SINR

SINR is the metric that actually governs performance in a loaded network, because it accounts for the thing SNR ignores: signal from other cells leaking into yours. In a dense urban deployment, your neighbours' transmissions are usually a bigger problem than thermal noise, so SINR — wanted power over interference plus noise — is what really maps to throughput and to the modulation the scheduler dares to use.

This is also why simply cranking up transmit power across the board doesn't help: every cell gets louder, interference rises in lockstep, and SINR barely moves. Improving SINR is instead about spatial discipline — beamforming to aim energy where it's wanted, interference coordination between cells, careful frequency reuse, and good tilt planning. A handset can show a strong RSRP yet a poor SINR if it sits where several cells overlap, and that mismatch is a classic source of "full bars, slow data" complaints.