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: "when pilots should not be reused across interfering cells in massive mimo"
  Abstract: The pilot reuse issue in massive multi-input multi-output (MIMO) antenna systems with interfering cells is closely examined. This paper considers scenarios where the ratio of the channel coherence time to the number of users in a cell may be sufficiently large. One such practical scenario arises when the number of users per unit coverage area cannot grow freely while user mobility is low, as in indoor networks. Another important scenario is when the service provider is interested in maximizing the sum rate over a fixed, selected number of users rather than the sum rate over all users in the cell. A sum-rate comparison analysis shows that in such scenarios less aggressive reuse of pilots involving allocation of additional pilots for interfering users yields significant performance advantage relative to the case where all cells reuse the same pilot set. For a given ratio of the normalized coherence time interval to the number of users per cell, the optimal pilot assignment strategy is revealed via a closed-form solution and the resulting net sum-rate is compared with that of the full pilot reuse.

Connected through hyperedge HE-1 (induced by source paper "on reusing pilots among interfering cells in massive mimo"):
  with members:
    - "cell free massive mimo versus small cells"
    - "no downlink pilots are needed in tdd massive mimo"
    - "interference management in 5g reverse tdd hetnets with wireless backhaul a large system analysis"
    - "a multi cell mmse precoder for massive mimo systems and new large system analysis"
    - "5g ultra dense cellular networks"
    - "massive mimo performance evaluation based on measured propagation data"
    - "smart pilot assignment for massive mimo"
    - "massive mimo systems with non ideal hardware energy efficiency estimation and capacity limits"

Connected through hyperedge HE-2 (induced by source paper "pilot reuse strategy maximizing the weighted sum rate in massive mimo systems"):
  with members:
    - "massive mimo performance evaluation based on measured propagation data"
    - "smart pilot assignment for massive mimo"
    - "massive mimo for next generation wireless systems"
    - "what will 5g be"
    - "massive mimo for maximal spectral efficiency how many users and pilots should be allocated"
    - "a coordinated approach to channel estimation in large scale multiple antenna systems"
    - "pilot contamination and precoding in multi cell tdd systems"

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.IT(Information Theory)