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Impact of non-ideal UE hardware on cell-free massive MIMO network with centralized operation

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Science China(Information Sciences) 2024年第4期67卷 255-271页

作者： Ning LI Pingzhi FAN institute of mobile Communications Southwest Jiaotong University

This paper investigates the impact of non-ideal user equipment(UE) hardware on a cell-free(CF) massive MIMO(mMIMO) network with centralized operation under spatially correlated channels. The minimum mean-squared error(MMSE) estimator can be derived with the help of the generic non-ideal UE hardware model. It is demonstrated that even if the effective signal-to-noise ratio approaches infinity, pilot contamination and imperfect hardware can cause a non-zero estimation error floor. After that, a lower bound is determined for the ergodic uplink capacity of the centralized CF mMIMO network under non-ideal UE hardware. Moreover, the optimal receive combining vector is obtained to maximize the uplink spectral efficiency(SE). The maximum ratio(MR) and regularized zero-forcing(RZF) combining schemes are offered as alternatives in light of the computational complexity of the MMSE receiver. Comparing the RZF to the MMSE scheme under different levels of hardware impairments, our findings indicate that the RZF receiver suffers a negligible loss in total SE. For MR combining, a novel closed-form uplink achievable SE expression is obtained based on the MMSE estimator and the use-and-then-forget bounding technique. This expression gives vital insights into the achievable uplink performance with UE hardware impairments. Besides, for various hardware impairment factors, the impact of pilot sequence length on average sum SE is disclosed for different receive combining schemes. To increase the overall SE of the max-min fairness scheme, a heuristic fractional power control scheme with UE hardware impairments is developed, which can essentially avoid sacrificing the SE of other UEs while maximizing the SE of the unluckiest UE in the whole network. Finally,our theoretical performance analysis and power control algorithm are validated by simulation results, and fundamental design guidelines are provided for selecting hardware satisfying the practical UE requirements.

关键词： cell-free massive MIMO centralized operation spatially correlated channels hardware impairments channel estimation uplink spectral efficiency optimal receive combining pilot length design fractional power control

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Signal Clipping at Transmitter and Receiver of O-OFDM for VLC under Optical Power Constraint

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China Communications 2022年第6期19卷 154-168页

作者： Liang Xia Xiaoqian Wang Zhiwen Sun Zhitian Cheng Jing Jin Yifei Yuan Guangyi Liu Tao Jiang Yuhong Huang Future mobile Technology Lab China Mobile Research InstituteBeijing 100053China

Visible light communications(VLC)is considered as an effective supplement technology for next-generation(6G)communications due to its abundant spectrum,high power efficiency and easy *** orthogonal frequency division multiplexing(O-OFDM)is a common technology to obtain further *** this paper,two typical O-OFDM schemes direct current biased O-OFDM(DCO-OFDM)and asymmetrically clipped O-OFDM(ACO-OFDM)are analyzed in terms of signal clipping at both transmitter and receiver under the constraints of maximum optical power and non-negative optical *** effective electrical SNR models after signal clipping are proposed and verified by link *** a noise cancellation scheme is proposed based on received signal clipping and is proved to bring a significant gain for *** system simulation,we find that under a certain optical power limitation,most users can achieve above 4 Gbps in indoor scenario when modulation bandwidth of the light emit diode(LED)or laser diode(LD)is 1 ***,it can be expected that the throughput could reach tens Gbps when the LED/LD modulation bandwidth is increased and multiple LEDs/LDs are deployed.

关键词： 6G visible light communications optical orthogonal frequency division multiplexing clipping bit error rate throughput

A low-floor bit-mapping scheme for LDPC coded BICM for 5G and beyond systems

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Science China(Information Sciences) 2023年第10期66卷 263-277页

作者： Mingyang ZHU Ming JIANG Chunming ZHAO Lijie HU Xiaodong XU National mobile Communications Research Laboratory Southeast University Purple Mountain Laboratories China mobile Research institute

This paper proposes a low-floor bit-mapping(LFBM) scheme for bit-interleaved coded modulation(BICM) systems to meet more stringent quality of service requirements of 5G and beyond. For highefficiency transmissions, we consider the 5G low-density parity-check codes with high-order 2m-quadrature amplitude modulations(QAMs). The proposed LFBM scheme overcomes plenty of trapping sets induced by the bit interleaver, which focuses on the waterfall performance too aggressively. When the high-order QAM is used, the row-column interleaver specified by the 5G standard is such a bit interleaver. The LFBM scheme only optimizes the rule of mapping an m-bit tuple output by the row-column interleaver to a modulation symbol, rather than the entire bit interleaver. Therefore, the optimized bit mapper is actually an m-bit permutation module concatenated with the original bit interleaver employed in the current 5G BICM *** simulation results confirm that the LFBM scheme can lower the error floor of the 5G BICM system by approximately two orders of magnitude, while with negligible performance loss in the waterfall region.

关键词： bit-interleaved coded modulation low-density parity-check codes error floors bit mapping high-order modulation

Energy-efficiency-aware relay selection in distributed full duplex relay network with massive MIMO

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Science China(Information Sciences) 2017年第2期60卷 126-140页

作者： Yongzhi LI Cheng TAO Liu LIU Lingwen ZHANG institute of Broadband Wireless mobile Communications Beijing Jiaotong University National mobile Communications Research Laboratory Southeast University

This paper considers a distributed full duplex relay network where multiple sources simultaneously transmit their signals to multiple destinations via the cooperation of a set of relay stations(RSs). Each RS is assumed to be equipped with large antenna arrays while all sources and destinations only have a single *** assume the channels are Rician fading and the RSs use linear processing to process the signals with imperfect channel state information(CSI). We derive the closed-form expressions of the end-to-end achievable rates for the maximum-ratio combining/matched-filter(MRC/MF) and the zero-forcing(ZF) processing. These results are then used to pursue a detailed analysis of the power saving of the relay network. Then we study the energy-efficiency-aware relay selection strategy since the energy efficiency affects network lifetime in future wireless network. We propose a sub-optimal strategy with low complexity that only requires the statistical *** show that the energy efficiency of the system can be improved with optimal power allocation and our proposed strategy performs very close to the exhaustive search algorithm which is optimal.

关键词： relay network full duplex massive MIMO relay selection energy efficiency

Preparation of AZ91D magnesium alloy semi-solid billet by new strain induced melt activated method

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中国有色金属学会会刊：英文版 2006年第5期16卷 1080-1085页

作者：姜巨福罗守靖邹经湘 School of Materials Science and Engineering Harbin Institute of Technology Postdoctoral mobile Station of Mechanics Harbin Institute of TechnologyHarbin 150001China Postdoctoral mobile Station of Mechanics Harbin Institute of Technology

New strain induced melt activated (new SIMA) method for preparing AZ91D magnesium alloy semi-solid billet is introduced by applying equal channel angular extrusion into strain induced step in SIMA method, by which semi-solid billet with fine spheroidal grains and average grain size of 18 μm can be prepared. Furthermore, average grain size of semi-solid billet is reduced with increasing extrusion pass of AZ91D magnesium alloy obtained in ECAE process. By using semi-solid billet prepared by new SIMA, thixoforged magazine plates component with high mechanical properties such as yield strength of 201.4 MPa, ultimate tensile strength of 321.8 MPa and elongation of 15.3%, can be obtained.

关键词：等通道角挤压半固体坯料机械性能镁合金

AI-Enhanced Constellation Design for NOMA System: A Model Driven Method

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China Communications 2020年第11期17卷 100-110页

作者： Sen Wang Hanxiao Yu Yifei Yuan Guangyi Liu Zesong Fei Future mobile Technology Lab China Mobile Research InstituteBeijing 100053China Beijing institute of Technology Beijing 100081China

Grant-free Non-orthogonal Multiple Access(GF-NOMA)is a promising technology for massive access users and sporadic small-packet transmission for Beyond the 5th Generation mobile communication system(B5G)/the 6th Generation mobile communication system(6G).One of the key aspects in GF-NOMA system is the signature/constellation ***,due to the channel variation and random activation of users,conventional optimization approaches seem unsuitable for such complex *** this paper,as an initial attempt,we propose a human intelligence(HI)-guided artificial intelligence(AI)-enhanced signature/constellation design *** separate design of modulation and power allocation inspired by prior knowledge,the proposed deep neuron network(DNN)for NOMA signature/constellation design not only has smaller size of DNN and less training data,but also has stronger *** the last section,via simulations we demonstrate that in terms of bit error rate,the proposed scheme can achieve significant performance gain over the conventional NOMA schemes.

关键词： NOMA system DNN constellation design power allocation

Slicing capacity-centered mode selection and resource optimization for network-assisted full-duplex cell-free distributed massive MIMO systems

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Science China(Information Sciences) 2024年第1期67卷 203-220页

作者： Jie WANG Jiamin LI Pengcheng ZHU Dongming WANG Hongbiao ZHANG Yue HAO Bin SHENG National mobile Communications Research Laboratory Southeast University 2. Purple Mountain Laboratories China mobile Research institute

Network-assisted full-duplex(NAFD) cell-free distributed massive multiple-input multipleoutput(MIMO) systems enable uplink(UL) and downlink(DL) communications within the same timefrequency resources,which potentially reduce latency by avoiding the overhead of switching UL/DL ***,how to choose UL/DL modes remains an important factor affecting system *** the dramatic increase in the number of users and access points(APs),massive access brings significant overhead in the mode ***,the different quality of service(QoS) among users also makes the effective utilization of resources *** one of the most promising technologies in sixth-generation(6G),network slicing enables the adaptive configuration of limited UL/DL resources through the resource isolation assisted NAFD ***,we propose a slicing capacity-centered *** this scheme,APs are motivated by slicing requirements and associated slices to form different *** mode selection and resource allocation are performed within each subsystem to reduce overhead and improve resource *** implement this scheme efficiently,a double-layer deep reinforcement learning(DRL)mechanism is used to realize the joint optimization of mode selection and resource *** results show that the slicing capacity-centered scheme can effectively improve resource utilization and reduce overhead.

关键词： network-assisted full-duplex network slicing mode selection resource optimization deep reinforcement learning

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5G High Mobility Wireless Communications: Challenges and Solutions

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China Communications 2016年第S2期13卷 1-13页

作者： Pingzhi Fan Jing Zhao Chih-Lin I institute of mobile Communications School of Information Science and Technology Southwest Jiaotong University The Green Communication Research Center China Mobile Research Institute

The fifth generation(5G) network is expected to support significantly large amount of mobile data traffic and huge number of wireless connections,to achieve better spectrum- and energy-efficiency,as well as quality of service(QoS) in terms of delay,reliability and ***,the 5G network shall also incorporate high mobility requirements as an integral part,providing satisfactory service to users travelling at a speed up to 500 km/*** paper provides a survey of potential high mobility wireless communication(HMWC) techniques for 5G *** discussing the typical requirements and challenges of HMWC,key techniques to cope with the challenges are reviewed,including transmission techniques under the fast timevarying channels,network architecture with mobility support,and mobility ***,future research directions on 5G high mobility communications are given.

关键词： 5G high mobility wireless communications fast time-varying channel network architecture mobility management

Preparation and thixoforging of semisolid billet of AZ80 magnesium alloy

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Transactions of Nonferrous Metals Society of China 2010年第9期20卷 1731-1736页

作者：姜巨福王迎曲建俊杜之明罗守靖 School of Materials Science and Engineering Harbin Institute of Technology Postdoctoral mobile Station of Mechanical Engineering Harbin Institute of Technology School of Mechatronics Engineering Harbin Institute of Technology Postdoctoral mobile Station of Mechanics Harbin Institute of Technology

Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was *** results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic *** with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new *** process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and *** fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.

关键词： AZ80 magnesium alloy semi-solid forming thixoforging semisolid billet strain induced melt activation