Carl Fischer Kavitha Muthukrishnan Mike Hazas Hans Gellersen Ultrasound-aided pedestrian dead reckoning for indoor navigation. 31-36 2008 MELT http://doi.acm.org/10.1145/1410012.1410020 conf/mobicom/2008melt db/conf/mobicom/melt2008.html#FischerMHG08