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: "secrecy transmit beamforming for heterogeneous networks"
  Abstract: In this paper, we pioneer the study of physical-layer security in heterogeneous networks (HetNets). We investigate secure communications in a two-tier downlink HetNet, which comprises one macrocell and several femtocells. Each cell has multiple users and an eavesdropper attempts to wiretap the intended macrocell user. First, we consider an orthogonal spectrum allocation strategy to eliminate co-channel interference, and propose the secrecy transmit beamforming only operating in the macrocell (STB-OM) as a partial solution for secure communication in HetNet. Next, we consider a secrecy-oriented non-orthogonal spectrum allocation strategy and propose two cooperative STBs which rely on the collaboration amongst the macrocell base station (MBS) and the adjacent femtocell base stations (FBSs). Our first cooperative STB is the STB sequentially operating in the macrocell and femtocells (STB-SMF), where the cooperative FBSs individually design their STB matrices and then feed their performance metrics to the MBS for guiding the STB in the macrocell. Aiming to improve the performance of STB-SMF, we further propose the STB jointly designed in the macrocell and femtocells (STB-JMF), where all cooperative FBSs feed channel state information to the MBS for designing the joint STB. Unlike conventional STBs conceived for broadcasting or interference channels, the three proposed STB schemes all entail relatively sophisticated optimizations due to QoS constraints of the legitimate users. To efficiently use these STB schemes, the original optimization problems are reformulated and convex optimization techniques, such as second-order cone programming and semidefinite programming, are invoked to obtain the optimal solutions. Numerical results demonstrate that the proposed STB schemes are highly effective in improving the secrecy rate performance of HetNet.

Connected through hyperedge HE-1 (induced by source paper "secrecy outage and diversity analysis of multiple cooperative source destination pairs"):
  with members:
    - "modulation and multiple access for 5g networks"
    - "physical layer security in heterogeneous networks with jammer selection and full duplex users"
    - "physical layer security for spectrum sharing systems"
    - "on secrecy performance of antenna selection aided mimo systems against eavesdropping"
    - "artificial noise aided secure transmission in large scale spectrum sharing networks"
    - "location based beamforming for enhancing secrecy in rician wiretap channels"
    - "physical layer security in heterogeneous cellular networks"
    - "proactive eavesdropping via cognitive jamming in fading channels"

Connected through hyperedge HE-2 (induced by source paper "multi antenna aided secrecy beamforming optimization for wirelessly powered hetnets"):
  with members:
    - "optimal beamforming and time allocation for partially wireless powered sensor networks with downlink swipt"
    - "energy efficient user association and power allocation in millimeter wave based ultra dense networks with energy harvesting base stations"
    - "wireless power transfer in massive mimo aided hetnets with user association"
    - "evolution toward 5g multi tier cellular wireless networks an interference management perspective"
    - "five disruptive technology directions for 5g"
    - "outage constrained robust secure transmission for miso wiretap channels"
    - "heterogeneous cellular networks with flexible cell association a comprehensive downlink sinr analysis"
    - "optimal and robust transmit designs for miso channel secrecy by semidefinite programming"

Connected through hyperedge HE-3 (induced by source paper "robust beamforming and jamming for enhancing the physical layer security of full duplex radios"):
  with members:
    - "a new design paradigm for secure full duplex multiuser systems"
    - "iterative distributed minimum total mse approach for secure communications in mimo interference channels"
    - "detecting byzantine attacks without clean reference"
    - "robust beamforming for secure communication in systems with wireless information and power transfer"
    - "secure beamforming for mimo broadcasting with wireless information and power transfer"
    - "security versus reliability analysis of opportunistic relaying"
    - "in band full duplex wireless challenges and opportunities"
    - "robust secure transmission in miso channels based on worst case optimization"

Connected through hyperedge HE-4 (induced by source paper "a survey of physical layer security techniques for 5g wireless networks and challenges ahead"):
  with members:
    - "secure massive mimo systems with limited rf chains"
    - "secure transmission with large numbers of antennas and finite alphabet inputs"
    - "probabilistically robust swipt for secrecy misome systems"
    - "exploiting full duplex receivers for achieving secret communications in multiuser miso networks"
    - "full duplex bidirectional secure communications under perfect and distributionally ambiguous eavesdropper s csi"
    - "safeguarding decentralized wireless networks using full duplex jamming receivers"
    - "physical layer security aware routing and performance tradeoffs in ad hoc networks"
    - "hybrid procoder and combiner design for secure transmission in mmwave mimo systems"

Connected through hyperedge HE-5 (induced by source paper "security reliability tradeoff for distributed antenna systems in heterogeneous cellular networks"):
  with members:
    - "game based approach for qos provisioning and interference management in heterogeneous networks"
    - "intelligent interference exploitation for heterogeneous cellular networks against eavesdropping"
    - "energy efficiency analysis of heterogeneous cellular networks with extra cell range expansion"
    - "secrecy optimized resource allocation for device to device communication underlaying heterogeneous networks"
    - "safeguarding decentralized wireless networks using full duplex jamming receivers"
    - "optimal beamforming for gaussian mimo wiretap channels with two transmit antennas"
    - "relay selection for wireless communications against eavesdropping a security reliability trade off perspective"
    - "a survey on wireless security technical challenges recent advances and future trends"

Connected through hyperedge HE-6 (induced by source paper "secure transmission with covert requirement in untrusted relaying networks"):
  with members:
    - "covert communications versus physical layer security"
    - "joint relay selection and power allocation in large scale mimo systems with untrusted relays and passive eavesdroppers"
    - "covert communication achieved by a greedy relay in wireless networks"
    - "optimal power allocation by imperfect hardware analysis in untrusted relaying networks"
    - "on covert communication with noise uncertainty"
    - "covert communication in the presence of an uninformed jammer"
    - "joint relay and jammer selection improves the physical layer security in the face of csi feedback delays"
    - "massive mimo for next generation wireless systems"

Connected through hyperedge HE-7 (induced by source paper "secrecy beamforming for swipt miso heterogeneous cellular networks"):
  with members:
    - "physical layer security in heterogeneous cellular networks"

Connected through hyperedge HE-8 (induced by source paper "robust chance constrained optimization for power efficient and secure swipt systems"):
  with members:
    - "probabilistically robust swipt for secrecy misome systems"
    - "robust resource allocation for mimo wireless powered communication networks based on a non linear eh model"
    - "robust an aided beamforming and power splitting design for secure miso cognitive radio with swipt"
    - "safe and secure wireless power transfer networks challenges and opportunities in rf based systems"
    - "wireless powered communication networks an overview"
    - "multi objective resource allocation in full duplex swipt systems"
    - "secrecy wireless information and power transfer challenges and opportunities"
    - "ambient rf energy harvesting in ultra dense small cell networks performance and trade offs"

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)