最优天线选择的空时分组编码

本文针对TD－SCDMA系统的MIMO（Multiple-Input Multiple-Output)信道，采用天线选择技术来提高空时分组码（Space-Time Block Coding)的分集性能。其依据是利用TDD系统上、下行信道的互易性，将系统对上行信道的估计直接应用于行链路。仿真结果表明，将天线选择技术与空时分组码（STBC）相结合对系统的误码率性能有较大的改善。     

结合STBC的一种分层空时编码结构模型

本文讨论了结合空时分组码(STBC Space Time Block Coding)的一种分层空时编码(Layered Space Time)结构模型。VBLAST(Vertical Bell Laboratories Layered Space Time)作为LST的一种结构，其性能受到最先译码信息符号准确度的影响，本文通过在VBLAST的首层采用STBC结构，从而增加了第一层信息符号的分集度。在接收端，采用组干扰抑制同时结合STBC和VBLAST译码，降低了接收机的复杂度提高了系统的性能。仿真结果表明结合STBC的VBLAST结构模型性能明显好于传统的VBLAST。     

LTE中基于发送分集的预编码

MIMO技术是LTE中采用的关键技术之一,本文研究的基于发送分集的预编码技术就是MIMO技术中的一种方案。本文对LTE中使用的2发射天线和4发射天线的基于发送分集的预编码方案进行了推导,并对其性能进行了仿真,将其与空时分组码方案进行了性能比较。推导结果表明LTE中基于发送分集的预编码方案与2根发射天线的空时分组码的编码原理相同。仿真结果表明在两根发射天线情况下,空时分组码的误码率性能和预编码方案相同;在4发射天线的情况下,空时分组码的误码率低于预编码方案,但预编码方案的传码率要高于空时分组码。     

一种协同分集方案的误码性能分析

协同分集(cooperative diversity)技术通过为网络中某些单天线用户寻找若干个用户作为"伙伴",并共享彼此天线,形成虚拟的多天线阵列,来实现多天线分集,结合分布式空时分组编码(Distributed Space Time Block Code,DSTBC),可以有效地提高系统性能.多载波码分多址(Multi-Carrier Code Division Multiple Access,MC-CDMA)技术将数据调制到各个子载波上发送,可以有效地抵抗信道频率选择性衰落的影响.本文提出了无线网络中频率选择性衰落信道环境下的一种基于分布式空时分组码和MC-CDMA的协同发射分集方案,建立了协同用户间的误码表示模型,基于该模型推导了协同分集方案误码性能的理论表达式,并分析了协同用户间的平均解码差错概率对系统方案误码性能的影响,同时给出了仿真结果.结果表明,DSTBC-MC-CDMA相对于未协同的MC-CDMA系统获得了明显的性能增益,同时仿真也较好地验证了理论结果.     

基于DSTBC-MC-CDMA的无线网络协同发射分集系统

协同分集(cooperative diversity)技术通过使网络中各单天线用户共享彼此天线,形成虚拟的多天线阵列来实现发射或接收分集,可以有效地提高系统性能。该文提出无线网络中频率选择性衰落信道环境下的一种基于分布式空时分组码(Distributed Space Time Block Code, DSTBC)和MC-CDMA的协同发射分集方案,并给出了系统实现。建立了误码模型,探讨了协同用户间的信道状态信息(CSI)对系统误码性能的影响,分析了误码性能的上限,并给出了仿真结果。结果表明,DSTBC-MC-CDMA系统相对于未协同的MC-CDMA系统,获得了明显的性能增益。     

正交空时分组码在瑞利衰落信道中的性能估计

根据Alamouti最大似然译码方法，给出了在正交空时分组码传输的衰落信道条件下接收机输出瞬时信噪比的一般表达式，分析了瑞利衰落信道条件下引入正交空时分组码的多天线系统的符号差错性能，研究表明采用正交空时码传输信号，增加发送天线数量和接收天线数量都可以得到更大的分集增益；在接受天线数量一定的情况下，增加发送天线的数量可以带来更大的分集增益，但当发送天线数量增加到一定程度后，再增加发送天线数量就不能带来明显的分集改善了。     

无线通信中的空时分组码

空时分组码技术结合信道编码、调制和天线分集技术,当发送天线一定时,他的解码复杂度正比于发送速率,在3G标准中,该技术有着重要的地位。对空时分组码及相关知识进行了介绍,并对可变速率的空时分组码设计进行了探讨,最后展望了空时分组码技术的应用前景。     

四发送天线无线通信系统的空时分组编码

介绍了用于四发送天线无线通信系统的完全正交的空时分组码、准正交的空时分组码及利用星座旋转的空时分组码的编译码方案；给出了它们的性能仿真结果，并进行了分析比较；得出了在同等条件下，能同时获得全分集和全速率的空时分组码的性能更优的结论。     

旋转星座下匙孔信道的四元素准正交空时分组码研究

提出了一种基于匙孔信道的旋转四元素准正交空时分组码(QQOSTBC-CR,Constellation Rotation Quaternion Quasi-Orthogonal Space Time Block Code),该码可以通过极化天线进行发射和接收,设计出发射天线数为8的QOSTPBC-CR,并对N＝8的情况进行成对译码,最后与匙孔信道下传统旋转准正交空时分组码(QOSTBC CR,Constellation Rotation Quasi Orthogonal Space Time Block Code)、准正交空时分组码(QOSTBC,Quasi Orthogonal Space Time Block Code)以及瑞利信道下QQOSTBC-CR进行了仿真比较.结果表明:对4个发射天线的情况,当BER＝10(-3)时,BPSK和QPSK调制下本文所提QQOSTBC-CR分别比QOSTBC-CR有4.5dB和7dB的增益,分别比瑞利信道下QQOSTBC-CR有-4dB和-3dB的增益.     

一种新的准正交空时分组码的设计

根据正交设计理论,当发送天线数大于2时,不存在可以获得完全分集增益和全速率的复正交空时分组码.对空时分组码采用准正交设计,能够保证数据以全速率传输,但是会使其误码性能降低.文章在对准正交空时分组码(QOSTBC)结构研究的基础上,提出了一种全速率的四发射天线准正交空时分组码,并给出了基于最大似然译码方法.仿真结果表明,文章方案与已有典型的Jafarkhani准正交空时分组码相比,在高信噪比时有更好的误码性能.     

Codes de blocs a préfixe pour la réduction de redondance d’images

A simple coding technique, called block coding, is presented for source coding of two-level digital pictures. Its efficiency can be increased by using a special form of psychovisual coding with almost invisible distortions. With an increase in complexity, this technique can be made adaptable in a number of ways, leading to higher compression ratios. Theoretical models devised to predict the performances yield very satisfactory results. Furthermore, block coding is generalized for grey level pictures. In this case, it is applied to bit planes. The simplicity and the performances of block coding make it a valid alternative for digital transmission or storage of images.     

Rayleigh衰落信道中分组码最大似然译码的性能

摆脱了传统代数译码方法,对分组码进行基于广义阵列码（ＧＡＣ）结构的网格译码（Ｔｒｅｌｌｉｓ ｄｅｃｏｄｉｎｇ）,研究了Ｒａｙｌｅｉｇｈ衰落信道中分组码与这种软判决最大似然译码方法相结合的性能。模拟结果显示。分组码采用网格译码,可为移动衰落信道带来显著的性能改善。     

Generalized block coding of black and white images

A generalized approach to block coding of two-tone images is introduced. Binary N-sequences (blocks) are described. Various conventional block coding techniques are shown to be particular cases of this approach. Numerical examples confirm that, based on the approach, the coding technique outperforms existing techniques. Generalized block coding is proved to be near optimum for encoding sparse binary patterns and advantageous for sources with unknown models.     

大规模MU-MIMO系统下的预编码技术研究

在大规模MU-MIMO系统中提出一种预编码技术,即特征波束形成结合空时分组编码.在发射端,利用大规模MI-MO形成正交波束,将空时分组码分布在这些波束上进行传输.而在接收端,空时分组码根据传统的译码算法解码.此技术能够同时获得分集增益和波束形成增益,还可以大大降低接收端的复杂度.在多用户系统中,它的性能都优于其他传统的编码方式.仿真结果也验证了该方法的有效性.     

Multilevel graphics representation using block truncation coding

In this paper a modified version of a noninformation preserving coding technique known as block truncation coding (BTC)is used to code multilevel graphics. The method is based on-local binarization of nonoverlapping blocks in the graphics image such that the sample mean and sample variance in each block is preserved. BTC is easy to implement, does not require multiple passes through the data, does not degrade when compressing noisy images, and can be made relatively insensitive to channel errors. Examples of the coding technique are given and compared to other compression methods. This technique shows promise for coding 32-level (or 32-color) graphic images at data rates of about 1 bit/pel.     

Adaptive block scheme for source coding of black-and-white facsimile

A simple adaptive block coding method is proposed which could be useful for efficient transmission or storage of 2-level images (black-and-white facsimile). A comparison of this autoadaptive technique with optimum run-length coding and nonadaptive block coding shows that a significant improvement in redundancy reduction can generally be obtained.     

A Video Coding Algorithm Based on Intraframe and Interframe Joint Prediction of Wavelet Coefficients

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A Rate-1 Space-Time Diversity Method for Rotated 4-QAM Constellations

We propose a rate-1 space-time transmit diversity technique. We obtained second-order diversity by transmitting the real and imaginary parts of the symbols from two antennas. With four transmit antennas, we can add Alamouti coding to reach fourth-order transmit diversity. There is no need to detect symbols jointly in either of these applications. It is possible to use both Alamouti coding and Hadamard spreading diversity with the proposed method, thereby obtaining eighth-order (or even higher) transmit diversity. However, joint detection of the symbols is again required at this point. The proposed technique is a suitable space-frequency coding method for OFDM systems. We used computer simulations to compare our technique with the Alamouti coding, quasi-orthogonal space-time block coding (QOSTBC), and orthogonal space–time block coding (OSTBC) methods. We also compared its performance to that of Hadamard spreading diversity. Alamouti coding performs better than the proposed technique at the second order of transmit diversity, but is also limited to that order. The proposed technique performs better than OSTBC at the same order of the transmit diversity. QOSTBC performs slightly better than the proposed technique at the same order of transmit diversity. However, when all methods have the same detection complexity, the proposed technique performs better than both QOSTBC and Hadamard spreading diversity.     

A Video Coding Algorithm Based on Intraframe and Interframe Joint Prediction of Wavelet Coeffictients

A novel video coding algorithm based on intraframe and interframe prediction of wavelet coefficients is described in this paper.A BZT(Block Zero Tree)coding scheme represents the position of zero coefficients block efficiently,For nonzero coefficients block,temporal redundancy is removed using MultiResolution Motion Estimation(MRME).The proposed algorithm improves the coding performance significantly over the baseline MRME technique.In addition,the computational complexity is further reduced.