Equalization for Multiband OFDM based UWB Systems

The focus for ultra-wideband (UWB) technology has recently shifted to applications involving short-range, high-speed wireless communications like IEEE 802.15.3a for personal area network (PAN). FCC defines UWB signals as one that occupies more than 500 MHz bandwidth in the 3.1 to 10.6 GHz band and meets the output power limit of -41.3 dBm/MHz. This paper addresses the problem of equalizer design for multi-band OFDM based UWB systems. The novelty of the proposed solution is that it is based on joint MLSE equalization & diversity-combining for both QPSK & DCM modes and it performs reliably at low SNRs. The solution is amenable for VLSI implementation. Maximal-ratio-combining (MRC) based alternatives are also analyzed in details and it is shown that an MRC receiver for DCM is very sensitive to timing errors, which reduces its usefulness. Finally we develop alternatives to DCM that are robust to timing errors.