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 beamforming for mimo two way communications with an untrusted relay"
  Abstract: This paper studies the secure beamforming design in a multiple-antenna three-node system where two source nodes exchange messages with the help of an untrusted relay node. The relay acts as both an essential signal forwarder and a potential eavesdropper. Both two-phase and three-phase two-way relay strategies are considered. Our goal is to jointly optimize the source and relay beamformers for maximizing the secrecy sum rate of the two-way communications. We first derive the optimal relay beamformer structures. Then, iterative algorithms are proposed to find source and relay beamformers jointly based on alternating optimization. Furthermore, we conduct asymptotic analysis on the maximum secrecy sum-rate. Our analysis shows that when all transmit powers approach infinity, the two-phase two-way relay scheme achieves the maximum secrecy sum rate if the source beamformers are designed such that the received signals at the relay align in the same direction. This reveals an important advantage of signal alignment technique in against eavesdropping. It is also shown that if the source powers approach zero, the three-phase scheme performs the best while the two-phase scheme is even worse than direct transmission. Simulation results have verified the efficiency of the proposed secure beamforming algorithms as well as the analytical findings.

Connected through hyperedge HE-1 (induced by source paper "energy harvesting based secure two way communication using an untrusted relay"):
  with members:
    - "joint relay selection and power allocation in large scale mimo systems with untrusted relays and passive eavesdroppers"
    - "optimal power allocation and secrecy sum rate in two way untrusted relaying"
    - "joint relay and jammer selection improves the physical layer security in the face of csi feedback delays"
    - "wireless powered relays in cooperative communications time switching relaying protocols and throughput analysis"
    - "secure communication via a wireless energy harvesting untrusted relay"
    - "security versus reliability analysis of opportunistic relaying"
    - "secure communication with a wireless powered friendly jammer"

Connected through hyperedge HE-2 (induced by source paper "truth telling mechanism for secure two way relay communications with energy harvesting revenue"):
  with members:
    - "joint source and relay optimization for interference mimo relay networks"
    - "relaying protocols for wireless energy harvesting and information processing"
    - "truthful mechanisms for secure communication in wireless cooperative system"
    - "mimo broadcasting for simultaneous wireless information and power transfer"

Connected through hyperedge HE-3 (induced by source paper "secure routing in multihop wireless ad hoc networks with decode and forward relaying"):
  with members:
    - "when does relay transmission give a more secure connection in wireless ad hoc networks"
    - "physical layer security in downlink multi antenna cellular networks"
    - "optimal relay selection for physical layer security in cooperative wireless networks"
    - "physical layer security in cellular networks a stochastic geometry approach"
    - "relay placement for physical layer security a secure connection perspective"
    - "on cooperative relaying schemes for wireless physical layer security"
    - "on the throughput cost of physical layer security in decentralized wireless networks"

Connected through hyperedge HE-4 (induced by source paper "joint secure beamforming for cognitive radio networks with untrusted secondary users"):
  with members:
    - "secrecy wireless information and power transfer in ofdma systems"
    - "energy harvesting for physical layer security in ofdma networks"
    - "spectrum leasing via cooperation for enhanced physical layer secrecy"
    - "discrete memoryless interference and broadcast channels with confidential messages secrecy rate regions"

Connected through hyperedge HE-5 (induced by source paper "energy efficient power allocation for secure communications in large scale mimo relaying systems"):
  with members:
    - "on the secrecy outage capacity of physical layer security in large scale mimo relaying systems with imperfect csi"
    - "energy efficient joint source and channel sensing in cognitive radio sensor networks"
    - "performance analysis for physical layer security in multi antenna downlink networks with limited csi feedback"
    - "optimal relay selection for physical layer security in cooperative wireless networks"
    - "large system analysis of linear precoding in miso broadcast channels with confidential messages"
    - "energy efficient optimization for physical layer security in multi antenna downlink networks with qos guarantee"
    - "cooperative jamming for secure communications in mimo relay networks"

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)