Phase error compensation for downlink systems with four correlated and uncalibrated antennas

A network node configured to compensate for phase error between antennas of a four-antenna dual-polarization antenna array of a radio of the network node, the network node comprising:

• processing circuitry configured to apply N incremented phase rotations to one of the four antennas to produce N channel state information reference signal, CSI-RS, resources, N being an integer greater than 1, the N incremented phase rotations being obtained by multiplying a precoder codebook by a diagonal matrix whose diagonal elements are equal to one, except for one diagonal element corresponding to the one of the four antennas and being equal to exp(j2πn/N), where n is an integer from zero to N−1;
• a radio interface in communication with the processing circuitry, the radio interface configured to:
• transmit the N CSI-RS resources on 4 CSI-RS ports to a wireless device, WD, each of the N CSI-RS resources being transmitted with a different one of the incremented phase rotations;
• and
• receive from the WD a CSI-RS resource indication, CRI, indicating a particular one of the N CSI-RS resources;
• and
• the processing circuitry further configured to apply, in subsequent transmissions to the WD, a phase rotation to the one of the four antennas, the phase rotation corresponding to the indicated CSI-RS resource.

A method in a wireless device, WD, the method comprising:

• receiving a signal from a network node, the signal having N channel state information reference signals, CSI-RS, resources transmitted by a four-antenna dual polarization antenna array of a radio of the network node, the signal generated by the network node by applying N incremented phase rotations to one of the four antennas to produce N channel state information reference signal, CSI-RS, resources, N being an integer greater than 1, the N incremented phase rotations being obtained by multiplying a precoder codebook by a diagonal matrix whose diagonal elements are equal to one, except for one diagonal element corresponding to one of the four antennas and being equal to exp(j2πn/N), where n is an integer from zero to N−1;
• determining a CSI-RS resource of the N CSI-RS resources resulting in a highest spectrum efficiency of all the N CSI-RS resources;
• and
• transmitting to the network node a CSI resource indicator, CRI, indicating the determined CSI-RS resulting in the highest spectrum efficiency of all the N CSI-RS resources.

A wireless device, WD, the WD comprising:

• a radio interface configured to receive a signal from a network node, the signal having N channel state information reference signals, CSI-RS, resources transmitted by a four-antenna dual polarization antenna array of a radio of the network node, the signal generated by the network node by applying N incremented phase rotations to one of the four antennas to produce N channel state information reference signal, CSI-RS, resources, N being an integer greater than 1, the N incremented phase rotations being obtained by multiplying a precoder codebook by a diagonal matrix whose diagonal elements are equal to one, except for one diagonal element corresponding to one of the four antennas and being equal to exp(j2πn/N), where n is an integer from zero to N−1;
• processing circuitry in communication with the radio interface, the processing circuitry configured to determine a CSI-RS resource of the N CSI-RS resources resulting in a highest spectrum efficiency of all the N CSI-RS;
• and
• the radio interface further configured to transmit to the network node a CSI resource indicator, CRI, indicating the determined CSI-RS resource resulting in the highest spectrum efficiency of all the N CSI-RS resources.