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 (121, 122, 123), the method comprising: obtaining, by the RRU, uplink signals y as received at the N antennas (121, 122, 123) from a number of User Equipment, UEs (131, 132, 133), 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 (131, 132, 133) and the N antennas (121, 122, 123) 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 (121, 122, 123) from a number of User Equipment, UEs (131, 132, 133), 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 (131, 132, 133) and the N antennas (121, 122, 123) 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.