Cooperative Multicasting Based on Superposition and Layered Coding

Cooperative diversity plays an important role in achieving efficient multicast transmissions for wireless applications. In this paper, we propose a novel two-phase cooperative multicast scheme based on superposition coding. In the first phase, the Base Station (BS) broadcasts a composite message. Most of the subscribers in the multicast group will decode the base message and the subscribers who experience better channel conditions will decode the enhancement message (referred to as the first enhancement message) as well. In the second phase, a fraction of the subscribers who decoded the first enhancement message, cooperatively transmit the first enhancement message to the subscribers who failed to decode it. The remaining subscribers who successfully received the first enhancement message will not participate in the cooperative transmission and will receive a second enhancement message transmitted by the BS. The proposed scheme exploits spatial diversity gain across multiple subscribers to maintain higher average throughput for each subscriber in addition to enabling scalable delivery of multimedia data. Simulations show that, under the same total energy consumption, the proposed scheme outperforms the conservative scheme and schemes exploiting cooperative relaying or superposition solely.