Methods, distributed base station system, remote radio unit and base band unit system for handling uplink signals

A method performed by a Base Band Unit, BBU, system of a wireless communication network, the wireless communication network comprising a distributed base station system having a BBU and a Remote Radio Unit, RRU, connected to the BBU over a fronthaul link, the RRU having N antennas, the method comprising:

• receiving, from the RRU, a plurality of intermediate signals {tilde over (y)} with K+L components, where (K+L) is smaller than N, determined by the RRU based on a channel estimation matrix Ĥ, on an interference covariance estimation matrix {circumflex over (R)} determined based on the channel estimation matrix Ĥ and on other channel information different from the channel estimation matrix, and on uplink signals y with N components as received by the N antennas from a number of UEs, the uplink signals y comprising K user-layer signals overlaid with J interference signals and noise, where L is a number of fronthaul streams transported via the fronthaul link additional to K;
• receiving, from the RRU, information on the channel estimation matrix Ĥ and on the interference covariance estimation matrix {circumflex over (R)};
• determining a beamforming matrix WK based on the received information on the channel estimation matrix Ĥ and on the interference covariance estimation matrix {circumflex over (R)}, and
• determining output signals r, which are an estimation of the K user-layer signals, by multiplying the intermediate signals {tilde over (y)} with beamforming weights of the beamforming matrix WK.

A Remote Radio Unit, RRU, operable in a distributed base station system of a wireless communication network, the distributed base station system further comprising a base band unit, BBU, connected to the RRU over a fronthaul link, the RRU being operable to be connected to N antennas, the RRU comprising a processing circuitry and a memory, said memory containing instructions executable by said processing circuitry, whereby the RRU is operative for:

• obtaining uplink signals y as received at the N antennas from a number of User Equipment (UEs) wireles sly connected to the RRU, the uplink signals comprising K user-layer signals overlaid with J interference signals and noise;
• obtaining a channel estimation matrix Ĥ of wireless communication channels H between the number UEs and the N antennas from reference signals yref,l as received at the N antennas from the number of UEs;
• determining an interference covariance estimation matrix {circumflex over (R)} based on the obtained channel estimation matrix Ĥ and on other channel information different from the channel estimation matrix;
• sending information on the channel estimation matrix Ĥ and on the interference covariance estimation matrix {circumflex over (R)} over the fronthaul link to the BBU;
• determining intermediate signals {tilde over (y)}, based on the uplink signals y, the channel estimation matrix Ĥ and the interference covariance estimation matrix {circumflex over (R)}, the intermediate signals having K+L components, where (K+L) is smaller than N, and L is larger than zero and L is a number of fronthaul streams transported via the fronthaul link additional to K, and
• sending to the BBU over the fronthaul link, the determined intermediate signals {tilde over (y)}.

A Base Band Unit, BBU, system operable in a wireless communication network, the wireless communication network comprising a distributed base station system having a BBU and a Remote Radio Unit, RRU, connected to the BBU over a front haul connection, the RRU having N antennas, the BBU system comprising a processing circuitry and a memory, said memory containing instructions executable by said processing circuitry, whereby the BBU system is operative for:

• receiving, from the RRU, a plurality of intermediate signals {tilde over (y)} with K+L components, where (K+L) is smaller than N, determined by the RRU based on a channel estimation matrix Ĥ, on an interference covariance estimation matrix {circumflex over (R)} determined based on the channel estimation matrix Ĥ and on other channel information different from the channel estimation matrix, and on uplink signals y with N components as received by the N antennas from a number of UEs, the uplink signals y comprising K user-layer signals overlaid with J interference signals and noise, where L is a number of fronthaul streams transported via the fronthaul link additional to K;
• receiving, from the RRU, information on the channel estimation matrix Ĥ and on the interference covariance estimation matrix {circumflex over (R)};
• determining a beamforming matrix WK based on the received information on the channel estimation matrix Ĥ and on the interference covariance estimation matrix {circumflex over (R)}, and
• determining output signals r, which are an estimation of the K user-layer signals, by multiplying the intermediate signals {tilde over (y)} with beamforming weights of the beamforming matrix WK.