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: "smart pilot assignment for massive mimo"
  Abstract: A massive multiple-input multiple-output (MIMO) system, which utilizes a large number of antennas at the base station (BS) to serve multiple users, suffers from pilot contamination due to inter-cell interference. A smart pilot assignment (SPA) scheme is proposed in this letter to improve the performance of users with severe pilot contamination. Specifically, by exploiting the large-scale characteristics of fading channels, the BS first measures the inter-cell interference of each pilot sequence caused by the users with the same pilot sequence in other adjacent cells. Then, in contrast to the conventional schemes which assign the pilot sequences to the users randomly, the proposed SPA method assigns the pilot sequence with the smallest inter-cell interference to the user having the worst channel quality in a sequential way to improve its performance. Simulation results verify the performance gain of the proposed scheme in typical massive MIMO systems.

Connected through hyperedge HE-1 (induced by source paper "on the pilot contamination attack in multi cell multiuser massive mimo networks"):
  with members:
    - "pilot spoofing attack by multiple eavesdroppers"
    - "multiple antennas secure transmission under pilot spoofing and jamming attack"
    - "active attack on user load achieving pilot design in massive mimo networks"
    - "user load analysis and pilot sequence design for multi cell massive mimo networks"
    - "the world s first real time testbed for massive mimo design implementation and validation"
    - "multi cell multiuser massive mimo networks user capacity analysis and pilot design"
    - "massive mimo pilot retransmission strategies for robustification against jamming"
    - "subverting massive mimo by smart jamming"

Connected through hyperedge HE-2 (induced by source paper "enhanced channel estimation in massive mimo via coordinated pilot design"):
  with members:
    - "pilot contamination mitigation with reduced rf chains"
    - "fractional programming for communication systems part i power control and beamforming"
    - "optimization of mimo device to device networks via matrix fractional programming a minorization maximization approach"
    - "a successive optimization approach to pilot design for multi cell massive mimo systems"
    - "joint pilot design and uplink power allocation in multi cell massive mimo systems"
    - "pilot beam pattern design for channel estimation in massive mimo systems"
    - "massive mimo for next generation wireless systems"
    - "blind pilot decontamination"

Connected through hyperedge HE-3 (induced by source paper "large scale fading decoding in cellular massive mimo systems with spatially correlated channels"):
  with members:
    - "two layer decoding in cellular massive mimo systems with spatial channel correlation"
    - "uplink massive mimo for channels with spatial correlation"
    - "massive mimo has unlimited capacity"
    - "performance of cell free massive mimo systems with mmse and lsfd receivers"
    - "uplink interference reduction in large scale antenna systems"
    - "massive mimo with non ideal arbitrary arrays hardware scaling laws and circuit aware design"
    - "what will 5g be"
    - "massive mimo for maximal spectral efficiency how many users and pilots should be allocated"

Connected through hyperedge HE-4 (induced by source paper "pilot contamination mitigation with reduced rf chains"):
  with members:
    - "hybrid analog digital beamforming for massive mimo systems"
    - "partially connected hybrid precoding in mm wave systems with dynamic phase shifter networks"
    - "alternating minimization algorithms for hybrid precoding in millimeter wave mimo systems"
    - "hybrid mimo architectures for millimeter wave communications phase shifters or switches"
    - "channel estimation and hybrid precoding for millimeter wave cellular systems"
    - "pilot beam pattern design for channel estimation in massive mimo systems"
    - "what will 5g be"
    - "spatially sparse precoding in millimeter wave mimo systems"

Connected through hyperedge HE-5 (induced by source paper "location aided pilot contamination avoidance for massive mimo systems"):
  with members:
    - "massive mimo has unlimited capacity"
    - "mitigating pilot contamination through location aware pilot assignment in massive mimo networks"
    - "performance analysis of massive mimo for cell boundary users"
    - "spatially common sparsity based adaptive channel estimation and feedback for fdd massive mimo"
    - "pilot reuse for massive mimo transmission over spatially correlated rayleigh fading channels"
    - "massive mimo for next generation wireless systems"
    - "optimizing multi cell massive mimo for spectral efficiency how many users should be scheduled"
    - "blind pilot decontamination"

Connected through hyperedge HE-6 (induced by source paper "location aware pilot allocation in multi cell multi user massive mimo networks"):
  with members:
    - "massive mimo with imperfect channel covariance information"
    - "cell free massive mimo versus small cells"
    - "multi cell multiuser massive mimo networks user capacity analysis and pilot design"
    - "mitigating pilot contamination through location aware pilot assignment in massive mimo networks"
    - "blind pilot decontamination"
    - "a coordinated approach to channel estimation in large scale multiple antenna systems"
    - "pilot contamination and precoding in multi cell tdd systems"

Connected through hyperedge HE-7 (induced by source paper "a successive optimization approach to pilot design for multi cell massive mimo systems"):
  with members:
    - "joint pilot design and uplink power allocation in multi cell massive mimo systems"
    - "massive mimo ten myths and one critical question"
    - "pilot reuse for massive mimo transmission over spatially correlated rayleigh fading channels"
    - "outage constrained robust transmit optimization for multiuser miso downlinks tractable approximations by conic optimization"

Connected through hyperedge HE-8 (induced by source paper "on reusing pilots among interfering cells in massive mimo"):
  with members:
    - "cell free massive mimo versus small cells"
    - "no downlink pilots are needed in tdd massive mimo"
    - "interference management in 5g reverse tdd hetnets with wireless backhaul a large system analysis"
    - "a multi cell mmse precoder for massive mimo systems and new large system analysis"
    - "5g ultra dense cellular networks"
    - "when pilots should not be reused across interfering cells in massive mimo"
    - "massive mimo performance evaluation based on measured propagation data"
    - "massive mimo systems with non ideal hardware energy efficiency estimation and capacity limits"

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)