Hybrid interference cancellation in millimeter-wave MIMO systems

Abstract

We consider a millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) systems and design a hybrid beamformer that cancels interference in the analog domain under the hardware constraints. In particular, the phase-adjustment-only limitation of a phase array and limited RF chains render the conventional design of purely digital beam-former inapplicable for the hybrid beamforming architecture. To address this issue, a novel design of hybrid beamformer, comprising a digital and an analog (phase-array) components, is presented for hybrid interference cancellation, which is tailored for the mmWave channel characteristics and overcomes the hardware constraint of massive MIMO. The systematic design approach builds on the recently developed method of decomposing the analog beamformer into Kronecker products of unit-modulus component vectors which are designed to cancel interference arriving from different directions. Then a follow-up low-dimension digital beamformer is designed to further enhance the signal quality for a given number of RF chains. It is shown that the proposed hybrid beamformer attains similar performance as the fully digital minimum-mean-square-error (MMSE) beamformer in the interference-limited regime.