Cooperative Communications has become an increasingly extensive research area recently in advanced wireless communication system design. It employs the broadcast nature of the wireless transmissions and achieves spatial diversity by creating a virtual antenna array using distributed antennas belonging to different users. We study the resource allocation issue among the cooperating users in this thesis and optimize the power allocation strategies to enhance the reliability of the system....[ Read more ]

Cooperative Communications has become an increasingly extensive research area recently in advanced wireless communication system design. It employs the broadcast nature of the wireless transmissions and achieves spatial diversity by creating a virtual antenna array using distributed antennas belonging to different users. We study the resource allocation issue among the cooperating users in this thesis and optimize the power allocation strategies to enhance the reliability of the system.

We consider a two-phase transmission scheme with a broadcast phase followed by a retransmission phase based on positive or negative acknowledgement (i.e. ACK or NAK) feedback from the destination. We proposed, under the average power constraint, two cooperative protocols with power allocation to improve the system performance. Specifically, the first protocol made use of the ACK/NAK feedback to determine the transmit power of each packet. The ACK/NAK feedback was utilized to eliminate unnecessary transmission and collectively the number of ACKs indicates the channel condition that was used to adjust the power level. The second protocol further assumed that the inter-relay channels are reciprocal. This assumption allows further optimization in power allocation.

To avoid inter-relay communications, a new space-time code design was proposed for both protocols. Moreover, the power allocation strategies are designed in a distributed manner to minimize any inter-relay communications.