The accuracy that GNSS and GBAS can provide is the key to improve air traffic where bottlenecks appear: terminal areas surrounding main airports. Its implementation would represent lower budgets in cost and maintenance in comparison to current guidance systems that would remain as backup. This project focuses on processing raw satellite data and producing a standard output to increase air traffic navigation, approach and landing capacities in terminal areas. This involves tasks such as algorithm prototyping in Matlab and -integrity monitoring testing- with bad ephemeris data to check the output response. The impact of known errors will be analyzed to obtain a robust and scalable system. The next step will be the GBAS message codification and generation (Type 1) for a GBAS station. This station will be made up of four reference receivers located in the proximity of airport's Runways to accomplish CAT (I) requirements and provide the best measurements in approach and landing maneuvers. The project is located in the base of an ambitious bigger scheme (CATGOS) under development by Indra, which aims to implement and certificate a GBAS station for an airport environment in a four-year prospect.