Title: Capacity Region and Degrees of Freedom of Bidirectional Networks
Description: The increasing complexity of communication networks in size and density provides us enormous opportunities to exploit interaction among multiple nodes, thus enabling higher rate of data streams. On the flip side, however, this complexity comes with challenges in managing interference that multiple source-destination pairs in the network may cause to each other. In this dissertation, we make progress on how to exploit the opportunities, as well as how to overcome the challenges for various communication networks. In the first part, we focus on developing fundamental principles for communication network design, especially networks with multiple antenna transceivers, with an emphasis on (1) understanding the role of feedback and cooperation, and (2) developing interference management methods. In this part, we find that feedback and cooperation have promising roles in improving the capacity performance of several interference networks. We show that in stark contrast to the point-to-point case, a limited feedback can improve the capacity of interference-limited networks.

In fact, the improvement can be unbounded. This result shows that feedback can have a potentially significant role to play in mitigating interference. Then, in part two we study several bidirectional networks. We study the bidirectional diamond network and show that for deterministic and some Gaussian models the capacity is doubled for full-duplex channel in comparison with one-way networks. In addition, we study the degrees of freedom of two-way four-unicast MIMO networks, and provide upper and lower bounds that are tight in several cases. We also study the impact of caching in relay nodes for these models. We find a number of cases that bidirectional links can double the degrees of freedom with the help of relay caching and/or multiple relay antennas.