Diversity Order and Degrees of Freedom for Cooperative Communication Networks

Abstract

This dissertation contains the following three contributions to the interesting research topics on diversity techniques and interference alignment (IA) for cooperative communication networks.

*Relay on-off threshold (ROT) for non-orthogonal decode and forward (NDF) protocol with distributed orthogonal space-time block codes (DOSTBCs) - Calculate the optimal ROT for NDF protocol with DOSTBCs in high signal to noise power ratio (SNR) region. - Propose suboptimal ROT for NDF protocol with DOSTBCs in low SNR region. - Analyze the diversity order of the proposed scheme. *New IA schemes aided by relays for quasi-static MX2 X channel - Propose IA scheme aided by one full-duplex relay. - Propose IA scheme aided by two half-duplex relay. - Prove that the proposed IA schemes achieve the maximum degrees of freedom (DoF) for quasi-static MX2 X channel. * Selection diversity on the IA for multi-input and multi-output (MIMO) interference channel - Propose the selection criterion of beamforming matrices of IA for MIMO interference channel. - Analyze the diversity order of the proposed scheme.

First, we construct the DOSTBCs using source and relay in the cooperative communication networks. In order to decode the DOSTBCs, the destination uses the linear combining (LC) decoding scheme. In this system models, the symbol error rate (SER) is formulated and the ROT is calculated to minimize the SER. It is proved that the full diversity order of NDF protocol can be achieved by using the relay on-off scheme with the optimal threshold. In the second part of this dissertation, two new IA schemes aided by relays for quasi-static MX2 X channel are proposed. The first proposed scheme uses one full-duplex relay and it can achieves the maximum DoF. However, at the full-duplex relay, the transmit signal can be strong self-interference, called echo and thus it is difficult to implement practically. To resolve this problem, at the second proposed IA scheme, two half-duplex relays are used and it is proved that the second proposed IA scheme can also achieve the maximum DoF of MX2 X channel. Finally, the selection scheme for IA is proposed for MIMO interference channel. Most of IA schemes are focused on DoF but there is only a few research results for diversity order which is a crucial measure of reliability. Therefore, we propose a selection criterion to minimize SER and analyze the diversity order of the proposed scheme in the MIMO interference channel.