Rate-Loss Mitigation for a Millimeter-Wave Beamspace MIMO Lens Antenna Array System Using a Hybrid Beam Selection Scheme

The rate loss is an important issue in multiuser beamspace multiple-input-multiple-output (MIMO) millimeter-wave systems. In such systems, multicluster channel propagation results in quantization error (QE), and consequently, each active user suffers a significant rate loss. A conventional single beam selection (SBS) scheme is used in an equivalent beamspace MIMO channel to reduce the number of radio frequency (RF) chains required. However, this scheme does not properly mitigate the QE due to the limited number of channel propagation clusters per user. In addition, optimally selected RF chains are operated at the same number of precoded data streams. As a result, each active user inherently loses a huge number of data streams when utilizing the conventional SBS scheme. Therefore, we propose a novel hybrid beam selection scheme in an equivalent beamspace MIMO channel to enable multiple beam group selection and to achieve a reliable channel cluster for every active user, which directly aids in the mitigation of the QE. The numerical result is verified using computer simulations in a millimeter-wave MIMO downlink channel environment.