【作者】 梁前浩；

【导师】 蔡伯根；

【作者基本信息】 北京交通大学 ， 智能交通工程， 2008， 硕士

【摘要】 近年来,以GPS为代表的卫星导航产品越来越多的进入人们的生活,然而普通的GPS接收机在高楼密集、树荫遮挡、室内等环境中定位的可用性与可靠性下降。因为在这些区域GPS信号受到障碍物遮挡、多径效应等影响,衰减严重,导致信号功率低于-150 dBm,而普通GPS接收机的灵敏度仅为-130 dBm。因此如何提高GPS接收机的灵敏度成为当前迫切需要解决的问题。研究发现,GPS信号捕获与跟踪模块的灵敏度决定了GPS接收机在弱信号环境中的性能,因此研究能够捕获、跟踪微弱信号的算法就成为提高接收机灵敏度的关键。GPS信号仿真器可以有效仿真受到各种干扰的微弱GPS信号,是捕获、跟踪算法研究与验证的基础。因此,本文的工作包括:仿真器设计,弱信号捕获、跟踪算法研究三方面:1、在对GPS信号结构、特性以及主要干扰源进行分析的基础上,利用数学模型仿真受干扰的微弱GPS中频信号,完成GPS中频信号仿真器设计。仿真器能够有效仿真受到多普勒效应,多径干扰、热噪声影响的GPS L1载波中频信号。2、在弱信号捕获算法设计中,为提高捕获灵敏度,本文首先采用相干积分与非相干积分结合的方式消除了数据码长度对相干积分增益的影响,其次采用差分相干积分减小非相干积分中的平方衰耗。为提高信号捕获速度和精度,本文利用FFT工具进行伪码捕获、2次载波频率捕获,代替传统的顺序搜索法,FFT法,提高了捕获速度与精度。3、在弱信号跟踪环设计中,针对传统非线性PLL环易受噪声干扰的缺点,本文提出一种简化模型的自适应卡尔曼、扩展卡尔曼载波跟踪环代替传统的PLL环。设计中,对状态方程模型进行了简化,并采用基于协方差修正等方法优化环路,提高了环路稳定性和精度。仿真实验表明:仿真信号的频域、功率、自相关特性与实际信号相符。相干-非相干算法、差分相干算法能捕获载噪比为25 dB/Hz微弱信号,其中码捕获、频率捕获精度分别达到2.5Hz,0.2码元。卡尔曼、扩展卡尔曼跟踪算法能够有效跟踪到载噪比分别为26 dB/Hz、24 dB/Hz的微弱信号。更多还原

【Abstract】 GPS receiver has been widely used. However, the reliability and accuracy of general GPS receiver suffers from limitations indoors or in urban canyons. In these perturbed signal environments, the signal strength is less than -150dBm and the general receiver only has a sensitivity of -130dBm. So improving the sensitivity of GPS receiver becomes the problem that should be addressed.Signal acquisition and tracking is critical for a GPS receiver to function in perturbed signal environments. The design of weak signals acquisition and tracking algorithm has become the key to achieve high sensitivity. GPS signal simulator which can be used to simulate GPS signal and interference, is the foundation of algorithm verification. Above all, this thesis includes three parts.1. GPS IF signal simulator design. Based on the analyzing of GPS signal and errors, the GPS L1 carrier interfered by multipath effects and white noise are simulated based on mathematical models. A user interface is designed for GPS IF signal simulator.2. Weak signal acquisition. In order to enhance the acquisition sensitivity, firstly, the coherent-noncoherent integration was adopted to eliminate the restrictions on coherent integration gain. Secondly, the differential coherent integration, which allows a 1.5 dB SNR improvement in processing loss as compared to noncoherent methods, is proposed. At last, the FFT based code and carrier acquisition algorithm is implemented to improve the acquisition speed and accuracy instead of the traditional method.3. Weak GPS signal tracking. Traditional non-linear PLL is vulnerable to noise interference. In this thesis, the simplified adaptive kalman, EKF based weak signal carrier phase tracking loop are proposed. The tracking loop model has been simplified and optimized by covariance medication and adaptive algorithm.The simulation shows that:The characteristics of simulation signals are consistent with the real one. The noncoherent integration, differential integration acquisition algorithm can acquire the weak signal at the CNR of 25dB/Hz with the frequency, code accuracy of 2.5Hz and 0.2 code. Kalman, EKF tracking algorithm can effectively track weak signal at the CNR of26,24dB/Hz.更多还原