590 research outputs found
Design and development of mobile channel simulators using digital signal processing techniques
A mobile channel simulator can be constructed either in the time domain using a tapped delay line filter or in the frequency domain using the time variant transfer function of the channel. Transfer function modelling has many advantages over impulse response modelling. Although the transfer function channel model has been envisaged by several researchers as an alternative to the commonly employed tapped delay line model, so far it has not been implemented. In this work, channel simulators for single carrier and multicarrier OFDM system based on time variant transfer function of the channel have been designed and implemented using DSP techniques in SIMULINK. For a single carrier system, the simulator was based on Bello's transfer function channel model. Bello speculated that about 10Βτ(_MAX) frequency domain branches might result in a very good approximation of the channel (where в is the signal bandwidth and τ(_MAX) is the maximum excess delay of the multi-path channel). The simulation results showed that 10Bτ(_MAX) branches gave close agreement with the tapped delay line model(where Be is the coherence bandwidth). This number is π times higher than the previously speculated 10Bτ(_MAX).For multicarrier OFDM system, the simulator was based on the physical (PHY) layer standard for IEEE 802.16-2004 Wireless Metropolitan Area Network (WirelessMAN) and employed measured channel transfer functions at the 2.5 GHz and 3.5 GHz bands in the simulations. The channel was implemented in the frequency domain by carrying out point wise multiplication of the spectrum of OFDM time The simulator was employed to study BER performance of rate 1/2 and rate 3/4 coded systems with QPSK and 16-QAM constellations under a variety of measured channel transfer functions. The performance over the frequency selective channel mainly depended upon the frequency domain fading and the channel coding rate
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Performance evaluation of fixed WiMax physical layer under high fading channels
This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.A radio channel characteristic modelling is essential in every network planning. This project deals with the performance of WiMax networks in an outdoor environment while using fading channel models. The radio channels characteristics are analyzed by simulations have been done using Matlab programming. Stanford University Interim(SUI) Channels set was proposed to simulate the fixed broadband wireless access channel environments where IEEE 802.16d is to be deployed. It has six channel models that are grouped into three categories according to three typical different outdoor Terrains, in order to give a comprehensive study of fading channels on the overall performance of the system, WiMax system has been tested under SUI channels that modified into account for 30o directional antennas, with 90% cell coverage and with 99.9% reliability in its geographical covered area. Furthermore, in order to combat the fading which occurs in urban areas and improve the capacity and the throughput of the system, multiples antennas at both ends of communication link are used, the transmission gain obtained when using multiple antennas instead of only a single antenna. Space-time coding and maximum ratio combining for more than one transmit and receive antenna is implemented to allow performance investigations in various MIMO scenarios. It has been concluded that uses multiple antennas at the receiver offers a significant improvement of 3 dB of gain in the channel SNR. This thesis also contain implementation of all compulsory features of the WiMax OFDM physical layer specified in IEEE 802.16-2004 using Matlab coding. In order to combat the temporal variations in quality on a multipath fading channel, an adaptive modulation technique is used. This technique employs multiple modulation schemes to instantaneously adapt to the variations in the channel SNR, thus maximizing the system throughput and improving BER performance. WiMax transceiver has been tested with and without encoding and studied the effect of encoding on multipath channel. Testing the system with flexible channel bandwidth has been part of this thesis. Finally it has been explained in this thesis the affect of increasing the size of cyclic prefix on overall performance of WiMax system
Spectrum Sharing Methods in Coexisting Wireless Networks
Radio spectrum, the fundamental basis for wireless communication, is a finite resource. The development of the expanding range of radio based devices and services in recent years makes the spectrum scarce and hence more costly under the paradigm of extensive regulation for licensing. However, with mature technologies and with their continuous improvements it becomes apparent that tight licensing might no longer be required for all wireless services. This is from where the concept of utilizing the unlicensed bands for wireless communication originates. As a promising step to reduce the substantial cost for radio spectrum, different wireless technology based networks are being deployed to operate in the same spectrum bands, particularly in the unlicensed bands, resulting in coexistence. However, uncoordinated coexistence often leads to cases where collocated wireless systems experience heavy mutual interference. Hence, the development of spectrum sharing rules to mitigate the interference among wireless systems is a significant challenge considering the uncoordinated, heterogeneous systems. The requirement of spectrum sharing rules is tremendously increasing on the one hand to fulfill the current and future demand for wireless communication by the users, and on the other hand, to utilize the spectrum efficiently. In this thesis, contributions are provided towards dynamic and cognitive spectrum sharing with focus on the medium access control (MAC) layer, for uncoordinated scenarios of homogeneous and heterogeneous wireless networks, in a micro scale level, highlighting the QoS support for the applications. This thesis proposes a generic and novel spectrum sharing method based on a hypothesis: The regular channel occupation by one system can support other systems to predict the spectrum opportunities reliably. These opportunities then can be utilized efficiently, resulting in a fair spectrum sharing as well as an improving aggregated performance compared to the case without having special treatment. The developed method, denoted as Regular Channel Access (RCA), is modeled for systems specified by the wireless local resp. metropolitan area network standards IEEE 802.11 resp. 802.16. In the modeling, both systems are explored according to their respective centrally controlled channel access mechanisms and the adapted models are evaluated through simulation and results analysis. The conceptual model of spectrum sharing based on the distributed channel access mechanism of the IEEE 802.11 system is provided as well. To make the RCA method adaptive, the following enabling techniques are developed and integrated in the design: a RSS-based (Received Signal Strength based) detection method for measuring the channel occupation, a pattern recognition based algorithm for system identification, statistical knowledge based estimation for traffic demand estimation and an inference engine for reconfiguration of resource allocation as a response to traffic dynamics. The advantage of the RCA method is demonstrated, in which each competing collocated system is configured to have a resource allocation based on the estimated traffic demand of the systems. The simulation and the analysis of the results show a significant improvement in aggregated throughput, mean delay and packet loss ratio, compared to the case where legacy wireless systems coexists. The results from adaptive RCA show its resilience characteristics in case of dynamic traffic. The maximum achievable throughput between collocated IEEE 802.11 systems applying RCA is provided by means of mathematical calculation. The results of this thesis provide the basis for the development of resource allocation methods for future wireless networks particularly emphasized to operate in current unlicensed bands and in future models of the Open Spectrum Alliance
Handover analysis over mobile WiMAX technology.
As new mobile devices and mobile applications continue to growth, so does the data traffic demand for broadband services access and the user needs toward mobility, thereby, wireless application became today the fastest solution and lowest cost implementation unlike traditional wired deployment such as optical fibers and digital lines. WiMAX technology satisfies this gap through its high network performance over the air interface and high data rates based on the IEEE 802.16-2004 standards, this original specification does not support mobility.
Therefore, the IEEE introduces a new standard that enables mobility profiles under 802.16e-2005, from which three different types of handovers process are introduced as hard handover (HHO), macro diversity handover (MDHO) and fast base station switching (FBSS) handover.
The objective of this master thesis is to analyze how the handover process affects network performance. The analysis propose three scenarios, built over OPNET simulator to measure the most critical wireless parameter and performance indicator such as throughput, handover success rate, packet drop, delay and network usage.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format
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
Performance analysis of 4G wireless networks using system level simulator
Doutoramento em Engenharia ElectrotécnicaIn the last decade, mobile wireless communications have witnessed an explosive
growth in the user’s penetration rate and their widespread deployment around the
globe. In particular, a research topic of particular relevance in telecommunications
nowadays is related to the design and implementation of mobile communication
systems of 4th generation (4G). 4G networks will be characterized by the support
of multiple radio access technologies in a core network fully compliant with the
Internet Protocol (all IP paradigms). Such networks will sustain the stringent
quality of service (QoS) requirements and the expected high data rates from the
type of multimedia applications (i.e. YouTube and Skype) to be available in the
near future. Therefore, 4G wireless communications system will be of paramount
importance on the development of the information society in the near future.
As 4G wireless services will continue to increase, this will put more and more
pressure on the spectrum availability. There is a worldwide recognition that
methods of spectrum managements have reached their limit and are no longer
optimal, therefore new paradigms must be sought. Studies show that most of the
assigned spectrum is under-utilized, thus the problem in most cases is inefficient
spectrum management rather spectrum shortage. There are currently trends
towards a more liberalized approach of spectrum management, which are tightly
linked to what is commonly termed as Cognitive Radio (CR).
Furthermore, conventional deployment of 4G wireless systems (one BS in cell and
mobile deploy around it) are known to have problems in providing fairness (users
closer to the BS are more benefited relatively to the cell edge users) and in
covering some zones affected by shadowing, therefore the use of relays has been
proposed as a solution.
To evaluate and analyse the performances of 4G wireless systems software tools
are normally used. Software tools have become more and more mature in recent
years and their need to provide a high level evaluation of proposed algorithms and
protocols is now more important. The system level simulation (SLS) tools provide
a fundamental and flexible way to test all the envisioned algorithms and protocols
under realistic conditions, without the need to deal with the problems of live
networks or reduced scope prototypes. Furthermore, the tools allow network
designers a rapid collection of a wide range of performance metrics that are useful
for the analysis and optimization of different algorithms.
This dissertation proposes the design and implementation of conventional system
level simulator (SLS), which afterwards enhances for the 4G wireless technologies
namely cognitive Radios (IEEE802.22) and Relays (IEEE802.16j). SLS is then
used for the analysis of proposed algorithms and protocols.FC
EVM as generic QoS trigger for heterogeneous wieless overlay network
Fourth Generation (4G) Wireless System will integrate heterogeneous wireless
overlay systems i.e. interworking of WLAN/ GSM/ CDMA/ WiMAX/ LTE/ etc with
guaranteed Quality of Service (QoS) and Experience (QoE).QoS(E) vary from
network to network and is application sensitive. User needs an optimal mobility
solution while roaming in Overlaid wireless environment i.e. user could
seamlessly transfer his session/ call to a best available network bearing
guaranteed Quality of Experience. And If this Seamless transfer of session is
executed between two networks having different access standards then it is
called Vertical Handover (VHO). Contemporary VHO decision algorithms are based
on generic QoS metrics viz. SNR, bandwidth, jitter, BER and delay. In this
paper, Error Vector Magnitude (EVM) is proposed to be a generic QoS trigger for
VHO execution. EVM is defined as the deviation of inphase/ quadrature (I/Q)
values from ideal signal states and thus provides a measure of signal quality.
In 4G Interoperable environment, OFDM is the leading Modulation scheme (more
prone to multi-path fading). EVM (modulation error) properly characterises the
wireless link/ channel for accurate VHO decision. EVM depends on the inherent
transmission impairments viz. frequency offset, phase noise,
non-linear-impairment, skewness etc. for a given wireless link. Paper provides
an insight to the analytical aspect of EVM & measures EVM (%) for key
management subframes like association/re-association/disassociation/ probe
request/response frames. EVM relation is explored for different possible
NAV-Network Allocation Vectors (frame duration). Finally EVM is compared with
SNR, BER and investigation concludes EVM as a promising QoS trigger for OFDM
based emerging wireless standards.Comment: 12 pages, 7 figures, IJWMN 2010 august issue vol. 2, no.
Assessment and Real Time Implementation of Wireless Communications Systems and Applications in Transportation Systems
Programa Oficial de Doutoramento en Tecnoloxías da Información e das Comunicacións en Redes Móbiles. 5029V01[Resumo]
Os sistemas de comunicación sen fíos de cuarta e quinta xeración (4G e 5G) utilizan unha capa física
(PHY) baseada en modulacións multiportadora para a transmisión de datos cun gran ancho de banda.
Este tipo de modulacións proporcionan unha alta eficiencia espectral á vez que permiten corrixir de
forma sinxela os efectos da canle radio.
Estes sistemas utilizan OFDMA como mecanismo para a repartición dos recursos radio dispoñibles
entre os diferentes usuarios. Este repartimento realízase asignando un subconxunto de subportadoras a
cada usuario nun instante de tempo determinado. Isto aporta unha gran flexibilidade ó sistema que lle
permite adaptarse tanto ós requisitos de calidade de servizo dos usuarios como ó estado da canle radio.
A capa de acceso ó medio (MAC) destes sistemas encárgase de configurar os diversos parámetros
proporcionados pola capa física OFDMA, ademais de xestionar os diversos fluxos de información de
cada usuario, transformando os paquetes de capas superiores en paquetes da capa física.
Neste traballo estúdase o deseño e implementación das capas MAC e PHY de sistemas de
comunicación 4G ademais da súa aplicabilidade en sistemas de transporte ferroviarios.
Por unha parte, abórdase o deseño e implementación en tempo real do estándar WiMAX. Estúdanse
os mecanismos necesarios para establecer comunicacións bidireccionais entre unha estación base e
múltiples dispositivos móbiles. Ademais, estúdase como realizar esta implementación nunha arquitectura
hardware baseada en DSPs e FPGAs, na que se implementan as capas MAC e PHY. Dado que esta
arquitectura ten uns recursos computacionais limitados, tamén se estudan as necesidades de cada módulo
do sistema para poder garantir o funcionamento en tempo real do sistema completo.
Por outra parte, tamén se estuda a aplicabilidade dos sistemas 4G a sistemas de transporte públicos.
Os sistemas de comunicacións e sinalización son unha parte vital para os sistemas de transporte
ferroviario e metro. As comunicacións sen fíos utilizadas por estes sistemas deben ser robustas e
proporcionar unha alta fiabilidade para permitir a supervisión, control e seguridade do tráfico ferroviario.
Para levar a cabo esta avaliación de viabilidade realízanse simulacións de redes de comunicacións
LTE en contornos de transporte ferroviarios, comprobando o cumprimento dos requisitos de fiabilidade
e seguridade. Realízanse diferentes simulacións do sistema de comunicacións para poder ser avaliadas e
seleccionar a configuración e arquitectura do sistema máis axeitada en función do escenario considerado.
Tamén se efectúan simulacións de redes baseadas en Wi-Fi, dado que é a solución máis utilizada nos
metros, para confrontar os resultados cos obtidos para LTE.
Para que os resultados das simulacións sexan realistas débense empregar modelos de propagación
radio axeitados. Nas simulacións utilízanse tanto modelos deterministas como modelos baseados nos
resultados de campañas de medida realizadas nestes escenarios.
Nas simulacións empréganse os diferentes fluxos de información destes escenarios para comprobar
que se cumpren os requisitos de calidade de servicio (QoS). Por exemplo, os fluxos críticos para o control
ferroviario, como European Train Control System (ETCS) ou Communication-Based Train Control (CBTC), necesitan unha alta fiabilidade e un retardo mínimo nas comunicacións para garantir o correcto
funcionamento do sistema.[Resumen]
Los sistemas de comunicación inalámbricos de cuarta y quinta generación (4G y 5G) utilizan una capa
física (PHY) basada en modulaciones multiportadora para la transmisión de datos con un gran ancho
de banda. Este tipo de modulaciones han demostrado tener una alta eficiencia espectral a la vez que
permiten corregir de forma sencilla los efectos del canal radio.
Estos sistemas utilizan OFDMA como mecanismo para el reparto de los recursos radio disponibles
entre los diferentes usuarios. Este reparto se realiza asignando un subconjunto de subportadoras a cada
usuario en un instante de tiempo determinado. Esto aporta una gran flexibilidad al sistema que le permite
adaptarse tanto a los requisitos de calidad de servicio de los usuarios como al estado del canal radio.
La capa de acceso al medio (MAC) de estos sistemas se encarga de configurar los diversos parámetros
proporcionados por la capa física OFDMA, además de gestionar los diversos flujos de información de
cada usuario, transformando los paquetes de capas superiores en paquetes de la capa física.
En este trabajo se estudia el diseño e implementación de las capas MAC y PHY de sistemas de
comunicación 4G además de su aplicabilidad en sistemas de transporte ferroviarios.
Por una parte, se aborda el diseño e implementación en tiempo real del estándar WiMAX. Se
estudian los mecanismos necesarios para establecer comunicaciones bidireccionales entre una estación
base y múltiples dispositivos móviles. Además, se estudia cómo realizar esta implementación en una
arquitectura hardware basada en DSPs y FPGAs, en la que se implementan las capas MAC y PHY. Dado
que esta arquitectura tiene unos recursos computacionales limitados, también se estudian las necesidades
de cada módulo del sistema para poder garantizar el funcionamiento en tiempo real del sistema completo.
Por otra parte, también se estudia la aplicabilidad de los sistemas 4G a sistemas de transporte
públicos. Los sistemas de comunicaciones y señalización son una parte vital para los sistemas de
transporte ferroviario y metro. Las comunicaciones inalámbricas utilizadas por estos sistemas deben ser
robustas y proporcionar una alta fiabilidad para permitir la supervisión, control y seguridad del tráfico
ferroviario.
Para llevar a cabo esta evaluación de viabilidad se realizan simulaciones de redes de comunicaciones
LTE en entornos de transporte ferroviarios, comprobando si se cumplen los requisitos de fiabilidad y
seguridad. Se realizan diferentes simulaciones del sistema de comunicaciones para poder ser evaluados y
seleccionar la configuración y arquitectura del sistema más adecuada en función del escenario planteado.
También se efectúan simulaciones de redes basadas en Wi-Fi, dado que es la solución más utilizada en
los metros, para comparar los resultados con los obtenidos para LTE.
Para que los resultados de las simulaciones sean realistas se deben utilizar modelos de propagación
radio apropiados. En las simulaciones se utilizan tanto modelos deterministas como modelos basados en
los resultados de campañas de medida realizadas en estos escenarios.
En las simulaciones se utilizan los diferentes flujos de información de estos escenarios para
comprobar que se cumplen sus requisitos de calidad de servicio. Por ejemplo, los flujos críticos para el control ferroviario, como European Train Control System (ETCS) o Communication-Based Train
Control (CBTC), necesitan una alta fiabilidad y un retardo bajo en las comunicaciones para garantizar el
correcto funcionamiento del sistema.[Abstract]
The fourth and fifth generation wireless communication systems (4G and 5G) use a physical layer (PHY)
based on multicarrier modulations for data transmission using high bandwidth. This type of modulations
has shown to provide high spectral efficiency while allowing low complexity radio channel equalization.
These systems use OFDMA as a mechanism for distributing the available radio resources among
different users. This allocation is done by assigning a subset of subcarriers to each user in a given instant
of time. This provides great flexibility to the system that allows it to adapt to both the quality of service
requirements of users and the radio channel state.
The media access layer (MAC) of these systems is in charge of configuring the multiple OFDMA
PHY layer parameters, in addition to managing the data flows of each user, transforming the higher layer
packets into PHY layer packets.
This work studies the design and implementation of MAC and PHY layers of 4G communication
systems as well as their applicability in rail transport systems.
On the one hand, the design and implementation in real time of the WiMAX standard is addressed.
The required mechanisms to establish bidirectional communications between a base station and several
mobile devices are also evaluated. Moreover, a MAC layer and PHY layer implementation is
presented, using a hardware architecture based in DSPs and FPGAs. Since this architecture has limited
computational resources, the requirements of each processing block of the system are also studied in
order to guarantee the real time operation of the complete system.
On the other hand, the applicability of 4G systems to public transportation systems is also studied.
Communications and signaling systems are a vital part of rail and metro transport systems. The
wireless communications used by these systems must be robust and provide high reliability to enable
the supervision, control and safety of rail traffic.
To carry out this feasibility assessment, LTE communications network simulations are performed in
rail transport environments to verify that reliability and safety requirements are met. Several simulations
are carried out in order to evaluate the system performance and select the most appropriate system
configuration in each case. Simulations of Wi-Fi based networks are also carried out, since it is the
most used solution in subways, to compare the results with those obtained for LTE.
To perform the simulations correctly, appropriate radio propagation models must be used. Both
deterministic models and models based on the results of measurement campaigns in these scenarios are
used in the simulations.
The simulations use the different information flows present in the railway transportation systems to
verify that its quality of service requirements are met. For example, critical flows for railway control,
such as the European Train Control System (ETCS) or Communication-Based Train Control (CBTC),
require high reliability and low delay communications to ensure the proper functioning of the system
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