QoS enhancement in space data communication: a network coding approach

With the rapid increase of space applications, the amount of information to be transmitted between spacecrafts and ground stations increases exponentially and space–sky–ground Transport Control Protocol (TCP) network is highly demanded. However, the traditional TCP cannot be directly applied to space data communication. This article deeply studies the TCP/Network Coding (NC), which can effectively improve terrestrial wireless communication system throughput. Combined with characteristics of Space Communication Protocol Specification-Transport Protocol (SCPS-TP) and advantages of terrestrial TCP/NC, an improved protocol referred to as SCPS-TP/NC, is proposed for space data communication. This article provides detailed process of protocol design, mathematical modelling and throughput analysis of the proposed SCPS-TP/NC. Finally, we implement the SCPS-TP/NC protocol and evaluate its performance by Network Simulator (Version 2). Simulation results show that SCPS-TP/NC can effectively increase the end-to-end system throughput, reduce the packet loss rate, shorten the transmission delay and improve the Quality of Service (QoS) of space data communication to a certain degree.     

Quaternion structural similarity: a new quality index for color images

One of the most important issues for researchers developing image processing algorithms is image quality. Methodical quality evaluation, by showing images to several human observers, is slow, expensive, and highly subjective. On the other hand, a visual quality matrix (VQM) is a fast, cheap, and objective tool for evaluating image quality. Although most VQMs are good in predicting the quality of an image degraded by a single degradation, they poorly perform for a combination of two degradations. An example for such degradation is the color crosstalk (CTK) effect, which introduces blur with desaturation. CTK is expected to become a bigger issue in image quality as the industry moves toward smaller sensors. In this paper, we will develop a VQM that will be able to better evaluate the quality of an image degraded by a combined blur/desaturation degradation and perform as well as other VQMs on single degradations such as blur, compression, and noise. We show why standard scalar techniques are insufficient to measure a combined blur/desaturation degradation and explain why a vectorial approach is better suited. We introduce quaternion image processing (QIP), which is a true vectorial approach and has many uses in the fields of physics and engineering. Our new VQM is a vectorial expansion of structure similarity using QIP, which gave it its name-Quaternion Structural SIMilarity (QSSIM). We built a new database of a combined blur/desaturation degradation and conducted a quality survey with human subjects. An extensive comparison between QSSIM and other VQMs on several image quality databases-including our new database-shows the superiority of this new approach in predicting visual quality of color images.     

Structural similarity image quality reliability: Determining parameters and window size

The need to obtain objective values of the quality of distorted images with respect to the original is fundamental in multimedia and image processing applications. It is generally required that this value correlates well with the human vision system (HVS). In spite of the properties and the general use of the mean square error (MSE) measurement, this has a poor correlation with HSV, which has led to the development of methods such as structural similarity (SSIM). This metric improves the correlation with respect to the classic MSE and PSNR (peak signal to noise ratio). However, its behavior depends on the values assigned to constants and on the windows size selected. These values are usually assigned arbitrarily and there have been no studies on how they affect the SSIM. In this work, we have analyzed empirically the most appropriate values for the different constants used in the SSIM equations. We have also analyzed the importance of window size in the calculation of MSSIM, and propose a method for determining the window size based on image complexity. Using the values selected and the window size defined, the correlation between SSIM and DMOS (differential mean opinion score) is significantly improved by around 17% with respect to the values commonly used.     

On the performance of objective quality metrics for lightfields

Lightfield (LF) technology has attained significant attention in recent years due to its capability to capture much richer textural and geometric information in the scene compared to the classical 2D representation. The resampling and compression operations on LFs often lead to visual quality degradation, thus, sophisticated visual quality assessment methods play a crucial role to ensure a pleasant viewing experience. To this end, it is necessary to examine the performance of quality assessment methods for LF contents. The paper provides a comprehensive study on the reliability of various objective algorithms for LF quality prediction. Three subjectively-annotated LF data sets were selected and an extensive quality estimation analysis has been conducted using several objective quality assessment methods. In total, 250 LFs (more than 48000 perspective images) were evaluated. The results were compared against human opinion scores using various correlation indices and their statistical significance. Next, a decision-making strategy was adopted to choose the most reliable quality metrics for evaluation of LFs and finally, a metric fusion framework was proposed to further improve the quality prediction accuracy. To best of our knowledge, the benchmark and the analytical methodologies used in this paper are the most comprehensive study on the objective quality assessment methods for LF application.     

针对不同融合算法的质量评价指标性能评估

融合质量评价指标的性能对图像融合方法的提出和改进十分重要。讨论了目前常用的三种参考图像的构建方法,并对常用融合质量评价指标(相关系数CC、偏差指数RB、结构相似度SSIM、均方根误差RMSE、光谱角SAM和ERGAS)从三方面进行性能评价分析:(1)功能相似指标间评价结果的一致性;(2)对同一融合算法、不同图像的评价结果的鲁棒性;(3)与目视评价结果的一致性。中、高空间分辨率遥感影像融合实验结果表明:CC、SSIM和SAM选择原始低分辨率多光谱图像作为参考图像性能最好,仅适合做融合图像光谱质量评价;RMSE和ERGAS选择原始低分辨率多光谱图像或高分辨率图像作为参考图像性能最好,因此这两个指标既可以做融合图像光谱质量评价,也可以做空间质量评价。     

空间通信中调制与编码热点技术探析

深空探测、卫星导航及卫星遥感技术的迅猛发展对空间通信的数据处理速率和抗干扰性能提出了更高要求。因此,更高的频谱利用率和抗强干扰能力是未来空间通信的发展方向。本文分析了空间通信中制约信息传输性能的主要因素,着重对近年来空间通信中调制及编码热点技术的工作原理、性能及应用情况进行描述,并针对复杂电磁环境下新型调制与编码技术的联合应用提出了解决方案。分析表明,联合应用方案可以同时提高频谱利用率和抗干扰能力。     

Performance of robust metrics with convolutional coding anddiversity in FHSS systems under partial-band noise jamming

The performance of robust metrics (metrics that can be computed from the outputs of the matched filters only) with convolutional coding and diversity under worst-case partial-band noise jamming is analyzed. Both binary and dual-k convolutional codes employing these metrics with diversity are compared via Union-Chernoff bounds. The performances of metrics considered in the literature that assume perfect side-information are given for comparison purposes. It is found that there exist very good robust metrics that provide performance comparable to metrics using perfect side-information. Among the robust metrics considered, the self-normalized metric offers the best performance and achieves performance practically identical to that of the square-law-combining metric with perfect side-information for M=8     

Ambiguity of objective image quality metrics: A new methodology for performance evaluation

Objective image quality metrics try to estimate the perceptual quality of the given image by considering the characteristics of the human visual system. However, it is possible that the metrics produce different quality scores even for two images that are perceptually indistinguishable by human viewers, which have not been considered in the existing studies related to objective quality assessment. In this paper, we address the issue of ambiguity of objective image quality assessment. We propose an approach to obtain an ambiguity interval of an objective metric, within which the quality score difference is not perceptually significant. In particular, we use the visual difference predictor, which can consider viewing conditions that are important for visual quality perception. In order to demonstrate the usefulness of the proposed approach, we conduct experiments with 33 state-of-the-art image quality metrics in the viewpoint of their accuracy and ambiguity for three image quality databases. The results show that the ambiguity intervals can be applied as an additional figure of merit when conventional performance measurement does not determine superiority between the metrics. The effect of the viewing distance on the ambiguity interval is also shown.     

A hybrid approach for the optimization of quality of service metrics of WSN

The core objective behind this research paper is to implement a hybrid optimization technique along with proactive routing algorithm to enhance the network lifetime of wireless sensor networks (WSN). The combination of two soft computing techniques viz. genetic algorithm (GA) and bacteria foraging optimization (BFO) techniques are applied individually on destination sequence distance vector (DSDV) routing protocol and after that the hybridization of GA and BFO is applied on the same routing protocol. The various simulation parameters used in the research are: throughput, end to end delay, congestion, packet delivery ratio, bit error rate and routing overhead. The bits are processed at a data rate of 512 bytes/s. The packet size for data transmission is 100 bytes. The data transmission time taken by the packets is 200 s i.e. the simulation time for each simulation scenario. Network is composed of 60 nodes. Simulation results clearly demonstrates that the hybrid approach along with DSDV outperforms over ordinary DSDV routing protocol and it is best suitable under smaller size of WSN.

     

A survey on addressing privacy together with quality of context for context management in the Internet of Things

Making the Internet of Things (IoT) a reality will contribute to extend the context-aware ability of numerous sensitive applications. We can foresee that the context of users will include not only their own spatio-temporal conditions but also those of the things situated in their ambient environment and at the same time, thanks to the IoT, those that are located in other remote spaces. Consequently, next-generation context managers have to interact with the IoT underlying technologies and must, even more than before, address both privacy and quality of context (QoC) requirements. In this article, we show that the notions of privacy and QoC are intimately related and sometimes contradictory and survey the recent works addressing them. Current solutions usually consider only one notion, and very few of them started to bridge privacy and QoC. We identify some of the remaining challenges that next-generation context managers have to deal with to favour users’ acceptability by providing both the optimal QoC level and the appropriate privacy protection.     

Robust defocus blur identification in the context of blind image quality assessment

A defocus blur metric for use in blind image quality assessment is proposed. Blind image deconvolution methods are used to determine the metric. Existing direct deconvolution methods based on the cepstrum, bicepstrum and on a spectral subtraction technique are compared across 210 images. A variation of the spectral subtraction method, based on a power spectrum surface of revolution, is proposed and is found to compare favourably with existing direct deconvolution methods for defocus blur identification. The method is found to be especially useful when distinguishing between in-focus and out-of-focus images.     

Dispersion distortions of a complex signal in gyrotropic plasma

The problem on a frequency-modulated radio pulse propagating along the magnetic field in cold collisional plasma is solved analytically. The character of distortions of a rectangular quasi-harmonic pulse and ultrawideband pulses with the widebandedness parameter ranging from 0.3 to 1.33 is considered in the case of ionospheric conditions when distortions are due to the gyrotropicity of the plasma medium. It is found that, for long paths, the radiated monopulse may split into series of ordinary and extraordinary subpulses. This effect is observed when the frequency modulation law is appropriately chosen.     

Color distortions on the screen of a television receiver as functions of ambient illumination and a method for correction of these distortions

It is shown that ambient illumination of the TV screen introduces color distortions in viewed TV programs. The magnitude and type of these distortions depend on the brightness and spectrum of the source of ambient illumination. A method for correction of these distortions is proposed and two ways of its implementation are considered.     

Dispersion distortions of a two-frequency radio pulse in cold plasma

Dispersion distortions of a two-frequency radio pulse in cold isotropic plasma are analyzed in meter- and decameter-wavelength ranges. It is demonstrated that the pulse envelope tends to the limiting two-peak shape that reproduces the shape of the energy spectrum of the emitted pulse when the total electron content (TEC) along the path increases. In this case, TEC can be determined using characteristics of the envelope. Effect of the parameters of emitted pulse on its deformation in the course of propagation is described.     

空间遥感相机成像单元结构设计

根据某型号空间遥感相机的技术指标要求,对成像单元进行了详细的设计与分析。首先,给出了一种小体积、轻质量、高稳定性成像单元的结构形式;其次,针对遥感相机电子学设备在轨工作的复杂工况,提出了成像单元防护性设计方法,对大功耗元器件设计了主动热控措施;最后用有限元法对成像单元进行了详细分析,分析结果表明,成像单元一阶模态为184 Hz,远大于遥感相机基频106 Hz,具有较好的动态性能;成像单元在自重、25℃工况条件下,力学及热稳定性较高。对成像单元进行了力学和热光学试验,力学试验结果表明成像单元的一阶频率为185 Hz,与理论分析结果一致性较好,热光学试验结果表明:成像单元对整机热光学性能影响很小,各项指标均满足设计要求。     

Grounding the displaced: local media reception in a transnational context

Local media perform a linking function for displaced audiences in a global landscape. Consumption of home-based press when one is in a foreign context is mainly a ritualistic cultural practice in securing personal identity, familiar formulations of cultural spaces, and communities of origin. Ethnographic research revealed that national newspapers allowed readers to (re)produce situated identity marks menaced by globalization. Audiences may use local media to ground themselves in symbolic environments in which external and internal boundaries are reassured through time and space. In this local cultural setting, individual and collective identities acquire stability and self-confidence.     

Accuracy and cross-calibration of video quality metrics: new methods from ATIS/T1A1

Video quality metrics (VQMs) have often been evaluated and compared using simple measures of correlation to subjective mean opinion scores from panels of observers. However, this approach does not fully take into account the variability implicit in the observers. We present techniques for determining the statistical resolving power of a VQM, defined as the minimum change in the value of the metric for which subjective test scores show a significant change. Resolving power is taken as a measure of accuracy. These techniques have been applied to the video quality experts group (VQEG) data set and incorporated into the recent Alliance for Telecommunications Industry Solutions (ATIS) Committee T1A1 series of technical reports (TRs), which provide a comprehensive framework for characterizing and validating full-reference VQM. These approved TRs, while not standards, will enable the US telecommunications industry to incorporate VQMs into contracts and tariffs for compressed video distribution. New methods for assessing VQM accuracy and cross-calibrating VQMs are an integral part of the framework. These methods have been applied to two VQMs at this point: peak-signal-to-noise ratio and the version of Sarnoff's just noticeable difference metric (JNDmetrix^®) tested by VQEG (Rapporteur Q11/12 (VQEG): Final report from the VQEG on the validation of objective models of video quality assessment, June 2000). The framework is readily extensible to additional VQMs.     

不同品质类型小麦籽粒结构的观察比较

应用扫描电子显微镜观察了3个不同品质类型的小麦品种（强筋小麦济南17号、中筋小麦扬麦12号和弱筋小麦扬麦9号）的籽粒断面结构。结果表明,济南17号胚乳舍有丰富的基质蛋白质,淀粉粒被包埋在基质蛋白质中间,胚乳结构致密;扬麦12号胚乳淀粉粒与基质蛋白质所连接,胚乳结构较疏松;扬麦9号胚乳蛋白质基质含量很少．淀粉粒与蛋白质结合不紧密。采用碱处理和差速沉淀法分离了籽粒胚乳大、小淀粉粒,扫描电镜观察发现品种间淀粉粒的形态无明显差别,但大、小淀粉粒的尺寸和含量在品种间存在很大差异。