A Novel Approach For NavIC &Pseudolite Combined User Position Algorithm

Conventional navigation systems such as GPS, GLONASS, NavIC etc. use iterative position estimation algorithm after linearizing nonlinear pseudorange equations and convergence is achieved comfortably after 4-5 iterations. However, Pseudolite based navigation system is sensitive to the initial guess due to the nonlinearity of pseudoranges over the short distances. Due to this fact, the conventional Global Navigation Satellite Systems (GNSS) position estimation algorithm does not work well for Pseudolite based navigation system giving very high position error. Therefore, in this paper, a novel approach has been proposed in which position has been estimated using NavIC pseudorange measurements for the first instant using conventional GNSS algorithm. Thereafter, this position estimate was used as an initial guess for the combined NavIC and Pseudolite position estimation using conventional GNSS algorithm. It was interesting to note that the pseudolite only position was not converging with conventional GNSS algorithm when used in standalone mode, however, NavIC and pseudolite combined algorithm convergence was achieved comfortably using the proposed approach with very good position accuracy. Testing was done using simulated data of NavIC generated from commercial Spirent GNSS simulator available at Space Applications Centre (SAC) and simulated data of pseudolite transceivers placed at a selected location in India. Furthermore, Gaussian error with known mean (10m) and variance (9 m) was introduced in each pseudoranges of NavIC and Pseudolite. 3-D Position accuracy of around 2-4 m was achieved from the combined NavIC & Pseudolite measurements. It was also observed that combined NavIC and Pseudolite Position Dilution of Precision (PDOP) was around 0.94 whereas PDOP with NavIC only constellation is around 3.1, which gives huge improvement in position accuracy over NavIC only scenario. Combined NavIC and Pseudolite positioning finds applications in myriad of areas such as automatic landing of aircraft, landing of Re-usable launch vehicle, mining, GNSS obstructed environments coastal and marine environment.