For anyone developing a GNSS-enabled device, the ability to test it with reliability and repeatability will shorten development times, and reduce costs.
No matter what market a new GPS/GNSS product is aimed at, or the features that it contains, testing will be a necessity. Signal acquisition, retention, and performance in varying environments, are all key factors in determining how successful a new device might be.
It isn't enough to simply go outside, obtain satellite lock, and sign off as a completed test procedure. This is not how the unit will actually be used: in many cases, it will be subjected to multipath reflection, obscuration, or interference, so understanding how a device will perform in these situations is vital. However, introducing these variables into a 'real world' testing schedule may be wholly impractical and will have a large impact on the amount of time it takes to bring the product to market.
A GPS simulator gives the developer a number of advantages. The most obvious is that of convenience – being able to replay raw RF satellite signals directly into GPS equipment in the confines of the lab or office, without having to venture outdoors, clearly makes testing easier.