1,064 research outputs found
Adaptive OFDM Index Modulation for Two-Hop Relay-Assisted Networks
In this paper, we propose an adaptive orthogonal frequency-division
multiplexing (OFDM) index modulation (IM) scheme for two-hop relay networks. In
contrast to the traditional OFDM IM scheme with a deterministic and fixed
mapping scheme, in this proposed adaptive OFDM IM scheme, the mapping schemes
between a bit stream and indices of active subcarriers for the first and second
hops are adaptively selected by a certain criterion. As a result, the active
subcarriers for the same bit stream in the first and second hops can be varied
in order to combat slow frequency-selective fading. In this way, the system
reliability can be enhanced. Additionally, considering the fact that a relay
device is normally a simple node, which may not always be able to perform
mapping scheme selection due to limited processing capability, we also propose
an alternative adaptive methodology in which the mapping scheme selection is
only performed at the source and the relay will simply utilize the selected
mapping scheme without changing it. The analyses of average outage probability,
network capacity and symbol error rate (SER) are given in closed form for
decode-and-forward (DF) relaying networks and are substantiated by numerical
results generated by Monte Carlo simulations.Comment: 30 page
Efficient PHY Layer Abstraction under Imperfect Channel Estimation
As most existing work investigate the PHY layer abstraction under an
assumption of perfect channel estimation, it may become unreliable if there
exists channel estimation error in a real communication system. This letter
improves an efficient PHY layer method, EESM-log-SGN PHY layer abstraction, by
considering the presence of channel estimation error. We develop two methods
for implementing the EESM-log-SGN PHY abstraction under imperfect channel
estimation. We show that the effective SINR is not impacted by the channel
estimation error under multiple-input and single-output (MISO)/single-input and
single-output (SISO) configuration, which is also verified by the full PHY
simulation. The developed methods are then validated under different orthogonal
frequency division multiplexing (OFDM) scenarios.Comment: Submitted to IEEE Wireless Communications Letters. 5 pages, 7 figure
Sub-Nanosecond Time of Flight on Commercial Wi-Fi Cards
Time-of-flight, i.e., the time incurred by a signal to travel from
transmitter to receiver, is perhaps the most intuitive way to measure distances
using wireless signals. It is used in major positioning systems such as GPS,
RADAR, and SONAR. However, attempts at using time-of-flight for indoor
localization have failed to deliver acceptable accuracy due to fundamental
limitations in measuring time on Wi-Fi and other RF consumer technologies.
While the research community has developed alternatives for RF-based indoor
localization that do not require time-of-flight, those approaches have their
own limitations that hamper their use in practice. In particular, many existing
approaches need receivers with large antenna arrays while commercial Wi-Fi
nodes have two or three antennas. Other systems require fingerprinting the
environment to create signal maps. More fundamentally, none of these methods
support indoor positioning between a pair of Wi-Fi devices
without~third~party~support.
In this paper, we present a set of algorithms that measure the time-of-flight
to sub-nanosecond accuracy on commercial Wi-Fi cards. We implement these
algorithms and demonstrate a system that achieves accurate device-to-device
localization, i.e. enables a pair of Wi-Fi devices to locate each other without
any support from the infrastructure, not even the location of the access
points.Comment: 14 page
End-to-End Simulation of 5G mmWave Networks
Due to its potential for multi-gigabit and low latency wireless links,
millimeter wave (mmWave) technology is expected to play a central role in 5th
generation cellular systems. While there has been considerable progress in
understanding the mmWave physical layer, innovations will be required at all
layers of the protocol stack, in both the access and the core network.
Discrete-event network simulation is essential for end-to-end, cross-layer
research and development. This paper provides a tutorial on a recently
developed full-stack mmWave module integrated into the widely used open-source
ns--3 simulator. The module includes a number of detailed statistical channel
models as well as the ability to incorporate real measurements or ray-tracing
data. The Physical (PHY) and Medium Access Control (MAC) layers are modular and
highly customizable, making it easy to integrate algorithms or compare
Orthogonal Frequency Division Multiplexing (OFDM) numerologies, for example.
The module is interfaced with the core network of the ns--3 Long Term Evolution
(LTE) module for full-stack simulations of end-to-end connectivity, and
advanced architectural features, such as dual-connectivity, are also available.
To facilitate the understanding of the module, and verify its correct
functioning, we provide several examples that show the performance of the
custom mmWave stack as well as custom congestion control algorithms designed
specifically for efficient utilization of the mmWave channel.Comment: 25 pages, 16 figures, submitted to IEEE Communications Surveys and
Tutorials (revised Jan. 2018
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
Models of Control Channels in the LTE System
Dizertační práce se zabývá zpracováním signálu fyzických řídicích kanálů systému LTE a vyšetřováním bitové chybovosti při přenosu řídicí informace z vysílače do přijímače v závislosti na podmínkách příjmu. Práce je rozdělena do dvou hlavních částí. První část práce je zaměřena na simulaci přenosu řídicí informace LTE v základním pásmu. Jsou zde prezentovány vytvořené simulátory řídicích kanálů ve směru uplink i downlink. Simulace jsou provedeny pro všechny druhy nastavení systému a základní modely přenosového prostředí. Jsou zde popsány výsledky vlivu použití MIMO technologií na kvalitu příjmu řídicí informace především v únikových kanálech. Druhá část práce je zaměřena na možnost nasazení systému LTE ve sdíleném pásmu ISM (2.4 GHz). Jsou zde představeny základní koncepce použití, na jejichž základě je vytvořen scénář simulací. Kapitola dále popisuje tvorbu simulátoru koexistence LTE a systému Wi-Fi v přeneseném pásmu ISM 2.4GHz. Jsou zde uvedeny výsledky simulací koexistence LTE a rušivého systému Wi-Fi provedených dle vytvořeného scénáře. Výsledky simulací koexistence LTE a Wi-Fi jsou ověřeny měřením v laboratorních podmínkách. Toto porovnání je důležité z hlediska optimalizace simulátoru koexistence. Dle výsledků obou typů simulací a měření jsou stanovena provozní doporučení, která mají přispět k bezpečnému a spolehlivému vysílání a příjmu řídicích informací LTE i při nepříznivých podmínkách příjmu.The doctoral thesis is focused on a signal processing in the LTE physical control channels and performance analysis of control information transmission according to receiving conditions. The thesis is divided into two parts. The first part deals with simulation of the transmission of control information in baseband. The created simulators for uplink and downlink are presented. The simulations are performed for all possible system settings and various channel models. The MIMO influence on a quality of control information reception under fading channels is also presented. The second part of the thesis is focused on LTE utilization in shared channel ISM (2.4 GHz). The basic LTE application concept for ISM band is presented. This concept is fundamental to created simulation scenario. The chapter also presents the LTE and Wi-Fi coexistence simulator in 2.4 GHz ISM passband. The coexistence simulation are presented according to simulation scenario and the results are shown. The simulated coexistence analysis results are verified in laboratory environment. The comparison of the simulated and the measured coexistence analysis results is crucial for further optimization of the coexistence simulator. Recommendations for optimal and reliable operation of LTE are specified according to the simulated and the measured results. Recommendations should be useful to the reliable transmission of LTE control information in bad receiving conditions.
Performance Comparison of Dual Connectivity and Hard Handover for LTE-5G Tight Integration in mmWave Cellular Networks
MmWave communications are expected to play a major role in the Fifth
generation of mobile networks. They offer a potential multi-gigabit throughput
and an ultra-low radio latency, but at the same time suffer from high isotropic
pathloss, and a coverage area much smaller than the one of LTE macrocells. In
order to address these issues, highly directional beamforming and a very
high-density deployment of mmWave base stations were proposed. This Thesis aims
to improve the reliability and performance of the 5G network by studying its
tight and seamless integration with the current LTE cellular network. In
particular, the LTE base stations can provide a coverage layer for 5G mobile
terminals, because they operate on microWave frequencies, which are less
sensitive to blockage and have a lower pathloss. This document is a copy of the
Master's Thesis carried out by Mr. Michele Polese under the supervision of Dr.
Marco Mezzavilla and Prof. Michele Zorzi. It will propose an LTE-5G tight
integration architecture, based on mobile terminals' dual connectivity to LTE
and 5G radio access networks, and will evaluate which are the new network
procedures that will be needed to support it. Moreover, this new architecture
will be implemented in the ns-3 simulator, and a thorough simulation campaign
will be conducted in order to evaluate its performance, with respect to the
baseline of handover between LTE and 5G.Comment: Master's Thesis carried out by Mr. Michele Polese under the
supervision of Dr. Marco Mezzavilla and Prof. Michele Zorz
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