Research On Channel Estimation And Phase Noise Suppression For Distributed Millimeter Wave System

Distributed antenna system(DAS),serving multiple users on the same time-frequency resources,provides sufficient spatial degrees of freedom to facilitate ultra-high speed wireless communications,and ameliorates inter-cell interference.Such a distributed architecture is very suitable for radio transmission in millimeter-wave(mm Wave)frequency bands.Firstly,the densely deployed RAUs can shorten the distances between transceivers,thus compensating for the significant propagation loss at high frequencies;Secondly,they are highly resistant to the severe blockage effect in mm Wave channels.However,due to the different distances between each RAU and the user,asynchronous reception effects will occur which result in delay spread differences(DSDs)on received signal.How to obtain the accurate channel estimation in the case of DSDs is a significant challenge for a distributed mm Wave massive system.The combination of distributed massive MIMO technology and mm Wave technology makes the system more sensitive to phase noise.Therefore,it is very important to reduce the influence of phase noise on system performance.The two challenges mentioned above are studied in this paper.Considering the impact of DSD,a high precision composite channel estimation algorithm using channel state information reference signal(CSI-RS)and demodulation reference signal(DMRS)is proposed to solve the channel estimation issue.Firstly,an estimation algorithm based on single-port design is proposed to reduce overhead of pilot and design complexity,that is,all RAUs send the same pilot symbol simultaneously.And the receiver only estimates the composite signals,which are regarded as multipath signals,from all RAUs to the UE.The power and delay of each path are estimated based on the distinguishable time-domain multipath signals.Secondly,a channel estimation algorithm using multiple resource blocks(RBs)in coherent bandwidth is proposed to reduce the computational complexity.After obtaining the estimated value of channel in DMRS,the estimated value of channel in the frequency domain is obtained through the interpolation matrix.Simulation results show that this algorithm can achieve high precision estimation of the channel and has certain robustness.To mitigate the influence of phase noise,a phase noise suppression algorithm using blockpilots and comb-pilots is proposed.In the absence of channel state information,the algorithm uses a block-pilots symbol to estimate the initial channel with phase noise,and then uses combpilots to track the change of phase noise in subsequent symbols.Firstly,a linear channel estimation algorithm,which can estimate channel more precisely,is derived to minimize inter-carrier interference(ICI)power in the block-pilots symbol.We derive the closed-form expression of ICI power,and the minimizztion problem is converted to multiple quadratic programming problem.Secondly,comb-pilots are used to estimate and compensate the common phase error(CPE)caused by phase noise.Simulation results show that the proposed algorithm,whose performance is superior to LS algorithm,effectively restrains the influence of phase noise.It is worth mentioning that it also has a good performance in high order modulation system.