I don't know the exact configuration Airtel was using as i don't have a rooted device (or something convenient like Samsung's engineering mode) but Airtel was on carrier aggregation during most of my underground metro travelling
I also tried Jio on Kalkaji metro station (which is underground) on the platform and initially got 130-135 Mbps which throttled down to 100 Mbps and was using carrier aggregation.
I also tried Jio on Kalkaji metro station (which is underground) on the platform and initially got 130-135 Mbps which throttled down to 100 Mbps and was using carrier aggregation.