垂直分层空时码系统下的信道盲估计

对垂直分层空时码系统进行信道估计时，常需采用训练序列，发射天线个数的增加会使得所需的训练符号个数增加，减少了传输数据的有效时间。本文将信号处理中的子空间方法同分层空时码的编码结构相结合，提出了一种垂直分层空时码，实现了无需训练序列的信道估计。Monte Carlo仿真结果表明，在相干时间允许的范围内，利用本文算法估计出的信道进行信号检测时，其性能十分接近使用准确信道信息的检测结果。     

增加时间分集的空时编码OFDM系统

提出了一种改进的空时编码正交频分复用(OFDM)系统,在经典的Alamouti空时编码的OFDM系统中增加了时域分集.在接收端运用等效信道的原理,使信道均衡过程容易实现.仿真选择低复杂度的MMSE信道均衡算法分别进行信道均衡,并比较它们的性能.仿真结果表明,该结构配合合适的均衡算法,系统的时间分集和空间分集能够被有效地利用,从而可以提高和稳定系统在高速移动信道环境下的性能.     

无线衰落信道的空时编码技术研究

移动无线通信是一种典型的衰落信道,空时编码技术是解决无线通信中信号衰落最有效的手段之一,简要介绍了移动通信系统中衰落对传输信号产生的4种效应,研究了移动衰落信道中的信道特性及衰落信号的分布特性。从空时编码技术原理出发,认真推导了空时编码系统的差错概率边界,分析了空时编码系统的误码性能,并以此为基础确定了最佳空时编码的设计准则,可为结合多天线系统的空时编码设计提供参考。     

部分信道状态信息对空时OFDM 系统性能的影响

在无线通信系统中,当发射端未知信道的状态特性时,采用空时编码可得到分集增益与编码增益.然而,在一些无线通信系统中,发射端可能已知部分信道状态特性,因此空时编码与自适应调制相结合可更进一步提高通信系统的性能.部分信道状态信息对自适应与空时编码相结合的OFDM系统性能的影响进行了讨论.仿真比较了自适应的空时OFDM与普通的空时OFDM的性能,可为时变信道的多天线OFDM系统设计提供参考.     

基于空时分组码及空频分组码的OFDM系统性能分析

讨论了正交频分复用系统中空时分组码与空频分组码的基本原理,并对信道条件为快变或慢变的多径信道下的两种系统误码性能进行分析与比较,指出在慢变信道条件下采用空时分组码的系统可取得较空频分组码系统更佳的性能。     

天线阵CDMA蜂窝无线通信系统的空时处理

本文围绕天线阵ＣＤＭＡ蜂容无线通信系统,简介了无线信道、单时间与单空间处理的特点,综述了空时自理即矢量均衡技术,包括系统模型与空时过取样信号的结构特性以基于某些优化准则和结构特性的空时处理方法,论证了将空时处理嵌入ＩＭＴ－２０００的可行性。     

MIMO系统在空时二维相关莱斯快衰落信道下的性能

与准静态独立的瑞利衰落信道模型相比较,在MIMO(Multi-Input Multi-Output)系统中,实际信道更趋向于空时相关莱斯快衰落。考虑到MIMO系统的收发分集优势以及收发两端天线阵列的空时相关性,在简单论述了MIMO系统和信道模型的基础上,该文利用多变量统计学理论,推导出MIMO系统在空时相关莱斯快衰落信道下平均成对差错概率上界的闭合表达式,并探讨了信道特性对系统性能的影响,然后给出相应仿真结果。     

空时编码在莱斯信道下精确成对误码率公式

文中针对研究空时编码误码率的需要,得出了空时编码系统在莱斯信道下新的精确的误码率公式,该式可以看作是把现有的结果从瑞利信道推广到了莱斯信道。     

宽带移动通信系统中基于梳状导频的信道估计

本文主要研究了OFDM系统中基于梳状导频的空时信道估计方法,并提出一种新的信道估计算法,即实现了空时二维信道估计。基于梳状导频的空时信道估计的算法分为两步:第一步是利用导频信号对导频位置的信道进行估计,第二步是信道插值,得到所有频域位置的信道信息。同时还研究了基于LS准则的信号估计以及基于线性插值的信道插值。     

空间相关连续衰落信道下对角酉空时星座的最大似然多符号差分检测算法

空间相关性会造成MIMO系统的性能损失.针对这种空间相关性,大部分酉空时系统利用反馈信道将空间相关信息反馈给发射机,发射机通过有效利用该信息,进一步提高系统的性能.本文针对实际应用的另一种情形,当酉空时系统不存在反馈信道时,提出了空间相关连续衰落信道下,对角酉空时星座的最大似然多符号差分检测算法.与传统的准静态信道模型相比,本算法基于连续衰落假设,是一种更一般的信道模型.计算机仿真结果表明:本算法可以在不明显增加开销的情况下,有效的提高空间相关连续衰落信道下对角酉空时星座的误码率性能.     

A space-time correlation model for multielement antenna systems inmobile fading channels

Analysis and design of multielement antenna systems in mobile fading channels require a model for the space-time cross correlation among the links of the underlying multiple-input multiple-output (MIMO) channel. In this paper, we propose a general space-time cross-correlation function for mobile frequency nonselective Rice fading MIMO channels, in which various parameters of interest such as the angle spreads at the base station and the user, the distance between the base station and the user, mean directions of the signal arrivals, array configurations, and Doppler spread are all taken into account. The new space-time cross-correlation function includes all the relevant parameters of the MIMO fading channel in a clean compact form, suitable for both mathematical analysis and numerical calculations/simulations. It also covers many known correlation models as special cases. We demonstrate the utility of the new space-time correlation model by clarifying the limitations of a widely accepted correlation model for MIMO fading channels. As another application, we quantify the impact of nonisotropic scattering around the user, on the capacity of a MIMO fading channel     

A novel repetition space-time coding scheme for mobile FSO systems

In this paper,we present an innovative method of double balanced differential configuration,in which two adjacent single photon avalanche diodes(SPADs)from the same wafer are configured as the first balanced structure,and the output signal from the first balanced stage is subtracted by the attenuated gate driving signal as the second balanced stage.The compact device is cooled down to 236 K to be characterized.At a gate repetition rate of 400 MHz and a1 550 nm laser repetition rate of 10 MHz,the maximum photon detection efficiency of 13.5%can be achieved.The dark count rate is about 10-4 ns-1 at photon detection efficiency of 10%.The afterpulsing probability decreases with time exponentially.It is shown that this configuration is effective to discriminate the ultra-weak avalanche signal in high speed gating rates.     

MIMO信道的GBDB模型及其信道容量分析

针对非频率选择性Rice衰落MIMO移动信道，建立GBDB模型，并推导出新的MIMO系统的GBDB模型的空时联合相关函数。新的GBDB模型统一现有的多种MIMO信道模型，新的空时联合相关函数综合考虑了无线衰落信道收发两端的多普勒扩展、非均匀角度扩展以及平均发射与到达方向，综合考虑了收发端天线阵的配置。最后基于新的空时联合相关函数，分析了非均匀散射参数以及Rice分布参数变化对MIMO信道统计容量的影响。     

A space-time model for frequency nonselective Rayleigh fadingchannels with applications to space-time modems

This paper extends the traditional Clarke/Jakes (1968, 1974) model for a frequency flat fading process in a land mobile radio system to facilitate the examination of coherent space-time demodulation systems. The work develops a space-time correlation function using a ring of scatterers model around the mobile unit. The resulting correlation function permits the investigation of a variety of issues concerning base station configurations in space-time systems. The interrelationship of the fading process between the space and the time domain is explored. A detailed example regarding the effects of antenna separation in a receiver diversity system is considered. A set of design rules for interleaving depth and antenna separation in a space-time modem is presented and quantified     

一种基于空时相关的MIMO OFDM系统信道估计算法

提出了一种基于空时相关的MIMO OFDM系统信道估计算法,该算法以时域最小二乘信道估计(TD-LS-CE)为初始估计,充分利用在接收端已知的空时相关性,通过最小化FIR窗内多符号平均意义上的信道估计均方误差(MSE),获得对初始信道估计进行空时滤波的最优权系数,并进一步利用奇异值分解的方法大大降低该信道估计算法的复杂度。最后仿真结果表明,在相同的条件下,该信道估计算法在MSE、BER方面优于传统滑动平均(MA)信道估计算法在其最佳窗长时的性能,且在一定条件下可逼近理想信道估计性能。此外,空时相关性的增强还可进一步改善该信道估计算法的性能。     

Space-time communication for OFDM with implicit channel feedback

We consider wideband communication (e.g., using orthogonal frequency-division multiplexed (OFDM) systems) over a typical cellular "downlink," in which both the base station and the mobile may have multiple antennas, but the number of antennas at the mobile is assumed to be small. Implicit channel feedback can play a powerful role in such systems, especially for outdoor channels, which typically exhibit narrow spatial spreads. A summary of our findings is as follows: a) Implicit channel feedback regarding the covariance matrix for the downlink space-time channel can be obtained, without any power or bandwidth overhead, by suitably averaging uplink channel measurements across frequency. Since this approach relies on statistical reciprocity, it applies to both time-division duplex (TDD) and frequency-division duplex (FDD) systems. Using such covariance feedback yields significantly better performance at lower complexity than conventional space-time or space-frequency codes, which do not employ feedback; b) We provide guidelines for optimizing antenna spacing in systems with covariance feedback. Theoretical investigation of a hypothetical system with completely controllable channel eigenvalues shows that the optimal number of channel eigenmodes is roughly matched to the (small) number of receive antenna elements. Thus, while antenna elements in conventional systems without feedback should be spaced far apart in order to ensure uncorrelated responses, the optimal antenna spacing with covariance feedback is much smaller, thereby concentrating the channel energy into a small number of eigenmodes.     

无线通信领域中酉空时调制(USTM)技术的研究

多天线系统是第三代甚至未来的第四代无线移动通信中极具前途的一种技术。在研究了酉空时调制的必要性和信道模型的基础上,详细讨论了酉空时编码的原理,重点对酉空时星座图的构造准则和几种设计方案进行了讨论。最后给出了酉空时编码的最新动态和目前需要解决的问题。     

空时码

提高频率利用率一直是移动通信系统中的研究热点,而近年来提出的空时码又是其关键技术之一.从当前的研究情况来看,空时码技术主要分为以下两大类:一是分层空时码(LST);二是基于发射分集的空时分组码和空时格码.由于空时码具有良好的频带利用率及性能,3GPP已将空时分组码作为一可选方案列在所提规范之中.相信在不远的将来,空时码必将广泛应用于未来的移动通信系统.     

空时分组码MC-CDMA系统多用户检测

本文研究了在频率选择性瑞利衰落信道中工作于时分双工(TDD)模式的多载波码分多址(MC-CDMA)系统上行链路,在用户终端处使用两个发射天线,采用基于空时分组码的发射分集。考虑对应于子载波的衰落系数是信道冲激响应的离散傅里叶变换,给出了基于空时分组码的MC-CDMA系统上行链路信号模型。采用适用于同步CDMA系统的低代价Steiner估计器来进行基于空时分组码的MC-CDMA系统的信道估计,每个用户终端的两个发射天线各分配一个midamble。研究了基于空时分组码的MC-CDMA系统的解相关多用户检测、最小均方误差(MMSE)多用户检测,进行联合的多用户检测和空时码解码。仿真结果验证了上述模型及算法的有效性。