[1] Middlesex Univ, Dept Comp Sci, London N17 8HR, England
[2] Middlesex Univ, Res Grp Dev Intelligent Environm, London N17 8HR, England
[3] Stanford Univ, AIR Ambient Intelligence Res Lab, Stanford, CA 94305 USA
[4] Univ Ghent, iMinds, Ghent, Belgium