SINR Calculation in LTE

• S: indicates the power of measured usable signals. Reference signals (RS) and physical downlink shared channels (PDSCHs) are mainly involved

• I: indicates the average interference power - the power of measured signals or channel interference signals from other cells in the current system
•  N: indicates background noise, which is related to measurement bandwidths and receiver noise coefficients

SINR is a measure of signal quality as well but it is not defined in the 3GPP specs but defined by the UE vendor.

It is not reported to the network. SINR is used a lot by operators, and the LTE industry in general, as it better quantifies the relationship between RF conditions and Throughput. UEs typically use SINR to calculate the CQI (Channel Quality Indicator) they report to the network.

It is a common practice to use Signal-toInterference Ratio (SINR) as an indicator for network quality. It should be however noted that 3GPP specifications do not define SINR and  therefore UE does not report SINR to the network. SINR is still internally measured by most UEs and recorded by drive test tools.

Unfortunately UE chipset and RF scanner manufacturers have implemented SINR measurement in various different ways which in the authors’ field experience are not always easily comparable. While at first it may seem that defining SINR should be unambiguous, in case of LTE downlink this is not the case. This is because different REs within a radio frame carry different physical signals and channels each of which, in turn, see different interference power depending on inter-cell radio frame synchronization.