A Reduced Search Space Maximum Likelihood Delay Estimator for Mitigating Multipath Effects in Satellite-based Positioning

Multipath is one of the dominant error sources in global navigation satellite systems, such as the Global Positioning System or the future European satellite navigation system, Galileo. The reception of multipath may create a bias into the time delay estimate of the delay lock loop of a conventional navigation receiver, which eventually leads to an error in the receiver's position estimate. In order to mitigate the impact of multipath on navigation receivers, the multipath problem has been approached from several directions, including the development of novel signal processing techniques. In this paper, we propose a maximum likelihood based algorithm, namely the Reduced Search Space Maximum Likelihood (RSSML) delay estimator, which is capable of mitigating the multipath effects in moderate-to-high carrier-to-noise-ratios. The proposed RSSML attempts to compensate the multipath error contribution by estimating the multipath parameters along with the line-of-sight signal. The multipath performance of other state-ofthe-art delay tracking methods previously studied for Binary Phase Shift Keying (BPSK) and Sine Binary Offset Carrier (SinBOC) modulated signals, is also analyzed here, together with the new Multiplexed BOC (MBOC) modulation. Simulations are carried out in closely space multipath scenarios for two-path Rayleigh fading channel model. The simulation results show that the RSSML achieves the best multipath mitigation performance in root-mean-square-error sense for all three different modulated signals (i.e., BPSK, SinBOC(1,1) and MBOC), compared with four other multipath delay estimation techniques, namely the Narrow Correlator, the High Resolution Correlator, the Teager-Kaiser estimator and the Peak Tracking estimator.