Closed-form Approximations for Coverage and Rate in a Multi-tier   Heterogeneous Network in Nakagami-m Fading
  In this paper, we consider the downlink in a K-tier heterogeneous network in the presence of Nakagami-m fading and noise. For such a system, we derive closed-form approximations of coverage probability and average rate achievable. A piece-wise linear approximation is employed in obtaining the simplified expressions. The proposed results are verified numerically through simulations. A comparison with existing work shows that the proposed work is a good approximation. 
G. V. S. S. Praneeth Varma, G. V. V. Sharma and A. Kumar
cs.IT math.IT