This paper considers the problem of beam alignment in a cell-free massive MIMO deployment with multiple access points (APs) and multiple user equipments (UEs) simultaneously operating in the same millimeter wave frequency band. Assuming the availability of a control channel at sub-6 GHz frequencies, a protocol is developed that permits estimating, for each UE, the strongest propagation path from each of the surrounding APs, and to perform user-centric association between the UEs and the APs. Estimation of the strongest paths from nearby APs is realized at the UE in a one-phase procedure, during which all the APs simultaneously transmit on pseudo-randomly selected channels with pseudo-random transmit beamformers. An algorithm for orthogonal channels assignment to the APs is also proposed, with the aim of minimizing the mutual interference between APs that transmit on the same channels. The performance of the proposed strategy is evaluated both in terms of probability of correct detection of the directions of arrival and of departure associated to the strongest beam from nearby APs, and in terms of downlink and uplink signal-to-interference-plus-noise ratio. Numerical results show that the proposed approach is effective and capable of efficiently realizing beam alignment in a multi-UE multi-AP wireless scenario.
翻译:本文考虑了在同一个毫米波频波带同时运行的无细胞大规模MIMO部署中,使用多个接入点和多用户设备(UEs)进行波束对齐的问题。假设在5-6千兆赫频率上有一个控制通道,将制定一个协议,为每个UE估计每个周围AP的最强传播路径,并进行UE和AP之间的以用户为中心的联系。在UE以一个阶段的程序对附近APs的最强路径进行估计,在这一过程中,所有APs同时以假随机传输伪随机选择的频道的假随机传输信号。还提议对APs进行正方形通道分配算法,以尽量减少在同一频道上传输的APs之间的相互干扰。对拟议战略的效绩进行评估,一方面是为了正确探测附近APs最强的抵达和离开方向的概率,另一方面是为了从下链接和上连接信号-连接到假随机传输信号发送信号信号信号信号。还提议为APs设定一个高效的多级定位方案,以显示一个有效的多级定位方案。