[1] Univ Ulster, Sch Comp & Math, Coleraine BT52 1SA, Londonderry, North Ireland
[2] Univ Ulster, Comp Sci Res Inst, Coleraine BT52 1SA, Londonderry, North Ireland
[3] Stanford Univ, Dept Elect Engn, AIR Ambient Intelligence Res Lab, Stanford, CA 94305 USA