Cooperative space-time codes with opportunistic network coding with increasing numbers of nodes

The benefits of diversity offered by multiple-input-multiple-output (MIMO) can only be achieved with the concept of cooperative communications in nodes having single antenna. Cooperative communications is a way of communications where users, besides transmitting their own information, also transmit re-encoded version of other users´ information to a common destination. We extend our study of cooperative communications with opportunistic network coding to more than one idle/free user acting as a relay for two space-time cooperating users. In our study we have taken two cooperating users using space-time (ST) codes, and multiple other free users in their vicinity. These users are free in the sense that they are not demanding the service at the time of transmission from cooperative users. These free users receive in one phase from cooperating users, and send network coded bits from cooperating users to destination in the next phase. We have taken two scenarios to discuss the potential benefits of the scheme. In the first scenario, each free node, added one after the other to the network, is taken to be at the same distance from transmitting users. In the second scenario, every other node added to the network is placed a distance farther from the previous one. The results show that the investigated scheme outperforms, for a range of SNR with fixed number of nodes, user cooperation using ST codes only.