GPS Key Technologies Research Based On Software Receiver

GPS is the first and the most mature member of global navigation satellite system,and has the advantages of high accuracy,good applicability and low cost.Nowadays,GPS has been widely used in various civilian and military fields.However,since the GPS receiver must gather and process the external satellite signals,its performance is vulnerable to environmental factors.In this sense,in-depth studies of advanced acquisition,anti-spoofing and tracking algorithms are still needed.Moreover,though INS has the problem of error accumulation,it realizes autonomous navigation and is robust to environmental factors.Making full use of the complementary characteristics of GPS and INS to construct GPS/INS ultra-tight integration can not only correct the navigation results of INS,but also improve the performance of GPS.Therefore,to further expand the application scope of GPS,this paper studies several key techniques of independent GPS and GPS/INS ultra-tight integration on the basis of software receiver.The main work and research results are as follows:1.To improve the acquisition accuracy and sensitivity of GPS receiver in low SNR environment,a new kind of acquisition method for weak signal is proposed.This method makes use of differential coherent integration to reduce power loss,and breaks the restriction of searching step size on the estimation accuracy of carrier Doppler shift by utilizing the phase information of integration results.Moreover,based on the relationship between carrier and code Doppler shifts,this method amends the local code phase directly.As a result,it ensures different correlation peaks overlap with each other and can obtain the accurate code phase of the received signal.2.Spoofing detection algorithms cannot help the victim receiver retrieve its navigation abilities unless the tracking channels influenced by counterfeit signals are shut down.To neutralize counterfeit signals,based on analyzing the similarities and differences between spoofing and multipath,a new anti-spoofing method is developed from multipath estimating technique.Concretely,the receiver utilizes multi-correlators and maximum likelihood estimators deployed in the tracking channels to perform spoofing detection and cancellation.As a result,even if counterfeit signals have different delays,the receiver can keep tracking the authentic signals in an optimal way.3.A new single pre-filter is developed from the traditional error-state single pre-filter.It utilizes state feedback values,which are calculated based on the principle that the carrier phase error and the code phase error must return to 0 in the shortest amount of time,to control local signal generation,and shows better tracking performance than the traditional one.Furthermore,to avoid carrier tracking being subjected to code tracking errors,a dual pre-filter architecture is designed on the basis of the proposed single pre-filter.And finally,this architecture is applied in a GPS/INS tight integration to help the whole system obtain navigation solutions in the missile-data-based semi-physical simulation.4.A Cascaded GPS/INS ultra-tight integration,whose tracking channels adopt the dual pre-filter architecture,is constructed to achieve mutual assistance between GPS and INS.After correcting pseudorange rate by the output of the carrier phase discriminator,even the traditional navigation filter can make the whole system work well in extreme high dynamic situations.To obtain better navigation results,the pseudorange rate tracking errors are modeled and treated as the state variables of the navigation filter.However,the computational complexity of the filter with expanded dimension is too high.So,dimension reduction is performed through the use of inter-satellite single-difference and two-stage Kalman filtering algorithm,while the navigation precision is maintained.