Motivated by the need to use spectrum more efficiently, this paper investigates fine grained spectrum sharing (FGSS) in Multi-User massive MIMO (MU-mMIMO) systems where a neutral host enables users from different operators to share the same resource blocks. To be accepted by operators, FGSS must i) guarantee isolation so that the load of one operator does not impact the performance of another, and ii) avoid cross-subsidization whereby one operator gains more from sharing than another. We first formulate and solve an offline problem to assess the potential performance gains of FGSS with respect to the static spectrum sharing case, where operators have fixed separate sub-bands, and find that the gains can be significant, motivating the development for online solutions for FGSS. Transitioning from an offline to an online study presents unique challenges, including the lack of apriori knowledge regarding the performance of the fixed sharing case that is required to ensure isolation and cross-subsidization avoidance. We overcome these challenges and propose an online algorithm that is fast and significantly outperforms the static case. The main finding is that FGSS for a MU-mMIMO downlink system is doable in a way that is ``safe" to operators and brings large gains in spectrum efficiency (e.g., for 4 operators, a gain above 60\% is seen in many cases).

翻译：本文以提高频谱利用效率为出发点，研究了多用户大规模MIMO（MU-mMIMO）系统中的细粒度频谱共享（FGSS）方案，其中中立主机使不同运营商的用户能够共享相同的资源块。为获得运营商接纳，FGSS必须满足两大条件：其一，确保隔离性，使某一运营商的负载不会影响其他运营商的性能；其二，避免交叉补贴现象，即防止某一运营商从共享中获益超过其他运营商。我们首先构建并求解离线问题，以评估FGSS相对于静态频谱共享方案（运营商固定分配独立子频段）的潜在性能增益，发现其增益可能非常显著，这推动了FGSS在线解决方案的开发。从离线研究转向在线研究面临独特挑战，包括缺乏确保隔离性和避免交叉补贴所需的、关于固定共享方案性能的先验知识。我们克服了这些挑战，提出了一种快速在线算法，其性能显著优于静态方案。主要研究结论表明：MU-mIMO下行链路系统的FGSS能够以对运营商“安全”的方式实现，并为频谱效率带来大幅提升（例如在四运营商场景中，多数情况下可获得超过60%的增益）。