Rigth next to the Vodafone site, o2 has a site, that is sending out 3G for some time and since September 2019 LTE on Band 3 as well. The 3 antennas are at one mast at Am Elsenbruch 5 close to the crossing Telowkanalstraße / Am Elsenbruch, which is also very close to o2's 4G site at Siemensstraße.
Rear view from the south-east with the o2 mast to the left, and one of two neighboring Vodafone masts to the right:
The o2 mast to the right of the Vodafone mast seen from the opposite river side north-west:
Construction works on the old o2 panels in late February 2019; seen from south at Am Elsenbruch (two of the vodafone antennas on the right):