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: "flip ofdm for unipolar communication systems"
  Abstract: Unipolar communications systems can transmit information using only real and positive signals. This includes a variety of physical channels ranging from optical (fiber or free-space), to RF wireless using amplitude modulation with non-coherent reception, to baseband single wire communications. Unipolar OFDM techniques enable to efficiently compensate frequency selective distortion in the unipolar communication systems. One of the leading examples of unipolar OFDM is asymmetric clipped optical OFDM (ACO-OFDM) originally proposed for optical communications. Flip-OFDM is an alternative approach that was proposed in a patent, but its performance and full potentials have never been investigated in the literature. In this paper, we first compare Flip-OFDM and ACO-OFDM, and show that both techniques have the same performance but different complexities (Flip-OFDM offers 50% saving). We then propose a new detection scheme, which enables to reduce the noise at the Flip-OFDM receiver by almost 3dB. The analytical performance of the noise filtering schemes is supported by the simulation results.

Connected through hyperedge HE-1 (induced by source paper "a comparative study of unipolar ofdm schemes in gaussian optical intensity channel"):
  with members:
    - "on the capacity of bandlimited optical intensity channels with gaussian noise"
    - "comparisons of spectrally enhanced asymmetrically clipped optical ofdm systems"
    - "spectrally and energy efficient ofdm see ofdm for intensity modulated optical wireless systems"
    - "evm and achievable data rate analysis of clipped ofdm signals in visible light communication"
    - "a general framework for transmission with transceiver distortion and some applications"
    - "on the capacity of free space optical intensity channels"

Connected through hyperedge HE-2 (induced by source paper "localisation communication and networking with vlc challenges and opportunities"):
  with members:
    - "adaptive coding and modulation for large scale antenna array based aeronautical communications in the presence of co channel interference"
    - "impact of multipath reflections on the performance of indoor visible light positioning systems"
    - "non orthogonal multiple access for visible light communications"

Connected through hyperedge HE-3 (induced by source paper "quad led and dual led complex modulation for visible light communication"):
  with members:
    - "generalized spatial modulation in indoor wireless visible light communication"
    - "quad led complex modulation qcm for visible light wireless communication"
    - "coded index modulation for non dc biased ofdm in multiple led visible light communication"
    - "flip ofdm for optical wireless communications"

Connected through hyperedge HE-4 (induced by source paper "indoor location estimation with optical based ofdm communications"):
  with members:
    - "impact of multipath reflections on the performance of indoor visible light positioning systems"
    - "indoor positioning in high speed ofdm visible light communications"
    - "robust timing synchronization for ac ofdm based optical wireless communications"
    - "on the performance of single and multi carrie modulation schemes for indoor visible light communication systems"

Connected through hyperedge HE-5 (induced by source paper "quad led complex modulation qcm for visible light wireless communication"):
  with members:
    - "generalized spatial modulation in indoor wireless visible light communication"
    - "flip ofdm for optical wireless communications"

Connected through hyperedge HE-6 (induced by source paper "coded index modulation for non dc biased ofdm in multiple led visible light communication"):
  with members:
    - "flip ofdm for optical wireless communications"

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)