What does bit error rate measure and how is it characterized?

• A. The ratio of corrected bits to total transmitted bits.
• B. The ratio of incorrectly received bits to total transmitted bits.
• C. The ratio of noise power to signal power.
• D. The rate of bit transitions per second.

Answer: (C)

Bit error rate tells you how often the received bits are incorrect in a digital link. It is defined as the number of bit errors divided by the total number of transmitted bits, giving a dimensionless probability between 0 and 1 (often expressed in scientific notation, like 10^-6). This metric directly reflects link quality: as signal-to-noise ratio improves, the BER typically drops because fewer bits are corrupted by noise. Different modulation schemes and channel conditions yield different BER vs. SNR behavior, so these curves are used to compare system reliability. It’s important to separate BER from the ratio of noise power to signal power (SNR) and from frame error rate, which counts entire frames rather than individual bit errors. In practice, BER is measured by counting how many bit errors occur over a known number of transmitted bits.