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: "how much do downlink pilots improve cell free massive mimo"
  Abstract: In this paper, we analyze the benefits of including downlink pilots in a cell- free massive MIMO system. We derive an approximate per-user achievable downlink rate for conjugate beamforming processing, which takes into account both uplink and downlink channel estimation errors, and power control. A performance comparison is carried out, in terms of per-user net throughput, considering cell-free massive MIMO operation with and without downlink training, for different network densities. We take also into account the performance improvement provided by max-min fairness power control in the downlink. Numerical results show that, exploiting downlink pilots, the performance can be considerably improved in low density networks over the conventional scheme where the users rely on statistical channel knowledge only. In high density networks, performance improvements are moderate.

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 efficient downlink transmission for multicell massive das with pilot contamination"
    - "energy efficiency in cell free massive mimo with zero forcing precoding design"
    - "cell free massive mimo versus small cells"

Connected through hyperedge HE-2 (induced by source paper "optimal downlink transmission for cell free swipt massive mimo systems with active eavesdropping"):
  with members:
    - "ubiquitous cell free massive mimo communications"
    - "cell free massive mimo networks optimal power control against active eavesdropping"
    - "spectral and energy efficiency of cell free massive mimo systems with hardware impairments"
    - "on the total energy efficiency of cell free massive mimo"
    - "energy efficiency in cell free massive mimo with zero forcing precoding design"
    - "secrecy and energy efficiency in massive mimo aided heterogeneous c ran a new look at interference"
    - "cell free massive mimo versus small cells"
    - "wireless power transfer in massive mimo aided hetnets with user association"

Connected through hyperedge HE-3 (induced by source paper "ubiquitous cell free massive mimo communications"):
  with members:
    - "downlink training in cell free massive mimo a blessing in disguise"
    - "scalability aspects of cell free massive mimo"
    - "making cell free massive mimo competitive with mmse processing and centralized implementation"
    - "fog massive mimo a user centric seamless hot spot architecture"
    - "enhancing favorable propagation in cell free massive mimo through spatial user grouping"
    - "on the total energy efficiency of cell free massive mimo"
    - "channel hardening and favorable propagation in cell free massive mimo with stochastic geometry"
    - "cell free massive mimo versus small cells"

Connected through hyperedge HE-4 (induced by source paper "downlink training in cell free massive mimo a blessing in disguise"):
  with members:
    - "ubiquitous cell free massive mimo communications"
    - "on the total energy efficiency of cell free massive mimo"
    - "channel hardening and favorable propagation in cell free massive mimo with stochastic geometry"
    - "on the ergodic rate lower bounds with applications to massive mimo"
    - "cell free massive mimo versus small cells"
    - "no downlink pilots are needed in tdd massive mimo"
    - "massive mimo ten myths and one critical question"
    - "power scaling of uplink massive mimo systems with arbitrary rank channel means"

Connected through hyperedge HE-5 (induced by source paper "uplink power control in cell free massive mimo via deep learning"):
  with members:
    - "learning to optimize training deep neural networks for interference management"
    - "user association and load balancing for massive mimo through deep learning"
    - "on the total energy efficiency of cell free massive mimo"

Connected through hyperedge HE-6 (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"
    - "downlink power control in user centric and cell free massive mimo wireless networks"
    - "cell free massive mimo versus small cells"
    - "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-7 (induced by source paper "utility based downlink pilot assignment in cell free massive mimo"):
  with members:
    - "channel hardening and favorable propagation in cell free massive mimo with stochastic geometry"
    - "cell free massive mimo versus small cells"
    - "no downlink pilots are needed in tdd massive mimo"
    - "massive mu mimo downlink tdd systems with linear precoding and downlink pilots"
    - "network mimo with linear zero forcing beamforming large system analysis impact of channel estimation and reduced complexity scheduling"
    - "pilot contamination and precoding in multi cell tdd systems"

Connected through hyperedge HE-8 (induced by source paper "channel hardening and favorable propagation in cell free massive mimo with stochastic geometry"):
  with members:
    - "ubiquitous cell free massive mimo communications"
    - "on the ergodic rate lower bounds with applications to massive mimo"
    - "massive mimo with imperfect channel covariance information"
    - "cell free massive mimo versus small cells"
    - "no downlink pilots are needed in tdd massive mimo"
    - "the meta distribution of the sir in poisson bipolar and cellular networks"
    - "cell free massive mimo uniformly great service for everyone"
    - "stochastic geometry modeling of cellular networks analysis simulation and experimental 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)