If I use a mobile modem and I have my 945 link with WiFi, is It possibile use live track? If not, how I can do it without smartphone that is usually too much big and heavy for running?
This is a very special case. Not many users are carrying around LTE routers. Most users got their phones so they can take photos, call for help etc. A solution that works is that you get yourself a tiny phone that runs Android and Garmin Connect. A phone can also work as an LTE router and act as a wifi hotspot.
Here is a recent discussion about just that: Smallest possible android phone that can run Garmin Connect