What is SINR?

Detailed explanation

SINR measures how much the useful signal exceeds interference and noise combined. Unlike RSRP which only indicates signal strength, SINR captures the actual quality of the radio channel experienced by the user. Two locations with identical RSRP can deliver vastly different throughput if their SINR values differ due to varying interference levels.

The base station uses SINR (reported as CQI by the device) to select the optimal Modulation and Coding Scheme (MCS). High SINR values above 20 dB enable 256-QAM modulation with aggressive coding rates, achieving peak throughput. Low SINR forces the use of robust QPSK modulation with heavy coding protection, significantly reducing throughput but maintaining link reliability.

In dense urban environments, inter-cell interference is often the dominant factor limiting SINR. Cell-edge users typically experience low SINR because they receive comparable power levels from multiple cells. Techniques such as ICIC (Inter-Cell Interference Coordination), eICIC and advanced MIMO help improve SINR in these challenging scenarios.

In 5G NR, SINR measurement is extended with beam-specific reporting. Each SSB beam has its own SINR value, enabling the network to select the best beam for each user. The wider bandwidth and higher frequencies of 5G make SINR optimization even more critical for achieving the promised throughput improvements.