System and method of rank adaptation in mimo communication system

A method comprising:

• causing, at a baseband processor for user equipment (UE)), channel status reports for channels within a transmission band to be transmitted, the channel status reports including:
• a plurality of sub-band channel quality indicator (CQI) reports, each sub-band CQI report to comprise a measurement of a respective sub-band of the transmission band;
• a sub-band rank indicator (RI) report from among a plurality of RI reports, the sub-band RI report to accompany the plurality of sub-band CQI reports;
• and
• a plurality of sub-band precoding matrix index (PMI) reports, one or more sub-band PMI reports from among the plurality of sub-band PMI reports to correspond to one or more respective sub-band CQI reports from among the plurality of sub-band CQI reports;
• and
• receiving downlink communications that include one or more data streams over the transmission band, at least portions of the downlink communications to occur at a first sub-band of the transmission band, the first sub-band characterized by a rank r to specify a number of data streams to be substantially simultaneously communicated over the first sub-band;
• searching a multiple rank codebook to determine a respective best PMI ir for each of a plurality of ranks of the multiple rank codebook;
• selecting a rank rbest to be used at the first sub-band based on the respective best PMIs ir for the plurality of ranks;
• causing the selected rank rbest to be transmitted in via the sub-band RI report for the first sub-band;
• and
• causing the respective best PMI ir to be transmitted via a first PMI report for the first sub-band.

At least one non-transitory machine readable medium comprising a plurality of instructions that in response to being executed by a system cause the system to:

• cause channel status reports to be transmitted for channels within a transmission band, the channel status reports to include:
• a plurality of sub-band channel quality indicator (CQI) reports, each sub-band CQI report to comprise a measurement of a respective sub-band of the transmission band;
• a sub-band rank indicator (RI) report from among a plurality of RI reports, the sub-band RI report to accompany the plurality of sub-band CQI reports;
• and
• a plurality of sub-band precoding matrix index (PMI) reports, one or more sub-band PMI reports from among the plurality of sub-band PMI reports to correspond to one or more respective sub-band CQI reports from among the plurality of sub-band CQI reports;
• and
• receive downlink communications that include one or more data streams over the transmission band, at least portions of the downlink communications to occur at a first sub-band of the transmission band, the first sub-band characterized by a rank r to specify a number of data streams to be substantially simultaneously communicated over the first sub-band;
• search a multiple rank codebook to determine a respective best PMI ir for each of a plurality of ranks of the multiple rank codebook;
• select a rank rbest to be used at the first sub-band based on the respective best PMIs ir for the plurality of ranks;
• cause the selected rank rbest to be transmitted via the sub-band RI report for the first sub-band;
• and
• cause the respective best PMI ir to be transmitted via a first PMI report for the first sub-band.