What is a characteristic of orthogonal frequency division multiplexing (OFDM) channel subcarriers?

Orthogonal frequency division multiplexing (OFDM) is a method of encoding digital data on multiple carrier frequencies. A key characteristic of OFDM subcarriers is that each subcarrier can indeed be modulated at the maximum modulation order that the bandwidth allows. This allows for efficient use of the available spectrum since each subcarrier can carry a distinct signal, maximally utilizing the channel's capacity under specific conditions.

In practical applications, the modulation order for each subcarrier can vary based on the channel conditions, which means that, theoretically, they can support higher modulation orders when the signal-to-noise ratio is favorable. This adaptability leads to enhanced data rates and improved transmission efficiency in systems utilizing OFDM.

The other options do not align with the fundamental principles of OFDM. For example, while it's important to manage modulation schemes, subcarriers are not inherently limited to fixed modulation orders; rather, they can adjust depending on the conditions of the transmission environment. Additionally, OFDM does not require a specific number of channels to function, nor is it restricted to one-directional data transmission, as it can support bidirectional communication depending on the network design.