Cooperative MAC design for ad hoc wireless networks

Cooperative diversity is proposed to combat the detrimental effects of channel fading. In this thesis, we investigate the effectiveness of cooperative diversity in interference limited ad hoc networks. The throughput performance of ad hoc networks that employ cooperative diversity techniques is examined. The negative effects of relay transmission blocking and extra time delay due to using the relay node, on the network throughput are investigated. We show that cooperative diversity based ad hoc networks inherits relay blocking problem which causes net network throughput degradation. To solve the relay blocking problem, we propose a new cooperative medium-access-control (MAC) protocol where each relay is equipped with directive antennas and the transmitter-relay-receiver transmission mode is designed using two frequency channels. Furthermore, we discuss the throughput performance considering single and multiple relay scenarios and analyze the effect of interference on the throughput. Then we investigate the throughput performance of the proposed cooperative MAC protocol in the presence of position estimation errors. In the literature, a perfect position estimation of all nodes is commonly assumed. Here, we focus on the throughput performance of the cooperative network when taking into consideration the effect of directional-of-arrival (DOA) error caused by imperfect global-positioning system (GPS) position estimation. Our results show that using adaptive antennas at the relay becomes advantageous when the DOA error is less than 20 degrees. We noted that increasing the number of antennas (at the relay station) can improve the throughput performance but, on the other hand, the effect of node position error becomes more substantial.