1. Concordia Institute for Information Systems Engineering, Concordia University, Montréal, Quebec, Canada H3G 1T7. E-mail: hamza@ciise.concordia.ca
2. Tality Corporation, Cary, NC 27511, USA. E-mail: yhe@tality.com
3. Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7914, USA. E-mail: ahk@ncsu.edu
4. Laboratory for Information and Decision Systems, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA. E-mail: willsky@mit.edu