"New signal processing challenges arise with the transition from GPS only to combined Galileo/GPS, e.g. due to the BOC Modulation scheme or longer PRN sequences, which require high bandwidth signal processing capabilities of high complexity. Therefore, a flexible architecture that enables reuse of communication and signal processing components throughout the different navigation standards is a possible solution for a multi-standard receiver... The received signal can either be correlated with the GPS C/A code or with a Galileo PRN code. Even though Galileo BOC signals require additional correlators (very-early and very-late code replicas besides the early, prompt, and late correlators for GPS C/A code), the basic architecture remains the same. It is therefore possible, to form a combined correlation processor architecture, where the early-prompt-late correlator structure is used for both Galileo and GPS signals, while the additional correlators required for Galileo are activated only on demand. This allows to switch between Galileo and GPS signals during runtime."*

Think that means a new gizmo will need a Galileo/GPS 'switch' :-)

"Bell said that potentially the most serious military issue related to Galileo/GPS compatibility and interoperability is that the European Commission is considering placing one of the four services proposed by Galileo directly on top of -- or "overlaying" -- the "M-Code," the encrypted future military GPS capability that will be used by U.S. and NATO forces for crucial military operations.

"If the Galileo signal directly overlays the GPS M-code signal, he warned, "jamming one would also jam the other, resulting in a negative impact on NATO's military effectiveness in the area of operations, potentially risking fratricide on friendly forces and civil populations." **

Mmm... more going on here than meets the eye (in the sky :-)

* http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=121495&sk=&date=&pageID=4

** http://www.useu.be/Galileo/June1902NATOBellGalileoGPS.html