Techniques for beamforming in multi-user systems

A user terminal, comprising:

• a digital precoder and an analog precoder which are configured to precode a second training signal;
• a radio transceiver configured to transmit the precoded second training signal and to receive a precoded first training signal in response to transmission of the precoded second training signal;
• and
• a controller configured to, after each reception of the first training signal in a ping-pong process including multiple transmissions of second training signals and receptions of first training signals:
• adjust a precoding of the digital precoder based on processing of the first training signal with respect to a normalization criterion;
• cause the radio transceiver to transmit a subsequent second training signal, and
• after transmission of the subsequent second training signal, adjust a precoding of the analog precoder based on processing of the first training signal using a codebook selection according to a multi-user beamforming criterion.

A multi-user precoding method, comprising:

• precoding, by a digital precoder and an analog precoder, a first training signal;
• transmitting the precoded first training signal by a radio transceiver;
• receiving a precoded second training signal by the radio transceiver upon transmission of the precoded first training signal;
• and
• after each reception of the second training signal in a ping-pong process including multiple transmissions of first training signals and receptions of second training signals:
• adjusting a precoding of the digital precoder based on processing the second training signal with respect to a normalization criterion;
• transmitting a subsequent first training signal;
• and
• after transmission of the subsequent first training signal, adjusting a precoding of the analog precoder based on processing the second training signal with respect to a multi-user beamforming criterion.

A precoding method, comprising:

• precoding a second training signal by a digital precoder and an analog precoder;
• transmitting the precoded second training signal by a radio transceiver;
• receiving a precoded first training signal by the radio transceiver upon transmission of the precoded second training signal;
• and
• after each reception of the first training signal in a ping-pong process including multiple transmissions of second training signals and receptions of first training signals:
• adjusting a precoding of the digital precoder based on processing the first training signal with respect to a normalization criterion;
• transmitting a subsequent second training signal;
• and
• after transmission of the subsequent second training signal, adjusting a precoding of the analog precoder based on processing the first training signal with respect to a beamforming criterion.

A multi-user precoding device, comprising:

• means for precoding a first training signal by a digital precoder and an analog precoder;
• means for transmitting the precoded first training signal by a radio transceiver;
• means for receiving a precoded second training signal by the radio transceiver upon transmission of the precoded first training signal;
• and
• means for adjusting a precoding of the digital precoder based on processing the second training signal with respect to a normalization criterion;
• causing the means for transmitting to transmit a subsequent first training signal;
• and, after transmission of the subsequent first training signal, adjusting a precoding of the analog precoder based on processing the second training signal with respect to a multi-user beamforming criterion.

A precoding system for serving multiple user terminals, the precoding system comprising:

• a digital precoder and an analog precoder component which are configured to precode a first training signal;
• a radio transceiver component configured to transmit the precoded first training signal and to receive a precoded second training signal upon transmission of the precoded first training signal;
• and
• a controller component configured to, after each reception of the second training signal in a ping-pong process including multiple transmissions of first training signals and receptions of second training signals:
• adjust a precoding of the digital precoder based on processing the second training signal with respect to a normalization criterion;
• cause the radio transceiver component to transmit a subsequent first training signal, and
• after transmission of the subsequent first training signal, to adjust a precoding of the analog precoder based on processing of the second training signal using a codebook selection according to a multi-user beamforming criterion.