Benefits of using lower chip rates for Galileo OS and PRS signals

Recent GNSS-related agreements have selected the chip rates for Galileo signals to be 1.023 MHz for Open Services (OS) and 2.5575 MHz for Publicly Regulated Services (PRS), respectively. For future developments of the satellite navigation systems, it might be however of importance to understand better the impact of the chip rate on the system properties. The purpose of this paper is to analyze the situations when the chip rates are decreased to smaller values than those used by the current candidates, while still keeping similar spectral and timeresolution properties as the current proposals. A particular situation that might be of high interest for future standardization is when both OS and PRS services would use the same chip rate, that is 1.023 MHz, as the standard-GPS chip frequency. This would allow a better convergence between various services of Galileo, while the good separation between Galileo-PRS signal and GPS M-code is still preserved. The lowering of the chip rate is used in conjunction with the increase of the Binary-Offset-Modulation (BOC) modulation order. We present here the steps of designing jointly the chip rate, the sub-carrier frequency, and the BOC type (i.e., sine or cosine) in order to achieve the target spectral properties defined by the current proposals. We also introduce, for the first time in the scientific literature (to the authors’ knowledge), the formulas for the power spectral densities of cosine-BOC modulation for both even and odd modulation orders. We also show here the benefits of lowering the chip rate for OS and PRS Galileo signals and we discuss its impacts on the system complexity and performance.