【作者】 关庆阳；

【导师】 赵洪林；

【作者基本信息】 哈尔滨工业大学 ， 信息与通信工程， 2011， 博士

【摘要】 空天地一体化信息网络是当前通信领域的研究热点。低轨宽带卫星移动通信系统将随时随地为各种接入用户终端提供宽带服务,成为空天地一体化信息网络的重要组成部分。低轨宽带卫星移动通信系统信道具有频率选择性衰落特性、并且系统频带资源受限,因此需要通信链路所采用的传输技术不仅仅能够抗信道频率选择性衰落,而且具有较高的频带利用率。正交频分复用技术(Orthogonal Frequency Division Multiple, OFDM)是一种采用正交子载波进行信息传输技术,具有抗信道频率选择性衰落能力,并且具有较高的频带利用率;同时可以进行子载波灵活分配以实现低轨宽带卫星系统上、下行链路用户业务的非对称传输。因此研究低轨宽带卫星移动通信系统OFDM传输技术具有重要意义。在这样的背景下,本文针对低轨宽带卫星移动通信系统的OFDM传输技术进行研究,以下是研究的几个主要方面。第一,低轨宽带卫星移动通信系统的OFDM传输技术适用性研究。首先针对低轨宽带卫星系统的典型仿真场景信道统计特性进行描述,针对低轨宽带卫星的通信系统上、下行链路,分别采用DFT-S OFDM(Discrete Fourier Transformation Spread Orthogonal Frequency Division Multiple),OFDM建立链路模型。根据低轨宽带卫星移动通信信道特性,分析研究了上、下行链路DFT-S OFDM与OFDM传输体制抗信道多径衰落性能、多普勒频移下性能,峰均比(Peak to Average Power Ratio, PAPR)性能,及高斯白噪声(Additive White Gaussian Noise, AWGN)信道下性能。证明OFDM传输技术在低轨宽带卫星移动通信系统中具有适用性,从而为后面章节的低轨宽带卫星移动通信系统的OFDM传输技术研究奠定基础。第二,低轨宽带卫星系统DFT-S OFDM上行链路用户检测方法。针对传统单用户信号检测算法不能跟踪低轨宽带卫星时变信道,提出一种改进递归最小二乘(Recursive Least Squares, RLS)单用户信号检测算法;该算法能够对时变信道进行较好跟踪,以适应低轨宽带卫星系统信道的时变性。针对低轨宽带卫星移动通信系统上行链路的多用户由于频偏差异引入接入干扰,传统并行干扰消除(Parallel Interference Cancellation, PIC)算法或者串行干扰消除(Successive Interference Cancellation, SIC)算法干扰消除精度不高,迭代次数过多的问题,提出一种最优权值并行干扰消除(Optimal Weight Parallel Interference Cancellation, OWPIC)算法消除多用户接入干扰(Multi-user Access Interference, MUI),该算法干扰消除精度较高与迭代次数较低。第三,低轨宽带卫星系统OFDM下行链路信号检测方法。由于较大载波频偏破坏OFDM的子载波正交性而引入干扰,针对传统频偏干扰消除算法的复杂度过高,频偏消除范围有限,提出一种低复杂度的时频联合最小均方误差(Time and Frequency Domain Least Mean Square, TF-LMS)算法来消除频偏干扰。该算法对于较大频偏引入干扰有较好的消除性能。针对低轨宽带卫星服务诸如城区等信道多径衰落严重的场景,提出一种联合信道及载波频偏干扰消除的频域空间选择性期望最大化(Frequency Space Alternating Generalized Expectation Maximization, FSAGE)算法。该算法首先进行频域频偏预估计及预消除,然后进行联合信道及频偏干扰的精跟踪及消除。为了降低低轨宽带卫星移动通信系统传输信号的冗余信息,提高信号传输效率,提出一种级联的MCMA-RLS(Modified Constant Modulus and Recursive Least Squares Algorithm)用户信号盲检测算法。该算法无需采用训练序列并且收敛速度较快。第四,低轨宽带卫星OFDM系统资源分配方法。为了提高上行链路用户终端功率利用率,提出一种基于星上功率检测的用户功率控制算法,有效降低用户功率损耗。针对保证低轨宽带卫星服务不同用户业务的速率比例以及用户传输速率的最优化,提出一种低复杂度的均分联合功率、载波、比特资源分配算法。该算法首先在保证接入用户的速率比例的条件下,通过功率、子载波均分的方式降低资源分配的复杂度,并且在一定程度上满足用户传输速率最大化的需求。第五,低轨宽带卫星OFDM系统链路吞吐量分析。结合自适应调制编码(Adaptive Modulation and Coding, AMC)建立链路模型,对接入用户的链路吞吐量进行分析。通过与低轨宽带卫星多频时分多址接入(Muti-Frequency Time Division Multiple, MF-TDMA)通信系统的链路吞吐量进行比较,表明低轨宽带卫星OFDM系统具有更好的链路吞吐量性能。更多还原

【Abstract】 Air-space-ground of integrated information communication network becomes focus field of research in the world communications technology. The broadband LEO satellite mobile communication system will play an important role in providing services to mobile terminal user anytime and anywhere, which becomes a significant component of the air-space-ground integrated information network. The broadband LEO satellite mobile confronts with the frequency selectivity channel fading characteristic, and bandwidth resources are inefficient. Therefore the special transmission technique which could not only counteract anti-channel frequency selective fading, but also has high bandwidth utilization efficiency is needed. OFDM (Orthogonal Frequency Division Multiplexing) is a multicarrier transmission technology, which could counteract the anti-channel frequency selective fading, and has high bandwidth utilization efficiency. Simultaneously subcarrier may be flexibly allocated to realize asymmetrical transmission for uplink, downlink of the broadband LEO satellite system. Therefore utilization of OFDM for broadband LEO satellite mobile communication to improve system performance is an important research topic.In this dissertation, OFDM transmission technique for broadband LEO communication system is researched. The dissertation mainly focuses on the following aspects.Firstly, the applicability research of OFDM transmission technique based on broadband LEO satellite communication system. The channel statistical property of typical simulation scene for broadband LEO satellite has been described. DFT-S OFDM (Discrete Fourier Transformation Spread Orthogonal Frequency Division Multiple) transmission system for uplink broadband LEO satellite and OFDM transmission system for downlink broadband LEO satellite have been established. According to LEO satellite mobile channel characteristic, Analysis shows comparison of anti-muti channel fading, anti-Doppler shift, PAPR (Peak to Average Power Ratio), anti-AWGN (Additive White Gaussian Noise) channel based on DFT-S OFDM and OFDM transmission system separately. It proves that OFDM transmission technique is suitable for the broadband LEO satellite communication system, which is the key point for the following researches.Secondly, signal detecting algorithms have been researched for uplink broadband LEO satellite system. Because traditional detecting algorithm in frequency domain is not suitable for tracking channel, the improved RLS (Recursive Least Squares) algorithm for single user signal detecting has been proposed, which is quite suitable for tracking fast LEO satellite changing channel. In view of the multi-user interference caused by different frequency offsets for uplink LEO satellite, the precision of tradition PIC (Parallel Interference Cancellation) algorithm or the SIC (Successive Interference Cancellation) algorithm is not high, and the iterative numbers are excessively large, which is not suitable for the broadband LEO satellite. OWPIC algorithm has been proposed for cancelling multi-user interference, which simplifies the iterative step, improves the precision.Thirdly, signal detecting algorithms have been researched for downlink broadband LEO satellite system. The larger frequency offset destroys the orthogonality of sub-carrier and introduces interference. For the complexity of tradition cancellation algorithms is high, and frequency offset scope that can be captured is limited, TF-LMS (Time and Frequency Domain Least Mean Square) algorithm has been proposed to cancel the interference introduced by large frequency offset with low complexity. In view of serious multi-channel fading such as urban service scene for broadband LEO satellite, FSAGE (Frequency Space Alternating Generalized Expectation Maximization) algorithm is proposed to cancel the interference introduced by frequency offset and channel fading, which firstly estimates and pre-cancel the frequency offset, then tracks the disturbance introduced by both frequency offset and channel fading. In order to reduce redundant information and enhance the transmission efficiency for broadband LEO satellite communication system, MCMA-RLS (Modified Constant Modulus and Recursive Least Squares Algorithm) blind algorithm has been proposed, which does not need to use training sequence, and has fast convergence.Fourthly, resources allocation method for LEO satellite OFDM system. In order to enhance power utilization for uplink mobile user terminal, user power control algorithm with satellite power detecting has been proposed, which reduces the power loss effectively for users. In view of ratio proportion for different user terminals and optimizing transmission rate in downlink broadband LEO satellite transmission system, a low complexity average resource allocation algorithm united with power, sub-carrier, bit has been proposed, which firstly guarantees ratio proportion of user terminals with low complexity in average way, and fulfills the maximized rate in a certain extent.Fifthly, analysis of throughput of OFDM transmission technique for broadband LEO communication system has been given. Broadband LEO link transmission system has been firstly established combined with AMC (Adaptive Modulation and Coding), and performance of throughput for mobile user terminal has been shown. Compared with MF-TDMA transmission technique for broadband LEO communication system, OFDM is superior in broadband LEO satellite.更多还原