Indoor Positioning System Using TOA Method with USRP Based on IEEE802.11v

Chun-Huai Fu and Shau-Shiun Jan

Abstract: With the arising of smart mobile device, WiFi (IEEE802.11) is widely used. WiFi hotspot is everywhere in urban area and it is therefore chosen as our signal of opportunity for indoor positioning. For an indoor positioning system, there are two main positioning methods. The first positioning method is based on the received signal strength (RSS) that takes advantage of the signal propagation model to determine the position. The second positioning method is based on the time-of-arrival (TOA) of signal that estimates the pseudorange to determine transmitter location by trilateration. The presurveyed RSS database is needed to perform the RSS method for indoor positioning in different environments. On the other hand, the TOA method requires precise timing measurement between transmitter and receiver. In our previous work, we presented the WiFi indoor positioning system based on the RSS method with Kriging algorithm, and there was no WiFi access point (AP) available on the market that supported IEEE 802.11v. As a result, in this paper, we propose using the universal software radio peripheral (USRP) based software defined radio (SDR) to implement the WiFi TOA method for the indoor positioning system. The TOA method needs a common protocol for timing standards. With the growth of WiFi enabled devices in indoors, the demand of the wireless network management promotes the new IEEE802.11v protocol standard. The two main features of the IEEE802.11v are 1) the time stamps in the transmission and reception of specific message frame, and 2) the time synchronization between the connected WiFi nodes. These two features enable us to estimate the pseudorange and thus we could directly use the time information to apply the TOA technique. We use the USRP based SDR platform for both transmitter and receiver with the concept of IEEE802.11v. A TOA based positioning algorithm is investigated in this paper. In general, the two dominant factors of the TOA method affecting the positioning performance are 1) the relative geometry of transmitter and receiver and 2) the quality of the timing measurement. In order to get a better positioning performance, a Rubidium clock is used as our external oscillator for the developed USRP based SDR platform, and the GPS disciplined oscillator (GPSDO) is another considered oscillator. The cost of Rubidium clock is much higher than that of GPSDO, but the timing precision of Rubidium clock is better than that of GPSDO. Specifically, a prototype indoor positioning system using WiFi is developed in this work, and the positioning engine is based on the TOA technique with IEEE802.11v protocol. This involved developing an USRP based SDR with a stable external oscillator as the positioning performance node to assess the performance of various software and hardware architectures for the indoor positioning system. Finally, the preliminary results of the indoor positioning experiments are presented in the paper.
Published in: Proceedings of the ION 2015 Pacific PNT Meeting
April 20 - 23, 2015
Marriott Waikiki Beach Resort & Spa
Honolulu, Hawaii
Pages: 365 - 372
Cite this article: Fu, Chun-Huai, Jan, Shau-Shiun, "Indoor Positioning System Using TOA Method with USRP Based on IEEE802.11v," Proceedings of the ION 2015 Pacific PNT Meeting, Honolulu, Hawaii, April 2015, pp. 365-372.
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