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: "fractional pilot reuse in massive mimo systems"
  Abstract: Pilot contamination is known to be one of the main impairments for massive MIMO multi-cell communications. Inspired by the concept of fractional frequency reuse and by recent contributions on pilot reutilization among non-adjacent cells, we propose a new pilot allocation scheme to mitigate this effect. The key idea is to allow users in neighboring cells that are closest to their base stations to reuse the same pilot sequences. Focusing on the uplink, we obtain expressions for the overall spectral efficiency per cell for different linear combining techniques at the base station and use them to obtain both the optimal pilot reuse parameters and the optimal number of scheduled users. Numerical results show a remarkable improvement in terms of spectral efficiency with respect to the existing techniques.

Connected through hyperedge HE-1 (induced by source paper "stochastic geometry based uplink analysis of massive mimo systems with fractional pilot reuse"):
  with members:
    - "johnson mehl cell based analysis of ul cellular network with coupled user and bs locations"
    - "fog massive mimo a user centric seamless hot spot architecture"
    - "massive mimo has unlimited capacity"
    - "modeling and analysis of cellular networks using stochastic geometry a tutorial"
    - "a primer on cellular network analysis using stochastic geometry"
    - "user point processes in cellular networks"
    - "poisson hole process theory and applications to wireless networks"
    - "massive mimo enabled full duplex cellular networks"

Connected through hyperedge HE-2 (induced by source paper "cell edge aware precoding for downlink massive mimo cellular networks"):
  with members:
    - "distributed optimization of hierarchical small cell networks a gnep framework"
    - "massive mimo ten myths and one critical question"
    - "operating massive mimo in unlicensed bands for enhanced coexistence and spatial reuse"
    - "energy efficient design of mimo heterogeneous networks with wireless backhaul"
    - "a stochastic geometry framework for analyzing pairwise cooperative cellular networks"
    - "three practical aspects of massive mimo intermittent user activity pilot synchronism and asymmetric deployment"
    - "a tractable model for noncoherent joint transmission base station cooperation"
    - "linear precoding based on polynomial expansion large scale multi cell mimo systems"

Connected through hyperedge HE-3 (induced by source paper "uplink sounding reference signal coordination to combat pilot contamination in 5g massive mimo"):
  with members:
    - "massive mimo unlicensed a new approach to dynamic spectrum access"
    - "massive mimo for next generation wireless systems"

Connected through hyperedge HE-4 (induced by source paper "an overview of transmission theory and techniques of large scale antenna systems for 5g wireless communications"):
  with members:
    - "channel acquisition for massive mimo ofdm with adjustable phase shift pilots"
    - "mixed adc massive mimo detectors performance analysis and design optimization"
    - "performance analysis and location optimization for massive mimo systems with circularly distributed antennas"
    - "uplink achievable rate for massive mimo systems with low resolution adc"
    - "spatially common sparsity based adaptive channel estimation and feedback for fdd massive mimo"
    - "a stochastic geometry framework for analyzing pairwise cooperative cellular networks"
    - "structured compressive sensing based superimposed pilot design in downlink large scale mimo systems"
    - "pilot reuse for massive mimo transmission over spatially correlated rayleigh fading channels"

Connected through hyperedge HE-5 (induced by source paper "robust pilot decontamination based on joint angle and power domain discrimination"):
  with members:
    - "pilot decontamination through pilot sequence hopping in massive mimo systems"
    - "dealing with interference in distributed large scale mimo systems a statistical approach"
    - "blind pilot decontamination"
    - "interference reduction in multi cell massive mimo systems i large scale fading precoding and decoding"
    - "joint spatial division and multiplexing opportunistic beamforming and user grouping"
    - "a coordinated approach to channel estimation in large scale multiple antenna systems"
    - "large system analysis of linear precoding in correlated miso broadcast channels under limited feedback"
    - "energy and spectral efficiency of very large multiuser mimo systems"

Connected through hyperedge HE-6 (induced by source paper "analyzing uplink sinr and rate in massive mimo systems using stochastic geometry"):
  with members:
    - "deploying dense networks for maximal energy efficiency small cells meet massive mimo"
    - "an uplink interference analysis for massive mimo systems with mrc and zf receivers"
    - "on stochastic geometry modeling of cellular uplink transmission with truncated channel inversion power control"
    - "aspects of favorable propagation in massive mimo"
    - "joint rate and sinr coverage analysis for decoupled uplink downlink biased cell associations in hetnets"
    - "analysis and optimization of inter tier interference coordination in downlink multi antenna hetnets with offloading"
    - "massive mimo for next generation wireless systems"
    - "coverage and rate analysis for millimeter wave cellular networks"

Connected through hyperedge HE-7 (induced by source paper "a multi cell mmse precoder for massive mimo systems and new large system analysis"):
  with members:
    - "massive mimo with multi cell mmse processing exploiting all pilots for interference suppression"
    - "massive mimo systems with non ideal hardware energy efficiency estimation and capacity limits"
    - "massive mimo for next generation wireless systems"
    - "uplink linear receivers for multi cell multiuser mimo with pilot contamination large system analysis"
    - "massive mimo for maximal spectral efficiency how many users and pilots should be allocated"
    - "scaling up mimo opportunities and challenges with very large arrays"
    - "large system analysis of linear precoding in correlated miso broadcast channels under limited feedback"
    - "energy and spectral efficiency of very large multiuser mimo systems"

Connected through hyperedge HE-8 (induced by source paper "three practical aspects of massive mimo intermittent user activity pilot synchronism and asymmetric deployment"):
  with members:
    - "deploying dense networks for maximal energy efficiency small cells meet massive mimo"
    - "massive mimo for next generation wireless systems"
    - "massive mimo for maximal spectral efficiency how many users and pilots should be allocated"
    - "five disruptive technology directions for 5g"
    - "achieving massive mimo spectral efficiency with a not so large number of antennas"
    - "transmission capacity of wireless networks"
    - "energy and spectral efficiency of very large multiuser mimo systems"
    - "a tractable approach to coverage and rate in cellular networks"

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)