Time hopping versus frequency hopping in ultrawideband systems

In English 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 FCC-compliant 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.