Implementation of an optimized code loop for indoor positioning

Indoor localization based on GNSS repeaters, as described in previous works [1-2], has only been achieved to within a range of few meters. This is due to many error sources among which thermal noise has the greatest impact after multipath error (which is not included in the present paper). But when dealing with indoor positioning, precision should be higher. Therefore, when using the existing GPS signals, one way to satisfy this precision requirement from a signal processing point of view, consists of acting on the tracking loops of the GNSS receiver. Consequently, the present paper will describe new code loop architecture specific to repeater based indoor positioning. Previous studies [3] have shown significant differences of behaviour in the resulting measured noise and accuracy in the code phase jump measurements for different receivers (a MIRA-16 from Martec, including an Aschtech GG-16 board, a PolaR×2 from Septentrio and an R-25 software receiver from NordNav). The complete analysis of these differences leads us to consider the architecture of the code loop and to propose a new structure for improving code phase jump detection and accuracy. Simulations are carried out with the new code loop and the final design is implemented in a NordNav R30 software receiver. Experimental results are then obtained that validate the efficiency of the proposedarchitecture. Note that the improvement allows for a noise reduction coefficient of 5 in the code phase jump detection (from 2.70 meter down to 0.5 meter obtained with simulations).