Adaptive GPS Acquisition Technique in Weak Signal Environment

Abstract

In recent years, there has been increasing demands in providing precise location estimation in weak signal environment (e.g. in urban area or inside a building). Conventional GPS acquisition techniques are considered to be adequate on positioning capability in outdoor environment. However, most of them are not satisfactory for applications with weak signals. It has been studied that a longer time of data integration is required in order to provide sufficient data for acquisition under weak signal circumstances. In this paper, an adaptive GPS acquisition technique is proposed, which adaptively adjusts the detection threshold and the length of data integration for signal acquisition. The location of the navigation bit-transition is perceived within the acquisition data in order to adaptively determine either the coherent or the differential coherent combining method should be used. The simulation results show that the proposed adaptive acquisition technique outperforms both the non-coherent combining and the differential-coherent combining algorithms. As the SNR value of the incoming signal decreases, the effectiveness of the proposed adaptive scheme can be observed.