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 transmission in multi cell massive mimo systems"
  Abstract: In this paper, we consider physical layer security provisioning in multi-cell massive multiple-input multiple-output (MIMO) systems. Specifically, we consider secure downlink transmission in a multi-cell massive MIMO system with matched-filter precoding and artificial noise (AN) generation at the base station (BS) in the presence of a passive multi-antenna eavesdropper. We investigate the resulting achievable ergodic secrecy rate and the secrecy outage probability for the cases of perfect training and pilot contamination. Thereby, we consider two different AN shaping matrices, namely, the conventional AN shaping matrix, where the AN is transmitted in the null space of the matrix formed by all user channels, and a random AN shaping matrix, which avoids the complexity associated with finding the null space of a large matrix. Our analytical and numerical results reveal that in multi-cell massive MIMO systems employing matched-filter precoding (1) AN generation is required to achieve a positive ergodic secrecy rate if the user and the eavesdropper experience the same path-loss, (2) even with AN generation secure transmission may not be possible if the number of eavesdropper antennas is too large and not enough power is allocated to channel estimation, (3) for a given fraction of power allocated to AN and a given number of users, in case of pilot contamination, the ergodic secrecy rate is not a monotonically increasing function of the number of BS antennas, and (4) random AN shaping matrices provide a favourable performance/complexity tradeoff and are an attractive alternative to conventional AN shaping matrices.

Connected through hyperedge HE-1 (induced by source paper "secure massive mimo systems with limited rf chains"):
  with members:
    - "analysis and design of secure massive mimo systems in the presence of hardware impairments"
    - "linear precoding of data and artificial noise in secure massive mimo systems"
    - "limited feedback hybrid precoding for multi user millimeter wave systems"
    - "large scale mimo relaying techniques for physical layer security af or df"
    - "jamming aided secure communication in massive mimo rician channels"
    - "physical layer security for massive mimo an overview on passive eavesdropping and active attacks"
    - "channel estimation and hybrid precoding for millimeter wave cellular systems"
    - "spatially sparse precoding in millimeter wave mimo systems"

Connected through hyperedge HE-2 (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"
    - "secure massive mimo transmission in the presence of an active eavesdropper"
    - "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"

Connected through hyperedge HE-3 (induced by source paper "secure massive mimo transmission with an active eavesdropper"):
  with members:
    - "channel acquisition for massive mimo ofdm with adjustable phase shift pilots"
    - "linear precoding of data and artificial noise in secure massive mimo systems"
    - "physical layer security in heterogeneous cellular networks"
    - "an overview of transmission theory and techniques of large scale antenna systems for 5g wireless communications"
    - "joint csit acquisition based on low rank matrix completion for fdd massive mimo systems"
    - "physical layer security in massive mimo"
    - "large scale mimo relaying techniques for physical layer security af or df"
    - "multi antenna relay aided wireless physical layer security"

Connected through hyperedge HE-4 (induced by source paper "jamming aided secure communication in massive mimo rician channels"):
  with members:
    - "secure massive mimo transmission with an active eavesdropper"
    - "secure massive mimo transmission in the presence of an active eavesdropper"
    - "pilot reuse for massive mimo transmission over spatially correlated rayleigh fading channels"
    - "power scaling of uplink massive mimo systems with arbitrary rank channel means"
    - "massive mimo for next generation wireless systems"
    - "what will 5g be"
    - "principles of physical layer security in multiuser wireless networks a survey"
    - "scaling up mimo opportunities and challenges with very large arrays"

Connected through hyperedge HE-5 (induced by source paper "secret key agreement with large antenna arrays under the pilot contamination attack"):
  with members:
    - "the sender excited secret key agreement model capacity reliability and secrecy exponents"
    - "secrecy sum rates for multi user mimo regularized channel inversion precoding"
    - "exploiting channel diversity in secret key generation from multipath fading randomness"
    - "secret sharing ldpc codes for the bpsk constrained gaussian wiretap channel"
    - "achieving the secrecy capacity of wiretap channels using polar codes"
    - "channel estimation and linear precoding in multiuser multiple antenna tdd systems"
    - "polar coding for secure transmission and key agreement"
    - "nested polar codes for wiretap and relay channels"

Connected through hyperedge HE-6 (induced by source paper "an uplink interference analysis for massive mimo systems with mrc and zf receivers"):
  with members:
    - "the interplay between massive mimo and underlaid d2d networking"
    - "blind pilot decontamination"
    - "scaling up mimo opportunities and challenges with very large arrays"
    - "a coordinated approach to channel estimation in large scale multiple antenna systems"

Connected through hyperedge HE-7 (induced by source paper "physical layer security for massive mimo an overview on passive eavesdropping and active attacks"):
  with members:
    - "massive mimo for next generation wireless systems"
    - "scaling up mimo opportunities and challenges with very large arrays"
    - "pilot contamination and precoding in multi cell tdd systems"

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)