  In this paper, we present and study a digital-controlled method, called
SoftNull, to enable full-duplex in many-antenna systems. Unlike most designs
that rely on analog cancelers to suppress self-interference, SoftNull relies on
digital transmit beamforming to reduce self-interference. SoftNull does not
attempt to perfectly null self-interference, but instead seeks to reduce
self-interference sufficiently to prevent swamping the receiver's dynamic
range. Residual self-interference is then cancelled digitally by the receiver.
We evaluate the performance of SoftNull using measurements from a 72-element
antenna array in both indoor and outdoor environments. We find that SoftNull
can significantly outperform half-duplex for small cells operating in the
many-antenna regime, where the number of antennas is many more than the number
of users served simultaneously.
