OFDM-CPM系统降低PAPR新方案研究

正交频分复用-连续相位调制(OFDM-CPM)系统通过CPM相关相位状态引入记忆,从而获得比传统调制方式更好的误码性能。降低OFDM-CPM系统中的峰值平均功率比(PAPR)是关键技术之一。利用恒包络的概念提出一种新的CE-OFDM-CPM调制方案,可以把OFDM-CPM系统的PAPR降至零分贝。     

Comparison between time shifted non-orthogonal frequency division multiplexing and OFDM

通过将时移参数引入多载波调制,形成了一种具有全新思想的时移非正交频分复用(TS-NFDM)调制技术,并通过理论分析和仿真实验将该技术的性能与当前在无线通信中扮演重要角色的正交频分复用(OFDM)技术进行了比较.比较结果表明,TS-NFDM技术具有明显的优势,其时移特性使其表现出许多优良的性能,其中最突出的是频带利用率高,约为OFDM的4.29倍,另外,信号功率的峰值均值比也明显低于OFDM.     

一种差分调制的水声MC-CDMA通信系统

0引言正交频分复用(OFDM)技术在高速水声通信系统中的应用已得到广泛研究。OFDM采用并行多载波,子载波间频谱重叠实现高速传输,循环前缀的加入则可有效对抗ISI[1],然而水声信道中除了相位起伏和多普勒频移造成的解调困难,频率选择性深度幅度衰落往往造成子载波解码错误[2]。     

抑制OFDM信号峰均比对直接检测光传输系统的性能影响

高峰均比是OFDM通信系统的主要缺点之一,光OFDM通信系统也存在同样的问题.本文将联合Hadamard变换和限幅(Clipping)方法抑制峰均功率比算法成功应用到直接检测的光正交频分复用光纤传输实验平台,重点研究了算法对系统误码性能的影响.实验中产生的2.5 Gb/s QPSK OFDM光信号在标准单模光纤中传输1...     

滤波器组多载波系统的干扰分析和性能验证

分析了多普勒频偏以及多径时延对滤波器组多载波(FBMC)系统的影响,给出了多普勒频偏以及多径时延造成干扰的闭合定量分析式,该分析式对正交频分复用(OFDM)系统同样适用,并据此对无线多径衰落信道场景中的FBMC系统与传统OFDM系统性能进行了对比.研究结果表明,FBMC系统对多普勒频偏的抵抗性优于OFDM系统,但是系统性能会随信道多径时延的增大而降低.在多径时延相对较小的快衰落信道中,符号间干扰并非影响系统性能的主要因素,FBMC系统可以利用简单的频域均衡获得足够好的性能,仿真结果验证了这一点.     

基于OFDM编码的水声通信差分解码技术

正交频分复用（OFDM）具有良好的抗频率选择性衰落性能,抗多径和脉冲噪声能力强,同时具有在高效带宽利用率情况下的高速传输能力以及简单的实现方法。OFDM在应用中也存在一些问题,例如对频率偏移和相位噪声敏感等。研究了基于正交频分复用编码的水声通信差分解码技术。所提出的差分解码方案通过测量相邻OFDM信号的相位差进行解码,从而降低了信道时变特性对水声通信系统的影响,特别是相位误差的累积效应。湖上试验数据差分解码的结果显示了所提方案的有效性,极大地降低了通信系统的误码率。     

基于正交复小波变换和小波去噪的改进系统De-OCWDM

用近似线性相位正交复小波变换(ALOCWT)取代了正交频分复用(OFDM)系统中的离散傅立叶变换(DFT),形成了正交复小波波分复用(OCWDM)系统.ALOCWT具有时频特性、正交特性、重构特性等特性,能够很好地取代DFT,同时ALOCWT能够保留复信号的相位信息,使得信号重构精度更高,从而提高了信号传输的准确性和系...     

对称与非对称Doherty功放的研究

LTE移动通信的来临,高峰均比(PAR)的调制方式不断出现,如正交频分复用(OFDM)调制方式,这就对功放的线性度提出较高的要求。为保证信号的线性度和效率,一般采用功率回退的方法来实现。但是这样的方案是以牺牲效率为代价的。1936年Doherty提出的高效率方案能够很好解决这一难题,对称与非Doherty技术能够使放大器在很宽的功率变化范围内保持高效率输出。     

多进制连续相位调制技术(CPM)的计算机仿真研究

本文是对连续相位调制技术(CPM)的探索性研究.通过计算机仿真实验,研究了CPM调制体系的参数选取以及在一定信噪比条件下影响CPM调制体系误码率性能的因素.并且在仿真的基础上进一步对CPM技术在高速数据传输通信系统中的实现技术进行研究.     

基于OFDM技术电力通信系统的仿真研究

<正>交频分复用(OFDM)技术是常用的电力通信调制技术。本文在深入研究OFDM基本原理和电力线信道特性的基础上,建立电力通信系统模型,对该模型采用4QAM、16QAM、BPSK三种调制方式以及DTF、LS、MMSE三种信道估计算法进行了MATLAB性能仿真,得出结论在一定条件下运用QAM调制方式及LS算法更能体现了OFDM技术应用于电力线通信的优越性。同时,也为我们在不同环境下为提高通信系统整体性能,信道估计算法的选择提供了有力依据。     

Cross-layer adaptive resource allocation for OFDM systems with hybrid smart antennas

Orthogonal frequency division multiplex (OFDM) has become one of the most popular air-link technologies for future broadband wireless communications. To further improve its bandwidth efficiency and system performance, adaptive resource allocation and smart antenna techniques have been widely used in the OFDM system. However, the use of fully adaptive beamforming in an OFDM system significantly increases the complexity of the medium access control layer design and thus affects the implementation of adaptive resource allocation. A novel cross-layer adaptive resource allocation strategy with hybrid adaptive array and switched- beam smart antennas suitable for the OFDM systems has been proposed. With the help of different smart antennas schemes based on different users' quality of service requirements, the strategy effectively reduces the complexity of adaptive resource allocation in an OFDM system, while still maintaining a satisfactory system performance.     

钻柱声传输信号多载波调制激励分析

在随钻声遥测技术中,周期性钻柱结构产生的多重回波极易造成严重的码间干扰和较高误码率,为此,根据钻柱信道的多径传输特性,基于短钻杆条件下多载波传输的实验分析,建立了多节钻杆与管箍的周期性信道有限差分模型。考虑地面噪声和信道内多径回波干扰,利用最小均方自适应均衡,基于“4钻杆—3管箍”信道结构进行了多载波调制性能仿真分析。仿真结果表明,与单载波PSK（Phase-Shift-Keying）调制相比,OFDM（Orthogonal Frequency Division Multiplexing）多载波调制可使误码率平均降低约50%;在非周期性结构下其传输性能受信道变化敏感,但相同条件下仍优于PSK调制,且通过子载波相位补偿可有效改善误码率、提高传输性能。     

Durham extremely large telescope adaptive optics simulation platform

Adaptive optics systems are essential on all large telescopes for which image quality is important. These are complex systems with many design parameters requiring optimization before good performance can be achieved. The simulation of adaptive optics systems is therefore necessary to categorize the expected performance. We describe an adaptive optics simulation platform, developed at Durham University, which can be used to simulate adaptive optics systems on the largest proposed future extremely large telescopes as well as on current systems. This platform is modular, object oriented, and has the benefit of hardware application acceleration that can be used to improve the simulation performance, essential for ensuring that the run time of a given simulation is acceptable. The simulation platform described here can be highly parallelized using parallelization techniques suited for adaptive optics simulation, while still offering the user complete control while the simulation is running. The results from the simulation of a ground layer adaptive optics system are provided as an example to demonstrate the flexibility of this simulation platform.     

40 Gb/s 4-QAM OFDM radio over fiber system at 60 GHz employing coherent detection

In this paper, the simulation of 60 GHz millimeter-wave radio over fiber link with 4-QAM OFDM modulation format at 40 Gb/s over 150 km SMF is proposed. The 60 GHz millimeter-wave signal is generated by the optical heterodyne method. Coherent detection has been used at the receiver to down-convert millimeter-wave signal to IF band. Introduction of the OFDM modulation in RoF-based system realizes the benefits of higher order modulations (such as 4-QAM, 16-QAM, etc.) to ensure the good spectral efficiency and multi-gigabit access. The performance of the system is analyzed by Q-factor and BER by which it can be shown that the best results are obtained at the input power of 10 dBm. The simulation results clearly demonstrate the feasibility of this 4-QAM OFDM RoF system over 150 km fiber link.     

Nonaxial Strehl ratio of wavefront coding systems with a cubic phase mask

An approximate expression of the peak position of the point-spread function (PSF) of wavefront coding systems with a cubic phase mask (CPM) is derived and verified by simulation results. An approach called the nonaxial Strehl ratio (NASR) is used to evaluate the performance of wavefront coding systems with defocus aberrations. The characteristics of the NASR are investigated. The relationships between the NASR and the similarity of out-of-focus modulation transfer function (MTF) and recoverability of blurred encoding images are presented, and some useful guidelines are given for the optimization of phase mask parameters according to these relationships.     

WLAN smart antenna with Bluetooth interference reduction

Because of the coexistence of wireless local area network (WLAN) and Bluetooth at the same ISM band, WLAN systems cannot eliminate the interference by Bluetooth in the physical layer by carrier sense multiple access/collision avoidance. A novel smart antenna system for the WLAN systems to suppress the Bluetooth interference is proposed. The proposed smart antenna system employs the property of multi-carrier transmission of an orthogonal frequency-division multiplexing (OFDM) system to eliminate the correlation among the multi-path components, and the direction of arrival (DOA) estimation algorithm can estimate the correct DOAs. In the simulation, we apply the proposed smart antenna to the 802.11 system using OFDM. The simulation results demonstrate a superior performance under Bluetooth interference.     

Adaptive optics and ground-to-space laser communications

The relationships between laser communication system parameters and adaptive optics system parameters are addressed. Improvement in optical signal propagation between space-based receivers and ground-based transmitters is possible with adaptive optics systems that compensate for a few degrees of freedom. Beginning with the relationship between optical signal fade and surge and the atmospheric log-amplitude variance and coupling to expressions that combine adaptive optics systems performance with the reduction in log-amplitude variance, system level examinations of the effects of adaptive optics can be done. Examples are given that show the advantageous reduction in signal fade and surge when adaptive optics are built into the optical system.     

V-BLAST/OFDM系统的多用户分集性能研究

为改善V-BLAST/OFDM系统的性能,提出了子载波动态分配准则.该准则可以有效地利用多用户分集,明显提高V-BLAST/OFDM系统的整体性能.采用随机矩阵和排序统计的数学方法对取得的性能增益作了定量分析,仿真试验结果证明了分析的正确性.将取得的性能增益与空间分集系统中取得的多用户分集增益进行了比较,比较结果说明,将基于V-BLAST的多用户OFDM系统与子载波动态分配相结合,更能改善系统的整体性能.     

基于OFDM的大气激光通信湍流抑制关键技术研究

文章在分析无线激光通信(FSO)存在两种主要的大气信道问题的基础上,针对激光大气信道问题尤其是在复杂湍流环境下的频率选择性衰落问题和多径效应问题,提出了基于正交频分复用(OFDM)的湍流效应抑制方法,构建了FSO-OFDM系统,研究了该系统的基带模型以及信号的多载波调制与解调方法。分析了无线激光通信中存在复杂湍流环境下的大气信道问题,讨论了大气湍流影响下的平面波激光通信系统模型,建立了大气湍流影响下对数正态湍流通道的高斯光束空间光通信系统模型,推导了光波强度的概率密度函数,研究了利用信噪比概率密度函数分析各种大气湍流效应对系统性能影响的方法;设计了无线光通信系统的OFDM多载波调制方案,构建了FSO-OFDM系统基带模式模型,并基于该模型研究了其信号的调制与解调原理。最后,采用MATLAB编程实现FSO-OFDM系统,对多径干扰下的FSO通信系统进行仿真实验,进行了不同保护间隔下的误码率特性实验,验证了FSO-OFDM系统具有很强的抗多径干扰和频谱选择性衰落能力以及良好的BER性能,可有效解决码间干扰大、链路不可靠的问题,具有非常广泛的应用前景和使用价值。