Which statement defines spectral efficiency in modulation?

• A. The ratio of data rate to bandwidth.
• B. The inverse of modulation order.
• C. The module used for error correction.
• D. The energy-per-bit to noise ratio.

Answer: (A)

Spectral efficiency tells us how much information we can fit into a given amount of spectrum. It is defined as the data rate (bits per second) divided by the bandwidth (hertz), giving units of bits per second per hertz. This captures the trade-off between sending more data and using the same frequency range.

The statement that the ratio of data rate to bandwidth is the spectral efficiency fits this definition exactly, so it’s the best answer.

The inverse of the modulation order isn’t correct because modulation order describes how many distinct symbols are used, and spectral efficiency depends on how many bits per symbol (log2 of the order) and how much bandwidth is required, not simply the inverse of the order. The module used for error correction relates to coding, which affects reliability and sometimes effective data rate, but not the fundamental definition of spectral efficiency. The energy-per-bit to noise ratio is a measure of energy efficiency and link quality, not how efficiently spectrum is used.