天线与天线系统

0617287分布式目标下行波束形成〔刊,中〕/徐卫//中国电子科学研究院学报.—2006,1(1).—98-101(G)研究了智能天线在下行链路的应用,利用上行链路接收数据,建立分布式目标信道模型,估计移动用户的发射角、扩展角度和发射功率以及下行信道相关矩阵,确定下行链路的波束形成方法,即对频分复用(FDD)系统进行上行相关矩阵变换,构建下行信道协方差矩阵,利用最大合并比准则获得下行链路权值。计算机仿真证实了这种方法的有效性。参50617288基于数字波束合成的空间信号分离研究〔刊,中〕/贾朝文//中国电子科学研究院学报.—2006,1(1).—86-88,65(G…     

FDD-CDMA的下行链路的波束形成

本文研究了在智能天线在ＦＤＤ－ＣＤＭＡ中的下行链路的应用，利用上行链路接收数据，估计了下行链路的信道相关矩阵和对其它小区用户的相对干扰总量，给出下行链路的波束形成方法，即在保证一定的有效发送功率的同时，使得对其他小区的用户干扰最小。计算机仿真表明：（在多小区蜂窝ＣＤＭＡ环境中，采用上述方法比仅保证用户方向的最大发送功率，有更小的中断率。     

FDD—CDMA的下行链路的波束形成

本文研究了在智能天线在ＦＤＤ－ＣＤＭＡ中的下行链路的应用，利用上行链路接收数据，估计了下行链路的信道相关矩阵和对其它小区用户的相对干扰总量，给出下行链路的波束形成方法，即在保证一定的有效发送功率的同时，使得对其他小区的用户干扰最小。计算机仿真表明：（在多小区蜂窝ＣＤＭＡ环境中，采用上述方法比仅保证用户方向的最大发送功率，有更小的中断率。     

WCDMA增强的上行链路关键技术及性能分析

文章首先介绍了上行链路提出的背景以及与下行链路的区别，接着介绍了上行链路的整体结构，重点分析了增强上行链路的关键技术，以及为了增加上行链路需要增加的物理信道，最后分析了增强上行信道的性能。     

阵列天线波束成形技术在宽带CDMA下行链路中的应用

本文利用自适应天线阵列上行链路信号到达角估计信息,并结合导频辅助下行链路信道矩阵估计值,在前人提出的具有反馈特性的自适应发送阵列原理基础上,提出一种简单可行的宽带CDMA下行链路天线阵列波束成形权重计算方法,并进一步分析了到达角估计误差和信道信息反馈时延对权重计算的影响,最后给出系统误码率性能的计算机仿真结果。     

Adaptive Antenna和Switched Beam相结合的新型智能天线

提出了一种上行链路采用Adaptive Beam,下行链路采用Switched Beam的新颖智能天线.其中上行链路是通过由信道估计得到的导向矢量形成指向各用户的Adaptive Beam,下行链路则是通过估计得到的用户分布形成Switched Beam.该智能天线系统既可以抑制上行链路中多用户信号的干扰,也可以使下行波束易于对准用户,使系统有尽可能高的容量且便于实现.     

LTE上行引入MIMO后的MLE信道估计算法

主要介绍LTE系统上行链路引入MIMO后的信道估计技术。首先介绍了基础的上行和下行信道估计的方法以及他们的区别,然后着重指出了在进行上行MIMO的信道估计时遇到的问题,并阐述了该问题的具体解决方法和详细的公式推导,最后通过对含有MIMO技术的上行LTE链路层的仿真,对在LTE上行MIMO系统中采用MLE算法进行信道估计的精确性进行了验证。     

WCDMA BTS接收系统中信道译码单元的研究与实现

该文简单介绍了WCDMA移动通信上行链路BTS接收系统中信道译码单元的处理过程,并给出了一种切实可行的具体实现方案。该方案对下行链路信道译码单元的实现同样具有重要的参考价值。     

多载波码分多址系统在瑞利衰落信道中的性能分析

多载波码分多址(MC-CDMA)是一种把多载波和CDMA相结合的技术方案。在MC-CDMA中,每个数据符号通过N个子载波传输,且根据扩频码对每个子载波以0或π相位偏移进行编码。分别研究了MC-CDMA系统上行链路和下行链路的瑞利衰落信道模型以及采用等增益组合和最大比组合的接收机模型,并对上行链路和下行链路的系统误码率性能进行了分析和计算。数值结果表明,MRC在上行链路中的性能要优于EGC,但在下行链路中的抗干扰性能不如EGC。     

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。     

Downlink channel covariance matrix (DCCM) estimation and itsapplications in wireless DS-CDMA systems

The downlink channel covariance matrix (DCCM) is of vital importance in determining downlink beamforming weights for base station (BS) antenna array systems. For the frequency-division-duplex (FDD) mode, DCCM is difficult to obtain due to a lack of direct measurement of downlink channel responses. In this paper, a novel technique is proposed for estimating DCCM using uplink channel responses only, which does not need direction-of-arrival (DOA) estimation and its association. The downlink beamforming scheme is then proposed for wireless DS-CDMA systems, using the obtained DCCM information together with the so-called virtual uplink beamforming and power control technique. Computer simulations show that using the BS antenna array together with this new beamforming technique can provide larger system capacity than traditional DOA-based approaches, which just direct the main beam toward the desired user     

带内全双工多用户MIMO系统中的用户选择

考虑一种多用户MIMO的传输设计,配置发射天线阵列和接收天线阵列的蜂窝基站可以工作在带内全双工传输模式。在该全双工通信方案中,基站的下行发射信号对基站的上行接收产生显著的干扰,即自干扰。这里,下行预编码处理和上行发射协方差矩阵处理将被依次进行,以简化全双工的设计。其次,为了进一步改善上、下行信道的和速率性能,我们提出一种尝试性的下行用户选择方案,其基本思想是:当某一个下行用户的信道矩阵的范数较小时,关闭该下行用户的数据流。计算机仿真结果表明,在基站下行总发射功率受限时,在低的和中等的下行信噪比区域,用户选择有助于提高下行和速率;在高的上行信噪比区域,简化的用户选择使得上行和速率明显提高。      

FDD-CDMA系统下行信道协方差矩阵的估计

针对在基站采用天线阵列的FDD-CDMA系统下,讨论利用上行链路的接收数据,通过码滤波后的数据协方差矩阵得到某一条路径的等效方向向量。在不求出DOA的情况下,采用离散傅里叶变换来估计该路径下行信道协方差矩阵。计算机仿真表明:在FDD-CDMA系统中,尽管上下行载波频率相差很大,采用上述方法仍能将波束的主瓣对准期望用户,并且与传统的DOA方法相比较,降低了由于解非线性优化所带来的计算复杂度。     

Adapting a downlink array from uplink measurements

In a frequency division duplex system, a transmitter adaptive antenna array can potentially improve the performance of a wireless downlink, but because the uplink and downlink channels have different wavelengths, and, therefore, different responses, direct downlink adaptation based on channel estimates of the uplink is generally not feasible. Instead, there has been some interest in adaptations that require only the second-order statistics of the uplink and downlink to be similar. These algorithms derive adaptive weights from the covariance of the received signal to apply to a downlink transmitter array. We make two contributions to this area. First, we introduce an array configuration employing M+1 elements with log-periodic spacing that comprises two overlapping subarrays, each with M elements, that are scaled versions of each other, with the scale factor equal to the ratio of the uplink wavelength to the downlink wavelength. This array has identical beampatterns at the two wavelengths, thus helping to fulfill the requirement that the uplink and downlink second-order statistics be the same. Second, we demonstrate that obtaining a good estimate of the uplink covariance matrix is not essential for the successful operation of the adaptive scheme. Even when the mobile is at rest and the uplink information comprises only a single snapshot from the receiver array, an adaptive scheme can improve the SNR     

Interference alignment scheme for massive MIMO system

The performance of massive multiple-input multiple-output （MIMO） system is limited by pilot contamination. To reduce the pilot contamination, uplink and downlink precoding algorithms are put forward based on interference alignment criterion. In the uplink receiving processing, the target function aligns the pilot contamination and the interference signals to the same null space and acquires the maximal space degree of the desired signals. The uplink receiving precoding matrix is solved on maximal signal to interference plus noise ratio （SINR） criterion considering the impact of the pilot contamination on channel estimations. The uplink receiving precoding matrix is used as the downlink transmitting precoding matrix. Exploiting the channel reciprocity, it is proved that, if the uplink receiving precoding matrix achieves maximal S1NR, the identical precoding matrix can be used in the downlink transmission and acquires maximal signal to leakage plus noise ratio （SLNR）. Simulations show that the spectrum efficiency of the proposed algorithm can reach about 1.5 times higher than that of popular matched filtering （MF） precoding algorithm, and about 1.1 times higher than multi-cell minimum mean square error （MMSE） precoding algorithm. The performance of the proposed algorithm can be improved approximately linearly with the increasing of the number of antennas.     

Capacity bounds of MIMO channels with asymmetric channel state information at transmitter

Using two receive antennas at a mobile phone improves downlink performance. But because of the correlation of the two antennas, using one of them to transmit in the uplink is a good performance-complexity tradeoff. This creates an interesting scenario of asymmetric channel state information at the transmitter in a time division duplex system, where the downlink channel coefficients related to one of the two receive antennas can be learned by the base station from the uplink training due to reciprocity. We provide near optimal transmitter design by obtaining upper and lower bounds of the downlink ergodic capacity.     

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.     

Joint utility function-based scheduling for two-way communication services in wireless networks

A type of joint utility function-based scheduling is proposed for two-way communication services in wireless networks. The scheduling of uplink and downlink services is done jointly so that the base station selects a user efficiently and fairly while considering the channel state of both the uplink and the downlink. Because a user generally has two communication links, an uplink and a downlink, the overall satisfaction with a communication service can be formulated as the sum of the quality of the uplink and downlink services. However, most of the previous types of scheduling for the uplink and downlink were designed separately and independently. This paper proposes a joint scheduling algorithm for integrated uplink and downlink services: a base station selects a user while simultaneously considering both the uplink channel state and the downlink channel state. An analytical model is developed for the purpose of determining the scheduling metric, the system throughput, and the level of fairness. The numerical and computer simulation results show that in comparison with conventional proportional fair scheduling the proposed joint scheduling achieves a better throughput while satisfying the fairness among users.