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Partial intersection sphere decoding with weighted voting for sparse rotated V-OFDM systems

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Science China(Information Sciences) 2018年第2期61卷 77-89页

作者： Qi FENG xiang-gen xia Naitong ZHANG School of Electronic Science and Engineering Nanjing University College of Information Engineering Shenzhen University Department of Electrical and Computer Engineering University of Delaware School of Electronics and Information Engineering Harbin Institute of Technology

Vector orthogonal frequency division multiplexing(V-OFDM) is a general system that builds a bridge between OFDM and single-carrier frequency domain equalization in terms of intersymbol interference level and receiver complexity. In this paper, we focus on a rotated V-OFDM system over a broadband sparse channel owing to its large time delay spread and fewer nonzero taps. In order to collect the multipath diversity,a simple rotation matrix is designed, independent of the number of subchannels at the transmitter. For the rotated V-OFDM receiver, a partial intersection sphere decoding with weighted voting method is proposed by exploiting the sparse nature of the multipath channel. The proposed receiver chooses the transmitted vector from the set with the maximum likelihood estimation generated using the partial intersection sphere decoding method. For an extreme case, such as when a candidate set is empty, which usually occurs at a low signal-to-noise ratio(SNR), an efficient weighted voting system is used to estimate the transmitted vectors symbol-by-symbol. Simulation results indicate that the proposed receiver improves the symbol error rate performance with reduced complexity, especially for low SNR scenarios.

关键词： vector orthogonal frequency division multiplexing sparse multipath channel partial intersection sphere decoding weighted voting diversity order

Performance analysis of MIMO systems with arbitrary number transmit antenna selection and OSTBC in the presence of imperfect CSI

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Science China(Information Sciences) 2016年第8期59卷 164-179页

作者： xiangbin YU xiang-gen xia Shuhung LEUNG Department of Electronic Engineering Nanjing University of Aeronautics and Astronautics Department of Electrical and Computer Engineering University of Delaware Department of Electronic Engineering City University of Hong Kong State Key Laboratory of Millimeter Waves City University of Hong Kong

In this paper, the performance analysis of MIMO systems with arbitrary number transmit antenna selection(TAS) and orthogonal space-time block coding(STBC) in Rayleigh fading channels for imperfect channel state information(CSI) is presented. For the performance analysis, the moment generating function of the system effective SNR as well as its upper and lower bounds are derived. Then, accurate and approximate expressions of bit error rate(BER) of MIMO-TAS-STBC with MPSK and MQAM are further derived. Using the approximate BER formula and imperfect CSI, an adaptive antenna selection scheme is developed for minimizing the BER. The diversity gain and coding gain are analyzed at high SNR. The results indicate that the MIMOTAS-STBC for imperfect CSI can only achieve partial diversity order K N and the coding gain is affected by K,N, code rate, modulation pattern, and channel correlation coefficients, when K transmit antennas are selected and N receive antennas are used. Simulation results show that the theoretical analysis matches the simulation result well, and the approximate expressions are close to the accurate ones but have a lower complexity.

关键词： MIMO arbitrary number antenna selection imperfect CSI space-time block coding diversity gain bit error rate

Variation of a signal in Schwarzschild spacetime

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Science China(Information Sciences) 2019年第8期62卷 172-191页

作者： Huan LIU xiang-gen xia Ran TAO School of Information and Electronics Beijing Institute of Technology Department of Electrical and Computer Engineering University of Delaware

In this paper, the variation of a signal in Schwarzschild spacetime is studied and a general equation for frequency shift parameter(FSP) is presented. The FSP is found to depend on the gravitationally modified Doppler effects and the gravitational effects of observers. In addition, the time rates of a transmitter and receiver may differ. When the FSP is a function of the receiver time, the FSP contributed through the gravitational effect(GFSP) or the gravitationally modified Doppler effect(GMDFSP) may convert a bandlimited signal into a non-bandlimited signal. Using the general equation, the FSP as a function of receiver time is calculated in three scenarios:(a) a spaceship leaving a star at constant velocity communicating with a transmitter at a fixed position;(b) a spaceship moving around a star with different conic trajectories communicating with a transmitter at a fixed position; and(c) a signal transmitted from a fixed position in a star system to a receiver following an elliptic trajectory in another star system. The studied stars are a Sun-like star, a white dwarf, and a neutron star. The theory is illustrated with numerical examples.

关键词： deep space communications general relativity Schwarzschild spacetime bandlimited signal gravitationally modified Doppler effect

CP-based MIMO OFDM radar IRCI free range reconstruction using real orthogonal designs

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Science China(Information Sciences) 2017年第2期60卷 40-48页

作者： Tianxian ZHANG xiang-gen xia Lingjiang KONG The School of Electronic Engineering University of Electronic Science and Technology of China The Department of Electrical and Computer Engineering University of Delaware

In this paper, we propose a range reconstruction method for a frequency-band shared multipleinput multiple-output(MIMO) orthogonal frequency-division multiplexing(OFDM) radar with sufficient cyclic prefix(CP) by using real orthogonal designs. Compared with the application of complex orthogonal designs in our previous work, the application of real orthogonal designs can significantly reduce the number of the all-zero-valued pulses in a coherent processing interval(CPI) for each transmitter and increase the efficiency of radar transmitters. Meanwhile, it still maintains the advantages of full spatial diversity without inter-range-cell interference(IRCI). We also apply the rate-1 real orthogonal designs for different numbers of transmitters and pulses for range reconstruction without any idleness of radar transmitters. Simulation results are presented to illustrate the performances of the OFDM pulse design and the CP-based MIMO OFDM radar using real orthogonal designs.

关键词： cyclic prefix(CP) inter-range-cell interference(IRCI) multiple-input multiple-output(MIMO) radar real orthogonal designs orthogonal frequency division multiplexing(OFDM) pulse

UAV Communications with Millimeter-Wave Beamforming:Potentials,Scenarios,and Challenges

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China Communications 2020年第9期17卷 147-166页

作者： Zhenyu xiao Lipeng Zhu xiang-gen xia School of Electronic and Information Engineering Beihang UniversityBeijing 100191China Department of Electrical and Computer Engineering University of DelawareNewarkDE 19716USA

Unmanned aerial vehicle(UAV)has been widely used in many fields and is arousing global *** the resolution of the equipped sensors in the UAV becomes higher and the tasks become more complicated,much higher data rate and longer communication range are required in the foreseeable *** the millimeter-wave(mm Wave)band can provide more abundant frequency resources than the microwave band,much higher achievable rate can be guaranteed to support UAV services such as video surveillance,hotspot coverage,and emergency communications,*** flexible mm Wave beamforming can be used to overcome the high path loss caused by the long propagation *** this paper,we study three typical application scenarios for mm Wave-UAV communications,namely communication terminal,access point,and backbone *** present several key enabling techniques for UAV communications,including beam tracking,multi-beam forming,joint Tx/Rx beam alignment,and full-duplex relay *** show the coupling relation between mm Wave beamforming and UAV positioning for mm Wave-UAV ***,we summarize the challenges and research directions of mm Wave-UAV communications in detail.

关键词： unmanned aerial vehicle(UAV) millimeter-wave(mmWave)communications beamforming beam tracking deployment

维普期刊数据库

Robust MMSE precoding for massive MIMO transmission with hardware mismatch

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Science China(Information Sciences) 2018年第4期61卷 173-186页

作者： Yan CHEN Xiqi GAO xiang-gen xia Li YOU National Mobile Communication Research Laboratory Southeast University Department of Electrical and Computer Engineering University of Delaware

Due to hardware mismatch, the channel reciprocity of time-division duplex massive multipleinput multiple-output system is impaired. Under this condition, there exist several different approaches for base station(BS) to obtain downlink(DL) channel information based on the minimum mean-square-error(MMSE) estimation method. In this paper, we show that with the hardware mismatch parameters BS can obtain the same DL channel information via these different approaches. As the obtained DL channel information is usually imperfect, we propose a precoding technique based on the criterion that minimizes the mean-square-error(MSE) of signal detection at the user terminals(UTs). The proposed precoding is robust to the channel estimation error and significantly improves the system performance compared to the conventional regularized zero-forcing precoding. Furthermore, we derive an asymptotic approximation of the ergodic sum rate for the proposed precoding using the large dimensional random matrix theory, which is tight as the number of antennas both at the BS and UT approach infinity with a fixed non-zero and finite ratio. This approximation can provide a reliable sum rate prediction at a much lower computation cost than Monte Carlo simulations. Simulation results show that the approximation is accurate even for a realistic system dimension.

关键词： robust precoding massive MIMO hardware mismatch channel estimation large dimensional RMT

Underwater sonar target imaging via compressed sensing with M sequences

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Science China Earth Sciences 2016年第12期59卷 111-120页

作者： Huichen YAN Jia XU xiang-gen xia Xudong ZHANG Teng LONG Department of Electronic Engineering Tsinghua University School of Information and Electronics Beijing Institute of Technology Department of Electrical and Computer Engineering University of Delaware

Due to the low sound propagation speed, the tradeoff between high azimuth resolution and wide imaging swath has severely limited the application of sonar underwater target imaging. However, based on compressed sensing(CS) technique, it is feasible to image targets with merely one pulse and thus avoid the above tradeoff. To investigate the possible waveforms for CS-based underwater imaging, the deterministic M sequences widely used in sonar applications are introduced in this paper. By analyzing the compressive matrix constructed from M sequences, the coherence parameter and the restricted isometry property(RIP) of the matrix are derived. Also, the feasibility and advances of M sequence are demonstrated by being compared with the existing Alltop sequence in underwater CS imaging framework. Finally, the results of numerical simulations and a real experiment are provided to reveal the effectiveness of the proposed signal.

关键词： sonar high-resolution imaging compressed sensing M sequence coherence parameter restricted isometry property

维普期刊数据库

MMSE channel estimation for two-port demodulation reference signals in new radio

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Science China(Information Sciences) 2021年第6期64卷 247-248页

作者： Dejin KONG xiang-gen xia Pei LIU Qibiao ZHU School of Electronic and Electrical Engineering Wuhan Textile University Department of Electrical and Computer Engineering University of Delaware School of Information Engineering Wuhan University of Technology School of Information Engineering Nanchang University

Dear editor,Orthogonal frequency division multiplexing(OFDM) has been adopted in new radio(NR) [1], and multiple-port demodulation reference signal(DMRS) has been designed to achieve channel estimation. In NR, two ports of DMRS share the same frequency resource elements(RE) by employing an orthogonal code comprising cyclic shift phase. In general, channel estimation can be achieved via the classical discrete Fourier transform(DFT) scheme [2, 3] as channels for the two ports of DMRS can be separated in the time domain via the DFT scheme.

关键词： MMSE channel estimation for two-port demodulation reference signals in new radio

Special focus on distributed storage coding

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Science China(Information Sciences) 2018年第10期61卷 5-6页

作者： xiaohu TANG Shu-Tao xia Chao TIAN Qin HUANG xiang-gen xia Southwest Jiaotong University Tsinghua University Texas A&M University Beihang University University of Delaware

Due to their low cost and feasibility, distributed storage systems (DSSs) have been widely applied in large data centers, peer-to-peer storage systems such as Ocean Store, Total Recall, and DHash++, and for storage in wireless networks. However, as the storage scale dramatically increases, reliability becomes a critical issue in applications involving the DSSs. The most efficient way to guarantee reliability is to employ erasure coding. However, it brings many new challenges that need to be addressed in terms of scalable deployment, security, efficiency, new devices, and so on.

关键词： Special focus on distributed storage coding PIR