RSRP, RSRQ ,RSSI are the measurements that the UE takes for cell reselection or handover puroposes. It is not used for the purposes of the transmission settings, but to take the decision (by the UE – in case of cell reselection; or eNB – in case of handover) to move the UE to other cell. In the case of handover, the UE sends the measurement results according to the eNB commands (e.g. periodically or triggered by event). The power of the eNB is constant and does not depend on the RSRP / RSRQ / RSSI measurements.
The measurements and feedback that relate to the transmission settings are known as CQI (channel quality indicator). Depending on that value (CQI index), the eNB takes the decision to assign a particular MCS (modulation and coding scheme) for a particular UE. The higher the CQI (ranging from 0 up to 15) the higher the modulation and coding scheme and the higher the throughput. However it is up to the implemented receiver algorithms in the UE, at which SNIR the good throughput can be achieved (the algorithms are vendor dependent so the “good SNIR” may vary for various UEs).
Your explanation does not clarify why SINR cannot be used for cell reselection and HO, and why RSRQ is not used for transmission settings.
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