统计和瞬时CSI混合的3D MIMO预编码

本文针对分别具有统计信道状态信息（Channel State Information,CSI）和瞬时CSI的用户,研究了两类用户在三维多输入多输出（Three-Dimension Multiple-Input Multiple-Output,3D MIMO）系统中的下行链路传输模式,解决了混合利用统计和瞬时CSI的下行预编码的设计问题。利用3D MIMO信道的克罗内克积的性质,提出了一种用于最小化基站总发射功率的扩展迫零预编码的方法,并分别求解其最优水平预编码矩阵和最优垂直预编码矩阵。仿真结果表明,该方案具有更低的复杂度和良好的速率。      

毫米波MIMO系统离散化混合预编码设计

为了提高毫米波大规模多输入多输出（MIMO）系统波束成形增益,降低天线与移相器的硬件成本,提出一种基于离散移相器的混合预编码设计方案。以最优化频谱效率为目标,该方案通过分析均匀直线阵列与均匀平面阵列的响应矢量,将毫米波信道的空间特性预编码的设计考虑为空间稀疏重构问题,采用离散化正交匹配追踪原理求出数字预编码与离散化的模拟预编码。仿真结果表明,同等条件下平面阵列的频谱效率优于直线阵列,同时所提出的离散化混合预编码方案中低精度移相器的性能近乎达到全精度移相器的性能增益。     

毫米波MIMO系统中部分连接型混合预编码设计

为了提高毫米波通信系统中混合预编码频谱效率,考虑交替使用最小化架构来提高波束形成增益。然而,这种架构因为射频域调相网络通常使用移相器构成,导致非凸约束,并且已知解决方案具有更高的计算复杂度。在使用交替最小化架构之前,证明了信道矩阵的有序右奇异向量的相位角可以用来初始化模拟预编码器,从而避免了采用搜索近似最佳模拟预编码矩阵的复杂优化过程。另外,不需要发射机处的天线阵列响应矢量。仿真结果表明,提出的算法性能优于传统部分连接型算法且复杂度更低,尤其在高信噪比情况下,更加明显。     

基于极化状态调制的无线通信物理层安全传输技术

针对无线通信系统中物理层信息安全风险问题,提出了一种基于极化状态调制的物理层安全传输技术。在无线通信中,引入极化状态调制,在经典的空域、时频域的基础上,增加了对信号极化域的描述。一方面,设计高维星座映射方案,利用信号的幅度、相位和极化状态共同承载信息,将传统调制技术和极化状态调制有效地结合在一起;另一方面,在高维星座映射方案的基础上,进一步设计基于去极化效应的信道预编码机制,通过增大Bob和Eve在极化域的信道差异实现物理层保密传输。安全性分析和仿真实验结果表明,利用该机制能够提升系统的保密容量,在接收信噪比为22dB时,窃听者接收到的星座图仍然是十分紊乱的,无法恢复出有效信息。     

基于GMD-BD预编码的多用户MIMO可见光通信系统

在基于奇异值分解(singular value decomposition,SVD)的块对角(block diagonal,BD)预编 码多用户多输入多输出(multiple input multiple output,MIMO) 室内可见光通信(visible light communication,VLC)系统中,同一用户终端的不同光接收机误码率性能有较大差别,而 用户终端误码率性能受限于最差性能的接收机。针对此问题,本文利用决策反馈均衡(decision feedback equalization,DFE) 非线性接收机,提出了基于几何均值分解(geometric mean decomposition,GMD)的BD预编码多用户MIMO室内VLC 系统,并利用同一用户终端采用不同视场角(field of view,FOV)的接收机进一步提高用户终端误码率性 能,分析了用户终端位置对用户终端误码率性能的影响。最后通过仿真验证了本文提出的系 统使同一用户终端的不同接收机获得相近的误码率性能,提高了最差接收机的性能,降低了 用户终端误码率。当单个发光二极管 (light emitting diode,LED)的发射功率为10 mW和系 统传输速率为100Mbit/s 时,在室内95%的区域内用户终端能够达到10－6左右的误码率性能。     

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.     

A low-complexity Lanczos-algorithm-based detector with soft-output for multiuser massive MIMO systems

Zero-Forcing (ZF) algorithm achieves the near-optimal detection performance for massive multiple-input multiple-output (MIMO) systems at expense of performing the complicated matrix inversion of a high dimensional matrix. In this paper, a novel Lanczos-algorithm-based signal detection method with soft-output is proposed to iteratively realize ZF algorithm for multiuser massive MIIMO systems, which avoids the exact computation of matrix inversion and in turn reduces the computational complexity from $O(K^3)$ to $O(K^2)$, where K denotes the number of users. In the development of the proposed method, by analyzing the iterative process of Lanczos algorithm, an approximate low-complexity scheme is proposed to calculate the log likelihood ratios (LLRs) for soft channel decoding. Simulation results show that the proposed detector provides a relatively good tradeoff between the complexity and performance compared with the several recently proposed detectors, and achieves almost the same performance as the ZF algorithm with only 3 iterations.     

多波束卫星系统中低复杂度分组预编码算法

针对格基约减辅助的THP(LRA-THP)算法运算复杂度高问题,在一种分组预编码算法的基础上,提出一种适用于多波束卫星系统的低复杂度分组预编码算法,该算法根据波束间的距离对用户进行分组,通过最大化SSLNR得到预处理矩阵,抑制组间干扰,各组内采用LRA-THP算法,计算预处理矩阵时充分利用多波束卫星信道的特点,降低需要求解的预处理矩阵的维度,从而减小算法的运算复杂度.理论及仿真分析结果显示,该算法的运算量远低于LRA-THP,与原分组预编码算法相比,该算法的复杂度能够降低24%,同时性能损失不超过0.1 d B.另外,该算法中引入一组参数,使其能够灵活地在复杂度与可靠性之间进行折中.     

Per-layer transmit and receive filters design for Tomlinson-Harashima precoding in multiuser MIMO systems

In this paper,the per-layer design for Tomlinson-Harashima precoding (THP) in the downlink of multiuser multiple-input multiple-output (MIMO) systems is investigated.In these systems,the number of the receivers is equal to that of the transmit antennas.Based on the criterion of maximum system sum-capacity,we study two per-layer joint transmit and receive filters design schemes with receive antenna beamforming (RAB) and receive antenna selection (RAS),respectively.Moreover,the differences of the equivalent channel gains and capacities between these two schemes are analyzed theoretically.Simulation results show that by these per-layer schemes,the system sum-rate is improved significantly with respect to the per-user processing scheme.     

鲁棒线性预测编码器设计

为消除多用户广播信道下反馈时延和用户速度对系统性能的影响,采用信道的统计信息和过
时信息联合估计当前信道信息,在发射端获得了不完全信道状态信息(CSIT). 在此基础上,
设计了一种鲁棒线性迫零预编码器. 仿真结果证明,鲁棒预编码器具有良好的性能,并且验
证了系统性能与反馈时延或用户速度的关系.