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Analyzing Local Positioning Systems Without Satellites

Ramezanpour, Keyvan | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40641 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Fotowat-Ahmady, Ali; Hossein Khalaj, Babak
  7. Abstract:
  8. Increasing needs for wireless positioning systems, especially in modern wireless networks, have emerged new trends in research on local positioning systems and algorithms. In this dissertation, several geometric arrangement of positioning systems, different types of wireless measurements used for positioning, and estimation of desirable coordinate parameters based on them are investigated. The set of constrained linearized equations, by introducing intermediate variables are developed and compared with Cramer-Rao bounds. Performance bounds of ToA, TDoA and round-trip ToA systems are obtained and their sensitivity to the location changes of the target and reference stations is examined through simulations. One of the most important features of wireless channels is multipath propagation. Time and spatial diversity provided by multipath signals may be exploited to improve detection layer performance. However, multipath fading effects restrict the performance. Using wideband signals such as direct sequence spread spectrum signals as well as antenna arrays are popular solutions to the fading problem. Optimal and sub-optimal strategies of spread-spectrum signal acquisition in multipath environments, with single antenna and antenna arrays are introduced and analyzed with simulations. The most significant effect of multipath propagation in positioning systems is the error they introduce in the estimation of signal parameters. As a consequence, the multipath propagation imposes harsh restrictions on the accuracy of positioning systems. Several algorithms for alleviating multipath errors in the tracking of spreadspectrum signals are introduced and analyzed. The set of feedforward algorithms provide promising solutions to the estimation of receiving code phase in the presence of multipath signals. However, they involve high complexity burden, in addition to their high sensitivity to the noise thresholds and the receiver front-end bandwidths. Feedback algorithms, although have simple structures and acceptable noise behavior, multipath signals deteriorate their performance substantially. A new tracking algorithm is proposed based on a feedback structure that significantly improves the multipath performance of feedback structures. This is done by separating the phase discriminator and utilizing suitable reference waveforms. Thus a novel method with the simplicity of feedback structures and a multipath performance comparable to feedforward algorithms is designed. Finally, three different layouts for positioning system are adopted for given requirements and resources. A system with two layers of reference stations based on round-trip ToA method is proposed for the situation when the strict synchronization of ToA system is not practical. Although robust to geometric changes, the system has worse performance relative to ToA and TDoA systems. The second design consists of three layers of reference stations based on TDoA positioning. In the third scheme for a positioning system, relays are included to extend the range of the system. In this way, the concept of relay may be used for the purpose of positioning in the area where the signals of reference stations are blocked. Relays may also be utilized to provide spatial diversity for improved accuracy.

  9. Keywords:
  10. Antenna Array ; Tracking ; Kalman Filters ; Code Acquisition ; Least Squares Estimation ; Spread Spectrum Signal Aquisition

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