UE aided antenna calibration for NR-optimal port to antenna mapping

1 . A method implemented in a base station for a cellular communications system, the method comprising:

retrieving a plurality of phase rotations associated with a codebook for precoding matrix indicator, PMI, feedback;

transmitting, to a User Equipment, UE, a plurality of Channel State Information Reference Signals, CSI-RSs, on a plurality of beams that correspond to the plurality of phase rotations;

receiving, from the UE, a plurality of precoding matrix indicators (PMIs) associated with the plurality of CSI-RSs, respectively, wherein the plurality of PMIs are indicative of a plurality of quantized precoding matrices from the codebook; and

combining the plurality of quantized precoding matrices based on the plurality of phase rotations to compute an estimated precoding matrix as:

where:

W k is the estimated precoding matrix for a k-th subband in which the plurality of CSI-RSs are transmitted;

W′ k,nr is a quantized precoding matrix indicated by a PMI received for a non-rotated CSI-RS;

w′ k,i for i=0 to N−1 are the plurality of quantized precoding matrices indicated by the received PMIs, where N is the number of CSI-RSs in the plurality CSI-RSs; and

Ω (i) for i=0 to N−1 are the plurality of phase rotations; and

the estimated precoding matrix is used for estimating at least one of phase errors or delay errors for a plurality of transmit antenna branches of the base station.

2 . The method of claim 1 further comprising transmitting signals from the base station to the UE while compensating for the estimated at least one of the phase errors or the delay errors.

3 . The method of claim 1 wherein the plurality of phase rotations are a function of the codebook.

4 . The method of claim 3 wherein the codebook comprises a plurality of matrices each corresponding to a different set of precoding weights, and the plurality of phase rotations are such that, for any two phase rotations Ω (i) and Ω (j) from among the plurality of phase rotations and any two matrices w k and w l from among the plurality of matrices comprised in the codebook, a minimum distance between a respective first phase rotated vector Ω (i) W k and a respective second phase rotated vector Ω (j) w l is maximized.

5 . A base station for a cellular communications system, the base station comprising processing circuitry configured to cause the base station to:

retrieve a plurality of phase rotations associated with a codebook for precoding matrix indicator, PMI, feedback;

transmit, to a User Equipment, UE, a plurality of Channel State Information Reference Signals, CSI-RSs, on a plurality of beams that correspond to the plurality of phase rotations;

receive, from the UE, a plurality of precoding matrix indicators (PMIs) associated with the plurality of CSI-RSs, respectively, wherein the plurality of PMIs are indicative of a plurality of quantized precoding matrices from the codebook; and

combine the plurality of quantized precoding matrices based on the plurality of phase rotations to compute an estimated precoding matrix as:

where:

W k is the estimated precoding matrix for a k-th subband in which the plurality of CSI-RSs are transmitted;

w′ k,nr is a quantized precoding matrix indicated by a PMI received for a non-rotated CSI-RS;

w′ k,i for i=0 to N−1 are the plurality of quantized precoding matrices indicated by the received PMIs, where N is the number of CSI-RSs in the plurality CSI-RSs; and

Ω (i) for i=0 to N−1 are the plurality of phase rotations; and

the estimated precoding matrix is used for estimating at least one of phase errors or delay errors for a plurality of transmit antenna branches of the base station.