Jaakko Suutala Susanna Pirttikangas Jukka Riekki Juha Röning Reject-Optional LVQ-Based Two-Level Classifier to Improve Reliability in Footstep Identification. 182-187 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3001&spage=182 2004 conf/pervasive/2004 Pervasive db/conf/pervasive/pervasive2004.html#SuutalaPRR04