Adaptive explicit CSI feedback and overhead reduction

An apparatus, comprising:

• at least one processor;
• and
• at least one non-transitory memory including computer program code,
• the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to at least:
• evaluate, using circuitry of a user terminal, a number of constituent precoders to be used in providing a single vector to include in an explicit channel state information report, to be transmitted from the user terminal to at least one device in a network;
• wherein the evaluating of the number of constituent precoders to be used in providing the single precoder is at least partially based on a measurement using the user terminal comprising:
• a speed of the user terminal, and/or an angular spread associated with the at least one device in the network;
• determine, using the circuitry of the user terminal, the number of constituent precoders based on the user terminal measurement;
• wherein the constituent precoders comprise eigenvectors and the single precoder comprises at least one of a dominant eigenvector and a single vector combined of several eigenvectors;
• wherein determining a number of eigenvectors to be used in providing the single vector comprises determining the angular spread associated with the at least one device in the network based on eigen-decomposition of a channel covariance matrix;
• determine that the single precoder is the dominant eigenvector, in response to a determination that the number of constituent precoders to be used in providing the single precoder is equal to or less than one;
• determine the angular spread based on:
• a power gain difference between respective eigenvalues of the eigenvectors and a dominant eigenvalue;
• and a steering direction difference between respective eigenvectors and the dominant eigenvector;
• combine the constituent precoders to form the single vector in response to a determination that the number of constituent precoders to be used is greater than one;
• and
• configure a signal to transmit the explicit channel state information report including the single precoder from the user terminal to the at least one device in the network.

A non-transitory computer readable medium encoded with instructions that, when executed by a computer, cause performance of:

• evaluating, using circuitry of a user terminal, a number of constituent precoders to be used in providing a single precoder to include in an explicit channel state information report, to be transmitted from the user terminal to at least one device in a network;
• wherein the evaluating of the number of constituent precoders to be used in providing the single precoder is at least partially based on a measurement using the user terminal comprising:
• a speed of the user terminal, and/or an angular spread associated with the at least one device in the network;
• determining, using the circuitry of the user terminal, the number of constituent precoders based on the user terminal measurement;
• wherein the constituent precoders comprise eigenvectors and the single precoder comprises at least one of a dominant eigenvector and a single vector combined of several eigenvectors;
• wherein determining a number of eigenvectors to be used in providing the single vector comprises determining the angular spread associated with the at least one device in the network based on eigen-decomposition of a channel covariance matrix;
• determining that the single precoder is the dominant eigenvector, in response to a determination that the number of constituent precoders to be used in providing the single precoder is equal to or less than one;
• determining the angular spread based on:
• a power gain difference between respective eigenvalues of the eigenvectors and a dominant eigenvalue;
• and a steering direction difference between respective eigenvectors and the dominant eigenvector;
• combining the constituent precoders to form the single precoder in response to a determination that the number of constituent precoders to be used in providing the single precoder is greater than one;
• and
• configuring a signal to transmit the explicit channel state information report including the single precoder from the user terminal to the at least one device in the network.