437 research outputs found
An Innovative Signal Detection Algorithm in Facilitating the Cognitive Radio Functionality for Wireless Regional Area Network Using Singular Value Decomposition
This thesis introduces an innovative signal detector algorithm in facilitating the
cognitive radio functionality for the new IEEE 802.22 Wireless Regional Area
Networks (WRAN) standard. It is a signal detector based on a Singular Value
Decomposition (SVD) technique that utilizes the eigenvalue of a received signal. The
research started with a review of the current spectrum sensing methods which the
research classifies as the specific, semiblind or blind signal detector. A blind signal detector, which is known as eigenvalue based detection, was found to be the most
desired detector for its detection capabilities, time of execution, and zero a-priori knowledge. The detection algorithm was developed analytically by applying the Signal Detection Theory (SDT) and the Random Matrix Theory (RMT). It was then simulated
using Matlab® to test its performance and compared with similar eigenvalue based
signal detector. There are several techniques in finding eigenvalues. However, this
research considered two techniques known as eigenvalue decomposition (EVD) and
SVD. The research tested the algorithm with a randomly generated signal, simulated
Digital Video Broadcasting-Terrestrial (DVB-T) standard and real captured digital
television signals based on the Advanced Television Systems Committee (ATSC)
standard. The SVD based signal detector was found to be more efficient in detecting
signals without knowing the properties of the transmitted signal. The algorithm is
suitable for the blind spectrum sensing where the properties of the signal to be detected
are unknown. This is also the advantage of the algorithm since any signal would
interfere and subsequently affect the quality of service (QoS) of the IEEE 802.22
connection. Furthermore, the algorithm performed better in the low signal-to-noise
ratio (SNR) environment. In order to use the algorithm effectively, users need to
balance between detection accuracy and execution time. It was found that a higher
number of samples would lead to more accurate detection, but will take longer time.
In contrary, fewer numbers of samples used would result in less accuracy, but faster
execution time. The contributions of this thesis are expected to assist the IEEE
802.22 Standard Working Group, regulatory bodies, network operators and end-users
in bringing broadband access to the rural areas
Enhanced Spectrum Sensing for Cognitive Cellular Systems
This dissertation aims at improving spectrum sensing algorithms in order to effectively apply
them to cellular systems. In wireless communications, cellular systems occupy a significant
part of the spectrum. The spectrum usage for cellular systems are rapidly expanding due to the
increasing demand for wireless services in our society. This results in radio frequency spectrum
scarcity. Cellular systems can effectively handle this issue through cognitive mechanisms for
spectrum utilization. Spectrum sensing plays the first stage of cognitive cycles for the adaptation
to radio environments.
This dissertation focuses on maximizing the reliability of spectrum sensing to satisfy
regulation requirements with respect to high spectrum sensing performance and an acceptable
error rate. To overcome these challenges, characteristics of noise and manmade signals are
exploited for spectrum sensing. Moreover, this dissertation considers system constraints, the
compatibility with the current and the trends of future generations. Newly proposed and existing
algorithms were evaluated in simulations in the context of cellular systems. Based on a prototype
of cognitive cellular systems (CCSs), the proposed algorithms were assessed in realistic scenarios.
These algorithms can be applied to CCSs for the awareness of desired signals in licensed and
unlicensed bands.
For orthogonal frequency-division multiplexing (OFDM) signals, this dissertation exploits
the characteristics of pilot patterns and preambles for new algorithms. The new algorithms
outperform the existing ones, which also utilize pilot patterns. Additionally, the new algorithms
can work with short observation durations, which is not possible with the existing algorithms. The
Digital Video Broadcasting - Terrestrial (DVB-T) standard is taken as an example application for
the algorithms. The algorithms can also be developed for filter bank multicarrier (FBMC) signals,
which are a potential candidate for multiplexing techniques in the next cellular generations. The
experimental results give insights for the reliability of the algorithms, taking system constraints
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into account. Another new sensing algorithm, based on a preamble, is proposed for the DVBT2
standard, which is the second generation of of DVB system. DVB-T2 systems have been
deployed in worldwide regions. This algorithm can detect DVB-T2 signals in a very short
observation interval, which is helpful for the in-band sensing mode, to protect primary users (in
nearly real-time) from the secondary transmission.
An enhanced spectrum sensing algorithm based on cyclostationary signatures is proposed
to detect desired signals in very low signal-to-noise ratios (SNRs). This algorithm can be
developed to detect the single-carrier frequency division multiple access (SC-FDMA) signal,
which is adopted for the uplink of long-term evolution (LTE) systems. This detector substantially
outperforms the existing detection algorithms with the marginal complexity of some scalar
multiplications. The test statistics are explicitly formulated in mathematical formulas, which
were not presented in the previous work. The formulas and simulation results provide a useful
strategy for cyclostationarity-based detection with different modulation types.
For multiband spectrum sensing, an effective scheme is proposed not only to detect but
also to classify LTE signals in multiple channels in a wide frequency range. To the best of our
knowledge, no scheme had previously been described to perform the sensing tasks. The scheme is
reliable and flexible for implementation, and there is almost no performance degradation caused
by the scheme compared to single-channel spectrum sensing. The multiband sensing scheme was experimentally assessed in scenarios where the existing infrastructures are interrupted to
provide mobile communications.
The proposed algorithms and scheme facilitate cognitive capabilities to be applied to real
cellular communications. This enables the significantly improved spectrum utilization of CCSs
Cognitive-Based Solutions to Spectrum Issues in Future Satellite Communication Systems
With particular attention to Satellite Communications (SatComs), cognitive-based solutions are investigated. With cognitive-based solutions we refer to all those techniques that aim at improving spectrum utilization of the available spectrum and rely on the knowledge of the environment in which the systems operate. As a matter of fact, an improved spectrum utilization enables higher throughput capacities that will satisfy the future markets and demands of an increasingly connected world.
Throughout the thesis, several techniques are proposed, developed, and assessed with respect to specific scenarios of interest. Particular focus has been put on spectrum awareness techniques for system coexistence, and on spectrum exploitation techniques for an improved efficiency in terms of resource utilization
Energy-detection based spectrum sensing for cognitive radio on a real-time SDR platform
There has been an increase in wireless applications due to the technology boom; consequently raising the level of radio spectrum demand. However, spectrum is a limited resource and cannot be infinitely subdivided to accommodate every application. At the same time, emerging wireless applications require a lot of bandwidth for operation, and have seen exponential growth in their bandwidth usage in recent years. The current spectrum allocation technique, proposed by the Federal Communications Commission (FCC) is a fixed allocation technique. This is inefficient as the spectrum is vacant during times when the primary user is not using the spectrum. This strain on the current available bandwidth has revealed signs of an upcoming spectrum crunch; hence the need to find a solution that satisfies the increasing spectrum demand, without compromising the performance of the applications. This work leverages on cognitive radio technology as a potential solution to the spectrum usage challenge. Cognitive radios have the ability to sense the spectrum and determine the presence or absence of the primary user in a particular subcarrier band. When the spectrum is vacant, a cognitive radio (secondary user) can opportunistically occupy the radio spectrum, optimizing the radio frequency band. The effectiveness of the cognitive radio is determined by the performance of the sensing techniques. Known spectrum-sensing techniques are reviewed, which include energy detection, entropy detection, matched-filter detection, and cyclostationary detection. In this dissertation, the energy sensing technique is examined. A real-time energy detector is developed on the Software-Defined Radio (SDR) testbed that is built with Universal Software Radio Peripheral (USRP) devices, and on the GNU Radio software platform. The noise floor of the system is first analysed to determine the detection threshold, which is obtained using the empirical cumulative distribution method. Simulations are carried out using MATrix LABoratory (MATLAB) to set a benchmark. In both simulations and the SDR development platform, an Orthogonal Frequency Division Multiplexing (OFDM) signal with Quadrature Phase Shift Keying (QPSK) modulation is generated and used as the test signal
Spectrum Monitoring Algorithms for Wireless and Satellite Communications
Nowadays, there is an increasing demand for more efficient utilization of the radio frequency
spectrum as new terrestrial and space services are deployed resulting in the
congestion of the already crowded frequency bands. In this context, spectrum monitoring
is a necessity. Spectrum monitoring techniques can be applied in a cognitive radio
network, exploiting the spectrum holes and allowing the secondary users to have access
in an unlicensed frequency band for them, when it is not occupied by the primary user.
Furthermore, spectrum monitoring techniques can be used for interference detection in
wireless and satellite communications. These two topics are addressed in this thesis.
In the beginning, a detailed survey of the existing spectrum monitoring techniques according
to the way that cognitive radio users 1) can detect the presence or absence of
the primary user; and 2) can access the licensed spectrum is provided. Subsequently, an
overview of the problem of satellite interference and existing methods for its detection
are discussed, while the contributions of this thesis are presented as well.
Moreover, this thesis discusses some issues in a cognitive radio system such as the reduction
of the secondary user's throughput of the conventional \listen before talk" access
method in the spectrum. Then, the idea of simultaneous spectrum sensing and data
transmission through the collaboration of the secondary transmitter with receiver is
proposed to address these concerns. First, the secondary receiver decodes the signal
from the secondary transmitter, then, removes it from the total received signal and finally, applies spectrum sensing in the remaining signal in order to decide if the primary
user is active or idle. The effects of the imperfect signal cancellation due to decoding
errors, which are ignored in the existing literature, are considered in our analysis. The
analytical expressions for the probabilities of false alarm and detection are derived and
numerical results through simulations are also presented to validate the proposed study.
Furthermore, the threat of interference for the satellite communications services is studied
in this thesis. It proposes the detection of interference on-board the satellite by
introducing a spectrum monitoring unit within the satellite transponder. This development
will bring several benefits such as faster reaction time and simplification of the
ground stations in multi-beam satellite systems. Then, two algorithms for the detection
of interference are provided. The first detection scheme is based on energy detector with
signal cancellation exploiting the pilot symbols. The second detection scheme considers
a two-stage detector, where first, the energy detector with signal cancellation in the pilot
domain is performed, and if required, an energy detector with signal cancellation in the
data domain is carried out in the second stage. Moreover, the analytical expressions for the probabilities of false alarm and detection are derived and numerical results through
simulations are provided to verify the accuracy of the proposed analysis.
Finally, this thesis goes one step further and the developed algorithms are evaluated
experimentally using software defined radios, particularly universal software radio peripherals
(USRPs), while it concludes discussing some open research topics
New challenges in wireless and free space optical communications
AbstractThis manuscript presents a survey on new challenges in wireless communication systems and discusses recent approaches to address some recently raised problems by the wireless community. At first a historical background is briefly introduced. Challenges based on modern and real life applications are then described. Up to date research fields to solve limitations of existing systems and emerging new technologies are discussed. Theoretical and experimental results based on several research projects or studies are briefly provided. Essential, basic and many self references are cited. Future researcher axes are briefly introduced
High Performance Signal Processing-Based Collision Resolution for Random Access Schemes
Els darrers anys han experimentat un augment de la demanda de serveis interactius per satèl·lit per al gran consum, cobrint serveis fixes i mòbils, tal i com accés de banda ampla, comunicacions mà quina-mà quina (M2M), supervisió, control i adquisició de dades (SCADA), transaccions i aplicacions de seguretat crÃtiques. Aquestes xarxes de comunicacions es caracteritzen per tenir una gran població d’usuaris compartint l’amplada de banda amb unes condicions de trà fic molt dinà miques. Concretament, en el canal de retorn (de l’usuari a la xarxa) de xarxes d’accés de banda ampla, els usuaris residencials generen grans rà fegues de trà fic amb perÃodes d’inactivitat freqüents. Una situació similar succeeix en xarxes de comunicacions mòbils per satèl·lit, on una gran població de terminals generen transmissions infreqüents de senyalització, serveis basats en la localització or altres aplicacions de missatgeria.
Aquests serveis requereixen el desenvolupament de protocols d’accés múltiple eficients que puguin operar en les condicions descrites anteriorment. Els protocols d´accés aleatori són bons candidats per servir trà fic poc predictiu, amb transmissions infreqüents aixà com sensibles amb el retard. A més, els protocols d´accés aleatori suporten un gran nombre de terminals compartint el canal de comunicacions i requereixen poca complexitat en el terminals. El protocols d´accés aleatori han estat à mpliament estudiats i desplegats en xarxes terrestres, però les seves prestacions són pobres en el entorn satèl·lital, que està caracteritzat per retards de propagació molt grans. Avui en dia, el seu ús en les xarxes de comunicacions per satèl·lit està principalment limitat a la senyalització d’inici de sessió, transmissió de paquets de control i en alguns casos a la transmissió de petits volums de dades amb unes eficiència d’utilització del canal molt baixa.
Aquesta tesi proposa tres noves tècniques d’accés aleatori, bens adaptades per proveir els serveis esmentats anteriorment en un entorn satèl·lital, amb altes prestacions i una complexitat en el terminal d’usuari reduïda. Les noves tècniques d’accés aleatori són Contention Resolution Diversity Slotted Aloha (CRDSA), Asynchronous Contention Resolution Diversity Aloha (ACRDA) i Enhanced Spread Spectrum Aloha (E-SSA), adaptades per un tipus d’accés ranurat, asÃncron i d’espectre eixamplat respectivament. Les tres tècniques utilitzen una codificació de canal (FEC) robusta, capaç d’operar en front de interferències elevades, que són tÃpiques en l’accés aleatori, i d’un mecanisme de cancel·lació successiva d’interferència que s’implementa en el receptor sobre els paquets descodificats satisfactòriament. Els nous protocols obtenen un throughput normalitzat superior a 1 bit/s/Hz amb una tassa de pèrdua de paquets inferior a 10-3, el qual representa un factor de millora de 1000 respecte a protocols d’accés aleatori tradicionals com l’ALOHA ranurat. Les prestacions de les noves tècniques d’accés aleatori has estat analitzades per mitjà de simulacions, aixà com amb nou models analÃtics desenvolupats en aquesta tesi capaços de caracteritzar el trà fic, la distribució estadÃstica de la potència dels paquets, les prestacions de la codificació de canal (FEC) i el procés de cancel·lació d’interferència successiva.Los últimos años han experimentado un crecimiento de la demanda de servicios interactivos por satélite para el gran consumo, cubriendo servicios fijos i móviles, como el acceso de banda ancha, comunicaciones máquina a máquina (M2M), supervisión, control y adquisición de datos (SCADA), transacciones i aplicaciones criticas de seguridad. Estas redes de comunicaciones se caracterizan por tener una gran población de usuarios compartiendo el ancho de banda en unas condiciones de tráfico muy dinámicas. Concretamente, en el canal de retorno (del usuario a la red) de redes de acceso de banda ancha, los usuarios residenciales generan grandes ráfagas de tráfico con periodos frecuentes de inactividad. Una situación similar ocurre en las redes de comunicaciones móviles por satélite, donde una gran población de terminales generan transmisiones infrecuentes de señalización, servicios basados en la localización u otras aplicaciones me mensajerÃa.
Estos servicios requieren el desarrollo de protocolos de acceso múltiple eficientes capaces de operar en las condiciones descritas anteriormente. Los protocolos de acceso aleatorio son buenos candidatos para servir el tráfico poco predictivo, con transmisiones infrecuentes asà como sensibles al retardo. Además, los protocolos de acceso soportan un gran número de terminales compartiendo el canal de comunicaciones y requieren poca complejidad en los terminales. Los protocolos de acceso aleatorio han estado ampliamente estudiados i desplegados en las redes terrestres, pero sus prestaciones son pobres en el entorno satelital, que se caracteriza por retardos de comunicaciones muy elevados. Hoy en dÃa, su uso en la redes de comunicaciones por satélite está principalmente limitado a la señalización de inicio de sesión, transmisión de pequeños volumenes de datos con eficiencia de utilización del canal muy baja.
Esta tesis propone tres nuevas técnicas de acceso aleatorio bien adaptadas para proveer los servicios mencionados anteriormente en un entorno de comunicaciones por satélite, con altas prestaciones y una complejidad en el terminal de usuario reducida. Las nuevas técnicas de acceso aleatorio son Contention Resolution Diversity Slotted Aloha (CRDSA), Asynchronous Contention Resolution Diversity Aloha (ACRDA) y Enhanced Spread Spectrum Aloha (E-SSA), adaptadas para un tipo de acceso ranurado, asÃncrono y de espectro ensanchado respectivamente. Las tres técnicas utilizan una codificación de canal (FEC) robusta, capaz de operar en condiciones de interferencia elevadas, que son tÃpicas en el acceso aleatorio, y de un mecanismo de cancelación sucesiva de interferencias que se implementa en el receptor sobre los paquetes que han sido decodificados satisfactoriamente. Los nuevos protocolos obtienen un throughput normalizado superior a 1 bit/s/Hz con una tasa de pérdida de paquetes inferior a 10-3, lo cual representa un factor de mejora de 1000 respecto a los protocolos de acceso aleatorio tradicionales como el ALOHA ranurado. Las prestaciones de las nuevas técnicas de acceso aleatorio han sido analizadas con simulaciones asà como con nuevos modelos analÃticos desarrollados en esta tesis, capaces de caracterizar el tráfico, la distribución estadÃstica de la potencia de los paquetes, las prestaciones de la codificación de canal (FEC) y el proceso de cancelación sucesiva de interferencias.Over the past years there has been a fast growing demand for low-cost interactive satellite terminals supporting both fixed and mobile services, such as consumer broadband access, machine-to-machine communications (M2M), supervisory control and data acquisition (SCADA), transaction and safety of life applications. These networks, are generally characterized by a large population of terminals sharing the available resources under very dynamic traffic conditions. In particular, in the return link (user to network) of commercial satellite broadband access networks, residential users are likely to generate a large amount of low duty cycle bursty traffic with extended inactivity periods. A similar situation occurs in satellite mobile networks whereby a large number of terminals typically generate infrequent packets for signaling transmission as well for position reporting or other messaging applications.
These services call for the development of efficient multiple access protocols able to cope with the above operating conditions. Random Access (RA) techniques are by nature, good candidates for the less predictive, low duty cycle as well as time sensitive return link traffic. Besides, RA techniques are capable of supporting large population of terminals sharing the same capacity and require low terminal complexity. RA schemes have been widely studied and deployed in terrestrial networks, but do not perform well in the satellite environment, which is characterized by very long propagation delays. Today, their use in satellite networks is mainly limited to initial network login, the transmission of control packets, and in some cases, for the transmission of very small volumes of data with very low channel utilization.
This thesis proposes three novel RA schemes well suited for the provision of the above-mentioned services over a satellite environment with high performance and low terminal complexity. The new RA schemes are Contention Resolution Diversity Slotted Aloha (CRDSA), Asynchronous Contention Resolution Diversity Aloha (ACRDA) and Enhanced Spread Spectrum Aloha (E-SSA), suited for slotted, unslotted and spread spectrum-based systems respectively. They all use strong Forward Error Correction (FEC) codes, able to cope with heavy co-channel interference typically present in RA, and successive interference cancellation implemented over the successfully decoded packets. The new schemes achieve a normalized throughput above 1 bit/s/Hz for a packet loss ratio below 10-3, which represents a 1000-fold increase compared to Slotted ALOHA. The performance of the proposed RA schemes has been analyzed by means of detailed simulations as well as novel analytical frameworks that characterize traffic and packets power statistical distributions, the performance of the FEC coding as well as the iterative interference cancellation processing at the receiver
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A Cognitive TV White Space Access Framework
Given the current boom in applications and services for mobile devices, data traffic is rapidly expanding, with the consequence that increasing spectrum capacity is being mandated. Following the switchover from analogue to digital platforms, Television White Space (TVWS) affords a fertile opportunity to supplement existing licensed spectrum to ease this scarcity. There are however, a number of obstacles to wide-scale TVWS adoption, including the accurate detection of primary users (PU), the hidden node problem and bandwidth availability for unlicensed secondary users (SU). Regulatory and industry bodies have sought to address some of these issues using a static database for spectrum access decisions, though this involves manual maintenance and accuracy can be compromised due to a lack of real-time information. While the new IEEE802.11af wireless local area network (WLAN) standard attempts to resolve some SU access issues, there remain many challenges, such as the critical asymmetry between mobile and base station power resources.
This thesis presents a new cognitive TVWS access framework encompassing a real-time sensing paradigm for TVWS deployment that uses a spectrum-efficient scheme to uphold quality-of-service (QoS) for both PU and SU. A novel dynamic spectrum allocation (DSA) model has been formulated allied with a resilient interference management system which exploits the unique way digital terrestrial TV channels are allocated in different geographical areas. A margin strategy has been framed to support efficient TVWS channel reuse, with an exclusion zone established to overcome the hidden node problem, while an innovative routing algorithm using cross-layer information, both extends coverage capacity and maximises QoS provision by ensuring a more balanced resource allocation.
Critical evaluation of the new access framework confirms that significant QoS improvements for SU are achieved compared to existing TVWS techniques. It importantly embodies a generic, practical, resource-efficient solution for TVWS deployment, which is compliant with current PU regulatory requirements
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