Adaptive protocols for interactive communication

How much adversarial noise can protocols for interactive communication tolerate? This question was examined by Braverman and Rao (IEEE Trans. Inf. Theory, 2014) for the case of “robust” protocols, where each party sends messages only in fixed and predetermined rounds. We consider a new class of protocols for interactive communication, which we call adaptive protocols. Such protocols adapt structurally to the noise induced by the channel in the sense that both the order of speaking, and the length of the protocol may vary depending on observed noise. We define models that capture adaptive protocols and study upper and lower bounds on the permissible noise rate in these models. When the length of the protocol may adaptively change according to the noise, we demonstrate a protocol that tolerates noise rates up to 1/3. When the order of speaking may adaptively change as well, we demonstrate a protocol that tolerates noise rates up to 2/3. Hence, adaptivity circumvents an impossibility result of 1/4 on the fraction of tolerable noise (Braverman and Rao, 2014).