Distributed Amplify-and-Forward Cooperation Through Message Partitioning

This paper proposes a message partitioning-based distributed amplify-and-forward (MPDAF) cooperative scheme. In this scheme, the message transmitted by a user is partitioned into several equal parts, each of which will be relayed by a different user. It enables the cooperative users to share the relaying burden in a distributed network. As a result, each cooperative user deploys half of its transmission for broadcasting and the other half for relaying, maintaining both the degree of its broadcasting transmission and the spectral efficiency. Since cooperation does not require decoding and encoding processes at the relays, the system complexity of the MPDAF scheme is less than that of the space-time-coded (STC) distributed cooperative scheme, but some additional effort is required to achieve signal timing synchronization. Information theoretic analysis of the proposed scheme shows that it can achieve the same diversity-multiplexing tradeoff (DMT) performance bound as the STC scheme, achieving extra diversity gain without affecting its multiplexing gain. It is superior to the existing repetition-based distributed cooperative scheme. The scheme's outage performance substantiates this claim by showing that a significant diversity gain can be achieved. The impact of the MPDAF scheme when used in a practical coded system is analyzed, and it is shown that a diversity gain on the order of the number of relays can be achieved. We present simulation results for an MPDAF scheme employing the spectrally efficient bit-interleaved coded modulation and show that a significant diversity gain can be also achieved in a practical coded system.