What does coding gain provide in a communication system?

• A. It reduces data rate
• B. It increases channel bandwidth
• C. It lowers the required SNR to achieve a target BER
• D. It increases decoding complexity

Answer: (C)

Coding gain is the reduction in the required signal-to-noise ratio to achieve a given bit error rate when an error-correcting code is used. The redundancy added by the code lets the receiver detect and correct errors, so you can reach the same BER at a lower SNR. In practical terms, if a code provides a coding gain of several decibels, you can operate with that much less SNR and still meet the target BER. This effect is about how efficiently the system uses the channel's quality, not about increasing bandwidth. While adding a code does introduce redundancy that can reduce the raw data rate (depending on the code rate), the fundamental benefit described by coding gain is the improved BER performance at lower SNR. Note that decoding complexity can rise because of the more sophisticated error-correcting process, but that is a separate consideration from the gain itself.