Study of signal combining methodologies for future GPS flexible navigation payload (Part II)

Abstract

The number of GPS ranging signals has increased steadily from GPS IIR to IIR-M and IIF. This trend will continue for the future GPS system-GPS III. Besides the increase in number of ranging signals, the future GPS system is also envisioned to implement a flexible navigation payload. This payload will have the ability to modify the number, the configuration and the power of ranging signals while the satellite is in orbit. In designing this flexible navigation payload, one of the tasks is to find the right signal combing methodology to be implemented for combining multiple signals together. This paper will study two well-known signal combining methodologies, coherent adaptive subcarrier modulation (CASM) and majority-vote. In addition, a new methodology, inter-vote, will also be studied. The assessment of those three combining methodologies will be focused on their power efficiency performance, which is closely related to the efficient usage of satellite power. The impact of inter-modulation signal, which is generated when the above three combining methodologies are used, will be briefly discussed at the end.