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: "opportunistic downlink interference alignment"
  Abstract: A communication system configured to send data using an interference alignment scheme is disclosed herein. The disclosed communication system includes an MS and a BS. The disclosed BS sends data using a transmission beamforming matrix that minimizes intra-cell interference. The disclosed MS receives the data using a reception beamforming matrix that minimizes inter-cell interference. The BS sends information about a reference beamforming matrix to the MS, and sends a pilot signal to the MS using the reference beamforming matrix. The MS estimates an effective channel using the reference beamforming matrix, and calculates the intensity of an interference signal from an interference BS.

Connected through hyperedge HE-1 (induced by source paper "opportunistic downlink interference alignment for multi cell mimo networks"):
  with members:
    - "codebook based opportunistic interference alignment"
    - "on the achievable dof and user scaling law of opportunistic interference alignment in 3 transmitter mimo interference channels"
    - "effect of receive spatial diversity on the degrees of freedom region in multi cell random beamforming"
    - "parallel opportunistic routing in wireless networks"
    - "opportunistic interference alignment for mimo interfering multiple access channels"
    - "multiuser diversity in interfering broadcast channels achievable degrees of freedom and user scaling law"
    - "multi cell random beamforming achievable rate and degrees of freedom region"
    - "can one achieve multiuser diversity in uplink multi cell networks"

Connected through hyperedge HE-2 (induced by source paper "opportunistic network decoupling with virtual full duplex operation in multi source interfering relay networks"):
  with members:
    - "on the degrees of freedom of the large scale interfering two way relay network"
    - "codebook based opportunistic interference alignment"
    - "real interference alignment exploiting the potential of single antenna systems"
    - "parallel opportunistic routing in wireless networks"
    - "opportunistic interference alignment for mimo interfering multiple access channels"
    - "degrees of freedom of two hop wireless networks everyone gets the entire cake"
    - "opportunistic interference mitigation achieves optimal degrees of freedom in wireless multi cell uplink networks"
    - "opportunistic relaying in wireless networks"

Connected through hyperedge HE-3 (induced by source paper "distributed energy spectral efficiency optimization for partial full interference alignment in multi user multi relay multi cell mimo systems"):
  with members:
    - "limited feedback based interference alignment for interfering multi access channels"
    - "performance analysis and optimization for interference alignment over mimo interference channels with limited feedback"
    - "spectral and energy spectral efficiency optimization of joint transmit and receive beamforming based multi relay mimo ofdma cellular networks"
    - "maximizing energy efficiency in multi relay ofdma cellular networks"
    - "achieving maximum energy efficiency in multi relay ofdma cellular networks a fractional programming approach"
    - "a reconfigurable distributed algorithm for k user mimo interference networks"
    - "exploiting interference alignment in multi cell cooperative ofdma resource allocation"
    - "framework for link level energy efficiency optimization with informed transmitter"

Connected through hyperedge HE-4 (induced by source paper "interference alignment for downlink cellular networks joint scheduling and precoding"):
  with members:
    - "spectral and energy efficiency trade offs in cellular networks"
    - "interference alignment for the k user mimo interference channel"
    - "downlink interference alignment"
    - "degrees of freedom of the k user m times n mimo interference channel"
    - "approaching the capacity of wireless networks through distributed interference alignment"

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)