1. a School of Electrical Engineering and Computer Science , Washington State University , Pullman, WA, 99164-2752, U.S.A
2. b Department of Electrical Engineering , National University of Singapore , 10 Kent Ridge Crescent, Singapore , 0511
3. c Department of Applied Mathematics and Statistics , State University of New York at Stony Brook , Stony Brook, NY, 11794-3600, U.S.A.