多用户毫米波MIMO系统中基于信道互易性的混合模数预编码算法

本文针对多用户毫米波多输入多输出(Multiple Input Multiple Output,MIMO)系统,首次提出了分离子阵列MIMO混合模数预编码架构毫米波系统的一种模拟接收方案。将最大化和速率求解混合模数预编码的三元联合优化问题分成模拟和数字两部分求解,进一步提出了基于信道互易性的混合模数预编码算法。该算法通过最大化下行各个用户和上行各个子阵列的接收信干噪比分别求解模拟合并矢量和模拟预编码矢量;优化模拟部分后,设计发射端数字预编码器消除多用户数据流之间的干扰。数值仿真表明所提算法收敛速度快,且可获得接近最优纯数字预编码算法的性能。      

基于连续干扰消除的毫米波MIMO系统混合预编码算法

该文研究多用户毫米波MIMO系统的混合模数预编码器和合并器设计。针对因信号传播漫散射造成的多用户间信号干扰问题,提出一种基于连续干扰消除(SIC)的鲁棒混合预编码算法。首先对信道矩阵进行正交分解,以消除来自已知用户信号的干扰,从而将含有非凸约束的多用户链路优化问题分解为多个单用户链路优化问题。然后采用相位提取算法逐个求解每个用户的最优传输链路,并结合最小均方误差(MMSE)准则求得多用户混合预编码矩阵。仿真结果表明,与现有的混合预编码算法相比,所提算法在强干扰环境下具有显著的性能优势。     

利用无监督学习的RIS辅助毫米波通信系统鲁棒传输设计

本文研究了利用无监督学习的可重构智能表面（reconfigurable intelligent surface,RIS）辅助毫米波大规模多输入多输出（multiple input multiple output,MIMO）下行传输设计。首先,针对发送端信道状态信息（channel state information,CSI）非理想场景,推导了RIS辅助的毫米波下行传输系统平均频谱效率闭式上界。进一步,考虑实际系统硬件受限的条件,本文采用基于离散傅里叶变换（discrete Fourier transform,DFT）码本的模拟预编码,且RIS各反射单元仅能取有限的离散相移值。在此基础上,以所推导的平均频谱效率上界最大化为目标,提出一种基于无监督学习的发送端混合预编码、接收端数字合并以及RIS反射单元相移联合设计方法。所提方法采用两阶段无监督学习模型,分别生成RIS反射单元相移与发送端混合预编码,而接收端数字合并矩阵则采用最小均方误差（minimum mean squared error,MMSE）准则生成。同时,本文针对该模型提出了一种高效的分段训练方法。该训练方法分别对生成RIS反射...     

Improved Multiuser MIMO Unitary Precoding Using Partial Channel State Information and Insights from the Riemannian Manifold

Multiple-input multiple-output (MIMO) systems can be leveraged to increase capacity in fading channels. Especially in multiuser downlink communication systems, it has been shown that knowledge of channel state information at the transmitter (CSIT) is critical to leverage the capacity gain available from multiple antennas. When duplexing is performed using time division, CSIT can often be successfully obtained when channel reciprocity is available. CSIT acquisition, however, is much more difficult in frequency division duplexing. Sending feedback on the uplink has been shown to be a powerful technique to improve downlink performance in single user MIMO systems. The basic idea is to restrict the CSIT to a B bit codebook so that the mobiles can easily transmit these bits on the uplink. In this paper, we consider the multiuser downlink model with unitary precoding when there is a codebook consisting of 2^B unitary matrices that the precoder is restricted to lie in. This codebook is designed offline and known to both the basestation and all users. Each user sends back signal-to-interference plus noise ratio (SINR) information along with binary feedback about the unitary precoder. Based on the CSIT received on the uplink, the basestation selects one of the unitary matrices in the codebook to maximize the sum-rate. For this set-up, we first analyze the sum-rate performance of the unitary precoding scheme. We then show that the codebook of unitary precoders represents a collection of points in a special kind of manifold and show how the achievable sum-rate performance relates to the minimum distance of the codebook points in this space. Finally, we present a framework for constructing the codebook to maximize this minimum distance. Monte Carlo simulation results are presented to show the sum-rate performance of the proposed codebook design.     

融合蚁群算法MMSE准则在MMW 混合波束形成中的应用

波束形成预编码技术是毫米波通信的核心技术,其中模拟和数字混合波束形成技术可以很好地平衡 模拟预编码技术和数字预编码技术的优缺点,既可以得到足够的波束形成增益、减少传播损耗,又降低了硬件成本 和功耗。均方误差(MSE)是表征毫米波通信传输可靠性的性能指标,利用最小均方误差(MMSE)准则的混合预编码 设计可以在毫米波大规模多输入多输出(MIMO)系统中获得较好的频谱效率。将MMSE 与广泛应用于解决旅行商 问题的蚁群算法相融合,以进一步优化基于流形优化的混合预编码算法。仿真结果表明,融合后的优化算法具有更 低的误码率和更好的频谱效率。     

基于 Min-Sum-MSE的多用户MIMO训练序列与数据功率联合优化

本文研究了多用户MIMO系统中基于Sum-MSE最小准则预编码的训练序列与数据联合功率分配问题.考虑信道空间相关性,采用MMSE准则进行信道估计,在训练序列与数据总功率一定的条件下,通过分析上下行链路存在MSE对偶性,将下行Sum-MSE最小化转化为上行Sum-MSE最小化问题.然后推导了在发送端存在相关性时该功率联合...     

带内全双工多用户MIMO系统中的用户选择

考虑一种多用户MIMO的传输设计,配置发射天线阵列和接收天线阵列的蜂窝基站可以工作在带内全双工传输模式。在该全双工通信方案中,基站的下行发射信号对基站的上行接收产生显著的干扰,即自干扰。这里,下行预编码处理和上行发射协方差矩阵处理将被依次进行,以简化全双工的设计。其次,为了进一步改善上、下行信道的和速率性能,我们提出一种尝试性的下行用户选择方案,其基本思想是:当某一个下行用户的信道矩阵的范数较小时,关闭该下行用户的数据流。计算机仿真结果表明,在基站下行总发射功率受限时,在低的和中等的下行信噪比区域,用户选择有助于提高下行和速率;在高的上行信噪比区域,简化的用户选择使得上行和速率明显提高。      

Bat algorithm–based beamforming for mmWave massive MIMO systems

In this paper, an optimized analog beamforming scheme for millimeter‐wave (mmWave) massive MIMO system is presented. This scheme aims to achieve the near‐optimal performance.by searching for the optimized combination of analog precoder and combiner. In order to compensate for the occurrence of attenuation in the magnitude of mmWave signals, the codebook‐dependent analog beamforming in conjunction with precoding at transmitting end and combining signals at the receiving end is utilized. Nonetheless, the existing and traditional beamforming schemes involve a more difficult and complicated search for the optimal combination of analog precoder/combiner matrices from predefined codebooks. To solve this problem, we have referred to a modified bat algorithm to find the optimal combination value. This algorithm will explore the possible pairs of analog precoder/combiner as a way to come up with the best match in order to attain near‐optimal performance. The analysis shows that the optimized beamforming scheme presented in this paper can improve the performance that is very close to the beam steering benchmark that we have considered.     

基于毫米波大规模MIMO系统的混合预编码设计

大规模多输入多输出（MIMO）被认为是未来5G的关键技术之一。毫米波因其足够大的频谱带宽近来备受关注。针对部分连接结构、单用户下行链路毫米波大规模MIMO系统，提出了一种新型的混合预编码设计。利用分层设计思想，首先设计模拟预编码器，提出一种模拟预编码器算法；然后通过注水算法获得最佳数字预编码器；最后，将起始最优化问题转化为在每根天线功率分配约束下单个RF链路连接天线子阵列最优化问题，再根据迭代方法获得最佳混合预编码器。仿真结果表明，最佳混合预编码器性能接近纯数字预编码器的性能。     

Hybrid Analog and Digital Precoding Based on Adaptive Method in P2P Massive MIMO

To achieve a far higher capacity in massive multi-input multi-output, the hybrid analog and digital precoding has been studied recently. In this paper, we consider the downlink single user communication system and propose an efficient matrix adaptive gradient descent algorithm to design the radio frequency precoder and combiner, and use the singular value decomposition method to obtain the digital precoder and combiner. Simulation results show that the proposed method can approach the performance of the conventional full digital precoding with a fast convergence rate.     

Interference alignment scheme for massive MIMO system

The performance of massive multiple-input multiple-output （MIMO） system is limited by pilot contamination. To reduce the pilot contamination, uplink and downlink precoding algorithms are put forward based on interference alignment criterion. In the uplink receiving processing, the target function aligns the pilot contamination and the interference signals to the same null space and acquires the maximal space degree of the desired signals. The uplink receiving precoding matrix is solved on maximal signal to interference plus noise ratio （SINR） criterion considering the impact of the pilot contamination on channel estimations. The uplink receiving precoding matrix is used as the downlink transmitting precoding matrix. Exploiting the channel reciprocity, it is proved that, if the uplink receiving precoding matrix achieves maximal S1NR, the identical precoding matrix can be used in the downlink transmission and acquires maximal signal to leakage plus noise ratio （SLNR）. Simulations show that the spectrum efficiency of the proposed algorithm can reach about 1.5 times higher than that of popular matched filtering （MF） precoding algorithm, and about 1.1 times higher than multi-cell minimum mean square error （MMSE） precoding algorithm. The performance of the proposed algorithm can be improved approximately linearly with the increasing of the number of antennas.     

Spectral efficiency evaluation of full‐duplex mode of communications based on SLNR approach

Full‐duplex (FD) mode of communication with efficient transmission scheme is a promising approach for 5G wireless systems by improving the spectral efficiency. This can be attained by making use of various precoding approaches. We propose a new co‐channel interference (CCI)‐aware improvement to signal‐to‐leakage‐and‐noise ratio (SLNR) technique and a suppression filter at the receiver to whiten the interference for the downlink channel. As well, for the uplink (UL) communication, we propose a self‐interference (SI)‐aware enhancement to SLNR scheme and designing a precoder using self‐interference plus noise covariance matrix. The total spectral efficiency is obtained from the sum‐rates of both downlink and uplink communication systems. Simulation results verify that the spectral efficiency (SE) of FD using the proposed scheme performs well relative to the half‐duplex system for all Rician factor and for small powers at the base station (BS) and UL communication channel users. Moreover, as the number of users grows, which entails that as the number of receiving antennas greater than the number of antennas at the BS the SLNR scheme still works, nonetheless, zero‐forcing (ZF) and block‐diagonalization (BD) precoding schemes failed. This is due to the fact that designing a precoder based on SLNR scheme supports multiple numbers of antennas at the base station and users compared with ZF and BD by compromising the interference and noise. However, for the cases of ZF and BD approaches failed due to both schemes require the number of transmit antennas at the BS to be larger than the sum of the receiving antennas at all users.     

多小区MIMO系统中基于泄漏的多用户下行链路预编码新算法

针对多小区MIMO系统的多用户下行链路预编码设计是未来移动通信系统研究的重要内容之一。本文在蜂窝多小区MIMO通信环境下,基于信漏噪声比(Signal-to-Leakage-Noise Ratio,SLNR)最大准则,提出了改进的多用户下行链路线性预编码算法。通过在优化目标中考虑接收端白化滤波器的影响,该预编码算法实现了对用户间干扰和小区间干扰(OCI)的同步抑制消除;在求解预编码矩阵优化问题时,本文基于QR分解提出了一种新的低复杂度求解算法,该算法能以较低的计算复杂度实现系统性能的有效提升。仿真实验结果表明,本文的改进SLNR线性预编码算法能有效抑制小区间干扰(OCI)的影响,使多小区MIMO系统获得更高的和速率(Sum Rate)容量。      

基于码本的有限反馈非酉矩阵预编码多用户MIMO系统

该文提出了一种基于码本的有限反馈非酉矩阵预编码下行多用户MIMO系统。该方案根据用户反馈的信道信息SINR在发送端进行调度和预编码来提高系统容量。预编码的码本设计依据格拉斯曼空间装箱原理,并将码本中的向量按其相关性构成非酉矩阵来提高预编码增益和抑制多用户共道干扰。新方案反馈量少、复杂度低,在相同情况下比传统的单用户MIMO系统和基于码本的酉矩阵预编码多用户MIMO系统都具有更好的性能。     

基于毫米波通信的混合MIMO系统的信道估计

作为5G的一项关键技术,毫米波通信要求提出专有的信道估计和预编码算法,为此,针对毫米波MIMO系统的窄带平坦衰落信道研究下行信道估计方案.由于毫米波系统的稀疏特性,将稀疏多径信道的信道估计转化为稀疏信号的重建,基于压缩感知设计适用于毫米波通信系统的信道估计方案,深入研究了正交匹配追踪算法.仿真结果显示,它可以高概率地恢复信号,与传统的最小二乘法比较,能获得更好的信道估计性能.     

Joint linear precoder and power allocation design for uplink MIMO systems with limited feedback

In this article, the authors consider joint design of a linear precoder and power allocation for uplink multiuser multiple input multiple output (MIMO) communication systems with limited feedback to improve the bit error rate (BER) performance for all users. Precoder selection from the codebook set is directly based on the exact BER performance, instead of other suboptimal criteria, to achieve the optimal precoder matrix, but closed-form expressions may not exist in the view of power allocation based directly on the BER criterion. From this perspective, the authors propose the joint transmitter optimization algorithm for the consideration ofprecoder design, with total power constraint for asymptotic MBER (AMBER) criterion. In this AMBER criterion, a closed-form solution has been derived for power allocation with an optimal precoder. The simulation results show that the proposed joint design algorithm can achieve a much better performance than precoding with uniform power allocation and only consideration of power allocation.     

基于毫米波大规模MIMO的混合RZF预编码算法

针对毫米波大规模MIMO系统采用全数字预编码时,系统所需射频链路数量较大而导致实现成本和能耗较高的问题,提出了一种在基站端和用户端分别采用混合预编码和模拟合并的方案.在充分考虑信道特性的基础上,根据收发两端的天线阵列响应矢量分别设计模拟预编码矩阵和模拟合并矩阵,然后根据生成的有效信道矩阵,在基带部分设计低维的数字预编码,从而消除系统中噪声和用户间干扰的影响.仿真结果表明,在有效减少系统所需射频链路数量的基础上,所提混合预编码方案能够接近传统全数字预编码方案的性能.     

Robust Non-linear Precoder for Multiuser MISO Systems Based on Delay and Channel Quantization

In multiuser multiple-input single-output (MISO) systems, non-linear precoder is able to achieve the theoretical sum capacity of downlink channel with perfect channel state information (CSI). However, the perfect CSI is not available at the transmitter in practical system, especially in frequency division duplex (FDD) system where the imperfect CSI is the delayed, quantized channel direction information relayed back from the receiver through a dedicated feedback channel. So the performance of conventional non-linear precoder degrades significantly. In this paper, a robust non-linear Tomlinson–Harashima precoding (THP) based on sum mean squared error (SMSE) minimization for the downlink of multiuser MISO FDD systems is proposed. The proposed precoder is robust to the channel uncertainties arising from channel delay and quantization error. Furthermore, an improved non-linear THP with channel magnitude information (CMI) consideration is introduced to compensate the instantaneous CMI shortage at the transmitter. Additionally, the computational complexity of both proposed precoders can be reduced remarkably by Cholesky factorization with symmetric permutation. Simulation results demonstrate the improvement in bit error ratio performance and illustrate the SMSE performance of the proposed algorithms compared with conventional THP with perfect CSI in the literature.     

多小区多用户TDD MIMO下行链路干扰抑制预编码算法

针对多小区多用户TDD MIMO下行链路,提出了一种基于预编码的联合干扰抑制算法。首先,利用广义MMSE信道逆的QR分解设计预编码矩阵抑制下行链路的多用户干扰(MUI)。然后,从信号能量泄露的角度设计第二个预编码矩阵抑制小区间干扰(ICI)和残留的多用户干扰。该算法能够利用TDD MIMO信道的互易性,不需要用户端的反馈。在市区微小区组成的多用户TDD MIMO系统中的仿真结果表明,该算法能有效地提高系统容量和用户端平均信干噪比(SINR)。     

Cellular Downlink Performance with Covariance-CSIT-Based MIMO Precoding

The nature of the trade-off between reduced overhead of channel state information (CSI) and resultant performance losses influences the design of frequency-division duplexed practical cellular systems. One candidate for CSI feedback reduction is the use of covariance-matrix-based CSI at the transmitter (CSIT) in conjunction with linear precoding techniques. This paper analyzes the performance of such systems in the downlink for both single-user (SU-) and multiuser (MU-) multiple-input multiple output (MIMO) in comparison to those using optimal perfect-instantaneous-CSIT-based precoding. In addition, the effectiveness of techniques enforcing frequency domain diversity versus those based on the maximal ergodic channel capacity criterion is evaluated. A novel precoding scheme using covariance matrix information that supports spatial multiplexing in both SU- and MU-MIMO is proposed. Simulation results show that the spectral efficiency loss from covariance-CSIT-based techniques from those utilizing perfect, instantaneous CSIT is shown to be about 1 dB in a highly correlated urban channel environment for both SU- and MU-MIMO, whereas for microcell environments it is between 3 and 4 dB.