Signals and Modulation

Abstract

Satellite navigation relies on signals radiated by orbiting satellites and received by mobile satellite navigation receivers. This chapter addresses the fundamentals of such navigation signals and introduces the most important underlying concepts. It provides an introduction to radio frequency signals including the basics of electromagnetic waves, their carrier frequency, polarization, as well as group and phase velocity. The application of waves for carrying signals, their power and spectrum are addressed. It is shown how information-carrying signals can be modulated onto the wave using various modulation schemes such as binary phase shift keying, binary offset carrier, and alternating binary offset carrier. Setting out from international agreed allocations, the frequency bands used in GNSSglobal navigation satellite system (GNSS)global navigation satellite system (GNSS) are described. The concept of pseudo-random codes which is typically used for GNSS signals is introduced as well as their receiver side processing following a correlation principle.