Theoretical bounds for ranging with Multi Band OFDM and Direct Sequence UWB signals

The definition of Ultra Wide Band (UWB) signals set by the Federal Communications Commissions (FCC) opened the way to both impulse and non-impulse UWB signal formats. This possibility is reflected within the IEEE 802.15.3a TG, aiming at the definition of a standard for UWB-based high bit rate WPANs. The two main proposals considered in this group are in fact a Multi Band OFDM approach, based on the transmission of non-impulse OFDM signals combined with Frequency Hopping (FH), and the Direct-Sequence (DS) UWB approach, based on impulse radio transmission of UWB DS-coded pulses. In this paper, the ranging capabilities of these two proposals are analyzed by determining the Cramer-Rao Lower Bound (CRLB) for the distance estimation error. The CRLB is evaluated under the condition of both ideal and real, multipath-affected, channel models. Results show that DS-UWB is in general best suited for ranging, thanks to its larger bandwidth and its higher frequencies of operation, and also quantify the degree to which multipath may affect ranging accuracy. Index Terms—UWB, ranging, localization, Cramer–Rao Lower Bound