The problem of indoor navigation is investigated using a Commercial Off-the-Shelf (COTS)\npseudolite system. The system is operated in synchronous and asynchronous mode. It is\nshown that, when the system is operated in synchronous mode, it is unsuitable for deep\nindoor operations: in complex propagation environments, the synchronisation required for\nmetre level navigation is difficult to achieve and different solutions have to be adopted.\nTwo asynchronous approaches are thus considered and indoor navigation with metre level accuracy\nis demonstrated using C/N0 measurements. The approaches use a modified Receiver\nSignal Strength (RSS) navigation algorithm and a weighted centroid technique, respectively.\nIn both cases, a pre-filtering stage has been adopted to enhance the quality of C/N0 measurements.\nThe two methods have been compared under different operating conditions and the\nadvantages and drawbacks of the two techniques have been analysed. The experiments demonstrate\nthat metre level accuracy can be achieved using asynchronous pseudolites. These\nresults are particularly encouraging since they were obtained without exploiting map constraints\nand prior knowledge of the user position.
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