共查询到20条相似文献,搜索用时 31 毫秒
1.
A planar surface-wave antenna (SWA) that achieves radiation at end-fire by surface-wave (SW) excitation is presented for millimetre-wave frequencies of operation. The 2D SWA is fed by a two-element array of printed SW launchers for controlled beam steering in the far-field. Measured results demonstrate a highly directive beam pattern with a 3 dB beamwidth less than 5 at 22.71 GHz. Such a planar low-cost and low-profile SWA design may be advantageous for surveillance systems and radar applications where beam steering at end-fire is of interest. 相似文献
2.
We demonstrate that the use of a single SiO2 film, with thickness corresponding to one standing wave (SW) period allows the recording of deep photoresist structures on silicon substrates by laser interference, without use of any additional antireflecting coating. This condition corresponds just to the opposite thickness (half SW period) previously proposed for using the SiO2 films for phase-shifting the SW pattern. Theoretical and experimental results demonstrated that for the lithography of deep structures, the contrast of the SW pattern, the minimum light intensity of the SW pattern and the photoresist adhesion are the most important parameters of the process. 相似文献
3.
Mobile communication channels are frequently plagued by severe noise and disturbances such as multipath fading and doppler effects that severely degrade performance. Among the automatic-repeat-request (ARQ) protocols used to improve the communication channel reliability, the stop-and-wait (SW) is positively characterized by simple implementation and negatively by low throughputs. This work describes the application of some new SW protocols that retain the simple implementation of the classical SW schemes, while reducing the transmitter's wait state time to increase throughput. The performance of the modified SW protocols, derived through computer simulations, is shown to be comparable to that of more complex ARQ protocols. 相似文献
4.
Subcarrier weighting (SW) is a recognized technique for sidelobe suppression in OFDM systems. In this paper SW is discussed in the context of cognitive radios where some portion of the spectrum is shared with primary users so it is required to notch that portion. A major disadvantage with SW scheme is bit error rate (BER) degradation due to unequal power distribution among different subcarriers therefore the primary objective of the paper is to enhance the performance of SW without additional degradation in BER performance. To this extent we propose an Elliptical-SW scheme by expanding the locus of weights to elliptical region. Simulation results show that the proposed scheme can produce deeper notch as compared to Conventional-SW for same BER performance. In second part we present a Partial-SW scheme by applying SW to lesser number of subcarriers. It can enhance BER performance significantly with negligible loss in sidelobe suppression capacity. Another scheme namely Guarded-SW is also proposed in this paper to provide further means to obtain very deep notches without any additional degradation in BER however it has to scarify some throughput. Finally an effective way of implementing SW in MIMO systems is presented by jointly optimizing weights over selected number of antennas. 相似文献
5.
Enhanced solder wettability (SW) of oxidized-Cu (OC) with 96.5Sn-3Ag-0.5Cu lead-free solder (LFS) by Ar-H2 plasmas was investigated. The SW of OC was significantly improved from 0% wetting of Cu oxidized in air at 260°C for 1 h
to 100% wetting of OC modified by Ar-H2 plasmas for 10 min. The SW of Cu was found to be highly dependent on the surface characteristics of Cu. By decreasing the
total surface energy (TSE), decreasing the polar surface energy (PSE), and increasing the dispersive surface energy (DSE)
on the surfaces of OC modified by Ar-H2 plasmas, the SW with LFS improves. X-ray photoelectron spectroscopy (XPS) indicates that Ar-H2 plasma treatment is used to remove the copper oxides CuO and Cu2O from the OC surfaces. The ratio of the total amount of Cu2O to CuO was found to be a good indication of how the copper oxides CuO and Cu2O affect the PSE, DSE, and SW of Cu. 相似文献
6.
When performing hardware/software co-design for embedded systems, the problem of which functions of the system should be implemented in hardware (HW) or in software (SW) emerges. This problem is known as HW/SW partitioning. Over the last 10 years, a significant research effort has been carried out in this area. In this paper, we present two new approaches to solve the HW/SW partitioning problem by using verification techniques based on satisfiability modulo theories (SMT). We compare the results using the traditional technique of integer linear programming, specifically binary integer programming and a modern method of optimization by genetic algorithm. The experimental results show that SMT-based verification techniques can be effective in particular cases to solve the HW/SW partition problem optimally using a state-of-the-art model checker based on SMT solvers, when compared against traditional techniques. 相似文献
7.
Ming Gu Lang Tong 《Signal Processing, IEEE Transactions on》1999,47(10):2745-2756
Convergence properties of the constant modulus (CM) and the Shalvi-Weinstein (SW) algorithms in the presence of noise remain largely unknown. A new geometrical approach to the analysis of constant modulus and Shalvi-Weinstein receivers is proposed by considering a special constrained optimization involving norms of the combined channel-receiver response. This approach provides a unified framework within which various blind and (nonblind) Wiener receivers can all be analyzed by circumscribing an ellipsoid by norm balls of different types, A necessary and sufficient condition for the equivalence among constant modulus. Shalvi-Weinstein, zero forcing, and Wiener receivers are obtained. Answers to open questions with regard to CM and SW receivers, including their locations and their relationship with Wiener receivers, are provided for the special orthogonal channel and the general two-dimensional (2-D) channel-receiver impulse response. It is also shown that in two dimensions, each CM or SW receiver is associated with one and only one Wiener receiver 相似文献
8.
Jiann Shing Shieh Linkens D.A. Peacock J.E. 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》1999,29(1):98-109
A multi-stage hierarchical fuzzy control system with a multi-echelon structure for depth of anaesthesia (DOA) is described in this paper. There are four echelons that monitor, control, interpret and assess the whole surgical operation. Echelon 1 is a measurement and control action level that involves: instrument sensing (Dinamap); anaesthetist observations [measurement of sweating (SW), lacrimation (LA) and pupil response (PR)]; and a syringe pump (Graseby pump). Echelon 2 is an interpretation level that involves: interpreting systolic arterial pressure and heart rate to provide the primary DOA; interpreting SW, LA and PR to provide the degree of lightness; and interpreting bolus drug effects to estimate the sensitivity of patients. Echelon 3 is a regulation level that involves: controlling the drug from either a hand-crafted anaesthetists' rule-base or a self-organizing fuzzy logic controller algorithm; planning the drug profile to avoid long recovery; and managing alarm situations. Finally, echelon 4 is an assessment level that assesses the whole surgical procedure according to the patient recovery time. Testing this system in clinical trials as an intelligent adviser has provided a preliminary proof-of-concept of the applicability of this hierarchical structure for DOA management 相似文献
9.
Tiwari M. Yuming Zhu Chakrabarti C. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2005,13(4):494-498
The sliding window (SW) approach has been proposed as an effective means of reducing the memory requirements as well as the decoding latency of the maximum a posteriori (MAP) based soft-input soft-output (SISO) decoder in a Turbo decoder. In this paper, we present sub-banked memory implementations (both single port and dual port) of the SW SISO decoder that achieves high throughput, low decoding latency, and reduced memory energy consumption. Our contributions include derivation of the optimal memory sub-banked structure for different SW configurations, study of the relationship between memory size and energy consumption for different SW configurations and study of the effect of number of sub-banks on the throughput/decoding latency for a given SW configuration. 相似文献
10.
Bertrand C. Futyan J. Ipe A. Gonzalez L. Clerbaux N. 《Geoscience and Remote Sensing, IEEE Transactions on》2006,44(12):3585-3600
The launch of the Geostationary Earth Radiation Budget (GERB) instrument onboard the Meteostat 8 allows a diurnal sampling of the Earth's Radiation Budget for the first time, providing a unique and important addition to polar-orbiting measurements. However, preliminary data from the GERB instrument exhibit systematic asymmetry in the short-wave (SW) flux diurnal variation. Such asymmetries are not found in the Clouds and the Earth's Radiant Energy System angular distribution models used to convert the directional broad-band GERB SW radiances to fluxes. Comparison between angularly matched estimations of reflected SW flux at the top of the atmosphere from the Spinning Enhanced Visible and Infra Red Imager (SEVIRI) and GERB data indicates that the SEVIRI spectral modeling could be a major issue. In addition, the results indicate that other factors such as the GERB SW geolocation, the GERB detector spectral response functions, the GERB nominal footprint resolution, and cloud cover could also potentially have an influence on the diurnal evolution of the GERB SW fluxes, as they can erroneously impact on the GERB SW correction factor 相似文献
11.
12.
Automatic-repeat-request (ARQ) protocols have been analyzed for quite some time, but the issue of errors in the feedback channel has not received much attention. In some applications, such as digital mobile communications, this issue can be important. Accordingly, this paper examines the effect of feedback errors on the throughputs of the stop-and-wait (SW), go-back-N (GBN), and selective repeat (SR) ARQ protocols for the ease of a point-to-point channel under some feedback information assumptions. It is shown that the deleterious effects of feedback errors on the throughputs of continuous (e.g., GBN and SR) ARQ protocols can be greatly reduced by a simple modification in the retransmission operation, provided that the “complete state” of the receiver is sent back with each acknowledgment 相似文献
13.
Jianing Li Xuegang Lu Yin Zhang Xiaoqin Ke Xiaoxiang Wen Fei Cheng Chaoping Wei Yanlin Li Kangkang Yao Sen Yang 《Advanced functional materials》2021,31(32):2102350
Advanced optical materials with rational designs and tunable light transmission have been drawing increasing interest due to their great potential in energy-efficient buildings and on-demand optical devices. Mechanoresponsive smart windows (SWs) can modulate light transmittance by mechanical actuation, showing high energy efficiency, low cost, and chemical stability. However, current research mainly focuses on tensile strain-responsive SWs that typically require a large strain to achieve optical transparency switching-which causes great inconvenience to practical application and fatigue damage to matrix materials. Herein, a novel shear-responsive SW with high strain sensitivity is fabricated by vertically fixing a Fe3O4@SiO2 nanochains (NCs) array in an elastic polyacrylamide matrix. The flexible SW exhibits optically transparent with all NCs standing vertically to the SW surface at initial relaxation state, which enables a good shielding effect, with NCs tilting along the shearing direction as the strain applied. Critically, a rather small shear displacement (1.5 mm) applied on the surface of SW gives rise to tunable optical states varying from the transparency state of 65% transmittance to the opaque state of 10%. The as-prepared SW with novel tuning modulation, high shear strain sensitivity, and optical angle-dependence holds promising potential in smart windows, optical switches, anti-voyeurism, and etc. 相似文献
14.
Optimal mean velocity estimation for Doppler weather radars 总被引:1,自引:0,他引:1
Optimal Doppler velocity estimation is explored for a standard Gaussian signal measurement model and thematic maximum-likelihood (ML) and Bayes estimation. Because the model considered depends on a vector parameter [velocity, spectrum width (SW), and signal-to-noise ratio (SNR)], the exact formulation of an ML or Bayes solution involves a system of coupled equations that cannot be made explicit for any of the parameters. Simple computational forms are shown to exist when SW and SNR are assumed known. An information-theoretic concept is used to extend these equations to the general case of SW and SNR unknown. A Monte Carlo simulation experiment is used to verify that the method can work, with no a priori information for either SW or SNR and a very small (20 pulse) sample size. The improved performance of this new Doppler velocity estimator is documented by comparison with derived optimal bounds and with the performance of the pulse pair (PP) method. Bayes estimator results are used to provide true performance bounds for comparison. Cramer-Rao bounds are also derived and shown to be inferior to the Bayes bounds in the small sample case considered 相似文献
15.
Thomas D. Duvel J.P. Kandel R. 《Geoscience and Remote Sensing, IEEE Transactions on》1995,33(3):670-683
Examines the problem of determining the separate shortwave (SW) and longwave (LW) components of the Earth radiation budget from space. Because true broad-band longwave filters do not exist, daytime LW radiance determinations can depend entirely or in part on subtraction of the measured SW radiance from the “Total” (TW) radiance involving integration over the entire electromagnetic pectrum. Examining radiances measured in the three channels (SW, imperfectly filtered broad-band LW, TW) of the Earth Radiation Budget Experiment (ERBE) scanners on board the NOAA-9, ERBS and NOAA-10 satellites, the authors find small discrepancies in the daytime estimates of broad-band (“unfiltered”) LW radiances using the ERBE “spectral correction” procedure. The authors show that these result from errors (of order 2.5%) in the calibration of the SW channel and possibly in the spectral characterization of the SW and/or TW channel of the ERBE scanners on NOAA-9 and NOAA-10. Nighttime estimates show no such bias, and there appears to be no such error in the data from ERBS. Considering the LW radiant exitances determined from ERBE scanner data from the three satellites, the authors find systematic differences in individual satellite estimates of simultaneous instantaneous regional means and of regional monthly means, consistent with the radiance discrepancies, instantaneous daytime LW estimates can be in error by 20% in the extreme case of very bright cold cloud, and LW cloud radiative forcing may be significantly biased. They consider the implications of these small SW-dependent errors on the determination of diurnal variation and of cloud radiative forcing in the longwave domain. They show how the ERBE estimates can be corrected, and consider how procedures can be used to validate results of future experiments (ScaRaB and CERES) 相似文献
16.
软硬件协同验证是系统芯片设计的重要组成部分。针对基于32 Bit CPU核的某控制系统芯片的具体要求,提出了一种系统芯片软硬件协同验证策略,构建了一个软硬件协同验证环境。该环境利用处理器内核模型支持内核指令集的特性运行功能测试程序,实现SoC软硬件的同步调试,并能够快速定位软硬件的仿真错误点,有效提高了仿真效率。该SoC软硬件协同验证环境完成了设计目的,并对其他系统芯片设计具有一定的参考价值。 相似文献
17.
Existence and performance of Shalvi-Weinstein estimators 总被引:1,自引:0,他引:1
The Shalvi-Weinstein (1990) criterion has become popular in the design of blind linear estimators of i.i.d. processes transmitted through unknown linear channels in the presence of unknown additive interference. Here, we analyze SW estimators in a general multiple-input multiple-output (MIMO) setting that allows near-arbitrary source/interference distributions and noisy noninvertible channels. The main contributions of this paper are (i) simple tests for the existence of SW estimators for the desired source and (ii) bounding expressions for the MSE of SW estimators that are a function of the minimum attainable MSE and the kurtoses of the source and interferers 相似文献
18.
Shared-memory based packet switches are known to provide the best possible throughput performance for bursty data traffic in high-speed packet networks and internets compared with other buffering strategies under conditions of identical memory resources deployed in the switch. However, scaling of shared-memory packet switches to a larger size has been restricted mainly due to the physical limitations imposed by the memory-access speed and the centralized control for switching functions in shared-memory switches. A new scalable architecture for a shared-memory packet switch, called the sliding-window (SW) switch, is proposed to overcome these limitations. The SW switch introduces a new class of switching architecture, where physically separate multiple memory modules are logically shared among all the ports of the switch, and the control is decentralized. The SW switch alleviates the bottleneck caused by the centralized control of switching functions in large shared-memory switches. Decentralized switching functions enable the SW switch to operate in a pipeline fashion to enhance scalability and switching capacity compared with that of previously known classes of shared-memory switch architecture. 相似文献
19.
20.
Ahmed Patrice Fahmi Patrice Nouri Herve 《AEUE-International Journal of Electronics and Communications》2007,61(9):605-620
In this paper, we present an efficient HW/SW codesign architecture for H.263 video encoder and its FPGA implementation. Each module of the encoder is investigated to find which approach between HW and SW is better to achieve real-time processing speed as well as flexibility. The hardware portions include the Discrete Cosine Transform (DCT), inverse DCT (IDCT), quantization (Q) and inverse quantization (IQ). Remaining parts were realized in software executed by the NIOS II softcore processor. This paper also introduces efficient design methods for HW and SW modules. In hardware, an efficient architecture for the 2-D DCT/IDCT is suggested to reduce the chip size. A NIOS II Custom instruction logic is used to implement Q/IQ. Software optimization technique is also explored by using the fast block-matching algorithm for motion estimation (ME). The whole design is described in VHDL language, verified in simulations and implemented in Stratix II EP2S60 FPGA. Finally, the encoder has been tested on the Altera NIOS II development board and can work up to 120 MHz. Implementation results show that when HW/SW codesign is used, a 15.8-16.5 times improvement in coding speed is obtained compared to the software based solution. 相似文献