Computer simulation studies on overlapping polymer chains confined in narrow channels

Conformation of polymer chains strongly confined in a narrow channel space was studied over a broad range of polymer volume fractions φ using lattice Monte Carlo simulations. The longitudinal component of the chain dimension decreased in a power law of ∼φ⁻¹ as φ exceeded the overlap volume fraction. The conformation changed from the one extended along the channel to a random coil. The change occurred without much overlap between adjacent chains. As the conformational transition was completed, the chains started to penetrate each other. Contraction of the chains became more gradual, and eventually the longitudinal component of the chain dimension approached that of the unconfined chains with the overall chain dimension being smaller than that of the unconfined chains. Predictions of the scaling theory were thus confirmed with additional detailed information on the state of confined chains in each regime of characteristic φ dependence of chain dimensions.     

Cu－37at％ Ag共晶合金的离子溅射研究

侧重研究了入射Ａｒ＋离子不同剂量轰击时表面微形貌和溅射原子角分布之间的关联，并建议用“元素按靶点表面微形貌特征局域富集模型”来解释溅射原子角分布形状以及择优溅射曲线的变化；发现其结果与实验相符合。     

静场量与机械量转换守恒的直接例证

讨论了一特定的带电粒子、电磁场组合系统,以严格的解析结果证明了该系统由静场量及相应机械量构成的总力学量(总动量、总角动量)的转换守恒。     

脉冲噪声下的高可靠性OFDM信道估计

从信道估计内插误差角度分析了突发脉冲噪声干扰对无线OFDM接收机性能的影响,针对由脉冲噪声所导致的时间方向信道内插估计错误扩散,提出了旨在提高无线OFDM通信系统抵抗脉冲噪声能力的信道估计安全策略,包括:脉冲噪声突发位置检测、防止受损导频内插错误扩散算法、受干扰子载波数据可信度判决。仿真结果表明,在低复杂度条件下,可以显著提高无线OFDM接收机在脉冲噪声环境中的信道估计性能。     

揭阳电网高频保护现状分析与解决方案

介绍揭阳电网220 kV系统高频保护的现状,分析造成高频保护不正确动作的主要原因,并提出提高揭阳电网继电保护管理水平、确保电网安全稳定运行的几个建议.     

空时频互相关MIMO衰落信道仿真及其性能分析

本文针对频率选择性MIMO信道,提出扩展的抽头延迟线模型,推导出各抽头之间的互相关函数,得出了抽头之间相互独立的条件,并且针对MIMO信道的抽头延迟线模型,给出了AR模型仿真实现算法,最后用文献资料中的数据验证了仿真算法的准确性。     

COMPUTER SIMULATION OF RAYLEIGH FADING CHANNELS IN MC-CDMA SYSTEMS

For Multi-Carrier-Code Division Multiple Access (MC-CDMA) systems,it is usually as- sumed that the fading of the subcarriers is frequency non-selective and independent of each other. This paper shows that the two assumptions are incompatible.In fact,the MC-CDMA signals at each subcarrier undergo fading that are highly correlated.Based on this observation,this paper develops a simulation algorithm for Rayleigh fading channels via frequency-domain correlation function,which incorporates the Doppler effect simultaneously.Numerical examples are presented to demonstrate the effectiveness of the new algorithm,with the conclusion that the independence assumption of subcar- rier fading overrates the system performance.     

TIME-FREQUENCY 2-D LMS BASED LONG-RANGE CHANNEL PREDICTION FOR WIRELESS OFDM SYSTEMS

Adaptive modulation can optimize the spectrum efficiency and system performance with the channel state information achieved by the long-range channel prediction.To avoid re-estimating channel correlation function as the channel statioharity varies and to track the channel adaptively, LMS (Least-Mean-Square) based long-range channel prediction is discussed in the existing literature, but it needs long observation interval to reach the convergence.Given that all OFDM (Orthogonal Frequency Division Multiplexing) subcarriers have the identical time-domain correlation and sta- tionarity during the same time interval,this paper proposed a 2-D LMS based predictor which updates the filter weights in both time and frequency domain.The proposed scheme can effectively decrease the observation intervals and significantly speed up the convergence than the conventional LMS and Parallel LMS (PLMS).Complexity analysis and simulation results prove that the proposed scheme can improve the BER (Bit Error Rate) performance and spectrum efficiency with negligible complexity increase.     

ERGODIC CAPACITY FORMULA OF MIMO-OFDM SYSTEMS UNDER CORRELATED FREQUENCY SELECTIVE RAYLEIGH FADING CHANNELS

An explicit formula for the ergodic capacity of Orthogonal Frequency Division Multiplexing (OFDM)-based Multiple-Input Multiple-Output (MIMO) systems under correlated frequency selective Rayleigh channels is derived,by simplifying the channel response matrix in frequency domain into the so-called Kronecker model composed of three kinds of correlations,i.e.multipath tap gain correlation and spatial fading correlations at both transmitter and receiver.The derived formula is very simple and convenient for one to estimate the effects of all three kinds of correlations on MIMO-OFDM capacity.If taps are independent,there is a very simple expression for the ergodic capacity.In case of tap correlation,the capacity formula could be further given in an integral expression.The validity of the new formula is verified and the effects of correlations,delay spread as well as the number of subcarriers on the ergodic capacity are evaluated via Monte Carlo simulations.     

TMS320C6416器件的WCDMA信道编码的研究与实现

第三代移动通信系统在我国的商用日益临近,作为三大3G标准之一的WCDMA,可以通过GSM/GPRS平滑升级实现,研究其信道编码对于改善和提高WCDMA的通信能力是十分重要的.简单介绍WCDMA的网络单元结构,WCDMA的信道编码中主要采用的卷积码和Turbo码的编码和译码方式,以及数字信号处理器在通信领域的广泛应用.分析了WCDMA信道编码的相关协议,叙述了TI公司的数字信号处理器芯片TMS320C6416硬件架构,详细介绍基于该芯片的NodeB信道板的硬件原理,最后讨论了WCDMA信道编码在NodeB信道板上的软件模块化实现方法.