Capacity of the two-way channel

The capacity of the two-way channel (a channel in which information is sent in both directions simultaneously) is unknown. Capacity is known in special cases: for the two-way channel with additive white Gaussian noise, capacity is achieved without using feedback, by independent Gaussian codewords at each terminal. For the additive Gaussian multiway channel with a common output (a generalization to more than two users), the sum-rate capacity is known above a certain SNR threshold, and for all SNR under per-symbol power constraints.

Open the “Channel coding” section on Wikipedia →

Source: List of unsolved problems in information theory (CC BY-SA 4.0)