A GPS COLD-START is when it has no stored information about the it's last position or which satellites it was receiving. [ no memory back-up battery ] or if it does have a back-up battery , usually a tiny coin cell, but it [gps] was move a great distance between being powered ..or.. if it was a very long time between since it was last powered.
This means that the GPS has no idea where it is or which satellites to look for and it can take quite a while to get a lock.
A WARM-START is when the GPS 'knows' where it was but it does not know which satellites it was receiving signals from. [meaning that the last stored position is close to where it actually is]
This generally takes less than a few minutes... if the GPS was moved a great distance the acquisition time will increase.
A HOT-START is when the GPS knows where is was & where it is, what satellites it saw, and it can acquire a lock it very quickly as a result.
It's pretty much like a reset with out turning off the power.
I've avoided some of the details. but they do also store the UTC [universal time] and a GPS almanac which is data that is used to help determine where the satellites are located. it is always being updated.
A large back plane or ground plane will help to prevent noise generated from devices below it from affecting the GPS receiver as well as preventing interference from GPS signals that are reflected / scattered from below. Some people have used copper clad boards underneath or foil to help with interference.
I do not have any of the Neo series GPS units so I can't compare them personally . But I believe that the LEAH6 is able to receive Galileo and Glonass or do so with a firmware update , and that the NEO6M does not and cannot have it's firmware updated.
There are differences in the quality of different circuit boards that the GPS modules are mounted on and these vary from vendor to vendor.
For example the NeoM8 is more sensitive than the LeaH8 but it may suffer more from interference if it is mounted on a poorly made circuit board.
just to be clear ... the GPS module that is made by U-Blox is the metal module and other manufacturers put these onto circuit boards along with the ceramic patch antenna. So there can be different results in performance for what seems to be the same device.
Try comparing the two different modules with a ground station, in an open area with a clear view of the sky and see which one give a better HDOP, Satellite count, and the least amount of position wandering, then try it again , say in your back yard with partial obstruction of the sky and see the differences. Probably the LEAH6 is the better one of the two. But don't take my word for it try and test them for yourself.
I'm sure that I left out details but my post is getting to be too long.
Regards
Chris
