Partial CSI Feedback Mechanism Based Beamforming In Millimeter Wave Systems

In recent years,with people's urgent needs of high rate and high bandwidth of wireless communication system,millimeter wave communication has been becoming a research hotspot in the field of communications,multi-input and multi-output(MIMO)wireless communication systems and large-scale antenna array technology are also the key technologies for 5G communication due to high system capacity and high spectrum efficiency.In millimeter-wave systems,limitedfeedback beamforming(BF)systems utilize the spatial multiplexing method and significantly improve system capacity.Due to forming directional beams,BF technology can significantly reduce system's energy overhead compared with omni-directional antenna systems,meanwhile,the closed-loop beamforming system based on codebook can effectively estimate the channel using the part of the channel state infonnation(CSI)fed back by the receiver,and it can significantly reduce system complexity and improve system performance.This paper mainly studies limited CSI feedback based beamforming mechanism in millimeter-wave communication system.The main work is divided into the following three aspects:(1)In beamforming systems,when the problem of channel directional variation under temporally correlated channels is considered,this paper studies a rotation-codebook based differential feedback beamforming system.Using matrix analysis theory,by projecting the channel directional variation into Grassmannian manifold,the codebook updating strategy based on rotation codebook gives the method of tracking channel directional variation.In previous studies,only the channel tracking of the system under Gaussian Markov channel is considered.While,in the actual channel propagation environment,limited-path channel model can more accurately simulate the actual physical channel.Therefore,it is fairly necessary to study partial CSI limited-feedback tracking algorithms under the limited-path channel model.At the same time,considering the actual BF system,it is often the case that the signal is occluded during transmission.This article also expands to investigate the application of the system and considers the mathematical principle analysis of channel main path occlusion and recovery as well as the tracking effect verification.The simulation results show that under limited-path model,the rotation codebook based algorithm can effectively track channel directional variation and improve the system capacity for different application scenarios.(2)The existing codebook based limited feedback precoding beamforming system is of low efficiency due to the need for codeword search phase and channel index feedback phase prior to sending payload and highly computational complexity when the receiver uses the codeword selection criterion for optimal quantization codeword calculation.As to the above existing problems in signal-based beamforming mechanism,beamforming systems based on known position can provide good system performance due to the computational overhead and feedback overhead of codeword searching and feedback that can be omitted.As to the two different BF systems,to further comparatively analyze its spectral efficiency and energy efficiency is necessary.So,based on spectral efficiency and energy efficiency analysis model,this paper gives its comparison analysis.Simulation results show that this method can significantly improve the system spectral efficiency(SE)and energy efficiency(EE).(3)Given the fact that the beamforming design ultimately comes back to the actual system design and deployment,after analyzing the known-position based beamforming method,this paper also made corresponding efforts in this aspect.Assisted by the rapid prototyping hardware and software platform LabVIEW and USRP,this paper builds a 2×1 beamforming downlink system,the system uses M-QAM OFDM modulation and demodulation technologies,at the same time,the corresponding relationship between the beamforming transmission angle and the actual received signal strength is analyzed and simulated,the simulation results show that the beamforming platform can obviously observe the coherent enhancement and coherent weakening effect.Also,the system conducted a wireless transmission test,and it is verified by receiving constellation and system error rate,the results show that the system can achieve high signal reception performance and high system error rate performance.