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: "designing unimodular codes via quadratic optimization"
  Abstract: The NP-hard problem of optimizing a quadratic form over the unimodular vector set arises in radar code design scenarios as well as other active sensing and communication applications. To tackle this problem (which we call unimodular quadratic program (UQP)), several computational approaches are devised and studied. Power method-like iterations are introduced for local optimization of UQP. Furthermore, a monotonically error-bound improving technique (MERIT) is proposed to obtain the global optimum or a local optimum of UQP with good sub-optimality guarantees. The provided sub-optimality guarantees are case-dependent and may outperform the π/4 approximation guarantee of semi-definite relaxation. Several numerical examples are presented to illustrate the performance of the proposed method. The examples show that for several cases, including rank-deficient matrices, the proposed methods can solve UQPs efficiently in the sense of sub-optimality guarantee and computational time.

Connected through hyperedge HE-1 (induced by source paper "a single rf architecture for multiuser massive mimo via reflecting surfaces"):
  with members:
    - "intelligent reflecting surface enhanced wireless network via joint active and passive beamforming"
    - "scalable and energy efficient millimeter massive mimo architectures reflect array and transmit array antennas"
    - "reconfigurable intelligent surfaces for energy efficiency in wireless communication"

Connected through hyperedge HE-2 (induced by source paper "beam codebook design for 5g mmwave terminals"):
  with members:
    - "statistical blockage modeling and robustness of beamforming in millimeter wave systems"
    - "over sampling codebook based hybrid minimum sum mean square error precoding for millimeter wave 3d mimo"
    - "millimeter wave mimo prototype measurements and experimental results"
    - "hierarchical codebook design for beamforming training in millimeter wave communication"
    - "codebook design for millimeter wave channel estimation with hybrid precoding structure"
    - "beamforming tradeoffs for initial ue discovery in millimeter wave mimo systems"
    - "channel estimation and hybrid precoding for millimeter wave cellular systems"
    - "what will 5g be"

Connected through hyperedge HE-3 (induced by source paper "miso wireless communication systems via intelligent reflecting surfaces"):
  with members:
    - "smart radio environments empowered by ai reconfigurable meta surfaces an idea whose time has come"
    - "intelligent reflecting surface enhanced wireless network via joint active and passive beamforming"
    - "generalized low rank optimization for topological cooperation in ultra dense networks"
    - "large intelligent surface assisted wireless communication exploiting statistical csi"
    - "intelligent reflecting surface enhanced wireless network joint active and passive beamforming design"
    - "alternating minimization algorithms for hybrid precoding in millimeter wave mimo systems"
    - "multi objective optimization for robust power efficient and secure full duplex wireless communication systems"
    - "what will 5g be"

Connected through hyperedge HE-4 (induced by source paper "cross complementary pairs for optimal training in spatial modulation over frequency selective channels"):
  with members:
    - "a survey on spatial modulation in emerging wireless systems research progresses and applications"
    - "on multiple input multiple output ofdm with index modulation for next generation wireless networks"
    - "space shift keying ssk mimo with practical channel estimates"

Connected through hyperedge HE-5 (induced by source paper "an enhanced sdr based global algorithm for nonconvex complex quadratic programs with signal processing applications"):
  with members:
    - "joint user grouping and linear virtual beamforming complexity algorithms and approximation bounds"

Connected through hyperedge HE-6 (induced by source paper "optimized transmission for consensus in wireless sensor networks"):
  with members:
    - "massive mimo for wireless sensing with a coherent multiple access channel"
    - "optimal power allocation for parameter tracking in a distributed amplify and forward sensor network"
    - "estimation in phase shift and forward wireless sensor networks"
    - "optimal relay functionality for snr maximization in memoryless relay networks"

Connected through hyperedge HE-7 (induced by source paper "l1 norm principal component analysis of complex data"):
  with members:
    - "optimal algorithms for l_ 1 subspace signal processing"

Connected through hyperedge HE-8 (induced by source paper "constant envelope precoding for mimo systems"):
  with members:
    - "constant envelope precoding with adaptive receiver constellation in miso fading channel"
    - "constant envelope precoding with time variation constraint on the transmitted phase angles"
    - "constant envelope multi user precoding for frequency selective massive mimo systems"
    - "per antenna constant envelope precoding for large multi user mimo systems"
    - "single user beamforming in large scale miso systems with per antenna constant envelope constraints the doughnut channel"
    - "cooperative multi cell block diagonalization with per base station power constraints"
    - "on gaussian mimo bc mac duality with multiple transmit covariance constraints"

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.SY(Systems and Control)