Indoor positioning system based on ultrasound

Date:18-03-2014   |   【Print】 【close

Indoor positioning system based on ultrasound

1. System Overview

Mobile devices such as smartphones and tablets provide endless possibilities for location-based services (LBSs), which requires research and development of positioning and tracking systems. Since Global Navigation Satellite System (GNSS) provides reliable positioning, its accuracy can reach several meters, and outdoor LBSs have developed rapidly. However, the indoor performance of these services is very poor, and there is no sufficiently mature technology to solve the indoor fine positioning on mobile devices. Conversely, people spend almost 90% of their time in indoor environments. Compared with other traditional dedicated positioning hardware devices, the use of smartphones or other mobile devices greatly enhances location-based services, including allowing user interaction, augmented reality applications, and a series of multimedia services or social network that can enrich the location-based user experience. Specific applications include building navigation (such as airports, hospitals, factories, large shopping malls, etc.), augmented reality related to cultural tourism, games, and mobile models that provide targeted advertising or customized services.

Existing systems mainly adopt radio frequency (RF) -based methods and acoustic signals for the positioning of indoor mobile devices. Generally speaking, the positioning accuracy of the RF-based positioning system is meter-level, while the acoustic wave-based positioning system can achieve centimeter-level or even millimeter-level accuracy. However, traditional ultrasonic positioning systems require dedicated speakerphones, microphones, and signal acquisition hardware, which are not compatible with current mobile devices.

A method for indoor positioning of mobile devices based on ultrasound is proposed as follows. The mobile device can determine its 3D position information based on signals from multiple speakers at different indoor locations. The positioning accuracy can reach the centimeter level, which can meet most precision requirements for indoor positioning of mobile devices.

2. Indoor Positioning Scheme

Regarding the positioning of mobile terminals, most classical positioning systems rely on the estimation of the sound wave transmission time difference between the sound source and the mobile terminal. Moreover, most related mathematical models are generalized to the least squares (LS) problem, which is aimed at matching unknown variables (such as the 3-D position of a mobile phone) with the estimated time of arrival (or time difference of arrival).

For an indoor environment where several controllable speakers are placed at known locations, each speaker periodically sends a specific pseudo-random noise (known by mobile devices), and the mobile device can determine its own spatial location based on the sound signal from the speaker. Moreover, there is no synchronization between the mobile device and the speaker (except that the location of the speaker is imported into the mobile device when the positioning tool is first turned on in a specific environment). This scheme relies on the estimation of the time of arrival, or the time difference of arrival. From the perspective of the mobile device, since the mobile device works passively, there is no other energy consumption besides the energy consumption of position calculation. Therefore, the energy consumption of this type of positioning scheme is small. In addition, the use of additional speakers in indoor positioning has the following advantages:

1)        The speaker can better cover a required space area, and its position can be accurately measured and stored.

2)        Mobile devices can be independent of each other, so there is no need to communicate with each other, or require minimum number of mobile devices.

3)        Radiation-controlled signals bring speciality, since only mobile devices that know all speaker positions and detect signals can use the system.

4)        Speaker position does not change over time.



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