Does GPS work on a separate chip or is GPS built into the LTE modem?

[wibble]

but still uses the Qualcomm binary firmware for the radio layer

Thanks.
Is it possible to replace the radio firmware?

In theory a sufficiently well skilled, resourced and motivated team might be able to do it. In practice I'm not aware of anyone having done so - the skill and resource barriers are pretty high. The closest I'm aware of is OpenBTS.

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Hi.
Pinephone.
Does GPS work on a separate chip or is GPS built into the LTE modem?

in the LTE modem module.

Why was it decided to use the GNSS module as part of the LTE modem, and not separately?
Indeed, if the radio modem has a backdoor for remote connection and control, then the functionality of the GNSS module can be disrupted and the coordinates will not be correct.

Many (most?) LTE modems now have GNSS built in. Using a separate GNSS module means extra cost, board space and power usage. For most people that's a poor trade as their threat model just isn't that extreme. You still wouldn't know whether that GNSS module's firmware had a backdoor via one of its RF interfaces, so you might instead insist on a software defined radio implementation. Even that doesn't help when someone starts messing with the GNSS signals, as is apparently not uncommon in some parts of the world.