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: "massive mimo systems signal processing challenges and research trends"
  Abstract: This article presents a tutorial on multiuser multiple-antenna wireless systems with a very large number of antennas, known as massive multi-input multi-output (MIMO) systems. Signal processing challenges and future trends in the area of massive MIMO systems are presented and key application scenarios are detailed. A linear algebra approach is considered for the description of the system and data models of massive MIMO architectures. The operational requirements of massive MIMO systems are discussed along with their operation in time-division duplexing mode, resource allocation and calibration requirements. In particular, transmit and receiver processing algorithms are examined in light of the specific needs of massive MIMO systems. Simulation results illustrate the performance of transmit and receive processing algorithms under scenarios of interest. Key problems are discussed and future trends in the area of massive MIMO systems are pointed out.

Connected through hyperedge HE-1 (induced by source paper "uplink downlink rate balancing and throughput scaling in fdd massive mimo systems"):
  with members:
    - "uplink downlink rate balancing in cooperating cellular networks"
    - "a lower bound on the data rate of dirty paper coding in general noise and interference"
    - "massive mimo for next generation wireless systems"
    - "downlink training techniques for fdd massive mimo systems open loop and closed loop training with memory"
    - "noncoherent trellis coded quantization a practical limited feedback technique for massive mimo systems"
    - "designing multi user mimo for energy efficiency when is massive mimo the answer"
    - "scaling up mimo opportunities and challenges with very large arrays"
    - "a coordinated approach to channel estimation in large scale multiple antenna systems"

Connected through hyperedge HE-2 (induced by source paper "massive mimo and waveform design for 5th generation wireless communication systems"):
  with members:
    - "achievable rates of fdd massive mimo systems with spatial channel correlation"
    - "filter bank multicarrier for massive mimo"
    - "pilot decontamination in cmt based massive mimo networks"
    - "massive mimo for next generation wireless systems"
    - "what will 5g be"
    - "blind pilot decontamination"
    - "modulation formats and waveforms for the physical layer of 5g wireless networks who will be the heir of ofdm"
    - "generalized design of low complexity block diagonalization type precoding algorithms for multiuser mimo systems"

Connected through hyperedge HE-3 (induced by source paper "generalized spatial modulation in large scale multiuser mimo systems"):
  with members:
    - "massive mimo for next generation wireless systems"
    - "performance of spatial modulation using measured real world channels"
    - "channel hardening exploiting message passing chemp receiver in large scale mimo systems"
    - "scaling up mimo opportunities and challenges with very large arrays"
    - "practical implementation of spatial modulation"
    - "generalised sphere decoding for spatial modulation"

Connected through hyperedge HE-4 (induced by source paper "adaptive reduced rank receive processing based on minimum symbol error rate criterion for large scale multiple antenna systems"):
  with members:
    - "iterative detection and decoding algorithms for mimo systems in block fading channels using ldpc codes"
    - "robust adaptive beamforming using a low complexity shrinkage based mismatch estimation algorithm"
    - "scaling up mimo opportunities and challenges with very large arrays"
    - "adaptive reduced rank lcmv beamforming algorithms based on joint iterative optimization of filters design and analysis"
    - "high rate space time coded large mimo systems low complexity detection and channel estimation"

Connected through hyperedge HE-5 (induced by source paper "study of structured root ldpc codes and peg techniques for block fading channels"):
  with members:
    - "iterative detection and decoding algorithms for mimo systems in block fading channels using ldpc codes"
    - "adaptive distributed space time coding based on adjustable code matrices for cooperative mimo relaying systems"

Connected through hyperedge HE-6 (induced by source paper "multi user flexible coordinated beamforming using lattice reduction for massive mimo systems"):
  with members:
    - "robust adaptive beamforming using a low complexity shrinkage based mismatch estimation algorithm"
    - "multi branch tomlinson harashima precoding design for mu mimo systems theory and algorithms"
    - "generalized design of low complexity block diagonalization type precoding algorithms for multiuser mimo systems"
    - "blind adaptive interference suppression based on set membership constrained constant modulus algorithms with dynamic bounds"
    - "reduced rank doa estimation based on joint iterative subspace optimization and grid search"
    - "scaling up mimo opportunities and challenges with very large arrays"
    - "adaptive distributed space time coding based on adjustable code matrices for cooperative mimo relaying systems"
    - "adaptive reduced rank lcmv beamforming algorithms based on joint iterative optimization of filters design and 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)