一种多用户MIMO系统的公平调度算法

多用户多输入多输出(MIMO)系统中需要对用户进行合理调度,一般基于信道增益的调度算法忽略了用户之间的公平性。基于此,提出了一种公平的多用户调度算法,其思想是先根据信道条件数初选出用户,然后统计每个用户被选择的次数,如果次数之差的绝对值大于设定门限,则选择次数少的用户。这样既能获得多用户分集增益又兼顾了公平性。仿真结果表明,提出的调度算法在系统性能无明显损失的情况下保证了用户公平性。     

空时编码的多用户MIMO系统用户调度性能分析

文中针对正交空时编码的多用户MIMO系统,分析并比较了两种多用户调度方案的性能.第一种方案是基站在一个时隙内选择信噪比最大的用户进行通信,第二种方案是基站在一个时隙同时选择多个信噪比大的用户进行通信.文中对两种方案的容量都作了理论推导和仿真比较.仿真结果显示,前一种方案性能好于第二种方案,但是第二种方案可以同时服务多个用户.     

基于中继放大转发的多天线基站下行传输性能分析

研究基站具有多根天线、中继与用户具有单天线的中继放大转发多用户系统,利用正交空时分组编码和机会主义调度策略同时获得空间分集和多用户分集.针对自适应增益和固定增益转发策略,首先导出独立不同分布瑞利衰落下系统中断概率和误码率的闭合表达式;随后根据高信噪比下系统的渐近性能确定系统的分集阶数,分析空间分集和多用户分集对系统性能的联合影响,并与单跳多天线基站下行传输系统进行性能比较;最后利用计算机仿真验证理论分析结果的正确性.     

多用户多天线系统中基于THP的低复杂度调度排序算法

本文提出了下行多用户多天线系统中一种新的基于Tomlinson-Harashima预编码(THP)的低复杂度调度排序算法.该算法根据THP与误符号率的特点,将调度和排序结合在一起,有效降低了复杂度.仿真结果表明,本文提出的算法在平均误符号率性能上逼近贪婪调度best-first排序,而复杂度更低,在实际系统中有很好的应用价值.     

协调多点网络——下行MIMO上的开销削减聚类算法

Owing to the potential for intercell co-channel interference mitigation and significant spectral efficiency improvement, coordinating transmission techniques by multiple radio access points have recently attracted a lot of attention. In this paper, the system structure and mathematical signal model based on clustered structure are presented for multi-point coordinating downlink transmission, the clustered supercell configurations with static/dynamic approaches are discussed, and then optimal precoding design is provided for an accepted level of scheduling complexity and reduced signaling overhead. Some simulation results are given to evaluate the performance of different cell-clustering approaches, and to show that a clustered supercell size of 7 is a reasonable choice for clustered coordination with the given transmit power and the reduced feedback.     

A Novel Nonlinear Precoding Algorithm for the Downlink of Multiple Antenna Multi-User Systems

By pre-equalizing inter-stream interference at the transmitter, Tomlinson–Harashima precoding (THP) algorithm provides a solution for the downlink of multiple antenna multi-user systems, in which the decentralized structure of the receivers makes the receiver-processing impossible. However, for the zero-forcing (ZF) THP algorithm available in the literature there are significant performance differences between specific mobile stations. In this paper, a novel version of the THP algorithm is proposed. It greatly improves the worst mobile's performance and ensures balanced performance of all the mobiles. For the new THP algorithm, better performance can be obtained by suitably ordering the rows of the channel matrix. We show that the “best-first” ordering method achieves optimal order for BER performance in systems with two mobile stations and achieves near optimal order in systems with more than two mobile stations. Simulation is used to show the advantages of the new THP algorithm and the “best-first” ordering method. Jia Liu received the B.E. and M.Sc. degrees in electrical engineering from Beijing University of Posts and Telecommunications, Beijing, China, in 1998 and 2001, respectively. Between 2001 and 2002, she worked as a system engineer in Siemens Ltd. (China), ICM N R&D, TD-SCDMA. She is currently pursuing a Ph.D. degree at the Department of Electrical and Computer Engineering, University of Alberta, and at TRLabs in Edmonton, Alberta, Canada. Her current research interests include broadband wireless communications, multiple input multiple output (MIMO) antenna systems, precoding for multi-user MIMO, signal detection, and multi-user interference cancellation. Witold A. Krzymień received his M.Sc. (Eng.) and Ph.D. degrees (both in Electrical Engineering) in 1970 and 1978, respectively, from the Poznań University of Technology in Poznań, Poland. He received a Polish national award of excellence for his PhD thesis. Since April 1986 he has been with the Department of Electrical & Computer Engineering at the University of Alberta, Edmonton, Alberta, Canada, where he currently holds the endowed Rohit Sharma Professorship in Communications & Signal Processing. In 1986, he was one of the key research program architects of the newly launched TRLabs, Canada's largest industry-university-government pre-competitive research consortium in the Information & Communication Technology area, headquartered in Edmonton. His research activity has been closely tied to the consortium ever since. Over the years Dr. Krzymień has also done collaborative research work with Nortel Networks, Ericsson Wireless Communications, German Aerospace Centre (DLR -Oberpfaffenhofen), Telus Mobility and the University of Padova (Italy). He has held visiting research appointments at Twente University of Technology (Enschede, The Netherlands; 1980-1982), Bell-Northern Research (Montréal, Canada; 1993-1994), Ericsson Wireless Communications (San Diego, USA; 2000), Nortel Networks Harlow Laboratories (Harlow, UK; 2001), and the Department of Information Engineering at the University of Padova (2005). His research is currently focused on broadband high throughput packet data access for mobile and nomadic users, employing multi-carrier signalling, multiple antenna techniques and link adaptation, as well as on the related MAC and network layer issues of hybrid ARQ, packet scheduling and relaying. Dr. Krzymień is a Fellow of the Engineering Institute of Canada, and a licensed Professional Engineer in the Provinces of Alberta and Ontario, Canada. From 1999 to 2005 he was the Chairman of Commission C (Radio Communication Systems and Signal Processing) of the Canadian National Committee of URSI (Union Radio Scientifique Internationale). He received the 1991/1992 A.H. Reeves Premium Award from the Institution of Electrical Engineers (U.K.) for a paper published in the IEE Proceedings, Part I.     

Sum Throughput Enhancements in Quality of Service Constrained Multiuser MIMO OFDM Systems

In many wireless applications, such as video streaming, data transfer or mobile Internet, user satisfaction is directly related to the transmission rates of the wireless channels in the physical layer. If the transmission rate of one user undercuts a certain level, the quality of the application becomes unacceptable. Furthermore network operators are interested in maximizing overall system throughput. However, this aim can usually not be achieved without violating these minimum rate constraints. In this article we therefore consider a practical resource allocation scheme for MIMO OFDM systems that achieves both aims without requiring computationally expensive optimization algorithms. The main part consists of a user classification. Users in one group will only be served with their minimum required rates. The remaining users can exploit the additional system resources more effectively for strong throughput increases and are therefore put in the other group. An iterative application of the proposed scheme enables additional throughput increases and the consideration of maximum transmission rates.

The Effect of On-Off Scheduling to the Required Transmit Power in Systems with Fast Power Control

Physical layer channel-aware scheduling may significantly improve coverage and throughput of IP based services in wireless cellular networks, and the feasibility of such schedulers is actively studied within 3G and 4G systems. A channel-aware scheduler requires access to instantaneous channel state information in order to direct transmission to users with favorable channel conditions. In frequency division duplex (FDD) systems, this requires a fast feedback channel between mobile and base stations, and the overhead of the feedback control channel should be kept as low as possible.In this paper, we study the effect of control channel overhead to on-off scheduling (OOS) when fast transmit power control is applied in data and control channels. On-off scheduling is a simple channel-aware scheduling algorithm, where transmission to a user is suspended if the transmit power exceeds a given threshold. On-off scheduling is applied on the data channel while control channel is always on so that the scheduler is able to obtain channel state information from active users. The gain of OOS strongly depends on the power ratio between control and data channels, and increased interference due to control signaling and decreased interference due to channel-aware scheduling should be jointly considered in system design. Gains in the required transmit power are translated into gains in coverage and capacity assuming WCDMA parameters, and the results can be applied, e.g., when designing scheduling algorithms and corresponding signaling formats for WCDMA uplink.     

基站协作系统下行链路中基于不同QoS的用户调度策略

在基站协作通信中,协作用户的调度是关键的问题之一。传统的用户调度方法为了片面追求小区的边缘传输速率与平均传输速率,造成了资源分配的不合理。本文着眼于最大限度地提升小区用户容量,提出了一种基于用户服务质量的调度策略,依据用户的需求速率和允许时延等条件确定优先级合理地调度分配资源,同时兼顾考虑小区吞吐率的提升。仿真结果表明,与原有的用户调度策略相比,该策略能够以较小的吞吐率损失为代价,大大提高了小区的用户容量。      

基于不同调度算法的多用户分集MIMO中继信道容量分析

采用平均容量性能来定量分析多用户分集多输入多输出(MIMO)中继信道,中继节点使用放大转发(Amplify-and-forward,AF)协议将接收到的源节点的发送信号重发给目的节点.研究了多用户MIMO中继信道的不同调度算法,即容量公平、最大特征根、最小特征根调度策略和空间独立性调度算法,结果表明空间独立性调度算法有...     

On the Convergence of Genetic Scheduling Algorithms for Downlink Transmission in Multi-User MIMO Systems

In a multi-user MIMO system using a successive precoding method such as dirty paper coding, it is combinatorially complex to determine the optimal set of users to schedule and the proper order to encode their signals in order to optimize a utility function in a scheduling algorithm. Genetic algorithms represent a fast suboptimal approach to reducing the complexity of the search. In this paper, we build upon prior work that implements scheduling via genetic algorithms. We examine the impact of parameter values within the adaptive mutation rate of the algorithm on its convergence time. We demonstrate that although there is a range of values for the parameters that yields similar near-minimum convergence times, it is nonetheless important to ensure that the parameters are tuned to be within that range. In one case, tuning the parameter values reduces the time of convergence to less than 30% compared to that achievable with the initial parameter values. We also demonstrate that the proper parameter values are dependent on both the number of transmit antennas and the number of users in the pool of users to be scheduled. A simple equation is proposed that is linear in the adaptive mutation parameters to tune the values for different numbers of transmit antennas and users.     

OFDM系统分组调度算法仿真与分析

对于蜂窝正交频分复用(OFMA)系统,分组调度技术是影响系统性能提升的重要因素。分组调度算法是为分组业务提供资源分配及复用的方法。这里介绍了分组调度技术原理及几种经典的调度算法,并通过Matlab仿真,对几种调度算法的公平性和吞吐量进行了比较。通过仿真可知,比例公平算法(PF,Proportional Fair)平衡考虑了系统吞吐量与公平性,取得了较好的效果。     

分组调度算法的仿真与分析

介绍了现有分组调度算法的发展概况，主要探讨并分析了常见的几种无线分组调度算法的适用性及其存在的问题，并且对分组调度算法进行了仿真和分析．最后指出了分组调度算法的发展方向．     

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.     

窄带波束信道MIMO系统的容量分析

最近的研究表明,多输入多输出(MIMO)技术在不增加功率和带宽消耗的情况下具有大幅提高无线通信速率的潜力.在传统的MIMO系统(称为天线信道MIMO系统)中,多个接收天线的输出被直接选作多输出信号.提出了波束信道MIMO系统的结构.在波束信道MIMO系统中,多个波束的输出被选作多输出信号.基于阵列方向响应矢量,提出了窄带MIMO信道冲激响应矩阵的仿真算法.基于提出的信道冲激响应矩阵算法,给出了天线信道MIMO系统和波束信道MIMO系统容量极限的分析算法.理论分析和仿真结果都表明:波束信道能够提高信噪比(SNR),降低信道间的互相关性,因此波束信道MIMO系统比天线信道MIMO系统具有更大的容量极限.     

Joint Downlink Scheduling and Radio Resource Allocation for User-Individual QoS in Adaptive OFDMA Wireless Communication Systems

1Introduction Futurewirelessandmobilecommunicationsystems areexpectedtoofferhigherdatarates,tosupporta largenumberofsubscribersandtoensurethefulfillment ofQualityofService(QoS)requirements,giventhe limitedavailabilityoffrequencyspectrumandtimevary ingchan…     

Iterative Algorithms for Performance Evaluation of Wireless Networks with Guard Channels

Analytical and modeling work performed since the late eighties have led to nonlinear equations that relate important parameters used for performance evaluation of wireless networks. These nonlinear equations have no closed-form solution and iterative algorithms are used to find numerical solutions. However, iterative algorithms that are not designed to detect and overcome nonconvergence situations may fail to converge. We present an iterative algorithm that numerically solves six dependent nonlinear equations. The algorithm always converges and obtains values of blocking probability, p _b , and forced termination probability, p _ft , at any desired level of accuracy. We then used this algorithm to numerically show that for a given pair of values of p _b and p _ft , there is an optimal number of guard channels that supports a maximal new-call arrival rate.     

Distributed Power Balancing with Linear Prediction and Adaptive On-Off Strategies for CDMA Cellular Mobile Systems

Several distributed balance (DB) power control algorithms that can achieve SIRbalance have already been proposed for cellular mobile systems [1–3].In the present paper, two simple strategies, namely linear prediction andadaptive on-off strategies, are further applied to forward link distributedbalance (DB) power control in DS/CDMA cellular mobile systems. The linearprediction is used to track the variance of the short-term fading andcompensate it in advance, and the adaptive on-off strategy is applied to solvethe problem that the received SIR of all the communication links less than theminimum required SIR. Simulation results indicate that DB power control withthese two strategies can achieve much better performance than the original DBpower control.     

基于模糊逼近的非线性多时延系统的自适应跟踪控制

针对一类多输入多输出非线性多时延系统,提出了基于模糊逼近的自适应跟踪控制方案.该方案构建了基于模糊T-S模型的自适应时延模糊逻辑系统,用来逼近未知非线性时延函数.从而实现了对非线性系统的建模.根据跟踪误差给出了时延模糊逻辑系统的参数自适应律.设计了H_∞补偿器来抵消模糊逼近误差和外部扰动.基于Lyapunov稳定性理论,提出的控制方案保证了闭环系统的稳定性并获得了期望的H_∞跟踪性能.机械臂的仿真结果表明了该方案的有效性.     

基于内容的发布订阅系统路由算法

 本文综合评述了基于内容的P/S系统路由机制和算法.根据客户的移动性和网络结构的变化对路由算法进行了分类和归纳,分别论述了静态和变化拓扑环境下、支持客户移动情况下P/S系统各种路由算法的基本思想和优缺点等.在此基础上,针对P/S系统的动态、松耦合、多对多通信的特征,分析和提出了有待解决的问题以及进一步的研究方向.