@ARTICLE{2020-Xiaolu-Access-DirectionSensing,
  author={X. {Zeng} and F. {Zhang} and B. {Wang} and K. J. R. {Liu}},
  journal={IEEE Access}, 
  title={Radio Frequency Based Direction Sensing Using Massive MIMO}, 
  year={2020},
  volume={8},
  number={},
  pages={26827-26838},
  doi={10.1109/ACCESS.2020.2964525}}