Study Of BDS/GPS Week Signal Acquisition Based On High-altitude Orbit Spaceborne Receiver

High-Altitude Orbit includes GEO (Geostationary Orbit) and HEO (HighlyEccentric Orbit) whose altitude is always higher than20000km.The satellite onHigh-Altitude orbit has been widely applied in communication, navigation,atmosphere and early-warning in modern society. And the autonomous navigationtechnology for High-Altitude satellite has been an urgent need for our countryparticularly for the High-Altitude orbit maneuver. The spaceborne receiver can onlyreceive signals from the other side of the earth when its altitude is higher than thenavigation constellation. The received power will be lower than the ordinaryspaceborne receiver more than10dB, as the receiver need to receive antenna sidelobesignal from the navigation satellite and other negative factors such as the earth shelter,more free-space loss and lower transmitting antenna gain, and the visibility of thenavigation for the user and the signal strength will also be worse. So if we design thespaceborne receiver by rule, the number of the satellite usable will be lower than4which will result in a failure of position.We set the week signal acquisition target as-175dBW by making a simulation onthe signal property of the BDS/GPS signal. Then we carry out a research on theHigh-Altitude Orbit week BDS/GPS signal acquisition. In the matter of signal searchmode, we introduce and compare the difference between Line search, Parallelfrequency search based on FFT and Parallel code phase search. In the matter of thecumulative mode of gain, we introduce and compare the difference between coherentaccumulating，incoherent integration and differentially coherent integration. In themaster of eliminating the data code phase jump, we introduce the method of half-bitaccumulation and the full-bit accumulation. All above can provide theoretical basisfor the final solution of the weak BDS/GPS signal acquisition. The existence of theNH code which is the double coding on the BDS signal result in an unachievablelong-term coherent accumulation and there’s little literature on this problem.According to the autocorrelation of the superimposed code and the way of eliminating the data code phase jump, we process the20ms data with the improved differentiallycoherent integration algorithm to increase the gain of the BDS week signal as well asthe GPS week signal to achieve the week BDS/GPS signal acquisition.We also simulate other algorithm to compare with our improved algorithm. Itturned out that the improved algorithm can do better in week signal acquisitionespecially in the BDS week signal acquisition than other algorithm. The improvedalgorithm can acquire-178dBW week BDS/GPS signal based on the simulation, andcan meet the demand of the High-Altitude Orbit spaceborne receiver navigation.