CDMA系统中的功率控制

功率控制是CDMA移动通信系统中最为重要的核心技术之一。该文主要介绍CDMA系统反向链路和前向链路的各种功率控制技术。首先介绍功率控制对于CDMA系统的重要性及功率控制的分类，然后分别介绍CDMA系统反向链路和前向链路的功率控制算法。     

Frequency tracking by MAP demodulation and by linear prediction techniques

Maximum posterior probability (MAP) demodulation with delay of an FM signal in the presence of noise is realized and compared with a) Griffiths' linear prediction method, b) a complex-valued version of Griffiths' method, c) three new modifications of Griffiths' method which can improve the performance of this method, and d) maximum-likelihood (ML) frequency estimation. These first quantitative results on MAP demodulation with delay show an advantage of a few db in output SNR at high input CNR and much larger advantages at low input CNR, relative to the other techniques.     

光伏系统最大功率跟踪技术的研究

基于传统的滑膜控制算法,本文采用一种改进的指数趋近律方法,来实现最大功率跟踪,使得控制输出变量可以为连续变量,再通过调制器得到开关管的控制信号,实现控制,以弥补传统方法的参数灵敏度、适用范围受限制等方面的缺陷。通过对传统算法和改进算法的仿真比较,得出了改进的滑模控制法能够快速地跟踪最大功率点,振荡幅度较小,鲁棒性较好。     

Interval-analysis techniques in linear systems: An application in power systems

In this paper we apply the technique of interval analysis to get bounds on the initial value response of a linearized single machine infinite bus problem when a parameter is varied. It is generally believed that responses for parameter variations in an interval should lie within the responses for the extremums of the parameter variations. This is not generally true and our example demonstrates this. The interval-analysis technique permits getting the overall bound on the response. Further experimentation also revealed that the method has some limitations particularly involving lightly damped long-term dynamics.The technique is useful in finding the robustness of a particular design such as the power system stabilizer for parameter variations.The work of M. A. Pai and C. Kulig was supported by NSF Grant ECS 87-19055 and NSF Grant ECS 87-19055 REU, respectively. The work of A. N. Michel and H. F. Sun was supported by NSF Grant ECS 88-02924.     

Frequency acquisition and tracking for optical heterodyne communication systems

A frequency acquisition and tracking system for use in optical heterodyne communication systems employing semiconductor lasers is described. Analytical models for acquisition and tracking are used to predict performance; probability of incorrect acquisition is predicted for the acquisition system, and rms error is predicted for the tracker. Experimental data is presented and compared to the analytic results.     

Frequency stability requirements for space communications and tracking systems

Space communications and tracking systems impose stringent requirements on stable frequency sources. "Flicker" (1/f) noise and environmental modulation are two types of oscillator instability affecting typical space systems performance. Examples of several systems are presented with the source requirements for each. Earth satellite systems impose stability requirements of the order of 10^-10over periods of seconds to hours depending on the individual experiment. A typical system requires phase noise of less than 5° rms in a receiver of 12 Hz bandwidth at S-band. An example is presented of a spacecraft transponder which must maintain phase noise below 45° peak-to-peak under vibration of 3g peak from 10 Hz to 10 KHz.     

Some applications of optimization techniques to power systems problems

Important power system planning and operation problems have been formulated as mathematical optimization problems. Such problems as the economic dispatch, in many of its facets; var scheduling and allocation; pollution dispatch; maximum interchange; hydrothermal unit commitment and dispatch; generation, transmission, and distribution expansion planning; maintenance scheduling and substation switching, have been formulated and solved. Modern mathematical optimization techniques, such as nonlinear, quadratic, linear, integer and dynamic programming and their many combinations and extensions, have been exploited. Some of the formulations and solutions to these problems as presented in the recent literature within the power systems field are reviewed. The large number of papers available is a measure of the current immense activity in this area. Attempts are made to point out some specific areas where more work needs to be done.     

Adaptive power techniques for blind channel estimation in CDMA systems

The problem of blind adaptive channel estimation in code-division multiple access (CDMA) systems is considered. Motivated by the iterative power method, which is used in numerical analysis for estimating singular values and singular vectors, we develop recursive least squares (RLS) and least mean squares (LMS) subspace-based adaptive algorithms in order to identify the impulse response of the multipath channel. The schemes proposed in this paper use only the spreading code of the user of interest and the received data and are therefore blind. Both versions (RLS and LMS) exhibit rapid convergence combined with low computational complexity. With the help of simulations, we demonstrate the improved performance of our methods as compared with the already-existing techniques in the literature.     

Comparative study of maximum power point tracking techniques for hybrid renewable energy system

The power generation demand is increasing day-by-day throughout the world, therefore, the use of hybrid systems becomes a significant solution. The hybrid renewable energy system (HRES) is used for delivering power in various regions in order to overcome intermittence of wind and solar resources. Because of increasing environmental problems, for example, greenhouse gas emission and energy cost have interested novel research into substitute methods in favour of electrical power generation. Maximum Power Point Tracking (MPPT) control method is a vast deal of novel research used for enhancing the efficiency of HRES. The authors have revealed that the hybrid techniques i.e. Global MPPT, fuzzy-neuro systems, Adaptive Neuro-Fuzzy Inference System (ANFIS), Perturbed and Observe (P&O) + Adaptive Neural Network (ANN) etc. can provide best results as compared to other MPPT control methods. This paper offering a state of art review of MPPT control techniques for HRES.     

Multilayer power printed structures suitable for controlling EMI noises generated in power converters

Electromagnetic interference (EMI) noises generated in power converters are diffused on the surface of conductors. This means influences occur from radiated EMI noises emitted from power transmission lines as well as conducted EMI noises transmitted from them. EMI noises diffusing on the surface of conductors are generally difficult to control using conventional concentrated constant theory. Thus, a new approach based on distributed constant circuit theory is needed in order to control EMI noises. A power converter structure to control EMI noises using multilayer power printed circuit technology is studied in this paper. A structure which can control EMI noises should simultaneously satisfy two conditions, i.e., one to shut down and one to attenuate EMI noises. The structure satisfying these conditions is studied through simulations using the Transmission-Line Modeling Method. The simulations show that the diffusion of EMI noises is controlled by dividing the flow of currents produced by EMI noises into the horizontal and perpendicular directions. That is, the horizontal current flow is controlled inside using the differences in the resistance produced from differences between inner and outer diameter of power transmission lines and the perpendicular current flow can be controlled by properly designing the thickness of the dielectric layer sandwiched between P-and N-power transmission lines with the symmetrical structure. Moreover, it is confirmed by simulations and experiments that the attenuation of EMI noises is affected by the width of the power transmission lines. It is expected that the results obtained in this paper can provide important rules when designing power converters with EMI noise control functions which use the multilayer power printed circuit technology.     

A new algorithm for rapid tracking of approximate maximum power point in photovoltaic systems

This paper presents a new algorithm for tracking maximum power point in photovoltaic systems. This is a fast tracking algorithm, where an initial approximation of maximum power point is (MPP) quickly achieved using a variable step-size. Subsequently, the exact maximum power point can be targeted using any conventional method like the hill-climbing or incremental conductance method. Thus, the drawback of a fixed small step-size over the entire tracking range is removed, resulting in reduced number of iterations and much faster tracking compared to conventional methods. The strength of the algorithm comes from the fact that instead of tracking power, which does not have a one-to-one relationship with duty cycle, it tracks an intermediate variable /spl beta/, which has a monotonically increasing, one-to-one relationship. The algorithm has been verified on a photovoltaic system modeled in Matlab-Simulink software. The algorithm significantly improves the efficiency during the tracking phase as compared to a conventional algorithm. It is especially suitable for fast changing environmental conditions. The proposed algorithm can be implemented on any fast controller such as the digital signal processor. All the details of this study are presented.     

Interference potential of PC noises on MB-OFDM UWB systems

Since PC noises in the UWB frequency band mainly comprise the harmonics of clock signals, a numerical analysis is made on the influence of clock harmonics on the bit error rate (BER) of multiband OFDM (MB-OFDM) UWB systems. Results show that clock harmonics cause a considerable BER degradation when a UWB terminal is placed close to a PC. They further show that frequency modulation of a PC clock signal, so-called spread spectrum clocking (SSC), has no effect for mitigating BER degradation, though SSC techniques are commonly used in PCs for reducing the power spectral density of radiated clock harmonic noises     

New methods to suppress EMI noises in motor drive systems

New methods are studied that can suppress EMI noises, especially the common-mode current produced in motor drive systems. One is a packaging technique that forms power converters using a four-layer printed power circuit board. The other is a method based on the generation mechanism of the common-mode current which was developed from experimental analyses. It is proved by experiments that the former can effectively control the common-mode current, including radiated emissions, and the latter can suppress it without any compensators between the inverter and the motor     

高效率包络跟踪电源设计

包络跟踪技术是提高射频功率放大器的一项核心技术,该技术利用功放的供电跟随输入信号的包络幅度变化,使功放管子始终工作在临界饱和点,从而大大提高功放系统的效率。本文在开关电源技术的基础上,提出一种新型包络跟踪电源电路拓扑,为现代通信系统基站提供了一种高效的供电方案。然后,从理论和实验上论证了这种拓扑的可行性。最后,通过实验测试了该系统在实际应用中的一些性能指标,测试结果再次验证这种拓扑的实用价值。     

A novel robust filtering strategy for systems with Non-Gaussian noises

For estimating the states of moving targets in the nonlinear system with non-Gaussian noise, the combination of Gaussian Sum Filter (GSF) and other nonlinear filters has been chosen as the filtering algorithm conventionally. The Smooth Variable Structure Filter (SVSF) is a new predictor-corrector method used for state and parameter estimation, which has good stability and robustness. In this paper we propose a new strategy called the modified GS-EKF-SVSF, which inherits good robustness of Gaussian Sum and Smooth Variable Structure Filter (GS-SVSF) and high accuracy of Gaussian Sum and Extended Kalman Filter (GS-EKF). A nonlinear system with non-Gaussian noise for target tracking is used to test the proposed new strategy. The simulation results demonstrate that our proposed strategy has higher accuracy and better robustness when there are modelling uncertainties existing in the system.     

Electric load estimation techniques for high-speed railway (HSR)traction power systems

As modern (e.g., high-speed railway (HSR)) traction power systems (TPS) become more and more comparable in size to grid capacity, dynamic load estimation (DLE) has become not just an important tool for TPS planning, but also an indispensable tool for utility companies to evaluate traction system's accurate unbalance impact on the grid. Without a good DLE algorithm, unbalance impact can easily be underestimated and causes power system instabilities. A good DLE must be carried out with a power engineering perspective while incorporating real railway operating principles and practices. However, due to the lack of well-documented literature on this subject and the interdisciplinary nature of DLE, it usually presents a difficult task for the system planner. As such, this paper presents an accurate DLE algorithm capable of achieving these goals, while providing a complete coverage of all the principles and parameters used during the derivation. The methodology developed here is applicable to HSR TPS and to conventional railways as well with minor modifications. Unbalance impact evaluation of the new Taiwan HSR is presented in the last part of the paper, while further application of the proposed DLE algorithm is also proposed     

Evolution of the power control techniques for DS-CDMA toward 3G wireless communication systems

In this article we present a survey of the power control techniques for modern wireless DS-CDMA communication systems. Power control is the single most important system requirement for DS-CDMA systems. Well-defined power control is essential for proper functioning of the DS-CDMA system. In the absence of power control the effect of near⁄far phenomena is dominant, and the capacity of the DS-CDMA mobile system is very low, even lower than that of mobile systems based on FDMA. However, when the power control in DS-CDMA systems exists, it allows users to share resources of the system equally between themselves. Also, with a proper power control it is possible to lower total transmitting power of the mobiles and prolong the battery life.     

MIMO-OFDM系统中相噪公共相位误差的分析与抑制

随着无线通信频段的不断提高,非理想载波所引入的相位噪声对多输入多输出正交频分复用(MIMO-OFDM)系统性能的影响也越来越突出,不仅影响OFDM系统载波的正交性,同时导致多天线预编码性能急剧下降。相位噪声对MIMO-OFDM系统的影响可分为公共相位误差(CPE)和载波间干扰(ICI)两部分。本文对CPE影响MIMO-OFDM系统的性能进行深入分析,提出一系列基于频域正交导频设计的CPE估计算法,以实现对CPE的有效抑制;最后,在多个场景下进行链路仿真,充分验证了提出算法的有效性和可靠性。