We introduce the “blind index coding” (BIC) problem, which generalizes the classic index coding problem by considering a sender that has some uncertainty about the side information that is available at each receiver. This problem naturally arises in wireless networks in which users obtain their side information through wireless channels with errors that may be unknown to the sender. For the proposed BIC problem, we develop a new general outer bound by first proving it for the 3-user case and then generalizing its construction to K users. The proof of the outer bound relies on developing a key lemma that uses a strong data processing inequality to account for the sender's uncertainty. We also propose a hybrid coding scheme that XORs random combinations of bits from a subset of messages with uncoded bits of other messages in order to blindly exploit side information, and illustrate its gain.
