human: Given a hyperedge-centered hypergraph: <hypergraph>, where the center hyperedge is induced by one source paper and its member nodes are the cited papers.

Details of the hypergraph:
Center hyperedge (induced by source paper "massive mimo testbed implementation and initial results in system model validation"):
  Abstract: This paper presents the design and implementation of a novel SDR based massive MIMO testbed with up to 70 nodes built at Tennessee Technological University. The deployment can reach a $30 \times 30$ antenna MIMO scheme. With this testbed, we are able to measure the channel matrix and compute the achievable rate of the massive MIMO system using experimental data. The measured channel capacity is linearly increasing with the number of antennas of the base station. We also demonstrate the channel reciprocity including the circuits impact from the transmitter and receiver. We show that the Vandermonde channel model is more realistic to describe the massive MIMO architecture than the widely used Gaussian channel model, in terms of capacity. By adjusting the range for angle of arrival $\alpha$ and the base station antenna distance $d$ during the simulation, we find out the Vandermonde model agrees with our measured capacity at a certain $\alpha$ for each selected $d$ and the $\alpha$ is very close to that of the experiment deployment. It is the first time that the feasibility of Vandermonde channel model is demonstrated by the experiment for massive MIMO.

Includes members:
  Member "a wireless channel sounding system for rapid propagation measurements":
    also connected through other hyperedges:
      (none)
  Member "five disruptive technology directions for 5g":
    also connected through other hyperedges:
      - Hyperedge HE-1 (induced by source paper "deep learning enabled optimization of downlink beamforming under per antenna power constraints algorithms and experimental demonstration")
  Member "scaling up mimo opportunities and challenges with very large arrays":
    also connected through other hyperedges:
      - Hyperedge HE-2 (induced by source paper "downlink secrecy rate of one bit massive mimo system with active eavesdropping")
  Member "random vandermonde matrices part ii applications":
    also connected through other hyperedges:
      - Hyperedge HE-3 (induced by source paper "on the d dimensional quasi equally spaced sampling")
  Member "random vandermonde matrices part i fundamental results":
    also connected through other hyperedges:
      - Hyperedge HE-4 (induced by source paper "the impact of physical channel on performance of subspace based channel estimation in massive mimo systems")

Question: Please tell me which class the source paper 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)