结合波束形成与发射分集的闭环下行发射方案

多天线技术是提高下行发射性能的一种有效方法。波束形成(BF)和发射分集(TD)均通过使用多个天线来有效地改善系统性能并提高信道容量。该文提出了一种将BF和TD结合用于闭环通信系统的自适应下行发射方案, 它包括适合于慢变信道的分集阵列方法和适合于快变信道的波束形成阵列方法。基站可以根据实际的信道状况自适应地调整发射方法。文中详细地介绍了自适应方案的实现算法,并对算法的复杂度和适应环境进行了分析。仿真结果证明新方案可以同时获得BF增益和TD增益,在使系统的误比特率(BER)性能大幅提高的同时,增强了系统对信道变化的适应能力。     

Opportunistic Grassmannian Beamforming for Multiuser and Multiantenna Downlink Communications

Scheduling in a broadcast channel based on partial channel-state-information at the transmitter is carried out in an opportunistic way. In this paper, the number of generated beams is larger than the number of available base station antennas, where the beams are obtained through Grassmannian line packing to guarantee the largest orthogonality among them. Approximate expressions and bounds are derived for the sum capacity of the proposed approach together with its scaling law. For practical systems, we show that this scheme can increase the number of serviced users under a minimum-rate-per-user requirement.     

WCDMA软切换的下行发射分集与功率控制策略

分别介绍了传统软切换分集方式、单基站选择分集传输方式（S-SSDT）、多基站选择分集传输方式（M-SSDT）、基站独立分集传输方式（SIDT）等几种发射分集策略，并探讨了相应的下行功率控制方案。     

第三代移动通信系统中的发送分集技术

利用反馈的信道状态信息,可以使系统在获得分集增益的同时,又获得额外天线增益。因此,又可以根据是否采用反馈结构将TD技术分为开环和闭环两大类。现有的3G标准都在前向链路中采纳了不同的TD技术。     

用于移动通信系统的发送分集技术

在分析接收分集技术最大比率接收合并(MRRC)方案的基础上，介绍了一种两分支发送分集方案。该方案采用2个发射天线、1个接收天线，可提供与1个发送天线、2个接收天线情况下的MRRC方案相同的分集增益。由于发送符号采用了正交性设计，该发送分集方案在接收端可以将不同的发送符号分离开来，分别进行最大似然检测。仿真结果表明，运用分集技术可大大改善无线通信系统的性能，且该方案和一发两收的MRRC方案性能相似、计算复杂性相同。该发送分集方案能更好地应用于移动通信系统。     

TD-SCDMA系统下行波束赋形技术研究

结合TD-SCDMA系统的特点,深入研究了最大信噪比(MSNR)准则和最大信干噪比(MSINR)准则的下行波束赋形算法。理论分析和仿真结果表明,基于MSINR准则的算法性能优于基于MSNR准则的算法,但是计算量有所增加。     

Transmission Strategies for MISO Downlink MC-CDMA Mobile Systems

This paper proposes two space-frequency schemes with a multi-user pre-filtering technique for downlink (DL) multicarrier code division multiple access (MC-CDMA) systems. We consider the use of antenna arrays at the base station (BS) and a single antenna at the mobile terminal (MT) and derive the proposed multi-user pre-filtering technique that modulates the transmitted signal to eliminate the effects of multiple access interference (MAI) and channel distortions at the mobile terminals, while maintaining low MT complexity. Two types of detectors are considered at the MT: simple despreading and single user equalizers. The performances of the proposed schemes are compared to those of other transmit signal design approaches that have been recently proposed for DL MC-CDMA, considering both typical indoor and pedestrian scenarios, and channel coding based on UMTS specifications.     

Blind Signal Reception and Channel Estimation in Downlink MC-CDMA Communication System with Transmit Diversity

In this paper, we exploit transmit diversity in downlink multicarrier CDMA (MC-CDMA) system to provide a solution to a high data rate, high capacity, yet reliable and robust to fading channel network. Our first emphasis is on designing a blind (without knowing the undesired users' signatures and channel parameters) MC-CDMA receiver in the mobile station that can suppress the multiple access interference (MAI) and combine the desired signal stemmed from all the transmitting antennas. Two blind signal reception algorithms are proposed and the performances in terms of signal-to-interference-and-noise-ratio (SINR) are comprehensively analyzed. One is based on the decorrelating RAKE (DRAKE) scheme proposed in [IEEE Trans. Communs. 47(7), 1036–1045, 1999] and the other is designed to meet the minimum output energy (MOE) criterion [IEEE Trans. on Information Theory 41(4), 944–996, 1995]. The MOE receiver, though optimum in ideal situation, is semi-blind that the vector channel impulse responses (VCIR) should be explicitly known. While the proposed modified DRAKE receiver is completely blind that it does not require any information of VCIR. Furthermore, we demonstrate that in practical scenario, the modified DRAKE scheme substantially outperforms the MOE receiver. The second part of this paper is to develop an efficient and blind (without requiring training sequences) algorithm to estimate the VCIR of downlink antenna array MC-CDMA system. Simulation results show that both the channel estimation algorithm and the blind reception schemes are reliable and near-far resistant. Wei-Chiang Wu received the M.S. and Ph.D. degrees both in electrical engineering from the National Tsing Hua University, Hsin-chu, Taiwan, R.O.C., in 1992 and 1998, respectively. From 1992 to 1994, he was an assistant researcher in the Communication Department at Chung Shan Institute of Science and Technology (CSIST), Taiwan, R.O.C.. From 1998 to 2000, hewas in the Army of Taiwan, where he conducted the research of Integrated Logistic Support (ILS). Since 2000, he has been an assistant Professor at the Department of Electrical Engineering, Da Yeh University, Changhua, Taiwan. His current research interests are in multiuser detection, smart antenna technology, multi-carrier CDMA and ultra-wideband (UWB) impulse radio (IR) technology.     

Differentiated TCP User Perception over Downlink Packet Data Cellular Systems

Current downlink scheduling algorithms in the (enhanced) third-generation (3G) cellular packet systems exploit instantaneous channel status of multiple users, but most of them are blind to traffic information. To improve TCP users' perception of quality-of-services (QoSs), characterized by response delay, goodput, and always-on connectivity, we propose a cross-layer hierarchical scheduler with traffic awareness and channel dependence to properly prioritize buffer and radio resource allocation among different TCP classes. The scheduler has two tiers: at the IP layer, an intrauser scheduler enhances a common practice, i.e., the DiffServ-based buffer management, by dequeuing same-user TCP packets according to per-class specified and measured responsiveness; at the MAC layer, an interuser scheduler transmits the dequeued packets by considering the opportunistic channel states, mean throughput, and class ID of all users. Both tiers consider the online measured throughput, a cross-layer metric, to achieve resource and performance fairness and TCP classification. Experiments show that, compared with (variations of) proportional fairness (PF) and other schemes, our scheduler can notably speed up time-critical interactive TCP services (HTTP and TELNET) or TCP slow-starts with minor cost to bulk file transfer (FTP) or long-lived flows. It offers scalable and low-cost TCP performance enhancement over the emerging cellular systems     

基于公平效用函数的多波束卫星通信下行链路波束成形算法

为了更好地平衡多波束卫星通信系统的频谱效率和能量效率,以及保证多用户服务场景下的用户服务公平性,该文提出一种基于公平效用函数的波束成形(BF)方案。具体而言,首先在同时考虑卫星发射功率最小化准则以及系统和速率最大化准则的前提下,建立一个多目标优化问题,并在最大化系统频谱效率的同时利用$\alpha $公平效用函数提升用户间的服务公平性。然后利用加权和方法对复杂的多目标问题进行转换处理,并提出一种联合使用循环坐标上升(CCA)方法以及回溯直线搜索(BLS)方法的波束成形方案,从而求得最优的波束成形权矢量以及最优的帕累托解集。最后计算机仿真结果验证了所提方案的用户服务公平性,以及分析一些典型参数对公平性能的影响。并通过与其他传统方案相比,验证所提方案能够获得更高的系统频谱效率。     

Improved Opportunistic Beamforming in Ricean Channels

In order to improve the performance of opportunistic beamforming in Ricean channels, we propose an improved opportunistic beamforming scheme which forms beams intelligently to the users. First, a new concept of the generalized Ricean distribution is introduced. On the basis of this theory, we propose a maximum-likelihood (ML) estimator of the directions of arrival of the users, and we derive the Cramer-Rao lower bound to evaluate the performance of the ML estimator. Furthermore, the generalized Ricean K-factors are estimated by a moment-based method. With the same pilot overhead in the downlink and with the same feedback overhead in the uplink, the improved scheme considerably outperforms conventional opportunistic beamforming     

现代移动通信中发射分集技术研究

基于发送端多天线系统的发射分集技术是现代移动通信系统中抗信道衰落影响的一项关键技术。全面介绍发射分集技术的概念和实现方式,利用频率、时间、空间、极化、角度、调制等各种无线资源均可实现有效的发射分集方案,并且详细分析了各类典型的发射分集技术的特点和性能,理论分析有助于推广多天线发射分集系统在实际通信系统中的进一步应用。     

传输分集技术在第三代移动通信系统中的应用

本文首先分析了衰落信道中采用分集技术时卷积编码Viterbi软判算法的性能,指出具有独立衰落特性的分集信道数越多,接收的性能越好.并给出了采用不同的分集技术时系统性能的仿真结果,结果表明采用传输分集技术可以明显提高前向链路的性能,而不增加移动终端的复杂度.传输分集是一种有效可行的对抗衰落的技术,有望在第三代移动通信系统中得到广泛应用.     

MISO系统下行波束赋形及仿真

研究了基于TD-SCDMA系统的下行波束赋形,利用最大信干噪比准则计算出天线的加权系数,在发送端进行赋形,并做了仿真,结果表明下行波束赋形能明显降低接收端误码率,进而降低了基站发射功率。     

5G移动通信系统的下行控制信道传输

基于5G系统的控制信道结构和传输机制,通过多种场景下的性能仿真从而得到导频图案和聚合等级的优化准则。首先,用于解调控制信道的导频与控制信道采用相同的预编码以实现控制信道波束的透明传输;其次,控制信道在频域资源上打散,当信道状态未知则采用分集的传输机制;再次,导频分布随聚合等级的变化而调整,低聚合等级导频密度大,高聚合等级导频密度小。该方法可以根据信道状况是否可知采用波束赋形或分集的传输,实现控制信息的可靠、有效传输。     

A MC-CDMA Mobile Communication System Employing Pre-Rake and Transmit Diversity

In this paper, a multi-carrier code division multiple access (MC-CDMA) downlink mobile communication system employing pre-rake and dual transmit diversity is proposed. It combines high spectral efficiency with an immunity to channel dispersion and fading. It also ensures small size, cost and power consumption of the terminal. Theoretical and simulation results for the system under consideration are obtained. Depicted results show appreciable improvements of the proposed system over those previously known.Emad K. Al-Hussaini received his B.Sc degree in Electrical Communication Engineering from Ain-Shams University, Cairo, Egypt, in 1964 and his M.Sc and Ph.D. degrees from Cairo University, Giza, Egypt, in 1974 and 1977, respectively. From 1964 to 1970, he was with the General Egyptian Aeroorganization. Since 1970, he has been with the Department of Electronics and Communications, Faculty of Engineering, Cairo University, and is currently professor there. He was a research fellow at Imperial College, London, UK, and at the Moore School of Electrical Engineering, University of Pennsylvania, Philadelphia, PA, USA, in the academic years 1976/1977 and 1981/1982, respectively. In 1990, he received the Egyptian national encouragement award for outstanding engineering research. He has written several papers for technical international journals and conferences. His research interests include signal processing, fading channel communication, modulation, and cellular mobile radio systems. Dr Al-Hussaini is a senior member of IEEE. He is listed in Marquis Whos Who in the World and in the IBC (International Biographical Center, Cambridge) for outstanding people of the 20th century.Hebat-Allah M.Mourad received her B.Sc, M.Sc and Ph.D degrees in Electrical Communication Engineering from Cairo University, Egypt, in 1983, 1987 and 1994 respectively. Since 1983 she has been with the Electronics and Communications Department, Faculty of Engineering Cairo University and is currently associate professor there. Her research interests include mobile communications, satellite communications and optical fiber communications.Fatma A. Newagy received her B.Sc and M.Sc degrees in electrical communication engineering from Cairo University, Egypt in 1998 and 2002 respectively. Since 1999, she has been a research assistant with the Department of Electronics and Communications, Faculty of Engineering, Cairo University. She is pursuing her Ph.D. there. Her research interests include mobile communications and modulation techniques for spread spectrum and wireless communications.     

Level Crossing Rates in Transmit Beamforming Systems

In this paper, the second-order statistics of the signal to noise ratio (SNR) at the output of a multiple-input-multiple-output (MIMO) system employing maximal ratio combining (MRC) are analyzed. Exact expressions for the level crossing rate (LCR) and the average fade duration (AFD) are derived for the Rayleigh propagation and arbitrary channel matrix dimensions. The analytical results are validated by simulation     

Opportunistic Mobile Data Offloading Using Machine Learning Approach

Wireless Personal Communications - Currently, cellular networks both 3G and 4G are heavily overloaded due to increasing usage of mobile applications. Offloading mobile data traffic through...     

TD-SCDMA系统中一种快速的下行波束形成技术

利用阵列天线系统接收信号的自相关矩阵的最大特征值所对应的本征向量的信号处理(PSM)思想,提出一种适用于TD—SCDMA系统的快速下行波束形成技术。此方法利用各个用户的扩频码进行目标用户的数据分离,并用迭代的方法代替用户信号的自相关矩阵的特征分解,降低了计算复杂度。计算机仿真验证了该方法的有效性。     

Cooperative Multicell Zero-Forcing Beamforming in Cellular Downlink Channels

In this work, a multicell cooperative zero-forcing beamforming (ZFBF) scheme combined with a simple user selection procedure is considered for the Wyner cellular downlink channel. The approach is to transmit to the user with the ldquobestrdquo local channel in each cell. The performance of this suboptimal scheme is investigated in terms of the conventional sum-rate scaling law and the sum-rate offset for an increasing number of users per cell. We term this characterization of the sum-rate for large number of users as high-load regime characterization, and point out the similarity of this approach to the standard affine approximation used in the high-signal-to-noise ratio (SNR) regime. It is shown that, under an overall power constraint, the suboptimal cooperative multicell ZFBF scheme achieves the same sum-rate growth rate and slightly degraded offset law, when compared to an optimal scheme deploying joint multicell dirty-paper coding (DPC), asymptotically with the number of users per cell. Moreover, the overall power constraint is shown to ensure in probability, equal per-cell power constraints when the number of users per-cell increases.