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.     

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     

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。     

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     

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     

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。     

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.     

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.     

TD-SCDMA系统下行联合波束功控技术

TD-SCDMA系统最重要技术特征是智能天线技术。本文基于时延和角度扩散空间信道模型,提出了一种下行基站联合优化波束和发射功率的智能天线技术。     

TD-SCDMA高速下行分组接入技术

对TD-SCDMA高速下行分组接入技术(HSDPA)中的关键技术作了详细的描述,并与WCDMA高速下行分组接入技术作了比较。     

机会波束成形系统中一种新的调度方案

主要研究机会波束成形系统中的调度算法,将宽带无线IP网络调度算法应用于机会波束成形系统。提出了一个保证用户QoS要求的新方案。数值分析表明,所提的方案较之传统的方案在保证系统吞吐量和用户间公平性的同时,也保证了用户的QoS。     

维纳滤波在TD-SCDMA下行链路中的研究

在发送端对信号进行预处理,不仅可以降低接收端的计算量和实现复杂性,还可以提高系统传输性能,增加系统的容量。本文推导了发送维纳滤波（TxWF）,并将这种技术应用于TD-SCDMA多用户MIMO下行链路。通过仿真分析,说明发送维纳滤波的传输性能优于传统的联合发送（JT）技术,在高信噪比的情况下尤为显著,具有良好的应用前景。     

分布式移动通信系统中多用户分集分析

分析了分布式移动通信系统中,Rayleigh-lognormal复合信道下,发送分集对下行链路多用户分集的影响,发现基于最大比发送(MRT)和基于选择发送分集(STD)调度算法获得了几乎相同的多用户分集增益。该结论表明,在分布式移动通信系统中,采用基于发送分集的调度方案并不能有效地提高系统的吞吐量。     

Macroscopic Transmission Diversity for CDMA Mobile Systems

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一种新的下行高速数据传输技术--HSDPA

介绍了移动通信系统演进过程中基于第三代移动通信标准WCDMA的新技术———HSDPA,该技术可以达到最高10.8Mbps的峰值数据速率。文中首先对HS-DSCH进行了详细描述,然后分别介绍了HSDPA几项关键技术及其研究现状。