5,755 research outputs found
Joint Resource Partitioning and Offloading in Heterogeneous Cellular Networks
In heterogeneous cellular networks (HCNs), it is desirable to offload mobile
users to small cells, which are typically significantly less congested than the
macrocells. To achieve sufficient load balancing, the offloaded users often
have much lower SINR than they would on the macrocell. This SINR degradation
can be partially alleviated through interference avoidance, for example time or
frequency resource partitioning, whereby the macrocell turns off in some
fraction of such resources. Naturally, the optimal offloading strategy is
tightly coupled with resource partitioning; the optimal amount of which in turn
depends on how many users have been offloaded. In this paper, we propose a
general and tractable framework for modeling and analyzing joint resource
partitioning and offloading in a two-tier cellular network. With it, we are
able to derive the downlink rate distribution over the entire network, and an
optimal strategy for joint resource partitioning and offloading. We show that
load balancing, by itself, is insufficient, and resource partitioning is
required in conjunction with offloading to improve the rate of cell edge users
in co-channel heterogeneous networks
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
Analysis of LTE-A Heterogeneous Networks with SIR-based Cell Association and Stochastic Geometry
This paper provides an analytical framework to characterize the performance
of Heterogeneous Networks (HetNets), where the positions of base stations and
users are modeled by spatial Poisson Point Processes (stochastic geometry). We
have been able to formally derive outage probability, rate coverage
probability, and mean user bit-rate when a frequency reuse of and a novel
prioritized SIR-based cell association scheme are applied. A simulation
approach has been adopted in order to validate our analytical model;
theoretical results are in good agreement with simulation ones. The results
obtained highlight that the adopted cell association technique allows very low
outage probability and the fulfillment of certain bit-rate requirements by
means of adequate selection of reuse factor and micro cell density. This
analytical model can be adopted by network operators to gain insights on cell
planning. Finally, the performance of our SIR-based cell association scheme has
been validated through comparisons with other schemes in literature.Comment: Paper accepted to appear on the Journal of Communication Networks
(accepted on November 28, 2017); 15 page
Unified and Distributed QoS-Driven Cell Association Algorithms in Heterogeneous Networks
This paper addresses the cell association problem in the downlink of a
multi-tier heterogeneous network (HetNet), where base stations (BSs) have
finite number of resource blocks (RBs) available to distribute among their
associated users. Two problems are defined and treated in this paper: sum
utility of long term rate maximization with long term rate quality of service
(QoS) constraints, and global outage probability minimization with outage QoS
constraints. The first problem is well-suited for low mobility environments,
while the second problem provides a framework to deal with environments with
fast fading. The defined optimization problems in this paper are solved in two
phases: cell association phase followed by the optional RB distribution phase.
We show that the cell association phase of both problems have the same
structure. Based on this similarity, we propose a unified distributed algorithm
with low levels of message passing to for the cell association phase. This
distributed algorithm is derived by relaxing the association constraints and
using Lagrange dual decomposition method. In the RB distribution phase, the
remaining RBs after the cell association phase are distributed among the users.
Simulation results show the superiority of our distributed cell association
scheme compared to schemes that are based on maximum signal to interference
plus noise ratio (SINR)
On/Off Macrocells and Load Balancing in Heterogeneous Cellular Networks
The rate distribution in heterogeneous networks (HetNets) greatly benefits
from load balancing, by which mobile users are pushed onto lightly-loaded small
cells despite the resulting loss in SINR. This offloading can be made more
aggressive and robust if the macrocells leave a fraction of time/frequency
resource blank, which reduces the interference to the offloaded users. We
investigate the joint optimization of this technique - referred to in 3GPP as
enhanced intercell interference coordination (eICIC) via almost blank subframes
(ABSs) - with offloading in this paper. Although the joint cell association and
blank resource (BR) problem is nominally combinatorial, by allowing users to
associate with multiple base stations (BSs), the problem becomes convex, and
upper bounds the performance versus a binary association. We show both
theoretically and through simulation that the optimal solution of the relaxed
problem still results in an association that is mostly binary. The optimal
association differs significantly when the macrocell is on or off; in
particular the offloading can be much more aggressive when the resource is left
blank by macro BSs. Further, we observe that jointly optimizing the offloading
with BR is important. The rate gain for cell edge users (the worst 3-10%) is
very large - on the order of 5-10x - versus a naive association strategy
without macrocell blanking
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