In this paper, we investigate a cell-free massive MIMO system with both access points and user equipments equipped with multiple antennas over the Weichselberger Rayleigh fading channel. We study the uplink spectral efficiency (SE) based on a two-layer decoding structure with maximum ratio (MR) or local minimum mean-square error (MMSE) combining applied in the first layer and optimal large-scale fading decoding method implemented in the second layer, respectively. To maximize the weighted sum SE, an uplink precoding structure based on an Iteratively Weighted sum-MMSE (I-WMMSE) algorithm using only channel statistics is proposed. Furthermore, with MR combining applied in the first layer, we derive novel achievable SE expressions and optimal precoding structures in closed-form. Numerical results validate our proposed results and show that the I-WMMSE precoding can achieve excellent sum SE performance.
翻译:在本文中,我们研究了一个无细胞的大型MIMO系统,该系统有入口和用户设备,在Weichselberger Rayleigh 淡化的频道上安装了多天线。我们研究了上链光谱效率(SE),其基础是双层解码结构,其最大比值(MR)或当地最低平均平方差(MMSE)分别适用于第一层和第二层采用的最佳大规模解码方法。为了最大限度地增加SE的加权总和,SE是一种仅使用频道统计数据的循环加权总和(I-WMMSE)的上链预编码结构。此外,我们用在第一层应用的MR组合,在封闭式中产生了新的SE表达方式和最佳预码结构。数字结果证实了我们所提议的结果,并表明I-WMMSE预编码能够取得出色的SE性能。