A method performed by a base station for selecting a transmission rank, wherein the base station is serving a first radio cell and is operating in a shared radio cell environment where a single physical-layer cell identity ( abbreviated PCI) is shared among the base station and radio units serving other radio cells, and wherein the base station and the radio units are transmission points serving one or several user equipments in respective radio cells utilizing said single PCI, the method comprising: receiving a channel-state report from a user equipment; estimating a channel quality parameter, which reflects a relation (Δ) between estimated receive power on a data channel allocated to the user equipment and estimated receive power on a control channel allocated to the user equipment; and selecting the transmission rank on the basis of the received channel-state report as well as the estimated channel quality parameter, characterized in that, estimating the channel quality parameter comprises: deriving the relation (Δ) between estimated receive power on said data channel and estimated receive power on said control channel from respective transmit powers of selected transmission points of said data channel and said control channel, respectively, and wherein deriving the relation (Δ) between estimated receive power on said data channel and estimated receive power on said control channel from selected transmission points of said data channel (Sd) and said control channel (Sc), respectively, comprises: collecting (321 a) data related to the respective transmit powers (P i) of the selected transmission points of said data channel and said control channel, respectively; for each transmit power, calculating (321 b) a product from the transmit power (P i) multiplied by a respective path gain (G i); calculating (321 c) a sum (∑ i ∈ Sd Gi × Pi) of all products related to said data channel; calculating (321 d) a sum (∑ i ∈ Sc Gi × Pi) of all products related to said control channel; and calculating (321 e) a quotient ∑ i ∈ S d Gi × Pi ∑ i ∈ S c Gi × Pi from the sum (∑ i ∈ Sd Gi × Pi) of all products related to said data channel and the sum (∑ i ∈ Sc Gi × Pi) of all products related to said control channel. receiving a channel-state report from a user equipment; estimating a channel quality parameter, which reflects a relation (Δ) between estimated receive power on a data channel allocated to the user equipment and estimated receive power on a control channel allocated to the user equipment; and selecting the transmission rank on the basis of the received channel-state report as well as the estimated channel quality parameter, characterized in that, estimating the channel quality parameter comprises: deriving the relation (Δ) between estimated receive power on said data channel and estimated receive power on said control channel from respective transmit powers of selected transmission points of said data channel and said control channel, respectively, and wherein deriving the relation (Δ) between estimated receive power on said data channel and estimated receive power on said control channel from selected transmission points of said data channel (Sd) and said control channel (Sc), respectively, comprises: collecting (321 a) data related to the respective transmit powers (P i) of the selected transmission points of said data channel and said control channel, respectively; for each transmit power, calculating (321 b) a product from the transmit power (P i) multiplied by a respective path gain (G i); calculating (321 c) a sum (∑ i ∈ Sd Gi × Pi) of all products related to said data channel; calculating (321 d) a sum (∑ i ∈ Sc Gi × Pi) of all products related to said control channel; and calculating (321 e) a quotient ∑ i ∈ S d Gi × Pi ∑ i ∈ S c Gi × Pi from the sum (∑ i ∈ Sd Gi × Pi) of all products related to said data channel and the sum (∑ i ∈ Sc Gi × Pi) of all products related to said control channel. deriving the relation (Δ) between estimated receive power on said data channel and estimated receive power on said control channel from respective transmit powers of selected transmission points of said data channel and said control channel, respectively, and wherein deriving the relation (Δ) between estimated receive power on said data channel and estimated receive power on said control channel from selected transmission points of said data channel (Sd) and said control channel (Sc), respectively, comprises: collecting (321 a) data related to the respective transmit powers (P i) of the selected transmission points of said data channel and said control channel, respectively; for each transmit power, calculating (321 b) a product from the transmit power (P i) multiplied by a respective path gain (G i); calculating (321 c) a sum (∑ i ∈ Sd Gi × Pi) of all products related to said data channel; calculating (321 d) a sum (∑ i ∈ Sc Gi × Pi) of all products related to said control channel; and calculating (321 e) a quotient ∑ i ∈ S d Gi × Pi ∑ i ∈ S c Gi × Pi from the sum (∑ i ∈ Sd Gi × Pi) of all products related to said data channel and the sum (∑ i ∈ Sc Gi × Pi) of all products related to said control channel.