On the trade-off between uncertainty and delay in UWB and 5G localization
Abstract: Location-aware technologies in combination with emerging wireless communication systems have revolutionized many aspects of our daily lives by means of applications within the commercial, public and military sectors. Ultra-wideband (UWB) and 5G stand out as emerging radio frequency (RF) based technologies that tackle the limitations of Global Positioning System solutions. The thrive in search for better accuracy involves improved ranging algorithms, higher transmission powers, network densification, larger bandwidths, and the use of cooperation among nodes in the network. However, practical implementations introduce communication related constraints. In this thesis, we study the trade-off between localization accuracy and communication constraints in terms of delay. This trade-off is investigated and quantified for two of the most rapidly growing RF technologies for high precision positioning: UWB and 5G. In UWB, we investigate the trade-off between medium access control (MAC) delay and accuracy based on a two-way-ranging and a spatial time division multiple access scheme. We quantify this relationship by deriving lower bounds on localization accuracy and MAC delay during the measurements phase, which is often neglected in the analyses. We find that the traditional means to improve accuracy such as increased number of anchors, increased communication range, and cooperation among nodes, come at a significant cost in terms of delay, which can be mitigated by means of techniques such as selective ranging and eavesdropping. We summarize and generalize our findings by characterizing the position error and delay lower bounds by deriving asymptotic scaling laws. These scaling laws are presented for dense noncooperative and cooperative networks in combination with delay mitigation techniques. Moreover, we introduce a delay/accuracy trade-off parameter, which can uniquely quantify the trade-off as a function of the agent and anchor density. Finally, we consider the problem of fast link scheduling and propose an optimization strategy to perform robust ranging scheduling with localization constraints. We propose two MAC-aware link selection heuristic approximation approaches which show similar performance as the optimal solution, but alleviate the problem complexity. In 5G, we analyze the interplay between communication and positioning within the initial access procedure between a transmitter and a receiver in a millimeter-wave multipleinput multiple-output system. We exploit the ability of the receiver to determine its location during the beam selection process and thus, improve the subsequent selection of beams within initial access. First, assuming that only the transmitter has beamforming capabilities, we propose an in-band position-aided transmitter beam selection protocol for scenarios with direct line-of-sight and scattering. Then, we extend the work and propose an in-band position-aided beam selection protocol where we also allow for the receiver to perform beamforming in scenarios with line-of-sight, reflected paths, and possible beam alignment errors. Both protocols show similar performance compared to their conventional counterparts in terms of final achieved signal-to-noise ratio, but they are significantly faster and can additionally provide the position and orientation of the devices in an accurate manner.
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