【作者】 祖秉法；

【导师】 郝燕玲；

【作者基本信息】 哈尔滨工程大学 ， 导航、制导与控制， 2010， 博士

【摘要】 作为卫星导航系统的三大组成部分之一卫星导航接收机的主要任务是对卫星信号进行检测、接收,完成观测量提取及定位解算等功能。软件无线电是无线电发展的终极目标,它具有硬件的开放性、软件的可编程性和功能的兼容性等优点。本文以“北斗二号”民用软件接收机的原理、结构、实现方法及关键技术为中心,对软件接收机的总体结构、信号采集、伪码捕获、伪码/载波跟踪、抗多径等关键技术进行了深入研究,得出了软件接收机实现的可行方案。论文的主要工作有:在分析了BOC信号调制原理及其相关函数的基础上重点研究了MBOC(6,1,1/11)和AltBOC(15,10)信号的生成方式、功率谱密度及其相关函数特点,推导证明了AltBOC(15,10)信号的四路BPSK信号复用本质,为“北斗二号”民用软件接收机前端规划奠定了基础。基于软件无线电思想设计了“北斗二号”双频民用接收机的总体结构,对其关键模块进行了分析规划并选取了软件接收机满足直接射频采样要求的模数转换器;推导了带通采样原理并对带通采样方式进行了分析;提出了“北斗二号”双频民用信号不重叠射频带通采样最小采样频率的选取方法和步骤。针对软件接收机进行长码捕获的特点,对传统基于FFT的伪码/载波并行捕获方法进行了改进,提出了基于FFT多普勒补偿的双并行捕获方法,能够在对输入信号进行一次FFT变换的情况下同时完成载波和多普勒频移的二维搜索,大大加快了卫星信号的捕获速度;考虑到宽带方式在接收机复杂度、功耗和多模接收等方面的弊端和局限,确定了AltBOC(15,10)信号的单边带接收方式,提出将Tong算法作为软件接收机的捕获判决策略。为了消除MBOC(6,1,1/11)信号由于相关函数存在多峰而造成的捕获跟踪模糊度问题,基于ASPeCT技术分别对其FFT捕获电路和非相干DLL鉴相器进行了改进;推导了基于ASPeCT的DLL归一化鉴相算法,分析了带宽和超前滞后码间隔对MBOC(6,1,1/11)信号和单边带AltBOC(15,10)信号非相干码鉴相器输出方差的影响。建立了多径干扰的数学模型,分别推出了BOC(1,1)信号和单边带AltBOC(15,10)信号的超前减滞后功率和点积码鉴相器在相对直达信号幅度为0.5的单路多径的误差包络,并对窄相关抗多径技术的原理及其局限性进行了分析;采用MEDLL技术作为软件接收机的抗多径技术,提出了基于最小二乘法的MEDLL实现方法,该方法在具有低复杂度的同时可以很好地消除民用信号的多径干扰。对二阶Costas环和纯PLL的动态性能以及不同信噪比和动态应力条件下总的跟踪颤动进行了分析,在此基础上设计了基于导频的纯PLL“北斗二号”软件接收机载波跟踪环路;为了充分发挥纯PLL在跟踪精度和动态性上的优势,提出了一种可调带宽的纯PLL载波跟踪环结构并推导了该结构的实现原理以及数字化框图。更多还原

【Abstract】 Receiver is one of the three segments of satellite navigation system whose responsibility is to detect and receive satellite navigation signal together with observations extraction and positioning calculation.SDR ( Software Defined Radio) is the ultimate goal of radio development who has the merits of open in hardware, reprogrammabality in software and compatibility in function.Centering with the principle,stucuture,realization pattern and key techniques of Compass-M1 civilian software receiver,the thesis made a thoroughly research on its main structure design,signal collection,PN(Pseudo Noise)code acquisition and tracking,carrier tracking and multipath mitigation techniques and gained a feasible plan of Compass-M1 software receiver realization.The main works are as follows:The modulation principle,power density funtions and autocorrelation functions of MBOC(6,1,1/11)(-Multiplexed Binary Offset Carrier) and AltBOC(15,10)-(Alternate Binary Offset Carrier) modulations were investigated respectively based on that of BOC(Binary Offset Carrier)modulation and the four-BPSK(Binary Phase Shift Keying) multiplex character of AltBOC(15,10) is derived,which is the premise to design Compass-M1 civilian software receiver.The structure of double bands Compass-M1 civilian software receiver was designed based on SDR concept and the A/D converter was selected which is capable of direct radio frequency bandpass sampling for Compass-M1 civilian software receiver.The principle of bandpass sampling was derived and bandpass sampling pattern was analysed.The method and process of selecting the minmum sampling frequency for double bands Compass-M1 civilian software receiver when adopting direct bandpass sampling without aliasing was proposed.In view of long PN code acuqisition by software,the thesis proposed a method called FFT-based frequency complement parrallel search which can finish two-dimension search of code phase and Doppler frequency by only FFT-transforming of the incoming signal once to shorten the satellite navigation signal acquisition processure.The single side band processing pattern of AltBOC(15,10) was chosen to simplify receiver design,lower power consumption and facilitate multimode receiver design and the Tong algorithm was select as the software receiver acquisition decision strategy.To eliminate the threat of ambiguous acquisition and tracking of MBOC(6,1,1/11) signal,the FFT-based acquisition circuit and noncoherent DLL discriminators were modified for MBOC(6,1,1/11) signal by ASPeCT(Autocorrelation Side-Peak Cancellation Technique).The method of unifying ASPeCT-based DLL discriminators was derived and the RMS(Root Mean Squre) of EMLP(Ealy Minus Late Power) and DP(Dot Product) discriminators were analyzed.The mathematical model of multipath was established and the multipath error envelops of EMLP and DP DLL discriminators for BOC(1,1) and single side band AltBOC(15,10) caused by one multipath whose amplitude is half of that of the direct path were derived.The principle and limits of narrow correlator were analyzed.The MEDLL(Multipath Estimating Delay Lock Loop) technique was selected to allieviate the multipath effect for Compass-M1 software receiver and a LS(Least Square)-based realization method of MEDLL was brought forward which is effective in perfomance and simple in realization.Based on the performance of second order PLL(Phase Lock Loop) on dynamic and total phase viberation in different CNR(Carrier to Noise Ratio) and dynamic stress situations,a pilot based pure PLL was decided as the carrier tracking loop of Compass-M1 software receiver.To take advantage of the tracking accuracy and dynamic performance of pure PLL,a bandwidth adjustable PLL structure was proposed whose principle and digital diagram were derived.更多还原