Abstract
This paper describes the development and implementation of a robust high-accuracy ultrasonic indoor positioning system (UIPS). The UIPS consists of several wireless ultrasonic beacons in the indoor environment. Each of them has a fixed and known position coordinate and can collect all the transmissions from the target node or emit ultrasonic signals. Every wireless sensor network (WSN) node has two communication modules: one is WiFi, that transmits the data to the server, and the other is the radio frequency (RF) module, which is only used for time synchronization between different nodes, with accuracy up to 1 s. The distance between the beacon and the target node is calculated by measuring the time-of-flight (TOF) for the ultrasonic signal, and then the position of the target is computed by some distances and the coordinate of the beacons. TOF estimation is the most important technique in the UIPS. A new time domain method to extract the envelope of the ultrasonic signals is presented in order to estimate the TOF. This method, with the envelope detection filter, estimates the value with the sampled values on both sides based on the least squares method (LSM). The simulation results show that the method can achieve envelope detection with a good filtering effect by means of the LSM. The highest precision and variance can reach mm and mm, respectively, in pseudo-range measurements with UIPS. A maximum location error of mm is achieved in the positioning experiments for a moving robot, when UIPS works on the line-of-sight (LOS) signal.
Highlights
Satellite signaling systems are universally well known
The time protocol of the ultrasonic indoor positioning system (UIPS) is based on reference broadcast synchronization (RBS) [29], which works in the data link layer
This microcontroller unit (MCU) integrates 512 Kbytes Flash memory with protection mechanisms and 256 Kbytes of static random access memory (SRAM) on chip. It has an abundance of peripheral resources and interfaces, such as a 12-bit analog to digital converter (ADC), a digital to analog converter (DAC), a timer that can produce the pulse width modulation (PWM) signal, universal synchronous or asynchronous receiver transmitters (USARTs) and a direct memory access (DMA) channel [34]
Summary
Satellite signaling systems are universally well known. One example is the global positioning system (GPS), which has a high positioning accuracy at 0.15 m [1]. The other local positioning solutions consist of radio frequency identification (RFID) [11], WiFi [12], and ZigBee [13], and they have a low positioning accuracy Compared to these above technical solutions, a positioning system based on the ultrasonic signal and a wireless sensor network (WSN) has many advantages, including slow propagation speed The random signal processing method is used to estimate ultrasonic TOF in some works in the literature [18,19], considering environmental noise, but these algorithms are too complex for UIPSs based on WSNs. The ultrasonic signals are encoded into various digital codes, such as binary frequency shift-keyed and code division multiple access codes [20,21,22,23].
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