Time hopping and frequency hopping in ultrawideband systems

This paper analyzes frequency-hopping (FH) and time-hopping (TH) as multiple access format for ultrawideband communications. We apply the concept of fourthegy, recently introduced by Subramanian and Hajek, to both TH and FH.We find that the design rules are different for FCCcompliant systems(where the power spectral density is limited)than for conventional systems(where the energy per bit is limited). We find that fourthegy, and thus possible information rate, is maximized by using a bandwidth that is as large allowed by the FCC. For TH systems, a low duty cycle should be used. For FH, a subdivision into as many bands as possible should be used, and the dwell time on each frequency should be at least as long as the delay spread of the channel. This work may not be copied or reproduced in whole or in part for any commercial purpose. Permission to copy in whole or in part without payment of fee is granted for nonprofit educational and research purposes provided that all such whole or partial copies include the following: a notice that such copying is by permission of Mitsubishi Electric Research Laboratories, Inc.; an acknowledgment of the authors and individual contributions to the work; and all applicable portions of the copyright notice. Copying, reproduction, or republishing for any other purpose shall require a license with payment of fee to Mitsubishi Electric Research Laboratories, Inc. All rights reserved. Copyright c ©Mitsubishi Electric Research Laboratories, Inc., 2003 201 Broadway, Cambridge, Massachusetts 02139