The Design And Implementation Of Tracking Loop And Anti-Multipath In Pseudo Code Ranging Receiver

The three-dimensional coordinates of the pseudo code ranging receiver can be got by calculating of the comprehensive multi-channel data. Distance between the satellite and the receiver can be got by using the result of the speed of light times the time delay between the receiving signal times and satellite signal time,and the receiving signal need to be processed by antenna, RF chains, AD conversion, the local pseudo-code. Capture and tracking are the main two links in the process of signal processing. The main purpose of the capture which is the process of coarse synchronization for receiving signal is to screen the pseudo-code signal preliminary and then to pass the receiving signal to the tracking process. The function of the receiver to realize precise synchronization can be implemented only by the precise synchronization of the code and the carrier.So, the accuracy of signal in the process of tracking directly decided to receiver’s positioning accuracy.Multipath phenomenon refers to the receiver antenna in addition to receiving a navigation satellite launch by the linear electromagnetic signal propagation, and may also receive one or more reflection signals of the electromagnetic wave,it can be called as multipath interference or multipath effect. This kind of interference give rise to the error of navigation receiver on signal measurement and the difficulties of the signal tracking. So,the multipath effect is one of the main error sources. In multipath situation, the internal copy C/A code of receiver will do the related operations with the direct wave and the reflected wave at the same time. It will damage the correlation function peaks which only reflect the direct wave phase. It will reduce the accuracy of measurement of pseudorange, or will cause the code phase lock and the satellite signal missing seriously.The anti-multipath interference methods generally fall into two categories, one kind is to weaken the multipath interference by the design of the correlator or the phase discriminator, such as the narrow correlator、the double difference discriminator、the Vision correlator、PAC(Pluse Aperature Correlator), this kind of method has the characteristic of simple implementation, but further improving the positioning accuracy is difficultly. Another kind is to eliminate the multipath interference by estimating the parameters of the multipath signal with the combined method of software and hardware,such as MET(Multipath Eliminating Technology)、MEDLL(Multipath Estimation Delay Lock Loop), the result of this kind is much better,but with the increases of the hardware configuration, the computing complexity and instability of the system operation are much worse.This paper presents a method to suppress multipath with adaptive wavelet transform on the basis of software receiver. Multipath signal is removed from the original signal under the condition of a certain threshold with multi-level wavelet decomposition which is called mathematical microscope. Wavelet decomposition series has significant influence on multipath suppression effect, the higher the wavelet decomposition series,the local multipath signal is amplified much more, the better the multipath suppression effect.The threshold is the key parameter in wavelet decomposition series, the smaller the threshold value, the more meticulous the multipath signal is decomposed, the better the multipath suppression effect, but it also increases the decomposition series and the computational complexity.