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: "retrodirective multi user wireless power transfer with massive mimo"
  Abstract: This letter studies a radio-frequency (RF) multi-user wireless power transfer (WPT) system, where an energy transmitter (ET) with a large number of antennas delivers energy wirelessly to multiple distributed energy receivers (ERs). We investigate a low-complexity WPT scheme based on the retrodirective beamforming technique, where all ERs send a common beacon signal simultaneously to the ET in the uplink and the ET simply conjugates and amplifies its received sum-signal and transmits to all ERs in the downlink for WPT. We show that such a low-complexity scheme achieves the massive multiple-input multiple-output (MIMO) energy beamforming gain. However, a "doubly near-far" issue exists due to the round-trip (uplink beacon and downlink WPT) signal propagation loss where the harvested power of a far ER from the ET can be significantly lower than that of a near ER if the same uplink beacon power is used. To tackle this problem, we propose a distributed uplink beacon power update algorithm, where each ER independently adjusts the beacon power based on its current harvested power in an iterative manner. It is shown that the proposed algorithm converges quickly to a unique fixed-point solution, which helps achieve the desired user fairness with best efforts.

Connected through hyperedge HE-1 (induced by source paper "a retrodirective wireless power transfer scheme for ambient backscatter systems"):
  with members:
    - "design of ambient backscatter training for retrodirective wireless power transfer"
    - "retrodirective large antenna energy beamforming in backscatter multi user networks"
    - "modulation in the air backscatter communication over ambient ofdm carrier"
    - "performance analysis of massive mimo for cell boundary users"
    - "joint wireless information and energy transfer with reduced feedback in mimo interference channels"
    - "energy beamforming with one bit feedback"
    - "joint beamforming design for multi user wireless information and power transfer"
    - "optimized training design for wireless energy transfer"

Connected through hyperedge HE-2 (induced by source paper "design of ambient backscatter training for retrodirective wireless power transfer"):
  with members:
    - "retrodirective large antenna energy beamforming in backscatter multi user networks"
    - "next generation backscatter communication systems techniques and applications"
    - "ambient backscatter communications a contemporary survey"
    - "modulation in the air backscatter communication over ambient ofdm carrier"
    - "inter technology backscatter towards internet connectivity for implanted devices"
    - "communications and signals design for wireless power transmission"
    - "wireless powered communication opportunities and challenges"
    - "performance analysis of massive mimo for cell boundary users"

Connected through hyperedge HE-3 (induced by source paper "multi tone signal optimization for wireless power transfer in the presence of wireless communication links"):
  with members:
    - "low complexity adaptive multisine waveform design for wireless power transfer"
    - "waveform optimization for radio frequency wireless power transfer"
    - "waveform design for wireless power transfer"
    - "waveform optimization for swipt with nonlinear energy harvester modeling"
    - "wireless powered communication opportunities and challenges"
    - "practical non linear energy harvesting model and resource allocation for swipt systems"
    - "multi antenna wireless energy transfer for backscatter communication systems"
    - "simultaneous wireless information and power transfer in a two user ofdm interference channel"

Connected through hyperedge HE-4 (induced by source paper "simultaneous wireless information and power transfer for decode and forward multihop relay systems in energy constrained iot networks"):
  with members:
    - "end to end throughput maximization for underlay multi hop cognitive radio networks with rf energy harvesting"
    - "simultaneous information and energy flow for iot relay systems with crowd harvesting"
    - "wireless powered communication opportunities and challenges"
    - "resource allocation techniques for wireless powered communication networks with energy storage constraint"
    - "energy harvesting wireless communications a review of recent advances"
    - "wireless networks with rf energy harvesting a contemporary survey"
    - "application of smart antenna technologies in simultaneous wireless information and power transfer"
    - "wireless information and power transfer a dynamic power splitting approach"

Connected through hyperedge HE-5 (induced by source paper "retrodirective large antenna energy beamforming in backscatter multi user networks"):
  with members:
    - "some new research trends in wirelessly powered communications"
    - "communications and signals design for wireless power transmission"
    - "performance analysis of massive mimo for cell boundary users"
    - "on the efficiency of far field wireless power transfer"
    - "multi antenna wireless energy transfer for backscatter communication systems"
    - "energy beamforming with one bit feedback"
    - "optimized training design for wireless energy transfer"
    - "mimo broadcasting for simultaneous wireless information and power transfer"

Connected through hyperedge HE-6 (induced by source paper "optimal energy beamforming under per antenna power constraint"):
  with members:
    - "wireless energy beamforming using received signal strength indicator feedback"
    - "distributed wireless power transfer with energy feedback"
    - "communications and signals design for wireless power transmission"
    - "wireless powered communication opportunities and challenges"
    - "collaborative wireless energy and information transfer in interference channel"
    - "enhancing wireless information and power transfer by exploiting multi antenna techniques"
    - "multiuser mimo wireless energy transfer with coexisting opportunistic communication"
    - "energy beamforming with one bit feedback"

Connected through hyperedge HE-7 (induced by source paper "intelligent power control for spectrum sharing a deep reinforcement learning approach"):
  with members:
    - "deep learning for wireless physical layer opportunities and challenges"
    - "two sided matching based cooperative spectrum sharing"
    - "deep multi user reinforcement learning for distributed dynamic spectrum access"
    - "adam a method for stochastic optimization"
    - "playing atari with deep reinforcement learning"

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)