  Modern millimeter wave (mmWave) communication systems rely on beam alignment
to deliver sufficient beamforming gain to close the link between devices. We
present a novel beam selection methodology for multi-panel, full-duplex mmWave
systems, which we call STEER, that delivers high beamforming gain while
significantly reducing the full-duplex self-interference coupled between the
transmit and receive beams. STEER does not necessitate changes to conventional
beam alignment methodologies nor additional over-the-air feedback, making it
compatible with existing cellular standards. Instead, STEER uses conventional
beam alignment to identify the general directions beams should be steered, and
then it makes use of a minimal number of self-interference measurements to
jointly select transmit and receive beams that deliver high gain in these
directions while coupling low self-interference. We implement STEER on an
industry-grade 28 GHz phased array platform and use further simulation to show
that full-duplex operation with beams selected by STEER can notably outperform
both half-duplex and full-duplex operation with beams chosen via conventional
beam selection. For instance, STEER can reliably reduce self-interference by
more than 20 dB and improve SINR by more than 10 dB, compared to conventional
beam selection. Our experimental results highlight that beam alignment can be
used not only to deliver high beamforming gain in full-duplex mmWave systems
but also to mitigate self-interference to levels near or below the noise floor,
rendering additional self-interference cancellation unnecessary with STEER.
