Research On Hybrid Precoding In Millimeter Wave Massive MIMO Relay System

With the development of smart wireless devices,the demand for higher data transmission rates is increasing.Millimeter wave communication can meet the needs of future wireless communication.Since millimeter wave have very high propagation loss in the atmosphere and cannot penetrate buildings,massive multiple input multiple output(MIMO)and relay technology are combined with millimeter wave to effectively improve the quality of millimeter wave communication and expand the range of propagation.Hybrid precoding is a key technology for millimeter wave massive MIMO communication,which can effectively reduce the hardware complexity.Therefore,this paper mainly studies the hybrid precoding technology of narrowband and wideband millimeter wave massive MIMO amplify and forward(AF)relay systems.Major contributions are summarized as follows:(1)Firstly,we introduce a single-user alternating minimization algorithm for hybrid precoding based on fully connected structure and simulate its spectral efficiency.The simulation results show that the spectral efficiency of the single-user alternating minimization algorithm for hybrid precoding is better than the spectral efficiency of the orthogonal matching pursuit(OMP)hybrid precoding algorithm.(2)The single-user alternating minimization algorithm for hybrid precoding is introduced into the narrow band millimeter wave massive MIMO relay system.We derive the spectral efficiency expression of the optimal fully digital precoder in the half-duplex AF relay mode and simulate the spectral efficiency of single-user alternating minimization algorithm for hybrid precoding in the half-duplex and full-duplex AF relay modes.(3)We extend the single-user alternating minimization algorithm for hybrid precoding to the broadband massive MIMO Orthogonal AF relay systems based on orthogonal frequency division multiplexing(OFDM).Since massive MIMO-OFDM relay systems have multiple subcarriers,multiple digital precoding matrices are also required.We need to improve the alternating minimization algorithm for hybrid precoding so that it can be used in massive MIMO-OFDM relay systems.Then we simulate and analyze the spectral efficiency of the improved alternating minimization algorithm for hybrid precoding under massive MIMO-OFDM relay systems.(4)We extend the single-user alternating minimization algorithm for hybrid precoding to multi-user algorithm,and simulate the the spectral efficiency of the multi-user alternating minimization algorithm for hybrid precoding.The simulation results show that in millimeter wave massive MIMO systems,the multi-user alternating minimization algorithm for hybrid precoding can effectively suppress the interference between users.(5)We introduce the improved multi-user alternating minimization algorithm for hybrid precoding in half-duplex and full-duplex millimeter wave massive MIMO AF relay systems,and simulate the spectral efficiency.The simulation results show that in full-duplex relay systems,as loopback interferences increases,the difference between the spectral efficiency of the fully digital precoding and the spectral efficiency of the alternating minimization algorithm for hybrid precoding becomes smaller.When loopback interferences is large enough,the spectral efficiency of the fully digital precoding completely coincides with the spectral efficiency of the alternating minimization algorithm for hybrid precoding.