Efficient BeiDou DBZP-based weak signal acquisition scheme for software-defined receiver

Modulation with high-rate Neumann–Hoffman (NH) code in BeiDou signals increases the complexity and calculation load in acquisition as the data bit transitions are more frequent and there is no pilot component for synchronisation which is used in other constellations. Among the current state of the art, double block zero padding (DBZP) method has great potential in reducing the calculation. However, traditional DBZP is very sensitive to bit transition and the misalignment of bit edge will cause serious power loss. To relieve the calculation load and acquire the weak signal successfully, an efficient BeiDou DBZP-based scheme is proposed. The proposed scheme is optimised in two aspects: the NH code phase searching and correlation integration. The step size of the proposed NH code searching method is half an NH code bit which means the number of searches in one navigation message bit is only 40 and the computation load can be reduced greatly. Additionally, the proposed inherited correlation integration establishes a tight inherited structure between adjoining coherent integrations which can reduce the calculation burden further. The experiment results show that the proposed scheme can acquire as weak as 22 dBHz with only about 12% computation time of the traditional DBZP method.