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A low-latency list decoder for polar codes

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Science China(Information Sciences) 2018年第10期61卷 163-172页

作者： Qingyun XU Zhiwen PAN Nan LIU Xiaohu YOU national mobile communications research laboratory Southeast University

Successive cancellation(SC) is a low complexity serial decoding algorithm for polar codes, and successive cancellation list(SCL) can achieve excellent error-correcting performance. However, SCL decoder suffers from long decoding latency compared with belief propagation(BP) decoder. In this paper, a lowlatency list decoder whose latency performance can approach that of BP deocder is proposed. A prunable subtree recognizing scheme based on H-Matrix check is proposed by taking the reliability of frozen bits into account. Then, a latency-reduced list decoder based on the prunable constituent codes is *** results show that the decoding latency of proposed list scheme can be reduced significantly,especially for high signal noise ratio(SNR) region.

关键词： list decoder low latency polar codes successive cancellation

Multi-cell massive MIMO transmission with coordinated pilot reuse

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Science China(Technological Sciences) 2015年第12期58卷 2186-2194页

作者： ZHONG Wen YOU Li LIAN TengTeng GAO XiQi national mobile communications research laboratory Southeast University

In this paper, we propose a coordinated pilot reuse(CPR) approach to reduce the pilot overhead for multi-cell massive multi-input multi-output transmission. Unlike the conventional multi-cell pilot reuse approach in which pilots can only be reused among different cells, the proposed CPR approach allows pilots to be reused among both inter-cell and intra-cell user equipments, and thus, pilot overhead can be efficiently reduced. For spatially correlated Rayleigh fading channels, we first present a CPR-based channel estimation method and a low complexity pilot allocation algorithm. Because CPR might lead to additional pilot interference, we develop a statistically robust uplink receiver and downlink precoder that takes channel estimation errors into account. The proposed uplink receiver and downlink precoder are robust to channel state information inaccuracy, and thus, can guarantee a certain transmission performance. Monte-Carlo simulations illustrate the significant performance improvement in net spectral efficiency offered by the proposed CPR approach.

关键词： pilot overhead multi-cell massive MIMO coordinated pilot reuse robust transceiver net spectral efficiency

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Impacts of practical channel impairments on the downlink spectral efficiency of large-scale distributed antenna systems

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Science China(Information Sciences) 2019年第2期62卷 146-159页

作者： Jiamin LI Dongming WANG Pengcheng ZHU Xiaohu YOU national mobile communications research laboratory Southeast University

Channel impairments are major limiting factors in the performance of large-scale antenna systems. In this paper, we analyze the impacts of practical channel impairments caused by pilot contamination,Doppler shift, and phase noise on the downlink spectral efficiency of large-scale distributed antenna systems(L-DASs) with maximum ratio transmission(MRT) and zero-forcing(ZF) beamforming, in which per user power normalization is considered. Using a joint channel model that allows study of the simultaneous impacts of these channel impairments, we derive accurate and tractable closed-form approximations for the ergodic achievable downlink rate, thereby enabling spectral efficiency analysis of L-DASs and an efficient evaluation of the impacts of the channel impairments. It is shown that channel impairments reduce the downlink spectral efficiency and have a significant impact on ZF beamforming. The asymptotic user rate limit is also determined, from which we analyze the asymptotic performance of L-DASs with channel impairments. The analytical results show that MRT and ZF beamforming achieve the same asymptotic performance limit even with channel impairments. It is also found that the use of a large-scale antenna array at the base station sides can weaken the impacts of channel impairments.

关键词： Doppler shift phase noise large-scale distributed antenna systems spectral efficiency pilot contamination

Efficient co-channel interference suppression in MIMO-OFDM systems

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Science China(Information Sciences) 2015年第2期58卷 116-130页

作者： MENG Xin JIANG Bin GAO XiQi national mobile communications research laboratory Southeast University

In this paper, we investigate channel frequency response(CFR) matrix and interference-plus-noise covariance matrix(ICM) estimation in multiple-input multiple-output(MIMO) and orthogonal frequency division multiplexing(OFDM) systems to suppress co-channel interference at the receiver side. We employ least square criterion to perform the initial CFR estimation. Then we estimate the autocorrelation function of interference-plus-noise in the time domain, instead of estimating the ICM in the frequency domain *** autocorrelation function estimation has two steps. Firstly, we present the inherent relationship between the expectation of the sample autocorrelation function of the residual(SAFR) and the true autocorrelation function, which is actually a linear transformation. Based on this, we propose a compensating method. This compensation brings significant performance gains when the pilot OFDM symbol number is small. Secondly,since the compensated SAFR cannot be guaranteed to be an autocorrelation sequence(ACS), which will make the obtained ICM loss the positive semidefinite property, we utilize semidefinite programming(SDP) to find an ACS that is the nearest to the compensated SAFR. The SDP is solved in its dual form, which yields a significant reduced complexity. Finally the estimated ICM is reutilized to revise the CFR estimation. The estimated CFR and ICM show excellent interference suppression performances when being applied in an interference rejection combining receiver.

关键词： MIMO-OFDM channel estimation co-channel interference interference-plus-noise covariance ma-trix moving average autocorrelation sequence semidefinite programming interference rejection combining

A study of power allocation in multi-MRN aided multiuser networks

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Science China(Information Sciences) 2017年第2期60卷 64-73页

作者： Xiangyang WANG Xiaoteng GU Qifeng LI national mobile communications research laboratory Southeast University

It is promising that mobile relay nodes(MRNs), i.e., relays mounted on top of transportation vehicles, are deployed in future mobile communication systems in order to improve system performance. In this paper a multi-MRN aided multiuser system is studied. The system performance under direct transmission mode and MRN assisted transmission mode are compared with variable parameter of vehicle penetration loss(VPL). The mobile users are separated into two categories in which the direct transmission mode and the MRN assisted transmission mode are selected to transmit in downlink, respectively. A novel power allocation algorithm is proposed to increase the average system capacity under the constraint of total transmit power. The different power allocation schemes are applied for users in two categories to improve the system *** is demonstrated by simulation results that the proposed algorithm outperforms the average power allocation algorithm.

关键词： mobile relay nodes(MRN) vehicle penetration loss(VPL) transmission mode average system capacity power allocation

User scheduling for downlink FD-MIMO systems under Rician fading exploiting statistical CSI

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Science China(Information Sciences) 2018年第8期61卷 160-169页

作者： Xiao LI Tingting SUN Nana QIN Shi JIN Xiqi GAO national mobile communications research laboratory Southeast University

In this paper, we consider the user scheduling algorithm for downlink full-dimension multipleinput multiple-output(FD-MIMO) system under Rician fading channels. We assume that two-dimensional(2 D) large-scale antenna array is deployed at base station(BS). An approximation of user's signal-tointerference-plus-noise ratio(SINR) and a lower bound of user's average signal-to-leakage-plus-noise ratio(SLNR) are derived. Based on these, two user scheduling algorithms exploiting only statistical channel state information(CSI) are proposed. The proposed algorithms take both the achievable sum rate and fairness into account. Simulation results reveal that the proposed user scheduling algorithms can make good trade-off between the achievable rate and fairness.

关键词： scheduling FD-MIMO fairness Rician fading

Prophet model and Gaussian process regression based user traffic prediction in wireless networks

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Science China(Information Sciences) 2020年第4期63卷 207-214页

作者： Yu LI Ziang MA Zhiwen PAN Nan LIU Xiaohu YOU national mobile communications research laboratory Southeast University

User traffic prediction is an important topic for wireless network operators. A user traffic prediction method based on Prophet and Gaussian process regression is proposed in this paper. The proposed method first employs discrete wavelet transform to decompose the user traffic time series to high-frequency component and low-frequency component. The low-frequency component bears the long-range dependence of user network traffic, while the high-frequency component reveals the gusty and irregular fluctuations of user network traffic. Then Prophet model and Gaussian process regression are applied to predict the two components respectively based on the characteristics of the two components. Experimental results demonstrate that the proposed model outperforms the existing time series prediction method.

关键词： wireless networks traffic prediction prophet model Gaussian process regression

Upper bounds on the capacity for optical intensity channels with AWGN

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Science China(Information Sciences) 2017年第2期60卷 165-176页

作者： Yingying YU Zaichen ZHANG Liang WU Jian DANG national mobile communications research laboratory Southeast University

The channel capacity of the optical wireless communication(OWC) systems is still a problem that has not an optimal and close-form expression, in spite of OWC can be used to achieve high data rates. This paper presents novel upper bounds on the channel capacity of an optical intensity modulated and directed detection(IM/DD) system under peak-power and average-power constraints. The channel is modeled as an additive white Gaussian noise(AWGN) optical channel. The bounds are derived based on sphere-based signal space argument. Simulation results show the proposed bounds are tight at both high and low signal-to-noise ratios(SNRs). Compared to those reported bounds, the derived bounds are better at high SNRs region in particular, and the expressions are simpler and unique for the whole range of average-to-peak-power ratio.

关键词： channel capacity optical communication AWGN sphere-based signal space high signal-to-noise ratios(SNRs)

Transmission capacity maximization for LED array-assisted multiuser VLC systems

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Science China(Information Sciences) 2015年第8期58卷 117-130页

作者： KONG Lei SHEN Hong XU Wei ZHANG Hua ZHAO ChunMing YOU XiaoHu national mobile communications research laboratory Southeast University

In this paper, we present a light-emitting diode(LED) array-assisted visible light communication(VLC) system. Considering the requirements of illumination, the human eye safety, and the energy saving,we optimize the optical power allocation(PA) to maximize the transmission capacity of the overall ***, we discuss two typical scenarios where the LED array in each room serves multiple users either simultaneously or in a round-robin manner. The problem corresponding to the first case turns out to be nonconvex whose globally optimal solution is hard to obtain. To address this difficult problem, we first adopt the famous gradient projection algorithm to obtain a locally optimal solution, then we employ powerful convex relaxation techniques, and achieve a high-quality solution. While for the round-robin case, we are able to derive an optimal solution in closed form by virtue of Karush-Kuhn-Tucker conditions. Interestingly, the derived closedform solution follows a water-filling pattern with both square root and two-side clipping operations, which differs from the conventional water-filling-like PA in radiofrequency channels. Numerical results depict the performance advantage provided by the proposed PA strategies under various settings.

关键词： light-emitting diodes visible light communication power allocation multiuser transmission convex relaxation