@article{chen2022survey,
  title={A survey on user-centric cell-free massive {MIMO} systems},
  author={Chen, Shuaifei and Zhang, Jiayi and Zhang, Jing and Bj{\"o}rnson, Emil and Ai, Bo},
  journal={Digit. Commun. Netw.},
  volume={8},
  number={5},
  pages={695--719},
  year={2022},
  month={Oct.},
  publisher={Elsevier}
}