Simultaneous Multiuser Beam Training Using Adaptive Hierarchical Codebook for mmWave Massive MIMO

In this paper, a simultaneous multiuser hierarchical beam training scheme for multiuser mmWave massive MIMO systems is proposed based on the designed adaptive hierarchical codebook. Different from the existing work sequentially performing the beam training for different users with the same hierarchical codebook, in our work the hierarchical codebook is designed in an adaptive manner, where the codewords in the current layer are designed according to the beam training results of the previous layer. In particular, multi-mainlobe codewords are designed for simultaneously beam training with all the users, where each mainlobe of the multi-mainlobe codeword covers a spatial region that one or more users are probably in. Except for the bottom layer, there are only two codewords at each layer in the designed adaptive hierarchical codebook, which only requires two times of simultaneous beam training for all the users no matter how many users the BS serves. Simulation results verify the effectiveness of our scheme and show that our scheme can approach the performance of the beam scanning but with considerable reduction in training overhead.