Research On Millimeter-wave Analog Beamforming Technology

With the prosperity of the Internet, larger wireless transmission rate and bandwidth is needed. Because of its ease of integration of large-scale antennas and rich frequency resources, the millimeter-wave communication has been widely concerned. To compensate the large path loss characteristic of the millimeter-wave signal, the beamforming technique is used to increase the link budget. Therefore, the thesis mainly researches the millimeter-wave analog beamforming technology.1) The essence of millimeter-wave analog beamforming technology is beam search, which may also be referred to as switched-beam-based beamforming technology. In this thesis, we first summarize the existing research on millimeter-wave analog beamforming from the perspective of beam search complexity: including two-stage search scheme in IEEE 802.11 ad, gradient-ascent-based search algorithm and binary search algorithm. And then, by analyzing the above three types of algorithms'defects in multipath channel, a multi-path beam search scheme based on binary search algorithm is proposed. In this scheme, the number of selected beams in each level is greater than or equal to the number of paths, so it can increase the chance of finding several local optimal beams.And in the stage of finest beam search, we selectively delete beams, then we can obtain the available communication beams among a plurality of local optimal beams and their adjacent beams. Furthermore, for the transmitter we can also get the global optimal beam from these local optimal beams. The simulation results show that, comparing with exhaustive search algorithm, it has almost the same success rate and lower search complexity to get a number of alternative beams.Comparing with binary search algorithm, the proposed algorithm has higher success rate to find the global optimal communication beam in multipath environment.2) For keeping track of moving objects, the digital beam-tracking technology is mature. But this technology can't be applied to single-link analog beamforming antenna structure. IEEE 802.11 ad standard specifies beam tracking strategy as detection of the original communication beam's adjacent beams, but its tracking range is very small. Therefore, a fast beam-tracking scheme based on hierarchical search strategy is designed for LOS scenarios in the thesis. This scheme expands the tracking range by stepping back to a certain search level and then continuing the binary search process. Simulation results show that the proposed scheme has better performance than IEEE 802.11ad especially on large-scale antenna array.