Cooperative Interference Management in Multi-Antenna Wireless Networks

Abstract

Due to the rapidly increasing demand of higher data rate with a large number of connected devices, interference has become the key factor in designing future wireless networks, such as the fifth generation (5G) cellular network. This is mainly because the more nearby wireless devices transmit at the same time, more dominant interference causes the signal distortion, thereby limiting the overall system performance. Motivated by this, interference has been deemed an intrinsically destructive phenomenon so that it must be avoided as much as possible. In this dissertation, I reevaluate the fundamental notion of interference in wireless networks, and introduce a new paradigm that interference can be a friend in many wireless networks, rather than a foe in the prevailing traditional paradigm. To support this, I explore and discuss the new opportunities of harnessing interference to improve the system performance for a wide range of multi-antenna wireless networks, especially under the imperfect knowledge of channel state information at transmitter (CSIT). To begin with, I focus on interfering multiple access channel as a canonical model of uplink cellular networks. Under the assumption of delayed CSIT, I demonstrate that harnessing overheard interference signals at the receivers as side information brings significant performance gains. For a certain network configuration, it is shown that the proposed scheme achieves the optimal degrees-of-freedom (DoF) of the uplink cellular network. The same spirit of exploiting interference can be extended into multi-hop interference networks beyond single-hop network. I demonstrate that relays can be used to provide DoF gains in two-hop interference networks through the proposed cooperative relaying techniques even when imperfect CSI is available at relays. Under two different CSI assumptions at relays, I also characterize the feasibility conditions on relays configuration to accomplish the target DoF gains. A major implication is that the cooperative relay can help to steer the transmitters signals in a way that it judiciously exploits the past receptions to reconstruct the overheard interference at each receiver as side information for future transmissions, instead of the transmitters. Lastly, I turn my attention to the new interference issues, especially for key radio access technologies of 5G cellular systems: non-orthogonal multiple access (NOMA), full-duplex (FD) radios, and wireless powered communications network (WPCN). I shed light on the various potential benefits of harnessing interference via coordination between nodes. In particular, it is shown that interference can be exploited as a new source of energy harvesting to enable self-sustainable wireless networks as well as a means of increasing number of multiplexed users for the scenario in which massive connectivity is required over limited radio resources, such as massive machine-type communication (mMTC). The finding has a special importance in designing 5G new radio (NR) systems, showing that such a cooperation between nodes can help overcome the limiting effects of interference.