The problem of beam alignment (BA) in a cell-free massive multiple-input multiple-output (CF-mMIMO) system operating at millimeter wave (mmWaves) carrier frequencies is considered in this paper. Two estimation algorithms are proposed, in association with a protocol that permits simultaneous estimation, on a shared set of frequencies, for each user equipment (UE), of the direction of arrival and departure of the radio waves associated to the strongest propagation paths from each of the surrounding access points (APs), so that UE-AP association can take place. The proposed procedure relies on the existence of a reliable control channel at sub-6 GHz frequency, so as to enable exchange of estimated values between the UEs and the network, and assumes that APs can be identifies based on the prior knowledge of the orthogonal channels and transmit beamforming codebook. A strategy for assigning codebook entries to the several APs is also proposed, with the aim of minimizing the mutual interference between APs that are assigned the same entry. Numerical results show the effectiveness of the proposed detection strategy, thus enabling one shot fast BA for CF-mMIMO systems.
翻译:在以毫米波(mmWaves)载体频率运行的无细胞大规模多投入多输出多输出(CF-mMIMO)系统上,本文审议了波束对齐问题,并提出了两种估计算法,结合一项议定书,允许根据每个用户设备共用的频率,根据每个用户设备共用的一组频率,同时估计每个用户设备与每个周边接入点最强的传播路径相关的无线电波的进离方向,以便进行UE-AP联系。拟议程序依赖于在子6千兆赫频率上有一个可靠的控制频道,以便能够在UE和网络之间交换估计值,并假定AP可以根据事先对正方位通道的了解确定,并传送成型的代码簿。还提出了为几个AP提供编码条目的战略,目的是尽可能减少分配给同一条目的APA的相互干扰。数量结果显示拟议的探测战略的有效性,从而使得CFMIMIM系统能够有一个快速投射速的BA。