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: "a tutorial on the optimization of amplify and forward mimo relay systems"
  Abstract: The remarkable promise of multiple-input multiple-output (MIMO) wireless channels has motivated an intense research activity to characterize the theoretical and practical issues associated with the design of transmit (source) and receive (destination) processing matrices under different operating conditions. This activity was primarily focused on point-to-point (single-hop) communications but more recently there has been an extensive work on two-hop or multi-hop settings in which single or multiple relays are used to deliver the information from the source to the destination. The aim of this tutorial is to provide an up-to-date overview of the fundamental results and practical implementation issues in designing amplify-and-forward MIMO relay systems.

Connected through hyperedge HE-1 (induced by source paper "energy efficiency fairness for multi pair wireless powered relaying systems"):
  with members:
    - "joint power allocation and beamforming for energy efficient two way multi relay communications"
    - "energy efficiency maximization of full duplex two way relay with non ideal power amplifiers and non negligible circuit power"
    - "energy efficient beam coordination strategies with rate dependent processing power"
    - "relaying strategies for wireless powered mimo relay networks"
    - "wireless powered relays in cooperative communications time switching relaying protocols and throughput analysis"
    - "practical non linear energy harvesting model and resource allocation for swipt systems"
    - "wireless networks with rf energy harvesting a contemporary survey"
    - "energy efficiency optimization in relay assisted mimo systems with perfect and statistical csi"

Connected through hyperedge HE-2 (induced by source paper "energy efficiency in mimo underlay and overlay device to device communications and cognitive radio systems"):
  with members:
    - "energy efficient power control a look at 5g wireless technologies"
    - "energy efficiency and sum rate when massive mimo meets device to device communication"
    - "energy efficient resource allocation for device to device underlay communication"
    - "dynamic power control for delay aware device to device communications"
    - "resource allocation under channel uncertainties for relay aided device to device communication underlaying lte a cellular networks"
    - "energy efficiency and spectral efficiency tradeoff in device to device d2d communications"
    - "designing multi user mimo for energy efficiency when is massive mimo the answer"
    - "cognitive beamforming for multiple secondary data streams with individual snr constraints"

Connected through hyperedge HE-3 (induced by source paper "multi pair two way af full duplex massive mimo relaying with zfr zft processing"):
  with members:
    - "power allocation for multi pair massive mimo two way af relaying with linear processing"
    - "multipair full duplex relaying with massive arrays and linear processing"
    - "in band full duplex wireless challenges and opportunities"
    - "energy and spectral efficiency of very large multiuser mimo systems"
    - "pilot contamination and precoding in multi cell tdd systems"

Connected through hyperedge HE-4 (induced by source paper "apply artificial noise to secure fading relay networks a ser based approach"):
  with members:
    - "secure communication via an untrusted non regenerative relay in fading channels"
    - "imbalanced beamforming by a multi antenna source for secure utilization of an untrusted relay"
    - "jamming games in the mimo wiretap channel with an active eavesdropper"
    - "new results on multiple input multiple output broadcast channels with confidential messages"
    - "secrecy sum rates for multi user mimo regularized channel inversion precoding"
    - "physical layer network coding tutorial survey and beyond"
    - "solutions for the mimo gaussian wiretap channel with a cooperative jammer"
    - "secure transmission with artificial noise over fading channels achievable rate and optimal power allocation"

Connected through hyperedge HE-5 (induced by source paper "a framework for transceiver designs for multi hop communications with covariance shaping constraints"):
  with members:
    - "evolution toward 5g multi tier cellular wireless networks an interference management perspective"
    - "beamforming for miso interference channels with qos and rf energy transfer"
    - "a general robust linear transceiver design for multi hop amplify and forward mimo relaying systems"
    - "matrix monotonic optimization for mimo systems"
    - "robust transceiver with tomlinson harashima precoding for amplify and forward mimo relaying systems"
    - "transceiver design for dual hop nonregenerative mimo ofdm relay systems under channel uncertainties"
    - "ergodic capacity analysis of amplify and forward mimo dual hop systems"

Connected through hyperedge HE-6 (induced by source paper "a stochastic beamformed amplify and forward scheme in a multigroup multicast mimo relay network with per antenna power constraints"):
  with members:
    - "multicast multigroup beamforming for per antenna power constrained large scale arrays"
    - "weighted fair multicast multigroup beamforming under per antenna power constraints"
    - "physical layer multicasting by stochastic transmit beamforming and alamouti space time coding"
    - "group sparse beamforming for green cloud ran"
    - "sub optimality of treating interference as noise in the cellular uplink"
    - "a new outer bound and the noisy interference sum rate capacity for gaussian interference channels"
    - "capacity bounds for the gaussian interference channel"

Connected through hyperedge HE-7 (induced by source paper "convex separable problems with linear constraints in signal processing and communications"):
  with members:
    - "on the precoder design of a wireless energy harvesting node in linear vector gaussian channels with arbitrary input distribution"
    - "duality and optimization for generalized multi hop mimo amplify and forward relay networks with linear constraints"
    - "power allocation in two hop amplify and forward mimo relay systems with qos requirements"
    - "transmission with energy harvesting nodes in fading wireless channels optimal policies"
    - "separable convex optimization problems with linear ascending constraints"

Connected through hyperedge HE-8 (induced by source paper "capacity region bounds and resource allocation for two way ofdm relay channels"):
  with members:
    - "outer bounds for the capacity region of a gaussian two way relay channel"
    - "optimal power allocation for two way decode and forward ofdm relay networks"
    - "optimal real time spectrum sharing between cooperative relay and ad hoc networks"
    - "optimization framework and graph based approach for relay assisted bidirectional ofdma cellular networks"
    - "broadcast capacity region of two phase bidirectional relaying"
    - "on the capacity and diversity multiplexing tradeoff of the two way relay channel"
    - "mimo two way relay channel diversity multiplexing tradeoff analysis"

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)