Low-complexity ML timing acquisition for UWB communications in dense multipath channels

Timing acquisition for ultrawideband (UWB) communication systems operating in dense multipath environments faces major challenges due to the stringent requirements to resolve and capture ultrashort transmitted pulses. This paper develops low-complexity maximum-likelihood (LC-ML) acquisition methods that offer explicit design options to trade off acquisition accuracy and complexity. The proposed schemes are based on a tapped delay line (TDL) model whose tap spacing is set in accordance with a low frame-level rate. By avoiding subpulse rate sampling, the LC-ML methods achieve low complexity and fast acquisition speed and at the same time retain good estimation accuracy due to the underlying ML principle. Both the data-aided (DA) and nondata-aided (NDA) versions are derived. It is also demonstrated by simulations that the proposed synchronizers are markedly robust with respect to the effects of both multipath channel and multiple access interference.