Research On The Acquisition Of GPS Weak Signal

With the development of satellite navigation technology,its application filed is becoming more and more widely.At the same time,the requirements of users on location accuracy is becoming higher and higher.In the weak signal surroundings,the common GPS receiver can not work normally.Firstly,the satellite signal was received by GPS receiver antenna,after the processing of down conversion,it then enter the process of baseband position module,finally,we got the position after calculation.The baseband processing include the process of acquisition and tracking.The acquisition capability is a key indicator to measure the performance of receiver.so the acquisition technology for the weak GPS signal has been becoming a research hot spot.Currently weak signal acquisition is mainly divided into two directions: high sensitivity GPS and AGPS.This paper researches the weak signal acquisition algorithm for the high sensitivity GPS receiver.At first,this paper introduce the composition of GPS signal,spread spectrum technology by the pseudo-code acquisition and analyze the generation and features of C/A code thorougthly.Then the attenuation value under different environments is given,meanwhile the mathematical model of GPS signal is established.Secondly,this paper describe the basic theoretical of GPS signal acquisition,then by a detailed analysis of three traditional acquisition methods and their characteristics are given,also,the way to measure the performance of capture is provided.Then the relation between single detection probability and carrier noise radio has been simulated,we can get when carrier to noise ratio is bigger,the detection probability is bigger.Thirdly,this paper focus on the weak signal acquisition in different weak signal environments.Several main factors needed to be taken into consideration while acquiring the weak signals are analyzed,there are three ways: coherent integration,non-coherent integration and differential coherent integration.The key of the weak signal acquisition is to improve the S/N(Signal to Noise Ratio)gain.The diagram and advantages of coherent integration,non-coherent integration and differential coherent integration are analyzed and simulated.The differential coherent integration is most suitable for the weak signal acquisition.Feature of three classical method: the combination of coherent and non-coherent,half bit and full bit h acquisition methods are provided.Finally,the half bit alternate differential coherent for the weak signal acquisition is proposed and simulated,then it was compared with half bit method.Since longer dataintegration time will be selected for weak signal acquisition,the capture time is increased.In order to reduce the amount of the calculation,and to shorten the capture time,aliased on the time domain is introduced the acquisition algorithm in the processing of the weak signal acquisition algorithm,the aliased on the time domain is introduced is simulated and analyzed its property.