A method performed by a distributed base station system of a wireless communication network, the distributed base station system comprising a remote radio unit, RRU , and a base band unit, BBU, connected to the RRU over a fronthaul link , the RRU being connected to N antennas , the method comprising: obtaining , by the RRU , uplink signals y as received at the N antennas from a number of User Equipment, UEs , wirelessly connected to the RRU , the N uplink signals comprising K user-layer signals overlaid with J interference signals and noise; obtaining , by the RRU , a channel estimation matrix Ĥ of wireless communication channels H between the number UEs and the N antennas from reference signals y ref, l as received at the N antennas from the number of UEs; determining , by the RRU , an interference covariance estimation matrix R̂ based on the obtained channel estimation matrix Ĥ and on other channel information different from the channel estimation matrix; sending , by the RRU , information on the channel estimation matrix Ĥ and on the interference covariance estimation matrix R̂ over the fronthaul link to the BBU ; determining , by the RRU , intermediate signals ỹ , based on the uplink signals y, the channel estimation matrix Ĥ and the interference covariance estimation matrix R̂ , the intermediate signals having K+L components, where (K+L) is smaller than N, and L is larger than zero; sending , by the RRU , the determined intermediate signals ŷ over the fronthaul link to the BBU ; determining , by the BBU , a beamforming matrix W K based on the information sent by the RRU on the channel estimation matrix Ĥ and on the interference covariance estimation matrix R̂ , and determining , by the BBU , output signals r, which are estimations of the K user-layer signals, by multiplying the intermediate signals ŷ sent by the RRU with beamforming weights of the beamforming matrix W K . obtaining , by the RRU , uplink signals y as received at the N antennas from a number of User Equipment, UEs , wirelessly connected to the RRU , the N uplink signals comprising K user-layer signals overlaid with J interference signals and noise; obtaining , by the RRU , a channel estimation matrix Ĥ of wireless communication channels H between the number UEs and the N antennas from reference signals y ref, l as received at the N antennas from the number of UEs; determining , by the RRU , an interference covariance estimation matrix R̂ based on the obtained channel estimation matrix Ĥ and on other channel information different from the channel estimation matrix; sending , by the RRU , information on the channel estimation matrix Ĥ and on the interference covariance estimation matrix R̂ over the fronthaul link to the BBU ; determining , by the RRU , intermediate signals ỹ , based on the uplink signals y, the channel estimation matrix Ĥ and the interference covariance estimation matrix R̂ , the intermediate signals having K+L components, where (K+L) is smaller than N, and L is larger than zero; sending , by the RRU , the determined intermediate signals ŷ over the fronthaul link to the BBU ; determining , by the BBU , a beamforming matrix W K based on the information sent by the RRU on the channel estimation matrix Ĥ and on the interference covariance estimation matrix R̂ , and determining , by the BBU , output signals r, which are estimations of the K user-layer signals, by multiplying the intermediate signals ŷ sent by the RRU with beamforming weights of the beamforming matrix W K . <EOS>