Cyclic block filtered multitone modulation

n/

MIMO signal processing in offset-QAM based filter bank multicarrier systems

Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft

Rate improvements and power saving with a hybrid filtered multitone scheme

n/

Doctor of Philosophy

dissertationWireless communications pervade all avenues of modern life. The rapid expansion of wireless services has increased the need for transmission schemes that are more spectrally efficient. Dynamic spectrum access (DSA) systems attempt to address this need by building a network where the spectrum is used opportunistically by all users based on local and regional measurements of its availability. One of the principal requirements in DSA systems is to initialize and maintain a control channel to link the nodes together. This should be done even before a complete spectral usage map is available. Additionally, with more users accessing the spectrum, it is important to maintain a stable link in the presence of significant interference in emergency first-responders, rescue, and defense applications. In this thesis, a new multicarrier spread spectrum (MC-SS) technique based on filter banks is presented. The new technique is called filter bank multicarrier spread spectrum (FB-MC-SS). A detailed theory of the underlying properties of this signal are given, with emphasis on the properties that lend themselves to synchronization at the receiver. Proposed algorithms for synchronization, channel estimation, and detection are implemented on a software-defined radio platform to complete an FB-MC-SS transceiver and to prove the practicality of the technique. FB-MC-SS is shown through physical experimentation to be significantly more robust to partial band interference compared to direct sequence spread spectrum. With a higher power interfering signal occupying 90% of its band, FB-MC-SS maintains a low bit error rate. Under the same interference conditions, DS-SS fails completely. This experimentation leads to a theoretical analysis that shows in a frequency selective channel with additive white noise, the FB-MC-SS system has performance that equals that obtained by a DS-SS system employing an optimal rake receiver. This thesis contains a detailed chapter on implementation and design, including lessons learned while prototyping the system. This is to assist future system designers to quickly gain proficiency in further development of this technology

Comparison of different filter-bank based multicarrier systems with fractionally spaced equalisation

This paper compares two different filter bank multi carrier (FBMC) modulations: a critically sampled and therefore spectral maximally efficient FBMC orthogonal quadrature amplitude modulation (OQAM) approach, as well as an over sampled (OS)-FBMC system. Under a dispersive channel, FBMC/OQAM and OS-FBMC require equalisation and timing synchronisation, which here is accomplished by a fractionally spaced equaliser updated by a concurrent constant modulus and decision-directed algorithm. Simulation demonstrate that FBMC/OQAM is more difficult to equalise particularly at lower SNR, since its additional CCI terms amplify the equalisation algorithm’s gradient noise

MIMO designs for filter bank multicarrier and multiantenna systems based on OQAM

From the perspective of increasingly data rate requirements in mobile communications, it is deemed necessary to do further research so that the future goals can be reached. To that end, the radio-based communications are resorting to multicarrier modulations and spatial diversity. Until today, the orthogonal frequency division multiplexing (OFDM) modulation is regarded as the dominant technology. On one hand, the OFDM modulation is able to accommodate multiantenna configurations in a very straightforward manner. On the other hand, the poor stopband attenuation exhibited by the OFDM modulation, highlights that a definitely tight synchronization is required. In addition, the cyclic prefix (CP) has to be sufficiently long to avoid inter-block interference, which may substantially reduce the spectral efficiency. In order to overcome the OFDM drawbacks, the filter bank multicarrier modulation based on OQAM (FBMC/OQAM) is introduced. This modulation does not need any CP and benefits from pulse shaping techniques. This aspect becomes crucial in cognitive radio networks and communication systems where nodes are unlikely to be synchronized. In principle, the poor frequency confinement exhibited by OFDM should tip the balance towards FBMC/OQAM. However, the perfect reconstruction property of FBMC/OQAM systems does not hold in presence of multipath fading. This means that the FBMC/OQAM modulation is affected by inter-symbol and inter-carrier interference, unless the channel is equalized to some extent. This observation highlights that the FBMC/OQAM extension to MIMO architectures becomes a big challenge due to the need to cope with both modulation- and multiantenna-induced interference. The goal of this thesis is to study how the FBMC/OQAM modulation scheme can benefit from the degrees of freedom provided by the spatial dimension. In this regard, the first attempt to put the research on track is based on designing signal processing techniques at reception. In this case the emphasis is on single-input-multiple-output (SIMO) architectures. Next, the possibility of pre-equalizing the channel at transmission is investigated. It is considered that multiple antennas are placed at the transmit side giving rise to a multiple-input-single-output (MISO) configuration. In this scenario, the research is not only focused on counteracting the channel but also on distributing the power among subcarriers. Finally, the joint transmitter and receiver design in multiple-input-multiple-output (MIMO) communication systems is covered. From the theory developed in this thesis, it is possible to conclude that the techniques originally devised in the OFDM context can be easily adapted to FBMC/OQAM systems if the channel frequency response is flat within the subchannels. However, metrics such as the peak to average power ratio or the sensitivity to the carrier frequency offset constraint the number of subcarriers, so that the frequency selectivity may be appreciable at the subcarrier level. Then, the flat fading assumption is not satisfied and the specificities of FBMC/OQAM systems have to be considered. In this situation, the proposed techniques allow FBMC/OQAM to remain competitive with OFDM. In addition, for some multiantenna configurations and propagation conditions FBMC/OQAM turns out to be the best choice. The simulation-based results together with the theoretical analysis conducted in this thesis contribute to make progress towards the application of FBMC/OQAM to MIMO channels. The signal processing techniques that are described in this dissertation allow designers to exploit the potentials of FBMC/OQAM and MIMO to improve the link reliability as well as the spectral efficiency

Wavelet-based multi-carrier code division multiple access systems

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Broadband wireless communication systems for high mobility scenarios

Programa Oficial de Doutoramento en Tecnoloxías da Información e Comunicación en Redes Móbiles. 553V01[Resumen] A lo largo de los últimos años el uso de servicios multimedia y, en general, basados en el acceso a información “en la nube”, experimentó un auge sin precedentes. A diferencia respecto del pasado, los usuarios no solamente acceden a los servicios desde una ubicación estática; por contra, navegan libremente entre distintos lugares al tiempo que acceden, desde sus dispositivos móviles, a servicios en la nube. Debido al ritmo de vida actual, el tránsito entre zonas rurales y ciudades también se incrementó de modo notable, al ubicarse la mayor parte de los lugares de trabajo en ciudades o en sus respectivos entornos. Durante los períodos de transporte, cada vez más, los pasajeros emplean sus dispositivos móviles para trabajar, acceder a redes sociales o como dispositivos de entretenimiento. En la actualidad, GSM for Railways (GSM-R) es el sistema de comunicaciones más empleado entre los trenes y el resto de elementos involucrados en la infraestructura ferroviaria. Sin embargo, GSM-R no es adecuado para proporcionar servicios avanzados, tales como el control de piloto automático, así como para sustentar transmisiones de banda ancha a los operadores ferroviarios o proporcionar servicios de valor añadido a los pasajeros. Centrándonos en el mercado de dispositivos de comunicaciones de ámbito general, la explosión de usuarios y servicios multimedia de los últimos años motivó la migración, primero a las redes de tercera generación y, seguidamente, a las de cuarta, con Long Term Evolution (LTE) a la cabeza. Así, parece natural plantear a LTE como la tecnología candidata para la sustitución de GSM-R. En el presente trabajo se lleva a cabo un completo estudio de las prestaciones de sistemas de comunicaciones inalámbricas de banda ancha en vehículos de alta velocidad basado en campañas de medidas llevadas a cabo en entornos reales. Se estudió especialmente el caso de comunicaciones LTE en trenes de alta velocidad. Se proponen técnicas de reducción del coste y complejidad en relación a las evaluaciones en entornos de alta velocidad y se prueba su funcionamiento de modo analítico, mediante simulación y empíricamente. De cara a validar los desarrollos presentados en esta tesis en relación a los últimos avances en materia comunicaciones, se consideraron también las más novedosas propuestas para sistemas de quinta generación, actualmente aún en fase de definición. Es más, se evaluaron, tanto mediante simulación como vía medidas en entornos de alta velocidad, las prestaciones brindadas por las propuestas para sistemas de comunicaciones de quinta generación. El código fuente del GTEC Testbed y del GTEC 5G Simulator está disponible públicamente bajo la licencia GPLv3 en https://bitbucket.org/tomas_bolano/gtec_testbed_public.git.[Resumo] Ao longo dos últimos anos o uso de servizos multimedia e, en xeral, baseados no acceso a información contida “na nube”, experimentou un auxe sen precedentes. A diferencia respecto do pasado, os usuarios non soamente acceden aos servizos dende unha ubicación estática; pola contra, navegan libremente entre distintos lugares ao tempo que acceden, dende os seus dispositivos móbiles, a servizos na nube. Debido ao ritmo de vida actual, o tránsito entre zonas rurais e cidades tamén se incrementou de modo notable, ao ubicarse a maior parte dos lugares de traballo nas cidades ou nas súas respectivas contornas. Durante os períodos de transporte, cada vez máis, os pasaxeiros empregan os seus dispositivos móbiles para traballar, acceder a redes sociais ou como ferramenta de entretemento. O factor común da maior parte dos servizos típicamente empregados é a súa dependencia respecto do acceso á rede. Na actualidade, GSM for Railways (GSM-R), baseado no xa vetusto GSM, é o sistema de comunicacións máis empregado entre os trens e o resto dos elementos involucrados na infraestrutura ferroviaria. Sen embargo, GSM-R non é axeitado para proporcionar servizos avanzados, tales como o control de piloto automático, así como para sustentar transmisións de banda ancha aos operadores ferroviarios ou proporcionar servizos de valor engadido aos pasaxeiros. Botando unha ollada ao mercado de dispositivos de comunicacións de ámbito xeral, a explosión de usuarios e servizos multimedia dos últimos anos motivou a migración, primeiro ás redes de terceira xeración e, seguidamente, ás de cuarta, con Long Term Evolution (LTE) á cabeza. Así, parece natural plantexar LTE como o candidato para a substitución de GSM-R. No presente traballo lévase a cabo un completo estudo das prestacións de sistemas de comunicacións sen fíos de banda ancha en vehículos de alta velocidade baseado en campañas de medidas levadas a cabo en contornas reais de alta velocidade. Estudouse especialmente o caso de comunicacións LTE en trens de alta velocidade. Propóñense técnicas de redución de custo e complexidade en relación ás avaliacións en contornas de alta velocidade e valídase o seu funcionamento de xeito analítico, mediante simulación e empíricamente. Os desenvolvementos presentados nesta tese foron validados para os sistemas de quinta xeración, aínda en fase de definición. Avaliáronse, mediante simulación e experimentalmente en contornas de alta velocidade, as prestacións brindadas polas propostas para sistemas de comunicacións de quinta xeración. O código fonte do GTEC Testbed e do GTEC 5G Simulator está dispoñible públicamente baixo a licenza GPLv3 en https://bitbucket.org/tomas_bolano/gtec_testbed_public.git.[Abstract] Over the last few years multimedia and data-based services experienced a non-stopping growth. Unlike before, people do not use the services only from a static location, but they are continuously on the move between different scenarios, using their mobile devices to access data-based services. In parallel, commuter traffic from rural areas is also rising, since most of work places are in and around cities. During transportation, people intensively employ mobile devices to work, access to social networks, or as an entertainment means. Internet access is required for most of these services. Currently, GSM for Railways (GSM-R), which is based on the Global System for Mobile Communications (GSM), is the most widely used communication system between trains and the elements involved in operation, control, and intercommunication within the railway infrastructure. However, GSM-R is not well suited for supporting advanced services such as automatic pilot applications or provisioning broadband services to the train staff and passengers. Besides trains, the increasing number of broadband services available for mobile devices motivated the migration from third-generation mobile networks to fourth generation ones, mainly Long Term Evolution (LTE). Therefore, LTE seems to be a good candidate to substitute the GSM as the fundamental technology for railway communications. In this work a complete study on the performance of high capacity broadband wireless communication systems for high speed vehicles is presented, based on measurement campaigns in actual high speed environments. Special attention is devoted to the case of LTE in high speed trains. Techniques to greatly reduce the cost and complexity of measurement-based evaluations in high speed scenarios are proposed and proven to work analytically, by means of simulations and by measurements in actual high speed environments. With the aim of checking the validity of the findings of this work for the latest advances in wireless communication systems, proposals for fifth generation (5G) communication systems, currently still under definition, were also considered. Moreover, the performance of the proposals for 5G communication systems was also evaluated by means of simulations as well as by measuring in high speed environments. The source code of both the GTEC Testbed and the GTEC 5G Simulator is publicly available under the GPLv3 license at https://bitbucket.org/tomas_bolano/gtec_testbed_public.git