An efficient cooperative transmission scheme using multiple relays incrementally

We are motivated to exploit the broadcast nature of a radio medium in combating its unreliable and time-varying characteristics. This leads to cooperative transmission where a neighbor node keeps a copy of an overheard packet and helps in retransmitting the overheard packet to its intended destination when the original transmission fails. Cooperative transmission improve wireless network performance through diversity gain, and can be performed in the forms of amplify-and-forward. Existing amplify-and-forward schemes either: (a) use multiple relays but in a non-incremental way, or (b) use only a single relay in an incremental way. Non-incremental (simple) schemes do not provide a good spectral efficiency. Also, using multiple relays can further improve diversity. This paper aims at proposing an incremental amplify-and-forward scheme that uses n relays, where n >; 1. In the proposed scheme, a relay will retransmit an overheard packet in a time slot, only if all the previous transmissions are not successful. The transmission cycle of a packet ends as soon as a packet has been received successfully by the intended destination or all the n relays has retransmitted their overheard packets. Analytical and numerical results show that the proposed scheme outperforms both the simple amplify-and-forward scheme and the single-relay incremental scheme in terms of a lower outage probability for a given spectral efficiency.