human: Given a hyperedge-centered hypergraph: <hypergraph>, where the center hyperedge is induced by one source paper and its member nodes are the cited papers.

Details of the hypergraph:
Center hyperedge (induced by source paper "spectral efficiency analysis of cell free massive mimo systems with zero forcing detector"):
  Abstract: In this paper, we firstly derive two approximations of the achievable uplink rate with the perfect/imperfect channel state information (CSI) in cell-free massive multi-input multi-output (MIMO) systems, and all these approximations are not only in the simple, but also converge into the classical bounds achieved in conventional massive MIMO systems where the base-station (BS) antennas are co-located. It is worth noting that the obtained two approximations with perfect CSI could be regarded as the special cases of the obtained two approximations with imperfect CSI when the pilot sequence power becomes infinite, respectively. Moreover, the theory analysis shows that all obtained approximations with perfect/imperfect CSI have an asymptotic lower bound    $\frac {\alpha }{2}\log _{2} L$    thanks to the extra  distance diversity  offered by massively distributed antennas, where    $L$    is the number of BS antennas and the path-loss factor    $\alpha >2$   , except for the free space environment. Obviously, these results indicate that the cell-free massive MIMO system has huge potential of spectral efficiency than the conventional massive MIMO system with the asymptotically tight bound    $\log _{2} L$   .

Includes members:
  Member "downlink precoding with mixed statistical and imperfect instantaneous csi for massive mimo systems":
    also connected through other hyperedges:
      - Hyperedge HE-1 (induced by source paper "ieee 802 15 4 e tsch based scheduling for throughput optimization a combinatorial multi armed bandit approach")
  Member "enhanced max min sinr for uplink cell free massive mimo systems":
    also connected through other hyperedges:
      - Hyperedge HE-2 (induced by source paper "max min rate of cell free massive mimo uplink with optimal uniform quantization")
  Member "on the total energy efficiency of cell free massive mimo":
    also connected through other hyperedges:
      - Hyperedge HE-3 (induced by source paper "joint power control and lsfd for wireless powered cell free massive mimo")
  Member "performance analysis for massive mimo downlink with low complexity approximate zero forcing precoding":
    also connected through other hyperedges:
      - Hyperedge HE-4 (induced by source paper "average sep optimal precoding for correlated massive mimo with zf detection an asymptotic analysis")
  Member "pilot power allocation through user grouping in multi cell massive mimo systems":
    also connected through other hyperedges:
      - Hyperedge HE-5 (induced by source paper "a covariance based hybrid channel feedback in fdd massive mimo systems")
  Member "energy efficient downlink transmission for multicell massive das with pilot contamination":
    also connected through other hyperedges:
      - Hyperedge HE-6 (induced by source paper "reconfigurable intelligent surfaces for energy efficiency in wireless communication")
  Member "energy efficiency in cell free massive mimo with zero forcing precoding design":
    also connected through other hyperedges:
      - Hyperedge HE-7 (induced by source paper "joint power allocation and load balancing optimization for energy efficient cell free massive mimo networks")
  Member "cell free massive mimo versus small cells":
    also connected through other hyperedges:
      - Hyperedge HE-8 (induced by source paper "analysis of uav communications in cell free massive mimo systems")

Question: Please tell me which class the source paper 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)