Chapter 3 GNSS Signal
Principle of Pseudorange Measurement
Questions
What is pseudorange?
The pseudorange is the geometry distance between the satellite and receiver, which has not been modified by the sat. clock error,rec. clock error,troposphere error,ionosphere error,etc. It refers in particular to the distance that be generated by the ranging code.
什么是伪距？
伪距是卫星和接收机间的几何距离，未经修正的卫星钟差、接收机钟差、电离层、对流层误差等。它特指由测距码生成的距离。
How to generate the pseudorange?
What is the principle of pseudorange measurement?
Ranging Code: one kind of binary code,which be used to measure the distance between the sat. ans the rec.. The GNSS range code belong to pseudo-random code.
测距码： 一种二进制码，用来测量接收机和卫星之间的距离。测距码属于伪随机码。
1. Definition of Ranging Code
What is the code?
binary code: consist of ‘0’ or ‘1’.
What is the random code?
That is the random that each number of the serial binary code is 0 or 1. Then ,the serial binary code if called as random code.
什么是随机码？随机码是由0、1组成的随机二进制串。
Characters: aperiodicity,nonduplication,autocorreation.
特性：非周期性，非重复性，自相关性。
What is the pseudo-random code?
It possesses the characteristic of autocorrelation of the random code, while owns the periodicity and duplication.
什么是伪随机码? 伪随机码有自相关的特征，同时具有周期性和重复性。
autocorrelation:distinguish from other signals.
periodicity & duplication:generate the same signal.
自相关性：区别于其他信号。
周期性和重复性：生成相同的信号。
Generation of Ranging Code
Principle of Ranging Code Generation
Characters of Ranging Code
-
Easy to extra the weak nav. signal from massive signals
-
Improving the accuracy of distance measurement
-
Easy to use code division multiple access(CDMA).
-
Easy to control & administrate the system
测距码的特性：
- 容易从大量信号中分辨出微弱的导航信号。
- 提高测距的准确性。
- 容易使用码分多址（CDMA）。
- 容易控制和管理系统。
Principle of Pseudorange Measurement
Characters of Pseudorange Observation
伪距观测的特性
Advanteges
- long code element, easy to capture, be called as capture code.
- no multiple-valued problem, easy to process.
- no cycle slip problem, be suitable for real-time process.
- ion.err. of code is equal in size, opposite in sign,to that of carrier phase, can be used to eliminate the ion.err.
优点：
- 长码元，容易捕获。
- 没有多值问题，容易处理。
- 没有周跳问题，适合实时处理。
- 测距码与载波相位的电离层误差大小相等，方向相反，可用来消除电离层误差。
Disadvantages
- suffer more multipath errors than the carrier phase.
- the accuracy of obs. is not better than carrier phase.
缺点：
- 比载波相位更受多路径效应影响。
- 观测准确度比不上载波相位。
Improvement Methods
- use the carrier phase to smooth the pseudorange
- use the doppler obs. to smooth the pseudorange
- use baseband process to smooth hte pseudorange,such as narrow correlator, MET, MEDLL,PAC,Vision,etc.
改善措施：
- 使用载波相位来平滑伪距
- 使用多普勒观测来平滑伪距
- 使用baseband process 来平滑伪距
Homework
Please find out a new method or technology to improve the accuracy of pseudorange measurement.
请找出一个新的方法或技术来提高伪距测量的准确度。
How to integrate pseudorange,carrier phase and Doppler obs. for a special application?(make use of their own advantages)
如何结合伪距、载波相位和多普勒观测以用于特定用途？
- What is the specific form of code observation equation?
码观测方程具体形式
- What is the specific form of carrier observation equation?
载波观测方程具体形式
完整的载波（周）：$\varphi i= \varphi i+N0$
完整的载波（米）：$p=\lambda*\phi=\lambda *(\phi +N0)$
- What are the precisions of CA, P,L1 and L2 observables, respectively?
精确度分别是
sdfasdf