@ARTICLE {28321,
author={S.  Shah and A.  Mian and S.M. Mumtaz and J.  Crowcroft},
doi={10.1109/ACCESS.2019.2911409},
journal={IEEE Access},
title={System Capacity Analysis for Ultra-Dense Multi-Tier Future Cellular Networks},
year={2019},
month={April},
volume={7},
number={4},
pages={50503-50512},
ISSN={2169-3536}
}