What is CQI?
- Channel Quality Indicator/ Index (CQI). It an indicator of channel quality.
- It is an information that UE send to network based on network quality.
- Physical channel that carry this information/ report measurement is:
- PUCCH (if Periodic CQI)
- PUSCH (if Not Periodic).
- In HSDPA, CQI ranging from (0-30).
- In LTE it ranges from (0-15).
- The higher number the better quality; 0, 1 is the poorest quality.
- If network gets high CQI, it transmits larger transport block size & vice versa.
- Some situation like network send larger transport block size even though UE reports low CQI: This probably due to UE failed to decode it (CRC error on UE side). Due to this error, UE send a NACK message to network & network has to re-transmit it which cause more & more block size transmitted (wasting radio resources).
- Same explanation if UE reports good CQI, but network transmit small block size.
Factors that play important roles in report measurement:
- Signal-to-noise ratio (SNR)
- Signal-to-interference plus noise ratio (SINR)
- Signal-to-noise plus distortion ratio (SNDR)
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