To meet the long term goal of greater capacity in aviation, services must be expanded to provide more reliable and robust approach and landing operations in all weather conditions, globally using modernised navigation systems. This paper details the measurement processing techniques under investigation for the Multi-Constellation (MC) and Multi-Frequency (MF) Ground Based Augmentation System (GBAS) within the SESAR Framework Work Package 15.3.7. It deals with the performance improvements obtainable for CAT II/III precision approaches, the most stringent operation currently defined. GBAS has the potential to provide CAT II/III services without the need for expensive and regular maintenance and flight testing that comes with the current Instrument Landing System (ILS). Furthermore, in the case of ILS, multipath problems may restrict separation criteria in some conditions thus limiting capacity. SESAR WP15.3.7 is investigating a potential change in the message correction update rate. With the current correction rate of 2Hz it will not be possible to send multiple constellations and correction types beyond the bare minimum. This paper presents analyses relating to the error budget degradation when using lower frequency corrections.