Requirements of an OFDMA Pseudolite Indoor Geolocation System

Ilir F. Progri, Matthew C. Bromberg, William R. Michalson, Jinling Wang, R. James Duckworth and John Lavrakas

Abstract:	solution algorithm for self-calibrating pseudolite arrays presented in [2]. However, several modifications were necessary to adapt the algorithms to the SekaN system requirements. The rover which is used for data collection during the self-calibration process is designed as a Receiver-only module instead of a TC module. This makes the rover hardware less complex, smaller and lighter, but also complicates the self-calibration process. Self-differencing between the stationary TCs and the rover TC can no longer be applied. The ranges between the rover RX and the TCs are therefore not directly observable. The self-calibration and navigation algorithms developed for SekaN work for both 2-D and 3-D scenarios. Although multipath effects, non-linearities and the near-far-effect are inherent in these kind of groundbased navigation systems, precise user positioning at the sub-meter level becomes possible even with low-cost receivers within the self-calibrated navigation environment. The requirements of an OFDMA pseudolite indoor geolocation system consists primarily of: 1. OFDMA general system requirements 2. OFDMA pseudolite (or transmitter) requirements 3. OFDMA receiver requirements 4. OFDMA financial, business plan requirements. First, as far as general system requirements are concerned, the geolocation information for each pseudolite consists of the pseudolite’s position and time and the ability of the system to perform distance measurement under severe multipath conditions which is typical indoors. Second, OFDMA pseudolite requirements concern the signal design (or structure), signal modulation, power levels etc. For each pseudolite this information is binary encoded data at a symbol rate of 1 KHz. The encoded geolocation signal is modulated on the corresponding [100 200 300 400] MHz carrier signal via a Frequency Division Multiple Access (FDMA) modulator to mitigate cross-channel interference encountered in an indoor geolocation environment. The Orthogonal Frequency Division Multiplexed (OFDM) signal is then used to provide distance information. Four (4) transmitters are simulated to enable a geolocation estimate on the receiver. Third, the receiver consists of four channels, each one of which is designated to a single transmitter. On each receiving channel the received signal is down-converted, demodulated and decoded. Four distance estimates are used in a Least Squares filter to provide an estimate of the receiver location and time. We have added the ability to perform distance measurement; we have analyzed the effect of the transmitter stability on the position accuracy; we have assessed the effects of the transmitter and receiver oscillator drift (short term stability) on positioning accuracy; we are investigating techniques for detecting an extremely weak LOS signal in the presence of severe multipath; and finally, we are studying techniques for maintaining lock on the LOS signal in the presence of severe multipath; i.e., to enable a high sensitivity receiver. Fourth, we have provided a summary of the financial or business plan requirements which include financial requirements for phase I, II, and III of the analysis, development, and mass production of the system.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	1821 - 1829
Cite this article:	Progri, Ilir F., Bromberg, Matthew C., Michalson, William R., Wang, Jinling, Duckworth, R. James, Lavrakas, John, "Requirements of an OFDMA Pseudolite Indoor Geolocation System," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 1821-1829.
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