human: Given a node-centered hypergraph: <hypergraph>, where nodes represent papers and hyperedges represent sets of papers co-cited by a source paper.

Details of the hypergraph:
Center node: "optimal user association for massive mimo empowered ultra dense wireless networks"
  Abstract: Ultra network densification and Massive MIMO are considered major 5G enablers since they promise huge capacity gains by exploiting proximity, spectral and spatial reuse benefits. Both approaches rely on increasing the number of access elements per user, either through deploying more access nodes over an area or increasing the number of antenna elements per access node. At the network-level, optimal user-association for a densely and randomly deployed network of Massive MIMO empowered access nodes must account for both channel and load conditions. In this paper we formulate this complex problem, report its computationally intractability and reformulate it to a plausible form, amenable to acquire a global optimal solution with reasonable complexity. We apply the proposed optimization model to typical ultra-dense outdoor small-cell setups and demonstrate: (i) the significant impact of optimal user-association to the achieved rate levels compared to a baseline strategy, and (ii) the optimality of alternative network access element deployment strategies.

Connected through hyperedge HE-1 (induced by source paper "load optimization with user association in cooperative and load coupled lte networks"):
  with members:
    - "load balancing via joint transmission in heterogeneous lte modeling and computation"
    - "joint downlink base station association and power control for max min fairness computation and complexity"
    - "a stochastic geometry framework for analyzing pairwise cooperative cellular networks"
    - "a tractable model for noncoherent joint transmission base station cooperation"
    - "what will 5g be"
    - "on association cells in random heterogeneous networks"
    - "analysis of cell load coupling for lte network planning and optimization"
    - "user association for load balancing in heterogeneous cellular networks"

Connected through hyperedge HE-2 (induced by source paper "leveraging synergy of 5g sdwn and multi layer resource management for network optimization"):
  with members:
    - "virtualization of multi cell 802 11 networks association and airtime control"
    - "performance analysis of massive mimo for cell boundary users"
    - "joint user association and resource allocation in virtualized wireless networks"
    - "5g cellular key enabling technologies and research challenges"
    - "system architecture and key technologies for 5g heterogeneous cloud radio access networks"
    - "optimal user cell association for massive mimo wireless networks"

Question: Please tell me which class the center node belongs to. The 40 classes are: cs.NA(Numerical Analysis), cs.MM(Multimedia), cs.LO(Logic in Computer Science), cs.CY(Computers and Society), cs.CR(Cryptography and Security), cs.DC(Distributed, Parallel, and Cluster Computing), cs.HC(Human-Computer Interaction), cs.CE(Computational Engineering, Finance, and Science), cs.NI(Networking and Internet Architecture), cs.CC(Computational Complexity), cs.AI(Artificial Intelligence), cs.MA(Multiagent Systems), cs.GL(General Literature), cs.NE(Neural and Evolutionary Computing), cs.SC(Symbolic Computation), cs.AR(Hardware Architecture), cs.CV(Computer Vision and Pattern Recognition), cs.GR(Graphics), cs.ET(Emerging Technologies), cs.SY(Systems and Control), cs.CG(Computational Geometry), cs.OH(Other Computer Science), cs.PL(Programming Languages), cs.SE(Software Engineering), cs.LG(Machine Learning), cs.SD(Sound), cs.SI(Social and Information Networks), cs.RO(Robotics), cs.IT(Information Theory), cs.PF(Performance), cs.CL(Computation and Language), cs.IR(Information Retrieval), cs.MS(Mathematical Software), cs.FL(Formal Languages and Automata Theory), cs.DS(Data Structures and Algorithms), cs.OS(Operating Systems), cs.GT(Computer Science and Game Theory), cs.DB(Databases), cs.DL(Digital Libraries), cs.DM(Discrete Mathematics). Directly output the class name.

gpt: cs.NI(Networking and Internet Architecture)