Differential Relay Strategies Over Downlink Channel in Two-User Cooperative Communication System

In this paper, we propose two differential relaying strategies; Active User Strategy (AUS) and Passive Users Relaying Strategy (PURS), which could be used by the base-station to transmit data of two users over downlink channels in a two-user cooperative communication network. Differential schemes are used so the users do not require the knowledge of channel gains for decoding of their data. The performance of both schemes is evaluated for the decode-and-forward, selection relaying, and incremental relaying protocols. For the decode-and-forward protocol, the performance heavily depends upon the signal-to-noise ratio (SNR) of the link between source and relay. We propose a conditional probability of error based approach, which can be used to regulate the erroneous relaying of data. Both AUS and PURS are able to achieve performance gains as compared to the direct transmission differential scheme in the case of selection relaying and incremental relaying protocols at high SNRs. The proposed schemes perform better than their counterpart of the amplify-and-forward differential relaying proposed previously.     

On the Performance of Downlink MIMO Systems with Different Operating Frequencies

Currently, multiple input multiple output (MIMO) systems are adopted in many current cellular systems such as Long Term Evolution or 802.16 m. However, the performance of MIMO systems is greatly dependent on system parameters and environments. In this study, we evaluate the performance of downlink MIMO systems to find out which operating frequency among 800 MHz, 2.5 GHz, and 3.5 GHz is the best for next generation MIMO cellular systems. For each operating frequency, we consider the most prevalent types of mobile stations (MSs), the USB type, PDA type, and laptop type, which experience different mutual coupling between neighbor antenna elements mainly caused by the miniaturization of MSs. System simulation results show that regardless of the MS type, average and edge throughputs are almost the same for all the considered frequencies in the interference-limited environment. In contrast, the operating frequency of 800 MHz at which the mobile type with a larger antenna spacing has spatial multiplexing gain, provides the best average and edge throughputs in noise limited system environments.     

Downlink Performance Analysis of MIMO Relaying Networks

In recent years, there has been an upsurge of interest in relay-augmented infrastructure-based networks. On the other hand, multiple-input-multiple-output (MIMO) wireless system becomes a hot topic for it can achieve significant increases in overall system performance. This paper gives a detailed analysis of downlink performance of MIMO relaying networks, in which different channel models and classic MIMO cellular system model with fixed relay are considered. Our results in single cell scenario show that when meeting effective relay system efficiency of 100%, the required relay SNR gain of 2-antenna system can be reduced to less than half of that with only one transceiver antenna. We also observe that MIMO is more tolerant to interference compared with the one-transceiver antenna system. After that, multi-hop architecture is researched and statistics figures out the tolerable number of hops which is supported in wireless communication with a view to real application. In addition, multi-cell scenario is also studied. Statistics results show that there is more 8 dB average spectral efficiency gain in a two-hop fixed relay 4 × 4 MIMO system than that in a SISO system. These results present significant indications in deployment and optimization of relay-based MIMO networks.     

下行MIMO通信系统的多用户分集研究

该文研究了下行多用户MIMO通信系统中多用户分集问题,并且提出了两种基于最大系统容量准则的多用户分组调度算法。提出了一种基于相关用户的信道向量间内积的价值因子。通过使用该价值因子作为信道容量的评价标准,有效地降低了分组调度过程的复杂度。仿真结果显示该文提出的多用户调度算法可以明显提高系统容量;且随着系统中激活用户数量的增加,系统的调度增益不断增大。     

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.     

一种下行多用户MIMO系统中的鲁棒波束形成算法

提出了一种下行多用户MIMO系统中的鲁棒性线性处理算法.该算法利用了信道均值和天线相关矩阵等信道统计信息,在总发射功率不大于目标值的约束条件下,能够使所有用户的均方误差(total mean square error,TMSE)在随机信道上的平均值最小.该算法不明显依赖瞬时信道信息(channel state information,CSI),当信道估计得到的CSI不准确时,它能够有效降低由CSI偏差带来的性能损失.仿真结果表明提出的算法能够有效地降低由于不准确CSI带来的误码率和平均MSE的损失.     

LTE-A系统中下行MIMO检测的设计与实现

基于对MIMO-OFDM系统中信号检测算法的研究,设计了一种适用于LTE-A下行物理层接收机的MIMO检测方案。采用了一种基于子载波顺序检测的思想,针对发射分集和空间复用等传输场景下选取了复杂度较低且性能良好的MMSE检测算法,并给出MMSE检测器的FPGA设计方案。对于矩阵求逆模块,通过cholesky分解简化为下三角矩阵求逆问题并通过脉动阵列实现。最后以XC7Z045为硬件平台,通过仿真验证了该方案的准确性及可行性,该方案现已成功应用到LTE-A空口检测仪表项目中。     

Performance of a Hybrid Receiver in the Downlink Multicell CDMA System

In this paper, we propose a novel low-complexity receiver, namely, a hybrid receiver (HR) for the downlink of a multicell code-division multiple-access (CDMA) system with a transmit delay diversity transmission scheme. The proposed receiver is designed by combining the merits of the decorrelating receiver (DR) and the conventional receiver (CR). Unlike most multiuser receivers, HR operates with the same information as CR. For a target performance metric (e.g., bit error probability (BEP)=10^-2), the reduced-complexity HR significantly outperforms CR, DR, and minimum mean-square error (MMSE) receiver with estimated channel information. We also compare the performance of the reduced-complexity HR with a reduced-complexity MMSE receiver, which slightly outperforms the former at a price of higher complexity     

User Selection Method Adopting Cross-Entropy Method for a Downlink Multiuser MIMO System

This letter presents a novel method of user selection in a downlink multi-user multiple input multiple output (MU-MIMO) system employing the precoding procedures of zero forcing or block diagonalization (BD). The proposed technique utilizes the cross-entropy method (CEM) in order to maintain a performance level comparable to that of the full search (FS) method with reasonable complexity. With the CEM, the proposed system can select multiple users at once instead of selecting a single user at each step. From various computer simulations, it has been verified that the proposed method exhibits nearly 98 % of the sum-rate compared to the FS method, which implies that the proposed method far outperforms conventional methods such as semi-orthogonal user selection (SUS) or the capacity-based suboptimal user selection (CBSUS) algorithm. Compared to CBSUS, the proposed technique enhances the sum-rate by approximately 1.1 bps/Hz with about half the complexity when each user is equipped with two receiving antennas. In the case where each user is equipped with a single antenna, the proposed method outperforms the method of SUS by about 0.3 bps/Hz, at the expense of a complexity increase of $O(2M)$ times.     

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。     

TD-LTE中下行MIMO技术QRM-MLD信号检测算法

MIMO技术是LTE系统中的一个关键技术,在实际应用中,下行MIMO信号检测算法的选用需要在计算复杂度和系统性能之间取得合理折中.主要对QRM-MLD检测算法及其优化方案进行了分析与研究,同时结合ML算法仿真比较.结果表明,对于QRM-MLD算法,随M的增大,检测性能提高,同时计算复杂度也增大.在相同计算复杂度下,QRM-MLD优化方案的性能明显优于一般方案,是一种有效的MIMO检测算法.     

多用户MIMO系统下行链路的随机多波束复用技术

该文提出了一种随机多波束多用户复用技术,充分利用多用户分集以及基站多天线的空间自由度来提高系统吞吐量。不同于传统的随机波束形成技术,该技术首先在给定预编码码本内随机选取一个码字,然后调度多个空分复用用户以及其余预编码矩阵。该文采用了一种逐次调度的方式,第一次训练调度一个主发送用户并确定一个次发送预编码矩阵,通过第二次训练选择次发送用户,这种方式能以很小的反馈开销有效控制复用用户之间的相互干扰。同时,该文所提技术能进一步推广到用户具有不同天线配置的异构情形。仿真结果表明,该文技术在具有不同相关性的信道环境下都能获得较优的系统吞吐量。     

一种改进的多用户下行MIM0系统用户选择算法

为了克服多用户下行MIMO系统采用迫零波束成形算法时基站天线的数目要大于等于所有同时工作的用户接收天线的数目之和的缺点,丈中提出了一种改进的多用户下行MIMO系统用户选择算法。该算法具有较低的算法复杂度,性能优于常规的基于贪婪算法的用户选择方法。     

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.     

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。      

多用户FDD大规模MIMO下行系统能效功率分配算法

针对多用户频分双工(Frequency Division Duplexing,FDD)大规模多输入多输出(Multiple-Input MultipleOutput,MIMO)下行系统,从绿色通信角度出发,研究了能效准下基站训练序列信号和有效数据信号的功率分配问题。首先,利用大维随机矩阵理论,推导得出能效目标函数的解析表达式。基于此,采用高发射信噪比条件,将原始的非凸分式问题转化为拟凹问题。进而,证明了全局最优功率解的存在性和唯一性,并发现最优导频功率和数据功率之比为常数,且该常数仅由系统用户数、导频长度以及信道相干时长所决定。利用该关系式,获得最优功率的闭合形式解,并提出一种低复杂度的迭代优化算法。最后,通过Matlab数值仿真对所提功率分配算法进行了验证,分析了不同系统参数(如天线数、用户数、电路功耗等)对系统最优能效性能的影响,同时可以看到通过少量的迭代次数便可收敛到稳定点。     

TD-LTE系统中动态下行波束赋形算法性能分析

根据加权粒度的差别,介绍了per-RB-MRT算法和full-BW-EBB算法的原理,并对这两种算法的特点以及性能差异进行了理论分析.构建了符合3GPP规范定义的TD-LTE系统上下行仿真平台,对这两种算法在有信道估计误差(包括信道估计精准度和信道信息时延)的情况下的其性能进行了理论分析和仿真研究.仿真结果表明,per-RB-MRT算法在上行信道估计值和下行信道实际值契合较好的情况下能够趋于最佳理论性能,而full-BW-EBB算法由于利用了相对稳定的信道空间相关特性,因而能够在较差的信道环境中保持较高的性能鲁棒性.这些仿真结果对于实际场景中的算法选择提供了重要的参考依据.     

波束成形下DMIMO系统下行小区平均遍历容量分析

主要对波束成形下分布式MIMO系统下行小区平均遍历容量展开分析。首先建立了包含快衰落、阴影衰落和路径损耗的复合衰落信道模型。然后,在分布式基站功率受限条件下,推导各基站权重向量即最优波束;并基于ST-MRT传输策略,推导特定移动台位置条件下,小区下行点对点遍历容量表达式。最后,考虑移动台在小区内任意分布的特征,进一步推导出波束成形下小区平均遍历容量理论近似表达式。结果表明所推导的理论近似表达式可很好地反应系统的实际性能。     

Joint Beamforming and Power Control for Downlink Multi-cell Massive MIMO System

Wireless Personal Communications - Because of versatility and portability brought by remote system made it conceivable in numerous applications. Among all the contemporary remote systems, mobile ad...     

多用户准正交空时分组码MIMO系统的下行链路预编码

该文针对采用准正交空时分组码的多用户多输入多输出(QSTBC-MU-MIMO)系统,给出一种基于信漏噪声比(SLNR)准则的下行链路干扰抑制预编码方法。通过迭代优化,该文方法可以改善原始SLNR方法中由干扰用户增加所引起的系统性能下降问题,增强了算法对系统用户数的鲁棒性。由于在优化目标中考虑了系统噪声,该方法可通过恰当选取复比例因子来实现优化问题的简化求解。仿真结果验证了该文方法的有效性。