Many indoor navigation systems have been developed for pedestrians and assessing their performances is a real challenge. Benefiting from a reference solution that is accurate enough to evaluate other indoor navigation systems and assist novel research is of prime interest. The design and algorithms of a foot-mounted reference navigation system titled PERSY (PEdestrian Reference SYstem) are presented in this paper. Quasi static phases of the acceleration and the magnetic field are used to mitigate inertial sensor errors in indoor spaces. Differential indoor/outdoor GNSS phase measurements are added to the strapdown EKF to improve the positioning accuracy with a correlation between low and high frequency velocity estimates. Experiments conducted with four persons over a 1.4 km walking distance show a 0.22% positioning mean error.