What is the role of CQI?

Hello, dear.
The LTE PDSCH has three coding schemes: QPSK, 16QAM, and 64QAM. The coding efficiency varies with the channel conditions. The higher the coding efficiency is (QPSK < 16QAM < 64QAM), the higher the requirements for the channel conditions are. The PDSCH scheduling is determined by the eNodeB, which serves as the transmitter, it is unknown how the UE receives signals (how the downlink channel quality is). Therefore, the UE needs to measure the channel quality and feedback the channel quality to the eNodeB as the basis for channel coding. According to the protocol, the channel quality measured by the UE is quantified into a sequence of 0 to 15 (4 bits), which is called CQI.

The CQI reported by the UE to the eNodeB is used for the following purposes:

(1) Select the MCS and TBS.

(2) Time/frequency selective scheduling

(3) Interference management

(4) Physical channel transmission power control
Thanks！