UWB ranging accuracy for applications within IEEE 802.15.3a

The definition of ultra wide band (UWB) signals released by the Federal Communications Commissions (FCC) opened the way to both impulse and non-impulse UWB signal formats, as reflected within the IEEE 802.15.3a TG, devoted to the definition of a standard for UWB-based high bit rate WPANs. The two main proposals considered in this group are 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 the two proposals are investigated by determining the Cramer-Rao lower bound (CRLB) for the distance estimation error. The CRLB is evaluated with both ideal and real, multipath-affected, channel models and the impact of multipath on ranging accuracy is quantified. Results show that DS-UWB is, in general, best suited for ranging, thanks to its larger bandwidth and its higher frequencies of operation, although multipath may affect in a different way DS-UWB and MB-OFDM signals.