Step detector and step length estimator for an inertial pocket navigation system

The use of smartphones for pedestrian positioning applications has become important in recent years. Algorithms for detecting steps and estimating their length can be found throughout the literature. In this paper we present new algorithms that increase the accuracy of the estimated step length and decrease the number of undetected steps. Unlike state of the art algorithms, that use the acceleration to detect steps and the frequency or the acceleration to estimate the step length, we propose the use of the opening angle of the pedestrian's leg. An experiment with 18 volunteers was conducted in order to prove the relationship between the opening angle of the leg and the step length. Our results show that the estimation of the step length is robust against speed changes and the trajectory's estimated length has less than 1% error. Our step detector outperforms state of the art algorithms by presenting a higher step detection rate in challenging scenarios. In conclusion, it is possible and convenient to make use of the opening angle of the leg and its relationship with the step length.