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: "safeguarding massive mimo aided hetnets using physical layer security"
  Abstract: This paper exploits the potential of physical layer security in massive multiple-input multiple-output (MIMO) aided two-tier heterogeneous networks (HetNets). We focus on the downlink secure transmission in the presence of multiple eavesdroppers. We first address the impact of massive MIMO on the maximum receive power based user association. We then derive the tractable upper bound expressions for the secrecy outage probability of a HetNets user.We show that the implementation of massive MIMO significantly improves the secrecy performance, which indicates that physical layer security could be a promising solution for safeguarding massive MIMO HetNets. Furthermore, we show that the secrecy outage probability of HetNets user first degrades and then improves with increasing the density of PBSs.

Connected through hyperedge HE-1 (induced by source paper "multi user precoding and channel estimation for hybrid millimeter wave systems"):
  with members:
    - "modeling and analyzing millimeter wave cellular systems"
    - "millimeter wave mimo channel estimation using overlapped beam patterns and rate adaptation"
    - "doubly massive mmwave mimo systems using very large antenna arrays at both transmitter and receiver"
    - "an overview of signal processing techniques for millimeter wave mimo systems"
    - "hybrid digital and analog beamforming design for large scale antenna arrays"
    - "achievable rate of rician large scale mimo channels with transceiver hardware impairments"
    - "massive mimo ten myths and one critical question"
    - "limited feedback hybrid precoding for multi user millimeter wave systems"

Connected through hyperedge HE-2 (induced by source paper "secrecy energy efficiency analysis of uav enabled communication networks"):
  with members:
    - "placement optimization of uav mounted mobile base stations"
    - "cyclical multiple access in uav aided communications a throughput delay tradeoff"
    - "physical layer security in heterogeneous cellular networks"
    - "wireless communications with unmanned aerial vehicles opportunities and challenges"
    - "unmanned aerial vehicle with underlaid device to device communications performance and tradeoffs"
    - "secrecy transmit beamforming for heterogeneous networks"
    - "principles of physical layer security in multiuser wireless networks a survey"
    - "modeling and analysis of k tier downlink heterogeneous cellular networks"

Connected through hyperedge HE-3 (induced by source paper "physical layer security in three tier wireless sensor networks a stochastic geometry approach"):
  with members:
    - "physical layer security in downlink multi antenna cellular networks"
    - "enhancing secrecy with multi antenna transmission in wireless ad hoc networks"
    - "optimal relay selection for physical layer security in cooperative wireless networks"
    - "physical layer security in cellular networks a stochastic geometry approach"
    - "modeling and analysis of k tier downlink heterogeneous cellular networks"
    - "random deployment of data collectors for serving randomly located sensors"
    - "on the throughput cost of physical layer security in decentralized wireless networks"
    - "diversity multiplexing tradeoff for the multiple antenna wire tap channel"

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)