Amirreza Moradi - Department of Electrical Engineering, K. N. Toosi University of Technology Tehran, Iran.
K.Mohamed pour - Department of Electrical Engineering, K. N. Toosi University of Technology Tehran, Iran.
Nasim Jafari Farsani - Department of Electrical Engineering, K. N. Toosi University of Technology Tehran, Iran.

The use of millimeter wave (mmWave) massive multiple input multiple output (Ma-MIMO) systems makes it possible to meet the essential needs of future generation wireless systems and solve the impending wireless network crisis. mmWave Ma-MIMO systems offers higher numbers of antennas and carrier frequencies. Hybrid precoding is considered as a key technique for the practical deployment of mmWave Ma-MIMO systems since it significantly decreases the implementation costs, energy consumption, and hardware complexity. With the largly use of mmWave Ma-MIMO technologies in future generation wireless systems, it is imperative to develop cost-effective hybrid precoding solutions that match the various application cases of these systems. The fully-connected structure can offer spectral efficiency close to the fully-digital precoding but, unfortunately, it has high energy consumption, while the sub-connected structure with reduced power consumption, provides poor spectral efficiency. Therefore, for a better trade-off between spectral efficiency and energy efficiency, in this paper, we consider an adaptive sub-connected (ASC) hybrid precoding structure, where a switch network is able to provide dynamic connections from phase shifters to radio frequency (RF)chains. The simulation results indicate that in terms of spectral efficiency, the proposed algorithm with ASC structure obtains higher performance than the sub-connected structure. As a result, since the ASC structure reduces the number of phase shifters, it can offer a better energy efficiency compared to the sub-connected structure.

mmWave Ma-MIMO; Spectral efficiency; Hybrid precoding; ASC Structure; Energy efficiency.