The main requirements for 5G and beyond connectivity include a uniform high quality of service, which can be attained in crowded scenarios by extra-large MIMO (XL-MIMO) systems. Another requirement is to support increasing connected users in (over)crowded machine-type communication (mMTC). In such scenarios, pilot assignment (PA) becomes paramount to reduce pilot contamination and consequently improve spectral efficiency (SE). We propose a novel quasi-optimal low-complexity iterative pilot assignment strategy for XL-MIMO systems based on a genetic algorithm (GA). The proposed GA-based PA procedure turns the quality of service more uniform, taking into account the normalized mean-square error (NMSE) of channel estimation from each candidate of the population. The simulations reveal that the proposed iterative procedure minimizes the channel estimation NMSE averaged over the UEs. The second procedure is the subarray (SA) selection. In XL-MIMO systems, commonly, a UE is close to a SA antenna subset such that a sufficient data rate can be achieved if only a specific SA serves that UE. Thus, a SA selection procedure is investigated to make the system scalable by defining the maximum number of UEs each SA can help. Hence, the SA clusters are formatted based on the PA decision. Furthermore, we introduce an appropriate channel model for XL-MIMO, which considers a deterministic LoS component with a distance-dependent probability of existence combined with a stochastic spatially correlated Rayleigh NLoS fading component. The developed simulations and analyses rely on this suitable channel model under realistic assumptions of pilot contamination and correlated channels.
翻译:5G及以后的连接的主要要求包括在拥挤情况下通过超大型MIMO(XL-MIMO)系统实现统一的高质量服务。另一项要求是在(超)拥挤的机器类型通信(mMTC)中支持越来越多的连接用户。在这种场景下,导频分配(PA)变得至关重要,以减少导频污染,从而提高频谱效率(SE)。我们提出了一种基于遗传算法(GA)的新型准最优低复杂度迭代导频分配策略,用于XL-MIMO系统。所提出的GA-based PA过程使得服务质量更加统一,考虑每个候选个体的通道估计的归一化均方误差(NMSE)。仿真结果表明,所提出的迭代过程最小化了平均每个UE的通道估计NMSE。第二个过程是子阵列(SA)选择。在XL-MIMO系统中,通常,一个UE靠近一个SA天线子集,只需特定的SA服务该UE即可获得足够的数据传输速率。因此,通过定义每个SA可以帮助的UE的最大数量,研究了SA选择过程,使得系统具有可扩展性。因此,基于PA决策格式化SA集群。此外,我们引入了适合于XL-MIMO的适当的信道模型,该模型考虑了一种具有距离相关的存在概率的确定性LoS分量,结合了随机的空间相关的Rayleigh NLoS衰落分量。开发的仿真和分析基于这种适当的信道模型,在导频污染和相关信道的真实假设下。