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: "spectral and energy efficiency of parallel gaussian broadcast channels"
  Abstract: Spectral efficiency and energy efficiency are important design criteria for green communications systems and networks. In this paper, spectral efficiency and energy efficiency are addressed for communications over parallel Gaussian broadcast channels as the channels are orthogonal in frequency. The maximum sum rate is used in measuring spectral- and energy-efficiency. First, the maximum efficiency is obtained through two separated optimization problems. With a fixed transmit power allocation, the optimal bandwidth assignment is given and a procedure is provided to determine the total bandwidth for maximum spectral efficiency. With a fixed bandwidth assignment, the optimal transmit power allocation is given and a procedure is provided to determine the total transmit power for maximum energy efficiency. Secondly, the combined spectral- and energy-efficiency of particular total bandwidth and total transmit power is maximized with joint bandwidth assignment and transmit power allocation. With emphasis on spectral efficiency or energy efficiency, an algorithm is provided to further determine the optimal total bandwidth or the optimal total transmit power. Simulation results validate the transmission approaches over parallel Gaussian broadcast channel that achieve the best spectral efficiency and energy 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)