CQI, MCS, and link adaptation

The Link Adaptation Feedback Loop

Link adaptation is the closed-loop mechanism that continuously matches the Modulation and Coding Scheme to current radio channel conditions. The UE measures downlink SINR from reference signals and maps its measurement to a Channel Quality Indicator value ranging from zero to fifteen. It reports this CQI to the gNB on PUCCH or PUSCH. The gNB scheduler then maps the CQI to an MCS index from one of three standardized tables, where each index specifies both a modulation order and a target coding rate. Table 1 caps at 64QAM, Table 2 extends to 256QAM, and Table 3 provides low spectral efficiency…