© 1990-2000 IEEE. Personal use of the material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

Electronic Preprints.

The works have been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible.