Efficient implementation of filter bank multicarrier systems using circular fast convolution

In this paper, filter bank-based multicarrier systems using a fast convolution approach are investigated. We show that exploiting offset quadrature amplitude modulation enables us to perform FFT/IFFT-based convolution without overlapped processing, and the circular distortion can be discarded as a part of orthogonal interference terms. This property has two advantages. First, it leads to spectral efficiency enhancement in the system by removing the prototype filter transients. Second, the complexity of the system is significantly reduced as the result of using efficient FFT algorithms for convolution. The new scheme is compared with the conventional waveforms in terms of out-of-band radiation, orthogonality, spectral efficiency, and complexity. The performance of the receiver and the equalization methods are investigated and compared with other waveforms through simulations. Moreover, based on the time variant nature of the filter response of the proposed scheme, a pilot-based channel estimation technique with controlled transmit power is developed and analyzed through lower-bound derivations. The proposed transceiver is shown to be a competitive solution for future wireless networks

Filtered multi-carrier modulations for industrial wireless communications based on cognitive radio

Doktoretza-tesi honetako helburu nagusia, hari gabeko komunikazio industrialetarako fidagarritasun maila onargarria eman dezakeen maila fisikoko modulazio bat aurkitzea da. Eremu industrialetako radio bidezko kanaletan ematen diren komunikazioetarako baldintza bereziki aurkakoak direla eta, helburu hori lortzea benetako erronkatzat jo liteke. Gainera, modulazio horrek \Radio Cognitiva" deritzoten teknikekin bateragarria izan beharra dauka, hauek hari gabeko komunikazioen fidagarritasuna hobetzeko gaitasuna baitute. Bibliografian oinarrituz, gaur egungo baliabideekin hari gabeko komunikazio industrial kasu ugariri konponbidea emateko aukera badela ondoriozta genezake, baina ez kasu guztiei ordea. Hari gabeko kanalen egoera bereziki aurkakoa denerako eta komunikazio sistemek denbora muga bereziki zorrotzak bete behar dituztenerako, ezta erantzun nahikoa ona eman lezakeen hari gabeko komunikazio sistema industrialik bibliografia zientifikoan. Hori dela eta, doktoretza tesi honetan, \Radio Cognitiva" delakoa eta 5G-rako aurreikusita dauden filtro bankuetan oinarrituriko modulazio multigarraiatzaileak bezalako teknologia hasiberrietara jotzen dugu, aurrez aipaturiko arazoari konponbide berriak bilatu nahian. Bibliografian dauden filtro bankuetan oinarrituriko modulazio multi-garraiatzaileak aztertu eta ondoren beraien egokitasuna ebaluatzen dugu, kanal dispertsiboen aurkako sendotasuna eta \Radio Cognitiva" teknikekin izan lezaketen bateragarritasuna irizpide hartuz. Ebaluaketa horretan oinarrituz, doktoretza-tesi honetan \Radio Cognitiva" teknikekin bateragarria den WCP-COQAM proposatzen dugu modulazio industrial gisa. Modulazio teknika berau erakusteaz gain, bibliografian eskuragarri ez dauden WCP-COQAM-rentzat sinkronizazio eta kanal estimazio teknikak ere aurkezten ditugu.El objetivo principal de esta tesis doctoral consiste en encontrar una modulación de capa física capaz de proporcionar robustez y fiabilidad suficientes a sistemas de comunicaciones inalámbricas industriales. Esto supone un desafío, dadas las adversas condiciones del canal inalámbrico propias de entornos industriales. Además, dicha modulación debería presentar una alta compatibilidad con las técnicas de Radio Cognitiva, debido al potencial de éstas para mejorar la fiabilidad de las comunicaciones inalámbricas. Basándonos en la bibliografía, concluimos que las soluciones presentes en el estado del arte actual cubren una amplia variedad de escenarios dentro de las comunicaciones inalámbricas industriales, pero no todas. Para los escenarios con canales altamente dispersivos y requerimientos de tiempo especialmente estrictos, no existe ninguna solución en la industria ni dentro de la bibliografía científica. En esta tesis doctoral nos centramos en tecnologías incipientes como la Radio Cognitiva y las modulaciones multi-portadora con bancos de filtros para 5G para tratar de buscar nuevas soluciones al problema anteriormente descrito. Por lo tanto, analizamos algunas de las técnicas multi-portadora con bancos de filtros presentes en la bibliografía científica y las evaluamos basándonos en su robustez frente a canales altamente dispersivos y su compatibilidad con la Radio Cognitiva. Basándonos en dicha evaluación, proponemosWCP-COQAM como posible candidata a modulación industrial compatible con Radio Cognitiva. Además de la propia técnica de modulación, presentamos métodos de sincronización y estimación de canal para la misma que no se encuentran presentes en el estado del arte.The main goal of this doctoral thesis is to find a physical layer modulation able to provide high enough robustness and reliability levels for wireless industrial communications systems. Considering the harsh wireless channel conditions of industrial environments, that goal implies a considerable challenge. Besides, this modulation should be highly compatible with Cognitive Radio techniques, due to their potential to improve the reliability of wireless communications. Based on the bibliography, we conclude that the existent solutions in the current state of the art cover a wide range of wireless industrial communications scenarios, but not all of them. There is no solution, neither in the industry nor in the scientific bibliography, for those scenarios involving highly dispersive wireless channels and particularly stringent timeliness requirements. In this doctoral thesis, we focus on upcoming technologies such as Cognitive Radio and multi-carrier modulations based on filter banks for 5G, in order to search new solutions for the aforementioned problem. Therefore, we analyse some of the multi-carrier modulations based on filter banks of the scientific bibliography and we evaluate them in terms of robustness against highly dispersive channels and in terms of compatibility with Cognitive Radio. In this doctoral thesis we propose the modulation WCP-COQAM as possible candidate for industrial wireless modulation and compatible with Cognitive Radio. In addition to the modulation technique itself, we also introduce some synchronization and channel estimation techniques which are not present in the state of the art

Multiband Spectrum Access: Great Promises for Future Cognitive Radio Networks

Cognitive radio has been widely considered as one of the prominent solutions to tackle the spectrum scarcity. While the majority of existing research has focused on single-band cognitive radio, multiband cognitive radio represents great promises towards implementing efficient cognitive networks compared to single-based networks. Multiband cognitive radio networks (MB-CRNs) are expected to significantly enhance the network's throughput and provide better channel maintenance by reducing handoff frequency. Nevertheless, the wideband front-end and the multiband spectrum access impose a number of challenges yet to overcome. This paper provides an in-depth analysis on the recent advancements in multiband spectrum sensing techniques, their limitations, and possible future directions to improve them. We study cooperative communications for MB-CRNs to tackle a fundamental limit on diversity and sampling. We also investigate several limits and tradeoffs of various design parameters for MB-CRNs. In addition, we explore the key MB-CRNs performance metrics that differ from the conventional metrics used for single-band based networks.Comment: 22 pages, 13 figures; published in the Proceedings of the IEEE Journal, Special Issue on Future Radio Spectrum Access, March 201

Design of A Flexible Timing Synchronization Scheme For Cognitive Radio Applications

Advancements in wireless technology have increased different applications to demand higher data rate wireless access. Spectrum scarcity has come more into picture day by day. In this case, Cognitive Radios (CR)s are new emerged promising technology which are an alternative solution to use spectrum more efficiently. In concept, CR is defined as an intelligent wireless device which is always alerted about its environment by continuously sensing the spectrum as well as having the ability to dynamically adopt its radio parameters. Although, CRs can mitigate spectrum scarcity to some extent, a variety of challenges have emerged of which synchronization is one the most prominent. This thesis first presents some of common synchronization techniques used in conventional receivers and, based on them, presents a flexible timing synchronization scheme in which the CR receivers are able to adopt their radio parameters with new information regarding to the spectrum. The core content of the synchronizer is based on Finite Impulse Response (FIR) filter which performs as a multicorrelator on demand. To do so, different synchronization architectures have been applied to the design, including Multiplier-Less based correlator as well as Transposed, Sequential and Pipelined Direct Form FIR filters. Consequently, all the architectures are compared to each other in terms of power consumption, chip area, maximum frequency, etc. Compiled results show that the best strategy is to employ Multiplier-Less based multicorrelator as the fundamental functional unit of the synchronizer. The aforementioned synchronization block is implemented on an Altera family FPGA board series Stratix-V. All the components are written in VHDL language and simulated through ModelSim software. Quartus-II version 12.1 environment is used to compile simulated codes

SWIFT: A Narrowband-Friendly Cognitive Wideband Network

Wideband technologies in the unlicensed spectrum can satisfy the ever-increasing demands for wireless bandwidth created by emerging rich media applications. The key challenge for such systems, however, is to allow narrowband technologies that share these bands (say, 802.11 a/b/g/n, Zigbee) to achieve their normal performance, without compromising the throughput or range of the wideband network.This paper presents SWIFT, the first system where high-throughput wideband nodes are shown in a working deployment to coexist with unknown narrowband devices, while forming a network of their own. Prior work avoids narrowband devices by operating below the noise level and limiting itself to a single contiguous unused band. While this achieves coexistence, it sacrifices the throughput and operating distance of the wideband device. In contrast, SWIFT creates high throughput wireless links by weaving together non-contiguous unused frequency bands that change as narrowband devices enter or leave the environment. This design principle of cognitive aggregation allows SWIFT to achieve coexistence, while operating at normal power, and thereby obtaining higher throughput and greater operating range. We implement SWIFT on a wideband hardware platform, and evaluate it in the presence of 802.11 devices. In comparison to a baseline that coexists with narrowband devices by operating below their noise level, SWIFT is equally narrowband-friendly but achieves 3.6x-10.5x higher throughput and 6x greater range