Abstract
The two-sender unicast index coding problem consists of two senders collectively having all the demanded messages of a set of receivers, where each receiver demands a unique message. The senders avail the knowledge of the side- information present at all the receivers to reduce the total number of broadcast transmissions. This problem is relevant in many practical communication problems like multi-source satellite communication, multi-user coded cooperative data exchange, and other related problems. In this paper, the two-sender unicast index coding problem is analyzed using three independent singlesender subproblems. Optimal broadcast rate (total number of transmitted bits per message bit as the message length tends to infinity) for all the unsolved instances of a special class of the twosender unicast index coding problem is provided in terms of those of the three associated subproblems. The optimal broadcast rate established in this work serves as a lower bound for the optimal broadcast rate of any general associated two- sender unicast index coding problem. An achievable broadcast rate (total number of transmitted bits per message bit) with finite length messages for any finite length, is given for a subclass of the two-sender unicast index coding problem by providing a code-construction. This serves as a tighter upper bound when compared to the prior state of art.