Acquisition and Fine Acquisition of Weak GPS L2C and L5 Signals under High Dynamic Conditions for Limited-Resource Applications

摘要

Acquisition and fine acquisition algorithms are developed to work with weak L2C and L5 GPS signals. The algorithms utilize the structures and properties of the new signals to achieve high performance with reduced processing and memory requirements. This is to allow the use of the new signals with applications that have limited resources. Long coherent and incoherent integrations are used, without requiring any assisting information. Correlation is performed using new versions of the modified Double Block Zero Padding (MDBZP) that was introduced for weak L1 C/A signals. The acquisition of the L2C signal consists of three stages: Acquisition of the CM signal; fine acquisition of the phase, Doppler shift and Doppler rate; and acquisition of the CL signal. The acquisition of the I5 and Q5 channels is performed separately. The Q5 channel is used for the fine acquisition of the carrier. The coherent integration used with the acquisition of the L2C/CM code and the L5/I5 channel is a multiple of one data bit interval. The most likely data bit combination is estimated over each PIT and used to remove the data bits prior to including each coherent integration result into a longer incoherent accumulation. The coherent integration used with the data-less L2C/CL and Q5 channel can take any length. In addition, a method is introduced to deal with the acquisition of high dynamic signals The performance of the developed algorithms are (lemonstrated using simulated GPS signals with carrier to noise ratio down to 10 dB-Hz, and TCXO clocks. The results have shown the ability of the algorithms to work reliably with such weak signals.