The global satellite navigation signal works well in open areas outdoors. However, due to its weakness, it is challenging to position continuously and reliably indoors. In this paper, we developed a hybrid system that combines radio signals and acoustic signals to achieve decimeter-level positioning indoors. Specifically, acoustic transmitters are synchronized with different codes. At the same time, our decoding scheme only requires a simple cross-correlation operation without time-frequency analysis. Secondly, acoustic signals will be reflected by glass, walls and other obstacles in the indoor environment. Time difference of arrival (TDOA) measurement accuracy is seriously affected. We developed a robust first path detection algorithm to obtain reliable TDOA measurement values. Finally, we combine the maximum likelihood (ML) algorithm with the proposed TDOA measurement method to obtain the location of the smartphone. We carried out static positioning experiments for smartphones in two scenes. The experimental results show that the average positioning error of the system is less than 0.5 m. Our system has the following advantages: (1) smartphone access. (2) an unlimited number of users. (3) easily deployed acoustic nodes. (4) decimeter-level positioning accuracy.

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