| Location-based services (LBS) have brought much convenience to us, and the smartphone has been one indispensable part in our daily life. Research has shown that we usually spend 80 percent of our life in an indoor environment. As the indoor environment more and more enormous and complex, the requirement for indoor localization are becoming increasingly strong, for example, precision marketing, shopping positioning, medical care, intelligent storage and so on. Indoor positioning service based on smartphone has become one of the most popular research fields in the whole world.Complex and changeable indoor environment makes GPS unavailable, and WIFI, bluetooth, UWB and other technologies all exists shortages in the high positioning accuracy or smartphone compatibility. Based on the characteristics of low cost, high precision, and good compatibility with smart phone, acoustic indoor positioning technology will become one of the most popular technologies. Therefore, we propose a new approach of acoustic indoor localization with smartphone, and solve the problem of time delay estimation in multipath and strong noise environment. Besides, we also design and implement our positioning system. The experiment result shows that the system can achieve all of the three important indicators, including high precision, good real-time performance and strong stability. The contributions of this paper are mainly described as follows:1) In order to improve the estimation accuracy, robustness and real-time performance of time delay estimation, we design and optimize the acoustic signal. Upon analyzing the frequency response characteristic of the smartphone, we design an acoustic LFM signal with good antijamming capability. After analyzing the experiment results of different signals, we optimize the initial frequency, frequency change rate, termination frequency and the length of the signal.2) In view of the time delay estimation problem of acoustic signals with cross-correlation theory, we optimize the parameters so that it can work in multipath environment and even when the signal is very weak, and improve the estimation accuracy significantly. The multipath phenomenon is very serious in indoor scene, and the traditional cross-correlation approach may bring huge error, which regards the moment the max peak value appears as the time of signal arrival. In this paper, we optimize the approach of time delay estimation to improve the robustness of cross-correlation. In order to obtain the time of weak signal arrival successfully, we also formulate a kind of criterion to learn whether the peak is legal.3) Upon signal filtering with fuzzy function in time frequency domain, we propose a new approach to detect the signal arrival time, and achieve a more accurate result than cross-correlation. Besides, the projection solution from two dimensions to one dimension decreases the computation complexity significantly. By designing the fuzzy function in Doppler Time Delay Domain, we adopt AF filtering technology to filter the signal to obtain a high accurate performance. In order to improve the computational efficiency, we propose the concept of cumulative energy projective distribution and cumulative points projective distribution, and improve the real-time performance significantly. Result shows that this approach can obtain a more accurate performance.4) We propose a new indoor positioning approach, which optimizes the process of time synchronization among different nodes and target localization, and improves the real-time performance and stability without sacrificing the accuracy significantly. Experiment result shows that the system can obtain an error less than 25cm with 83.3 percent probability, and an error less than 10cm with 44.4 percent probability. The period of location update can achieve 400ms, and the system has a high stable performance. |
