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: "two stage subspace constrained precoding in massive mimo cellular systems"
  Abstract: We propose a subspace constrained precoding scheme to fully unleash the gain provided by massive antenna array with reduced channel state information (CSI) signaling overhead. The MIMO precoder at each base station (BS) is partitioned into an inner precoder and a Transmit (Tx) subspace control matrix. The inner precoder is adaptive to the local CSI at each BS for spatial multiplexing gain. The Tx subspace control is adaptive to the channel statistics for inter-cell interference mitigation. Specifically, the Tx subspace control is formulated as a QoS optimization problem which involves an SINR chance constraint where the probability of each user's SINR not satisfying a service requirement must not exceed a given outage probability. Such chance constraint cannot be handled by the existing methods due to the two-stage precoding structure. To tackle this, we propose a bi-convex approximation approach, which consists of three key ingredients: random matrix theory, chance constrained optimization and semidefinite relaxation. Then we propose an efficient algorithm to find the optimal solution of the resulting bi-convex approximation problem. Simulations show that the proposed design has significant gain over various baselines.

Connected through hyperedge HE-1 (induced by source paper "majorization minimization aided hybrid transceivers for mimo interference channels"):
  with members:
    - "a framework on hybrid mimo transceiver design based on matrix monotonic optimization"
    - "hybrid analog and digital beamforming for mmwave ofdm large scale antenna arrays"
    - "alternating minimization algorithms for hybrid precoding in millimeter wave mimo systems"
    - "hybrid digital and analog beamforming design for large scale antenna arrays"
    - "hybrid beamforming for massive mimo a survey"
    - "limited feedback hybrid precoding for multi user millimeter wave systems"
    - "near optimal hybrid processing for massive mimo systems via matrix decomposition"
    - "hybrid block diagonalization for massive multiuser mimo systems"

Connected through hyperedge HE-2 (induced by source paper "downlink precoding with mixed statistical and imperfect instantaneous csi for massive mimo systems"):
  with members:
    - "massive mimo with imperfect channel covariance information"
    - "a rate splitting strategy for massive mimo with imperfect csit"
    - "massive mimo ten myths and one critical question"
    - "power scaling of uplink massive mimo systems with arbitrary rank channel means"
    - "dealing with interference in distributed large scale mimo systems a statistical approach"
    - "pilot beam pattern design for channel estimation in massive mimo systems"
    - "two tier precoding for fdd multi cell massive mimo time varying interference networks"
    - "downlink training techniques for fdd massive mimo systems open loop and closed loop training with memory"

Connected through hyperedge HE-3 (induced by source paper "framework of channel estimation for hybrid analog and digital processing enabled massive mimo communications"):
  with members:
    - "multipair massive mimo relaying with pilot data transmission overlay"
    - "an overview of signal processing techniques for millimeter wave mimo systems"
    - "on the number of rf chains and phase shifters and scheduling design with hybrid analog digital beamforming"
    - "frequency selective hybrid precoding for limited feedback millimeter wave systems"
    - "hybrid beamforming for massive mimo a survey"
    - "limited feedback hybrid precoding for multi user millimeter wave systems"
    - "compressed sensing based multi user millimeter wave systems how many measurements are needed"
    - "power allocation for multi pair massive mimo two way af relaying with linear processing"

Connected through hyperedge HE-4 (induced by source paper "interference alignment and soft space reuse based cooperative transmission for multi cell massive mimo networks"):
  with members:
    - "structured compressive sensing based spatio temporal joint channel estimation for fdd massive mimo"
    - "on interference alignment with imperfect csi characterizations of outage probability ergodic rate and ser"
    - "two stage beamformer design for massive mimo downlink by trace quotient formulation"
    - "training sequence design for feedback assisted hybrid beamforming in massive mimo systems"
    - "two tier precoding for fdd multi cell massive mimo time varying interference networks"
    - "downlink training techniques for fdd massive mimo systems open loop and closed loop training with memory"
    - "five disruptive technology directions for 5g"
    - "scaling up mimo opportunities and challenges with very large arrays"

Connected through hyperedge HE-5 (induced by source paper "hybrid beamforming for massive mimo a survey"):
  with members:
    - "on the number of rf chains and phase shifters and scheduling design with hybrid analog digital beamforming"
    - "limited feedback hybrid precoding for multi user millimeter wave systems"
    - "two stage beamformer design for massive mimo downlink by trace quotient formulation"
    - "near optimal hybrid processing for massive mimo systems via matrix decomposition"
    - "hybrid block diagonalization for massive multiuser mimo systems"
    - "hybrid mimo architectures for millimeter wave communications phase shifters or switches"
    - "channel estimation and hybrid precoding for millimeter wave cellular systems"
    - "massive mimo for next generation wireless systems"

Connected through hyperedge HE-6 (induced by source paper "channel acquisition for massive mimo ofdm with adjustable phase shift pilots"):
  with members:
    - "pilot reuse for massive mimo transmission over spatially correlated rayleigh fading channels"
    - "massive mimo with non ideal arbitrary arrays hardware scaling laws and circuit aware design"
    - "distributed compressive csit estimation and feedback for fdd multi user massive mimo systems"
    - "massive mimo for next generation wireless systems"
    - "what will 5g be"
    - "five disruptive technology directions for 5g"
    - "effects of channel aging in massive mimo systems"
    - "a coordinated approach to channel estimation in large scale multiple antenna systems"

Connected through hyperedge HE-7 (induced by source paper "comparison of ofdm and single carrier for large scale antenna systems"):
  with members:
    - "linear precoding based on polynomial expansion large scale multi cell mimo systems"
    - "scaling up mimo opportunities and challenges with very large arrays"
    - "network mimo with linear zero forcing beamforming large system analysis impact of channel estimation and reduced complexity scheduling"
    - "energy and spectral efficiency of very large multiuser mimo systems"
    - "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)