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: "covariance matrix estimation in massive mimo"
  Abstract: Interference during the uplink training phase significantly deteriorates the performance of a massive MIMO system. The impact of the interference can be reduced by exploiting the second-order statistics of the channel vectors, e.g., to obtain the minimum mean squared error estimates of the channel. In practice, the channel covariance matrices have to be estimated. The estimation of the covariance matrices is also impeded by the interference during the training phase. However, the coherence interval of the covariance matrices is larger than that of the channel vectors. This allows us to derive methods for accurate covariance matrix estimation by the appropriate assignment of pilot sequences to the users in consecutive channel coherence intervals. To keep the computational complexity in check, we exploit common structure of the covariance matrices.

Connected through hyperedge HE-1 (induced by source paper "scalable cell free massive mimo systems"):
  with members:
    - "a new look at cell free massive mimo making it practical with dynamic cooperation"
    - "scalability aspects of cell free massive mimo"
    - "making cell free massive mimo competitive with mmse processing and centralized implementation"
    - "covariance matrix estimation for massive mimo"
    - "massive mimo in sub 6 ghz and mmwave physical practical and use case differences"
    - "on the performance of backhaul constrained cell free massive mimo with linear receivers"
    - "fog massive mimo a user centric seamless hot spot architecture"
    - "massive mimo has unlimited capacity"

Connected through hyperedge HE-2 (induced by source paper "on the spectral efficiency for massive mimo systems with imperfect spacial covariance information"):
  with members:
    - "covariance matrix estimation for massive mimo"
    - "massive mimo has unlimited capacity"
    - "superimposed pilots are superior for mitigating pilot contamination in massive mimo"
    - "massive mimo pilot decontamination and channel interpolation via wideband sparse channel estimation"
    - "massive mimo with imperfect channel covariance information"
    - "path loss shadow fading and line of sight probability models for 5g urban macro cellular scenarios"
    - "massive mimo for next generation wireless systems"
    - "what will 5g be"

Connected through hyperedge HE-3 (induced by source paper "massive mimo with spatially correlated rician fading channels"):
  with members:
    - "covariance matrix estimation for massive mimo"
    - "uplink spectral efficiency of massive mimo with spatially correlated rician fading"
    - "impact of line of sight and unequal spatial correlation on uplink mu mimo systems"
    - "massive mimo pilot decontamination and channel interpolation via wideband sparse channel estimation"
    - "massive mimo with imperfect channel covariance information"
    - "asymptotic analysis of multicell massive mimo over rician fading channels"
    - "power scaling of uplink massive mimo systems with arbitrary rank channel means"
    - "massive mimo for next generation wireless systems"

Connected through hyperedge HE-4 (induced by source paper "large system analysis of massive mimo with optimal m mmse processing"):
  with members:
    - "covariance matrix estimation for massive mimo"
    - "fundamental asymptotic behavior of two user distributed massive mimo"
    - "a bilinear equalizer for massive mimo systems"
    - "massive mimo has unlimited capacity"
    - "large system analysis of power normalization techniques in massive mimo"
    - "massive mimo with imperfect channel covariance information"
    - "massive mimo with multi cell mmse processing exploiting all pilots for interference suppression"
    - "massive mimo in real propagation environments do all antennas contribute equally"

Connected through hyperedge HE-5 (induced by source paper "a low complexity antenna layout aware spatial covariance matrix estimation method"):
  with members:
    - "massive mimo has unlimited capacity"
    - "massive mimo with imperfect channel covariance information"
    - "what will 5g be"
    - "pilot contamination and precoding in multi cell tdd systems"

Connected through hyperedge HE-6 (induced by source paper "fundamental asymptotic behavior of two user distributed massive mimo"):
  with members:
    - "covariance matrix estimation for massive mimo"
    - "a bilinear equalizer for massive mimo systems"
    - "massive mimo has unlimited capacity"
    - "massive mimo pilot decontamination and channel interpolation via wideband sparse channel estimation"
    - "massive mimo with imperfect channel covariance information"
    - "massive mimo for next generation wireless systems"

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)