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The secondary modulation with the NeumannHoffman code increases thepossibility of bit sign transition. Unlike other GNSS signals, there is nopilot component for synchronization in BeiDou B1/B3 signals, which increasesthe complexity in acquisition. A previous study has shown that the delay andmultiplication (DAM) method is able to eliminate the bit sign transitionproblem, but it only applies to pretty strong signals. In this paper, aDAM-based BeiDou signal acquisition approach, called variable length dataaccumulation (VLDA), is proposed to acquire weak satellite signals. Firstly,the performance of DAM method versus the different delays is analyzed. The DAMoperation not only eliminates bit sign transition, but it also increases noisepower. Secondly, long-term signal is periodically accumulated to improve signalintensity in order to acquire weak signals. While considering the Dopplerfrequency shift of ranging codes, the signal length must be compensated beforeaccumulating long-term signal. Finally, the fast-Fourier-transform basedparallel code phase algorithm are used for acquisition. The simulation resultsindicate that the proposed VLDA method has better acquisition sensitivity thantraditional non-coherent integration method under the same calculation amount.The VLDA method only requires approximately 27.5% of calculations to achievethe same acquisition sensitivity (35 dBHz). What is more, the actualexperimental results verify the feasibility of the VLDA method. It can beconcluded that the proposed approach is an effective and feasible method forsolving the bit sign transition problem.

A BeiDou Signal Acquisition Approach Using Variable Length Data Accumulation based on Signal Delay and Multiplication