Method for operating a first communication system according to an LTE standard and a second communication system according to a 5G standard in a same radio coverage area, to be used for communication (14, 15) between a user terminal (4', 4′′′) and an eNB base station of the first communication system and between the same or another user terminal (4', 4′′′) and a gNB base station of the second communication system, wherein each of the eNB and gNB base stations (5, 6) communicates downlink data over a sequence of downlink radio frames (F j, H k) and uplink data over a sequence of uplink radio frames (F j, H k), the downlink as well as the uplink radio frames (F j, H k) each comprising a predetermined number of subframes (SF i), wherein the eNB and gNB base stations (5, 6) are synchronized on a subframe level and use, at least for their downlink radio frames (F j, H k), overlapping frequency bands, wherein, at least for the downlink radio frames (F j, H k), the eNB base station uses a first set of subframes (SF i) for communication and the gNB base station uses a second set of subframes (SF 1) for communication, which first and second sets of subframes (SF 1) do not overlap during communication (14, 15), and wherein the sizes of the first and second sets are dynamically negotiated between the eNB and gNB base stations (5, 6) in response to a current or estimated data traffic volume over the eNB base station and the gNB base station, respectively, characterized in that the eNB and gNB base stations (5, 6) use overlapping frequency bands for their uplink radio frames (F j, H k), and in that the eNB and gNB base stations (5, 6) share coinciding subframes (SF i) of their uplink radio frames (F j, H k) for random-access transmissions received from user terminals (4', 4ʺ, 4′′′). to be used for communication (14, 15) between a user terminal (4', 4′′′) and an eNB base station of the first communication system and between the same or another user terminal (4', 4′′′) and a gNB base station of the second communication system, wherein each of the eNB and gNB base stations (5, 6) communicates downlink data over a sequence of downlink radio frames (F j, H k) and uplink data over a sequence of uplink radio frames (F j, H k), the downlink as well as the uplink radio frames (F j, H k) each comprising a predetermined number of subframes (SF i), wherein the eNB and gNB base stations (5, 6) are synchronized on a subframe level and use, at least for their downlink radio frames (F j, H k), overlapping frequency bands, wherein, at least for the downlink radio frames (F j, H k), the eNB base station uses a first set of subframes (SF i) for communication and the gNB base station uses a second set of subframes (SF 1) for communication, which first and second sets of subframes (SF 1) do not overlap during communication (14, 15), and wherein the sizes of the first and second sets are dynamically negotiated between the eNB and gNB base stations (5, 6) in response to a current or estimated data traffic volume over the eNB base station and the gNB base station, respectively, characterized in that the eNB and gNB base stations (5, 6) use overlapping frequency bands for their uplink radio frames (F j, H k), and in that the eNB and gNB base stations (5, 6) share coinciding subframes (SF i) of their uplink radio frames (F j, H k) for random-access transmissions received from user terminals (4', 4ʺ, 4′′′).