human: Given a node-centered hypergraph: <hypergraph>, where nodes represent authors and hyperedges represent groups of authors who co-authored the same paper.

Details of the hypergraph:
Center node: "Precoded massive MU-MIMO uplink transmission under transceiver I/Q imbalance"
  Abstract: In massive multiple-input multiple-output (MIMO) systems, combined with digital array processing, the amount of the associated radio frequency (RF) front-ends is inevitably high. This paper addresses how imperfections in these RF front-ends affect the overall system performance in precoded massive multiuser MIMO (MU-MIMO) uplink transmission. In particular, we focus on transceiver in-phase/quadrature (I/Q) imbalances and their mitigation with RF-aware spatial processing. We first derive the essential distortion and interference models for OFDMA-based massive MU-MIMO uplink system under I/Q imbalances, and then propose augmented spatial post-processing to be carried out in the uplink receiver (RX) for mitigating the harmful effects efficiently. Numerical examples show that the augmented spatial RX processing clearly outperforms the conventional linear processing, and thus provides significant performance improvements with practical low-cost RF front-ends.

Connected through hyperedge HE-1 (induced by source paper "Analysis and Augmented Spatial Processing for Uplink OFDMA MU-MIMO Receiver With Transceiver I/Q Imbalance and External Interference"):
  with members:
    (none)

Question: Please tell me which research area the center author belongs to. The 4 classes are: Computer science, Mathematics, Engineering, Economics, Psychology, Business. Directly output the class name.

gpt: Computer science