Simulation and Efficient Implementation of a Multipath Estimating Delay Locked Loop Using FIMLA Algorithm

Markus Langer, Stefan Kiesel, Karl-Friedrich Kief, Gert F. Trommer

Abstract:	In this paper, the Fast Iterative Maximum Likelihood Algorithm (FIMLA) is used to implement a Multipath Estimating Delay Locked Loop. The focus lies on the simulation environment and an efficient implementation of the algorithm. Either a MATLAB based signal simulator for simulating GNSS IF-samples or a correlation based IQ model for simulating I/Q samples is used for different scenarios. The IQ model and the simulation of IF-samples approaches are compared with respect to computational effort and comparability of the simulation results. For the implementation of the algorithm we make use of the Fourier transform to calculate correlations in the frequency domain to gain speed performance. A predefined bank of correlators and interpolation algorithms are used to achieve the needed resolution for the iteratively working FIMLA. The second part of the paper analyses the influence of varying reflected signals and proposes a way to handle rapidly changing and reappearing reflected signals in a Multipath Estimating Delay Locked Loop (MEDLL). The tracking of several reflected signals is assisted by a dynamic early-late spacing to enhance the performance of the tracking algorithm in different multipath environments. For example the algorithm can react differently on near or far reflected signals. The results are compared to a standard delay locked loop (DLL). The proposed techniques are not only limited to the FIMLA, but can also be applied to other Multipath estimating techniques.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	1152 - 1161
Cite this article:	Langer, Markus, Kiesel, Stefan, Kief, Karl-Friedrich, Trommer, Gert F., "Simulation and Efficient Implementation of a Multipath Estimating Delay Locked Loop Using FIMLA Algorithm," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 1152-1161.
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