【作者】 王伟；

【导师】 曹秀英；

【作者基本信息】 东南大学 ， 通信与信息系统， 2006， 硕士

【摘要】 宽带卫星通信已成为当前通信的新热点之一,未来的通信是建立在宽带基础上的多媒体通信。宽带卫星通信易受下雨等大气干扰影响,信道特性较差,且频谱资源紧张。正交频分复用(OFDM)技术具有抗多径衰落,频谱利用率高等优点,适合于在宽带卫星通信这种无线环境下进行高速传输。本文重点研究OFDM系统中的同步技术,及基于突发式宽带卫星通信的同步方案的设计。本文对宽带卫星通信信道特性进行了介绍,并提出本文仿真的信道模型。本文在简要介绍了OFDM的基本原理、关键技术的基础上,针对同步问题进行了深入研究。首先分析了同步偏差中的频率偏差、符号定时偏差及采样时钟偏差对系统性能的影响。接着针对本文所采用的突发式传输系统,对几种经典的同步算法进行了分析,研究及改进。对于Schmidl&Cox的小数频偏估计,提出一种削弱噪声影响的训练序列的设计方法,并对频偏估计取滑动平均。针对Schmidl&Cox的整数频偏估计的原理,对判决量进行分析,改进判决量来提高估计性能,并节省了符号开销。对于Schmidl&Cox的定时算法通过对PN序列的加权来获得尖锐的相关峰值。针对基于PN训练序列的定时算法,提出一种对PN序列的预处理方案来获得尖锐的相关峰值,从获得所有径能量的角度出发,在多径衰落条件下获得优于原算法的频偏估计性能。对Moose算法和基于导频序列的算法中参数对同步性能的影响进行分析和仿真,基于Schmidl&Cox整数频偏估计算法的改进思想,给出由Moose算法而来的一种整数频偏估计的改进算法。本文还设计了基于OFDM的突发式宽带卫星通信的一整套同步方案,根据对前述算法的仿真比较,给出帧格式。分别从帧检测、符号定时、频偏估计及相位跟踪等方面介绍整个系统的同步过程。文中还比较了理想同步与非理想同步情况下系统的性能。更多还原

【Abstract】 Broadband-satellite mobile communication pays an important role in modern wireless communication field, but it has so limited frequency resource, and is easily affected by circumstance condition such as rain, thus can be suppressed by nonideal channel characteristics.Orthogonal frequency division multiplex(OFDM) is suitable for Broadband-satellite mobile communication system with the advantage of robustness to muti-path and high bandwidth efficiency. In this thesis an OFDM based Broadband-satellite system is studied, emphasizing particularly on the synchronization technologies.This thesis describes the channel characteristics of Broadband-satellite communication system and establishes current channel simulation model. Following the introduction of the basic principle of OFDM, some nonideal effects on the performance of OFDM systems are discussed, such as carrier frequency offset, symbol timing offset and sampling clock deviation. Then synchronization technologies are analyzed in more detail, and some typical OFDM synchronization schemes are studied and improved.After investigating synchronization scheme proposed by Schmidl & Cox, an special training sequences with good auto correlation characteristics and less affected by noise are put forward, thus improve symbol timing and float frequency synchronization performance through average process.And a more effective integral frequency synchronization scheme by modify the adjudgement also is proposed. As the PN-sequence based scheme, a novel algorithm utilizing all the channel taps power is provided.This thesis also studied synchronization schemes based on pilots symbols and a scheme proposed by Moose, meanwhile, some modified points as above have been put forward.Besides, the whole synchronization schemes for the OFDM based Broadband-satellite communication system are designed .Through simulation and comparing, appropriate synchronization schemes for frame detection, symbol timing,frequency offset estimation and phase tracking are discussed separately, and the system performances with ideal and nonideal synchronization are compared.更多还原