Rake reception for UWB communication systems with intersymbol interference

Recently, ultra wideband (UWB) technology has been proposed for use in wireless personal area networks (WPANs). Under the conditions where such transceivers are expected to operate, intersymbol interference (ISI) will become a significant performance limitation, and improvements to conventional RAKE reception will be necessary. We propose a modified RAKE receiver that finds an optimal balance between the goal of gathering multipath signal energy, avoiding ISI, and suppressing narrowband interference. For fixed RAKE finger delays, we develop a closed-form expression for the minimum mean squared error (MMSE) combining weights that account for ISI. We then examine the optimal choice of RAKE finger delays, and show that significant performance gains can be achieved, particularly in an undermodeled situation when there are more channel paths than RAKE fingers. Several numerical examples are presented which compare our proposed scheme to a conventional RAKE with maximal ratio combining (MRC).