- 姚远;陈文华;黄斌;冯正和;张志军;
The tapered slot antenna, such as Vivaldi, has been widely used due to its ultra-wideband, high gain, simple feed structure, and easy fabrication. However, there is no rigorous analytical theory for this type of antenna. This paper analyzed the metal parts of a tapered slot antenna in a conical coordinate system with the medium analyzed in rectangular coordinates. This mixed mode gave an approximate analytical form for the tapered slot antenna with the field distribution and radiation characteristics. A planar tapered slot antenna was proposed according to the results of the analysis methods. Measured and simulated results demonstrate the antenna performance. The antenna shows good impedance matching over a wide bandwidth of 9 GHz, from 2 GHz to 11 GHz, and good radiation patterns. It is suitable for ultra-wideband applications.
2009年01期 v.14 1-6页 [查看摘要][在线阅读][下载 1061K] [下载次数：182 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：0 ] - 李国良;冯建华;周立柱;
This paper presents an effective keyword search method for data-centric extensive markup language (XML) documents. The method divides an XML document into compact connected integral subtrees, called self-integral trees (SI-Trees), to capture the structural information in the XML document. The SI-Trees are generated based on a schema guide. Meaningful self-integral trees (MSI-Trees) are identified, which contain all or some of the input Keywordsfor the keyword search in the XML documents. Indexing is used to accelerate the retrieval of MSI-Trees related to the input keywords. The MSI-Trees are ranked to identify the top-k results with the highest ranks. Extensive tests demonstrate that this method costs 10-100 ms to answer a keyword query, and outperforms existing approaches by 1-2 orders of magnitude.
2009年01期 v.14 7-18页 [查看摘要][在线阅读][下载 984K] [下载次数：94 ] |[网刊下载次数：0 ] |[引用频次：6 ] |[阅读次数：0 ] - 徐波;何飞;薛一波;李军;
Today's firewalls and security gateways are required to not only block unauthorized accesses by authenticating packet headers, but also inspect flow payloads against malicious intrusions. Deep inspection emerges as a seamless integration of packet classification for access control and pattern matching for intrusion prevention. The two function blocks are linked together via well-designed session lookup schemes. This paper presents an architecture-aware session lookup scheme for deep inspection on network processors (NPs). Test results show that the proposed session data structure and integration approach can achieve the OC-48 line rate (2.5 Gbps) with inline stateful content inspection on the Intel IXP2850 NP. This work provides an insight into application design and implementation on NPs and principles for performance tuning of NP-based programming such as data allocation, task partitioning, latency hiding, and thread synchronization.
2009年01期 v.14 19-28页 [查看摘要][在线阅读][下载 658K] [下载次数：43 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - 鞠大鹏;刘川意;汪东升;刘宏;汤志忠;
Dramatically increasing amounts of digital data are placing huge requirements on storage systems. IP-networked storage systems, such as the network file system (NFS)-based network-attached storage (NAS) systems and the iSCSI-storage area network (SAN) systems, have become increasingly common in today's local area network (LAN) environments. The emergence of new storage techniques, such as object-based storage (OBS) and content aware storage (CAS), significantly improves the functionality of storage devices to meet further needs for storage sub-systems. However, these may impact system performance. This paper compares the performance of NFS, iSCSI storage, object-based storage devices (OSDs), and CAS-based storage systems in an environment with no data sharing across host machines. A gigabit ethernet network is used as the storage network. Test results demonstrate that the performances of these systems are compa-rable with CAS being much better than the others for write operations. The performance bottlenecks in these systems are analyzed to provide insight into how future storage systems may be improved and possible optimization methods. The analysis shows how the I/O interfaces in these systems affect the application performance and that network-based storage systems require optimized I/O latency and reduced network and buffer processing in the servers.
2009年01期 v.14 29-40页 [查看摘要][在线阅读][下载 1732K] [下载次数：43 ] |[网刊下载次数：0 ] |[引用频次：7 ] |[阅读次数：0 ] -
<正>China’s Ministry of Science and Technology recently announced approval of China’s National Basic Research Program (the 973 Program) and the Major Research Plan projects in 2008. Five Tsinghua research projects will be
2009年01期 v.14 40页 [查看摘要][在线阅读][下载 163K] [下载次数：25 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 张悠慧;汪东升;
Content addressable storage (CAS) is a promising technology for improving storage efficiency as well as access throughput. Currently, many CAS products are implemented on the block level, which results in loss of file information. Thus, some sophisticated optimizations cannot be achieved, such as accurate file-prefetching. This paper presents a file-aware block-level storage system combined with the CAS function. In contrast with some existing file-level CAS, this system is transparent to upper-level applications, including the operating system and the file system. These features are achieved by using smart-disk technologies to help the storage system to learn the file-system layout. A prototype was implemented on an open-source vir-tual machine (VM) with the guest operating system being Windows XP. Tests show that this combination significantly reduces the size of the VM image file and improves the storage performance by discarding unused blocks and using a simple file-level prefetching strategy.
2009年01期 v.14 41-49页 [查看摘要][在线阅读][下载 533K] [下载次数：58 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 史广建;潘立阳;孙磊;张志刚;许军;
The reliability of silicon-oxide-nitride-oxide-silicon (SONOS) type memories was analyzed using the charge pumping method and I-V tests at different temperatures to study its endurance and retention char-acteristics. A simple model was used to explain the charge loss phenomenon, with a dual-erasure method developed to improve the endurance and retention characteristics. The results indicate that the coexistence of injected holes and electrons after long term cycling, referred to as the mismatch problem, leads to deg-radation of the device characteristics. With the dual-erasure method, the threshold voltage, VT, window is maintained after 1×104 programming and erasing cycles and the charge loss is reduced by 410 mV after 72 h baking at 120℃.
2009年01期 v.14 50-54页 [查看摘要][在线阅读][下载 1168K] [下载次数：48 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] - 徐淑正;张鹏;王鹏军;杨华中;
A high capacity data hiding technique was developed for compressed digital audio. As perceptual audio coding has become the accepted technology for storage and transmission of audio signals, compressed audio information hiding enables robust, imperceptible transmission of data within audio signals, thus allowing valuable information to be attached to the content, such as the song title, lyrics, composer's name, and artist or property rights related data. This paper describes simultaneous low bitrate encoding and information hiding for highly compressed audio signals. The information hiding is implemented in the quan-tization process of the audio content which improves robustness, signal quality, and security. The impercep-tibility of the embedded data is ensured based on the masking property of the human auditory system (HAS). The robustness and security are evaluated by various attacking algorithms. Tests with an extended MPEG4 advanced audio coding (AAC) encoder confirm that the method is robust to the regular and singular groups method (RS) and sample pair analysis (SPA) attacks as well as other statistical steganalysis method attacks.
2009年01期 v.14 55-61页 [查看摘要][在线阅读][下载 765K] [下载次数：131 ] |[网刊下载次数：0 ] |[引用频次：9 ] |[阅读次数：0 ] - 梁仁荣;王敬;许军;
High quality strain-relaxed thin SiGe virtual substrates have been achieved by combining the misfit strain technique and the point defect technique. The point defects were first injected into the coherently strained SiGe layer through the "inserted Si layer" by argon ion implantation. After thermal annealing, an intermediate SiGe layer was grown with a strained Si cap layer. The inserted Si layer in the SiGe film serves as the source of the misfit strain and prevents the threading dislocations from propagating into the next epitaxial layer. A strained-Si/SiGe/inserted-Si/SiGe heterostructure was achieved with a threading dislocation density of 1×104 cm-2 and a root mean square surface roughness of 0.87 nm. This combined method can effectively fabricate device-quality SiGe virtual substrates with a low threading dislocation density and a smooth surface.
2009年01期 v.14 62-67页 [查看摘要][在线阅读][下载 1499K] [下载次数：49 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：0 ] - 熊伟;张进宇;Min-Chun Tsai;王燕;余志平;
As mask features scale to smaller dimensions, the so-called "3-D mask effects" which have mostly been neglected before, become important. This paper properly models the 3-D thick mask effects, and then analyses the object-based inverse lithography technique using a simulated annealing algorithm to determine the mask shapes that produce the desired on-wafer results. Evaluations against rigorous simulations show that the synthesized masks provide good image fidelity up to 0.94, and this approach gives improved accuracy and faster results than existing methods.
2009年01期 v.14 68-74页 [查看摘要][在线阅读][下载 580K] [下载次数：45 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 殷翀元;罗贵明;
The construction of Büchi automata from linear temporal logic is a significant step in model check-ing. This paper presents a depth-first construction algorithm to obtain simple Büchi automata from linear-time temporal logic which significantly reduces the sizes of the state spaces. A form-filling algorithm was used to reduce the size of the generated automata and the algorithms were applied directly to state-based Büchi automata, without transformation into transition-based automata. A form-filling algorithm for the Büchi auto-mata, which is based on the form-filling algorithm for deterministic automata, was developed by redefining parts of the configuration of the Büchi automata as well as the transition function. The correctness of this form-filling algorithm was proven. Tests show that this approach is competitive, especially on LTL formulae in the form of G, F, and U.
2009年01期 v.14 75-82页 [查看摘要][在线阅读][下载 651K] [下载次数：91 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - 臧志远;罗贵明;殷翀元;
In networks, the stable path problem (SPP) usually results in oscillations in interdomain systems and may cause systems to become unstable. With the rapid development of internet technology, the occurrence of SPPs in interdomain systems has quite recently become a significant focus of research. A frame-work for checking SPPs is presented in this paper with verification of an interdomain routing system using formal methods and the NuSMV software. Sufficient conditions and necessary conditions for determining SPP occurrence are presented with proof of the method's effectiveness. Linear temporal logic was used to model an interdomain routing system and its properties were analyzed. An example is included to demon-strate the method's reliability.
2009年01期 v.14 83-89页 [查看摘要][在线阅读][下载 512K] [下载次数：48 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - 孙军波;罗贵明;
An abstraction method developed for the explicit linear temporal logic model checking was geared towards reducing the useless part of the state space during the abstraction period. This reduces the cost during the abstraction period relative to models requiring many useless states. A dining-philosophers example comparing this abstraction method with conventional methods indicates that a large proportion of the state space has been reduced by this abstraction method. Finally, the abstract method is shown to be correct and an analysis is given to show how such a large proportion of states can be reduced.
2009年01期 v.14 90-94页 [查看摘要][在线阅读][下载 418K] [下载次数：69 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 耿睿;程朋;崔德光;
Dynamic airspace management (DAM) is an important approach to extend limited air space resources by using them more efficiently and flexibly. This paper analyzes the use of the dynamic air-route adjustment (DARA) method as a core procedure in DAM systems. DARA method makes dynamic decisions on when and how to adjust the current air-route network with the minimum cost. This model differs from the air traffic flow management (ATFM) problem because it considers dynamic opening and closing of air-route segments instead of only arranging flights on a given air traffic network and it takes into account several new constraints, such as the shortest opening time constraint. The DARA problem is solved using a two-step heuristic algorithm. The sensitivities of important coefficients in the model are analyzed to determine proper values for these coefficients. The computational results based on practical data from the Beijing ATC region show that the two-step heuristic algorithm gives as good results as the CPLEX in less or equal time in most cases.
2009年01期 v.14 95-102页 [查看摘要][在线阅读][下载 580K] [下载次数：111 ] |[网刊下载次数：0 ] |[引用频次：6 ] |[阅读次数：0 ] - 王柳笛;张志刚;赵悦;毛平;潘立阳;
Nonvolatile memories (NVMs) with triple layers of silicon nanocrystals were fabricated with conventional CMOS technology. This paper explores the program/erase performance and reliability of NVMs with three layers of nanocrystals. The results indicate that the nanocrystals in the triple-layer nanocrystal NVM (NCNVM) are difficult to fully charge during the programming process. The programming speed of the triple-layer NCNVMs is quicker than that of single-layer NCNVMs, which means that the second and third layers of nanocrystals in the triple-layer NCNVM affect the charge of the first layer nanocrystals. Reliability tests show that the memory window has little degradation after 1×104 cycles.
2009年01期 v.14 103-105页 [查看摘要][在线阅读][下载 451K] [下载次数：35 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 刘斌彬;白栋;葛启宏;梅顺良;
In multipath environments, the error rate performance of orthogonal frequency division multiplexing (OFDM) is severely degraded by the deep fading subcarriers. Powerful error-correcting codes must be used with OFDM. This paper presents a quasi-cyclic low-density parity-check (LDPC) coded OFDM system, in which the redundant bits of each codeword are mapped to a higher-order modulation constellation. The optimal degree distribution was calculated using density evolution. The corresponding quasi-cyclic LDPC code was then constructed using circulant permutation matrices. Group shuffled message passing scheduling was used in the iterative decoding. Simulation results show that the system achieves better error rate performance and faster decoding convergence than conventional approaches on both additive white Gaussian noise (AWGN) and Rayleigh fading channels.
2009年01期 v.14 106-112页 [查看摘要][在线阅读][下载 509K] [下载次数：113 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] - 李景阳;孙茂松;
Chinese text categorization differs from English text categorization due to its much larger term set (of words or character n-grams), which results in very slow training and working of modern high-performance classifiers. This study assumes that this high-dimensionality problem is related to the redundancy in the term set, which cannot be solved by traditional term selection methods. A greedy algorithm framework named "non-independent term selection" is presented, which reduces the redundancy according to string-level correlations. Several preliminary implementations of this idea are demonstrated. Experiment results show that a good tradeoff can be reached between the performance and the size of the term set.
2009年01期 v.14 113-120页 [查看摘要][在线阅读][下载 483K] [下载次数：110 ] |[网刊下载次数：0 ] |[引用频次：7 ] |[阅读次数：0 ] - 张莉;张贤达;高秋彬;
This paper describes a distributed estimation scheme (DES) for a bandwidth constrained ad hoc sensor network. The DES is universal in the sense that operations on all sensors are identical and independent of noise distribution. The scheme requires each sensor to transmit just a 1-bit message per observation. Simulation results show that the scheme achieves much better mean-squares error (MSE) performance than the simplified isotropic universal DES and even outperforms the isotropic universal DES which requires more than twice the bandwidth of this scheme.
2009年01期 v.14 121-125页 [查看摘要][在线阅读][下载 403K] [下载次数：74 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 张延军;何虎;沈钲;孙义和;
The rapid development of multimedia techniques has increased the demands on multimedia processors. This paper presents a new design method to quickly design high performance processors for new multimedia applications. In this approach, a configurable processor based on the very long instruction-set word architecture is used as the basic core for designers to easily configure new processor cores for multi-media algorithm. Specific instructions designed for multimedia applications efficiently improve the perform-ance of the target processor. Functions not implemented in the digital signal processor (DSP) core can be easily integrated into the target processor as user-defined hardware to increase the performance. Several examples are given based on the architecture. The results show that the processor performance is en-hanced approximately 4 times on the H.263 codec and that the processor outperforms both DSPs and single instruction multiple data (SIMD) multimedia extension architectures by up to 8 times when computing the 2-D-IDCT.
2009年01期 v.14 126-132页 [查看摘要][在线阅读][下载 473K] [下载次数：95 ] |[网刊下载次数：0 ] |[引用频次：8 ] |[阅读次数：0 ] - 周宁;董未名;王家廞;Paul Jean-Claude;
This paper presents an image-based algorithm for simulating the visual adaptation of the human visual system to various illuminations, especially in dark nighttime conditions. The human visual system exhibits different characteristics depending on the illumination intensity, with photopic vision in bright conditions, scotopic vision in dark conditions, and mesopic vision between these two. A computational model is designed to simulate multiple features of mesopic vision and scotopic vision, including the chromaticity change, luminance change, and visual acuity loss. The system uses a source image under bright illumination as input. Then assuming that the viewer has already adapted to the new conditions, the color spectrum of the input image is reconstructed to replace the source with modifications of the chromaticity and the luminance of the relighted scene. A bilateral filter is used to simulate the visual acuity loss. The model parameters have clear physical meanings and can be obtained from experimental data to achieve realistic results.The algorithm can be used not only for visual perception simulation, but also as a day-for-night tool to produce realistic night-time images from daytime images.
2009年01期 v.14 133-138页 [查看摘要][在线阅读][下载 1674K] [下载次数：54 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 郑运平;陈传波;Sarem Mudar;
A representation method using the non-symmetry and anti-packing model (NAM) for data compression of binary images is presented. The NAM representation algorithm is compared with the popular linear quadtree and run length encoding algorithms. Theoretical and experimental results show that the algorithm has a higher compression ratio for both lossy and lossless cases of binary images and better reconstructed quality for the lossy case.
2009年01期 v.14 139-145页 [查看摘要][在线阅读][下载 472K] [下载次数：42 ] |[网刊下载次数：0 ] |[引用频次：4 ] |[阅读次数：0 ] - 武露;张贤达;
As a generalization of orthogonal frequency-division multiplexing (OFDM) systems, multi-input multi-output (MIMO) OFDM systems are very sensitive to carrier frequency offset (CFO). This paper proposes a blind CFO estimation method based on power spectrum analysis, which has high bandwidth efficiency and is much less complex. This method can be used to estimate the residual CFO, which is less than half of the subcarrier spacing. The method uses a cosine cost function to get a closed-form CFO estimate. Simulation results illustrate that the method is effective for MIMO OFDM systems.
2009年01期 v.14 146-150页 [查看摘要][在线阅读][下载 368K] [下载次数：110 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] -
<正>Tsinghua Science and Technology (Tsinghua Sci Technot), a comprehensive academic journal sponsored by Tsinghua University, is published bimonthly. This jour
2009年01期 v.14 151页 [查看摘要][在线阅读][下载 811K] [下载次数：12 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] 下载本期数据