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: "achieving massive mimo spectral efficiency with a not so large number of antennas"
  Abstract: Time-Division Duplexing (TDD) allows to estimate the downlink channels for an arbitrarily large number of base station antennas from a finite number of orthogonal uplink pilot signals, by exploiting channel reciprocity. Based on this observation, a recently proposed "Massive MIMO" scheme was shown to achieve unprecedented spectral efficiency in realistic conditions of distance-dependent pathloss and channel coherence time and bandwidth. The main focus and contribution of this paper is an improved Network-MIMO TDD architecture achieving spectral efficiencies comparable with "Massive MIMO", with one order of magnitude fewer antennas per active user per cell (roughly, from 500 to 50 antennas). The proposed architecture is based on a family of Network-MIMO schemes defined by small clusters of cooperating base stations, zero-forcing multiuser MIMO precoding with suitable inter-cluster interference mitigation constraints, uplink pilot signals allocation and frequency reuse across cells. The key idea consists of partitioning the users into equivalence classes, optimizing the Network-MIMO scheme for each equivalence class, and letting a scheduler allocate the channel time-frequency dimensions to the different classes in order to maximize a suitable network utility function that captures a desired notion of fairness. This results in a mixed-mode Network-MIMO architecture, where different schemes, each of which is optimized for the served user equivalence class, are multiplexed in time-frequency. In order to carry out the performance analysis and the optimization of the proposed architecture in a systematic and computationally efficient way, we consider the large-system regime where the number of users, the number of antennas, and the channel coherence block length go to infinity with fixed ratios.

Connected through hyperedge HE-1 (induced by source paper "performance of multi cell massive mimo systems with interference decoding"):
  with members:
    - "large scale fading decoding in cellular massive mimo systems with spatially correlated channels"
    - "massive mimo has unlimited capacity"
    - "gaussian multiple access via compute and forward"
    - "uplink interference reduction in large scale antenna systems"
    - "joint power allocation and user association optimization for massive mimo systems"
    - "robust pilot decontamination based on joint angle and power domain discrimination"
    - "optimal achievable rates for interference networks with random codes"
    - "system architecture and key technologies for 5g heterogeneous cloud radio access networks"

Connected through hyperedge HE-2 (induced by source paper "joint user selection power allocation and precoding design with imperfect csit for multi cell mu mimo downlink systems"):
  with members:
    - "optimal pilot and payload power control in single cell massive mimo systems"
    - "on the capacity of cloud radio access networks with oblivious relaying"
    - "on the ergodic rate lower bounds with applications to massive mimo"
    - "massive mimo with imperfect channel covariance information"
    - "sum rate maximization for linearly precoded downlink multiuser miso systems with partial csit a rate splitting approach"
    - "robust transmission in downlink multiuser miso systems a rate splitting approach"
    - "cell free massive mimo versus small cells"
    - "a rate splitting strategy for massive mimo with imperfect csit"

Connected through hyperedge HE-3 (induced by source paper "asymptotic analysis of rzf over double scattering channels with mmse estimation"):
  with members:
    - "massive mimo has unlimited capacity"
    - "multi cell massive mimo performance with double scattering channels"
    - "no downlink pilots are needed in tdd massive mimo"
    - "linear precoding based on polynomial expansion large scale multi cell mimo systems"
    - "a coordinated approach to channel estimation in large scale multiple antenna systems"
    - "random beamforming over quasi static and fading channels a deterministic equivalent approach"
    - "large system analysis of linear precoding in correlated miso broadcast channels under limited feedback"
    - "asymptotic analysis of double scattering channels"

Connected through hyperedge HE-4 (induced by source paper "fog massive mimo a user centric seamless hot spot architecture"):
  with members:
    - "a novel alternative to cloud ran for throughput densification coded pilots and fast user packet scheduling at remote radio heads"
    - "realizing the tactile internet haptic communications over next generation 5g cellular networks"
    - "modeling and analysis of cellular networks using stochastic geometry a tutorial"
    - "ergodic spectral efficiency in mimo cellular networks"
    - "unique coverage in boolean models"
    - "system level performance evaluation of lte v2x network"
    - "an uplink downlink duality for cloud radio access network"
    - "rrh based massive mimo with on the fly pilot contamination control"

Connected through hyperedge HE-5 (induced by source paper "5g massive mimo architectures self backhauled small cells versus direct access"):
  with members:
    - "performance analysis for practical unmanned aerial vehicle networks with los nlos transmissions"
    - "performance of massive mimo self backhauling for ultra dense small cell deployments"
    - "performance of dynamic and static tdd in self backhauled millimeter wave cellular networks"
    - "uplink sounding reference signal coordination to combat pilot contamination in 5g massive mimo"
    - "joint backhaul access analysis of full duplex self backhauling heterogeneous networks"
    - "analysis of massive mimo enabled downlink wireless backhauling for full duplex small cells"
    - "the new frontier in ran heterogeneity multi tier drone cells"
    - "performance impact of los and nlos transmissions in dense cellular networks"

Connected through hyperedge HE-6 (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"
    - "smart pilot assignment for massive mimo"
    - "massive mimo for next generation wireless systems"
    - "optimizing multi cell massive mimo for spectral efficiency how many users should be scheduled"

Connected through hyperedge HE-7 (induced by source paper "stochastic modeling and analysis of user centric network mimo systems"):
  with members:
    - "a stochastic analysis of network mimo systems"
    - "user centric intercell interference nulling for downlink small cell networks"
    - "adaptive multicell 3d beamforming in multi antenna cellular networks"
    - "a tractable model for noncoherent joint transmission base station cooperation"
    - "sparse beamforming and user centric clustering for downlink cloud radio access network"
    - "location aware cross tier coordinated multipoint transmission in two tier cellular networks"
    - "analytical modeling of uplink cellular networks"
    - "network mimo with linear zero forcing beamforming large system analysis impact of channel estimation and reduced complexity scheduling"

Connected through hyperedge HE-8 (induced by source paper "massive mimo performance tdd versus fdd what do measurements say"):
  with members:
    - "performance characterization of a real time massive mimo system with los mobile channels"
    - "overview of full dimension mimo in lte advanced pro"
    - "an overview of signal processing techniques for millimeter wave mimo systems"
    - "on the number of rf chains and phase shifters and scheduling design with hybrid analog digital beamforming"
    - "hybrid digital and analog beamforming design for large scale antenna arrays"
    - "no downlink pilots are needed in tdd massive mimo"
    - "massive mimo ten myths and one critical question"
    - "reciprocity calibration for massive mimo proposal modeling and validation"

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)