Hybrid beam selection scheme in millimeter-wave beamspace MIMO-NOMA with lens antenna array

Beam selection is a notable issue for recent wireless communications. A conventional single beam selection (SBS) concept is utilized to minimize the number of necessary radio frequency chains in millimeter-wave (mmWave) multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) systems. In general, the traditional SBS concept cannot implement a multiple beam group selection opportunity for every supported user. In this circumstance, the user side spends too much computational burden to measure the decoded message and suffer a beam optimization problem. Therefore, we propose a hybrid beam selection (HBS) scheme to utilize a multiple SBS scheme in beamspace MIMO-NOMA systems. Consequently, each supported user can easily achieve a low beam optimization problem by selecting a reliable SBS group from the proposed HBS scheme and significantly increase the spectral performance. Furthermore, we demonstrate an iterative beam power maximization algorithm utilizing the HBS scheme to solve the power allocation problem in this paper. The numerical results are verified by computer simulations in terms of a downlink beamspace MIMO-NOMA channel with a lens antenna array environment.