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: "downlink power control in user centric and cell free massive mimo wireless networks"
  Abstract: Recently, the so-called cell-free Massive MIMO architecture has been introduced, wherein a very large number of distributed access points (APs) simultaneously and jointly serve a much smaller number of mobile stations (MSs). A variant of the cell-free technique is the user-centric approach, wherein each AP just decodes the MSs that it receives with the largest power. This paper considers both the cell-free and user-centric approaches, and, using an interplay of sequential optimization and alternating optimization, derives downlink power-control algorithms aimed at maximizing either the minimum users' SINR (to ensure fairness), or the system sum-rate. Numerical results show the effectiveness of the proposed algorithms, as well as that the user-centric approach generally outperforms the CF one.

Connected through hyperedge HE-1 (induced by source paper "analysis of uav communications in cell free massive mimo systems"):
  with members:
    - "scalability aspects of cell free massive mimo"
    - "max min rate of cell free massive mimo uplink with optimal uniform quantization"
    - "ubiquitous cell free massive mimo communications"
    - "cellular uav to uav communications"
    - "making cell free massive mimo competitive with mmse processing and centralized implementation"
    - "understanding uav cellular communications from existing networks to massive mimo"
    - "tutorial on uav a blue sky view on wireless communication"
    - "cellular connected uav uplink association power control and interference coordination"

Connected through hyperedge HE-2 (induced by source paper "enabling uav communications with cell free massive mimo"):
  with members:
    - "ubiquitous cell free massive mimo communications"
    - "making cell free massive mimo competitive with mmse processing and centralized implementation"
    - "understanding uav cellular communications from existing networks to massive mimo"
    - "supporting uav cellular communications through massive mimo"
    - "the essential guide to realizing 5g connected uavs with massive mimo"
    - "the sky is not the limit lte for unmanned aerial vehicles"
    - "downlink performance of uplink fractional power control in 5g massive mimo systems"
    - "a tutorial on uavs for wireless networks applications challenges and open problems"

Connected through hyperedge HE-3 (induced by source paper "user centric 5g cellular networks resource allocation and comparison with the cell free massive mimo approach"):
  with members:
    - "cell free massive mimo with limited backhaul"
    - "cell free and user centric massive mimo at millimeter wave frequencies"
    - "cell free massive mimo versus small cells"
    - "how much do downlink pilots improve cell free massive mimo"
    - "compute and forward in cell free massive mimo great performance with low backhaul load"
    - "cell free massive mimo uniformly great service for everyone"
    - "what will 5g be"

Connected through hyperedge HE-4 (induced by source paper "energy efficient downlink power control in mmwave cell free and user centric massive mimo"):
  with members:
    - "cell free and user centric massive mimo at millimeter wave frequencies"
    - "energy efficient power control a look at 5g wireless technologies"
    - "cell free massive mimo versus small cells"
    - "on clustered statistical mimo millimeter wave channel simulation"
    - "a survey of energy efficient techniques for 5g networks and challenges ahead"
    - "what will 5g be"

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)