Research On Massive MIMO Transmit Beamforming Technology For CRAHNs Networks

In recent years,the CRAHNs network has been in-depth studied in order to improve spectrum efficiency,reliablity of communication and networking flexibility.The problems such as the main user interference caused by the frequent switching of frequency points,the energy consumption caused by node broadcasting and the decrease of communication reliability caused by muti-path effect are the focuses in this field.Therefore,the introduction of Massive MIMO technology brings the multi-antenna space freedom to improve the performance of the CRAHNs network.This paper mainly focuses on Massive MIMO transmitter beamforming based on CRAHNs network.(1)The problem is simulated and analyzed: when the traditional narrowband beamforming is applied to a broadband communication scenario,the mismatching of the beam pattern caused by the frequency mismatch will occur and causes the aggravation of the interference between users and the decreasing of communication performance.Then,based on the OFDM wideband communication system,a frequency domain wideband beamforming algorithm applied to the transmitting end is proposed.By compensating for the phase and amplitude changes of signal in the frequency domain,the phase and amplitude distortion due to multiple antennas are canceled in the receiver.The simulation results show that this algorithm can improve the performance degradation of narrowband beamforming algorithm applied to broadband scenarios.(2)The parameters of the antenna array that affect HPBW are analyzed.In order to quantitatively analyze the HPBW of the array,a set of HPBW estimation expressions for estimating linear arrays with arbitrary weights are deduced.The differences between the results of estimated expressions and the real values are analyzed by computer simulation.In order to solve the main beam widening problem in wideband scenario,an optimal sidelobe beamwidth constrained beamforming algorithm is proposed.By constructing an optimization model and using a gradient descending iteration method,a set of array weighting vector can be solved to constrain the main lobe beamwidth and minimize the sidelobe level even in the case of frequency mismatch.(3)This paper proposes the simulations of beam pattern of the traditional uniform linear array,circular array and rectangular planar antenna array in order to study the deversity of nodes in CRAHNs network and limitation of physical space for installation of multiple antennas.A spherical uniform hemispherical array antenna is proposed and its' array factor is deduced.Compared with the projection uniform hemisherical array antenna,the simulations show the proposed array antenna can install more 77 percent antenna elements and focuses a narrower main lobe beam which can improve the spatial resolution of the array.