Relay-Aided Communications in Large Interference Limited Networks

Relay-Aided Communications in Large Interference Limited Networks

In multiuser wireless communication networks, three important basic network topologies can be distinguished, namely ad-hoc networks where pairs of nodes exchange information with each other, cellular networks where base stations serve multiple mobile stations, and group communication networks where more than two nodes form a group and exchange messages. For all the three network topologies mentioned above, interferences are the major performance limiting factor. Recently, interference alignment has been proposed to eliminate the interferences in such networks, especially if the interference signals and the useful signals are of comparable strengths. Besides the conventional interference alignment using time extensions or a large number of antennas at the nodes, both involving disadvantages, amplify-and-forward relays can be employed to help the process of interference alignment. By utilizing relays, the effective end-to-end channels between the communicating nodes can be manipulated in such a way, that the interferences are aligned at the receiving nodes.

In this project, we will focus on investigating relay aided interference alignment for the above three topologies in large networks, i.e., in networks containing many nodes and relays deployed over a large area. In large networks, the distances between nodes and relays differ a lot, leading to some weak channels which can be ignored. Based on this, we will consider that these large networks are partially connected. More specifically, we will consider large networks being partitioned into multiple subnetworks, which are mutually connected by a limited number of links.

Furthermore, assuming half-duplex relays, both one-way and two-way relaying protocols will be applied. One-way relaying enables using the direct links between the communicating nodes, while two-way relaying does not. On the other hand, two-way relaying needs only two transmission phases for bidirectional communication while one-way relaying needs four transmission phases. Overall, the doubled number of transmission phases required by one-way relaying is compensated by the doubled number of dimensions of the receive signal space at every destination node compared with two-way relaying. The capability to utilize or not to utilize the direct link introduces different challenges for interference alignment. Note, that we do not aim at theoretical capacity bounds in this project, but at viable solutions for the given relaying protocols.

For large networks with all the three network topologies, which may be partially connected and for both, one-way and two-way relaying protocols, we will derive the properness or feasibility conditions for interference alignment, develop interference alignment algorithms, investigate the possibilities of doing interference alignment with partial channel state information only and consider scalability issues for interference alignment in large networks.