OFDM多载波系统无线图像的鲁棒性传输

将图像分级编码与OFDM多载波调制技术相结合,对图像进行分级编码,使经过编码的数据按视觉重要性不同进行排列。然后再根据无线信道的实际衰落情况,为重要性不同的比特分配不同的信道、比特速率和功率,在总的发送功率一定的条件下,以及在满足视觉重要性不同的误比特条件下,使系统的传输速率最大。在上述自适应分配的基础上,根据各子信道传输的比特重要性的不同,采用不同信道编码,实现对视觉重要性高的比特的更高级别的保护,使其在较低的误比特率下进性传输。     

Non-coherent space-time code based on full diversity space-time block coding

A non-unitary non-coherent space-time code which is capable of achieving full algebraic diversity is proposed based on full diversity space-time block coding, The error performance is optimized by transforming the non-unitary space-time code into unitary space-time code, By exploiting the desired structure of the proposed code, a grouped generalized likelihood ratio test decoding algorithm is presented to overcome the high complexity of the optimal algorithm, Simulation results show that the proposed code possesses high spectrum efficiency in contrast to the unitary space-time code despite slight loss in the SNR, and besides, the proposed grouped decoding algorithm provides good tradeoff between performance and complexity,     

Efficient detection methods for amplify-and-forward relay-aided device-to-device systems with full-rate space-time block code

Relay-aided device-to-device (D2D) communication is a promising technology for the next-generation cellular network. We study the transmission schemes for an amplify-and-forward relay-aided D2D system which has multiple antennas. To circumvent the prohibitive complexity problem of traditional maximum likelihood (ML) detection for full-rate space-time block code (FSTBC) transmission, two low-complexity detection methods are proposed, i.e., the detection methods with the ML-combining (MLC) algorithm and the joint conditional ML (JCML) detector. Particularly, the method with the JCML detector reduces detection delay at the cost of more storage and performs well with parallel implementation. Simulation results indicate that the proposed detection methods achieve a symbol error probability similar to that of the traditional ML detector for FSTBC transmission but with less complexity, and the performance of FSTBC transmission is significantly better than that of spatial multiplexing transmission. Diversity analysis for the proposed detection methods is also demonstrated by simulations.     

一种新的准正交空时分组码设计方法*

自Jafarkhani提出非正交空时分组码以来,其构造方法一直是研究热点之一。构造了一种发射天线为4的准正交空时分组码,为了改善该分组码性能,对输入信号进行了旋转预处理,得到旋转后的准正交空时分组码;系统的接收端采用最大似然译码方法。数值仿真显示,没有预处理的准正交空时分组码的误码率与已提出的准正交空时分组码相当。然而,经旋转后的空时分组码的误比特率至少有2 dB改善。     

Encrypted gray image transmission over OFDM channel for TV cloud computing

One of the most important issues which attract the researcher is to provide a secure channel to transfer data between many points. Television cloud has many contents which are needed to be transferred to authorized groups (AuthGs). Also, the transfer rate is an aspect to be considered. In this work, orthogonal frequency division multiplexing is investigated to be sure it is acceptable for the cloud and use many transforms to choose the perfect one for the cloud. The investigation is done under fading channel condition. Peak signal-to-noise ratio is used to differentiate between cases. Many tests are also suggested to confirm the high quality of performance for the cloud.     

Robust image hashing using progressive feature selection for tampering detection

The main problem addressed in this paper is the robust tamper detection of the image received in a transmission under various content-preserving attacks. To this aim the progressive feature point selection method is proposed to extract the feature points of high robustness; with which, the local feature and color feature are then generated for each feature point. Afterwards, the robust image hashing construction method is proposed by using the location-context information of the features. The constructed hash is attached to the image before transmission and it can be used for analyzing at destination to filter out the geometric transformations occurred in the received image. After image restoration, the similarity of the global hashes between the source image and restored image is calculated to determine whether the received image has the same contents as the trusted one or has been maliciously tampered. When the received image being judged as a tampered image, the hashes calculated with the proposed Horizontal Location-Context Hashing (HLCH) and Vertical Location-Context Hashing (VLCH) methods will be used to locate the tampered regions. Experimental results on different images with tampering of arbitrary size and location demonstrate that our image authentication and tampering localization scheme are superior to the state-of-the-art methods under various attacks.     

旋转星座准正交空时分组码的改进性研究

当发射天线数大于2时,复信号空时分组码不能实现满速率编码,可以通过星座旋转来设计发送矩阵,使系统同时获得满分集增益和最大的编码速率。通过对传统的旋转星座准正交空时分组码加以改进,使每根天线在不同时隙发射的信号属于不同星座,在保证满分集和最大的编码速率的同时,减小了码间干扰,更有利于译码器译码,提高了系统性能。     

ABBA码的两种改进方案及其性能仿真

ABBA码是一种可用于三个以上发送天线系统的准正交空时分组编码。该方案能获得最大传输速率．但不能提供最大的分集增益。为了改进这一不足．本文介绍了它的两种改进方案。这两种方案分别利用了星座旋转的方法和发射端已知的信道状态信息来增加ABBA码的分集增益．仿真结果表明这两种改进方案的误码率性能较原有的ABBA码性能均有一定程度的改善。     

Robust image and video transmission over spectrally shaped channelsusing multicarrier modulation

This paper presents a new parallel transmission framework for reliable multimedia data transmission over spectrally shaped channels using multicarrier modulation. We propose to transmit source data layers of different perceptual importance in parallel, each occupying a number of subchannels. New loading algorithms are developed to efficiently allocate the available resources, e.g., transmitted power and bit rate, to the subchannels according to the source layers they transmit. Instead of making the bit error rate of all the subchannels equal as in most existing loading algorithms, the proposed algorithm assigns different error performance to the subchannels to achieve unequal error protection for different layers. The channel induced distortion in mean-square sense is minimized. We show that the proposed system can be applied nicely to both fixed length coding and variable-length coding. Asymptotic gains with respect to channel distortion are also derived. Numerical examples show that the proposed algorithm achieves significant performance improvement compared to the existing work, especially for spectrally shaped channels commonly used in in ADSL systems     

空时网格编码和OFDM相结合的通信系统性能仿真分析

简单研究了空时网格编码和OFDM相结合的理论基础,详细介绍了空时编码和OFDM相结合的通信系统,通过仿真分析了该系统在高斯白噪声信道和频率选择性衰落信道下的系统性能。     

全速率满分集准正交空时分组码设计研究

自Alamouti提出空时分组码以来,空时分组码的构造得到广泛的研究。研究表明,复正交空时分组码当发射天线数大于3时,它的传输码率小于1。准正交空时分组码虽然能达到全速率,却牺牲了一定的分集增益。根据空时编码秩准则,通过对传统准正交空时分组码进行矩阵旋转处理,得到一种全速率满分集的空时分组码。数值仿真显示,这种全速率满分集空时分组码的性能较传统准正交空时分组码至少有4 dB的提高。     

Robust hierarchical image representation using non-negative matrix factorisation with sparse code shrinkage preprocessing

When analysing patterns, our goals are (i) to find structure in the presence of noise, (ii) to decompose the observed structure into sub-components, and (iii) to use the components for pattern completion. Here, a novel loop architecture is introduced to perform these tasks in an unsupervised manner. The architecture combines sparse code shrinkage with non-negative matrix factorisation, and blends their favourable properties: sparse code shrinkage aims to remove Gaussian noise in a robust fashion; non-negative matrix factorisation extracts substructures from the noise filtered inputs. The loop architecture performs robust pattern completion when organised into a two-layered hierarchy. We demonstrate the power of the proposed architecture on the so-called bar-problem and on the FERET facial database.     

发射天线选择正交空时码系统的性能分析

分别针对瑞利衰落信道和Nakagami衰落信道,研究了使用发射天线选择(TAS)和正交空时分组码(STBC)的多输入多输出系统的平均符号误码率(ASEP)性能。基于标量加性高斯白噪声(AWGN)信道的方法,推导出了采用脉冲幅度调制(PAM)、相移键控(PSK)和正交幅度调制(QAM)的精确和近似的ASEP闭合表达式。然后对不同条件下的系统性能做了数值仿真,验证了分析结果的正确性。     

渐进图像传输的码率分配快速算法

针对带限时变信道上的渐进图像传输,提出了一种信源信道联合编码码率分配快速算法,首先参考一组速率兼容信道码字的误码性能划分信道分区,在各分区内缩小可用信 道码率集后,通过前后向码率搜索求解最佳码率分配。该算法运算复杂度低,计算次数比启发式码率搜索算法降低了一个数量级,缩短了运算时间。因此,将其应用于自适应传输 系统,可根据信道状况快速调整码率分配。仿真结果表明,接收端重建图像的PSNR值始终在29.5 dB以上,同时波动范围小于4 dB,具有优良稳定的传输质量。     

Cyclic delay transmission for unique word OFDM systems

In this article, we propose a cyclic delay diversity （CDD） transmission scheme for unique word （UW） OFDM system, which is denoted as CDD-UW-OFDM. In our proposed CDD-UW-OFDM system, the first transmit antenna transmits a UW-OFDM and then, for every UW-OFDM block, the i-th transmit antenna transmits a cyclically delayed version of the symbols transmitted at the first transmit antenna. With this proposed CDD-OFDM system, each antenna transmission is a UW-OFDM. Also, at the receiver under a certain condition on the cyclic delay amounts, the received signal is equivMent to that of a single transmit antenna UW-OFDM transmission with a longer multipath channel. We design the lengths of UW and cyclic delays to achieve the full multipath and spatial diversities for the CDD-UW-OFDM system when the linear MMSE receiver is used. We then present some simulation results to illustrate the claimed performance of the proposed system.     

利用协方差矩阵法表示深度图像集的鲁棒人脸识别

针对深度图像集的人脸识别问题的鲁棒性问题,提出将多幅Kinect图像当作一个图像集,Kinect捕获的原始深度数据可用于姿态估计以及人脸区域的自动裁剪。首先,将图像集划分到c个图像子集,子集中的所有图像划分为4?4的图像块;然后,将图像集中的图像模拟为图像块的形式,按照姿势划分,每个子集使用协方差矩阵法表示;最后,在黎曼流形上的模拟子集图像,为了分类,黎曼流形的每个图像子集分别学习支持向量机模型,并引入一种融合方法来合并所有图像子集的结果。在三个最大的公开Kinect人脸数据集CurtinFaces、Biwi Kinect和UWA Kinect的实验结果验证了本文方法的有效性,与其他较先进的方法相比,识别率有较大提升,标准差保持较低,对图像集数量、图像子集划分数量和空间分辨率有较好的鲁棒性。     

Clipping distortion mitigation in OFDM systems over fading channels by using DFT-based method

Saeedi et al. have recently proposed a DFT-based method (DBM) for Orthogonal Frequency Division Multiplexing (OFDM) systems to compensate for the performance degradation caused by clipping distortion. They have analyzed the performance of the DBM only in an additive white Gaussian noise channel. But, it is known that the main advantage of an OFDM system is its robustness in fading channels where this system turns a frequency selective channel into a set of parallel flat non-selective fading sub-channels. In this paper, we analyze the performance of the DBM over a frequency selective fading channel with flat fading Rician sub-channels. Our results show that similar to additive white Gaussian noise channel case, the DBM can properly mitigate the clipping distortion in OFDM signals over fading channels. Furthermore, the performance of a Hybrid method that consists of a channel coding method and the DBM is also examined over fading channels.     

多线程遥感影像实时渐进传输

目的 针对异构网络环境下,不同终端用户对遥感影像质量的不同需求而导致的影像数据量过大、传输及显示延迟过长等问题,提出一种在线压缩—实时传输—实时解压缩的遥感影像渐进传输模型。方法 模型采用多线程流水线同步处理的加速算法,将基于质量渐进压缩的SPIHT算法与多线程流水线技术相结合,在VC++环境下,将遥感影像在线压缩成码流,在压缩的同时,启动多线程采用Socket信道对压缩码流实时发送,客户端收到码流后,利用多线程实时解压缩并显示。通过采用多线程技术,使得压缩、传输和解压缩同步进行,从而减少了整体处理时间。结果 实验结果表明,提出的实时压缩渐进传输模型,在不影响影像质量的前提下,算法处理速度提高近2倍。每个渐进分层影像与原影像的相似度比多分辨率渐进压缩分层影像与原影像的相似度平均增加20%。结论 该模型有效地解决了遥感影像渐进传输过程中压缩、传输和解压缩的不同步问题,从而提高了渐进传输效率。与多分辨率渐进传输比较,此渐进传输模型具有更好的视觉效果。     

Low-complexity progressive image transmission scheme based on quadtree segmentation

A novel progressive image transmission scheme based on the quadtree segmentation technique is introduced in this paper. A 3-level quadtree is used in the quadtree segmentation technique to partition the original image into blocks of different sizes. Image blocks of different sizes are encoded by their block mean values. The relatively addressing technique is employed to cut down the storage cost of block mean values.In the proposed scheme, the number of image hierarchies can be adaptively selected according to the specific applications. By exploiting inter-pixel correlation and differently sized blocks for segmentation, the proposed scheme provides good image qualities at low bit rates and consumes very little computational cost in both image encoding and decoding procedures. It is quite suitable for real-time progressive image transmission.     

正交空时分组码在瑞利衰落信道下的性能分析

基于典型的多输入—多输出无线通信系统,推导了在瑞利衰落信道下正交空时分组码的瞬时接收信噪比和抗噪声性能的一般表达式,并在MATLAB环境中对不同发送天线、接收天线、调制方式、传输速率下正交空时分组码的误码率性能进行了仿真与结果比较分析,得出误码率性能与分集增益、编码速率、比特传输率和调制方式存在内部关联。