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: "application of expurgated ppm to indoor visible light communications part i single user systems"
  Abstract: Visible light communications (VLC) in indoor environments suffer from the limited bandwidth of LEDs as well as from the inter-symbol interference (ISI) imposed by multipath. In this work, transmission schemes to improve the performance of indoor optical wireless communication (OWC) systems are introduced. Expurgated pulse-position modulation (EPPM) is proposed for this application since it can provide a wide range of peak to average power ratios (PAPR) needed for dimming of the indoor illumination. A correlation decoder used at the receiver is shown to be optimal for indoor VLC systems, which are shot noise and background-light limited. Interleaving applied on EPPM in order to decrease the ISI effect in dispersive VLC channels can significantly decrease the error probability. The proposed interleaving technique makes EPPM a better modulation option compared to PPM for VLC systems or any other dispersive OWC system. An overlapped EPPM pulse technique is proposed to increase the transmission rate when bandwidth-limited white LEDs are used as sources.

Connected through hyperedge HE-1 (induced by source paper "hadamard coded modulation for visible light communications"):
  with members:
    - "hadamard coded modulation an alternative to ofdm for optical wireless communications"
    - "high speed visible light indoor networks based on optical orthogonal codes and combinatorial designs"
    - "expurgated ppm using symmetric balanced incomplete block designs"

Connected through hyperedge HE-2 (induced by source paper "hadamard coded modulation an alternative to ofdm for optical wireless communications"):
  with members:
    - "the papr problem in ofdm transmission new directions for a long lasting problem"
    - "expurgated ppm using symmetric balanced incomplete block designs"

Connected through hyperedge HE-3 (induced by source paper "application of expurgated ppm to indoor visible light communications part ii access networks"):
  with members:
    - "high speed visible light indoor networks based on optical orthogonal codes and combinatorial designs"
    - "expurgated ppm using symmetric balanced incomplete block designs"

Connected through hyperedge HE-4 (induced by source paper "high speed visible light indoor networks based on optical orthogonal codes and combinatorial designs"):
  with members:
    - "expurgated ppm using symmetric balanced incomplete block designs"

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)