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 between a user terminal and an eNB base station of the first communication system and between the same or another user terminal and a gNB base station of the second communication system , wherein each of the eNB and gNB base stations 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 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 , and wherein the sizes of the first and second sets are dynamically negotiated between the eNB and gNB base stations 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 use overlapping frequency bands for their uplink radio frames (F j , H k ), and in that the eNB and gNB base stations 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 between a user terminal and an eNB base station of the first communication system and between the same or another user terminal and a gNB base station of the second communication system , wherein each of the eNB and gNB base stations 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 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 , and wherein the sizes of the first and second sets are dynamically negotiated between the eNB and gNB base stations 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 use overlapping frequency bands for their uplink radio frames (F j , H k ), and in that the eNB and gNB base stations 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′′′). <EOS>