COGNITIVE RADIO SOLUTION FOR IEEE 802.22

Current wireless systems suffer severe radio spectrum underutilization due to a number of problematic issues, including wasteful static spectrum allocations; fixed radio functionalities and architectures; and limited cooperation between network nodes. A significant number of research efforts aim to find alternative solutions to improve spectrum utilization. Cognitive radio based on software radio technology is one such novel approach, and the impending IEEE 802.22 air interface standard is the first based on such an approach. This standard aims to provide wireless services in wireless regional area network using TV spectrum white spaces. The cognitive radio devices employed feature two fundamental capabilities, namely supporting multiple modulations and data-rates based on wireless channel conditions and sensing a wireless spectrum. Spectrum sensing is a critical functionality with high computational complexity. Although the standard does not specify a spectrum sensing method, the sensing operation has inherent timing and accuracy constraints.This work proposes a framework for developing a cognitive radio system based on a small form factor software radio platform with limited memory resources and processing capabilities. The cognitive radio systems feature adaptive behavior based on wireless channel conditions and are compliant with the IEEE 802.22 sensing constraints. The resource limitations on implementation platforms post a variety of challenges to transceiver configurability and spectrum sensing. Overcoming these fundamental features on small form factors paves the way for portable cognitive radio devices and extends the range of cognitive radio applications.Several techniques are proposed to overcome resource limitation on a small form factor software radio platform based on a hybrid processing architecture comprised of a digital signal processor and a field programmable gate array. Hardware reuse and task partitioning over a number of processing devices are among the techniques used to realize a configurable radio transceiver that supports several communication modes, including modulations and data rates. In particular, these techniques are applied to build configurable modulation architecture and a configurable synchronization. A mode-switching architecture based on circular buffers is proposed to facilitate a reliable transitioning between different communication modes.The feasibility of efficient spectrum sensing based on a compressive sampling technique called "Fast Fourier Sampling" is examined. The configuration parameters are analyzed mathematically, and performance is evaluated using computer simulations for local spectrum sensing applications. The work proposed herein features a cooperative Fast Fourier sampling scheme to extend the narrowband and wideband sensing performance of this compressive sensing technique.The précis of this dissertation establishes the foundation of efficient cognitive radio implementation on small form factor software radio of hybrid processing architecture

Spectrum sensing algorithms and software-defined radio implementation for cognitive radio system

The scarcity of spectral resources in wireless communications, due to a fixed frequency allocation policy, is a strong limitation to the increasing demand for higher data rates. However, measurements showed that a large part of frequency channels are underutilized or almost unoccupied. The cognitive radio paradigm arises as a tempting solution to the spectral congestion problem. A cognitive radio must be able to identify transmission opportunities in unused channels and to avoid generating harmful interference with the licensed primary users. Its key enabling technology is the spectrum sensing unit, whose ultimate goal consists in providing an indication whether a primary transmission is taking place in the observed channel. Such indication is determined as the result of a binary hypothesis testing experiment wherein null hypothesis (alternate hypothesis) corresponds to the absence (presence) of the primary signal. The first parts of this thesis describes the spectrum sensing problem and presents some of the best performing detection techniques. Energy Detection and multi-antenna Eigenvalue-Based Detection algorithms are considered. Important aspects are taken into account, like the impact of noise estimation or the effect of primary user traffic. The performance of each detector is assessed in terms of false alarm probability and detection probability. In most experimental research, cognitive radio techniques are deployed in software-defined radio systems, radio transceivers that allow operating parameters (like modulation type, bandwidth, output power, etc.) to be set or altered by software.In the second part of the thesis, we introduce the software-defined radio concept. Then, we focus on the implementation of Energy Detection and Eigenvalue-Based Detection algorithms: first, the used software platform, GNU Radio, is described, secondly, the implementation of a parallel energy detector and a multi-antenna eigenbased detector is illustrated and details on the used methodologies are given. Finally, we present the deployed experimental cognitive testbeds and the used radio peripherals. The obtained algorithmic results along with the software-defined radio implementation may offer a set of tools able to create a realistic cognitive radio system with real-time spectrum sensing capabilities

MAC/PHY Co-Design of CSMA Wireless Networks Using Software Radios.

In the past decade, CSMA-based protocols have spawned numerous network standards (e.g., the WiFi family), and played a key role in improving the ubiquity of wireless networks. However, the rapid evolution of CSMA brings unprecedented challenges, especially the coexistence of different network architectures and communications devices. Meanwhile, many intrinsic limitations of CSMA have been the main obstacle to the performance of its derivatives, such as ZigBee, WiFi, and mesh networks. Most of these problems are observed to root in the abstract interface of the CSMA MAC and PHY layers --- the MAC simply abstracts the advancement of PHY technologies as a change of data rate. Hence, the benefits of new PHY technologies are either not fully exploited, or they even may harm the performance of existing network protocols due to poor interoperability. In this dissertation, we show that a joint design of the MAC/PHY layers can achieve a substantially higher level of capacity, interoperability and energy efficiency than the weakly coupled MAC/PHY design in the current CSMA wireless networks. In the proposed MAC/PHY co-design, the PHY layer exposes more states and capabilities to the MAC, and the MAC performs intelligent adaptation to and control over the PHY layer. We leverage the reconfigurability of software radios to design smart signal processing algorithms that meet the challenge of making PHY capabilities usable by the MAC layer. With the approach of MAC/PHY co-design, we have revisited the primitive operations of CSMA (collision avoidance, carrier signaling, carrier sensing, spectrum access and transmitter cooperation), and overcome its limitations in relay and broadcast applications, coexistence of heterogeneous networks, energy efficiency, coexistence of different spectrum widths, and scalability for MIMO networks. We have validated the feasibility and performance of our design using extensive analysis, simulation and testbed implementation.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/95944/1/xyzhang_1.pd

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

Spectrum Optimisation in Wireless Communication Systems: Technology Evaluation, System Design and Practical Implementation

Two key technology enablers for next generation networks are examined in this thesis, namely Cognitive Radio (CR) and Spectrally Efficient Frequency Division Multiplexing (SEFDM). The first part proposes the use of traffic prediction in CR systems to improve the Quality of Service (QoS) for CR users. A framework is presented which allows CR users to capture a frequency slot in an idle licensed channel occupied by primary users. This is achieved by using CR to sense and select target spectrum bands combined with traffic prediction to determine the optimum channel-sensing order. The latter part of this thesis considers the design, practical implementation and performance evaluation of SEFDM. The key challenge that arises in SEFDM is the self-created interference which complicates the design of receiver architectures. Previous work has focused on the development of sophisticated detection algorithms, however, these suffer from an impractical computational complexity. Consequently, the aim of this work is two-fold; first, to reduce the complexity of existing algorithms to make them better-suited for application in the real world; second, to develop hardware prototypes to assess the feasibility of employing SEFDM in practical systems. The impact of oversampling and fixed-point effects on the performance of SEFDM is initially determined, followed by the design and implementation of linear detection techniques using Field Programmable Gate Arrays (FPGAs). The performance of these FPGA based linear receivers is evaluated in terms of throughput, resource utilisation and Bit Error Rate (BER). Finally, variants of the Sphere Decoding (SD) algorithm are investigated to ameliorate the error performance of SEFDM systems with targeted reduction in complexity. The Fixed SD (FSD) algorithm is implemented on a Digital Signal Processor (DSP) to measure its computational complexity. Modified sorting and decomposition strategies are then applied to this FSD algorithm offering trade-offs between execution speed and BER

Subsampling receivers with applications to software defined radio systems

Este trabajo de tesis propone la utilización sistemas basados en submuestreo como una alternativa para la implementación de la etapa de down-conversion de los receptores de radio frecuencia (RF) empleados para aplicaciones multi-estándar y SDR (Software Defined Radio). El objetivo principal será el de optimizar el diseño en cuanto a flexibilidad y simplicidad, las cuales son propiedades inherentes en los sistemas basados en submuestreo. Por tanto, como reducir el número de componentes al mínimo es clave cuando un mismo receptor procesa diferentes estándares de comunicación, las arquitecturas basadas en submuestreo han sido seleccionadas, donde la reusabilidad de los componentes empleados es posible, así como la reducción de los costes totales de los receptores de comunicación y de los equipos de certificación que emplean estas arquitecturas. Un motivo adicional por el que los sistemas basados en submuestreo han sido seleccionados es el concerniente a la topología del receptor. Como la idea de la tecnología SDR es implementar todas las funcionalidades del receptor (filtrado, amplificación) en el dominio digital, el convertidores analógico-digital (ADC) deberá estar localizado en la cadena de recepción lo más cerca posible a la antena, siendo el objetivo final el convertir la señal directamente de RF a digital. Sin embargo, con los actuales ADC no es posible implementar esta idea debido al alto ancho de banda que necesitarían sin perder resolución para cubrir las especificaciones de los estándares de comunicaciones inalámbricas. Por tanto, los sistemas basados en submuestreo se presentan como la opción más adecuada para implementar este tipo de sistemas debido a que pueden muestrear la señal de entrada por debajo de la tasa de Nyquist, si se cumplen ciertas restricciones en cuanto a la elección de la frecuencia de muestreo. De este modo, los requerimientos del ADC serán relajados ya que, usando estas arquitecturas, este componente procesará la señal a frecuencias intermedias. Una vez se han introducido los conceptos principales de las técnicas de submuestreo, esta tesis doctoral presenta el diseño de una tarjeta de adquisición de datos basada en submuestreo con la finalidad de ser implementada como un receptor de test y certificación de banda ancha. El sistema propuesto proporciona una alta resolución para un elevado ancho de banda, a partir del uso de un S&H de bajo jitter y de un convertidor analógico digital ADC que trabaja a frecuencias intermedias. El sistema es implementado usando dispositivos comerciales en una placa de circuito impreso diseñada y fabricada, y cuya caracterización experimental muestra una resolución de más 8 bits para un ancho de banda analógico de 20 MHz. Concretamente, la resolución medida será mayor de 9 bits hasta una frecuencia de entrada de 2.9 GHz y mayor de 8 bits para una frecuencia de entrada de hasta 6.5 GHz, lo cual resulta suficiente para cubrir los requerimientos de la mayor parte de los actuales estándares de comunicaciones inalámbricas (GPS, GSM, GPRS, UMTS, Bluetooth, Wi-Fi, WiMAX). Sin embargo, los receptores basados en submuestreo presentan algunos importantes inconvenientes, como son adicionales fuentes de ruido (jitter y plegado de ruido térmico) y una dificultad añadida para implementarlo en escenarios multi-banda y no lineales. Acerca del plegado de ruido en la banda de interés, esta tesis propone el uso de una técnica basada en una arquitectura de reloj múltiple con el objetivo de aumentar la resolución y cubrir un número mayor de estándares para su test y certificación. Empleando una frecuencia de muestreo mayor para el caso del S&H, se conseguirá reducir este efecto, aumentando la resolución en aproximadamente 0.5-1 bit respecto al caso de sólo usar una fuente de reloj. Las expresiones teóricas de esta mejora son desarrolladas y presentadas en esta tesis, siendo posteriormente corroboradas de modo experimental. Por otra parte, esta tesis también propone novedosas técnicas para la aplicación de estos sistemas de submuestreo en entornos multi-banda y no lineales, los cuales presentan desafíos adicionales por el hecho de existir la posibilidad de solapamiento entre la señal de interés y los otros canales de comunicación, así como de solapamiento con sus armónicos. De este modo, esta tesis extiende el uso de los sistemas basados en submuestreo para este tipo de entornos, proponiendo técnicas para la elección de la frecuencia óptima de muestreo que evitan el solapamiento entre señales, a la vez que consiguen incrementar la resolución del receptor. Finalmente, se presentará la optimización en cuanto a características de ruido de un receptor concreto para aplicaciones de banda dual en entornos no lineales. Dicho receptor estará basado en las técnicas de reloj múltiple presentadas anteriormente y en una estructura de multi-filtro entre el S&H y el ADC. El sistema diseñado podrá emplearse para diversas aplicaciones a ambos lados de la cadena de comunicación, tal como en receptores de detección de espectro para radio cognitiva, o implementando el bucle de realimentación de un transmisor para la linealización de amplificadores de potencia. Por tanto, la presente tesis doctoral cuenta con tres contribuciones diferenciadas. La primera de ellas es la dedicada al diseño de un prototipo de recepción multi-estándar basado en submuestreo para aplicaciones de test y certificación. La segunda aportación es la dedicada a la optimización de las especificaciones de ruido a partir de las técnicas presentadas basadas en reloj múltiple. Por último, la tercera contribución principal es la relacionada con la extensión de este tipo de técnicas a sistemas multi-banda en entornos no lineales. Todas estas contribuciones han sido estudiadas teóricamente y experimentalmente validadas

SPECTRUM SENSING AND COOPERATION IN COGNITIVE-OFDM BASED WIRELESS COMMUNICATIONS NETWORKS

The world has witnessed the development of many wireless systems and applications. In addition to the large number of existing devices, such development of new and advanced wireless systems increases rapidly the demand for more radio spectrum. The radio spectrum is a limited natural resource; however, it has been observed that it is not efficiently utilized. Consequently, different dynamic spectrum access techniques have been proposed as solutions for such an inefficient use of the spectrum. Cognitive Radio (CR) is a promising intelligent technology that can identify the unoccupied portions of spectrum and opportunistically uses those portions with satisfyingly high capacity and low interference to the primary users (i.e., licensed users). The CR can be distinguished from the classical radio systems mainly by its awareness about its surrounding radio frequency environment. The spectrum sensing task is the main key for such awareness. Due to many advantages, Orthogonal Frequency Division Multiplexing system (OFDM) has been proposed as a potential candidate for the CR‟s physical layer. Additionally, the Fast Fourier Transform (FFT) in an OFDM receiver supports the performance of a wide band spectrum analysis. Multitaper spectrum estimation method (MTM) is a non-coherent promising spectrum sensing technique. It tolerates problems related to bad biasing and large variance of power estimates. This thesis focuses, generally, on the local, multi antenna based, and global cooperative spectrum sensing techniques at physical layer in OFDM-based CR systems. It starts with an investigation on the performance of using MTM and MTM with singular value decomposition in CR networks using simulation. The Optimal MTM parameters are then found. The optimal MTM based detector theoretical formulae are derived. Different optimal and suboptimal multi antenna based spectrum sensing techniques are proposed to improve the local spectrum sensing performance. Finally, a new concept of cooperative spectrum sensing is introduced, and new strategies are proposed to optimize the hard cooperative spectrum sensing in CR networks. The MTM performance is controlled by the half time bandwidth product and number of tapers. In this thesis, such parameters have been optimized using Monte Carlo simulation. The binary hypothesis test, here, is developed to ensure that the effect of choosing optimum MTM parameters is based upon performance evaluation. The results show how these optimal parameters give the highest performance with minimum complexity when MTM is used locally at CR. The optimal MTM based detector has been derived using Neyman-Pearson criterion. That includes probabilities of detection, false alarm and misses detection approximate derivations in different wireless environments. The threshold and number of sensed samples controlling is based on this theoretical work. In order to improve the local spectrum sensing performance at each CR, in the CR network, multi antenna spectrum sensing techniques are proposed using MTM and MTM with singular value decomposition in this thesis. The statistical theoretical formulae of the proposed techniques are derived including the different probabilities. ii The proposed techniques include optimal, that requires prior information about the primary user signal, and two suboptimal multi antenna spectrum sensing techniques having similar performances with different computation complexity; these do not need prior information about the primary user signalling. The work here includes derivations for the periodogram multi antenna case. Finally, in hard cooperative spectrum sensing, the cooperation optimization is necessary to improve the overall performance, and/or minimize the number of data to be sent to the main CR-base station. In this thesis, a new optimization method based on optimizing the number of locally sensed samples at each CR is proposed with two different strategies. Furthermore, the different factors that affect the hard cooperative spectrum sensing optimization are investigated and analysed and a new cooperation scheme in spectrum sensing, the master node, is proposed.Ministry of Interior-Kingdom of Saudi Arabi