Bibliographical noteFunding Information:
Manuscript received August 18, 2000. Recommended by Associate Editor C. Wen. This work was supported in part by the Natioanl Science Foundation, in part by the Air Force Office of Scientific Research, and in part by EPSRC. T. T. Georgiou is with the Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455, U.S.A. M. C. Smith is with the Department of Engineering, University of Cambridge, Cambridge, CB2 1PZ, U.K. Publisher Item Identifier S 0018-9286(01)00036-8.