EVEREST IST - 2002 - 00185 : D23 : final report

Deliverable públic del projecte europeu EVERESTThis deliverable constitutes the final report of the project IST-2002-001858 EVEREST. After its successful completion, the project presents this document that firstly summarizes the context, goal and the approach objective of the project. Then it presents a concise summary of the major goals and results, as well as highlights the most valuable lessons derived form the project work. A list of deliverables and publications is included in the annex.Postprint (published version

Final report on the evaluation of RRM/CRRM algorithms

Deliverable public del projecte EVERESTThis deliverable provides a definition and a complete evaluation of the RRM/CRRM algorithms selected in D11 and D15, and evolved and refined on an iterative process. The evaluation will be carried out by means of simulations using the simulators provided at D07, and D14.Preprin

Influence of Intercell Interference on HSDPA Indoor Networks

Nowadays the high demand of data based services has become one of the key issues in the telecommunications sphere. Mobile cellular networks are thus willing to provide the necessary capacity that this growth demands. While new third generation specifications keep on improving the HSPA and HSPA+ features, a parallel trend trying to provide enough indoor capacity is taking place. The performance of indoor dedicated systems is highly dependent on the interference present in the network. In this Thesis, the impact of intercell interference on indoor networks is studied. For that purpose, two different measurement campaigns were accomplished in Tampere University of Technology's Tietotalo building. The first of them was held in two small rooms, where picocells and distributed antenna systems (DAS) solutions were tested. The second campaign took place inside a large lecture hall representing an indoor open area, and here diverse picocell layouts were deployed. Analysis took into account interference indicators like signal-to-interference ratio and Ec/N0, and link adaptation parameters like CQI, modulation usage and transport block size. This Thesis provides guidelines for indoor planning. It demonstrates that in small rooms, given a fixed number of cells per room, picocells and DAS solutions show similar performance, so picocells are a better option since they require fewer components such as antennas. High-density cell layouts provide higher system TP, but the maximum system TP achievable is dramatically limited by interference. This Thesis also proofs that, in open areas, multicell layouts can give only a marginal increase in system TP with respect to one-cell layouts, and thus multicell configurations are not always needed to be deployed. High-interference regions need to be identified and cleverly located since they degrade the overall system performance and users in those areas experience unbearable low data rates. /Kir1

Esquemas de cooperação entre estações base para o LTE no sentido descendente

The explosive growth in wireless traffic and in the number of connected devices as smart phones or computers, are causing a dramatic increase in the levels of interference, which significantly degrades the capacity gains promised by the point-to-point multi input, multi output (MIMO) based techniques. Therefore, it is becoming increasingly clear that major new improvements in spectral efficiency of wireless networks will have to entail addressing intercell interference. So, there is a need for a new cellular architecture that can take these factors under consideration. It is in this context that LTE-Advanced arises. One of the most promising LTE-Advanced technology is Coordinated Multipoint (CoMP), which allows base stations to cooperate among them, in order to mitigate or eliminate the intercell interference and, by doing so, increase the system’s capacity. This thesis intends to study this concept, implementing some schemes that fall under the CoMP concept. In this thesis we consider a distributed precoded multicell approach, where the precoders are computed locally at each BS to mitigate the intercell interference. Two precoder are considered: distributed zero forcing (DZF) and distributed virtual signal-to-interference noise ratio (DVSINR) recently proposed. Then the system is further optimized by computing a power allocation algorithm over the subcarriers that minimizes the average bit error rate (BER). The considered algorithms are also evaluated under imperfect channel state information. A quantized version of the CSI associated to the different links between the BS and the UT is feedback from the UT to the BS. This information is then employed by the different BSs to perform the precoding design. A new DVSINR precoder explicitly designed under imperfect CSI is proposed. The proposed schemes were implemented considering the LTE specifications, and the results show that the considered precoders are efficiently to remove the interference even under imperfect CSI.O crescimento exponencial no tráfego de comunicações sem-fios e no número de dispositivos utilizados (smart phones, computadores portáteis, etc.) está a causar um aumento significativo nos níveis de interferência, que prejudicam significativamente os ganhos de capacidade assegurados pelas tecnologias baseadas em ligações ponto-a-ponto MIMO. Deste modo, torna-se cada vez mais necessário que os grandes aperfeiçoamentos na eficiência espectral de sistemas de comunicações sem-fios tenham em consideração a interferência entre células. De forma a tomar em consideração estes aspectos, uma nova arquitectura celular terá de ser desenvolvida. É assim, neste contexto, que surge o LTE-Advanced. Uma das tecnologias mais promissoras do LTE-Advanced é a Coordenação Multi-Ponto (CoMP), que permite que as estações base cooperem de modo a mitigar a interferência entre células e, deste modo, aumentar a capacidade do sistema. Esta dissertação pretende estudar este conceito, implementando para isso algumas técnicas que se enquadram no conceito do CoMP. Nesta dissertação iremos considerar a implementação de um sistema de pré-codificação em múltiplas células, em que os pré-codificadores são calculados em cada BS, de modo a mitigar a interferência entre células. São considerados dois pré-codificadores: Distributed Zero Forcing (DZF) e Distributed Virtual Signal-to-Interferance Noise Ratio (DVSINR), recentemente proposto. De seguida o sistema é optimizado com a introdução de algoritmos de alocação de potência entre as sub-portadoras com o objectivo de minimizar a taxa média de erros (BER). Os algoritmos considerados são também avaliados em situações em que a informação do estado do canal é imperfeita. Uma versão quantizada da CSI associada a cada uma das diferentes ligações entre as BS e os UT é assim enviada do UT para a BS. Esta informação é então utilizada para calcular os diferentes pré-codificadores em cada BS. Uma nova versão do pré-codificador DVSINR é proposta de modo a lidar com CSI imperfeito. Os esquemas propostos foram implementados considerandos especificações do LTE, e os resultados obtidos demonstram que os pré-codificadores removem de uma forma eficiente a interferência, mesmo em situações em que a CSI é imperfeita

Cooperative control of relay based cellular networks

PhDThe increasing popularity of wireless communications and the higher data requirements of new types of service lead to higher demands on wireless networks. Relay based cellular networks have been seen as an effective way to meet users’ increased data rate requirements while still retaining the benefits of a cellular structure. However, maximizing the probability of providing service and spectrum efficiency are still major challenges for network operators and engineers because of the heterogeneous traffic demands, hard-to-predict user movements and complex traffic models. In a mobile network, load balancing is recognised as an efficient way to increase the utilization of limited frequency spectrum at reasonable costs. Cooperative control based on geographic load balancing is employed to provide flexibility for relay based cellular networks and to respond to changes in the environment. According to the potential capability of existing antenna systems, adaptive radio frequency domain control in the physical layer is explored to provide coverage at the right place at the right time. This thesis proposes several effective and efficient approaches to improve spectrum efficiency using network wide optimization to coordinate the coverage offered by different network components according to the antenna models and relay station capability. The approaches include tilting of antenna sectors, changing the power of omni-directional antennas, and changing the assignment of relay stations to different base stations. Experiments show that the proposed approaches offer significant improvements and robustness in heterogeneous traffic scenarios and when the propagation environment changes. The issue of predicting the consequence of cooperative decisions regarding antenna configurations when applied in a realistic environment is described, and a coverage prediction model is proposed. The consequences of applying changes to the antenna configuration on handovers are analysed in detail. The performance evaluations are based on a system level simulator in the context of Mobile WiMAX technology, but the concepts apply more generally

Radio resource management strategies for interference mitigation in 4G heterogeneous wireless networks

The new era of mobile communications is dictated by the user demand for robust and high speed connections, data hungry applications and seamless connectivity. Operators and researchers all over the world are challenged to fulfill these requirements by providing enhanced coverage, increased capacity and efficient usage of the scarce spectrum. The introduction of the fourth generation systems (4G), LTE and LTE-A, have set the initiative for a technology evolution that offers new possibilities and is able to satisfy the user requirements and overcome the imposed challenges. However, and despite the improvements brought by the LTE and LTE-A systems, there are certain constraints that still need to be surpassed. LTE for example adopts innovating technologies, such as Orthogonal Frequency Division Multiplexing Access (OFDMA) that improves the spectral efficiency and reduces the Intra-Cell Interference. Nevertheless, Inter-Cell Interference (ICI) remains a constraining factor that can degrade the system capacity and limit the overall performance of the network. On that respect, Inter-Cell Interference Coordination (ICIC) techniques are adopted with target the interference mitigation. One of the limitations of these techniques is that follow static configurations lacking of flexibility and adaptation on network changes. Moreover, LTE-A employs enhanced and new techniques and involves alternative strategies. A promising solution lies on the introduction of Heterogeneous Networks (HetNets), which are networks that include low power small cells under the already existing macro cellular network and exploit several other technologies, such as WiFi. HetNets can further improve the network capacity, enhance the coverage and provide higher speed data transfer. However, due to the heterogeneous nature of the network, traditional methods for the user association, resource allocation and interference mitigation may not always be suitable since their design was based on homogeneous deployments. As such, new and enhanced methods are introduced, such as enhanced ICIC (eICIC), with their accompanied requirements and challenges. Motivated by the abovementioned aspects, this thesis has been focused on the study of ICIC and eICIC schemes, the identification of the related challenges, the enhancement of existing schemes and the proposal of novel solutions. In particular in the initial stages of the work, ICIC techniques have been studied and analyzed. A distributed algorithm that performs dynamic channel allocation has been developed for homogeneous deployments and extended later on to include heterogeneous networks. The solution has been optimized with the use of the Gibbs Sampler, while the setting of algorithm related parameters has been addressed through a detailed analysis. Moreover, a possible implementation of the solution has been presented in detail. The efficiency of the proposed schemes has been demonstrated through simulations and comparisons with benchmark schemes. In the next steps, the work has targeted eICIC techniques with purpose the investigation and analysis of the main constraining issues related to the user association, resource management and interference mitigation. Novel eICIC schemes that aim a better resource management and the overall capacity improvement have been developed and presented in detail, while the performance of the solutions has been shown through simulations and comparisons with reference schemes. Moreover, an optimized eICIC solution has been implemented based on genetic algorithms. Simulation results and comparisons with reference schemes have demonstrated the efficiency of the solution, while the selected configurations are discussed and analyzed.La nueva era de las comunicaciones móviles viene marcada por la demanda de los usuarios por conseguir conexiones robustas de alta velocidad que permitan soportar aplicaciones de datos de elevados requerimientos. El cumplimiento de estos requisitos conlleva la necesidad de mejorar la cobertura, incrementar la capacidad y utilizar el espectro eficientemente. La introducción de los sistemas de cuarta generación (4G), LTE y LTE-A, ha dado lugar a una tecnología que ofrece nuevas posibilidades y es capaz de satisfacer las necesidades de los usuarios y superar los retos impuestos. Sin embargo, y a pesar de las mejoras introducidas por estos sistemas, hay ciertas limitaciones que todavía tienen que ser superadas. LTE, por ejemplo, adopta tecnologías tales como OFDMA que mejora la eficiencia espectral y reduce la interferencia intracelular. Sin embargo, la interferencia intercelular (ICI) sigue siendo un factor limitante que puede degradar la capacidad del sistema y limitar el rendimiento global de la red. En ese sentido, se requieren técnicas de coordinación de interferencias intercelulares (ICIC) con el objetivo de mitigar dicha interferencia. Una de las limitaciones de estas técnicas es que siguen configuraciones estáticas que carecen de flexibilidad y capacidad de adaptación a los cambios de la red. Por otra parte, LTE-A introduce nuevas mejoras, como las redes heterogéneas (HetNets), que son redes que incluyen pequeñas células de baja potencia conjuntamente con la red macrocellular y también pueden explotar diferentes tecnologías, como WiFi. Las HetNets pueden mejorar aún más la capacidad de la red, mejorar la cobertura y facilitar la transferencia de datos de mayor velocidad. Sin embargo, debido a la naturaleza heterogénea de la red, los métodos tradicionales para la asociación de usuarios, asignación de recursos y reducción de la interferencia pueden no ser siempre adecuados, ya que su diseño se basó en despliegues homogéneos. En este sentido, es preciso introducir técnicas mejoradas de ICIC, denominadas en inglés eICIC (enhanced-ICIC), que involucran nuevos requerimientos y retos. En base a todos estos aspectos, esta tesis se ha centrado en el estudio de los sistemas de ICIC y eICIC en redes celulares, incluyendo la identificación de los retos relacionados con la mejora de los sistemas existentes y la propuesta de soluciones novedosas. En particular, en las etapas iniciales de la tesis se han estudiado y analizado las técnicas ICIC, y se ha desarrollado un algoritmo distribuido que realiza la asignación dinámica de canales para despliegues homogéneos, ampliándose posteriormente para su utilización en redes heterogéneas. La solución opera de forma optimizada mediante el uso de la técnica denominada Gibbs Sampler, mientras que el ajuste de parámetros relacionado con el algoritmo se ha abordado a través de un análisis detallado basado en simulaciones. Por otra parte, una posible implementación de la solución se ha presentado en detalle. La eficiencia de los esquemas propuestos se ha demostrado a través de simulaciones y comparaciones con sistemas de referencia. En los siguientes pasos, el trabajo se ha centrado en las técnicas eICIC con el propósito de investigar y analizar los principales problemas relacionadas con la asociación de usuarios, gestión de recursos y mitigación de la interferencia. A partir de aquí se han desarrollado nuevos esquemas de eICIC que tienen como objetivo una mejor gestión de los recursos y la mejora general de la capacidad. El rendimiento de las soluciones se ha demostrado a través de simulaciones y comparaciones con sistemas de referencia. Por otra parte, se ha propuesto una solución eICIC optimizada basada en algoritmos genéticos. La eficacia de dicha solución se ha demostrado mediante simulaciones, a la vez que se han analizado las diferentes configuraciones seleccionadas por el proceso de optimización.Postprint (published version

Channel estimation and parameters acquisition systems employing cooperative diversity

Doutoramento em Engenharia Eletrotécnica e TelecomunicaçõesThis work investigates new channel estimation schemes for the forthcoming and future generation of cellular systems for which cooperative techniques are regarded. The studied cooperative systems are designed to re-transmit the received information to the user terminal via the relay nodes, in order to make use of benefits such as high throughput, fairness in access and extra coverage. The cooperative scenarios rely on OFDM-based systems employing classical and pilot-based channel estimators, which were originally designed to pointto-point links. The analytical studies consider two relaying protocols, namely, the Amplifyand-Forward and the Equalise-and-Forward, both for the downlink case. The relaying channels statistics show that such channels entail specific characteristics that comply to a proper filter and equalisation designs. Therefore, adjustments in the estimation process are needed in order to obtain the relay channel estimates, refine these initial estimates via iterative processing and obtain others system parameters that are required in the equalisation. The system performance is evaluated considering standardised specifications and the International Telecommunication Union multipath channel models.Este trabalho tem por objetivo o estudo de novos esquemas de estimação de canal para sistemas de comunicação móvel das próximas gerações, para os quais técnicas cooperativa são consideradas. Os sistemas cooperativos investigados neste trabalho estão projetados para fazerem uso de terminais adicionais a fim de retransmitir a informação recebida para o utilizador final. Desta forma, pode-se usurfruir de benefícios relacionados às comunicações cooperativas tais como o aumento do rendimento do sistema, fiabilidade e extra cobertura. Os cenários são basedos em sistemas OFDM que empregam estimadores de canal que fazem uso de sinais piloto e que originalmente foram projetados para ligações ponto a ponto. Os estudos analíticos consideram dois protocolos de encaminhamento, nomeadamente, Amplify-and-Forward e Equalise-and-Forward, ambos para o caso downlink. As estatísticas dos canais em estudo mostram que tais canais ocasionam características específicas para as quais o filtro do estimador e a equalisação devem ser apropridamente projetados. Estas características requerem ajustes que são necessários no processo de estimação a fim de estimar os canais, refinar as estimativas iniciais através de processos iterativos e ainda obter outros parâmetros do sistema que são necessários na equalização. O desempenho dos esquemas propostos são avaliados tendo em consideração especificações padronizadas e modelos de canal descritos na International Telecommunication Union