多误码率固定速率OFDM自适应调制比特功率分配方法

一些应用中需要多误码率的固定速率OFDM自适应调制.本文首先对该多载波自适应调制需求中的比特功率优化分配问题建模,并进一步限定各OFDM子信道采用正交幅度调制(QAM),基于子信道调制比特的任意正实数和无限粒度假设详细分析了子信道集合划分和比特功率分配问题,由此得到一种实用的次最优子信道集合划分和比特功率分配方法.分析和仿真表明由于可得到比特分配的闭式表达,因此该方法计算复杂度低,且性能良好,是一种实用的多误码率固定速率OFDM自适应调制比特功率优化分配方法.     

第四代移动通信系统的调制技术

现有通信系统的调制技术限制了信号速率的进一步提高,即将推出的第四代(4G)移动通信系统需要更优良的调制技术。正交频分复用(OFDM)技术是很受欢迎的高速率无线通信技术,结合OFDM的调制技术将在4G系统中得到广泛应用。文中概要介绍了4G系统的特点及关键技术,然后系统介绍了OFDM多载波原理,最后重点介绍了多载波码分多址(MC-CDMA)和正交频分复用时分多址(OFDM-TDMA)两种多载波调制(MCM)技术。     

移动衰落信道中的自适应OFDM调制

在宽带移动OFDM(正交频分复用)系统中，不同的子信道经受不同的信道衰落，具有不同的传输能力。若采用固定速率调制方案，信道容量和发送功率未能获得充分应用。自适应调制技术能充分利用信道容量和信号功率，满足不同传输速率和服务质量的要求。研究了一种适用于宽带移动OFDM系统的自适应算法。在平均发送功率不变务件下，算法根据子信道的衰落特性，自适应地分配子信道中数据比特，选择不同的信号星座和发送功率，使得系统的功率和频谱效率达到最佳。首先推导了在平均发送功率受限条件下，瑞利衰落信道中最大频谱效率；其次，分析了在给定误比特率(BER)条件下，采用连续功率、连续星座MQAM(多进制正交幅度调制信号)调制的最大功率频谱效率，在此基础上提出适用于实际系统的离散功率、离散星座MQAM调制算法；最后进一步优化系统的功率密度谱。计算机模拟表明：该算法能明显地提高移动OFDM系统的频谱效率。     

用DSP实现基于802.16a的OFDM调制解调

正交频分复用(OFDM)技术是当今高速无线通信领域中的研究与应用热点,它具有抗多径衰落、频谱利用率高、采用自适应调制等优点,被普遍认为是宽带无线接入和第四代移动通信系统中的关键技术之一。研究了基于802.16a的OFDM技术,利用TMS320C6201实现了其基带调制解调,并对软件模块进行了优化,最高数据传输速率可达1.32Mbit/s。     

240 Gbit/s OFDM实时光通信系统的设计与实现

详细描述了240Gbit/s OFDM(正交频分复用)实时光通信系统的设计与实现。采用多载波发生装置产生3×15个相互正交的光子载波,并对每个光子载波调制4Gbaud/s速率OFDM信号,采用4QAM(二阶正交幅度调制)信号格式。在接收端,分别用对应的本征光子载波解调各路光OFDM信号,使用FPGA(现场可编程门阵列)对采样信号进行实时处理。总有效数据速率达到240Gbit/s。文章报道的传输速率为已报道实时OFDM传输的最高记录。     

可见光通信中自适应DFT-spread-OFDM性能研究

综合考虑可见光通信(VLC)中LED灯调制带宽受限及 非线性效应等问题,提出采用离散 傅里叶变换(DFT)-spread-OFDM与自适应调制OFDM相结合的一种自适应DFT-spread-OFDM ,保证通信可靠性的同时, 提高通信速率,通过仿真与实验相结合的方式,研究对比了自适应DFT-spread-OFDM与常 规 DFT-spread-OFDM及常规自适应调制OFDM之间的优劣。仿真和实验结果表明,自适应 DFT-spread-OFDM,能够取得良好的综合性能,较常规DFT-spread-OFDM能够实现更高速 率的通信,较常规自适应调制OFDM能够取得更佳的峰均功率比的(PAPR,peak-average power radio)性能。     

多用户自适应调制及功率分配

为了满足新一代无线通信系统的高数据速率、高频谱效率的通信要求,本文提出了基于正交频分复用(OFDM)技术的自适应调制、子载波分配及功率分配方法,它采用的多址方式是码分多址(CDMA).通过上行信道返馈获知下行信道参数,在一定服务质量要求(QoS)、一定传输速率下,通过本文的优化分配算法,使系统的频谱利率最高,所有子载波的发射功率之和最小.将本方法应用在下行同步信道环境下,系统具有较快的收敛速度;与非自适应OFDM比较,用户发射功率有较大降低,是一种工程可适用方案.     

基于可变速率OFDM系统的MATLAB仿真实现

正交频分复用(OFDM)是一种多载波宽带数字调制技术,它能有效地克服传输中的多径干扰和消除码间串扰,适合于高速率的数据传输.文中对OFDM系统原理进行分析的基础上,用MATLAB对802.11a标准下,可变速率的OFDM系统进行SIMULATION仿真实现,并对结果进行了分析.     

自适应比特分配光正交频分复用的实验研究

为解决塑料光纤(POF)带宽窄、模式色散大的缺陷,提高光接入网的带宽利用率和色散容限,本文在光接入网中使用自适应比特分配算法的正交频分复用(OFDM)调制方式,利用OFDM系统极佳的频带利用率特性,提高了光接入系统的带宽利用率,并降低了系统的误码率(BER)。在搭建的实验系统中,成功地在不足2.5GHz带宽的光信道中完成了10 Gb/s的光OFDM(OOFDM)系统,从而证明了自适应比特分配算法在OOFDM系统中的有效性和可行性。     

自适应OFDM中信号的调制识别算法研究

针对通信信号种类和调制方式的多样性、以及无线信道环境的复杂性,研究了自适应OFDM系统中信号调制方式的识别。在自适应OFDM(正交频分复用)信号产生的基础上,提出了一种新型调制识别算法,并分析了仿真参数对算法性能的影响。研究和仿真结果表明:该算法不仅性能稳定,而且可以有效地识别自适应OFDM信号的调制方式。该算法复杂度低,适合于实时处理。     

聚对苯撑苯并双(口恶)唑发光及其器件制备

采用光谱技术,研究了聚对苯撑苯并双(口恶)唑(PBO)溶液的光敏发光特性,并用相对法估算出溶液发光效率在50%范围.结合光谱技术、半导体电学和电化学等研究手段,具体研究了以PBO为发光层的单层电致发光器件,研究结果显示,电致发光与薄膜的光致发光有具有相同的发光中心,峰值位于510 nm左右.同时发现,由于存制备过程中不同处理条件使得不同厚度薄膜残留的掺杂物质浓度不同,从而引起薄膜的导电性的不同.使得器件的阈值场强随PBO厚度的减小而逐渐增加.     

系统级封装新型埋入式电源滤波结构的研究

在高密度小尺寸的系统级封装(SiP)中,对供电系统的完整性要求越来越高,多芯片共用一个电源网路所产生的电压抖动除了会影响到芯片的正常工作,还会通过供电网路干扰到临近电路和其他敏感电路,导致芯片误动作,以及信号完整性和其他电磁干扰问题.这种电压抖动所占频带相当宽,几百MHz到几个GHz的中频电源噪声普通方法很难去除.结合埋入式电容和电源分割方法的特点,提出一种新型高性能埋入式电源低通滤波结构直接替代电源/地平面.研究表明,在0.65～4GHz的频带内隔离深度可达-40～75 dB,电源阻抗均在0.25ohm以下,实现了宽频高隔离度的高性能滤波作用.分别用电磁场和广义传输线两种仿真器模拟,高频等效电路模型分析这种低通滤波器的工作原理以及结构对隔离性能的影响,并进行了实验验证.     

Emerging interconnects: a state-of-the-art review and emerging solutions

Aluminium was a primary material for interconnection in integrated circuits (ICs) since their inception. Later, copper was introduced as interconnect material which has better metallic conductivity and resistance to electromigration. As the aggressive technology scaling continues, the copper resistivity increased because of size effects, which causes increase in delay, power dissipation and electromigration. The need to reduce the resistor-capacitor??????? delay, dynamic power utilisation and the crosstalk commotion is as of now the fundamental main impetus behind the presentation of new materials. The purpose of this paper is to do a survey of interconnect material used in IC from introduction of ICs to till date. This paper studies and reviews new materials available for interconnect application which are optical interconnects, carbon nanotube (CNT), graphene nanoribbons (GNRs) and silicon nanowires which are alternatives to copper. While doing a survey of interconnect material, it is found that multiwalled CNTs, multilayer GNR and mixed CNT bundles are promising candidates and are ultimate choice that can strongly address the problems faced by copper but on integration basis copper would last for coming years.     

Arsenic deposition as a precursor layer on silicon (211) and (311) surfaces

We investigate the properties of arsenic (As) covered Si(211) and Si(311) surfaces by analyzing data from x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) images. We then create a model using total surface energy calculations. It was found that both Si(211) and Si(311) had 0.68±0.08 surface As coverage. Si(211) had 0.28±0.04 Te coverage and Si(311) had 0.24±0.04 Te coverage. The Si(211) surface replaces the terrace and trench Si atoms with As for a lower surface energy, while the Si edge atoms form dimers. The Si(311) surface replaces all terrace atoms and adsorbs an As dimer every other edge site. These configurations imply an improvement in the mean migration path from the bare silicon surface by allowing the impinging atoms for the next epitaxial layer, tellurium (Te), to bind at every other pair of edge atoms, and not the step terrace sites. This would ensure a nonpolar, B-face growth.     

光子晶体微腔发光二极管

光子晶体微腔因其具有增强自发辐射、定向输出和单模工作的能力而受到广泛关注。介绍了光子晶体微腔发光二极管的基本原理、设计、特性、制作及其典型器件。     

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.     

用于单光子TOF测量的时间-幅度变换器

基于新型共源共栅电流源的积分方法,设计了一种用于单光子飞行时间(TOF)测量的时间-幅度变换器(TAC).该方法有效简化了 TAC电路结构,减小了 TAC占用面积,显著提高了TOF的满量程范围(FSR).采用0.18 μm标准CMOS工艺设计.集成TAC的单光子探测器像素单元的填充因子可达到26.8％.后仿真结果表明,...     

Joint estimation of TOA and DOA in IR-UWB system using a successive propagator method

Impulse radio ultra-wideband (IR-UWB) ranging and positioning require accurate estimation of time-of-arrival (TOA) and direction-of-arrival (DOA). With receiver of two antennas, both of the TOA and DOA parameters can be estimated via two-dimensional (2D) propagator method (PM), in which the 2D spectral peak searching, however, renders much higher computational complexity. This paper proposes a successive PM algorithm for joint TOA and DOA estimation in IR-UWB system to avoid 2D spectral peak searching. The proposed algorithm firstly gets the initial TOA estimates in the two antennas from the propagation matrix, then utilises successively one-dimensional (1D) local searches to achieve the estimation of TOAs in the two antennas, and finally obtains the DOA estimates via the difference in the TOAs between the two antennas. The proposed algorithm, which only requires 1D local searches, can avoid the high computational cost in 2D-PM algorithm. Furthermore, the proposed algorithm can obtain automatically paired parameters and has better joint TOA and DOA estimation performance than conventional PM algorithm, estimation of signal parameters via rotational invariance techniques algorithm and matrix pencil algorithm. Meanwhile, it has very close parameter estimation to that of 2D-PM algorithm. We have also derived the mean square error of TOA and DOA estimation of the proposed algorithm and the Cramer-Rao bound of TOA and DOA estimation in this paper. The simulation results verify the usefulness of the proposed algorithm.     

超宽带脉冲信号的光学生成方法研究

近年来超宽带(UWB)通信技术迅猛发展,在测量、雷达技术、民用和军事无线通信中有着重要的应用,UWB-over-fiber技术已经成为目前研究的热点,其中就包括UWB脉冲信号的产生方法。区别于传统的电子学方法,光子学产生方法不受电子瓶颈制约,可以实现很高的带宽,并且具有抗电磁干扰、重量轻、结构紧凑的优点。通过对比国内外本领域研究成果,讨论及总结了以下三种原理的UWB脉冲信号的光学生成方法:1)相位调制-强度调制转换(PM-IM);2)半导体光放大器(SOA)的非线性效应;3)频谱塑形和色散所致频域-时域映射,然后对各种方案进行了对比分析。     

多孔硅发光机制的分析

从量子力学的基本理论出发讨论了量子限制效应，推导出多孔硅有效禁带宽度增量并用量子限制效应和表面态及其物质在发光中作用的理论解释了ＰＳ光致发光的实验现象。