LTE虚拟MIMO系统中用户正交配对改进算法

第三代合作伙伴计划(3GPP)在长期演进(LTE)上行传输中引入了虚拟多输入多输出(V-MIMO)技术,能够提升频谱效率,改善无线链路传输性能.用户配对是V-MIMO技术必不可少的环节.针对现有的正交配对算法由于不能准确衡量两用户的正交性而导致的性能恶化问题进行了理论分析,并提出更具有一般性的正交性定义.为适应LTE-Advanced上行最大支持4流、下行最大支持8流的特点,结合贪婪思想将正交配对的应用情形由两用户推广至多用户.为了进一步改善系统性能,提出基于范数的贪婪正交配对算法.仿真结果与复杂度分析表明,基于范数的贪婪正交配对算法与穷举的最优算法性能接近,且在计算复杂度上要远低于最优算法,对于V-MIMO技术的发展具有重要意义.     

Joint user pairing and power allocation in uplink virtual MIMO with imperfect CSI

User pairing strategy for virtual multi-input multi-output （VMIMO） has been widely studied to improve system throughput, but most studies are based on perfect channel state information （CSI） and uniform power allocation. However, perfect CSI is very difficult or even impossible to obtain in practical system. Moreover power allocation has significant impact on algorithm performance. Therefore, in this paper, a low-complex joint user pairing and power allocation algorithm based on aggressive discrete stochastic optimization and Lagrangian dual solution is proposed for uplink VMIMO with imperfect CSI. Simulation results show that the proposed algorithm can achieve desirable throughput performance, and restrict inter-user interference （IUI） efficiently.     

基于虚拟MIMO的TD-LTE终端省电机制

介绍了无线资源管理上行链路中的虚拟MIMO技术,分析了该技术几种常用的用户配对方案的优缺点,最后重点分析了虚拟MIMO技术在TD-LTE系统中用来提高能量有效性的可能,并提出了基于虚拟MIMO的TDLTE终端省电机制的构想。     

LTE-Advanced上行虚拟MIMO系统用户配对算法研究

LTE引入了虚拟MIMO技术来解决终端天线数目较少的问题。用户配对是进行虚拟MIMO传输的重要环节,传统的配对算法只进行两用户配对,但在LTE-Advanced中,由于基站端最多支持8根发送天线,因此可以进行多用户虚拟MI-MO传输。文章提出了根据传输速率进行自适应用户配对数量选择的算法,并提出最低配对调制编码方案的概念,从而能在保证边缘用户吞吐量的基础上提升系统平均性能。     

MIMO技术在LTE中的应用

MIMO技术是未来LTE网络的重要的关键技术之一.本文介绍了MIMO的发展及技术原理,研究和分析了MIMO技术在LTE中的应用.     

Parallel relay‐assisted three‐phase MIMO space division multiple access transmission for multi‐hop throughput improvement

Multi‐hop communications equipped with parallel relay nodes is an emerging network scenario visible in environments with high node density. Conventional interference‐free medium access control (MAC) has little capability in utilizing such parallel relays because it essentially prohibits the existence of co‐channel interference and limits the feasibility of concurrent communications. This paper aims at presenting a cooperative multi‐input multi‐output (MIMO) space division multiple access (SDMA) design that uses each hop's parallel relay nodes to improve multi‐hop throughput performance. Specifically, we use MIMO and SDMA to enable concurrent transmissions (from multiple Tx nodes to single/multiple Rx nodes) and suppress simultaneous links' co‐channel interference. As a joint physical layer (MAC/PHY) solution, our design has multiple MAC modules including load balancing that uniformly splits traffic packets at parallel relay nodes and multi‐hop scheduling taking co‐channel interference into consideration. Meanwhile, our PHY layer modules include distributive channel sounding that exchanges channel information in a decentralized manner and link adaptation module estimating instantaneous link rate per time frame. Simulation results validate that compared with interference‐free MAC or existing Mitigating Interference using Multiple Antennas (MIMA‐MAC), our proposed design can improve end‐to‐end throughput by around 30% to 50%. In addition, we further discuss its application on extended multi‐hop topology. Copyright © 2012 John Wiley & Sons, Ltd.     

3GPP LTE的预编码和空间多路复用MIMO技术

当多路径信道在一个或多个MIMO接收机上无法提供足够的SINR时,3GPP LTE中的预编码技术可以极大地提高系统性能.测试结果表明,各种测量均可在多路径和信道失真条件下,对预编码系统的操作和性能进行非常有用的深入分析.     

Cross‐layer 1 and 5 user grouping/power allocation/subcarrier allocations for downlink OFDMA/NOMA video communications

Wang et al proposed cross‐layer resource allocation for orthogonal frequency division multiple access (OFDMA) video transmission systems. Unlike Wang et al, we add non‐orthogonal multiple access (NOMA) to the downlink OFDMA video transmission system and propose power allocation for users on each subcarrier (cluster) to minimize sum of video mean square error (MSE) to increase the peak signal‐to‐noise ratio (PSNR), the video quality. For OFDMA/NOMA video communication systems, we propose cross‐layer user clustering to reassign the subcarriers based on sum video distortion minimization and derive the optimal power allocation among NOMA users on the same subcarrier to minimize the sum video distortion. Numerical results show that the proposed scheme outperforms the previous OFDMA cross‐layer scheme by Wang et al by 2.2 to 4.5 dB in PSNR and previous OFDMA NOMA physical layer scheme by Ali et al by 2 to 4.4 dB in PSNR, when SNR = 15 dB, and the number of users is 6 to 12.     

LTE中MIMO技术面临的挑战及其测试

分析了3GPP长期演进（LTE）标准中多输入多输出（MIMO）技术面临的挑战和相应的测试方法。LTE的MIMO技术引入了空间维度,但是空间维度的利用在现阶段仍然面临很大挑战,如方向控制信道受限,各种MIMO模式的应用场景不明确及各种MIMO模式间的切换等。针对各项挑战和不确定性,需要用大量的实验来验证和促进MIMO技术的发展。讨论了MIMO技术的室内测试方法和室外测试方法。     

一种基于SNR门限的上行虚拟MIMO配对算法

虚拟多输入多输出（VMIMO）系统由多个单天线的移动终端配成一组,占用相同的时频资源传输信息,关键技术之一是用户配对算法。基于传统的配对算法无法兼顾到配对用户间远近效应与系统吞吐量问题,提出了一种基于信噪比（SNR）门限融合调度的上行VMIMO配对算法。仿真结果表明,所提算法在保证低信噪比用户服务质量的基础上提高了系统吞吐量,同时可以降低对相邻小区的干扰,减小系统丢包率,更适合实际系统的应用。     

LTE小区间干扰抑制技术介绍及比较

主要介绍了LTE目前采用的干扰抑制的方法,说明了这些干扰抑制方法对抑制小区间干扰,提高系统性能的作用,并比较了不同方法的优劣。     

User pairing schemes for capacity maximization in non‐orthogonal multiple access systems

This paper addresses the issues related with conventional near–far user pairing in non‐orthogonal multiple access. Performance effects of near–far pairing on regions with negligible channel gain differences between users are investigated. These regions occur when pairing is performed between cell center and cell edge users, thus leaving the cell mid users to be either paired with each other or kept unpaired. Pairing these mid users with each other causes successive interference cancelation (SIC) performance degradation resulting in capacity reduction for these users. On the other hand, leaving these mid users unpaired perfectly avoids the SIC issue but makes these users unable to benefit from the capacity gains provided by non‐orthogonal multiple access. Therefore, two user pairing strategies have been proposed that can provide capacity gains to almost all the users by accommodating them in pairs, while avoiding or minimizing the mid users pairing problem. A generalized M‐users pairing scheme is also proposed. Simulations have been performed to investigate the performance of proposed schemes for both perfect and imperfect SIC receiver scenarios in comparison with conventional pairing where the mid users are kept paired with each other. Simulation results show that proposed schemes achieve high capacity gains, especially when imperfect SIC is considered. Copyright © 2016 John Wiley & Sons, Ltd.     

Dual‐polarized MIMO antenna system for WiFi and LTE wireless access point applications

In this paper, a dual‐polarized multiple‐input multiple‐output (MIMO) antenna system suitable for indoor wireless access point is proposed. The presented MIMO antenna system consists of two coplanar‐waveguide‐fed monopole antennas with orthogonally polarized modes. According to the closely spaced structure of the MIMO antenna system, the mutual coupling between the ports is a big challenge. Therefore, a new structure of parasitic element is introduced in order to improve the mutual coupling between the ports. For the purpose of validating the simulated results, the antenna prototype has been fabricated and measured; the comparison of the results shows that there is an acceptable agreement between the measurement and simulation results. The proposed design covers the frequency bands of WiFi (2.4 GHz), Worldwide Interoperability for Microwave Access (2.3 and 2.5 GHz), and Long‐Term Evolution (LTE; 1.5 and 2.6 GHz) applications with a reflection coefficient less than −10 dB and a mutual coupling coefficient better than −15 dB. The MIMO antenna system provides an envelope correlation coefficient less than 0.15, polarization diversity gain more than 9.985 dB, and quasi‐omnidirectional pattern within the expected frequency band. In addition, LTE downlink throughput measurements show that the proposed antenna system delivers data rates close to the theoretical maximum for quadrature phase shift keying, 16 quadrature amplitude modulation (QAM), and 64‐QAM modulations. Copyright © 2014 John Wiley & Sons, Ltd.     

Toward the Energy Efficiency of Resource Allocation Algorithms for OFDMA Downlink MIMO Systems

The problem of the simultaneous multi-user resource allocation algorithm in orthogonal frequency division multiple access (OFDMA) based systems has recently attracted significant interest. However, most studies focus on maximizing the system throughput and spectral efficiency. As the green radio is essential in 5G and future networks, the energy efficiency becomes the major concern. In this paper, we develop four resource allocation schemes in the downlink OFDMA network and the main focus is on analyzing the energy efficiency of these schemes. Specifically, we employ the advanced multi-antenna technology in a multiple input-multiple output (MIMO) system. The first scheme is based on transmit spatial diversity (TSD), in which the vector channel with the highest gain between the base station (BTS) and specific antenna at the remote terminal (RT) is chosen for transmission. The second scheme further employs spatial multiplexing on the MIMO system to enhance the throughput. The space-division multiple-access (SDMA) scheme assigns single subcarrier simultaneously to RTs with pairwise “nearly orthogonal” spatial signatures. In the fourth scheme, we propose to design the transmit beamformers based on the zero-forcing (ZF) criterion such that the multi-user interference (MUI) is completely removed. We analyze the tradeoff between the throughput and power consumption and compare the performance of these schemes in terms of the energy efficiency.     

宽带MIMO系统天线选择技术的研究

多入多出(MIMO)技术非常适合在未来无线通信系统中应用.同时,天线选择技术因其能有效地降低MIMO系统的实现成本而受到业界的广泛关注.本文首先阐述了天线选择技术的基本原理,然后分析了该技术在3G长期演进(LTE)系统中工程应用时需要解决的一些问题,最后展望了该技术未来的研究方向和应用前景.     

3D-MIMO codebook aided multiple user pairing scheme in LTE-Advanced systems简

Two-dimensional（2D） multiple-input multiple-output（MIMO） is currently concentrated on propagation in horizontal plane, but the impact of elevation angle is not considered. However, due to the three-dimensional（3D） character of the real MIMO channel, 2D MIMO cannot achieve the optimal system throughput. A multiple-user MIMO（MU-MIMO） user pairing scheme was proposed, in which the vertical dimension was taken into consideration. In the proposed scheme, a 3D codebook based on full dimension MIMO channel was designed; then two 3D MU-MIMO user＇s pairing schemes are proposed combining the proposed joint and separate 3D codebook. Simulation evaluates the proposed 3D codebook aided user pairing scheme and compares with the previous 2D MU-MIMO user pairing technology. Owing to the additional spatial degree of freedom in vertical dimension, the proposed 3D MU-MIMO user pairing schemes can effectively improve the overall system performance.     

Spatial compatible user grouping algorithm for multiuser MIMO systems

A spatial compatible user grouping algorithm is proposed to reduce CoChannel Interference （CCI） in Space Division Multiple Access （SDMA） multiuser Multiple Input Multiple Output （MIMO） systems. We evaluate the interferences among Users by use of distances between row spaces spanned by users＇ channel matrixes, then control frequency sharing according to the compatible user grouping algorithm. Results show that the row space distance algorithm outperforms others because it can fully utilize the information from users＇ channel matrixes, especially the matrix structure information. The results also prove that the algorithm based on channel matrix structure analysis is a better candidate for spatial compatibility approximation.     

Multiuser MIMO receivers for space frequency block coded SC‐FDMA systems

Single carrier‐frequency division multiple access (SC‐FDMA) has been adopted as the uplink transmission standard in fourth generation cellular network to enable the power efficiency transmission in mobile station. Because multiuser MIMO (MU‐MIMO) is a promising technology to fully exploit the channel capacity in mobile radio network, this paper investigates the uplink transmission of SC‐FDMA systems with orthogonal space frequency block codes (SFBC). Two linear MU‐MIMO receivers, orthogonal SFBC (OSFBC) and minimum mean square error (MMSE), are derived for the scenarios with limited number of users or adequate receive antennas at base station. In order to effectively eliminate the multiple access interference (MAI) and fully exploit the capacity of MU‐MIMO channel, we propose a turbo MU‐MIMO receiver, which iteratively utilizes the soft information from maximum a posteriori decoder to cancel the MAI. By the simulation results in several typical MIMO channels, we find that the proposed MMSE MU‐MIMO receiver outperforms the OSFBC receiver over 1 dB at the cost of higher complexity. However, the proposed turbo MU‐MIMO receivers can effectively cancel the MAI under overloaded channel conditions and really achieve the capacity of MU‐MIMO channel. Copyright © 2014 John Wiley & Sons, Ltd.     

3D-MIMO技术在TDD-LTE商用网络中的应用比较研究

随着国家互联网+战略部署、物联网技术和移动互联网的广泛发展,需要移动通信网络不断提升业务承载能力。在5G大规模商用前,在现有TDD-LTE Advance网络上部署5G新技术,升级现有4G+网络,是一项很有必要的工作。本文首先对MIMO、3D MIMO技术原理进行了分析比较,通过区域试点评估了3D MIMO技术在复杂场景中的应用效果,为TDD LTE网络上快速部署3D MIMO提供借鉴。     

Unified Optimal Power Allocation Strategy for MIMO Candidates in 3GPP HSDPA

We compare the achievable throughput of time division multiple access (TDMA) multiple‐input multiple‐output (MIMO) schemes illustrated in the 3rd Generation Partnership Project (3GPP) MIMO technical report, versus the sum‐rate capacity of space‐time multiple access (STMA). These schemes have been proposed to improve the 3GPP high speed downlink packet access (HSDPA) channel by employing multiple antennas at both the base station and mobile stations. Our comparisons are performed in multi‐user environments and are conducted using TDMA such as Qualcomm's High Data Rate and HSDPA, which is a simpler technique than STMA. Furthermore, we present the unified optimal power allocation strategy for HSDPA MIMO schemes by exploiting the similarity of multiple antenna systems and multi‐user channel problems.