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: "a hierarchical modulation for upgrading digital broadcast systems"
  Abstract: A hierarchical modulation scheme is proposed to upgrade an existing digital broadcast system, such as satellite TV, or satellite radio, by adding more data in its transmission. The hierarchical modulation consists of a basic constellation, which is the same as in the original system, and a secondary constellation, which carries the additional data for the upgraded system. The upgraded system with the hierarchical modulation is backward compatible in the sense that receivers that have been deployed in the original system can continue receiving data in the basic constellation. New receivers can be designed to receive data carried in the secondary constellation, as well as those in the basic constellation. Analysis will be performed to show the tradeoff between bit rate of the data in secondary constellation and the penalty to the performance of receiving the basic constellation.

Connected through hyperedge HE-1 (induced by source paper "digital domain power division multiplexed dual polarization coherent optical ofdm transmission"):
  with members:
    - "non orthogonal multiple access for visible light communications"

Connected through hyperedge HE-2 (induced by source paper "64 apsk constellation and mapping optimization for satellite broadcasting using genetic algorithms"):
  with members:
    - "on the genetic optimization of apsk constellations for satellite broadcasting"
    - "random access in dvb rcs2 design and dynamic control for congestion avoidance"
    - "constellation design for transmission over nonlinear satellite channels"
    - "combining adaptive coding and modulation with hierarchical modulation in satcom systems"
    - "providing local content in a hybrid single frequency network using hierarchical modulation"

Connected through hyperedge HE-3 (induced by source paper "on optimizing hierarchical modulation in awgn channel"):
  with members:
    - "combining adaptive coding and modulation with hierarchical modulation in satcom systems"

Connected through hyperedge HE-4 (induced by source paper "the application of mimo to non orthogonal multiple access"):
  with members:
    - "a minorization maximization method for optimizing sum rate in the downlink of non orthogonal multiple access systems"
    - "fairness for non orthogonal multiple access in 5g systems"
    - "5g wireless backhaul networks challenges and research advances"
    - "uplink non orthogonal multiple access for 5g wireless networks"
    - "impact of user pairing on 5g non orthogonal multiple access"
    - "on the performance of non orthogonal multiple access in 5g systems with randomly deployed users"

Connected through hyperedge HE-5 (induced by source paper "asynchronous convolutional coded physical layer network coding"):
  with members:
    - "physical layer network coding for two way relaying with qam"
    - "asynchronous physical layer network coding"
    - "joint ldpc and physical layer network coding for asynchronous bi directional relaying"
    - "optimal decoding algorithm for asynchronous physical layer network coding"
    - "physical layer network coding tutorial survey and beyond"
    - "implementation of physical layer network coding"
    - "channel coding and decoding in a relay system operated with physical layer network coding"

Connected through hyperedge HE-6 (induced by source paper "dvb s2 spectrum efficiency improvement with hierarchical modulation"):
  with members:
    - "generic approach for hierarchical modulation performance analysis application to dvb sh"
    - "combining adaptive coding and modulation with hierarchical modulation in satcom systems"
    - "providing local content in a hybrid single frequency network using hierarchical modulation"

Connected through hyperedge HE-7 (induced by source paper "combining adaptive coding and modulation with hierarchical modulation in satcom systems"):
  with members:
    - "generic approach for hierarchical modulation performance analysis application to dvb sh"
    - "improving broadcast channel rate using hierarchical modulation"
    - "providing local content in a hybrid single frequency network using hierarchical modulation"

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)