1,278 research outputs found
Power Control in Two-Tier Femtocell Networks
In a two tier cellular network -- comprised of a central macrocell underlaid
with shorter range femtocell hotspots -- cross-tier interference limits overall
capacity with universal frequency reuse. To quantify near-far effects with
universal frequency reuse, this paper derives a fundamental relation providing
the largest feasible cellular Signal-to-Interference-Plus-Noise Ratio (SINR),
given any set of feasible femtocell SINRs. We provide a link budget analysis
which enables simple and accurate performance insights in a two-tier network. A
distributed utility-based SINR adaptation at femtocells is proposed in order to
alleviate cross-tier interference at the macrocell from cochannel femtocells.
The Foschini-Miljanic (FM) algorithm is a special case of the adaptation. Each
femtocell maximizes their individual utility consisting of a SINR based reward
less an incurred cost (interference to the macrocell). Numerical results show
greater than 30% improvement in mean femtocell SINRs relative to FM. In the
event that cross-tier interference prevents a cellular user from obtaining its
SINR target, an algorithm is proposed that reduces transmission powers of the
strongest femtocell interferers. The algorithm ensures that a cellular user
achieves its SINR target even with 100 femtocells/cell-site, and requires a
worst case SINR reduction of only 16% at femtocells. These results motivate
design of power control schemes requiring minimal network overhead in two-tier
networks with shared spectrum.Comment: 29 pages, 10 figures, Revised and resubmitted to the IEEE
Transactions on Wireless Communication
Integration of TV White Space and Femtocell Networks.
PhDFemtocell is an effective approach to increase system capacity in cellular networks.
Since traditional Femtocells use the same frequency band as the cellular network,
cross-tier and co-tier interference exist in such Femtocell networks and have a major
impact on deteriorating the system throughput. In order to tackle these challenges,
interference mitigation has drawn attentions from both academia and industry. TV
White Space (TVWS) is a newly opened portion of spectrum, which comes from the
spare spectrum created by the transition from analogue TV to digital TV. It can be
utilized by using cognitive radio technology according to the policies from
telecommunications regulators. This thesis considers using locally available TVWS to
reduce the interference in Femtocell networks. The objective of this research is to
mitigate the downlink cross-tier and co-tier interference in different Femtocell
deployment scenarios, and increase the throughput of the overall system.
A Geo-location database model to obtain locally available TVWS information in UK
is developed in this research. The database is designed using power control method
to calculate available TVWS channels and maximum allowable transmit power based
on digital TV transmitter information in UK and regulations on unlicensed use of
TVWS. The proposed database model is firstly combined with a grid-based resource
allocation scheme and investigated in a simplified Femtocell network to demonstrate
the gains of using TVWS in Femtocell networks.
Furthermore, two Femtocell deployment scenarios are studied in this research. In the
suburban Femtocell deployment scenario, a novel system architecture that consists of
the Geo-location database and a resource allocation scheme using TVWS is proposed
to mitigate cross-tier interference between Macrocell and Femtocells. In the dense
Femtocell deployment scenario, a power efficient resource allocation scheme is
proposed to maximize the throughput of Femtocells while limiting the co-tier
interference among Femtocells. The optimization problem in the power efficient
scheme is solved by using sequential quadratic programming method. The
simulation results show that the proposed schemes can effectively mitigate the
interference in Femtocell networks in practical deployment scenarios
Price-Based Resource Allocation for Spectrum-Sharing Femtocell Networks: A Stackelberg Game Approach
This paper investigates the price-based resource allocation strategies for
the uplink transmission of a spectrum-sharing femtocell network, in which a
central macrocell is underlaid with distributed femtocells, all operating over
the same frequency band as the macrocell. Assuming that the macrocell base
station (MBS) protects itself by pricing the interference from the femtocell
users, a Stackelberg game is formulated to study the joint utility maximization
of the macrocell and the femtocells subject to a maximum tolerable interference
power constraint at the MBS. Especially, two practical femtocell channel
models: sparsely deployed scenario for rural areas and densely deployed
scenario for urban areas, are investigated. For each scenario, two pricing
schemes: uniform pricing and non-uniform pricing, are proposed. Then, the
Stackelberg equilibriums for these proposed games are studied, and an effective
distributed interference price bargaining algorithm with guaranteed convergence
is proposed for the uniform-pricing case. Finally, numerical examples are
presented to verify the proposed studies. It is shown that the proposed
algorithms are effective in resource allocation and macrocell protection
requiring minimal network overhead for spectrum-sharing-based two-tier
femtocell networks.Comment: 27 pages, 7 figures, Submitted to JSA
Open vs Closed Access Femtocells in the Uplink
Femtocells are assuming an increasingly important role in the coverage and
capacity of cellular networks. In contrast to existing cellular systems,
femtocells are end-user deployed and controlled, randomly located, and rely on
third party backhaul (e.g. DSL or cable modem). Femtocells can be configured to
be either open access or closed access. Open access allows an arbitrary nearby
cellular user to use the femtocell, whereas closed access restricts the use of
the femtocell to users explicitly approved by the owner. Seemingly, the network
operator would prefer an open access deployment since this provides an
inexpensive way to expand their network capabilities, whereas the femtocell
owner would prefer closed access, in order to keep the femtocell's capacity and
backhaul to himself. We show mathematically and through simulations that the
reality is more complicated for both parties, and that the best approach
depends heavily on whether the multiple access scheme is orthogonal (TDMA or
OFDMA, per subband) or non-orthogonal (CDMA). In a TDMA/OFDMA network,
closed-access is typically preferable at high user densities, whereas in CDMA,
open access can provide gains of more than 200% for the home user by reducing
the near-far problem experienced by the femtocell. The results of this paper
suggest that the interests of the femtocell owner and the network operator are
more compatible than typically believed, and that CDMA femtocells should be
configured for open access whereas OFDMA or TDMA femtocells should adapt to the
cellular user density.Comment: 21 pages, 8 figures, 2 tables, submitted to IEEE Trans. on Wireless
Communication
Coalitional Games with Overlapping Coalitions for Interference Management in Small Cell Networks
In this paper, we study the problem of cooperative interference management in
an OFDMA two-tier small cell network. In particular, we propose a novel
approach for allowing the small cells to cooperate, so as to optimize their
sum-rate, while cooperatively satisfying their maximum transmit power
constraints. Unlike existing work which assumes that only disjoint groups of
cooperative small cells can emerge, we formulate the small cells' cooperation
problem as a coalition formation game with overlapping coalitions. In this
game, each small cell base station can choose to participate in one or more
cooperative groups (or coalitions) simultaneously, so as to optimize the
tradeoff between the benefits and costs associated with cooperation. We study
the properties of the proposed overlapping coalition formation game and we show
that it exhibits negative externalities due to interference. Then, we propose a
novel decentralized algorithm that allows the small cell base stations to
interact and self-organize into a stable overlapping coalitional structure.
Simulation results show that the proposed algorithm results in a notable
performance advantage in terms of the total system sum-rate, relative to the
noncooperative case and the classical algorithms for coalitional games with
non-overlapping coalitions
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