Research On Hybrid Precoding In Millimeter Wave Communication Systems

Millimeter wave(mmWave)communications have been considered as one of the most promising technologies for 5G and beyond as a benefit of their substantial bandwidth and high spectral efficiency.Since the number of RF chains in the hybrid precoding architecture is dramatically reduced so as the power consumption,hybrid precoding constitutes one of the most significant technologies for mmWave communications.Recent years,researches in academia and industry have dedicated great efforts to designing energy and spectrum efficient hybrid precoding schemes.However,the existing algorithms still face huge challenges when applied into reality,such as the high computational complexity,high feedback overhead,low energy efficiency,limited broadband transmission rate,and dependence on the instantaneous channel state information(CSI).Therefore,to circumvent the above problems,this thesis is devoted to the systematical researches of high performance hybrid precoding schemes from the perspectives of single user,multiple users,narrowband and wideband communications.The main contributions are as follows:By exploiting the spatial lobe property of the mmWave in the angular domain,a low complexity hybrid precoding scheme is proposed.According to the measurement results of NEWYORK WIRELESS,the cluster based mmWave channel can be divided into multiple low-rank subchannels.Since the angles of paths in different spatial lobes are sufficiently separable,these subchannels are approximately orthogonal.Therefore,the total optimization problem can be divided into several subproblems,so that the total computational complexity can be dramatically reduced.For each subproblem,the method of orthogonal matching pursuit(OMP)is utilized to construct the hybrid precoding matrix.Through the complexity analysis and simulation,it can be observed that the proposed hybrid precoding scheme achieves similar performance with the traditional OMP based scheme while is able to reduce the computational complexity more than 99%.By utilizing the sparseness property of the mmWave in the angular domain,a nonuniform quantization(NUQ)codebook based hybrid precoding schemes are proposed to effectively reduce the feedback overhead.By fully exploiting the sparseness property of the mmWave in the angular domain,the total quantization bits are mapped non-uniformly into the whole angular domain,where the high quantization bits are employed to quantize the effective spatial lobes' coverage angles and low or even zero bits are employed to the other coverage angles.According to different antenna indexes of different hybrid precoding architectures,the beamsteering based NUQ codebooks are constructed.Based on the NUQ codebooks,the OMP based hybrid precoding schemes are proposed.The simulation results validate the effectiveness of the proposed schemes in reducing the feedback overhead.A generalized sub-array connected architecture based hybrid precoding scheme is proposed for the best energy-efficient mmWave transmission.The GSAC architecture,in which the number of RF chains connected to a sub-array and the number of antennas in each subarray can be arbitrary,is proposed.For any given RF chain and antenna configuration,a successive interference cancellation based hybrid precoding algorithm is firstly proposed for maximizing the spectral efficiency.Considering the number of total RF chains is limited,an exhaustive search scheme with moderate complexity is proposed for determining the configuration having the best energy efficiency.Simulation results demonstrate that the proposed scheme is capable of achieving the best energy efficiency for any given numbers of RF chains and antennas.The effects of the beam squint on the performance of ultral-wideband transmission are comprehensively studied,and several hybrid precoding schemes are proposed for effectively suppressing these harmful effects.Several polar diagrams,as well as the defined mean chordal distance and average achievable rate gap metrics,are provided for quantifying the performance losses caused by the beam squint,respectively.When the perfect CSI is known at the transmitter,mean channel matrix,mean channel-covariance matrix and generalized extrinsic mean of subspaces based schemes are proposed by exploiting the correlation between both the paths and the subcarries.When only the angular information is available,several wide beams inspired hybrid precoding schemes are proposed for alleviating the effect of beam squint,which is assisted by multiple sets of phase shifters.Simulation results validate the superiority of the proposed hybrid precoding schemes in terms of suppressing the effect of beam squint and these schemes is capable of achieving near-optimal performance when applying as high as 0.5 GHz bandwidth.A hybrid precoding scheme which is only based on the long-term mmWave statistical CSI is proposed for the wideband multiple-user scenario.According to the sparseness property of the mmWave and the parameters distributions,the covariance matrix associated with the channel matrix for each user on each subcarrier is derived.Then,a SVD and phase extraction based analog precoding matrix designing scheme is proposed for both perfect feedback and limited feedback.For alleviating the effect of the beam squint in the wideband scenario,a phase compensation operation is carried out.In the phase of digital precoding designing,the block diagonalization operation is utilized to handling the interuser interference,while the spectral efficiency is further improved by focusing the power to the low-dimensional effective subspaces.This thesis proposes effective solutions to the problems of high computational complexity,high feedback overhead,low energy efficiency,limited broadband transmission rate and dependence on instantaneous CSI of hybrid precoding in mmWave communications,which provides theoretical support for its development and application.