- 范达;曹志刚;
This paper reports an investigation of the carrier frequency offset (CFO) compensation in the up-link of the orthogonal frequency division multiple access (OFDMA) system with interleaved subcarrier as-signment. The presence of CFOs between the transmitters and the uplink receiver will destroy the orthogo-nality among the different subcarriers,resulting in inter-carrier interference and multiuser interference. This paper proposes a pseudoinverse CFO compensation method based on the signal structure. The proposed method can compensate the CFOs of all users simultaneously and isolate the signals from all users at the same time. Compared with the existing CFO compensation methods,the new method provides a consider-able signal-to-noise ratio gain on the bit error rate performance and has a relatively low implementation complexity.
2008年01期 1-8页 [查看摘要][在线阅读][下载 311K] [下载次数：53 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] <正>A project named "A New Generation of Energy Management with Three Dimensional Coordination" has recently passed technical appraisal from the Ministry of Education.
2008年01期 8页 [查看摘要][在线阅读][下载 144K] [下载次数：52 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 李洪;陆明泉;冯振明;
Recently,direct acquisition of GPS P-code has received considerable attention to enhance the anti-jamming and anti-spoofing capabilities of GPS receivers. This paper describes a P-code acquisition method that uses block searches with large-scale FFT to search code phases and carrier frequency offsets in parallel. To limit memory use,especially when implemented in hardware,only the largest correlation result with its position information was preserved after searching a block of resolution cells in both the time and frequency domains. A second search was used to solve the code phase slip problem induced by the code frequency offset. Simulation results demonstrate that the probability of detection is above 0.99 for carrier-to-noise density ratios in excess of 40 dB ? Hz when the predetection integration time is 0.8 ms and 6 non-coherent integrations are used in the analysis.
2008年01期 9-16页 [查看摘要][在线阅读][下载 193K] [下载次数：165 ] |[网刊下载次数：0 ] |[引用频次：13 ] |[阅读次数：0 ] - 李辉;王德生;陈兆武;
The digital baseband predistorter is an effective technique to compensate for the nonlinearity of power amplifiers (PAs) with memory effects. However,most available adaptive predistorters based on direct learning architectures suffer from slow convergence speeds. In this paper,the recursive prediction error method is used to construct an adaptive Hammerstein predistorter based on the direct learning architecture,which is used to linearize the Wiener PA model. The effectiveness of the scheme is demonstrated on a digi-tal video broadcasting-terrestrial system. Simulation results show that the predistorter outperforms previous predistorters based on direct learning architectures in terms of convergence speed and linearization. A simi-lar algorithm can be applied to estimate the Wiener PA model,which will achieve high model accuracy.
2008年01期 17-22页 [查看摘要][在线阅读][下载 147K] [下载次数：50 ] |[网刊下载次数：0 ] |[引用频次：4 ] |[阅读次数：0 ] - 刘向阳;彭应宁;王秀坛;
Data selection-based summation fusion (DSSF) was developed to overcome the shortcomings of previously developed likelihood ratio tests based on channel statistics (LRT-CS) for the problem of fusing censored binary decisions transmitted over Nakagami fading channels in a wireless sensor network (WSN). The LRT-CS relies on detection probabilities of the local sensors,while the detection probabilities are a pri-ori unknown for uncooperative targets. Also,for Nakagami fading channels,the LRT-CS involves an infinite series,which is cumbersome for real-time application. In contrast,the DSSF only involves data comparisons and additions and does not require the detection probabilities of local sensors. Furthermore,the perform-ance of DSSF is only slightly degraded in comparison with the LRT-CS when the detection probabilities of local sensors are a priori unknown. Therefore,the DSSF should be used in a WSN with limited resources.
2008年01期 23-29页 [查看摘要][在线阅读][下载 168K] [下载次数：51 ] |[网刊下载次数：0 ] |[引用频次：11 ] |[阅读次数：0 ] - 李华;汤俊;彭应宁;
Single orbit bistatic space-based radar (SBR) is composed of two radars in the same orbit. The characteristics of the clutter Doppler-angle spectrum of a single orbit bistatic SBR show that the slope of the mainbeam clutter spectrum is highly sensitive to the cone angles. Therefore,the minimum detectable veloc-ity of the bistatic system is dependent on the cone angle. Then a new combined working mode of single-orbit bistatic SBR system was developed in which one radar will act as the transmitter and another as the receiver to improve detection performance for all angles. Simulation results by space-time adaptive process-ing verify the improved detection performance. The new design also reduces the average power of each ra-dar system and the size and weight of the on-board solar array-battery system.
2008年01期 30-34页 [查看摘要][在线阅读][下载 87K] [下载次数：42 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] -
<正>Large-scale public buildings have high energy density, which on average consume 5 to 15 times more electricity than residential buildings.
2008年01期 34页 [查看摘要][在线阅读][下载 16K] [下载次数：30 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] - 刘宇靖;孟华东;王德生;
Navigation and surveillance applications require tracking constant input/bias targets. When the target’s trajectory follows a constant input/bias constraint,model mismatching caused by conventional track-ing algorithms can be handled by a delayed update filter (DUF). The statistical convergence and stability properties of the delayed update filter were studied to insure the rationality of its steady-state analysis. A steady-state filter gain was then designed for a constant-gain DUF to reduce the computations without much performance loss. Simulations demonstrate the potential of the constant-gain DUF,and the CGDUF is nearly 60% faster than the DUF without much loss in steady-state tracking accuracy.
2008年01期 35-42页 [查看摘要][在线阅读][下载 165K] [下载次数：33 ] |[网刊下载次数：0 ] |[引用频次：4 ] |[阅读次数：0 ] -
<正>Since its launching on September 13, 2007, the Tsinghua Global Vision Lectures series, which has been incorpo-rated into Tsinghua's elective course system, has received a warm welcome from students.
2008年01期 42页 [查看摘要][在线阅读][下载 61K] [下载次数：14 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 皮燕燕;张巍;王胤;黄翊东;彭江得;
The almost equal height dual peak spontaneous Brillouin scattering spectrum of a piece of micro-structure fiber with a small core was investigated at various temperatures using the heterodyne method. The central frequencies of the two peaks increase linearly with increasing temperature with temperature coeffi-cients of 1.05 MHz/℃ and 1.13 MHz/℃. The height difference between the two peaks decreases linearly with a coefficient of ?0.06 dB/℃. The results show that microstructure fibers with a small core have great po-tential for fiber Brillouin distributed sensing.
2008年01期 43-46页 [查看摘要][在线阅读][下载 103K] [下载次数：55 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] -
<正>Professor Jun Murai,distinguished IT expert in Japan and Vice President of Keio University,was appointed Tsinghua Guest Professor on December 10,2007.
2008年01期 46页 [查看摘要][在线阅读][下载 16K] [下载次数：11 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 孙喆;王焕钢;张曾科;
Precise,real-time measurements of overflow particle size distributions in hydrocyclones are nec-essary for accurate control of the comminution circuits. Soft sensing measurements provide real-time,flexi-ble,and low-cost measurements appropriate for the overflow particle size distributions in hydrocyclones. Three soft sensing methods were investigated for measuring the overflow particle size distributions in hy-drocyclones. Simulations show that these methods have various advantages and disadvantages. Optimal Bayesian estimation fusion was then used to combine three methods with the fusion parameters determined according to the performance of each method with validation samples. The combined method compensates for the disadvantages of each method for more precise measurements. Simulations using real operating data show that the absolute root mean square measurement error of the combined method was always about 2% and the method provides the necessary accuracy for beneficiation plants.
2008年01期 47-53页 [查看摘要][在线阅读][下载 228K] [下载次数：73 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] -
<正>According to the Ministry of Education,22 Tsinghua University disciplines were evaluated as First Category National Key Disciplines,ranking first nationwide.
2008年01期 53页 [查看摘要][在线阅读][下载 103K] [下载次数：12 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 姜敏;张曾科;Tzyh-Jong Tarn;
In quantum circuits,importing of additional qubits can reduce the operation time and prevent de-coherence induced by the environment. However,excessive qubits may make the quantum system vulner-able. This paper describes how to relax existing qubits without additional qubits to significantly reduce the operation time of the quantum Fourier circuit compared to a circuit without optimization. The results indicate that this scheme makes full use of the qubits relaxation. The concepts can be applied to improve similar quantum circuits and guide the physical implementations of quantum algorithms or devices.
2008年01期 54-58页 [查看摘要][在线阅读][下载 81K] [下载次数：24 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 杨飚;张曾科;孙政顺;
Nonlinear least trimmed squares (NLTS) estimator is a very important kind of nonlinear robust es-timator,which is widely used for recovering an ideal high-quality signal from contaminated data. However,the NLTS estimator has not been widely used because it is hard to compute. This paper develops an algo-rithm to compute the NLTS estimator based on a random differential evolution (DE) strategy. The strategy which uses random DE schemes and control variables improves the DE performance. The simulation results demonstrate that the algorithm gives better performance and is more convenient than existing computing algorithms for the NLTS estimator. The algorithm makes the NLTS estimator easy to apply in practice,even for large data sets,e.g. in a data mining context.
2008年01期 59-64页 [查看摘要][在线阅读][下载 138K] [下载次数：34 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - 杨红英;叶昊;王桂增;
This paper presents a method for detecting weak fault signals in chaotic systems based on the chaotic dynamics reconstruction technique and the fuzzy neural system (FNS). The Grassberger-Procaccia algorithm and least squares regression were used to calculate the correlation dimension for the model order estimate. Based on the model order,an appropriately structured FNS model was designed to predict system faults. Through reasonable analysis of predicted errors,the disturbed signal can be extracted efficiently and correctly from the chaotic background. Satisfactory results were obtained by using several kinds of simula-tive faults which were extracted from the practical chaotic fault systems. Experimental results demonstrate that the proposed approach has good prediction accuracy and can deal with data having a ?40 dB signal to noise ratio (SNR). The low SNR requirement makes the approach a powerful tool for early fault detection.
2008年01期 65-70页 [查看摘要][在线阅读][下载 134K] [下载次数：99 ] |[网刊下载次数：0 ] |[引用频次：10 ] |[阅读次数：0 ] - 李洪波;孙增圻;陈霸东;刘华平;
The use of communication networks in control loops has gained increasing attention in recent years due to its advantages and flexible applications. The network quality-of-service (QoS) in those so-called networked control systems always fluctuates due to changes of the traffic load and available network resources. This paper presents an intelligent scheduling controller design approach for a class of NCSs to handle network QoS variations. The sampling period and control parameters in the controller are simultane-ously scheduled to compensate for the network QoS variations. The estimation of distribution algorithm is used to optimize the sampling period and control parameters for better performance. Compared with exist-ing networked control methods,the controller has better ability to compensate for the network QoS varia-tions and to balance network loads. Simulation results show that the plant setting time with the intelligent scheduling controller is reduced by about 64.0% for the medium network load and 49.1% for high network load and demonstrate the effectiveness of the proposed approaches.
2008年01期 71-77页 [查看摘要][在线阅读][下载 163K] [下载次数：102 ] |[网刊下载次数：0 ] |[引用频次：12 ] |[阅读次数：0 ] - 周强;蔡懿慈;黄亮;洪先龙;
Power is the major challenge threatening the progress of very large scale integration (VLSI) tech-nology development. In ultra-deep submicron VLSI designs,clock network size must be minimized to re-duce power consumption,power supply noise,and the number of clock buffers which are vulnerable to process variations. Traditional design methodologies usually let the clock router independently undertake the clock network minimization. Since clock routing is based on register locations,register placement actu-ally strongly influences the clock network size. This paper describes a clock network design methodology that optimizes register placement. For a given cell placement result,incremental modifications are per-formed based on the clock skew specifications by moving registers toward preferred locations that may re-duce the clock network size. At the same time,the side-effects to logic cell placement,such as signal net wirelength and critical path delay,are controlled. Test results on benchmark circuits show that the methodol-ogy can considerably reduce clock network size with limited impact on signal net wirelength and critical path delay.
2008年01期 78-84页 [查看摘要][在线阅读][下载 123K] [下载次数：45 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 杨孟辉;杨维康;王小鸽;廖建新;陈俊亮;
The hardware and software architectures of core service platforms for next-generation networks were analyzed to compute the minimum cost hardware configuration of a core service platform. This method gives a closed form expression for the optimized hardware cost configuration based on the service require-ments,the processing features of the computers running the core service platform software,and the proc-essing capabilities of the common object request broker architecture middleware. Three simulation scenar-ios were used to evaluate the model. The input includes the number of servers for the protocol mapping (PM),Parlay gateway (PG),application sever (AS),and communication handling (CH) functions. The simu-lation results show that the mean delay meets requirements. When the number of servers for PM,PG,AS,and CH functions were not properly selected,the mean delay was excessive. Simulation results show that the model is valid and can be used to optimize investments in core service platforms.
2008年01期 85-90页 [查看摘要][在线阅读][下载 148K] [下载次数：65 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 易荣;赵争鸣;钟玉林;
The busbars in high power neutral point clamped three-level inverters are modeled using the Maxwell Q3D Extractor software,which is based on the partial element equivalent circuits method. The equivalent circuits of the busbars and devices model are simulated in the electric simulator PSIM to analyze the effects of the parasitic inductance on the switching characteristics of the integrated gate commutated thyristor (IGCT) in different topology positions. The simulation results agree well with the measured imped-ance analyzer results and the IGCT test results,which proves the effectiveness of the modeling method for the large,complex busbars.
2008年01期 91-97页 [查看摘要][在线阅读][下载 313K] [下载次数：125 ] |[网刊下载次数：0 ] |[引用频次：5 ] |[阅读次数：0 ] - 马立伟;孙义和;
Network-on-chip (NoC) technology enables a new system-on-chip paradigm,the system-on-network-on-chip (SoNoC) paradigm. One of the challenges in designing application-specific networks is modeling the on-chip system behavior and determining on-chip traffic characteristics. A universal object message level model for SoNoC was defined and an object-oriented methodology was developed to imple-ment this model in hardware and software. The model supports "object to core" synthesis and "function in-voking to network" mapping. A case study of an H.263 system verifies the model and methodology. System prototypes are easily built and on-chip traffic can be observed using the SoNoC model to provide real benchmarks for on-chip network design.
2008年01期 98-105页 [查看摘要][在线阅读][下载 218K] [下载次数：90 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - 王俊艳;赵瑞清;唐万生;
This paper characterizes quality,budget,and demand as fuzzy variables in a fuzzy vendor selec-tion expected value model and a fuzzy vendor selection chance-constrained programming model,to maxi-mize the total quality level. The two models have distinct advantages over existing methods for selecting vendors in fuzzy environments. A genetic algorithm based on fuzzy simulations is designed to solve these two models. Numerical examples show the effectiveness of the algorithm.
2008年01期 106-111页 [查看摘要][在线阅读][下载 87K] [下载次数：192 ] |[网刊下载次数：0 ] |[引用频次：14 ] |[阅读次数：0 ] - 丁文锐;佟雨兵;张其善;杨东凯;
An image and video quality assessment method was developed using neural network and support vector machines (SVM) with the peak signal to noise ratio (PSNR) and the structure similarity indexes used to describe image quality. The neural network was used to obtain the mapping functions between the objec-tive quality assessment indexes and subjective quality assessment. The SVM was used to classify the im-ages into different types which were accessed using different mapping functions. Video quality was as-sessed based on the quality of each frame in the video sequence with various weights to describe motion and scene changes in the video. The number of isolated points in the correlations of the image and video subjective and objective quality assessments was reduced by this method. Simulation results show that the method accurately accesses image quality. The monotonicity of the method for images is 6.94% higher than with the PSNR method,and the root mean square error is at least 35.90% higher than with the PSNR.
2008年01期 112-116页 [查看摘要][在线阅读][下载 124K] [下载次数：141 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：0 ] - 梁锐;高金伍;
Capital budgeting is concerned with maximizing the total net profit subject to budget constraints by selecting an appropriate combination of projects. This paper presents chance maximizing models for capital budgeting with fuzzy input data and multiple conflicting objectives. When the decision maker sets a prospec-tive profit level and wants to maximize the chances of the total profit achieving the prospective profit level,a fuzzy dependent-chance programming model,a fuzzy multi-objective dependent-chance programming model,and a fuzzy goal dependent-chance programming model are used to formulate the fuzzy capital budgeting problem. A fuzzy simulation based genetic algorithm is used to solve these models. Numerical examples are provided to illustrate the effectiveness of the simulation-based genetic algorithm and the po-tential applications of these models.
2008年01期 117-120页 [查看摘要][在线阅读][下载 65K] [下载次数：97 ] |[网刊下载次数：0 ] |[引用频次：9 ] |[阅读次数：0 ] -
<正>Tsinghua Science and Technology (Tsinghua Sci Technol),a comprehensive academic journal sponsored by Tsinghua University,is published bimonthly.
2008年01期 121页 [查看摘要][在线阅读][下载 584K] [下载次数：18 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] 下载本期数据