# Advanced Hybrid Beamforming Technique in MU-MIMO Systems
## 6 Conclusions  
In 5G NR, wireless communication technology evolved as demand for increasing the data rate in MU-MIMO systems. In particular, the improvement of the data rate is important in mmWave communication technology using the large-scale arrays. In 5G NR, the technique improving the average sum rate was studied continuously. In this paper, the advanced hybrid beamforming system is proposed to improve the error performance and the average sum rate. The transmitter receives the information of azimuth and elevation angles for the multi-paths by the feedback process. In addition, the azimuth and elevation angles are determined according to the number of \(B\)-bits used by the transmitter and the beam patterns are formed according to the \(B\)-bits. By using the azimuth and elevation angles of multi-paths proportional to the number of \(B\)-bits, \(B^{2}\) beam patterns are formed. Finally, the azimuth and elevation angles among the formed beam patterns are estimated according to Equation (9). It is shown that the proposed hybrid beamforming system has higher error performance and the average sum rate than the conventional hybrid beamforming system. Also, the proposed hybrid beamforming system has better error performance and the average sum rate than the conventional hybrid beamforming system when transmitter sends the data stream using the same number of beam patterns.  
This paper is designed to improve the bit error rate and the average sum rate in codebook based hybrid beamforming applied in 5G NR. However, the technique proposed in this paper has some performance degradation factors. An accuracy of channel estimations are very low when the number of RF chains is decreased. Specifically, the proposed codebook design is based on the channel state information. Thus, the error performance and average sum rate performance are degraded seriously as the number of RF chains is decreased, and the performance limitations are noticeable. Also, in the frequency selective fading, the design of analog precoding which copes with severe selectivity perfectly is very complex. If the above problems are solved with feature work, the proposed technique will be an efficient beamsearch algorithm in 5G NR.  
Conceptualization, S.-J.S.; methodology, S.-J.S. and S.L.; software, S.-J.S. and J.-H.R.; validation, S.-J.S., S.L., W.-S.L., and H.-K.S.; formal analysis, J.-I.B., S.-J.S.; investigation, J.-I.B., S.L. and W.-S.L.; writing--original draft preparation, S.-J.S.; writing--review and editing, S.-J.S. and [PERSON]-H.R.; supervision, H.-K.S.; project administration, H.-K.S. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the MSIT(Ministry of Science and ICT), Korea, under the IITRC(Information Technology Research Center) support program(IITP-2019-2018-0-01423) supervised by the IITP(Institute for Information & communications Technology Promotion) and was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(2020R1A6A1A03038540). The authors declare no conflict of interest.