Precoding a Transmission From an Antenna Array That Includes Co-Polarized Antenna Elements Aligned in a Given Spatial Dimension

A method for receiving a transmission from an antenna array that includes co-polarized antenna elements aligned in a given spatial dimension of the array, wherein the antenna array is associated with a transmitting radio node, wherein the method is performed by a receiving radio node and comprises:

• receiving a first reference signal transmitted from the antenna array;
• based on measurement of the first reference signal, generating a first type of recommendation that recommends either:
• a multi-granular precoder in a multi-granular codebook targeting the given spatial dimension of the array at different granularities, each multi-granular precoder in the codebook comprising a combination of a coarse-granularity precoder and one or more finer-granularity precoders;
• or
• a coarse-granularity precoder in a coarse-granularity codebook and one or more finer-granularity precoders in one or more finer-granularity codebooks, the combination of which corresponds to a multi-granular precoder targeting the given spatial dimension of the array at different granularities;
• transmitting the first type of recommendation to the transmitting radio node;
• receiving a second reference signal transmitted from the antenna array;
• based on measurement of the second reference signal, generating a second type of recommendation that recommends one or more finer-granularity precoders factorizable from a multi-granular precoder;
• transmitting the second type of recommendation to the transmitting radio node;
• and
• receiving from the antenna array a data transmission that is precoded based on the first and second types of recommendations.

A method for receiving a transmission from an antenna array that includes co-polarized antenna elements aligned in a given spatial dimension of the array, wherein the antenna array is associated with a transmitting radio node, wherein the method is performed by a receiving radio node and comprises:

• receiving codebook subset restriction signaling from the transmitting radio node that indicates one or more coarse-granularity precoders, each coarse-granularity precoder factorizable along with one or more finer-granularity precoders from a multi-granular precoder targeting the given spatial dimension of the array at different granularities;
• and
• based on said signaling, restricting precoders from which the receiving radio node selects for recommending to the transmitting radio node to a subset of precoders in a codebook that correspond to the one or more indicated coarse-granularity precoders;
• transmitting to the transmitting radio node a recommended precoder that is selected according to said restricting;
• and
• receiving from the antenna array a data transmission that is precoded based on the recommended precoder.

A receiving radio node configured to receive a transmission from an antenna array that includes co-polarized antenna elements aligned in a given spatial dimension of the array, wherein the antenna array is associated with a transmitting radio node, the receiving radio node comprising one or more processing circuits and a memory, the memory containing program code executable by the one or more processing circuits whereby the receiving radio node is configured to

• receive a first reference signal transmitted from the antenna array;
• based on measurement of the first reference signal, generate a first type of recommendation that recommends either:
• a multi-granular precoder in a multi-granular codebook targeting the given spatial dimension of the array at different granularities, each multi-granular precoder in the codebook comprising a combination of a coarse-granularity precoder and one or more finer-granularity precoders;
• or
• a coarse-granularity precoder in a coarse-granularity codebook and one or more finer-granularity precoders in one or more finer-granularity codebooks, the combination of which corresponds to a multi-granular precoder targeting the given spatial dimension of the array at different granularities;
• transmit the first type of recommendation to the transmitting radio node;
• receive a second reference signal transmitted from the antenna array;
• based on measurement of the second reference signal, generate a second type of recommendation that recommends one or more finer-granularity precoders factorizable from a multi-granular precoder in the multi-granular codebook, without also recommending a coarse-granularity precoder;
• transmit the second type of recommendation to the transmitting radio node;
• and
• receive from the antenna array a data transmission that is precoded based on the first and second types of recommendations.

A receiving radio node configured to receive a transmission from an antenna array that includes co-polarized antenna elements aligned in a given spatial dimension of the array, wherein the antenna array is associated with a transmitting radio node, the receiving radio node comprising one or more processing circuits and a memory, the memory containing program code executable by the one or more processing circuits whereby the receiving radio node is configured to:

• receive codebook subset restriction signaling from the transmitting radio node that indicates one or more coarse-granularity precoders, each coarse-granularity precoder factorizable along with one or more finer-granularity precoders from a multi-granular precoder targeting the given spatial dimension of the array at different granularities;
• and
• based on said signaling, restrict precoders from which the receiving radio node selects for recommending to the transmitting radio node to a subset of precoders in a codebook that correspond to the one or more indicated coarse-granularity precoders;
• transmit to the transmitting radio node a recommended precoder that is selected according to said restricting;
• and
• receive from the antenna array a data transmission that is precoded based on recommended precoder.