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: "energy efficient downlink transmission for multicell massive das with pilot contamination"
  Abstract: In this paper, we study the energy efficiency (EE) of a downlink multicell massive distributed antenna system (DAS) in the presence of pilot contamination (PC), where the antennas are clustered on the remote radio heads (RRHs). We employ a practical power consumption model by considering the transmit power, the circuit power, and the backhaul power, in contrast to most of the existing works which focus on colocated antenna systems (CASs), where the backhaul power is negligible. For a given average user rate, we consider the problem of maximizing the EE with respect to the number of antennas of each RRH   $n$  , the number of RRHs   $M$  , and the number of users   $K$   and study the impact of system parameters on the optimal   $n$  ,   $M$  , and   $K$  . Specifically, by applying random matrix theory, we derive the closed-form expressions of the optimal   $n$   and find the solution of the optimal   $M$   and   $K$   under a simplified channel model with maximum ratio transmission. From the results, we find that, to achieve the optimal EE, a large number of antennas is needed for a given user rate and PC. As the number of users increases, EE can be improved further by having more RRHs and antennas. Moreover, if the backhauling power is not large, a massive DAS can be more energy efficient than a massive CAS. These insights provide a useful guide to the practical deployment of massive DASs.

Connected through hyperedge HE-1 (induced by source paper "spectral efficiency analysis of cell free massive mimo systems with zero forcing detector"):
  with members:
    - "downlink precoding with mixed statistical and imperfect instantaneous csi for massive mimo systems"
    - "enhanced max min sinr for uplink cell free massive mimo systems"
    - "on the total energy efficiency of cell free massive mimo"
    - "performance analysis for massive mimo downlink with low complexity approximate zero forcing precoding"
    - "pilot power allocation through user grouping in multi cell massive mimo systems"
    - "energy efficiency in cell free massive mimo with zero forcing precoding design"
    - "cell free massive mimo versus small cells"
    - "how much do downlink pilots improve cell free massive mimo"

Connected through hyperedge HE-2 (induced by source paper "reconfigurable intelligent surfaces for energy efficiency in wireless communication"):
  with members:
    - "energy efficient multi user miso communication using low resolution large intelligent surfaces"
    - "achievable rate maximization by passive intelligent mirrors"
    - "using any surface to realize a new paradigm for wireless communications"
    - "energy efficiency of mmwave massive mimo precoding with low resolution dacs"
    - "intelligent reflecting surface enhanced wireless network via joint active and passive beamforming"
    - "deep learning coordinated beamforming for highly mobile millimeter wave systems"
    - "capacity degradation with modeling hardware impairment in large intelligent surface"
    - "asymptotically optimal estimation algorithm for the sparse signal with arbitrary distributions"

Connected through hyperedge HE-3 (induced by source paper "large system analysis of power normalization techniques in massive mimo"):
  with members:
    - "massive mimo has unlimited capacity"
    - "reducing the computational complexity of multicasting in large scale antenna systems"
    - "joint power allocation and user association optimization for massive mimo systems"
    - "convergence analysis and assurance for gaussian message passing iterative detector in massive mu mimo systems"
    - "pilot contamination is not a fundamental asymptotic limitation in massive mimo"
    - "massive mimo ten myths and one critical question"
    - "performance analysis of massive mimo for cell boundary users"
    - "power allocation schemes for multicell massive mimo systems"

Connected through hyperedge HE-4 (induced by source paper "on the total energy efficiency of cell free massive mimo"):
  with members:
    - "cell free massive mimo versus small cells"
    - "energy efficiency of downlink transmission strategies for cloud radio access networks"
    - "networked mimo with fractional joint transmission in energy harvesting systems"
    - "how much do downlink pilots improve cell free massive mimo"
    - "compute and forward in cell free massive mimo great performance with low backhaul load"
    - "deploying dense networks for maximal energy efficiency small cells meet massive mimo"
    - "energy efficiency optimization for mimo distributed antenna systems"
    - "optimal design of energy efficient multi user mimo systems is massive mimo the answer"

Connected through hyperedge HE-5 (induced by source paper "reducing the computational complexity of multicasting in large scale antenna systems"):
  with members:
    - "a robust design for miso physical layer multicasting over line of sight channels"
    - "multicast multigroup beamforming for per antenna power constrained large scale arrays"
    - "massive mimo multicasting in noncooperative cellular networks"
    - "what will 5g be"
    - "weighted fair multicast multigroup beamforming under per antenna power constraints"
    - "physical layer multicasting by stochastic transmit beamforming and alamouti space time coding"
    - "waveform design for secure siso transmissions and multicasting"
    - "coordinated multicast beamforming in multicell networks"

Connected through hyperedge HE-6 (induced by source paper "energy efficiency in cell free massive mimo with zero forcing precoding design"):
  with members:
    - "cell free massive mimo versus small cells"
    - "energy efficiency of downlink transmission strategies for cloud radio access networks"
    - "how much do downlink pilots improve cell free massive mimo"
    - "optimal design of energy efficient multi user mimo systems is massive mimo the answer"

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)