Ionospheric information broadcasting methods for standardization in SBAS L5

Satellite-based Augmentation Systems (SBAS) such as the European Geostationary Navigation Overlay Service (EGNOS) augment GPS and GLONASS, providing and guaranteeing the availability of navigation signals for aeronautical, maritime and land mobile applications. The ionospheric information provided by the augmentation system is a key issue for accuracy and integrity. However, the actual SBAS standards for broadcasting ionospheric information in L1 band might be insufficient during high solar activity or storm periods, specially in equatorial regions. The availability of a new frequency band (L5) opens the possibility for broadcasting enhanced ionospheric information. This document presents a review of concepts that improve the available ionospheric broadcast information in SBAS. Those concepts might be considered as candidates for standardization in SBAS L5. They can be classified by the kind of improvement to the system: increase of robustness, spatial resolution or temporal resolution; reduction of ionospheric mismodelling and efficient use of bandwidth. The application of compression techniques were studied for improving the bandwidth use or equivalently for the broadcasting of more detailed information using the same bandwidth. Different algorithms were designed including data compression techniques based on a semi-predictive Huffman encoding and image compression techniques using the Discrete Wavelet Transform (DWT), considering the Vertical Total Electron Content as pixels of the image. Compression ratios ranging from 1.2 to 3 were achieved for different scenarios, techniques, power/memory requirements, and residual errors.