In this paper, we investigate a cell-free massive MIMO system with both access points (APs) and user equipments (UEs) equipped with multiple antennas over jointly correlated Rayleigh fading channels. We study four uplink implementations, from fully centralized processing to fully distributed processing, and derive achievable spectral efficiency (SE) expressions with minimum mean-squared error successive interference cancellation (MMSE-SIC) detectors and arbitrary combining schemes. Furthermore, the global and local MMSE combining schemes are derived based on full and local channel state information (CSI) obtained under pilot contamination, which can maximize the achievable SE for the fully centralized and distributed implementation, respectively. We study a two-layer decoding implementation with an arbitrary combining scheme in the first layer and optimal large-scale fading decoding in the second layer. Besides, we compute novel closed-form SE expressions for the two-layer decoding implementation with maximum ratio combining. We compare the SE of different implementation levels and combining schemes and investigate the effect of having additional UE antennas. Note that increasing the number of antennas per UE may degrade the SE performance and the optimal number of UE antennas maximizing the SE is related to the implementation levels, the length of the resource block, and the number of UEs.

翻译：在本文中,我们调查了一个无细胞的大型大型MIMO系统,其接入点和用户设备都配有多个天线,这些天线由Raylei Layle 淡化管道共同连接。我们研究了四个从完全集中处理到完全分布的处理的连接实施,并取得了可实现的光谱效率(SE)的表达方式,其中最小平均和平均差错的连续取消干扰检测器(MMSE-SIC)和任意组合计划。此外,全球和地方的MMSE组合计划是根据在试点污染下获得的全面和当地频道状态信息(CSI)制定的,这可以最大限度地实现完全集中和分布执行的SE。我们研究的是两层解码实施过程,其中有一个任意的组合方案,第二个层是最佳的大规模解密处理。此外,我们还将两层解码实施的新封闭式SEE表达方式与最大混合。我们比较了不同执行水平的SEEEE和组合计划,并调查增加UE天线的效果。我们注意到,增加每层天线的数量可能会降低SEA的性能和最优度。