Enhanced Differential Detection Scheme for Weak GPS Signal Acquisition

In this paper several detector schemes for processing weak GPS signals in an unaided acquisition scenario are described and analyzed. Fundamental theoretical considerations based on the generalized likelihood ratio test (GLRT), as applied to GPS signal detection, are discussed. It is shown that the asymptotic version of the GLRT is equivalent to an estimator correlator (EC). For assumed deterministic signals the GLRT further reduces to a matched filter. This implies that the navigation data code phase and carrier parameters are known. In this paper, we unify the well-known post-correlation noncoherent detection and the newly proposed postcorrelation differential detection in terms of GLRT and EC formulation. As well the generalized post-correlation differential detector scheme, which is a hybrid of postcorrelation, non-coherent integration and differential detectors is analyzed. Simulation results, as well as hardware based experimental measurements, are given to validate the claims of the acquisition sensitivity improvements of the proposed detection scheme.