Joint null: Combining partial analog cancellation with transmit beamforming for large-antenna full-duplex wireless systems

In this paper, we study the performance of a full-duplex architecture for large-antenna systems, where analog cancelers can be fewer in number than receive antennas. We study two methods of partial analog self-interference cancellation: The one, where the analog cancelers are assigned to a fixed set of antennas and the other, where analog cancelers are reconfigurable such that they can be dynamically assigned to any receive antennas based on channel conditions. We propose JointNull that jointly optimizes partial analog cancellation and transmit beamforming. With reconfigurable cancelers, JointNull assigns each antenna one of the three roles - full-duplex, half-duplex receive, and half-duplex transmit antennas - and then designs a transmit precoder to suppress self-interference on receive antennas. As a special case of reconfigurable cancellation, fixed partial cancellation method is also addressed. We evaluate JointNull using channel measurements from a 72-antenna array. JointNull achieves close to ideal full-duplex sum rates using very few analog cancelers. For example, JointNull achieves 90% of ideal sum rate using only eight poor quality analog cancelers, each of which can cancel 20 dB of self-interference. When demand is highly downlink biased, JointNull achieves 90% of ideal sum rate with no analog cancelers. Finally, we find that reconfigurable cancelers provide only a marginal gain over fixed assignment; this points to a simpler system design, which uses fixed assignment for partial analog cancellation.