179 research outputs found
On the spectral-energy efficiency and rate fairness tradeoff in relay-aided cooperative OFDMA systems
In resource constrained wireless systems, achieving higher spectral efficiency (SE) and energy efficiency (EE), and greater rate fairness are conflicting objectives. Here a general framework is presented to analyze the tradeoff among these three performance metrics in cooperative OFDMA systems with decode-and-forward (DF) relaying, where subcarrier pairing and allocation, relay selection, choice of transmission strategy, and power allocation are jointly considered. In our analytical framework, rate fairness is represented utilizing -fairness model and the resource allocation problem is formulated as a multiobjective optimization (MOO) problem. We then propose a cross-layer resource allocation algorithm across application and physical layers, and further devise a heuristic algorithm to tackle the computational complexity issue. The SE-EE tradeoff is characterized as a Pareto optimal set, and the efficiency and fairness tradeoff is investigated through the price of fairness (PoF). Simulations indicate that higher fairness results in a worse SE-EE tradeoff. It is also shown imposing fairness helps to reduce the outage probability. For a fixed number of relays, by increasing circuit power, the performance of SE-EE tradeoff is degraded. Interestingly, by increasing the number of relays, although the total circuit power is increased, the SE-EE tradeoff is not necessarily degraded. This is thanks to the extra degree of freedom provided in relay selection
Eficiência energética avançada para sistema OFDMA CoMP coordenação multiponto
Doutoramento em Engenharia EletrotécnicaThe ever-growing energy consumption in mobile networks stimulated by
the expected growth in data tra ffic has provided the impetus for mobile
operators to refocus network design, planning and deployment towards reducing
the cost per bit, whilst at the same time providing a signifi cant step
towards reducing their operational expenditure. As a step towards incorporating
cost-eff ective mobile system, 3GPP LTE-Advanced has adopted the
coordinated multi-point (CoMP) transmission technique due to its ability
to mitigate and manage inter-cell interference (ICI). Using CoMP the cell
average and cell edge throughput are boosted. However, there is room for
reducing energy consumption further by exploiting the inherent
exibility of
dynamic resource allocation protocols. To this end packet scheduler plays
the central role in determining the overall performance of the 3GPP longterm
evolution (LTE) based on packet-switching operation and provide a
potential research playground for optimizing energy consumption in future
networks. In this thesis we investigate the baseline performance for down
link CoMP using traditional scheduling approaches, and subsequently go
beyond and propose novel energy e fficient scheduling (EES) strategies that
can achieve power-e fficient transmission to the UEs whilst enabling both
system energy effi ciency gain and fairness improvement. However, ICI can
still be prominent when multiple nodes use common resources with di fferent
power levels inside the cell, as in the so called heterogeneous networks (Het-
Net) environment. HetNets are comprised of two or more tiers of cells. The
rst, or higher tier, is a traditional deployment of cell sites, often referred
to in this context as macrocells. The lower tiers are termed small cells, and
can appear as microcell, picocells or femtocells. The HetNet has attracted
signiffi cant interest by key manufacturers as one of the enablers for high
speed data at low cost. Research until now has revealed several key hurdles
that must be overcome before HetNets can achieve their full potential:
bottlenecks in the backhaul must be alleviated, as well as their seamless
interworking with CoMP. In this thesis we explore exactly the latter hurdle,
and present innovative ideas on advancing CoMP to work in synergy with
HetNet deployment, complemented by a novel resource allocation policy
for HetNet tighter interference management. As system level simulator has
been used to analyze the proposed algorithm/protocols, and results have
concluded that up to 20% energy gain can be observed.O aumento do consumo de energia nas TICs e em particular nas redes de
comunicação móveis, estimulado por um crescimento esperado do tráfego de
dados, tem servido de impulso aos operadores m oveis para reorientarem os
seus projectos de rede, planeamento e implementa ção no sentido de reduzir
o custo por bit, o que ao mesmo tempo possibilita um passo signicativo no
sentido de reduzir as despesas operacionais. Como um passo no sentido de
uma incorporação eficaz em termos destes custos, o sistema móvel 3GPP
LTE-Advanced adoptou a técnica de transmissão Coordenação Multi-Ponto
(identificada na literatura com a sigla CoMP) devido à sua capacidade de
mitigar e gerir Interferência entre Células (sigla ICI na literatura). No entanto
a ICI pode ainda ser mais proeminente quando v arios n os no interior
da célula utilizam recursos comuns com diferentes níveis de energia,
como acontece nos chamados ambientes de redes heterogéneas (sigla Het-
Net na literatura). As HetNets são constituídas por duas ou mais camadas
de células. A primeira, ou camada superiora, constitui uma implantação
tradicional de sítios de célula, muitas vezes referidas neste contexto como
macrocells. Os níveis mais baixos são designados por células pequenas, e
podem aparecer como microcells, picocells ou femtocells. A HetNet tem
atra do grande interesse por parte dos principais fabricantes como sendo
facilitador para transmissões de dados de alta velocidade a baixo custo. A
investigação tem revelado at e a data, vários dos principais obstáculos que
devem ser superados para que as HetNets possam atingir todo o seu potencial:
(i) os estrangulamentos no backhaul devem ser aliviados; (ii) bem
como sua perfeita interoperabilidade com CoMP. Nesta tese exploramos
este ultimo constrangimento e apresentamos ideias inovadoras em como a
t ecnica CoMP poder a ser aperfeiçoada por forma a trabalhar em sinergia
com a implementação da HetNet, complementado ainda com uma nova
perspectiva na alocação de recursos rádio para um controlo e gestão mais
apertado de interferência nas HetNets. Com recurso a simulação a níível de
sistema para analisar o desempenho dos algoritmos e protocolos propostos,
os resultados obtidos concluíram que ganhos at e a ordem dos 20% poderão
ser atingidos em termos de eficiência energética
Resource and Bandwidth Allocation in Hybrid Wireless Mobile Networks
In the lead up to the implementation of 802.16 and 4G wireless networks,
there have been many proposals for addition of multi-hop MANET zones or relay
stations in order to cut the cost of building a new backbone infrastructure from the
ground up. These types of Hybrid Wireless Networks will certainly be a part of
wireless network architecture in the future, and as such, simple problems such as
resource allocation must be explored to maximize their potential. This study
explores the resource allocation problem in three distinct ways. First, this study
highlights two existing backbone architectures: max-coverage and max-resource,
and how hybridization will affect bandwidth allocation, with special emphasis on
OFDM-TMA wireless networks. Secondly, because of the different goals of these
types of networks, the addition of relay stations or MANET zones will affect
resource availability differently, and I will show how the addition of relay stations
impacts the backbone network. Finally, I will discuss specific allocation algorithms
and policies such as top-down, bottom-up, and auction-based allocation, and how
each kind of allocation will maximize the revenue of both the backbone network as
well as the mobile subscribers while maintaining a minimum Quality of Service (or
fairness). Each of these approaches has merit in different hybrid wireless systems,
and I will summarize the benefits of each in a study of a network system with a
combination of the elements discussed in the previous chapters
Uplink Transceiver Design and Optimization for Transmissive RMS Multi-Antenna Systems
In this paper, a novel uplink communication for the transmissive
reconfigurable metasurface (RMS) multi-antenna system is investigated.
Specifically, a transmissive RMS-based receiver equipped with a single
receiving antenna is first proposed, and a far-near field channel model is also
given. Then, in order to maximize the system sum-rate, we formulate a joint
optimization problem over subcarrier allocation, power allocation and RMS
transmissive coefficient design. Since the coupling of optimization variables,
the problem is non-convex, so it is challenging to solve it directly. In order
to tackle this problem, the alternating optimization (AO) algorithm is used to
decouple the optimization variables and divide the problem into two subproblems
to solve. Numerical results verify that the proposed algorithm has good
convergence performance and can improve system sum-rate compared with other
benchmark algorithms.Comment: arXiv admin note: text overlap with arXiv:2109.0546
Multi-cell Coordination Techniques for DL OFDMA Multi-hop Cellular Networks
The main objective of this project is to design coordinated spectrum sharing and reuse
techniques among cells with the goal of mitigating interference at the cell edge and
enhance the overall system capacity. The performance of the developed algorithm will be
evaluated in an 802.16m (WiMAX) environment.
In conventional cellular networks, frequency planning is usually considered to keep an
acceptable signal-to-interference-plus noise ratio (SINR) level, especially at cell
boundaries. Frequency assignations are done under a cell-by-cell basis, without any
coordination between them to manage interference. Particularly this approach, however,
hampers the system spectral efficiency at low reuse rates. For a specific reuse factor, the
system throughput depends highly on the mobile station (MS) distribution and the channel
conditions of the users to be served. If users served from different base stations (BS)
experience a low level of interference, radio resources may be reused, applying a high
reuse factor and thus, increasing the system spectral efficiency. On the other side, if the
served users experience large interference, orthogonal transmissions are better and
therefore a lower frequency reuse factor should be used. As a consequence, a dynamic
reuse factor is preferable over a fixed one.
This work addresses the design of joint multi-cell resource allocation and scheduling with
coordination among neighbouring base stations (outer coordination) or sectors belonging to
the same one (inner coordination) as a way to achieve flexible reuse factors. We propose a
convex optimization framework to address the problem of coordinating bandwidth
allocation in BS coordination problems.
The proposed framework allows for different scheduling policies, which have an impact on
the suitability of the reuse factor, since they determine which users have to be served.
Therefore, it makes sense to consider the reuse factor as a result of the scheduling decision.
To support the proposed techniques the BSs shall be capable of exchanging information
with each other (decentralized approach) or with some control element in the back-haul
network as an ASN gateway or some self-organization control entity (centralized
approach)
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