[1] Univ Toronto, Dept Elect & Comp Engn, Toronto, ON M5S 3G4, Canada
[2] Columbia Univ, Dept Elect Engn, New York, NY 10027 USA
[3] Natl Chiao Tung Univ, Dept Elect Engn, Hsinchu 30010, Taiwan
[4] Natl Tsing Hua Univ, Dept Elect Engn, Hsinchu 300, Taiwan