平流层通信系统的收发链路性能研究

针对平流层定点信息平台低空试验艇的工作特点,分析了该系统无线数据链路中上下行信道天线收发信号与平台运动方式的关系,分析表明现有天线结构存在传输信号盲区的问题。为此提出了一种基于天线分集的天线收发模型,以改善数据链路性能。该模型实现简单,仿真结果表明该结构可显著提高信噪比并有效消除信号传输盲区,实现信号的可靠传输。     

Proposal for spotbeam pattern for GSM-based satellite personalcommunications

A novel satellite footprint design is presented in order to mitigate the GSM synchronisation problems, caused by the potential wide variety of required timing advances, during the access phase of the signalling procedure. It is applied to LEO and MEO constellations and for different satellite channel parameters. Different approaches are presented and their tradeoff in terms of signalling load is discussed     

Correcting phased arrays for multipath or for conformal topography

The theoretical basis for a calibration scheme for phasedarray antennas is presented. A modified beamforming matrix is produced that will correct for the effects of multipath propagation. An extension of this is that, since it is not necessary to know the exact disposition of the array elements, the same scheme can be used to derive beamformers for conformal arrays.     

Statistical processing method for sidelobe peaks for earth-station antennas

For coordination studies and for the assessment of mutual interference between radiocommunication-satellite systems and between earth stations and radio-relay stations sharing the same frequency band, the method which represents off-axis radiation characteristics of the earth-station antenna is desirable. For this purpose, International Radio Consultative Committee (CCIR) Report 391-4 describes a statistical processing method of sidelobe peaks which was adopted at the XVth Plenary Assembly in 1982. This statistical processing method is based on the slope of reference radiation pattern, while the old one, which has been used, is based on the absolute peak value. Therefore, the results of the statistical evaluation using the current (new) method may differ from that using the old method. According to the measured data on a Cassegrain antenna of 13 m in diameter at about 12 GHz, it is shown that the worst 10 percent value of sidelobe peaks of the new processing method, which is the level exceeded by 10 percent of the peaks, is statistically about 0.8 dB lower than that of the old method.     

一种电磁环境量化分析方法

提出了一种电磁环境量化分析的新方法.该方法充分考虑了电磁环境信号的极化方式、调制方式,给出了极化因子、调制因子的内涵和定义基于不同极化方式、调制方式之间影响特性的理论分析和仿真,给出了典型电磁环境的极化因子、调制因子及其变化特性.所得成果为深入研究复杂电磁环境的量化分析和评估方法提供了积极的理论探索.     

Cross residual transform for lossless intra-coding for HEVC

A new lossless intra-coding method based on a cross residual transform is applied to the next generation video coding standard HEVC (High Efficiency Video Coding). HEVC includes a multi-directional spatial prediction method to reduce spatial redundancy by using neighboring pixels as a prediction for the pixels in a block of data to be encoded. In the new lossless intra-coding method, the spatial prediction is performed as pixelwise DPCM but is implemented as block-based manner by using cross residual transform on the HEVC standard. The experimental results show that the new lossless intra-coding method reduces the bit rate of approximately 8.43% in comparison with the lossless-intra coding method in the HEVC standard and the proposed method results in slightly better compression ratio than the JPEG200 lossless coding.     

Microstrip system for voltage-controlled phase equalisation for microwaves

A group-delay reflective-mode microwave equaliser is proposed. The required delay is obtained combining several voltagecontrolled circulator-coupled elementary cells. For an assigned phase response, the circuit is designed by an interactive program. Experimental results are reported relative to L band systems with constant and linear delay.     

General Design for Test Guidelines for RF IC

While the cost of silicon drops over years, the IC test cost basically stays flat. Hence, the percentage of the test cost in the overall chip cost increases significantly. For the total test cost, the RF test cost is a major contributor due to its tester requirement as well as the complexity of the RF parametric and functional tests. Design for Test (DFT) is a natural step to take to reduce the overall testing cost when the cost of the silicon to implement many Built-In Self Test (BIST) is virtually negligible. This article presents general guidelines for the RF IC, especially for the System on Chip (SoC) and System in Package (SiP) parts. It discusses the specific guidelines for DFT in order to reduce the RF test cost while still keeping acceptable test quality for both RF parameters and functionalities.     

Splines for electromagnetics

The theory of splines for approximation is developed. The theory is presented in a general form applicable to other than just piecewise polynomial approximation. The relationship of spline approximation and finite elements is shown with an example given to demonstrate the procedure as applied to the solution of Poisson's equation. The use of spline functions in the method of moments is also discussed. The results of this use is then presented for the solution of a center-fed wire antenna.     

A system for systolic modules for the MUSIC algorithm

The authors believe that special-purpose architectures for digital signal processing (DSP) real-time applications will use closely coupled processing elements as array processor modules to implement the various portions of the new algorithms, and several such modules will cooperate in a pipelined manner to implement complete algorithms. Such an architecture, based upon systolic modules, for the MUSIC algorithm is presented. The architecture is suitable for VLSI implementation. The throughput of the pipelined approach is O(N), whereas the sequential approach is O(N³)     

牛奶成份检测仪光强检测电路设计

介绍牛奶成份检测仪应用激光散透比法检测牛奶的成份,利用半导体激光器照射牛奶试样,分别在散射光和透射光方向检测光强值,由于激光透过牛奶试样后的光信号非常微弱,使得精确检测光强信号比较困难。介绍一种牛奶成份检测仪光强检测电路的设计方案,该电路具有精密、简洁、可靠性高等特点。     

Jitter analysis for two methods of synchronization for externaltiming injection

The jitter generated by two different approaches to synchronization of an external timing source is analyzed. The two approaches are: the use of conventional stuffing and the use of a simpler frame sampling synchronizer. It is shown that these two approaches have the same jitter power density spectrum. The result is obtained using a new time domain method developed in the paper. Exact expressions for the jitter on the synchronized external timing source are obtained. Furthermore, the effect of quantization in the conventional stuffing synchronizer on the jitter expressions obtained is also explored. Jitter generated by the frame sampling synchronizer is also analyzed using the time domain method, which again produces an exact expression. In the case where certain parameters of the two approaches are related, the location of spectral lines in their respective jitter spectra is shown to be identical. It is also shown that both approaches to synchronization introduce the so-called waiting-time jitter     

Efficient ray-tracing methods for propagation prediction for indoorwireless communications

The application of several ray-tracing techniques, in combination with the uniform theory of diffraction, is presented for efficient prediction of propagation in the UHF (communication) band in an indoor environment. First, we improve the computational efficiency of the two-dimensional (2D) ray-tracing method by reorganizing the objects in an indoor environment into irregular cells. Second, by making use of the two-dimensional ray-tracing results, a new three-dimensional (3D) propagation-prediction model is developed, which can save 99% of the computation time of a traditional three-dimensional model. This new hybrid model is more accurate than two-dimensional models, and more efficient in computing the path loss to any point in the building than traditional three-dimensional models. In this model, reflection and refraction by layered materials, and diffraction for the corners of the walls, are considered. A patched-wall model is used to improve the accuracy of prediction in the method. Finally, a comparison between simulation and measurements shows good agreement     

Methods for Calculating Distance Separation for Noninterfering Transmissions

Methods are presented for computing the distance required between transmitters with co-channel frequency assignments so that interference between them may be held below a specified level. Separate consideration is given to utilization probabilities resulting from communications traffic volume and to factors which are a function of the transmission medium and equipment characteristics. A graphical-analytic method is developed which reduces the usual path attenuation vs distance charts to normalized form. This permits rapid translation of the prescribed path attenuation into distance for any combination of antenna heights and wavelength in the line-of-sight region. The normalized charts also facilitate establishment of a probability, due to lobing, that path attenuation in a given region will be above or below a specified value when the transmitters or receivers are in motion. The basic methods are developed for distances well within the line-of-sight region, but special consideration also is given to distances near the horizon where the usual approximations do not apply.     

Methods for Compensating for Variable Electrode Contact in EIT

Electrical impedance tomography (EIT) is an imaging modality that currently shows promise for the detection and characterization of breast cancer. A very significant problem in EIT imaging is the proper modeling of the interface between the body and the electrodes. We have found empirically that it is very difficult, in a clinical setting, to assure that all electrodes make satisfactory contact with the body. In addition, we have observed a capacitive effect at the skin/electrode boundary that is spatially heterogeneous. To compensate for these problems, we have developed a hybrid nonlinear–linear reconstruction algorithm using the complete electrode model in which we first estimate electrode surface impedances, by means of a Levenberg–Marquardt iterative optimization procedure with an analytically computed Jacobian matrix. We, subsequently, use a linearized algorithm to perform a 3-D reconstruction of perturbations in both contact impedances, and in the spatial distributions of conductivity and permittivity. Results show that, with this procedure, artifacts due to electrodes making poor contact can be greatly reduced. If the experimental apparatus physically applies voltages and measures currents, we show that it is preferable to compute the reconstruction with respect to the Dirichlet-to-Neumann map rather than the Neumann-to-Dirichlet map if there is a significant possibility that electrodes will be fully disconnected. Finally, we test our electrode compensation algorithms for a set of clinical data, showing that we can significantly improve the fit of our model to the measurements by allowing the electrode surface impedances to vary.      

Design technique for MESFET mixers for maximum conversion gain

A design technique for MESFET mixers is described. This technique is based on a mixer analysis program (MIXAN) designed to obtain the value of conversion gain and evaluate the influence of the embedding impedances for any local oscillator power and DC bias, in order to optimized the mixer performance. The MIXAN program, which uses SPICE as a subroutine to determine large-signal current and voltage waveforms, is able to obtain the operating conditions for maximum conversion gain. The good agreement between experimental and simulation results for X-band drain and gate mixers proves the validity of the design technique     

An algorithm for the design of generalized quantizers for detection

A procedure based on the generalized Lloyd algorithm approach using a sequence of independent noise samples to design M-region generalized quantizers for signal detection is presented. Included in this case are the conventional M-interval quantizer detectors. The quantizer parameters for S.A. Kassam's (1985) four-region generalized quantizer detector are computed using various sample sizes for the known sequence of independent noise samples. Two families of densities which cover a wide spectrum of possible nonGaussian densities are considered: the generalized Gaussian densities and the Johnson S_u family of densities. The performance of the quantizer detector is compared to that of the locally optimum detector, and the results are presented as the asymptotic relative efficiencies of the respective detectors. The case when the noise density is not known before analysis is considered, and the detection performance is examined using an estimate of the density. A mean-squared-error distortion criterion is used in the proposed algorithm to obtain quantizers that yield maximum efficacy. It is shown through numerical examples that the design procedure is simple, fast, and applicable to a wide range of nonGaussian distributions     

On metrics for comparing interconnect estimation methods for FPGAs

Interconnect management is a critical design issue for large field-programmable gate arrays (FPGA) based designs. One of the most important issues for planning interconnection is the ability to reliably and efficiently predict the interconnect requirements of a given design on a given FPGA architecture. Many interconnect estimation methods have been reported so far and the estimation problem is also under active research. From a CAD tool deployment point of view, comparing these estimation methods is very difficult because of the different reporting methods used by the authors. We make an argument for and propose a new uniform reporting metric, based on comparing the estimates with the results of an actual detailed router on both local and global levels. We then compare some of the well known and promising interconnect estimation methods using our new metric on a large number of benchmark circuits.     

Criteria for nearly omnidirectional radiation patterns for printed antennas

Radiation from printed antennas is investigated with emphasis placed on producingbar{E}- andbar{H}-plane radiation patterns that are as nearly omnidirectional as possible. This is achieved using criteria which are derived for a nonzero radiation field extending down to the layer surface (radiation into the horizon). It is determined that this phenomenon arises when a surface wave pole coincides with a branch point in the complex plane. A simple ray optics interpretation is given for the phenomenon, and graphs are presented to easily enable design of printed antenna geometry to achieve nearly omnidirectionalbar{E}- orbar{H}-plane patterns.