Codebook subset restriction for full-dimension MIMO

A method, in a wireless device operating in a wireless network, the method comprising:

• receiving, from a radio network node, a bitmap indicating, among a predetermined codebook of precoding matrix codewords, a subset of precoding matrix codewords that are not to be reported by the wireless device in channel-state-information (CSI) feedback;
• and
• identifying, using the bitmap, the subset of precoding matrix codewords that are not to be reported by the wireless device in CSI feedback,
• wherein each bit in the bitmap corresponds to only one combination of a first dimension index l′1 and a second dimension index l′2 out of possible combinations of the first dimension index l′1 and the second dimension index l′2, and wherein the first dimension index l′1 and the second dimension index l′2 identify a two-dimensional beam, the two-dimensional beam being defined by a vector of complex numbers comprised within at least one column of a precoding matrix codeword in the codebook, and wherein the bits of the bitmap are indexed with index n and the index n for any given bit in the bitmap equals a linear combination of the form n=l′2+Cl′1, where C is a positive integer, and l′1 and l′2 are first and second dimension indices, respectively, for the two-dimensional beam identified by the bit.

A radio network node, for configuring a wireless device in a wireless network, the radio network node comprising processing circuitry and a memory, said memory containing instructions executable by said processing circuitry, whereby said radio network node is configured to:

• identify, among a predetermined codebook of precoding matrix codewords, a subset of precoding matrix codewords that are not to be reported by the wireless device in channel-state-information (CSI) feedback;
• and
• transmit, to the wireless device, a bitmap identifying the subset of precoding matrix codewords that are not to be reported by the wireless device;
• wherein each bit in the bitmap corresponds to only one combination of a first dimension index l′1 and a second dimension index l′2 out of the possible combinations of the first dimension index l′1 and the second dimension index l′2, and wherein the first dimension index l′1 and the second dimension index l′2 identify a two-dimensional beam, the two-dimensional beam being defined by a vector of complex numbers comprised within at least one column of a precoding matrix codeword in the codebook, and wherein the bits of the bitmap are indexed with index n and the index n for any given bit in the bitmap equals a linear combination of the form n=l′2+Cl′1, where C is a positive integer, and l′1 and l′2 are first and second dimension indices, respectively, for the two-dimensional beam identified by the bit.

A wireless device for operating in a wireless network, the wireless device comprising processing circuitry and a memory, said memory containing instructions executable by said processing circuitry, whereby said wireless device is configured to:

• receive, from a radio network node, a bitmap indicating, among a predetermined codebook of precoding matrix codewords, a subset of precoding matrix codewords that are not to be reported by the wireless device in channel-state-information (CSI) feedback;
• and
• identify, using the bitmap, the subset of precoding matrix codewords that are not to be reported by the wireless device in CSI feedback,
• wherein each bit in the bitmap corresponds to only one combination of a first dimension index l′1 and a second dimension index l′2 out of possible combinations of the first dimension index l′1 and the second dimension index l′2, and wherein the first dimension index l′1 and the second dimension index l′2 identify a two-dimensional beam, the two-dimensional beam being defined by a vector of complex numbers comprised within at least one column of a precoding matrix codeword in the codebook, and wherein the bits of the bitmap are indexed with index n and the index n for any given bit in the bitmap equals a linear combination of the form n=l′2+Cl′1, where C is a positive integer, and l′1 and l′2 are first and second dimension indices, respectively, for the two-dimensional beam identified by the bit.