Candidate Designs for an Additional Civil Signal in GPS Spectral Bands

As modernization of radio-navigation satellite systems (RNSS) proceeds, there is increasing interest in new signals for civilian use. New signals must coexist with current and already planned signals on the GPS L1 and L2 frequencies, offer more robustness, higher performance, and greater capacity. There are significant motivations, as well as significant challenges, to placing new civil signals within the existing GPS bands at L1 and L2. RF compatibility with existing and planned signals is a particular challenge. This paper motivates and describes designs suitable for an additional civil signal that fits within the existing spectrum allocations at L1 and L2. It discusses the benefits of sharing the existing spectrum, and outlines the constraints that must be satisfied for successful sharing. It then provides insight into the needed spectral characteristics, identifies a class of modulations that provides these characteristics, and shows advantages of these designs over others that have been considered. It also discusses aspects of the signal's spreading code and data message.