Orthogonal Decomposition Algorithm for Ionospheric Delay Estimation for Precise GPS Applications

The time delay of GPS link1 (L1) and link2 (L2) signals in ionosphere is one of the propagation path effects caused when the signal is travelling from satellite to receiver. The absence of the Selective Availability (SA) made the ionospheric delay as the predominant accuracy limiting factor for GPS. As the density of the ionized plasma varies, the velocity of the GPS signals differs from the velocity of light. Due to this the GPS radio frequency (RF) signals experience the group delay or phase advance. Hence the one way time transfer of the GPS is affected, inturn resulting in pseudorange error varying from few meters to tens of meters at zenith. To correct the GPS range measurements this delay is estimated using conventional Code Range technique which models the Total Electron Content (TEC). In this method the TEC is an additional parameter to be calculated and the accuracy of the TEC depends on the inter channel biases and solar activity. To overcome this, an orthogonal decomposition algorithm is proposed in this paper. The proposed algorithm decomposes the coefficient matrix derived from the linear combination of GPS measurements. The proposed algorithm not only avoids TEC calculation but also minimizes complex computations. The comparative analysis of the estimates of the proposed algorithm and conventional method are presented in this paper. The proposed algorithm is implemented and estimates are validated for the ephemerides data collected on 07th April 2015 from the Dual Frequency GPS (DFGPS) receiver located in the Department of Electronics and Communications Engineering (ECE), Andhra University College of Engineering (AUCE), Visakhapatnam (Lat:17.730N/Long:83.3190E). The proposed algorithm can be implemented for precise navigation and tracking applications like Category I (CAT I) precision approach (PA), Precise Point Positioning (PPP), geographic information systems (GIS) and Real Time Kinematic (RTK) positioning.