85 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
Open, Closed, and Shared Access Femtocells in the Downlink
A fundamental choice in femtocell deployments is the set of users which are
allowed to access each femtocell. Closed access restricts the set to
specifically registered users, while open access allows any mobile subscriber
to use any femtocell. Which one is preferable depends strongly on the distance
between the macrocell base station (MBS) and femtocell. The main results of the
paper are lemmas which provide expressions for the SINR distribution for
various zones within a cell as a function of this MBS-femto distance. The
average sum throughput (or any other SINR-based metric) of home users and
cellular users under open and closed access can be readily determined from
these expressions. We show that unlike in the uplink, the interests of home and
cellular users are in conflict, with home users preferring closed access and
cellular users preferring open access. The conflict is most pronounced for
femtocells near the cell edge, when there are many cellular users and fewer
femtocells. To mitigate this conflict, we propose a middle way which we term
shared access in which femtocells allocate an adjustable number of time-slots
between home and cellular users such that a specified minimum rate for each can
be achieved. The optimal such sharing fraction is derived. Analysis shows that
shared access achieves at least the overall throughput of open access while
also satisfying rate requirements, while closed access fails for cellular users
and open access fails for the home user.Comment: 26 pages, 8 figures, Submitted to IEEE Transactions on Wireless
Communication
An MBS-Assisted Femtocell Transmit Power Control Scheme with Mobile User QoS Guarantee in 2-Tier Heterogeneous Femtocell Networks
This study investigates how to adjust the transmit power of femto base station (FBS) to mitigate interference problems between the
FBSs and mobile users (MUs) in the 2-tier heterogeneous femtocell
networks. A common baseline of deploying the FBS to increase the
indoor access bandwidth requires that the FBS operation will not
affect outdoor MUs operation with their quality-of-service (QoS)
requirements. To tackle this technical problem, an FBS
transmit power adjustment (FTPA) algorithm is proposed to adjust
the FBS transmit power (FTP) to avoid unwanted cochannel
interference (CCI) with the neighboring MUs in downlink
transmission. FTPA reduces the FTP to serve its femto users (FUs)
according to the QoS requirements of the nearest neighboring MUs
to the FBS so that the MU QoS requirement is guaranteed.
Simulation results demonstrate that FTPA can achieve a low MU
outage probability as well as serve FUs without violating the MU
QoS requirements. Simulation results also reveal that FTPA has
better performance on voice and video services which are the major
trend of future multimedia communication in the NGN
Improving Frequency Reuse and Cochannel Interference Coordination in 4G HetNets
This report describes my M.A.Sc. thesis research work. The emerging 4th generation
(4G) mobile systems and networks (so called 4G HetNets) are designed as multilayered cellular topology with a number of asymmetrically located, asymmetrically powered, self-organizing, and user-operated indoor small cell (e.g., pico/femto cells and WLANs) with a variety of cell architectures that are overlaid by a large cell (macro cell) with some or all interfering wireless links. These designs of 4G HetNets bring new challenges such as increased dynamics of user mobility and data traffic trespassing over the multi-layered cell boundaries. Traditional approaches of radio resource allocation and inter-cell (cochannel) interference management that are mostly centralized and static in the network core and are carried out pre-hand by the operator in 3G and lower cellular technologies, are liable to increased signaling overhead, latencies, complexities, and scalability issues and, thus, are not viable in case of 4G HetNets. In this thesis a comprehensive research study is carried out on improving the radio resource sharing and inter-cell interference management in 4G HetNets. The solution strategy exploits dynamic and adaptive channel allocation approaches such as dynamic and opportunistic spectrum access (DSA, OSA) techniques, through exploiting the spatiotemporal diversities among transmissions in orthogonal frequency division multiple access (OFDMA) based medium access in 4G HetNets.
In this regards, a novel framework named as Hybrid Radio Resource Sharing (HRRS) is introduced. HRRS comprises of these two functional modules: Cognitive Radio Resource Sharing (CRRS) and Proactive Link Adaptation (PLA) scheme. A dynamic switching algorithm enables CRRS and PLA modules to adaptively invoke according to whether orthogonal channelization is to be carried out exploiting the interweave channel allocation (ICA) approach or non-orthogonal channelization is to be carried out exploiting the underlay channel allocation (UCA) approach respectively when relevant conditions regarding the traffic demand and radio resource availability are met. Benefits of CRRS scheme are identified through simulative analysis in comparison to the legacy cochannel and dedicated channel deployments of femto cells respectively. The case study and numerical analysis for PLA scheme is carried out to understand the dynamics of threshold interference ranges as function of transmit powers of MBS and FBS, relative ranges of radio entities, and QoS requirement of services with the value realization of PLA scheme.1 yea
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Interference management and decentralized channel access schemes in hotspot-aided cellular networks
A system and method are provided wherein one or more femtocell base stations are deployed within a range of a cellular base station and utilize substantially the same frequency band as the cellular base station. Each femtocell base station may be configured to employ one or more interference avoidance techniques such that coexistence between the cellular and the corresponding femtocell base station is enabled. The interference avoidance techniques employed may include use of randomized time or frequency hopping; randomly selecting a predetermined number, or identifying one or more unutilized, frequency subchannels for signal transmission; using two or more transmit and two or more receive antennas; nulling one or more transmissions in a direction of a nearby cellular base station user; handing off at least one cellular user to one of the femtocell base stations and vice versa; and/or reducing the transmission power of at least one femtocell base station.Board of Regents, University of Texas Syste
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Green cell planning and deployment for small cell networks in smart cities
In smart cities, cellular network plays a crucial role to support wireless access for numerous devices anywhere and anytime. The future 5G network aims to build the infrastructure from mobile internet to connected world. Small Cell is one of the most promising technologies of 5G to provide more connections and high data rate. In order to make the best use of small cell technology, smart cell planning should be implemented to guarantee connectivity and performance for all end nodes. It is particularly a challenging task to deploy dense small cells in the presence of dynamic traffic demands and severe co-channel interference. In this paper, we model various traffic patterns using stochastic geometry approach and propose an energy-efficient scheme to deploy and plan small cells according to the prevailing traffic pattern. The simulation results indicate that our scheme can meet dynamic traffic demands with optimized deployment of small cells and enhance the energy efficiency of the system without compromising on quality-of-service (QoS) requirements. In addition, our scheme can achieve very close performance compared with the leading optimization solver CPLEX and find solutions in much less computational times than CPLEX
Coverage in Multi-Antenna Two-Tier Networks
In two-tier networks -- comprising a conventional cellular network overlaid
with shorter range hotspots (e.g. femtocells, distributed antennas, or wired
relays) -- with universal frequency reuse, the near-far effect from cross-tier
interference creates dead spots where reliable coverage cannot be guaranteed to
users in either tier. Equipping the macrocell and femtocells with multiple
antennas enhances robustness against the near-far problem. This work derives
the maximum number of simultaneously transmitting multiple antenna femtocells
meeting a per-tier outage probability constraint. Coverage dead zones are
presented wherein cross-tier interference bottlenecks cellular and hotspot
coverage. Two operating regimes are shown namely 1) a cellular-limited regime
in which femtocell users experience unacceptable cross-tier interference and 2)
a hotspot-limited regime wherein both femtocell users and cellular users are
limited by hotspot interference. Our analysis accounts for the per-tier
transmit powers, the number of transmit antennas (single antenna transmission
being a special case) and terrestrial propagation such as the Rayleigh fading
and the path loss exponents. Single-user (SU) multiple antenna transmission at
each tier is shown to provide significantly superior coverage and spatial reuse
relative to multiuser (MU) transmission. We propose a decentralized
carrier-sensing approach to regulate femtocell transmission powers based on
their location. Considering a worst-case cell-edge location, simulations using
typical path loss scenarios show that our interference management strategy
provides reliable cellular coverage with about 60 femtocells per cellsite.Comment: 30 Pages, 11 figures, Revised and Resubmitted to IEEE Transactions on
Wireless Communication
Design of in-building wireless networks deployments using evolutionary algorithms
In this article, a novel approach to deal with the design of in-building wireless networks deployments is proposed. This approach known as MOQZEA (Multiobjective Quality Zone Based Evolutionary Algorithm) is a hybr id evolutionary algorithm adapted to use a novel fitness function, based on the definition of quality zones for the different objective functions considered. This approach is conceived to solve wireless network design problems without previous information of the required number of transmitters, considering simultaneously a high number of objective functions and optimizing multiple configuration parameters of the transmitters
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