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

A method performed by a radio remote unit (RRU) of a distributed base station system;

• the RRU being connected to N antennas, the distributed base station system further comprising a base band unit (BBU) connected to the RRU over a fronthaul link;
• the method comprising:
• receiving, from the BBU, K user-layer downlink signals to be sent to a number of User Equipments (UEs) wirelessly connected to the RRU;
• receiving, from the BBU, a first part of beamforming weights and a compressed second part of beamforming weights for beamforming the K user-layer signals;
• the first and second parts of the beamforming weights being determined by the BBU from a downlink channel estimate;
• decompressing the compressed second part of the beamforming weights;
• beamforming the received K user-layer signals into antenna signals using the first part and the decompressed second part of the beamforming weights;
• sending the antenna signals to the number of UEs via the N antennas;
• wherein the user-layer signals are beamformed so that the first part of the beamforming weights are adapted for interference cancellation between the user-layer signals, and the second part of the beamforming weights are adapted for expanding the user-layer signals to antenna signals.

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 fronthaul link, with the RRU further having N antennas;
• the BBU system comprising:
• processing circuitry;
• memory containing instructions executable by the processing circuitry whereby the BBU is operative to:
• determine a second part of beamforming weights based on a determined downlink channel estimate;
• compress the second part of the beamforming weights;
• determine a first part of the beamforming weights based on the determined downlink channel estimate;
• wherein the first and the second part of the beamforming weights are to be used for beamforming K user-layer downlink signals to be sent to a number of User Equipments (UEs) wirelessly connected to the RRU;
• trigger sending the first part of the beamforming weights and the compressed second part of the beamforming weights to the RRU;
• trigger sending the K user-layer signals to the RRU;
• wherein the first part of the beamforming weights are determined for performing interference cancellation between the user-layer signals;
• wherein the second part of the beamforming weights are determined for expanding the user-layer signals to antenna signals.

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 configured to be connected to N antennas;
• the RRU comprising:
• processing circuitry;
• memory containing instructions executable by the processing circuitry whereby the RRU is operative to:
• receive, from the BBU, K user-layer downlink signals to be sent to a number of UEs wirelessly connected to the RRU;
• receive, from the BBU, a first part of beamforming weights and a compressed second part of beamforming weights for beamforming the K user-layer signals, the first and the second part of the beamforming weights being determined by the BBU from a downlink channel estimate;
• decompress the compressed second part of the beamforming weights;
• beamform the received K user-layer signals into antenna signals using the first part and the decompressed second part of the beamforming weights;
• send the antenna signals to the number of UEs via the N antennas;
• wherein the user-layer signals are beamformed so that the first part of the beamforming weights are adapted for interference cancellation between the user-layer signals, and the second part of the beamforming weights are adapted for expanding the user-layer signals to antenna signals.