Positioning in ultra wideband systems

After the use of unlicensed ultra wideband (UWB) communication was allowed by FCC in 2002, UWB technology has received great interest among telecom companies. The large bandwidth allows speedy wireless data transfer and the system can also be used for high precision indoor localization.

This thesis explores the positioning capabilities in UWB systems. Two data aided synchronization/timing acquisition algorithms were implemented and evaluated. Both use the received signal as correlation template, thus making adaptive multipath-reducing equalizers unnecessary. The first one is based on stepwise line search where the accuracy is determined by the step size, while the latter one provides a coarse timing acquisition in closed form. Those algorithms were then used together with time based positioning methods in order to see how timing errors affects the positioning precision. Timing and positioning accuracy were evaluated as functions of the signal-to-noise ratio and the length of the channel impulse response.

Since a hardware implementation of the positioning system would include advanced analog circuitry, only simulations in MATLAB were done. he results show that the time estimation errors approaches the asymptotic performance limit already at negative SNR’s, something that is of great importance since UWB radios transmits below the noise floor. It is also discovered that the timing acquisition error will approach a non-zero offset as the search step is reduced. Still, the position estimate gets better for higher search resolution when considering time differences of arrivals (TDOA). Finally there seem to be an optimal length of the channel impulse response for which the best positioning results are achieved.

Author: Johansson, Olov

Source: Lulea University of Technology

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