57 research outputs found
Analysis Framework for Opportunistic Spectrum OFDMA and its Application to the IEEE 802.22 Standard
We present an analytical model that enables throughput evaluation of
Opportunistic Spectrum Orthogonal Frequency Division Multiple Access (OS-OFDMA)
networks. The core feature of the model, based on a discrete time Markov chain,
is the consideration of different channel and subchannel allocation strategies
under different Primary and Secondary user types, traffic and priority levels.
The analytical model also assesses the impact of different spectrum sensing
strategies on the throughput of OS-OFDMA network. The analysis applies to the
IEEE 802.22 standard, to evaluate the impact of two-stage spectrum sensing
strategy and varying temporal activity of wireless microphones on the IEEE
802.22 throughput. Our study suggests that OS-OFDMA with subchannel notching
and channel bonding could provide almost ten times higher throughput compared
with the design without those options, when the activity and density of
wireless microphones is very high. Furthermore, we confirm that OS-OFDMA
implementation without subchannel notching, used in the IEEE 802.22, is able to
support real-time and non-real-time quality of service classes, provided that
wireless microphones temporal activity is moderate (with approximately one
wireless microphone per 3,000 inhabitants with light urban population density
and short duty cycles). Finally, two-stage spectrum sensing option improves
OS-OFDMA throughput, provided that the length of spectrum sensing at every
stage is optimized using our model
A Cooperative Overlay Approach at the Physical Layer of Cognitive Radio for Digital Agriculture
In digital agriculture, the cognitive radio technology is being envisaged as solution to spectral shortage problems by allowing agricultural cognitive users to co-exist with noncognitive users in the same spectrum on the field. Cognitive radios increase system capacity and spectral efficiency by sensing the spectrum and adapting the transmission parameters. This design requires a robust, adaptable and flexible physical layer to support cognitive radio functionality. In this paper, a novel physical layer architecture for cognitive radio based on cognition, cooperation, and cognitive interference avoidance has been developed by using power control for digital agriculture applications. The design is based on sensing of spectrum usage, detecting the message/spreading code of noncognitive users, cognitive relaying, cooperation, and cognition of channel parameters. Moreover, the power and rate allocation, ergodic, and outage capacity formulas are also presented
Performance analysis of 4G wireless networks using system level simulator
Doutoramento em Engenharia ElectrotécnicaIn the last decade, mobile wireless communications have witnessed an explosive
growth in the user’s penetration rate and their widespread deployment around the
globe. In particular, a research topic of particular relevance in telecommunications
nowadays is related to the design and implementation of mobile communication
systems of 4th generation (4G). 4G networks will be characterized by the support
of multiple radio access technologies in a core network fully compliant with the
Internet Protocol (all IP paradigms). Such networks will sustain the stringent
quality of service (QoS) requirements and the expected high data rates from the
type of multimedia applications (i.e. YouTube and Skype) to be available in the
near future. Therefore, 4G wireless communications system will be of paramount
importance on the development of the information society in the near future.
As 4G wireless services will continue to increase, this will put more and more
pressure on the spectrum availability. There is a worldwide recognition that
methods of spectrum managements have reached their limit and are no longer
optimal, therefore new paradigms must be sought. Studies show that most of the
assigned spectrum is under-utilized, thus the problem in most cases is inefficient
spectrum management rather spectrum shortage. There are currently trends
towards a more liberalized approach of spectrum management, which are tightly
linked to what is commonly termed as Cognitive Radio (CR).
Furthermore, conventional deployment of 4G wireless systems (one BS in cell and
mobile deploy around it) are known to have problems in providing fairness (users
closer to the BS are more benefited relatively to the cell edge users) and in
covering some zones affected by shadowing, therefore the use of relays has been
proposed as a solution.
To evaluate and analyse the performances of 4G wireless systems software tools
are normally used. Software tools have become more and more mature in recent
years and their need to provide a high level evaluation of proposed algorithms and
protocols is now more important. The system level simulation (SLS) tools provide
a fundamental and flexible way to test all the envisioned algorithms and protocols
under realistic conditions, without the need to deal with the problems of live
networks or reduced scope prototypes. Furthermore, the tools allow network
designers a rapid collection of a wide range of performance metrics that are useful
for the analysis and optimization of different algorithms.
This dissertation proposes the design and implementation of conventional system
level simulator (SLS), which afterwards enhances for the 4G wireless technologies
namely cognitive Radios (IEEE802.22) and Relays (IEEE802.16j). SLS is then
used for the analysis of proposed algorithms and protocols.FC
Traffic Scheduling in Point-to-Multipoint OFDMA-based Systems
The new generation of wireless networks (e.g., WiMAX, LTE-Advanced, Cognitive Radio) support many high resource-consuming services (e.g., VoIP, video conference, multiplayer interactive gaming, multimedia streaming, digital video broadcasting, mobile commerce). The main problem of such networks is that the bandwidth is limited, besides to be subject to fading process, and shared among multiple users. Therefore, a combination of sophisticated transmission techniques (e.g., OFDMA) and proper packet scheduling algorithms is necessary, in order to provide applications with suitable quality of service.
This Thesis addresses the problem of traffic scheduling in Point-to-Multipoint OFDMA-based systems. We formally prove that in such systems, even a simple scheduling problem of a Service Class at a time, is NP-complete, therefore, computationally intractable. An optimal solution is unfeasible in term of time, thus, fast and simple scheduling heuristics are needed. First, we address the Best Effort traffic scheduling issue, in a system adopting variable-length Frames, with the objective of producing a legal schedule (i.e., the one meeting all system constraints) of minimum length. Besides, we present fast and simple heuristics, which generate suboptimal solutions, and evaluate their performance in the average case, as in the worst one. Then, we investigate the scheduling of Real Time traffic, with the objective of meeting as many deadlines as possible, or equivalently, minimizing the packet drop ratio. Specifically, we propose two scheduling heuristics, which apply two different resource allocation mechanisms, and evaluate their average-case performance by means of a simulation experiment
Cognitive Radio Systems
Cognitive radio is a hot research area for future wireless communications in the recent years. In order to increase the spectrum utilization, cognitive radio makes it possible for unlicensed users to access the spectrum unoccupied by licensed users. Cognitive radio let the equipments more intelligent to communicate with each other in a spectrum-aware manner and provide a new approach for the co-existence of multiple wireless systems. The goal of this book is to provide highlights of the current research topics in the field of cognitive radio systems. The book consists of 17 chapters, addressing various problems in cognitive radio systems
Detection of OFDM Signals Using Pilot Tones and Applications to Spectrum Sensing for Cognitive Radio Systems
Nowadays there are an increasing number of wireless devices which support wireless networking and the need for higher data rate communication is increasing rabidly. As more and more systems go wireless, approaching technologies will face spectral crowding and existence of wireless devices will be an important issue. Because of the limited bandwidth availability, accepting the request for higher capacity and data rates is a challenging task, demanding advanced technologies that can offers new methods of using the available radio spectrum. Cognitive radio introduces a key solution to the spectral increasing issue by presenting the opportunistic usage of spectrum that is not heavily occupied by licensed users. It is a latest idea in wireless communications systems which objective to have more adaptive and aware communication devices which can make better use of available natural resources.
Cognitive radio appears to be an attractive solution to the spectral congestion problem by introducing the notion of opportunistic spectrum use. Cognitive radios can operate as a secondary systems on top of existence system which are called primary (or licensed) systems. In this case, secondary (cognitive) users need to detect the unused spectrum in order to be able to access it. Because of its many advantages, orthogonal frequency division multiplexing (OFDM) has been successfully used in numerous wireless standards and technologies.
It\u27s shown that OFDM will play an important role in realizing the cognitive radio concept as well by providing a proven, scalable, and adaptive technology for air interface. Researches show that OFDM technique is considered as a candidate for cognitive radio systems.
The objective of this dissertation is to explore detecting of OFDM modulated signals using pilot tones information. Specifically we applying Time-Domain Symbol Cross-Correlation (TDSC) method in the confect of actual 4G wireless standards such as WIMAX and LTE. This detection is only based upon the knowledge of pilot structures without knowledge of received signal so that, it can be performed on every portion of the received signal. The approach induces Cross-Correlation between pilots subcarriers and exploits the deterministic and periodic characteristics of pilot mapping in the time frequency domain
Resource Management in Multicarrier Based Cognitive Radio Systems
The ever-increasing growth of the wireless application and services affirms the importance of the effective usage of the limited radio spectrum. Existing spectrum management policies have led to significant spectrum under-utilization. Recent measurements showed that large range of the spectrum is sparsely used in both temporal and spatial manner. This conflict
between the inefficient usage of the spectrum and the continuous evolution in the wireless communication calls upon the development of more flexible management policies. Cognitive radio (CR) with the dynamic spectrum access (DSA) is considered to be a key technology in making the best solution of this conflict by allowing a group of secondary users (SUs) to share the radio spectrum originally allocated to the primary user (PUs). The operation of CR should not negatively alter the performance of the PUs. Therefore, the interference control along with the highly dynamic nature of PUs activities open up new resource allocation problems in CR systems. The resource allocation algorithms should ensure an effective share of the temporarily available frequency bands and deliver the solutions in timely fashion to cope with quick changes in the network.
In this dissertation, the resource management problem in multicarrier based CR systems is considered. The dissertation focuses on three main issues: 1) design of efficient resource allocation algorithms to allocate subcarriers and powers between SUs such that no harmful interference is introduced to PUs, 2) compare the spectral efficiency of using different multicarrier schemes in the CR physical layer, specifically, orthogonal frequency division multiplexing (OFDM) and filter bank multicarrier (FBMC) schemes, 3) investigate the impact of the different constraints values on the overall performance of the CR system.
Three different scenarios are considered in this dissertation, namely downlink transmission, uplink transmission, and relayed transmission. For every scenario, the optimal solution is examined and efficient sub-optimal algorithms are proposed to reduce the computational burden of obtaining the optimal solution. The suboptimal algorithms are developed by separate the subcarrier and power allocation into two steps in downlink and uplink scenarios. In the relayed scenario, dual decomposition technique is used to obtain an asymptotically optimal solution, and a joint heuristic algorithm is proposed to find the suboptimal solution. Numerical simulations show that the proposed suboptimal algorithms achieve a near optimal performance and perform better than the existing algorithms designed for cognitive and non-cognitive systems. Eventually, the ability of FBMC to overcome the OFDM drawbacks and achieve more spectral efficiency is verified which recommends the consideration of FBMC in the future CR systems.El crecimiento continuo de las aplicaciones y servicios en sistemas inal´ambricos, indica la
importancia y necesidad de una utilizaci´on eficaz del espectro radio. Las pol´ıticas actuales de
gesti´on del espectro han conducido a una infrautilizaci´on del propio espectro radioel´ectrico.
Recientes mediciones en diferentes entornos han mostrado que gran parte del espectro queda
poco utilizado en sus ambas vertientes, la temporal, y la espacial. El permanente conflicto
entre el uso ineficiente del espectro y la evoluci´on continua de los sistemas de comunicaci´on
inal´ambrica, hace que sea urgente y necesario el desarrollo de esquemas de gesti´on del espectro
m´as flexibles.
Se considera el acceso din´amico (DSA) al espectro en los sistemas cognitivos como una
tecnolog´ıa clave para resolver este conflicto al permitir que un grupo de usuarios secundarios
(SUs) puedan compartir y acceder al espectro asignado inicialmente a uno o varios usuarios
primarios (PUs). Las operaciones de comunicaci´on llevadas a cabo por los sistemas radio
cognitivos no deben en ning´un caso alterar (interferir) los sistemas primarios. Por tanto, el
control de la interferencia junto al gran dinamismo de los sistemas primarios implica nuevos
retos en el control y asignaci´on de los recursos radio en los sistemas de comunicaci´on CR. Los
algoritmos de gesti´on y asignaci´on de recursos (Radio Resource Management-RRM) deben
garantizar una participaci´on efectiva de las bandas con frecuencias disponibles temporalmente,
y ofrecer en cada momento oportunas soluciones para hacer frente a los distintos cambios
r´apidos que influyen en la misma red.
En esta tesis doctoral, se analiza el problema de la gesti´on de los recursos radio en sistemas
multiportadoras CR, proponiendo varias soluciones para su uso eficaz y coexistencia con los
PUs. La tesis en s´ı, se centra en tres l´ıneas principales: 1) el dise˜no de algoritmos eficientes de gesti´on de recursos para la asignaci´on de sub-portadoras y distribuci´on de la potencia en
sistemas segundarios, evitando asi cualquier interferencia que pueda ser perjudicial para el
funcionamiento normal de los usuarios de la red primaria, 2) analizar y comparar la eficiencia
espectral alcanzada a la hora de utilizar diferentes esquema de transmisi´on multiportadora en
la capa f´ısica del sistema CR, espec´ıficamente en sistemas basados en OFDM y los basados en
banco de filtros multiportadoras (Filter bank Multicarrier-FBMC), 3) investigar el impacto de
las diferentes limitaciones en el rendimiento total del sistema de CR.
Los escenarios considerados en esta tesis son tres, es decir; modo de transmisi´on
descendente (downlink), modo de transmisi´on ascendente (uplink), y el modo de transmisi´on
”Relay”. En cada escenario, la soluci´on ´optima es examinada y comparada con algoritmos sub-
´optimos que tienen como objetivo principal reducir la carga computacional. Los algoritmos
sub-´optimos son llevados a cabo en dos fases mediante la separaci´on del propio proceso de
distribuci´on de subportadoras y la asignaci´on de la potencia en los modos de comunicaci´on
descendente (downlink), y ascendente (uplink). Para los entornos de tipo ”Relay”, se ha
utilizado la t´ecnica de doble descomposici´on (dual decomposition) para obtener una soluci´on
asint´oticamente ´optima. Adem´as, se ha desarrollado un algoritmo heur´ıstico para poder obtener
la soluci´on ´optima con un reducido coste computacional.
Los resultados obtenidos mediante simulaciones num´ericas muestran que los algoritmos
sub-´optimos desarrollados logran acercarse a la soluci´on ´optima en cada uno de los entornos
analizados, logrando as´ı un mayor rendimiento que los ya existentes y utilizados tanto en
entornos cognitivos como no-cognitivos. Se puede comprobar en varios resultados obtenidos
en la tesis la superioridad del esquema multiportadora FBMC sobre los sistemas basados en
OFDM para los entornos cognitivos, causando una menor interferencia que el OFDM en
los sistemas primarios, y logrando una mayor eficiencia espectral. Finalmente, en base a lo
analizado en esta tesis, podemos recomendar al esquema multiportadora FBMC como una
id´onea y potente forma de comunicaci´on para las futuras redes cognitivas
Spectrum Policy and Management
This project provides an examination of the FCC’s policies towards spectrum reallocation. The project examines the National Broadband Plan and how the FCC has approached the goals described within it. The demand for broadband communications has increased dramatically in recent years and has resulted in a predicted spectrum deficit in the near future. In addition to a number of spectrum auctions and their winners the project examines how the redistribution of spectrum impacts the broadband community. The project also provides an examination of spectrum reallocation and policy in other countries, to provide a broader view of spectrum policy. Finally the project examines new spectrum technologies and spectrum usage policies to further examine how the US’s spectrum policies should evolve
OFDMA-based resource allocation for wireless communication systems
Ph.DDOCTOR OF PHILOSOPH
Recommended from our members
Cognitive radio systems in LTE networks
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London.The most important fact in the mobile industry at the moment is that demand for wireless services will continue to expand in the coming years. Therefore, it is vital to find more spectrums through cognitive radios for the growing numbers of services and users. However, the spectrum reallocations, enhanced receivers, shared use, or secondary markets-will not likely, by themselves or in combination, meet the real exponential increases in demand for wireless resources. Network operators will also need to re-examine network architecture, and consider integrating the fibre and wireless networks to address this issue. This thesis involves driving fibre deeper into cognitive networks, deploying microcells connected through fibre infrastructure to the backbone LTE networks, and developing the algorithms for diverting calls between the wireless and fibre systems, introducing new coexistence models, and mobility management. This research addresses the network deployment scenarios to a microcell-aided cognitive network, specifically slicing the spectrum spatially and providing reliable coverage at either tier. The goal of this research is to propose new method of decentralized-to-distributed management techniques that overcomes the spectrum unavailability barrier overhead in ongoing and future deployments of multi-tiered cognitive network architectures. Such adjustments will propose new opportunities in cognitive radio-to-fibre systematic investment strategies. Specific contributions include:
1) Identifying the radio access technologies and radio over fibre solution for cognitive network infrastructure to increase the uplink capacity analysis in two-tier networks.
2) Coexistence of macro and microcells are studied to propose a roadmap for optimising the deployment of cognitive microcells inside LTE macrocells in the case of considering radio over fibre access systems.
3) New method for roaming mobiles moving between microcells and macrocell coverage areas is proposed for managing spectrum handover, operator database, authentication and accounting by introducing the channel assigning agent entity. The ultimate goal is to reduce unnecessary channel adaptation
- …