Quiz Entry - updated: 2026.07.14
What is SNR (Signal-to-Noise Ratio) and why does it matter for wireless communication?
SNR measures how much stronger the desired signal is compared to background noise — a higher SNR means cleaner reception and fewer bit errors.
Definition: SNR = signal power / noise power, expressed in decibels (dB).
- SNR = 0 dB — signal and noise are equally strong; extremely difficult to extract data
- SNR = 20 dB — signal is 100x stronger than noise; clean reception possible
Why it matters:
- Higher SNR → easier to extract the signal from noise → lower Bit Error Rate (BER)
- The physical layer can choose a modulation scheme based on the current SNR:
| Modulation | Required SNR | Throughput |
|---|---|---|
| BPSK | Low (~5 dB) | 1 Mbps |
| QAM16 | Medium (~15 dB) | 4 Mbps |
| QAM256 | High (~25 dB) | 8 Mbps |
Key insight: There's a direct trade-off between reliability and speed. With a good SNR, you can use aggressive modulation (QAM256) for high throughput. As SNR drops, you must fall back to simpler modulation (BPSK) that's more robust but slower. Modern systems like LTE and 5G do this dynamically — called Adaptive Modulation and Coding (AMC).
Go deeper:
Signal-to-noise ratio (Wikipedia) — defines SNR as signal power over noise power in dB and why a higher ratio means cleaner reception and fewer bit errors.