Research On Millimeter Wave Hybrid Beamforming Technology

As the next generation(5G) mobile communication technology, Millimeter wave communication technology, caused a great deal of attention, can provide up to GHz available frequency spectrum, and on this basis to increase the data transfer rate of the next generation of mobile communications to Gbps above, to achieve this goal, first of all, it needs to overcome that the loss and decay of millimeter wave in the process of wireless transmission of are several orders of magnitude higher than that of traditional microwave. Millimeter wave communication system, therefore, must use large array antenna to get array antenna beamforming gain, and to improve the spectrum efficiency in millimeter wave communication system.In traditional multiple antenna systems, multiple data stream of beamforming, precoding techniques namely, is coded by full digital baseband. Although full digital coding can get higher gain, but it must be deployed that the number of antenna equals to the number of transceiver, because the number antenna of millimeter wave communication system is more, strict requirements to real-time signal processing makes full digital implementation not workable, also, because of the high costs and great energy consumption, the digital coding of beamforming technology in millimeter wave communication system will be limited.Analog processing in RF domain can reduce the number of digital transceiver(less than sending and receiving antenna number), transceiver controls a certain number of antennas to produce a beam and point to a user through analog phase shifter, but when space distribution of users is intensive or overlap, this method will bring serious interference between users. In order to solve this problem, multiple data stream digital baseband coding can be done before the analog beamforming to improve performance, named hybrid beamforming system; The hybrid beamforming of millimeter wave communication system can effectively reduce the number of transceiver, and reduce degree of difficulty of implementation of beamforming.This paper's work is based on hybrid coding structure, beamforming technology is implemented in the millimeter wave communication system, the main contents are as follows:1. Analysis of the millimeter wave channel characteristic, as the millimeter wave frequency path loss is serious, leading to the limited space selectivity of propagation of the millimeter wave, the distribution in the antenna array also leads to high correlation between antenna array elements, so the space is not related to the space uncorrelated Rayleigh model is not suitable for millimeter wave channel. Sparse channel model is adopted in this article's research, the model describes the clustering characteristics of multipath, which contains a small amount of the main path, with the center of each main cluster contains a blade diameter, the channel can describe the small scope well, such as indoor scenarios of the millimeter wave propagation characteristics.2. Improved hybrid beamforming algorithm based on the traversing search: this search algorithm is divided into RF codebook search and baseband coding matrix calculation; First of all, based on the maximum mutual information criterion, get the optimal RF coding matrix by traversing search in the RF codebook, and then based on the optimal unconstrained coding criterion, using RF coding matrix computation to calculate the baseband coding matrix; Simulation analysis shows that the improved algorithm can reduce search complexity and achieve good performance.3. AoA estimation of hybrid beamforming algorithm based on MUSIC: algorithm is implemented by calculating the baseband coding matrix and RF coding matrix; Through orthogonal matching pursuit, the RF coding matrix is calculated, and then based on the maximum mutual information criterion, calculation of baseband coding matrix is done, After coding signal on the sending side and then through the channel, the receiver utilizes MUSIC algorithm to construct signal subspace and noise subspace, and make use of the orthogonality between noise subspace and signal subspace in the frequency domain spectrum peak search, with the spectral peak, angle of arrival and RF coding matrix of the received signal can be get, and then based on the maximum mutual information criterion, the receiving baseband coding matrix is calculated; The simulation analysis shows that the proposed algorithm has lower complexity and can achieve good performance in millimeter wave communication with large-scale array antenna.