On the BMW TV system, you do exactly the same as you do at home:

At home: add a digital TV receiver, connected to the house antenna and to the TV AV-IN

In the car: add a digital TV receiver, connected to the car antenna and to the TV AV-IN

In the car, you will need the following features:
1. 12V power source
2. Remote control IR-eye
3. Antenna connector adapter and DC-blocker

That's all