Autonomous WSN for Smart Living Technology Application: Acoustic & Radio Frequency Positioning
Date Issued
2011
Date
2011
Author(s)
Huang, Ji-De
Abstract
There are several requirements for wireless sensor network deployment. First is time synchronization and second is locatization capability. With time synchronization functioin, nodes can maintain active and sleeping sequence as well as keep working periodically to make sure data exchange correctly. Locatization capability provides the user with a way to identify where sensing data is collected and where the nodes are located. This thesis took WSN hardware/firmware design as the starting point followed by discussing the synchronization and locatization of Wireless Sensing Network (WSN).
As time goes by, WSN becomes more and more mature. Nevertheless, the development tools are still too expensive and the learning curve remains steep. In 2006, this thesis was based on two newly developed WSN hardware platforms sponsored by Taiwan’s National Science Council. The handly firmware library for each of these hardware platforms were also developed then. It is due to the ease of implementation, open source software and open source hardware configurations of these two platforms, these platforms were distributed to groups who determined to advance the application of WSN. The outcome of this action led to significant advancement of WSN technology and application in Taiwan.
During the year 2007 period, time synchronization methods cannot work properly in the two WSN hardware platforms mentioned above due to CSMA/CA function of IEEE802.15.4. To resolve this limitation, a new synchronization method was developed and detailed in this thesis. This method records timing error by utilitizing timer function in microcontroller and corrects it by using compensating method. With only single direction broadcast required to process the compensation, this method is sutiable for large network applications. Experimental results showed that this method is capable of keeping error under ±0.88us over three hops.
Locatization technology developed during the course of this research and presented in this thesis contains wired ultrasonic ranging, wireless ultrasonic ranging, and pure RF ranging. In wired ultrasonic ranging section, a new ranging system was developed. Two ultrasonic pulses with AM and PM are sent in this system, which interfere with respect to each other at the receiver end. By detecting the interference signal, system can precisely measure Time of Arrival (TOA). Experimental results showed this system can keep Standard Deviation error (STD error) under 0.15mm over 2000mm range.
In the wireless ultrasonic ranging section, a 2D ultrasonic WSN location system based on localization and time synchronization was developed and detailed. Although the performance is reduced by the synchronization error, this system still has precision up to 0.32mm over 1000mm range in linearity test.
In pure RF ranging section, multi-receivers with same clock source were found to achieve better TOA data than receivers with difference sources. Base on this idea, a synchronized phase ranging system was developed. In this system, all receivers were clocked by the same souce. Same phase shift between each other and SFD (Start Frame Delimiter) event detection from the same RF package were adopted. This system was examed in 100m indoor and 100m outdoor cases; results showed this system has precision of 3.38m with RMS error of about 5.03m and 6.86m respectively.
Subjects
WSN
Time Synchronization
Ultrasonic Ranging
TOA
Synchronized Receivers
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