Precoding in a multi-user multiple-input multiple-output wireless communication system

A radio network node configured for use in a multi-user multiple-input multiple-output (MU-MIMO) wireless communication system, the radio network node comprising communication circuitry and processing circuitry whereby the radio network node is configured to:

• precode a downlink reference signal to suppress the downlink reference signal in a certain direction that is subject to interference between MU-MIMO uplink transmissions received in the certain direction from different wireless devices;
• transmit, via the communication circuitry, the precoded downlink reference signal to at least a first one of the wireless devices;
• and
• transmit, via the communication circuitry, signaling indicating that the precoded downlink reference signal is usable by the first wireless device to derive a non-codebook based precoding of an uplink reference signal transmitted by the first wireless device.

A non-transitory computer-readable medium on which is stored instructions that, when executed by a processor of a radio network node configured for use in a multi-user multiple-input multiple-output (MU-MIMO) wireless communication system, causes the radio network node to:

• precode a downlink reference signal to suppress the downlink reference signal in a certain direction that is subject to interference between MU-MIMO uplink transmissions received in the certain direction from different wireless devices;
• transmit the precoded downlink reference signal to at least a first one of the wireless devices;
• and
• transmit signaling indicating that the precoded downlink reference signal is usable by the first wireless device to derive a non-codebook based precoding of an uplink signal transmitted by the first wireless device.