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: "ofdma based df secure cooperative communication with untrusted users"
  Abstract: In this letter we consider resource allocation for OFDMA-based secure cooperative communication by employing a trusted Decode and Forward (DF) relay among the untrusted users. We formulate two optimization problems, namely, (i) sum rate maximization subject to individual power constraints on source and relay, and (ii) sum power minimization subject to a fairness constraint in terms of per-user minimum support secure rate requirement. The optimization problems are solved utilizing the optimality of KKT conditions for pseudolinear functions.

Connected through hyperedge HE-1 (induced by source paper "subcarrier pairing as channel gain tailoring joint resource allocation for relay assisted secure ofdma with untrusted users"):
  with members:
    - "jammer assisted resource allocation in secure ofdma with untrusted users"
    - "utility regions for df relay in ofdma based secure communication with untrusted users"
    - "secure communications in noma system subcarrier assignment and power allocation"
    - "principles of physical layer security in multiuser wireless networks a survey"
    - "on the complexity of joint subcarrier and power allocation for multi user ofdma systems"
    - "joint subcarrier pairing and power allocation for ofdm transmission with decode and forward relaying"
    - "power and subcarrier allocation for physical layer security in ofdma based broadband wireless networks"

Connected through hyperedge HE-2 (induced by source paper "utility regions for df relay in ofdma based secure communication with untrusted users"):
  with members:
    - "principles of physical layer security in multiuser wireless networks a survey"
    - "power and subcarrier allocation for physical layer security in ofdma based broadband wireless networks"

Connected through hyperedge HE-3 (induced by source paper "enhancing physical layer security in af relay assisted multicarrier wireless transmission enhancing physical layer security in af relay assisted multicarrier wireless transmission"):
  with members:
    - "enhancing physical layer security in dual hop multiuser transmission"
    - "secure communication via an untrusted non regenerative relay in fading channels"
    - "relay placement for physical layer security a secure connection perspective"
    - "power and subcarrier allocation for physical layer security in ofdma based broadband wireless networks"

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)