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: "designing multi user mimo for energy efficiency when is massive mimo the answer"
  Abstract: Assume that a multi-user multiple-input multiple-output (MIMO) communication system must be designed to cover a given area with maximal energy efficiency (bit/Joule). What are the optimal values for the number of antennas, active users, and transmit power? By using a new model that describes how these three parameters affect the total energy efficiency of the system, this work provides closed-form expressions for their optimal values and interactions. In sharp contrast to common belief, the transmit power is found to increase (not decrease) with the number of antennas. This implies that energy efficient systems can operate at high signal-to-noise ratio (SNR) regimes in which the use of interference-suppressing precoding schemes is essential. Numerical results show that the maximal energy efficiency is achieved by a massive MIMO setup wherein hundreds of antennas are deployed to serve relatively many users using interference-suppressing regularized zero-forcing precoding.

Connected through hyperedge HE-1 (induced by source paper "optimal policies of advanced sleep modes for energy efficient 5g networks"):
  with members:
    - "energy efficiency of downlink networks with caching at base stations"
    - "a survey of green networking research"

Connected through hyperedge HE-2 (induced by source paper "non orthogonal multiple access in large scale heterogeneous networks"):
  with members:
    - "massive non orthogonal multiple access for cellular iot potentials and limitations"
    - "modulation and multiple access for 5g networks"
    - "nonorthogonal multiple access in large scale underlay cognitive radio networks"
    - "enhancing the physical layer security of non orthogonal multiple access in large scale networks"
    - "cooperative non orthogonal multiple access with simultaneous wireless information and power transfer"
    - "the application of mimo to non orthogonal multiple access"
    - "user association and interference management in massive mimo hetnets"
    - "fairness for non orthogonal multiple access in 5g systems"

Connected through hyperedge HE-3 (induced by source paper "energy efficiency in mimo underlay and overlay device to device communications and cognitive radio systems"):
  with members:
    - "energy efficient power control a look at 5g wireless technologies"
    - "energy efficiency and sum rate when massive mimo meets device to device communication"
    - "energy efficient resource allocation for device to device underlay communication"
    - "dynamic power control for delay aware device to device communications"
    - "resource allocation under channel uncertainties for relay aided device to device communication underlaying lte a cellular networks"
    - "energy efficiency and spectral efficiency tradeoff in device to device d2d communications"
    - "cognitive beamforming for multiple secondary data streams with individual snr constraints"
    - "efficiency resource allocation for device to device underlay communication systems a reverse iterative combinatorial auction based approach"

Connected through hyperedge HE-4 (induced by source paper "uplink downlink rate balancing and throughput scaling in fdd massive mimo systems"):
  with members:
    - "uplink downlink rate balancing in cooperating cellular networks"
    - "a lower bound on the data rate of dirty paper coding in general noise and interference"
    - "massive mimo for next generation wireless systems"
    - "downlink training techniques for fdd massive mimo systems open loop and closed loop training with memory"
    - "noncoherent trellis coded quantization a practical limited feedback technique for massive mimo systems"
    - "massive mimo systems signal processing challenges and research trends"
    - "scaling up mimo opportunities and challenges with very large arrays"
    - "a coordinated approach to channel estimation in large scale multiple antenna systems"

Connected through hyperedge HE-5 (induced by source paper "secrecy and energy efficiency in massive mimo aided heterogeneous c ran a new look at interference"):
  with members:
    - "user association in 5g networks a survey and an outlook"
    - "energy efficient resource assignment and power allocation in heterogeneous cloud radio access networks"
    - "fronthaul constrained cloud radio access networks insights and challenges"
    - "5g cellular key enabling technologies and research challenges"
    - "physical layer security for massive mimo an overview on passive eavesdropping and active attacks"
    - "large scale mimo versus network mimo for multicell interference mitigation"
    - "heterogeneous cloud radio access networks a new perspective for enhancing spectral and energy efficiencies"
    - "what will 5g be"

Connected through hyperedge HE-6 (induced by source paper "deploying dense networks for maximal energy efficiency small cells meet massive mimo"):
  with members:
    - "energy efficient future wireless networks a marriage between massive mimo and small cells"
    - "designing wireless broadband access for energy efficiency are small cells the only answer"
    - "interference management in 5g reverse tdd hetnets with wireless backhaul a large system analysis"
    - "massive mimo performance evaluation based on measured propagation data"
    - "massive mimo with non ideal arbitrary arrays hardware scaling laws and circuit aware design"
    - "massive mimo systems with non ideal hardware energy efficiency estimation and capacity limits"
    - "multiobjective signal processing optimization the way to balance conflicting metrics in 5g systems"
    - "impact of transceiver power consumption on the energy efficiency of zero forcing detector in massive mimo systems"

Connected through hyperedge HE-7 (induced by source paper "massive mimo with non ideal arbitrary arrays hardware scaling laws and circuit aware design"):
  with members:
    - "capacity of simo and miso phase noise channels with common separate oscillators"
    - "uplink performance of time reversal mrc in massive mimo systems subject to phase noise"
    - "massive mimo performance evaluation based on measured propagation data"
    - "optimal multiuser transmit beamforming a difficult problem with a simple solution structure"
    - "on the impact of oscillator phase noise on the uplink performance in a massive mimo ofdm system"
    - "filter bank multicarrier for massive mimo"
    - "massive mimo systems with non ideal hardware energy efficiency estimation and capacity limits"
    - "massive mimo for next generation wireless systems"

Connected through hyperedge HE-8 (induced by source paper "energy aware competitive power allocation for heterogeneous networks under qos constraints"):
  with members:
    - "power control in networks with heterogeneous users a quasi variational inequality approach"
    - "what will 5g be"
    - "optimal design of energy efficient multi user mimo systems is massive mimo the answer"
    - "framework for link level energy efficiency optimization with informed transmitter"
    - "energy efficient precoding for multiple antenna terminals"
    - "optimal linear precoding strategies for wideband noncooperative systems based on game theory part i nash equilibria"
    - "competitive design of multiuser mimo systems based on game theory a unified view"
    - "distributed power allocation with rate constraints in gaussian parallel interference channels"

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)