Steering vector calculation for hybrid beamforming remains open

Derive algorithms to calculate steering vectors for hybrid beamforming in millimeter-wave massive MIMO systems—covering both transmitter precoding and receiver weighting—in multi-user scenarios where a single analog beam cannot cover spatially distributed users without degrading radiation pattern gain.

Background

Accurate steering vectors are central to analog beamforming, but in multi-user mmWave settings users can occupy diverse angular directions. Hybrid architectures constrain amplitude control and rely on phase shifters, complicating steering vector computation that must balance analog beam coverage and digital processing.

The paper explicitly notes that computing these steering vectors is an open problem in hybrid beamforming, particularly due to the inability of one analog beam to cover all users without significant gain loss.