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: "secure massive mimo transmission in the presence of an active eavesdropper"
  Abstract: In this paper, we investigate secure and reliable transmission strategies for multi-cell multi-user massive multiple-input multiple-output (MIMO) systems in the presence of an active eavesdropper. We consider a time-division duplex system where uplink training is required and an active eavesdropper can attack the training phase to cause pilot contamination at the transmitter. This forces the precoder used in the subsequent downlink transmission phase to implicitly beamform towards the eavesdropper, thus increasing its received signal power. We derive an asymptotic achievable secrecy rate for matched filter precoding and artificial noise (AN) generation at the transmitter when the number of transmit antennas goes to infinity. For the achievability scheme at hand, we obtain the optimal power allocation policy for the transmit signal and the AN in closed form. For the case of correlated fading channels, we show that the impact of the active eavesdropper can be completely removed if the transmit correlation matrices of the users and the eavesdropper are orthogonal. Inspired by this result, we propose a precoder null space design exploiting the low rank property of the transmit correlation matrices of massive MIMO channels, which can significantly degrade the eavesdropping capabilities of the active eavesdropper.

Connected through hyperedge HE-1 (induced by source paper "vulnerabilities of massive mimo systems to pilot contamination attacks"):
  with members:
    - "optimal transmit antenna selection for massive mimo wiretap channels"
    - "massive mimo has unlimited capacity"
    - "exploiting full duplex receivers for achieving secret communications in multiuser miso networks"
    - "frequency synchronization for uplink massive mimo systems"
    - "linear precoding of data and artificial noise in secure massive mimo systems"
    - "massive mimo ten myths and one critical question"
    - "individual secrecy for broadcast channels with receiver side information"
    - "5g cellular key enabling technologies and research challenges"

Connected through hyperedge HE-2 (induced by source paper "energy efficient alternating iterative secure structure of maximizing secrecy rate for directional modulation networks"):
  with members:
    - "alternating iterative secure structure between beamforming and power allocation for uav aided directional modulation networks"
    - "robust secure transmission of using main lobe integration based leakage beamforming in directional modulation mu mimo systems"
    - "secure transmission with large numbers of antennas and finite alphabet inputs"
    - "artificial noise aided secure multicast precoding for directional modulation systems"
    - "low complexity and high resolution doa estimation for hybrid analog and digital massive mimo receive array"
    - "artificial noise aided secure transmission with directional modulation based on random frequency diverse arrays"
    - "optimal power allocation for artificial noise under imperfect csi against spatially random eavesdroppers"
    - "an overview of sustainable green 5g networks"

Connected through hyperedge HE-3 (induced by source paper "cell free massive mimo networks optimal power control against active eavesdropping"):
  with members:
    - "on the total energy efficiency of cell free massive mimo"
    - "mimo beamforming for secure and energy efficient wireless communication"
    - "energy efficiency in cell free massive mimo with zero forcing precoding design"
    - "mimo secret communications against an active eavesdropper"
    - "cell free massive mimo versus small cells"
    - "cell free massive mimo uniformly great service for everyone"
    - "secure massive mimo transmission with an active eavesdropper"
    - "secret key agreement with large antenna arrays under the pilot contamination attack"

Connected through hyperedge HE-4 (induced by source paper "power allocation strategy of maximizing secrecy rate for secure directional modulation"):
  with members:
    - "robust secure transmission of using main lobe integration based leakage beamforming in directional modulation mu mimo systems"
    - "artificial noise aided secure transmission in wiretap channels with transmitter side correlation"
    - "directional modulation via symbol level precoding a way to enhance security"
    - "relay selection improves the security reliability trade off in cognitive radio systems"

Connected through hyperedge HE-5 (induced by source paper "analysis and design of secure massive mimo systems in the presence of hardware impairments"):
  with members:
    - "secure massive mimo systems with limited rf chains"
    - "physical layer security for massive mimo systems impaired by phase noise"
    - "linear precoding of data and artificial noise in secure massive mimo systems"
    - "energy efficient power control a look at 5g wireless technologies"
    - "hardware impairments aware transceiver for full duplex massive mimo relaying"
    - "per antenna constant envelope precoding for secure transmission in large scale miso systems"
    - "secure massive mimo transmission with an active eavesdropper"
    - "large scale mimo relaying techniques for physical layer security af or df"

Connected through hyperedge HE-6 (induced by source paper "mimo secret communications against an active eavesdropper"):
  with members:
    - "secure degrees of freedom regions of multiple access and interference channels the polytope structure"
    - "linear precoding of data and artificial noise in secure massive mimo systems"
    - "improving wireless physical layer security via exploiting co channel interference"
    - "secure massive mimo transmission with an active eavesdropper"
    - "physical layer security for massive mimo an overview on passive eavesdropping and active attacks"
    - "secure degrees of freedom of one hop wireless networks"
    - "improving physical layer secrecy using full duplex jamming receivers"
    - "secure degrees of freedom of k user gaussian interference channels a unified view"

Connected through hyperedge HE-7 (induced by source paper "linear precoding of data and artificial noise in secure massive mimo systems"):
  with members:
    - "physical layer cryptography through massive mimo"
    - "large scale mimo relaying techniques for physical layer security af or df"
    - "physical layer security for massive mimo an overview on passive eavesdropping and active attacks"
    - "securing massive mimo at the physical layer"
    - "linear precoding based on polynomial expansion large scale multi cell mimo systems"
    - "physical layer security in downlink multi antenna cellular networks"
    - "principles of physical layer security in multiuser wireless networks a survey"
    - "secure transmission in multi cell massive mimo systems"

Connected through hyperedge HE-8 (induced by source paper "pilot contamination attack detection by key confirmation in secure mimo systems"):
  with members:
    - "physical layer security for massive mimo an overview on passive eavesdropping and active attacks"

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)