1,738 research outputs found
Load-Aware Modeling and Analysis of Heterogeneous Cellular Networks
Random spatial models are attractive for modeling heterogeneous cellular
networks (HCNs) due to their realism, tractability, and scalability. A major
limitation of such models to date in the context of HCNs is the neglect of
network traffic and load: all base stations (BSs) have typically been assumed
to always be transmitting. Small cells in particular will have a lighter load
than macrocells, and so their contribution to the network interference may be
significantly overstated in a fully loaded model. This paper incorporates a
flexible notion of BS load by introducing a new idea of conditionally thinning
the interference field. For a K-tier HCN where BSs across tiers differ in terms
of transmit power, supported data rate, deployment density, and now load, we
derive the coverage probability for a typical mobile, which connects to the
strongest BS signal. Conditioned on this connection, the interfering BSs of the
tier are assumed to transmit independently with probability ,
which models the load. Assuming - reasonably - that smaller cells are more
lightly loaded than macrocells, the analysis shows that adding such access
points to the network always increases the coverage probability. We also
observe that fully loaded models are quite pessimistic in terms of coverage.Comment: to appear, IEEE Transactions on Wireless Communication
Fundamentals of Heterogeneous Cellular Networks with Energy Harvesting
We develop a new tractable model for K-tier heterogeneous cellular networks
(HetNets), where each base station (BS) is powered solely by a self-contained
energy harvesting module. The BSs across tiers differ in terms of the energy
harvesting rate, energy storage capacity, transmit power and deployment
density. Since a BS may not always have enough energy, it may need to be kept
OFF and allowed to recharge while nearby users are served by neighboring BSs
that are ON. We show that the fraction of time a k^{th} tier BS can be kept ON,
termed availability \rho_k, is a fundamental metric of interest. Using tools
from random walk theory, fixed point analysis and stochastic geometry, we
characterize the set of K-tuples (\rho_1, \rho_2, ... \rho_K), termed the
availability region, that is achievable by general uncoordinated operational
strategies, where the decision to toggle the current ON/OFF state of a BS is
taken independently of the other BSs. If the availability vector corresponding
to the optimal system performance, e.g., in terms of rate, lies in this
availability region, there is no performance loss due to the presence of
unreliable energy sources. As a part of our analysis, we model the temporal
dynamics of the energy level at each BS as a birth-death process, derive the
energy utilization rate, and use hitting/stopping time analysis to prove that
there exists a fundamental limit on \rho_k that cannot be surpassed by any
uncoordinated strategy.Comment: submitted to IEEE Transactions on Wireless Communications, July 201
Modeling and Analysis of K-Tier Downlink Heterogeneous Cellular Networks
Cellular networks are in a major transition from a carefully planned set of
large tower-mounted base-stations (BSs) to an irregular deployment of
heterogeneous infrastructure elements that often additionally includes micro,
pico, and femtocells, as well as distributed antennas. In this paper, we
develop a tractable, flexible, and accurate model for a downlink heterogeneous
cellular network (HCN) consisting of K tiers of randomly located BSs, where
each tier may differ in terms of average transmit power, supported data rate
and BS density. Assuming a mobile user connects to the strongest candidate BS,
the resulting Signal-to-Interference-plus-Noise-Ratio (SINR) is greater than 1
when in coverage, Rayleigh fading, we derive an expression for the probability
of coverage (equivalently outage) over the entire network under both open and
closed access, which assumes a strikingly simple closed-form in the high SINR
regime and is accurate down to -4 dB even under weaker assumptions. For
external validation, we compare against an actual LTE network (for tier 1) with
the other K-1 tiers being modeled as independent Poisson Point Processes. In
this case as well, our model is accurate to within 1-2 dB. We also derive the
average rate achieved by a randomly located mobile and the average load on each
tier of BSs. One interesting observation for interference-limited open access
networks is that at a given SINR, adding more tiers and/or BSs neither
increases nor decreases the probability of coverage or outage when all the
tiers have the same target-SINR.Comment: IEEE Journal on Selected Areas in Communications, vol. 30, no. 3, pp.
550 - 560, Apr. 201
Dual-Branch MRC Receivers under Spatial Interference Correlation and Nakagami Fading
Despite being ubiquitous in practice, the performance of maximal-ratio
combining (MRC) in the presence of interference is not well understood. Because
the interference received at each antenna originates from the same set of
interferers, but partially de-correlates over the fading channel, it possesses
a complex correlation structure. This work develops a realistic analytic model
that accurately accounts for the interference correlation using stochastic
geometry. Modeling interference by a Poisson shot noise process with
independent Nakagami fading, we derive the link success probability for
dual-branch interference-aware MRC. Using this result, we show that the common
assumption that all receive antennas experience equal interference power
underestimates the true performance, although this gap rapidly decays with
increasing the Nakagami parameter of the interfering links. In
contrast, ignoring interference correlation leads to a highly optimistic
performance estimate for MRC, especially for large . In the low
outage probability regime, our success probability expression can be
considerably simplified. Observations following from the analysis include: (i)
for small path loss exponents, MRC and minimum mean square error combining
exhibit similar performance, and (ii) the gains of MRC over selection combining
are smaller in the interference-limited case than in the well-studied
noise-limited case.Comment: to appear in IEEE Transactions on Communication
- …