Is passive GPS retransmission possible?
We've done this for a development project that involved GPS reception. We just wanted to be able to get a GPS signal indoors at our engineering office, for basic development of the GPS drivers.

We put a good quality GPS antenna on the roof, with coax going down into the office below. On the ceiling of the office, the coax connected to a GPS-band RF amplifier, which output through an antenna also on the ceiling.

It was a low power amplifier, so it only radiated an effective signal over a short distance within the office space--less than 10 metres. But that was enough to serve our purposes.

The other equipment we used sometimes was a GPS simulator, which simulated a bunch of satellites, and could convince a GPS unit that it was at any location of our choosing. It radiated through an antenna, again, at low signal levels so it disrupted only a small area. And we only used it indoors, within our offices.