Modeling and Analysis of K-Tier Downlink Heterogeneous Cellular Networks

Abstract

Cellular networks are in a major transition from a carefully planned set of\nlarge tower-mounted base-stations (BSs) to an irregular deployment of\nheterogeneous infrastructure elements that often additionally includes micro,\npico, and femtocells, as well as distributed antennas. In this paper, we\ndevelop a tractable, flexible, and accurate model for a downlink heterogeneous\ncellular network (HCN) consisting of K tiers of randomly located BSs, where\neach tier may differ in terms of average transmit power, supported data rate\nand BS density. Assuming a mobile user connects to the strongest candidate BS,\nthe resulting Signal-to-Interference-plus-Noise-Ratio (SINR) is greater than 1\nwhen in coverage, Rayleigh fading, we derive an expression for the probability\nof coverage (equivalently outage) over the entire network under both open and\nclosed access, which assumes a strikingly simple closed-form in the high SINR\nregime and is accurate down to -4 dB even under weaker assumptions. For\nexternal validation, we compare against an actual LTE network (for tier 1) with\nthe other K-1 tiers being modeled as independent Poisson Point Processes. In\nthis case as well, our model is accurate to within 1-2 dB. We also derive the\naverage rate achieved by a randomly located mobile and the average load on each\ntier of BSs. One interesting observation for interference-limited open access\nnetworks is that at a given SINR, adding more tiers and/or BSs neither\nincreases nor decreases the probability of coverage or outage when all the\ntiers have the same target-SINR.\n

Affiliated Institutions

• The University of Texas at Austin US
• Indian Institute of Technology Madras IN
• Institut national de recherche en sciences et technologies du numérique FR

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