This paper presents results from the "Indoor Positioning"project conducted at Danish GPS Center (DGC), AalborgUniversity. We focus on creating theoretical backgroundand experimental verification for a software based indoorpositioning solution. We present a novel theory to improvethe ranging accuracy for a Time Of Arrival (TOA) basedranging system. We presume a system equipped with lowresolution clocks featuring a constant drift. We propose amethodology how to infer accurate TOA from aliased measurements.Additionally, results obtained via simulationand extensive experimental campaigns are presented andanalyzed.