28 research outputs found
Gestão comum de recursos rádio em redes sem fios de próxima geração
Mestrado em Electrónica e TelecomunicaçõesA tecnologia de sinais de rádio frequência sobre fibra óptica involve o uso
de links ópticos para transportar os sinais desde a unidade central de processamento
até aos sites remotos (e vice-versa). A centralização do processamento
dos sinais de rádio frequência permite a partilha de equipamentos,
alocação dinâmica de recursos e uma manutenção mais simplificada do sistema.
Embora o conceito de gestão comum dos recursos rádio tenha despertado
grande interesse na comunidade científica em termos da melhor utilização
desses recursos e de novos modelos de negócio, a verdade é que a sua implementação
não tem sido fácil. A interligação entre diferentes componentes
de rede, normalmente localizados em locais diferentes, introduz um grande
atraso nas comunicações; por outro lado as implementações proprietárias e
a escassez de informação global não satisfazem os requisitos de um ambiente
extremamente dinâmico, como é o ambiente wireless. Uma topologia
centralizada permite ultrapassar estas contrariedades, disponibilizando uma
interligação eficiente entre as entidades locais e comuns de gestão de recursos
rádio.
Nesta dissertação é apresentada uma nova arquitectura de gestão comum de
recursos rádio, baseada no conceito de interligação entre diferentes tecnologias
de acesso. Esta arquitectura faz a gestão dos recursos rádio de forma
centralizada, onde os sinais rádio chegam sem qualquer pré-processamento.
Essa arquitectura é avaliada com a implementação de um algoritmo simples
de balanceamento da carga que segue a politica de minimização da
interferência e aumento da capacidade.
As simulações com duas tecnologias de acesso, quando consideradas separas
ou em agregado, mostraram um aumento do débito de pelo menos 51% para
o mesmo valor de interferência enquanto que o erro de simbolo decresce pelo
menos 20%.Radio over fibre technology involves the use of optical fibre links to distribute
radio frequency signals from a central location to remote sites (and viceversa).
The centralisation of radio frequency signals processing functions
enables equipment sharing, dynamic allocation of resources, and simplified
system operation and maintenance.
Despite the unquestionable interest concept of common radio resource management
from the point of view of resource usage and novel business models,
its implementation has not been easy. The interworking between the different
local radio resource management entities, usually located on different
places will not satisfy the requirements of the wireless dynamic behaviour
due to increase of delay in communication process, less information availability
and proprietary implementations. A centralised topology can overcome
the drawbacks of former wireless systems architecture interconnection
by providing an efficient common radio communication flow with the local
radio resource management entities.
In this thesis a novel common radio resource management architecture is
presented based on the concept of inter-working between different technologies.
This is a centralised architecture where the radio frequency signals are
delivered to the central location through the optical links. The new architecture
is evaluated with a common policy that minimises interference while
the overall system capacity is increased. The policy is implemented through
the load balancing algorithm.
The simulations of two radio access technologies when separately and jointly
considered show that when the load balancing algorithm is applied the available
throughput increases in at least 51% while the symbol error rate decreases
at least 20%
Spatio-Temporal processing for Optimum Uplink-Downlink WCDMA Systems
The capacity of a cellular system is limited by two different phenomena, namely
multipath fading and multiple access interference (MAl). A Two Dimensional (2-D)
receiver combats both of these by processing the signal both in the spatial and temporal
domain. An ideal 2-D receiver would perform joint space-time processing, but at the
price of high computational complexity. In this research we investigate computationally
simpler technique termed as a Beamfom1er-Rake. In a Beamformer-Rake, the output of a
beamfom1er is fed into a succeeding temporal processor to take advantage of both the
beamformer and Rake receiver. Wireless service providers throughout the world are
working to introduce the third generation (3G) and beyond (3G) cellular service that will
provide higher data rates and better spectral efficiency. Wideband COMA (WCDMA)
has been widely accepted as one of the air interfaces for 3G. A Beamformer-Rake
receiver can be an effective solution to provide the receivers enhanced capabilities
needed to achieve the required performance of a WCDMA system.
We consider three different Pilot Symbol Assisted (PSA) beamforming techniques,
Direct Matrix Inversion (DMI), Least-Mean Square (LMS) and Recursive Least Square
(RLS) adaptive algorithms. Geometrically Based Single Bounce (GBSB) statistical
Circular channel model is considered, which is more suitable for array processing, and
conductive to RAKE combining. The performances of the Beam former-Rake receiver are
evaluated in this channel model as a function of the number of antenna elements and
RAKE fingers, in which are evaluated for the uplink WCDMA system. It is shown that,
the Beamformer-Rake receiver outperforms the conventional RAKE receiver and the
conventional beamformer by a significant margin. Also, we optimize and develop a
mathematical formulation for the output Signal to Interference plus Noise Ratio (SINR)
of a Beam former-Rake receiver.
In this research, also, we develop, simulate and evaluate the SINR and Signal to Noise
Ratio (Et!Nol performances of an adaptive beamforming technique in the WCDMA
system for downlink. The performance is then compared with an omnidirectional antenna
system. Simulation shows that the best perfom1ance can be achieved when all the mobiles
with same Angle-of-Arrival (AOA) and different distance from base station are formed in
one beam
Adaptive Beamforming and Adaptive Modulation-Assisted Network Performance of Multiuser Detection-Aided FDD and TDD CDMA Systems
The network performance of a frequency division duplex and time division duplex (TDD) code division multiple access (CDMA)-based system is investigated using system parameters similar to those of the Universal Mobile Telecommunication System. The new call blocking and call dropping probabilities, the probability of low-quality access, and the required average transmit power are quantified both with and without adaptive antenna arrays (AAAs), as well as when subjected to shadow fading. In some of the scenarios investigated, the system’s user capacity is doubled with the advent of adaptive antennas. The employment of adaptive modulation techniques in conjunction with AAAs resulted in further significant network capacity gains. This is particularly so in the context of TDD CDMA, where the system’s capacity becomes poor without adaptive antennas and adaptive modulation owing to the high base station (BS) to BS interference inflicted as a consequence of potentially using all time slots in both the uplink and downlink of the emerging wireless Internet. Index Terms—Adaptive beamforming, adaptive modulation, code division multiple access (CDMA) systems, Universal Mobile Telecommunication System Terrestrial Radio Access (UTRA), wireless network performance
Efficient Radio Resource Allocation Schemes and Code Optimizations for High Speed Downlink Packet Access Transmission
An important enhancement on the Wideband Code Division Multiple Access
(WCDMA) air interface of the 3G mobile communications, High Speed Downlink
Packet Access (HSDPA) standard has been launched to realize higher spectral
utilization efficiency. It introduces the features of multicode CDMA transmission
and Adaptive Modulation and Coding (AMC) technique, which makes radio resource
allocation feasible and essential. This thesis studies channel-aware resource
allocation schemes, coupled with fast power adjustment and spreading code optimization
techniques, for the HSDPA standard operating over frequency selective
channel.
A two-group resource allocation scheme is developed in order to achieve a
promising balance between performance enhancement and time efficiency. It only
requires calculating two parameters to specify the allocations of discrete bit rates
and transmitted symbol energies in all channels. The thesis develops the calculation
methods of the two parameters for interference-free and interference-present
channels, respectively. For the interference-present channels, the performance of
two-group allocation can be further enhanced by applying a clustering-based channel
removal scheme.
In order to make the two-group approach more time-efficient, reduction in
matrix inversions in optimum energy calculation is then discussed. When the
Minimum Mean Square Error (MMSE) equalizer is applied, optimum energy allocation
can be calculated by iterating a set of eigenvalues and eigenvectors. By
using the MMSE Successive Interference Cancellation (SIC) receiver, the optimum
energies are calculated recursively combined with an optimum channel ordering
scheme for enhancement in both system performance and time efficiency.
This thesis then studies the signature optimization methods with multipath
channel and examines their system performances when combined with different
resource allocation methods. Two multipath-aware signature optimization methods
are developed by applying iterative optimization techniques, for the system
using MMSE equalizer and MMSE precoder respectively. A PAM system using
complex signature sequences is also examined for improving resource utilization
efficiency, where two receiving schemes are proposed to fully take advantage of
PAM features. In addition by applying a short chip sampling window, a Singular
Value Decomposition (SVD) based interference-free signature design method is
presented
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
Spatio-Temporal processing for Optimum Uplink-Downlink WCDMA Systems
The capacity of a cellular system is limited by two different phenomena, namely
multipath fading and multiple access interference (MAl). A Two Dimensional (2-D)
receiver combats both of these by processing the signal both in the spatial and temporal
domain. An ideal 2-D receiver would perform joint space-time processing, but at the
price of high computational complexity. In this research we investigate computationally
simpler technique termed as a Beamfom1er-Rake. In a Beamformer-Rake, the output of a
beamfom1er is fed into a succeeding temporal processor to take advantage of both the
beamformer and Rake receiver. Wireless service providers throughout the world are
working to introduce the third generation (3G) and beyond (3G) cellular service that will
provide higher data rates and better spectral efficiency. Wideband COMA (WCDMA)
has been widely accepted as one of the air interfaces for 3G. A Beamformer-Rake
receiver can be an effective solution to provide the receivers enhanced capabilities
needed to achieve the required performance of a WCDMA system.
We consider three different Pilot Symbol Assisted (PSA) beamforming techniques,
Direct Matrix Inversion (DMI), Least-Mean Square (LMS) and Recursive Least Square
(RLS) adaptive algorithms. Geometrically Based Single Bounce (GBSB) statistical
Circular channel model is considered, which is more suitable for array processing, and
conductive to RAKE combining. The performances of the Beam former-Rake receiver are
evaluated in this channel model as a function of the number of antenna elements and
RAKE fingers, in which are evaluated for the uplink WCDMA system. It is shown that,
the Beamformer-Rake receiver outperforms the conventional RAKE receiver and the
conventional beamformer by a significant margin. Also, we optimize and develop a
mathematical formulation for the output Signal to Interference plus Noise Ratio (SINR)
of a Beam former-Rake receiver.
In this research, also, we develop, simulate and evaluate the SINR and Signal to Noise
Ratio (Et!Nol performances of an adaptive beamforming technique in the WCDMA
system for downlink. The performance is then compared with an omnidirectional antenna
system. Simulation shows that the best perfom1ance can be achieved when all the mobiles
with same Angle-of-Arrival (AOA) and different distance from base station are formed in
one beam
Wireless technology: current status and future directions
Wireless Technology is expected to be the dominant
mode of access technology in the future. Besides voice, a
new data range of services such as multimedia and high
speed data are being offered for delivery over wireless
network. Mobility will be seamless, realizing the concept
of persons' being in contact anywhere, at any time.
Throughout this paper, we review the long, interesting
development of wireless communication in the past,
examine the current progress in standards and
technologies, and finally discuss possible trends for
wireless communication solutions
Resource Allocation in Ad Hoc Networks
Unlike the centralized network, the ad hoc network does not have any central administrations and energy is constrained, e.g. battery, so the resource allocation plays a
very important role in efficiently managing the limited energy in ad hoc networks.
This thesis focuses on the resource allocation in ad hoc networks and aims to develop
novel techniques that will improve the network performance from different network
layers, such as the physical layer, Medium Access Control (MAC) layer and network
layer.
This thesis examines the energy utilization in High Speed Downlink Packet Access (HSDPA) systems at the physical layer. Two resource allocation techniques,
known as channel adaptive HSDPA and two-group HSDPA, are developed to improve the performance of an ad hoc radio system through reducing the residual
energy, which in turn, should improve the data rate in HSDPA systems. The channel adaptive HSDPA removes the constraint on the number of channels used for
transmissions. The two-group allocation minimizes the residual energy in HSDPA
systems and therefore enhances the physical data rates in transmissions due to adaptive modulations. These proposed approaches provide better data rate than rates
achieved with the current HSDPA type of algorithm.
By considering both physical transmission power and data rates for defining the
cost function of the routing scheme, an energy-aware routing scheme is proposed
in order to find the routing path with the least energy consumption. By focusing
on the routing paths with low energy consumption, computational complexity is
significantly reduced. The data rate enhancement achieved by two-group resource
allocation further reduces the required amount of energy per bit for each path. With
a novel load balancing technique, the information bits can be allocated to each path
in such that a way the overall amount of energy consumed is minimized.
After loading bits to multiple routing paths, an end-to-end delay minimization
solution along a routing path is developed through studying MAC distributed coordination function (DCF) service time. Furthermore, the overhead effect and the
related throughput reduction are studied. In order to enhance the network throughput at the MAC layer, two MAC DCF-based adaptive payload allocation approaches
are developed through introducing Lagrange optimization and studying equal data
transmission period
Contribución a la planificación sistémica de redes móviles 4G
El objetivo de esta Tesis consiste en el diseño, implementación y prueba de algoritmos, tanto convencionales –utilizados actualmente en la industria– como otros novedosos basados en Computación Evolutiva, que constituyan una contribución novedosa a la planificación sistémica de redes móviles LTE. En particular, se centra en el dimensionamiento estratégico de la red de acceso de LTE, debido a que constituye aproximadamente el 60% de la inversión total, e incluso una parte más elevada de los gastos OPEX (operating expense).
La Tesis establece una novedosa propuesta para el problema de asignación o asociación de usuarios a eNBs (evolved NBs) en LTE. La contribución es este aspecto es doble: por un lado, se plantea un nuevo método para asociar N_U usuarios a N_B eNBs en redes LTE. Consiste éste en modelar la asociación usuario-eNB como un problema de optimización combinatoria en el que la función a minimizar es una métrica novedosa conocida como “Tiempo de descarga total del sistema” –Download Time of the complete System (DTS). La minimización de DTS se traduce en una asignación de usuarios a celdas más eficiente que la que se consigue con métodos convencionales como el basado en maximizar CQI (Channel Quality Indicator) o en balanceo de carga (Load Balancing –LB–). Permite la asignación de usuarios desde celdas que, de otra forma, estarían sobrecargadas a otras con menos carga. Esto tiene un doble beneficio, tanto para el operador como para los usuarios. Por una parte, ayudar al operador de red a utilizar sus recursos de una manera más equilibrada y rentable. Por otra parte, la estrategia propuesta reduce el tiempo de descarga para la mayoría de los usuarios, e introduce cierta equidad en el reparto de recursos. La minimización de DTS es un problema de gran complejidad computacional. Ésta es justamente la razón que ha motivado la segunda contribución de esta Tesis: abordar el problema de la minimización de DTS mediante un algoritmo evolutivo (EA). El aspecto más interesante del EA propuesto es la forma en la que se realiza la codificación de las soluciones (asignaciones usuario-celda) candidatas. El cromosoma es un vector de dimensión N_U en el que cada elemento representa un usuario. El elemento en la posición j contiene cierta información sobre el usuario u_j. Esa información es un número entero que representa a qué eNB de los N_U disponibles se ha asignado dicho usuario. Los operadores de mutación, cruce y selección se han diseñado para que puedan trabajar con esta codificación. El operador de cruce, en particular, es un torneo de todos contra todos. El otro aspecto novedoso de la implementación del algoritmo evolutivo propuesto se encuentra en la población inicial. Como se tiene información de una solución sub-óptima del problema (la proporcionada por el método convencional basado en CQI –que asigna un usuario al eNB para el cual tiene mejor CQI–), se incluye ésta en la población inicial, y el resto de los individuos se genera, básicamente, aplicando los operadores de mutación y cruce sobre esa solución. En cualquier caso, la solución encontrada (asociación de cada usuario a un eNB) es mejor (menor DTS) que la asignación realizada con métodos convencionales.
El segundo conjunto de contribuciones de la Tesis consiste en el diseño de una herramienta de planificación estratégica LTE, centrada en el proceso de dimensionado de red en un entorno multiusuario y multiservicio, y en la que se ha integrado en módulo EA de asociación usuario-eNB. Mediante esta integración, dicha herramienta, permite realizar comparativas entre el enfoque propuesto de asignación en base al EA y otros métodos convencionales, integrados en la herramienta, como los basados en CQI y en LB. En concreto, la herramienta tiene (1) una parametrización sencilla y eficaz de los múltiples parámetros de entrada y de la ubicación inicial de los eNB, que (2) permite simular un entorno multi-servicio y multi-usuario, empleando (3) diferentes algoritmos de asociación usuario-eNB –como el propuesto en la Tesis– y (4) varios algoritmos de scheduling, de forma que (5) se garantiza el cumplimiento del requisito de Velocidad de Descarga Mínima de cada servicio. Para cumplir los requisitos (1)–(5), la herramienta calcula la velocidad media de los servicios ofertados, teniendo en cuenta los tiempos de descarga de cada uno de los usuarios. Si con el número de eNB, calculados previamente, se cumple el requisito de velocidad demandada por los distintos servicios simulados, entonces se dará́ por válido dicho valor. En caso de incumplimiento, se añaden eNBs de forma iterativa hasta cumplir el requisito anterior. Ninguna de las herramientas disponibles en el mercado, tanto comerciales como basadas en software libre, es capaz de cumplir estos requisitos.
Para cuantificar en qué medida la herramienta desarrollada, en general, y nuestra propuesta de asignación usuario-celda, en particular, son útiles en el dimensionamiento de LTE, se han llevado a cabo un conjunto amplio y variado de simulaciones, en diferentes escenarios realistas, tanto urbano como urbano denso, y se han comparado con dos métodos de asignación usuario-celda convencionales basados en CQI y en LB. Estos experimentos muestran que el método propuesto supera claramente a los convencionales, especialmente en áreas urbanas y urbana densa (entornos donde la asignación es más crítica en términos de capacidad) con macro-celdas de LTE, e incluso, en escenarios que modelan redes heterogéneas y ultra densas.
La herramienta y los algoritmos que se proponen en esta tesis pueden ayudar a los operadores a mejorar sus diseños previos al despliegue y a cuantificar la mejora potencial que se conseguiría en la red al añadir un nuevo nodo. Los resultados de la investigación realizada en la Tesis se han publicando en varias revistas y congresos internacionales