Galileo has been designed to be both independent and interoperable with other GNSSes, and particularly GPS. The search for interoperability makes Galileo look like GPS, while the desire of independence of both systems has the opposite effect. As Prof. Günter Hein summarized in a previous ?Working Papers? column in Inside GNSS, the degree of interoperability between the two systems will be a function of their compatibility with each other (and other GNSSes), the simplicity of the user segment, economic aspects, their independence, national security, and the vulnerability of a combined PVT (position, velocity, and time) solution. The current frequency plan for Galileo and modernized GPS (GPS IIRM, IIF, and III) completely reflects this dual aspect of the two systems. At first sight, the choice of multiple carriers, of the frequency bands, of some central frequencies, and of the modulations ? bi-phase shift key (BPSK) and binary offset carrier (BOC) ? indicates a similar system structure. However, a closer look reveals some major differences in the frequency occupation (carrier frequencies, bandwidth, spectrum shape, interplexed signals) of both systems.