A Low Complexity Downlink Beamforming Scheme for DS-CDMA System

The downlink capacity of frequency division duplex (FDD) based DS-CDMA system can be improved if multielement antenna array is equipped at the base station. In this paper, a novel two-path downlink beamforming (TPDB) scheme is proposed to reduce multiple access interference as well as providing two-order path diversity in downlink. An analysis model is presented for the capacity evaluation of multirate DS-CDMA system with base station antenna array, and the capacity performance of the TPDB is compared with other schemes based on this model. The comparison results show that the TPDB would be a promising candidate for the downlink transmission if both performance and implementation complexity are considered. Moreover, a simple algorithm is proposed for the steering vector estimation in the TPDB, and the robustness of this estimation algorithm in the presence of fading and interference is also confirmed by computer simulations.     

Beamforming for Downlink Multiuser MIMO Time‐Varying Channels Based on Generalized Eigenvector Perturbation

A beam design method based on signal‐to‐leakage‐plus‐noise ratio (SLNR) has been recently proposed as an effective scheme for multiuser multiple‐input multiple‐output downlink channels. It is shown that its solution, which maximizes the SLNR at a transmitter, can be simply obtained by the generalized eigenvectors corresponding to the dominant generalized eigenvalues of a pair of covariance matrices of a desired signal and interference leakage plus noise. Under time‐varying channels, however, generalized eigendecomposition is required at each time step to design the optimal beam, and its level of complexity is too high to implement in practical systems. To overcome this problem, a predictive beam design method updating the beams according to channel variation is proposed. To this end, the perturbed generalized eigenvectors, which can be obtained by a perturbation theory without any iteration, are used. The performance of the method in terms of SLNR is analyzed and verified using numerical results.     

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。     

无线通信中基于线性预测和参数反馈的下行波束形成方法

本文基于最大信号噪声比准则(MSNR，Maximum Signal Noise Ratio)提出一种新的下行波束形成方法，即根据天线收发的互易性原理，通过上行波束形成得到的上行天线阵列矢量，变换而得到下行天线阵列矢量，再通过移动端Rake接收机的合作，反馈回每一径的衰落系数，考虑到存在传输和处理时延并且在此时间内信道有明显变化时，反馈的衰落系数存在误差。因此，本文采用了信道预测的方法，估计即时衰落系数，这样求得期望信号的相关矩阵，计算相应的最大广义特征值所对应的特征矢量，进行下行波束形成。     

Multiuser MIMO Systems with Random Transmit Beamforming

This paper considers the wireless downlink transmissions in a single cell environment, for which the base station (BS) is assumed to schedule its transmission to each mobile station (MS) on a time-slot basis. Only one MS is selected for transmission during each time-slot and the selected MS possibly changes from one time-slot to another. This transmission scheme is thus referred to as dynamic time-division multiple-access (D-TDMA). Random transmit beamforming with the feedback of effective signal-to-noise ratio (ESNR) was proposed by Viswanath and Tse [IEEE Transactions on Information Theory, Vol. 48, No. 6, pp. 1277–1294, 2002] for D-TDMA-based systems in which multiple transmit antennas are equipped at the BS but only single receive antenna is equipped at each MS, or the so-called “MISO” systems. It was also shown in [Viswanath and Tse, 2002] that when the number of MSs in the system becomes large, the system throughput achieved by random transmit beamforming converges to that by coherent transmit beamforming which, however, requires the complete channel state information (CSI) of each MS at the BS. This paper extends upon the work in [Viswanath and Tse, 2002] to a more general scenario for which multiple transmit antennas and multiple receive antennas are equipped at the BS and each MS, respectively, or the so-called “MIMO” systems. We also consider several linear and nonlinear receiver structures and propose novel power allocation schemes to further improve the achievable system throughput. The throughput performance of the proposed receivers and power allocations schemes is compared through computer simulations and their fast convergence to the system throughput by coherent transmit beamforming is demonstrated.

Space-Time Coded Beamforming for DS CDMA Downlink

1　Introduction　 In 3G mobile system, Code Division Multiple Access(CDMA) is a promising multiple access techniques. It iswell know that BeamFormin ( BF), Space Time Coding(STC) and Multiuser Detection(MUD) techniques in CDMAsystem can effectively resist Multi Path Interference (MPI),MAI and near far effects. So the system capacity will be im proved greatly by employing these techniques[1,2,8]. In Ref.[3] introduces Water Filling(WF) theory into STC to assignth…     

Performance of a Digital Beamforming Concept in a GSM1800 Downlink: A Simulation Study

A smart antenna concept was studied in the context of a GSM1800 downlink. In practice, it is not possible to estimate the actual downlink channel when using frequency division duplexing (FDD). Therefore, the current approach is based on uplink direction-of-arrival (DoA) estimation. The downlink beam is then directed to the DoA obtained from the uplink. The purpose was to study the dependence of downlink performance on the angular and delay distribution of the desired signal. The downlink beamforming was studied in this work using simulations with 2D channel models for different test environments. The probability of error in DoA estimation of the desired mobile station was evaluated in conjunction with DoA averaging. In addition, downlink BER performance was examined in a noise-limited situation and compared to the results of the corresponding uplink and a conventional 2-branch GSM receiver. With a 1*8-element antenna configuration, downlink performance degradation compared to the corresponding uplink case was approximately 1.3 dB, 2.4 dB, and 0 dB in typical Urban, Suburban, and Rural environments. The losses were greater in environments with very large angular spread. It was also found that increasing accuracy in uplink DoA estimation does not necessarily correspond to improved downlink performance.     

LTE-Advanced中的下行8天线码本设计

LTE-Advanced在LTE下行MIMO4天线的基础上引入8天线的设计,预编码码本的设计是很重要的一项内容,影响到上行反馈模式和反馈开销等,因此需要针对8天线的配置优先场景,设计出性能和开销均为最优的码本。本文讨论了3GPP对8天线配置场景的优先级,分析了3种具体的码本设计方案,包括基于波束扫描的码本（GoB码本）、差分码本和自适应码本,并从性能、开销等方面比较了3种码本设计方案,最后对3GPP最终采用的8天线码本设计方案原理进行了介绍。     

5G下行CoMP技术研究及测试验证

对于同频干扰严重的重叠覆盖场景,CoMP可提高边缘用户SINR,降低小区间干扰,提高边缘用户的吞吐率.对下行CoMP技术进行介绍,并重点介绍了5G下行CoMP与技术与LTE下行CoMP的主要差异,5G下行CoMP JT的基本原理以及具体的实现流程.针对2种场景,对5G下行CoMP JT技术进行了性能验证及分析.测试结果...     

TD-SCDMA系统中基于上行参数的下行波束赋形算法

在TD－SCDMA系统中，我们在基站发送端进行波束赋形来提高下行链路的性能。以最优准则－最大信干噪比特征分解算法为例，我们分析基于上行参数进行下行赋形的基本原理，模拟了不同环境下赋形算法的性能，并与全向情况进行比较，得出了相应的结论。     

基于GGASA算法优化信号互相关的MIMO雷达波束形成技术

MIMO(Multiple-input Multiple-output)雷达系统的单元或子阵辐射互不相同的波形,提供了足够的自由度用于天线波束的灵活成形和捷变,可以作为常规相控阵和正交雷达信号MIMO体制的通用化推广。在研究分析具有任意互相关特性的信号集合的选择综合波束方向图的基础上,采用全局遗传模拟退火算法对MIMO雷达的波束综合问题进行了最优化搜索,仿真结果显示,该算法获得了较好的结果。     

多用户MIMO下行链路中线性预编码器和译码器的联合优化

文章研究多用户MIMO下行链路中线性预编码器和译码器的联合优化问题。采用的优化准则是在总发射功率约束下最小化系统的和均方误差（Sum MSE,SMSE）,提出了一种启发式的迭代算法。通过在接收端引入相同的自动增益控制因子,该算法对预编码器和译码器进行交替优化,直到SMSE达到最小值。分析和仿真结果表明：该算法具有较低的复杂度和良好的收敛特性,符号差错率也优于现有算法。     

Optimal Multi-User Interference Balancing Using Transmit Beamforming

Wireless Personal Communications - We study the problem of non-orthogonal spatial multiplexing under hard fairness constraints, assuming that the transmitter is equipped with multiple antennas and...     

Essential Considerations in Implementing the Smart Antenna System for Downlink Beamforming

This paper addresses some essential problems that have to be taken into consideration in implementing the smart antenna base station (SABS) for downlink beamforming. In order to provide proper downlink beamforming as well as uplink beamforming, a pragmatic procedure of automatic calibration is proposed. Through the experimental test, we confirm that the proposed calibration technique has eliminated the problem of the phase differences of the signal path associated with each antenna. Also, in this paper, we first analyze the multipath condition under which the auxiliary pilot becomes indispensable for detecting the data transmitted on the data channel and what happens if the auxiliary pilot is not available. Then, the performance of the downlink beamforming utilizing the auxiliary pilot is analyzed through the computer simulations. Finally, we present a comparison of downlink communications to uplink ones in terms of throughputs available at each of uplink and downlink communications. Weon-Cheol Lee received the B.S, M.S, and Ph.D. degree in Electronic Communication Engineering from Hanyang University, Korea, in 1992, 1994, 2005, respectively. From 1994 to 2000, he was with LG Electronic Inc., where he had worked for developing the digital VCR, digital cable modem, digital TV. Since 2001, he has been a professor with department of information and communications, Yong-in Songdam College, Korea. His research interests include smart antennas, mobile communications beyond the third generation, digital broadcasting technology, and communication signal processing. Dr. Lee also received the Best Research Paper Award and Excellent Research Engineer Award from LG Electronics, respectively. Seungwon Choireceived the BS degree from Hanyang University, Seoul, Korea, and the M.S. degree from Seoul National University, Korea, 1980 and 1982, respectively, both in electronics engineering, the MS degree (computer engineering) in 1985, and the PhD degree (electrical engineering), in 1988, both from Syracuse University, Syracuse, NY. From 1988 to 1989 he was with the Department of Electrical and Computer Engineering of Syracuse University, Syracuse, NY, as an Assistant Professor. In 1989 he joined the Electronics and Telecommunications Research Institute, Daejeon, Korea. From 1990 to 1992 he was with the Communications Research Laboratory, Tokyo, Japan, as a Science and Technology Agency fellow, developing the adaptive antenna array systems and adaptive equalizing filters. He joined Hanyang University, Seoul, Korea, in 1992 as an assistant professor. He is a professor in the School of Electrical and Computer Engineering of Hanyang University. Since 2003, Dr. Choi has been serving as a Vice Chairman and the representative of the ITU region 3 for SDR (Software Defined Radio) Forum and as a Director of the HY-SDR Research Center, MIC, Korea. His research interests include digital communications and adaptive signal processing with a recent focus on the implementation of the smart antenna systems for both mobile communication systems and wireless data systems. Jae-Moung Kim received the BS degree from Hanyang University, Korea in 1974, the MSEE degree from University of Southern California, USA in 1981, and the PhD degree from Yonsei University, Korea in 1987. He was a Vice President of Radio {&} Broadcasting Technology Laboratory and Director of Satellite Communication System Department at Electronics and Telecommunications Research Institute (ETRI) from September 1982 to March 2003. Since April of 2003, he has been a Professor in the Graduate School of Information Technology and Telecommunications, Inha University. He is a board member of directors of Korean Institute of Communication Science (KICS), a Vice President of Korea Society of Broadcast Engineers (KOSBE) and a senior member of IEEE. His research background is telecommunication systems modeling and performance analysis of broadband wireless access systems, mobile communications, satellite communications and broadcasting transmission technologies.     

面向大规模MIMO系统的下行预编码技术研究进展

大规模多入多出(Multiple-Input Multiple-Output,MIMO)技术在移动通信系统中发挥着至关重要的作用,但在部署中却引入了干扰.为了消除大规模MIMO干扰,业界围绕低复杂度的预编码算法开展了大量的研究工作.将已有大规模MIMO系统的预编码技术进行了归纳,重点分析了线性预编码和非线性预编码中经典算法的复杂度和优缺点,最后对大规模MIMO预编码技术的发展趋势进行了探讨.     

一种基于特定干扰图样的下行多用户MIMO预编码方法

本文在研究线性迫零类下行多用户MIMO预编码方法的基础上,提出了一种适用于单天线用户的预编码矩阵生成方法.利用信道补矩阵的奇异值分解,可以将下行多用户MIMO信道分解为多个带有基于干扰图样产生的多用户干扰的并行单用户信道.同时本文给出了一种特殊的干扰图样以及相应的显式参数优化方法,包括波束成型和功率分配.通过计算机仿真,重点在4天线场景下分析了该预编码器的系统性能.结果显示,相对于线性迫零类算法,本文提出的预编码方法可以有效的提高系统性能.在Pout等于0.1时,相对于单天线的BD方法,PBIF-Rp将损耗信道容量提高了超过45%,而PBIF-Op提高了100%以上.仿真结果和分析都证明了本方法的进一步研究的潜力.     

LTE-A下行单用户MIMO增强技术研究

无线通信系统中,基站可以针对信道空间特性采用不同的下行传输模式获得空间复用增益和波束成形增益以提升系统性能。LTE-A中的下行单用户MIMO增强技术,采用了基于码本以及非码本的预编码技术优化性能,有必要分析其技术特点和增益来源以指导产品设计。分析了LTE-A中单用户MIMO技术演进的新特点,着重研究了新的双码本结构,在对信道属性匹配、码本搜索运算复杂度和UE上报载荷方面的改进。针对LTE-A预编码技术性能问题,通过计算机链路级仿真比较了LTE—A中基于码本以及非码本预编码技术的吞吐量性能,仿真结果表明码本技术较非码本技术具有一定优势。     

Modified precoding strategy over MIMO double-correlated channels

Double-correlated channels commonly occur due to insufficient scattering around both the transmitting and receiving antennas. In this article, the authors propose a linear precoding strategy with a modified system model over double-correlated channels. In this system model, an inner decorrelation strategy is added combined with precoding. First, a linear precoder that achieves minimum bit error rate (MBER) is proposed and analyzed based on the modified system model. The simulation results show that the bit error rate (BER) performance can be improved by decorrelation. Second, the influence of double correlation on multiple input and multiple output (MIMO) capacity is analyzed and simulated.     

信道估计误差对MIMO系统信道容量的影响研究

为了分析信道估计误差对信道容量的影响,结合MIMO系统接收端信道估计误差的特点,重新构建了MIMO信道的统计模型。利用Wishart分布的性质,推导了当MIMO信道矩阵满秩时,仅接收端已知信道CSI情况下系统信道容量的下限。仿真结果表明,MIMO系统信道容量对信道估计误差比较敏感。     

阵列误差对Capon波束形成算法的影响分析

针对阵列误差存在时经典(Capon)波束形成算法的性能严重恶化问题,介绍了均匀圆阵阵列流型下的Capon波束形成算法,对阵列天线各阵元间的幅度误差、相位误差、水平位置误差和垂直位置误差进行了数学建模,仿真分析了各种阵列误差对Capon波束形成算法的影响,并给出了该影响的量化分析结果,从而对该算法工程实现时的指标确定提供依据。