SINR

Signal-to-interference-plus-noise ratio (SINR) is a measure of signal quality used in wireless communications. It is defined as the ratio of the power of the desired signal to the sum of the powers of interference sources and background noise within the same bandwidth. Mathematically, SINR = P_signal / (P_interference + P_noise). When expressed in decibels, SINR = 10 log10(P_signal / (P_interference + P_noise)). In practice, noise is often modeled as thermal noise with spectral density N0 and bandwidth B, so P_noise = N0 B, and P_interference accounts for all co-channel and adjacent-channel interference within the resource.

A higher SINR indicates a clearer link and generally enables higher-order modulation and lower error rates. The SINR is related to, but distinct from, the signal-to-noise ratio (SNR = P_signal / P_noise) and the signal-to-interference ratio (SIR = P_signal / P_interference). The Shannon capacity formula C = B log2(1 + SINR) provides an upper bound on the achievable data rate for a given bandwidth and SINR.

SINR can be measured as an instantaneous value at the receiver, or averaged over time or bandwidth for link budgeting and planning. It is commonly used in cellular networks (LTE, 5G), Wi-Fi, and other wireless systems to adapt modulation and coding, power control, and resource allocation.

Factors affecting SINR include transmission power, user mobility, environmental propagation, multi-user interference, network load, and receiver sensitivity. Practical SINR estimates must account for fast fading, shadowing, and non-ideal hardware.