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: "channel estimation and hybrid beamforming for reconfigurable intelligent surfaces assisted thz communications"
  Abstract: Terahertz (THz) communications are promising to be the next frontier for wireless network but suffer from severe attenuation and poor diffraction. To address these challenges, this paper integrates two state-of-the-art technology, i.e., massive multiple input multiple output (MIMO) and reconfigurable intelligent surfaces (RISs), into THz communication to stablish effective and stable connection. Owing to the passivity of the RISs, channel estimation remains an open problem, besides, traditional fully-digital beamforming (FDB) can not be applied in massive MIMO due to its high hardware cost. In sight of this, this paper develops a cooperative channel estimation procedure for RIS-assisted MIMO system via beam training that exploits the advantages of massive MIMO and poor scattering nature of THz channel. The whole procedure is developed based on cost-efficient hybrid beamforming (HB) architectures. Moreover, this paper designs two different codebooks for efficiently realizing the proposed estimation procedure via 3-tree hierarchical search. The two codebooks are referred to as tree dictionary (TD) codebook and phase shifter deactivation (PSD) codebook, with different advantages catering for various scenarios. Using the estimation information, this paper develops two closed-form transmission designs, i.e., direct allocation (DA) design and zero-forcing allocation (ZFA) design, for maximizing the overall spectral efficiency.

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)