The risks and limitations of GNSS live sky testing within a production ...

However, for those requiring a rigorous GPS test environment,
live sky testing has some serious limitations including a lack of
repeatability, control and scalability. Depending on the application,
it can also turn out to be a resource intensive test method with
potentially negative impacts on time to market, development and
support costs. There is also the issue that in some countries reradiation
of GNSS signals is illegal.
SPIRENT eBook Page 10