Wireless Side-Channels in MIMO Full-Duplex Systems
Doctor of Philosophy
In this thesis, we propose a new approach for enhanced interference management via wireless side-channels in advanced wireless systems such as MIMO full-duplex systems. The rise of multiple radio interfaces, such as WiFi (operating in unlicensed ISM bands) and cellular (operating in licensed bands), with near-default inclusion in smartphones, allows for a new use of the ISM bands to manage interference in cellular bands, by creating wireless “side-channels” between mobile users. In a multi-user MIMO full-duplex system, an in-band full-duplex base station (BS) with multiple antennas communicates with multiple up- and downlink users in the same time-frequency slot. We characterize the impact of side- channels in managing interference from uplink users to downlink users in such MIMO full-duplex system. First, we experimentally quantify the likelihood of establishing ISM side-channels between smartphones in WiFi-free areas such as highways. Next, we study a side-channel assisted two-user MIMO full-duplex sys- tem and characterize its generalized degrees-of-freedom and diversity- multiplexing tradeoff. For such a system, we show that the optimal perfor- mance is achieved by our proposed vector bin-and-cancel strategy which leverages Han-Kobayashi message splitting. Then, we study a side-channel assisted multi-user MIMO full-duplex system from a cross-layer protocol design perspective. Our protocol design integrates automatic repeat request (ARQ) at the medium access control (MAC) layer with enhanced interference management via side-channels at the physical layer (PHY). Our proposed joint PHY-MAC protocols exploit the ARQ information offered by the MAC layer to reduce the data retransmission time and improve system goodput. Finally, we study a multi-cell multi-user MIMO full-duplex system, where new forms of intra- and inter-cell interference appear due to the full-duplex operation. We characterize the up- and downlink ergodic achievable rates for the case of linear precoders and receivers. The rate analysis includes practical constraints such as imperfect full-duplex radio chains, channel estimation error, training overhead and pilot contamination. We show that with large antenna arrays at base-stations, the gains from full-duplex are available at the network level despite the increased interference in the full-duplex networks. Moreover, full-duplex networks can use fewer antennas to achieve spectral efficiency gain over the half-duplex counterparts. We also demonstrate that under realistic multi-cell MIMO full-duplex network scenarios, side-channels are effective in significantly improving the spectral efficiency of cell-edge users.
MIMO; Wireless side-channels; Full-duplex; Multi-cell networks