya, CHEN Rui, HUANG Xingang, ZHANG Junwen, NIU Wenqing, LU Qiuyi, CHI Nan
    ZTE Communications    2022, 20 (S1): 64-71.   DOI: 10.12142/ZTECOM.2022S1009
    Abstract107)   HTML1)    PDF (3357KB)(37)       Save

    Nonlinearity impairments and distortions have been bothering the bandwidth constrained passive optical network (PON) system for a long time and limiting the development of capacity in the PON system. Unlike other works concentrating on the exploration of the complex equalization algorithm, we investigate the potential of constellation shaping joint support vector machine (SVM) classification scheme. At the transmitter side, the 8 quadrature amplitude modulation (8QAM) constellation is shaped into three designs to mitigate the influence of noise and distortions in the PON channel. On the receiver side, simple multi-class linear SVM classifiers are utilized to replace complex equalization methods. Simulation results show that with the bandwidth of 25 GHz and overall bitrate of 50 Gbit/s, at 10 dBm input optical power of a 20 km standard single mode fiber (SSMF), and under a hard-decision forward error correction (FEC) threshold, transmission can be realized by employing Circular (4, 4) shaped 8QAM joint SVM classifier at the maximal power budget of 37.5 dB.

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    Some Observations and Thoughts about Reconfigurable Intelligent Surface Application for 5G Evolution and 6G
    HOU Xiaolin, LI Xiang, WANG Xin, CHEN Lan, SUYAMA Satoshi
    ZTE Communications    2022, 20 (1): 14-20.   DOI: 10.12142/ZTECOM.202201003
    Abstract103)   HTML15)    PDF (1684KB)(168)       Save

    Reconfigurable intelligent surface (RIS) is one of the hottest research topics for 5G evolution and 6G. It is expected that RIS can improve the system capacity and coverage with low cost and power consumption. This paper first discusses typical applications of RIS for 5G evolution and 6G, including RIS-aided smart channels and RIS-aided mega multiple-input multiple-output (MIMO). Then, several observations from RIS trials and system-level simulations are presented, especially those on the deployment strategy and the potential performance gain of RIS for coverage enhancement. The near-field effect and a two-step dynamic RIS beamforming method are also discussed. Finally, we summarize the challenges and opportunities of the RIS technology for 5G evolution and 6G, including hardware design, system and channel modeling, algorithm design and optimization, and standardization. We also suggest a step-by-step commercialization strategy as a conclusion.

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    Study on Security of 5G and Satellite Converged Communication Network
    YAN Xincheng, TENG Huiyun, PING Li, JIANG Zhihong, ZHOU Na
    ZTE Communications    2021, 19 (4): 79-89.   DOI: 10.12142/ZTECOM.202104009
    Abstract89)   HTML7)    PDF (1924KB)(76)       Save

    The 5G and satellite converged communication network (5G SCCN) is an important component of the integration of satellite-terrestrial networks, the national science, and technology major projects towards 2030. Security is the key to ensuring its operation, but at present, the research in this area has just started in our country. Based on the network characteristics and security risks, we propose the security architecture of the 5G SCCN and systematically sort out the key protection technologies and improvement directions. In particular, unique thinking on the security of lightweight data communication and design reference for the 5G SCCN network architecture is presented. It is expected to provide a piece of reference for the follow-up 5G SCCN security technology research, standard evolution, and industrialization.

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    Editorial: Special Topic on Federated Learning for IoT and Edge Computing
    ZTE Communications    2022, 20 (3): 1-2.   DOI: 10.12142/ZTECOM.202203001
    Abstract83)   HTML2)    PDF (481KB)(56)       Save
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    OTFS Enabled NOMA for MMTC Systems over LEO Satellite
    MA Yiyan, MA Guoyu, WANG Ning, ZHONG Zhangdui, AI Bo
    ZTE Communications    2021, 19 (4): 63-70.   DOI: 10.12142/ZTECOM.202104007
    Abstract76)   HTML3)    PDF (528KB)(158)       Save

    As a complement of terrestrial networks, non-terrestrial networks (NTN) have advantages of wide-area coverage and service continuity. The NTN is potential to play an important role in the 5G new radio (NR) and beyond. To enable the massive machine type communications (mMTC), the low earth orbit (LEO) satellite is preferred due to its lower transmission delay and path loss. However, the LEO satellite may generate notable Doppler shifts to degrade the system performance. Recently, orthogonal time frequency space (OTFS) modulation has been proposed. It provides the opportunity to allocate delay Doppler (DD) domain resources, which is promising for mitigating the effect of high mobility. Besides, as the LEO satellite constellation systems such as Starlink are thriving, the space spectrum resources have become increasingly scarce. Therefore, non-orthogonal multiple access (NOMA) is considered as a candidate technology to realize mMTC with limited spectrum resources. In this paper, the application of OTFS enabled NOMA for mMTC over the LEO satellite is investigated. The LEO satellite based mMTC system and the OTFS-NOMA schemes are described. Subsequently, the challenges of applying OTFS and NOMA into LEO satellite mMTC systems are discussed. Finally, the potential technologies for the systems are investigated.

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    Programmable Metasurface for Simultaneously Wireless Information and Power Transfer System
    CHANG Mingyang, HAN Jiaqi, MA Xiangjin, XUE Hao, WU Xiaonan, LI Long, CUI Tiejun
    ZTE Communications    2022, 20 (2): 48-62.   DOI: 10.12142/ZTECOM.202202008
    Abstract74)   HTML2)    PDF (5135KB)(61)       Save

    Implementing self-sustainable wireless communication systems is urgent and challenging for 5G and 6G technologies. In this paper, we elaborate on a system solution using the programmable metasurface (PMS) for simultaneous wireless information and power transfers (SWIPT), offering an optimized wireless energy management network. Both transmitting and receiving sides of the proposed solution are presented in detail. On the transmitting side, employing the wireless power transfer (WPT) technique, we present versatile power conveying strategies for near-field or far-field targets, single or multiple targets, and equal or unequal power targets. On the receiving side, utilizing the wireless energy harvesting (WEH) technique, we report our work on multi-functional rectifying metasurfaces that collect the wirelessly transmitted energy and the ambient energy. More importantly, a numerical model based on the plane-wave angular spectrum method is investigated to accurately calculate the radiation fields of PMS in the Fresnel and Fraunhofer regions. With this model, the efficiencies of WPT between the transmitter and the receiver are analyzed. Finally, future research directions are discussed, and integrated PMS for wireless information and wireless power is outlined.

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    Markovian Cascaded Channel Estimation for RIS Aided Massive MIMO Using 1‑Bit ADCs and Oversampling
    SHAO Zhichao, YAN Wenjing, YUAN Xiaojun
    ZTE Communications    2022, 20 (1): 48-56.   DOI: 10.12142/ZTECOM.202201007
    Abstract70)   HTML8)    PDF (1115KB)(123)       Save

    A reconfigurable intelligent surface (RIS) aided massive multiple-input multiple-output (MIMO) system is considered, where the base station employs a large antenna array with low-cost and low-power 1-bit analog-to-digital converters (ADCs). To compensate for the performance loss caused by the coarse quantization, oversampling is applied at the receiver. The main challenge for the acquisition of cascaded channel state information in such a system is to handle the distortion caused by the 1-bit quantization and the sample correlation caused by oversampling. In this work, Bussgang decomposition is applied to deal with the coarse quantization, and a Markov chain is developed to characterize the banded structure of the oversampling filter. An approximate message-passing based algorithm is proposed for the estimation of the cascaded channels. Simulation results demonstrate that our proposed 1-bit systems with oversampling can approach the 2-bit systems in terms of the mean square error performance while the former consumes much less power at the receiver.

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    Derivative-Based Envelope Design Technique for Wideband Envelope Tracking Power Amplifier with Digital Predistortion
    YI Xueya, CHEN Jixin, CHEN Peng, NING Dongfang, YU Chao
    ZTE Communications    2022, 20 (S1): 22-26.   DOI: 10.12142/ZTECOM.2022S1004
    Abstract67)   HTML10)    PDF (878KB)(95)       Save

    A novel envelope design for an envelope tracking (ET) power amplifier (PA) based on its derivatives is proposed, which can trade well off between bandwidth reduction and tracking accuracy. This paper theoretically analyzes how to choose an envelope design that can track the original envelope closely and reduce its bandwidth, and then demonstrates an example to validate this idea. The generalized memory polynomial (GMP) model is applied to compensate for the nonlinearity of ET PA with the proposed envelope design. Experiments are carried out on an ET system that is operated with the center frequency of 3.5 GHz and excited by a 20 MHz LTE signal, which show that the proposed envelope design can make a good trade-off between envelope bandwidth and efficiency, and satisfactory linearization performance can be realized.

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    RIS: Spatial‑Wideband Effect Analysis and Off‑Grid Channel Estimation
    JIAN Mengnan, ZHANG Nan, CHEN Yijian
    ZTE Communications    2022, 20 (1): 57-62.   DOI: 10.12142/ZTECOM.202201008
    Abstract65)   HTML6)    PDF (1069KB)(92)       Save

    As a critical candidate technology for 5G-advanced and 6G, reconfigurable intelligent surfaces (RIS) have received extensive attention from academia and industry. RIS has the promising features of passiveness, reconfigurable ability, and low cost. RIS channel estimation faces the challenges of high matrix dimension, passive estimation, and spatial-wideband effect. In this article, we analyze the impact of the spatial-wideband effect on the RIS channel to account for the propagation delay across RIS elements and estimate sparse channel parameters such as angle and gain through a super-resolution compressive sensing (CS) algorithm. The simulation results explore the influence of the spatial-wideband effect on the RIS channel and verify the effectiveness of the proposed algorithm.

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    Design of Raptor-Like Rate Compatible SC-LDPC Codes
    SHI Xiangyi, HAN Tongzhou, TIAN Hai, ZHAO Danfeng
    ZTE Communications    2022, 20 (S1): 16-21.   DOI: 10.12142/ZTECOM.2022S1003
    Abstract61)   HTML170)    PDF (1213KB)(52)       Save

    This paper proposes a family of raptor-like rate-compatible spatially coupled low-density parity-check (RL-RC-SC-LDPC) codes from RL-RC-LDPC block codes. There are two important keys. One is the performance of the base matrix. RL-LDPC codes have been adopted in the technical specification of 5G new radio (5G-NR). We use the 5G NR LDPC code as the base matrix. The other is the edge coupling design. In this regard, we have designed a rate-compatible coupling algorithm, which can improve performance under multiple code rates. The constructed RL-RC-SC-LDPC code property requires a large coupling length L and thus we improved the reciprocal channel approximation (RCA) algorithm and proposed a sliding window RCA algorithm. It can provide lower complexity and latency than RCA algorithm. The code family shows improved thresholds close to the Shannon limit and finite-length performance compared with 5G NR LDPC codes for the additive white Gaussian noise (AWGN) channel.

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    Coded Orthogonal Time Frequency Space Modulation
    LIU Mengmeng, LI Shuangyang, ZHANG Chunqiong, WANG Boyu, BAI Baoming
    ZTE Communications    2021, 19 (4): 54-62.   DOI: 10.12142/ZTECOM.202104006
    Abstract56)   HTML6)    PDF (1327KB)(118)       Save

    Orthogonal time frequency space (OTFS) modulation is a novel two-dimensional modulation scheme for high-Doppler fading scenarios, which is implemented in the delay-Doppler (DD) domain. In time and frequency selective channels, OTFS modulation is more robust than the popular orthogonal frequency division multiplexing (OFDM) modulation technique. To further improve transmission reliability, some channel coding schemes are used in the OTFS modulation system. In this paper, the coded OTFS modulation system is considered and introduced in detail. Furthermore, the performance of the uncoded/coded OTFS system and OFDM system is analyzed with different relative speeds, modulation schemes, and iterations. Simulation results show that the OTFS system has the potential of full diversity gain and better robustness under high mobility scenarios.

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    Resource Allocation for Two‑Tier RIS‑Assisted Heterogeneous NOMA Networks
    XU Yongjun, YANG Zhaohui, HUANG Chongwen, YUEN Chau, GUI Guan
    ZTE Communications    2022, 20 (1): 36-47.   DOI: 10.12142/ZTECOM.202201006
    Abstract54)   HTML1)    PDF (1761KB)(122)       Save

    Reconfigurable intelligent surface (RIS) as a promising technology has been proposed to change weak communication environments. However, most of the current resource allocation (RA) schemes have focused on RIS-assisted homogeneous networks, and there is still no open works about RA schemes of RIS-assisted heterogeneous networks (HetNets). In this paper, we design an RA scheme for a RIS-assisted HetNet with non-orthogonal multiple access to improve spectrum efficiency and transmission rates. In particular, we jointly optimize the transmit power of the small-cell base station and the phase-shift matrix of the RIS to maximize the sum rates of all small-cell users, subject to the unit modulus constraint, the minimum signal-to-interference-plus-noise ratio constraint, and the cross-tier interference constraint for protecting communication quality of microcell users. An efficient suboptimal RA scheme is proposed based on the alternating iteration approach, and successive convex approximation and logarithmic transformation approach. Simulation results verify the effectiveness of the proposed scheme in terms of data rates.

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    IRS‑Enabled Spectrum Sharing: Interference Modeling, Channel Estimation and Robust Passive Beamforming
    GUAN Xinrong, WU Qingqing
    ZTE Communications    2022, 20 (1): 28-35.   DOI: 10.12142/ZTECOM.202201005
    Abstract52)   HTML4)    PDF (1134KB)(86)       Save

    Intelligent reflecting surface (IRS), with its unique capability of smartly reconfiguring wireless channels, provides a new solution to improving spectrum efficiency, reducing energy consumption and saving deployment/hardware cost for future wireless networks. In this paper, IRS-enabled spectrum sharing is investigated, from the perspectives of interference modeling, efficient channel estimation and robust passive beamforming design. Specifically, we first characterize the interference in a spectrum sharing system consisting of a single primary user (PU) pair and a single secondary user (SU) pair, and extend it to the large-scale network by leveraging the Poisson point process (PPP). Then, we propose an efficient channel estimation framework based on decoupling the cascaded IRS channels. Moreover, the tradeoff between spectrum efficiency and energy efficiency is derived from the view of channel estimation accuracy. Finally, we discuss the robust passive beamforming design in presence of imperfect channel estimation and nonideal/discrete phase shifts. It is hoped that this paper provides useful guidance for unlocking the full potential of IRS for achieving efficient spectrum sharing for future wireless networks.

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    Orthogonal Time Frequency Space Modulation in Multiple-Antenna Systems
    WANG Dong, WANG Fanggang, LI Xiran, YUAN Pu, JIANG Dajie
    ZTE Communications    2021, 19 (4): 71-78.   DOI: 10.12142/ZTECOM.202104008
    Abstract52)   HTML3)    PDF (1729KB)(169)       Save

    The application of the orthogonal time frequency space (OTFS) modulation in multiple-antenna systems is investigated. The diversity and/or the multiplexing gain can be achieved by deploying various multiple-antenna techniques, and thus the reliability and/or the spectral efficiency are improved correspondingly. We provide two classes of OTFS-based multiple-antenna approaches for both the open-loop and the closed-loop systems. Specifically, in the open-loop system, a transmitting diversity approach, which resembles the space-time coding technique, is proposed by allocating the information symbols appropriately in the delay-Doppler domain. In the closed-loop system, we adopt the Tomlinson-Harashima precoding in our derived delay-Doppler equivalent transmission model. Numerical evaluations demonstrate the advantages of applying the multiple-antenna techniques to the OTFS. At last, several challenges and opportunities are presented.

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    An Improved Parasitic Parameter Extraction Method for InP HEMT
    DUAN Lanyan, LU Hongliang, QI Junjun, ZHANG Yuming, ZHANG Yimen
    ZTE Communications    2022, 20 (S1): 1-6.   DOI: 10.12142/ZTECOM.2022S1001
    Abstract51)   HTML180)    PDF (2023KB)(85)       Save

    An improved parasitic parameter extraction method for InP high electron mobility transistor (HEMT) is presented. Parasitic parameter extraction is the first step of model parameter extraction and its accuracy has a great impact on the subsequent internal parameter extraction. It is necessary to accurately determine and effectively eliminate the parasitic effect, so as to avoid the error propagation to the internal circuit parameters. In this paper, in order to obtain higher accuracy of parasitic parameters, parasitic parameters are extracted based on traditional analytical method and optimization algorithm to obtain the best parasitic parameters. The validity of the proposed parasitic parameter extraction method is verified with excellent agreement between the measured and modeled S-parameters up to 40 GHz for InP HEMT. In 0.1–40 GHz InP HEMT, the average relative error of the optimization algorithm is about 9% higher than that of the analysis method, which verifies the validity of the parasitic parameter extraction method. The extraction of parasitic parameters not only provides a foundation for the high-precision extraction of small signal intrinsic parameters of HEMT devices, but also lays a foundation for the high-precision extraction of equivalent circuit model parameters of large signal and noise signals of HEMT devices.

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    High-Power Simultaneous Wireless Information and Power Transfer: Injection-Locked Magnetron Technology
    YANG Bo, MITANI Tomohiko, SHINOHARA Naoki, ZHANG Huaiqing
    ZTE Communications    2022, 20 (2): 3-12.   DOI: 10.12142/ZTECOM.202202002
    Abstract51)   HTML19)    PDF (4645KB)(68)       Save

    Applications using simultaneous wireless information and power transfer (SWIPT) have increased significantly. Wireless communication technologies can be combined with the Internet of Things to develop many innovative applications using SWIPT, which is mainly based on wireless energy harvesting from electromagnetic waves used in communications. Wireless power transfer that uses magnetrons has been developed for communication technologies. Injection-locked magnetrons that can be used to facilitate high-power SWIPT for several devices are reviewed in this paper. This new technology is expected to pave the way for promoting the application of SWIPT in a wide range of fields.

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    Metric Learning for Semantic‑Based Clothes Retrieval
    YANG Bo, GUO Caili, LI Zheng
    ZTE Communications    2022, 20 (1): 76-82.   DOI: 10.12142/ZTECOM.202201010
    Abstract50)   HTML6)    PDF (1951KB)(80)       Save

    Existing clothes retrieval methods mostly adopt binary supervision in metric learning. For each iteration, only the clothes belonging to the same instance are positive samples, and all other clothes are “indistinguishable” negative samples, which causes the following problem. The relevance between the query and candidates is only treated as relevant or irrelevant, which makes the model difficult to learn the continuous semantic similarities between clothes. Clothes that do not belong to the same instance are completely considered irrelevant and are uniformly pushed away from the query by an equal margin in the embedding space, which is not consistent with the ideal retrieval results. Motivated by this, we propose a novel method called semantic-based clothes retrieval (SCR). In SCR, we measure the semantic similarities between clothes and design a new adaptive loss based on these similarities. The margin in the proposed adaptive loss can vary with different semantic similarities between the anchor and negative samples. In this way, more coherent embedding space can be learned, where candidates with higher semantic similarities are mapped closer to the query than those with lower ones. We use Recall@K and normalized Discounted Cumulative Gain (nDCG) as evaluation metrics to conduct experiments on the DeepFashion dataset and have achieved better performance.

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    Multi-Cell Uplink Interference Management: A Distributed Power Control Method
    HU Huimin, LIU Yuan, GE Yiyang, WEI Ning, XIONG Ke
    ZTE Communications    2022, 20 (S1): 56-63.   DOI: 10.12142/ZTECOM.2022S1008
    Abstract47)   HTML7)    PDF (1395KB)(186)       Save

    This paper investigates a multi-cell uplink network, where the orthogonal frequency division multiplexing (OFDM) protocol is considered to mitigate the intra-cell interference. An optimization problem is formulated to maximize the user supporting ratio for the uplink multi-cell system by optimizing the transmit power. This paper adopts the user supporting ratio as the main performance metric. Our goal is to improve the user supporting ratio of each cell. Since the formulated optimization problem is non-convex, it cannot be solved by using traditional convex-based optimization methods. Thus, a distributed method with low complexity and a small amount of multi-cell interaction is proposed. Numerical results show that a notable performance gain achieved by our proposed scheme compared with the traditional one is without inter-cell interaction.

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    Multi-Task Learning with Dynamic Splitting for Open-Set Wireless Signal Recognition
    XU Yujie, ZHAO Qingchen, XU Xiaodong, QIN Xiaowei, CHEN Jianqiang
    ZTE Communications    2022, 20 (S1): 44-56.   DOI: 10.12142/ZTECOM.2022S1007
    Abstract46)   HTML5)    PDF (1899KB)(66)       Save

    Open-set recognition (OSR) is a realistic problem in wireless signal recognition, which means that during the inference phase there may appear unknown classes not seen in the training phase. The method of intra-class splitting (ICS) that splits samples of known classes to imitate unknown classes has achieved great performance. However, this approach relies too much on the predefined splitting ratio and may face huge performance degradation in new environment. In this paper, we train a multi-task learning (MTL) network based on the characteristics of wireless signals to improve the performance in new scenes. Besides, we provide a dynamic method to decide the splitting ratio per class to get more precise outer samples. To be specific, we make perturbations to the sample from the center of one class toward its adversarial direction and the change point of confidence scores during this process is used as the splitting threshold. We conduct several experiments on one wireless signal dataset collected at 2.4 GHz ISM band by LimeSDR and one open modulation recognition dataset, and the analytical results demonstrate the effectiveness of the proposed method.

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    Performance of LDPC Coded OTFS Systems over High Mobility Channels
    ZHANG Chong, XING Wang, YUAN Jinhong, ZHOU Yiqing
    ZTE Communications    2021, 19 (4): 45-53.   DOI: 10.12142/ZTECOM.202104005
    Abstract46)   HTML6)    PDF (1808KB)(123)       Save

    The upcoming 6G wireless networks have to provide reliable communications in high-mobility scenarios at high carrier frequencies. However, high-mobility or high carrier frequencies will bring severe inter-carrier interference (ICI) to conventional orthogonal frequency-division multiplexing (OFDM) modulation. Orthogonal time frequency space (OTFS) modulation is a recently developing multi-carrier transmission scheme for wireless communications in high-mobility environments. This paper evaluates the performance of coded OTFS systems. In particular, we consider 5G low density parity check (LDPC) codes for OTFS systems based on 5G OFDM frame structures over high mobility channels. We show the performance of the OTFS systems with 5G LDPC codes when sum-product detection algorithm and iterative detection and decoding are employed. We also illustrate the effect of channel estimation error on the performance of the LDPC coded OTFS systems.

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    Editorial: Special Topic on Reconfigurable Intelligent Surface (RIS)
    ZTE Communications    2022, 20 (1): 1-2.   DOI: 10.12142/ZTECOM.202201001
    Abstract42)   HTML23)    PDF (455KB)(77)       Save
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    Editorial: Special Topic on OTFS Modulation for 6G and Future High Mobility Communications
    YUAN Jinhong, FAN Pingzhi, BAI Baoming, AI Bo
    ZTE Communications    2021, 19 (4): 1-2.   DOI: 10.12142/ZTECOM.202104001
    Abstract40)   HTML8)    PDF (365KB)(181)       Save
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    A Survey of Federated Learning on Non-IID Data
    HAN Xuming, GAO Minghan, WANG Limin, HE Zaobo, WANG Yanze
    ZTE Communications    2022, 20 (3): 17-26.   DOI: 10.12142/ZTECOM.202203003
    Abstract37)   HTML5)    PDF (3213KB)(28)       Save

    Federated learning (FL) is a machine learning paradigm for data silos and privacy protection,which aims to organize multiple clients for training global machine learning models without exposing data to all parties. However, when dealing with non-independently identically distributed (non-IID) client data, FL cannot obtain more satisfactory results than centrally trained machine learning and even fails to match the accuracy of the local model obtained by client training alone. To analyze and address the above issues, we survey the state-of-the-art methods in the literature related to FL on non-IID data. On this basis, a motivation-based taxonomy, which classifies these methods into two categories, including heterogeneity reducing strategies and adaptability enhancing strategies, is proposed. Moreover, the core ideas and main challenges of these methods are analyzed. Finally, we envision several promising research directions that have not been thoroughly studied, in hope of promoting research in related fields to a certain extent.

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    Truly Grant-Free Technologies and Protocols for 6G
    MA Yihua, YUAN Zhifeng, LI Weimin, LI Zhigang
    ZTE Communications    2021, 19 (4): 105-110.   DOI: 10.12142/ZTECOM.202104012
    Abstract34)   HTML3)    PDF (808KB)(106)       Save

    The further integration of telecommunications and industry has been considerable and is expected to bring significant benefits to society and economics in 6G. It also forms some evolution trends for next-generation communication systems, including further rises in machine-type communications (MTC), uplink-dominated systems, and decentralized structures. However, the existing access protocols are not friendly to these trends. This paper analyzes the problems of existing access protocols and provides novel access technologies to solve them. These technologies include contention-based non-orthogonal multiple access (NOMA), data features, enhanced pilot design and successive interference cancellation (SIC) of diversity. With these key enablers, truly grant-free access can be realized, and some potential modifications of protocols are then analyzed. Finally, this paper uses massive and critical scenarios in digital transformations to show the great necessity of introducing novel access technologies into future communication protocols.

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    Editorial: Special Topic on Simultaneous Wireless Information and Power Transfer: Technology and Practice
    ZTE Communications    2022, 20 (2): 1-2.   DOI: 10.12142/ZTECOM.202202001
    Abstract34)   HTML11)    PDF (386KB)(34)       Save
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    MSRA-Fed: A Communication-Efficient Federated Learning Method Based on Model Split and Representation Aggregate
    LIU Qinbo, JIN Zhihao, WANG Jiabo, LIU Yang, LUO Wenjian
    ZTE Communications    2022, 20 (3): 35-42.   DOI: 10.12142/ZTECOM.202203005
    Abstract31)   HTML7)    PDF (843KB)(18)       Save

    Recent years have witnessed a spurt of progress in federated learning, which can coordinate multi-participation model training while protecting the data privacy of participants. However, low communication efficiency is a bottleneck when deploying federated learning to edge computing and IoT devices due to the need to transmit a huge number of parameters during co-training. In this paper, we verify that the outputs of the last hidden layer can record the characteristics of training data. Accordingly, we propose a communication-efficient strategy based on model split and representation aggregate. Specifically, we make the client upload the outputs of the last hidden layer instead of all model parameters when participating in the aggregation, and the server distributes gradients according to the global information to revise local models. Empirical evidence from experiments verifies that our method can complete training by uploading less than one-tenth of model parameters, while preserving the usability of the model.

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    An Overview of SWIPT Circuits and Systems
    TORRES Ricardo, MATOS Diogo, PEREIRA Felisberto, CORREIA Ricardo, CARVALHO Nuno Borges
    ZTE Communications    2022, 20 (2): 13-18.   DOI: 10.12142/ZTECOM.202202003
    Abstract31)   HTML3)    PDF (2482KB)(20)       Save

    From a circuit implementation perspective, this paper presents a brief overview of simultaneous wireless information and power transmission (SWIPT). By using zero-power batteryless wireless sensors, SWIPT mixes wireless power transmission with wireless communications to allow the truly practical implementation of the Internet of Things as well as many other applications. In this paper, technical backgrounds, problem formation, state-of-the-art solutions, circuit implementation examples, and system integrations of SWIPT are presented.

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    Intelligent Antenna Attitude Parameters Measurement Based on Deep Learning SSD Model
    FAN Guotian, WANG Zhibin
    ZTE Communications    2022, 20 (S1): 36-43.   DOI: 10.12142/ZTECOM.2022S1006
    Abstract30)   HTML2)    PDF (1312KB)(9)       Save

    Due to the consideration of safety, non-contact measurement methods are becoming more acceptable. However, massive measurement will bring high labor-cost and low working efficiency. To address these limitations, this paper introduces a deep learning model for the antenna attitude parameter measurement, which can be divided into an antenna location phase and a calculation phase of the attitude parameter. In the first phase, a single shot multibox detector (SSD) is applied to automatically recognize and discover the antenna from pictures taken by drones. In the second phase, the located antennas’ feature lines are extracted and their attitude parameters are then calculated mathematically. Experiments show that the proposed algorithms outperform existing related works in efficiency and accuracy, and therefore can be effectively used in engineering applications.

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    Symbiotic Radio Systems: Detection and Performance Analysis
    CUI Ziqi, WANG Gongpu, WANG Zhigang, AI Bo, XIAO Huahua
    ZTE Communications    2022, 20 (3): 93-98.   DOI: 10.12142/ZTECOM.202203012
    Abstract29)   HTML5)    PDF (3975KB)(18)       Save

    Symbiotic radio (SR) is an emerging green technology for the Internet of Things (IoT). One key challenge of the SR systems is to design efficient and low-complexity detectors, which is the focus of this paper. We first drive the mathematical expression of the optimal maximum-likelihood (ML) detector, and then propose a suboptimal iterative detector with low complexity. Finally, we show through numerical results that our proposed detector can obtain near-optimal bit error rate (BER) performance at a low computational cost.

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    AI-Based Optimization of Handover Strategy in Non-Terrestrial Networks
    ZHANG Chenchen, ZHANG Nan, CAO Wei, TIAN Kaibo, YANG Zhen
    ZTE Communications    2021, 19 (4): 98-104.   DOI: 10.12142/ZTECOM.202104011
    Abstract28)   HTML3)    PDF (674KB)(83)       Save

    Complicated radio resource management, e.g., handover condition, will trouble the user in non-terrestrial networks due to the impact of high mobility and hierarchical layouts which co-exist with terrestrial networks or various platforms at different altitudes. It is necessary to optimize the handover strategy to reduce the signaling overhead and improve the service continuity. In this paper, a new handover strategy is proposed based on the convolutional neural network. Firstly, the handover process is modeled as a directed graph. Suppose a user knows its future signal strength, then he/she can search for the best handover strategy based on the graph. Secondly, a convolutional neural network is used to extract the underlying regularity of the best handover strategies of different users, based on which any user can make near-optimal handover decisions according to its historical signal strength. Numerical simulation shows that the proposed handover strategy can efficiently reduce the handover number while ensuring the signal strength.

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    Auxiliary Fault Location on Commercial Equipment Based on Supervised Machine Learning
    ZHAO Zipiao, ZHAO Yongli, YAN Boyuan, WANG Dajiang
    ZTE Communications    2022, 20 (S1): 7-15.   DOI: 10.12142/ZTECOM.2022S1002
    Abstract27)   HTML167)    PDF (3209KB)(40)       Save

    As the fundamental infrastructure of the Internet, the optical network carries a great amount of Internet traffic. There would be great financial losses if some faults happen. Therefore, fault location is very important for the operation and maintenance in optical networks. Due to complex relationships among each network element in topology level, each board in network element level, and each component in board level, the concrete fault location is hard for traditional method. In recent years, machine learning, especially deep learning, has been applied to many complex problems, because machine learning can find potential non-linear mapping from some inputs to the output. In this paper, we introduce supervised machine learning to propose a complete process for fault location. Firstly, we use data preprocessing, data annotation, and data augmentation in order to process original collected data to build a high-quality dataset. Then, two machine learning algorithms (convolutional neural networks and deep neural networks) are applied on the dataset. The evaluation on commercial optical networks shows that this process helps improve the quality of dataset, and two algorithms perform well on fault location.

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