多波束机会波束成形系统性能比较

研究了在多输入单输出（MISO）系统中通过加大、加快信道的波动来提高多用户分集增益的机会波束成形技术,并在此基础上研究了在每个时隙中采用多个加权矢量的多波束机会波束成形技术,着重对它们的性能作了仿真比较。结果表明,多波束机会波束成形技术可以提高系统吞吐量。     

基于多波束的机会波束成形在OFDMA系统中的使用

机会波束成形技术可以使信道的波动变大、变快，从而增大多用户分集增益。它同样也适用于OFDMA系统。对于OFDMA系统而言，我们还可以通过对所有子载波进行分簇，从而在牺牲系统性能很少的情况下，大大地减少系统反馈量。为了进一步提高系统吞吐量，还可以在每个时隙使用多个随机加权向量，然后基站从中选择一个最好的向量进行机会波束成形。     

自适应多天线OFDMA蜂窝系统中反馈压缩新方法

在自适应调制和调度的无线通信系统,特别是OFDMA系统中,反馈信息压缩技术已成为研究热点。文中研究了随机波束成形OFDMA系统中分簇反馈压缩技术以及门限信噪比压缩技术,结合二者的优点提出了一种改进方案——分簇门限信噪比压缩技术。仿真证明,采用分簇门限信噪比技术与分簇技术、门限信噪比技术相比,明显降低了反馈量,且在用户较多时系统容量损失很少。     

3D MIMO-OFDMA系统中基于垂直波束成形的能效优化算法

针对三维多输入多输出（3D MIMO）正交频分多址（OFDMA）系统,提出了一种能效优化算法。该算法在垂直波束成形技术下,以能量效率最大化为目标,通过调整资源分配、功率分配、天线的波束下倾角来提高系统能量效率。根据分数优化理论,将复杂的分数优化问题转化为较易求解的整式优化问题,然后引入拉格朗日乘子通过不断迭代得到能量效率的最优值。仿真结果表明,所提算法在较少迭代次数下可以获得更高的能量效率。     

高铁毫米波最优自适应波束成形与联合传输

高铁车地移动通信系统的吞吐量不仅受到频谱的限制,而且受到高移动性的限制,已成为制约智能高铁发展的重要瓶颈。一种提高系统吞吐量的有效方法是使用拥有较宽连续频谱的毫米波频段以及使用大规模多输入多输出(MIMO)和多波束成形技术。然而,使用固定波束宽度的多波束流在列车高速行驶过程中会产生严重的波束间干扰,因此,论文提出了基于最优波束宽度的自适应波束成形和联合传输方案。当列车距离基站较近时,激活全部波束,实现波束的空间复用,提高系统容量和传输可靠性。当列车距离基站较远时,为了避免波束间的严重干扰,用更多的天线阵元形成较少的波束,获得更大的波束增益,并与相邻基站进行波束联合传输,提升系统的吞吐量。仿真结果表明,与现有波束成形及传统自适应选择方案相比,所提方案吞吐量在小区边缘附近可以提升超过150%。     

MIMO系统中随机波束成形算法的研究

文章研究了MIMO(多输入多输出)系统中的随机波束成形(RBF)算法,仿真结果表明:随着用户数的增加,随机波束成形技术可以用最小的反馈获得相干波束成形情况下的吞吐量,并可获得MIMO系统慢衰落信道中下行链路的多用户分集增益和复用增益.     

三种波束形成技术的研究

多天线技术的使用已成为LTE系统中一个最显著的特点,而波束形成则是多天线的一种关键技术。文章深入分析了现有的几种波束形成技术：机会波束形成（OBF）、随机波束形成（RBF）、特征波束形成（EBF）,仿真比较了这几种技术的优缺点。     

基于波束成形天线的分簇时间同步算法

波束成形天线相比较定向天线具有波束集中,抗干扰能力强等特点,配备波束成形天线的节点间通信复杂,造成网络同步困难。文中提出一种分簇网络时间算法解决基于波束成形天线网络同步问题,算法分为选举,分簇,同步三个阶段,选举阶段选举网络根节点,分簇阶段工作于定向天线且网络时间异步场景下,利用网络根节点作为分簇的初始节点完成网络分簇,同步阶段利用簇间同步与簇内迭代完成全网节点同步。仿真分析了算法的开销并能够促使网络时间收敛。     

提高Ka频段系统点波束能力的网眼反射天线简介

一、发挥点波束系统优势的关键技术目前,大吞吐量卫星系统的成功主要凭借了三大关键技术,通过这些技术可以充分利用点波束系统的内在优势。这三大技术是更大孔径、多波束馈送以及更强的卫星总线能力技术。本文主要介绍可用来支持大吞吐量卫星系统的更大孔径方面的技术需求。更大孔径是未来大吞吐量卫星系统实现更小点波束以及通过更小的赋形反射天线来提高性能的关键性赋能技术。更小点波束可以实现大容量频率复用策略,而且还能提高增益,可     

毫米波大规模MIMO系统混合波束成形技术综述

毫米波通信和大规模多输入多输出（Multiple-Input Multiple-Output,MIMO）技术是5G的关键候选技术,在提高5G系统各项性能指标上潜力巨大。混合波束成形作为毫米波大规模MIMO系统中的关键点,能在系统性能和实现复杂度上取得较好平衡,受到业界和学术界广泛关注。首先给出了混合波束成形经典系统模型和常用信道模型,根据信道状态信息获取方式的不同,从基于理想信道条件和基于波束配对两个方面分析和归纳了现有的混合波束成形方案,最后指出了混合波束成形未来发展趋势以及尚未解决的难点。     

Opportunistic beamforming based on multiple weighting vectors

In order to improve the throughput of the opportunistic beamforming, the authors generalize the opportunistic beamforming by using multiple random weighting vectors at each time slot. The base station chooses the best weighting vector and performs the opportunistic beamforming with this optimum vector. For the case of equally strong independent fast Rayleigh fading channels, the throughput of the proposed scheme is analytically approximated and the optimum number of random weighting vectors per time slot is obtained. Numerical results demonstrate that the proposed scheme considerably improves the throughput compared to the conventional opportunistic beamforming for a low/realistic number of users.     

Performance of OFDMA Multicell Systems with Opportunistic Beamforming

The opportunistic beamforming (OB) technique in multicellular OFDMA networks is investigated in this paper. Three cross-layer radio resource management (RRM) algorithms for OFDMA operational scenarios are considered. These algorithms build upon typical network planning practices for OFDMA systems. The first two implement an OFDMA network with opportunistic rate adaptation while the third one aims at a network which guarantees QoS provision through power control on carrier basis. The RRM algorithms are based on typical OFDMA resource allocation targets such as minimization of transmit power, maximization of throughput and interference averaging. Then, the OB concept is combined with the considered RRM algorithms and a comparative performance analysis between the two types of networks (omni and opportunistic beamforming) is performed in terms of throughput, blocking probability and fairness. The paper aims at providing a useful insight into the way the OB technique affects the performance of different OFDMA networks based on large scale simulations. The simulation results suggest that OB is preferred for OFDMA systems with opportunistic rate adaptation rather than power controlled systems which offer QoS provision. According to the presented results, OB provides to OFDMA systems with opportunistic rate adaptation a ??13% throughput gain and ??75% gain in terms of blocking probability. In addition, it is shown that the combination of OB with interference averaging RRM algorithms has a minor beneficial impact only on the system fairness.     

Opportunistic Beamforming and Scheduling for OFDMA Systems

Orthogonal frequency-division multiple access (OFDMA) is an attractive technique for exploiting multiuser diversity in the downlink of a cellular system. This paper addresses three problems in multiuser diversity for OFDMA systems. First, we propose a way to significantly reduce the amount of channel state information (CSI) feedback without sacrificing performance too much, by selective and adaptive feedback. Second, we propose a way to increase the cell throughput and fairness by applying an opportunistic beamforming scheme to orthogonal frequency-division multiplexing. This beamforming scheme increases the frequency fading rate, which increases the multiuser diversity effect. Thirdly, we deal with the issue of fairness and quality-of-service (QoS) in opportunistic systems by proposing a modified proportional fair (PF) scheduler for OFDMA. Key features in the scheduler are that it incorporates QoS classes into the PF scheduler and that it has a tunable fairness level. Extensive simulation results are presented to evaluate the performance of the proposed schemes. The opportunistic beamforming scheme performed well in comparison with several other schemes. The modified PF scheduler was able to give users different QoS, based on their requirements, while still exploiting multiuser diversity     

Opportunistic Space-Division Multiple Access With Beam Selection

In this paper, a novel transmission technique for the multiple-input multiple-output (MIMO) broadcast channel is proposed that allows simultaneous transmission to multiple users with limited feedback from each user. During a training phase, the base station modulates a training sequence on multiple sets of randomly chosen orthogonal beamforming vectors. Each user sends the index of the best beamforming vector and the corresponding signal-to-interference-plus-noise ratio for that set of orthogonal vectors back to the base station. The base station opportunistically determines the users and corresponding orthogonal vectors that maximize the sum capacity. Based on the capacity expressions, the optimal amount of training to maximize the sum capacity is derived as a function of the system parameters. The main advantage of the proposed system is that it provides throughput gains for the MIMO broadcast channel with a small feedback overhead, and provides these gains even with a small number of active users. Numerical simulations show that a 20% gain in sum capacity is achieved (for a small number of users) over conventional opportunistic space division multiple access, and a 100% gain (for a large number of users) over conventional opportunistic beamforming when the number of transmit antennas is four.     

多用户MIMO网络的OFDM放大转发双向中继策略

在多用户MIMO通信网络中,该文提出一种新的放大转发双向中继策略,在第1时隙的多址传输中采用OFDMA,在第2时隙的广播传输中采用OFDM/SDMA,通过利用频率分集和空间分集提高了系统性能。针对双向中继传输的特点,采用两种方法在每个子载波上设计了中继波束形成矩阵,即信漏噪比(SLNR)准则和块对角化迫零(BDZF)准则。利用割集理论推导了该双向中继网络的容量域上界。仿真结论表明,所提出的双向中继策略在系统和速率性能上优于其他3种中继策略,并能逼近所推导的容量域上界。     

Opportunistic Beamforming over Rayleigh Channels with Partial Side Information

In recent years, diversity techniques have evolved into highly attractive technology for wireless communications in different forms. For instance, the channel fluctuations of the users in a network are exploited as multiuser diversity by scheduling the user with the best signal-to-noise ratio (SNR). When fading is slow, beamforming at a multiple antenna transmitter is used to induce artificial channel fluctuations to ensure multiuser diversity in the network. Such a beamforming scheme is called opportunistic beamforming since the transmitter uses random beamforming to artificially induce opportunism in the network [1]. Opportunism requires a large number of users in the system in order to reach the performance of the true beamforming that uses perfect channel state information (CSI). In this paper we investigate the benefit of having partial CSI at an opportunistic transmitter. In the investigation, we focus on the maximum normalized SNR scheduling where user?s feedback consists of SNR relative to its channel gain. We show that opportunism can be beneficially used to increase the average throughput of the system. Simulations support the analytical average throughput results obtained as the amount of CSI and the number of users vary.     

Differentiated rate scheduling for the down-link of cellular systems

We consider the problem of differentiated rate scheduling for the downlink (i.e., multi-antenna broadcast channel), in the sense that the rates required by different users must satisfy certain constraints on their ratios. When full channel state information (CSI) is available at the transmitter and receivers, the problem can be readily solved using dirty paper coding (DPC) and the application of convex optimization techniques on the dual problem which is the multiple access channel (MAC). Since in many practical application full CSI may not be feasible and computational complexity prohibitive when the number of users is large, we focus on other simple schemes that require very little CSI: time-division opportunistic (TO) beamforming where in different time slots (of different lengths) the transmitter performs opportunistic beamforming to the users requiring the same rate, and weighted opportunistic (WO) beamforming where the random beams are assigned to those users having the largest weighted SINR. For single antenna systems we also look at the capacity-achieving superposition coding (SC) scheme. In all cases, we determine explicit schedules to guarantee the rate constraints and show that, in the limit of large number of users, the throughput loss compared to the unconstrained throughput (sum-rate capacity) tends to zero. We further provide bounds on the rate of convergence of the sum-rates of these schemes to the sum-rate capacity. Finally, we provide simulation results of the performance of different scheduling schemes considered in the paper.     

多载波多用户下行NOMA系统的资源分配算法

非正交多址接入技术作为5G的候选技术之一受到了广泛关注。研究了以系统吞吐量优化为目标的多载波多用户NOMA系统下行链路的资源分配问题。在该问题的求解中,为了提高系统的吞吐量,子载波间采用线性注水算法,叠加用户间采用分数阶功率分配算法。同时,考虑了远近用户数目不等场景下能够调度更多的用户,在NOMA传输方案设计中引入时分的概念,将整个时间段t分为两个时隙,在不同时隙内实现不同远近用户分组的动态配对方案,从而在保证用户公平性的基础上,充分利用子信道资源,实现系统吞吐量的优化。仿真结果表明,对比于传统NOMA和OFDMA,提出的方法可以在相同的发射功率情况下传输更多的比特数。     

Inter‐cell coordinated beamforming with opportunistic scheduling

This paper proposes a distributed coordination framework with opportunistic scheduling among multiple users as opposed to the existing works on the multiple‐cell cooperative beamforming problem that deals with a single active user in each cell. In this cross‐layer design framework that deals with the beamforming in the physical layer and multiuser scheduling in the upper layer, radio resource management and inter‐cell coordination issues are jointly considered to improve the cell‐edge throughput performance by trading off their individual benefit in an optimal manner. Our simulation results demonstrated that its performance can reach up to 85% of its upper bound at the cell boundary. Copyright © 2015 John Wiley & Sons, Ltd.