Technique for precoder determination

A method of determining a precoder for a radio transmission from a base station to a mobile device via a channel including two or more transmit antennas, the method comprising:

• measuring at least one of a channel state (H) of the channel and a channel noise characteristic (N) of the channel;
• computing, based on a first objective function and the measurement, a first parameter indicative of a coarse direction of emission corresponding to a subset of precoders in a codebook including a plurality of precoders parametrized by the first parameter and a second parameter;
• selecting, based on the first parameter, the corresponding subset of precoders from the codebook;
• computing, based on a second objective function and the measurement, a second parameter that distinguishes different precoders in the subset;
• and
• determining, based on the second parameter, a precoder for precoding the transmission from the subset;
• wherein the first objective function is g(W,R)=det(I+WH R W), W denotes a precoder out of the codebook as a candidate precoder for the subset, R denotes a relation between the transmit antennas or groups of the transmit antennas and depends on the result of the measurement, and I is a unity matrix.

A computer program product stored in a non-transitory computer readable medium for determining a precoder for a radio transmission from a base station to a mobile device via a channel including two or more transmit antennas, the computer program product comprising software instructions which, when run one or more processing circuits of a computing device, causes the computing device to:

• measure at least one of a channel state (H) of the channel and a channel noise characteristic (N) of the channel;
• compute, based on a first objective function and the measurement, a first parameter indicative of a coarse direction of emission corresponding to a subset of precoders in a codebook including a plurality of precoders parametrized by the first parameter and a second parameter;
• select, based on the first parameter, the corresponding subset of precoders from the codebook;
• compute, based on a second objective function and the measurement, a second parameter that distinguishes different precoders in the subset;
• and
• determine, based on the second parameter, a precoder for precoding the transmission from the subset;
• wherein the first objective function is g(β,R)=Σm,n rm,n ej(m-n)β, where β denotes the first parameter, and rm,n denotes a correlation between the transmit antennas or groups of the transmit antennas and depends on the result of the measurement.

A mobile device comprising an apparatus for determining a precoder for a radio transmission from a base station via a channel including two or more transmit antennas, the apparatus comprising:

• a processing circuit;
• memory containing instructions executable by the processing circuitry whereby the mobile device is operative to:
• measure at least one of a channel state (H) of the channel and a channel noise characteristic (N) of the channel;
• compute, based on a first objective function and the measurement, a first parameter indicative of a coarse direction of emission corresponding to a subset of precoders in a codebook including a plurality of precoders parametrized by the first parameter and a second parameter;
• select, based on the first parameter, the corresponding subset of precoders from the codebook;
• compute, based on a second objective function and the measurement, a second parameter that distinguishes different precoders in the subset;
• and
• determine, based on the second parameter, a precoder for precoding the transmission from the subset;
• wherein the first objective function is g(β,R)=Σm,n rm,n ej(m-n)β, where β denotes the first parameter, and rm,n denotes a correlation between the transmit antennas or groups of the transmit antennas and depends on the result of the measurement.