Digital modulation and demodulation within E-systems differential GPS transmitter and receiver

The FAA has recently made a commitment to implement GPS Landing Systems as the primary IFR capability for all public use approach and landing systems. As an interim step, private use GPS Landing Systems have been authorized to advance the learning curve. A primary capability of a Local Area Augmentation System (LAAS) is the requirement to uplink differential correction data from a ground station to airborne users. Since this technology is relatively new and is rapidly changing, a robust data link is needed that can be easily modified and updated without investment risk to both the user and the supplier. Further, the ever increasing demand by airlines to drive initial investment cost down, reduce life cycle maintenance costs, and to realize operational savings through lower weight, power, and size results in identification of a 'Software Radio' being a logical architecture choice. E-Systems has implemented this technology in government applications and has successfully transitioned this technology to commercial applications such as the SCAT-I VHF Data Link using D8PSK modulation. This paper discusses the general concepts of a 'Software Radio' and then focuses on D8PSK digital modulation and demodulation techniques. Other potential modulations are briefly discussed along with a summary of performance demonstrations.