A New Adaptive Code Processing Scheme for High-Sensitivity Acquisition in Dual-Frequency GPS L1-L2C Receivers

摘要

The synchronized ranging codes on the L1-C/A and L2Crnsignals allow for their combined processing to enhancernthe acquisition sensitivity, in a dual-frequency GPS L1-rnL2C receiver. The presence of unknown and independentrnnavigation message bits on the C/A and L2C codes,rnhowever, prevents their coherent combination.rnConsequently, researchers so far have adapted only noncoherentrnand differentially-coherent combining schemesrnfor joint acquisition of the two codes.rnIn this paper, we propose an adaptive processing schemernfor coherent combining of L1 C/A and L2C codes in thernjoint L1-L2C signal acquisition. In this approach, L2 CLrnand C/A codes are compared with reference signalsrnavailable at the conventional CM correlator output. Therncomparison identifies chips of CL and C/A codes whichrndisagree with polarity of corresponding reference chips.rnThe polarity of identified CL and C/A chips is thenrninverted. This results in all three (C/A, CM and CL) codesrnlining up during correct CM code phase trial andrnmaximising the signal to noise ratio.rnThe proposed scheme is validated through theoreticalrnanalysis and testing with real GPS signals and it is shownrnthat the proposed approach outperforms all existingrnschemes of combined GPS L1-L2C signal processing inrnthe context of acquisition sensitivity.