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: "scalable synchronization and reciprocity calibration for distributed multiuser mimo"
  Abstract: Large-scale distributed Multiuser MIMO (MU-MIMO) is a promising wireless network architecture that combines the advantages of "massive MIMO" and "small cells." It consists of several Access Points (APs) connected to a central server via a wired backhaul network and acting as a large distributed antenna system. We focus on the downlink, which is both more demanding in terms of traffic and more challenging in terms of implementation than the uplink. In order to enable multiuser joint precoding of the downlink signals, channel state information at the transmitter side is required. We consider Time Division Duplex (TDD), where the {\em downlink} channels can be learned from the user uplink pilot signals, thanks to channel reciprocity. Furthermore, coherent multiuser joint precoding is possible only if the APs maintain a sufficiently accurate relative timing and phase synchronization. AP synchronization and TDD reciprocity calibration are two key problems to be solved in order to enable distributed MU-MIMO downlink. In this paper, we propose novel over-the-air synchronization and calibration protocols that scale well with the network size. The proposed schemes can be applied to networks formed by a large number of APs, each of which is driven by an inexpensive 802.11-grade clock and has a standard RF front-end, not explicitly designed to be reciprocal. Our protocols can incorporate, as a building block, any suitable timing and frequency estimator. Here we revisit the problem of joint ML timing and frequency estimation and use the corresponding Cramer-Rao bound to evaluate the performance of the synchronization protocol. Overall, the proposed synchronization and calibration schemes are shown to achieve sufficient accuracy for satisfactory distributed MU-MIMO performance.

Connected through hyperedge HE-1 (induced by source paper "amplitude and phase estimation for absolute calibration of massive mimo front ends"):
  with members:
    - "a framework for over the air reciprocity calibration for tdd massive mimo systems"
    - "impact of line of sight and unequal spatial correlation on uplink mu mimo systems"
    - "reciprocity calibration for massive mimo proposal modeling and validation"
    - "hybrid beamforming for massive mimo a survey"
    - "massive mimo in real propagation environments do all antennas contribute equally"
    - "massive mimo for next generation wireless systems"

Connected through hyperedge HE-2 (induced by source paper "making cell free massive mimo competitive with mmse processing and centralized implementation"):
  with members:
    - "ubiquitous cell free massive mimo communications"
    - "large scale fading decoding in cellular massive mimo systems with spatially correlated channels"
    - "few bit csi acquisition for centralized cell free massive mimo with spatial correlation"
    - "can massive mimo support uplink intensive applications"
    - "on the performance of backhaul constrained cell free massive mimo with linear receivers"
    - "massive mimo has unlimited capacity"
    - "performance of cell free massive mimo systems with mmse and lsfd receivers"
    - "on the total energy efficiency of cell free massive mimo"

Connected through hyperedge HE-3 (induced by source paper "deep learning for ul dl channel calibration in generic massive mimo systems"):
  with members:
    - "energy efficient multi user miso communication using low resolution large intelligent surfaces"
    - "achievable rate maximization by passive intelligent mirrors"
    - "asymptotically optimal estimation algorithm for the sparse signal with arbitrary distributions"
    - "a framework for over the air reciprocity calibration for tdd massive mimo systems"
    - "neural offset min sum decoding"
    - "iterative channel estimation using lse and sparse message passing for mmwave mimo systems"
    - "reciprocity calibration for massive mimo proposal modeling and validation"
    - "learning to communicate channel auto encoders domain specific regularizers and attention"

Connected through hyperedge HE-4 (induced by source paper "performance of cell free massive mimo with rician fading and phase shifts"):
  with members:
    - "a new look at cell free massive mimo making it practical with dynamic cooperation"
    - "two layer decoding in cellular massive mimo systems with spatial channel correlation"
    - "ubiquitous cell free massive mimo communications"
    - "large scale fading decoding in cellular massive mimo systems with spatially correlated channels"
    - "performance of cell free massive mimo systems with mmse and lsfd receivers"
    - "uplink interference reduction in large scale antenna systems"
    - "cell free massive mimo versus small cells"

Connected through hyperedge HE-5 (induced by source paper "fog massive mimo a user centric seamless hot spot architecture"):
  with members:
    - "a novel alternative to cloud ran for throughput densification coded pilots and fast user packet scheduling at remote radio heads"
    - "realizing the tactile internet haptic communications over next generation 5g cellular networks"
    - "modeling and analysis of cellular networks using stochastic geometry a tutorial"
    - "ergodic spectral efficiency in mimo cellular networks"
    - "unique coverage in boolean models"
    - "system level performance evaluation of lte v2x network"
    - "an uplink downlink duality for cloud radio access network"
    - "rrh based massive mimo with on the fly pilot contamination control"

Connected through hyperedge HE-6 (induced by source paper "performance analysis of multi user massive mimo downlink under channel non reciprocity and imperfect csi"):
  with members:
    - "a novel hybrid beamforming algorithm with unified analog beamforming by subspace construction based on partial csi for massive mimo ofdm systems"
    - "analysis of massive mimo with hardware impairments and different channel models"
    - "massive mimo for next generation wireless systems"
    - "what will 5g be"
    - "massive mimo for maximal spectral efficiency how many users and pilots should be allocated"
    - "five disruptive technology directions for 5g"
    - "massive mu mimo downlink tdd systems with linear precoding and downlink pilots"
    - "scaling up mimo opportunities and challenges with very large arrays"

Connected through hyperedge HE-7 (induced by source paper "advanced quantizer designs for fdd based fd mimo systems using uniform planar arrays"):
  with members:
    - "massive mimo has unlimited capacity"
    - "exploiting the preferred domain of fdd massive mimo systems with uniform planar arrays"
    - "pilot beam pattern design for channel estimation in massive mimo systems"
    - "kronecker product correlation model and limited feedback codebook design in a 3d channel model"
    - "downlink training techniques for fdd massive mimo systems open loop and closed loop training with memory"
    - "spatially sparse precoding in millimeter wave mimo systems"
    - "trellis extended codebooks and successive phase adjustment a path from lte advanced to fdd massive mimo systems"
    - "noncoherent trellis coded quantization a practical limited feedback technique for massive mimo systems"

Connected through hyperedge HE-8 (induced by source paper "estimation and mitigation of channel non reciprocity in massive mimo"):
  with members:
    - "performance analysis of multi user massive mimo downlink under channel non reciprocity and imperfect csi"
    - "joint beamforming and broadcasting in massive mimo"
    - "analysis of massive mimo with hardware impairments and different channel models"
    - "massive mimo for next generation wireless systems"
    - "five disruptive technology directions for 5g"
    - "massive mu mimo downlink tdd systems with linear precoding and downlink pilots"
    - "channel estimation and linear precoding in multiuser multiple antenna tdd 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.NI(Networking and Internet Architecture)