132 research outputs found
Mean Achievable Rates in Clustered Coordinated Base Station Transmission with Block Diagonalization
We focus on the mean achievable rate per user of the coordinated base station downlink transmission in a clustered cellular environment, with transmit power constraints at the base stations. Block Diagonalization is employed within the cluster to remove interference among users while the interference from other clusters remains. The average achievable rate per user is evaluated considering the effects of the propagation channel and the interference and a theoretical framework is presented to provide its analytical expression, validated by simulation results with different power allocation schemes. As an application, the number of cells of the cluster that maximizes the mean achievable rate per user is investigated. It can be seen that in most of the cases a reduced cluster size, close to seven cells, guarantees a rate very close to the maximum achievableThis work is partly funded by projects "GRE3N": TEC2011-29006-C03-03
and "COMONSENS": CSD2008-00010En-prens
Partial coordination in clustered base station MIMO transmission
This proceeding at: IEEE Wireless Communications and Networking Conference (WCNC, 2013), took place 2013, April, 7-10, in Shaghai (China)We present partial coordination strategies in a clustered cellular environment, evaluating the achievable rate in the downlink transmission. Block Diagonalization is employed for the coordinated users within the cluster to remove interference, while the interference from non-coordinated users remains. The achievable rate is evaluated resorting to an analytical expression conditioned on the position of the users in the cluster. A partial coordination approach is proposed to reduce the coordination complexity and overhead, where users close to the base station are not coordinated. Two approaches are considered, namely the non-coordinated users can be grouped and assigned separated resources from the coordinated ones, or they can be mixed.This work was supported by projects CSD2008-00010
“COMONSENS” and TEC2011-29006-C03-03 “GRE3N”
Achievable rate and fairness in coordinated base station transmission
This work focuses on the fairness in the distribution of the achievable rate per user in a cellular environment where clusters of base stations coordinate their transmissions in the downlink. Block Diagonalization is employed within the cluster to remove interference among users while the interference coming from other clusters remains. The probability distribution of the achievable rate per user shows a perfect match with a Gamma distribution so that a characterization in terms of mean and variance can provide a useful tool for the design of the clusters and the implementation of fairness strategies in a coordinated base station network with Block Diagonalization.This work is partly funded by the projects “GRE3N”: TEC2011-29006-
C03-03, and “COMONSENS”: CSD2008-00010.Publicad
Linear Transmit-Receive Strategies for Multi-user MIMO Wireless Communications
Die Notwendigkeit zur Unterdrueckung von Interferenzen auf der einen Seite
und zur Ausnutzung der durch Mehrfachzugriffsverfahren erzielbaren Gewinne
auf der anderen Seite rueckte die raeumlichen Mehrfachzugriffsverfahren
(Space Division Multiple Access, SDMA) in den Fokus der Forschung. Ein
Vertreter der raeumlichen Mehrfachzugriffsverfahren, die lineare
Vorkodierung, fand aufgrund steigender Anzahl an Nutzern und Antennen in
heutigen und zukuenftigen Mobilkommunikationssystemen besondere Beachtung,
da diese Verfahren das Design von Algorithmen zur Vorcodierung
vereinfachen. Aus diesem Grund leistet diese Dissertation einen Beitrag zur
Entwicklung linearer Sende- und Empfangstechniken fuer MIMO-Technologie mit
mehreren Nutzern. Zunaechst stellen wir ein Framework zur Approximation des
Datendurchsatzes in Broadcast-MIMO-Kanaelen mit mehreren Nutzern vor. In
diesem Framework nehmen wir das lineare Vorkodierverfahren regularisierte
Blockdiagonalisierung (RBD) an. Durch den Vergleich von Dirty Paper Coding
(DPC) und linearen Vorkodieralgorithmen (z.B. Zero Forcing (ZF) und
Blockdiagonalisierung (BD)) ist es uns moeglich, untere und obere Schranken
fuer den Unterschied bezueglich Datenraten und bezueglich Leistung zwischen
beiden anzugeben. Im Weiteren entwickeln wir einen Algorithmus fuer
koordiniertes Beamforming (Coordinated Beamforming, CBF), dessen Loesung
sich in geschlossener Form angeben laesst. Dieser CBF-Algorithmus basiert
auf der SeDJoCo-Transformation und loest bisher vorhandene Probleme im
Bereich CBF. Im Anschluss schlagen wir einen iterativen CBF-Algorithmus
namens FlexCoBF (flexible coordinated beamforming) fuer
MIMO-Broadcast-Kanaele mit mehreren Nutzern vor. Im Vergleich mit bis dato
existierenden iterativen CBF-Algorithmen kann als vielversprechendster
Vorteil die freie Wahl der linearen Sende- und Empfangsstrategie
herausgestellt werden. Das heisst, jede existierende Methode der linearen
Vorkodierung kann als Sendestrategie genutzt werden, waehrend die Strategie
zum Empfangsbeamforming frei aus MRC oder MMSE gewaehlt werden darf. Im
Hinblick auf Szenarien, in denen Mobilfunkzellen in Clustern
zusammengefasst sind, erweitern wir FlexCoBF noch weiter. Hier wurde das
Konzept der koordinierten Mehrpunktverbindung (Coordinated Multipoint
(CoMP) transmission) integriert. Zuletzt stellen wir drei Moeglichkeiten
vor, Kanalzustandsinformationen (Channel State Information, CSI) unter
verschiedenen Kanalumstaenden zu erlangen. Die Qualitaet der
Kanalzustandsinformationen hat einen starken Einfluss auf die Guete des
Uebertragungssystems. Die durch unsere neuen Algorithmen erzielten
Verbesserungen haben wir mittels numerischer Simulationen von Summenraten
und Bitfehlerraten belegt.In order to combat interference and exploit large multiplexing gains of the
multi-antenna systems, a particular interest in spatial division multiple
access (SDMA) techniques has emerged. Linear precoding techniques, as one
of the SDMA strategies, have obtained more attention due to the fact that
an increasing number of users and antennas involved into the existing and
future mobile communication systems requires a simplification of the
precoding design. Therefore, this thesis contributes to the design of
linear transmit and receive strategies for multi-user MIMO broadcast
channels in a single cell and clustered multiple cells. First, we present a
throughput approximation framework for multi-user MIMO broadcast channels
employing regularized block diagonalization (RBD) linear precoding.
Comparing dirty paper coding (DPC) and linear precoding algorithms (e.g.,
zero forcing (ZF) and block diagonalization (BD)), we further quantify
lower and upper bounds of the rate and power offset between them as a
function of the system parameters such as the number of users and antennas.
Next, we develop a novel closed-form coordinated beamforming (CBF)
algorithm (i.e., SeDJoCo based closed-form CBF) to solve the existing open
problem of CBF. Our new algorithm can support a MIMO system with an
arbitrary number of users and transmit antennas. Moreover, the application
of our new algorithm is not only for CBF, but also for blind source
separation (BSS), since the same mathematical model has been used in BSS
application.Then, we further propose a new iterative CBF algorithm (i.e.,
flexible coordinated beamforming (FlexCoBF)) for multi-user MIMO broadcast
channels. Compared to the existing iterative CBF algorithms, the most
promising advantage of our new algorithm is that it provides freedom in the
choice of the linear transmit and receive beamforming strategies, i.e., any
existing linear precoding method can be chosen as the transmit strategy and
the receive beamforming strategy can be flexibly chosen from MRC or MMSE
receivers. Considering clustered multiple cell scenarios, we extend the
FlexCoBF algorithm further and introduce the concept of the coordinated
multipoint (CoMP) transmission. Finally, we present three strategies for
channel state information (CSI) acquisition regarding various channel
conditions and channel estimation strategies. The CSI knowledge is required
at the base station in order to implement SDMA techniques. The quality of
the obtained CSI heavily affects the system performance. The performance
enhancement achieved by our new strategies has been demonstrated by
numerical simulation results in terms of the system sum rate and the bit
error rate
Block diagonalization techniques for cellular networks: clustering and scheduling
MenciĂłn Internacional en el tĂtulo de doctorLa necesidad de tasas de transmisiĂłn más elevadas y una mayor eficiencia en las redes celulares es la principal motivaciĂłn para considerar el uso de UFR. La coordinaciĂłn entre BSs se hace necesaria, entonces, para compensar los problemas introducidos por la interferencia. La coordinaciĂłn global de la red es demasiado compleja y, además, presenta limitaciones intrĂnsecas, que impiden su utilizaciĂłn en escenarios reales. La utilizaciĂłn de grupos reducidos de BSs es una alternativa para reducir los requisitos impuestos por la coordinaciĂłn. Como consecuencia de la agrupaciĂłn, aparece OCI, la
cual perjudica seriamente las comunicaciones.
Este trabajo se centra en BD, una técnica de precodificación lineal que combina unas buenas prestaciones con una complejidad relativamente baja. Sin embargo, la interferencia empeora notablemente su funcionamiento.
En esta tesis se estudia el canal descendente de una red celular conglomerada, donde se usa BD para coordinar las BSs que forman cada grupo. Se analiza la tasa media obtenible como función de múltiples parámetros del escenario. De especial interés es la dependencia con el tamaño de las agrupaciones, de donde se desprende que existe un tamaño óptimo para los grupos de BSs, por encima del cual no se obtienen mejoras significativas. La equidad del sistema se estudia en presencia de OCI, también como función de diversos parámetros del escenario, como puede ser la asignación de potencia.
Se propone una estrategia mixta de transmisiĂłn, que combina BD con procesado
SU, como mecanismo para combatir las dificultades introducidas por la interferencia que no se gestiona. La estrategia consiste en dos fases:
• Los usuarios deciden localmente quĂ© estrategia prefieren para la transmisiĂłn, y envĂan esta informaciĂłn a las BSs.
• Las BSs utilizan las decisiones recibidas para planificar las transmisiones, de modo que se pueda optimizar el funcionamiento de la red.
El resultado de la estrategia propuesta es una mejora de las prestaciones de BD en presencia de OCI, especialmente para los usuarios más desfavorecidos. Esto se traduce en que, adicionalmente, el sistema se vuelve más justo, al mismo tiempo que el rendimiento de la red aumenta.The need for higher data rates and higher efficiency in cellular networks motivates the use of Universal Frequency Reuse (UFR). Coordination among Base Stations (BSs) is required then to alleviate the performance penalty due to the interference. Global coordination is too complex and has inherent limitations that prevents it from being used in real world scenarios. Clusters of a reduced number of BSs can be considered in order
to ease off the requirements of coordination. As a result, Other Cluster Interference (OCI) appears, affecting negatively the communications.
This work focuses on Block Diagonalization (BD), a linear precoding technique that combines a good theoretical performance with a relatively low complexity. However, the unwanted interference seriously impacts the results obtained using BD.
This thesis studies the downlink of a clustered cellular network, where BD is used to coordinate the BS within each cluster. The mean achievable rate is analyzed as a function of several scenario parameters. Of particular interest is the dependence on the cluster size, which yields that there is an optimum cluster size, beyond which no significant gain is obtained. Fairness considerations are analyzed in the presence of OCI, also studied as a function of scenario parameters such as the power allocation.
A mixed strategy using BD and Single User (SU) processing is proposed as a means to overcome the impairment of the unhandled interference. The transmission consists of two stages:
• Users locally decide which transmission strategy they prefer and send this information to the BSs.
• BSs use the decisions of all users to schedule them for transmission so that the performance of the network is optimized.
The result of the proposed strategy is an improvement in the performance of BD in the presence of OCI, especially for the users experiencing the worst conditions. This means that the fairness of the system is also increased, along with the overall performance of the network.Programa Oficial de Doctorado en Multimedia y ComunicacionesPresidente: Lajos Hanzo.- Secretario: Raquel Perez Leal.- Vocal: Atilio Manuel da Silva Gameir
Radio-over-Fiber Aided Base Station Coordination for OFDM
This proceding at: IEEE 80th Vehicular Technology Conference (VTC)Fall. Took place 2014, September 15-19, in Vancouver (Canada).Radio over Fiber (RoF) distribution aided co-operation of Remote Access Points (RAPs) is proposed for jointly transmitting data to the users in the downlink (DL) of a Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system. Joint transmission is performed with the aid of Block Diagonalization (BD), where the transmitted signal is pre-distorted in order to overcome the non-linearity imposed by the optical modulator. We demonstrate that with adequate design, the users can obtain high data rates with very small degradation introduced by the RoF transmission. Quantitatively, when M=7 RAPs, each equipped with t=2 transmit antennas (TAs) each, cooperate to serve N=7 simultaneous users, also equipped with r=2 receive antennas (RAs), the SNR degradation is kept below 0.1 dB compared to a system assuming a perfect RoF channel. On the other hand, the SNR performance degradation is around 1.2 dB, when the number of antennas at the transmitters and the receivers is increased to t=r=8.This work was supported by projects CSD2008-00010, TEC2011-29006-
C03-03 and by a mobility grant of Spanish Ministry of Education.
The financial support of the UK Government’s Engineering & Physical Sciences
Research Council (EPSRC) as well as that of the Research Councils UK
(RCUK) and of the European Research Council’s Senior Research Fellow
Grant is also gratefully acknowledged.Publicad
Power allocation strategies for distributed precoded multicell based systems
Multicell cooperation is a promising solution for cellular wireless systems to mitigate intercell interference, improve system fairness, and increase capacity. In this article, we propose power allocation techniques for the downlink of distributed, precoded, multicell cellular-based systems. The precoder is designed in two phases: first the intercell interference is removed by applying a set of distributed precoding vectors; then the system is further optimized through power allocation. Three centralized power allocation algorithms with per-BS power constraint and diferente complexity trade-offs are proposed: one optimal in terms of minimization of the instantaneous average bit error rate (BER), and two suboptimal. In this latter approach, the powers are computed in two phases. First, the powers are derived under total power constraint (TPC) and two criterions are considered, namely, minimization of the instantaneous average BER and minimization of the sum of inverse of signal-to-noise ratio. Then, the final powers are computed to satisfy the individual per-BS power constraint. The performance of the proposed schemes is evaluated, considering typical pedestrian scenarios based on LTE specifications. The numerical results show that the proposed suboptimal schemes achieve a performance very close to the optimal but with lower computational complexity. Moreover, the performance of the proposed per-BS precoding schemes is close to the one obtained considering TPC over a supercell.Portuguese CADWIN - PTDC/ EEA TEL/099241/200
A Dynamic Clustering and Resource Allocation Algorithm for Downlink CoMP Systems with Multiple Antenna UEs
Coordinated multi-point (CoMP) schemes have been widely studied in the recent
years to tackle the inter-cell interference. In practice, latency and
throughput constraints on the backhaul allow the organization of only small
clusters of base stations (BSs) where joint processing (JP) can be implemented.
In this work we focus on downlink CoMP-JP with multiple antenna user equipments
(UEs) and propose a novel dynamic clustering algorithm. The additional degrees
of freedom at the UE can be used to suppress the residual interference by using
an interference rejection combiner (IRC) and allow a multistream transmission.
In our proposal we first define a set of candidate clusters depending on
long-term channel conditions. Then, in each time block, we develop a resource
allocation scheme by jointly optimizing transmitter and receiver where: a)
within each candidate cluster a weighted sum rate is estimated and then b) a
set of clusters is scheduled in order to maximize the system weighted sum rate.
Numerical results show that much higher rates are achieved when UEs are
equipped with multiple antennas. Moreover, as this performance improvement is
mainly due to the IRC, the gain achieved by the proposed approach with respect
to the non-cooperative scheme decreases by increasing the number of UE
antennas.Comment: 27 pages, 8 figure
Improving Performance-limited Interference System with Coordinated Multipoint Transmission
This paper describes an overview of the key component in coordinated multipoint in the context of LTE-Advanced which includes architectures, approaches, and main challenges. Most of the ideas presented are presently being studied and may vary throughout the standardization work. A system model is proposed to employ the cooperative communication in interference-limited scenario which may help to improve the cell-edge performance
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