Manuscript received May 24;
1993;
revised June 12;
1995. The material in this paper was presented in part at the IEEE International Symposium on Information Theory;
Trondheim;
Norway;
1994. Research of Z. Zhang was supported in part by the NSF under Grant NCR-91205265. Z. Zhang is with the Communication Sciences Institute;
Electrical Engineering-Systems;
University of Southern California;
Los Angeles;
CA 90089-2565 USA. V. K. Wei is with the Department of Information Engineering;
The Chinese University of Hong Kong;
Shatin;
New Territory;
Hong Kong. Publisher Item Identifier S 001 8-9448(96)0291:3-6;