87 research outputs found
Low-latency Networking: Where Latency Lurks and How to Tame It
While the current generation of mobile and fixed communication networks has
been standardized for mobile broadband services, the next generation is driven
by the vision of the Internet of Things and mission critical communication
services requiring latency in the order of milliseconds or sub-milliseconds.
However, these new stringent requirements have a large technical impact on the
design of all layers of the communication protocol stack. The cross layer
interactions are complex due to the multiple design principles and technologies
that contribute to the layers' design and fundamental performance limitations.
We will be able to develop low-latency networks only if we address the problem
of these complex interactions from the new point of view of sub-milliseconds
latency. In this article, we propose a holistic analysis and classification of
the main design principles and enabling technologies that will make it possible
to deploy low-latency wireless communication networks. We argue that these
design principles and enabling technologies must be carefully orchestrated to
meet the stringent requirements and to manage the inherent trade-offs between
low latency and traditional performance metrics. We also review currently
ongoing standardization activities in prominent standards associations, and
discuss open problems for future research
Application of network coding in satellite broadcast and multiple access channels
Satellite broadcasting and relaying capabilities enable mobile broadcast systems over wide geographical areas, which opens large market possibilities for handheld, vehicular and fixed user terminals. The geostationary (GEO) satellite orbit is highly suited for such applications, as it spares the need for satellite terminals to track the movement of the spacecraft, with important savings in terms of complexity and cost. The large radius of the GEO orbit (more than 40000 km) has two main drawbacks. One is the large free space loss experienced by a signal traveling to or from the satellite, which limits the signal-to-noise ratio (SNR) margins in the link budget with respect to terrestrial systems. The second drawback of the GEO orbit is the large propagation delay (about 250 msec) that limits the use of feedback in both the forward (satellite to satellite terminal) and the reverse (satellite terminal to satellite) link. The limited margin protection causes loss of service availability in environments where there is no direct line of sight to the satellite, such as urban areas. The large propagation delay on its turn, together with the large terminal population size usually served by a GEO satellite, limit the use of feedback, which is at the basis of error-control. In the reverse link, especially in the case of fixed terminals, packet losses are mainly due to collisions, that severely limit the access to satellite services in case a random access scheme is adopted. The need for improvements and further understanding of these setups lead to the development of our work. In this dissertation we study the application of network coding to counteract the above mentioned channel impairments in satellite systems. The idea of using network coding stems from the fact that it allows to efficiently exploit the diversity, either temporal or spatial, present in the system.
In the following we outline the original contributions included in each of the chapters of the dissertation.
Chapter 3. This chapter deals with channel impairments in the forward link, and specifically with the problem of missing coverage in Urban environments for land mobile satellite (LMS) networks. By applying the Max-flow Min-cut theorem we derive a lower bound on the maximum coverage that can be achieved through cooperation. Inspired by this result, we propose a practical scheme, keeping in mind the compatibility with the DVB-SH standard. We developed a simulator in Matlab/C++ based on the physical layer abstraction and used it to test the performance gain of our scheme with a benchmark relaying scheme that does allow coding at packet level.
Chapter 4. The second chapter of contributions is devoted to the information theoretical
study of real-time streaming transmissions over fading channels with channel state information at the transmitter only. We introduce this new channel model and propose several transmission schemes, one of which is proved to be asymptotically optimal in terms of throughput. We also provide an upper bound on the achievable throughput for the proposed channel model and compare it numerically with the proposed schemes over a Rayleigh fading channel.
Chapter 5. Chapter 5 is devoted to the study of throughput and delay in non-real-time streaming transmission over block fading channels. We derive bounds on the throughput and the delay for this channel and propose different coding techniques based on time-sharing. For each of them we carry out an analytical study of the performance. Finally, we compare numerically the performance of the proposed schemes over a Rayleigh fading channel.
Chapter 6. In the last technical chapter we propose a collision resolution method for the return link based on physical layer network coding over extended Galois field (EGF). The proposed scheme extracts information from the colliding signals and achieves important gains with respect to Slotted ALOHA systems as well as with respect to other collision resolution schemes.Una de les característiques mes importants de les plataformes de comunicacions per satèl.lit és la seva capacitat de retransmetre senyals rebuts a un gran número de terminals. Això es fonamental en contextes com la difusió a terminals mòbils o la comunicació entre màquines.
Al mateix temps, la disponibilitat d’un canal de retorn permet la creació de sistemes de comunicacions per satèl.lit interactius que, en principi, poden arribar a qualsevol punt del planeta. Els satèl.lits Geoestacionaris son particularment adequats per a complir amb aquesta tasca. Aquest tipus de satèl.lits manté una posició fixa respecte a la Terra, estalviant als terminals terrestres la necessitat de seguir el seu moviment en el cel. Per altra banda, la gran distància que separa la Terra dels satèl.lits Geoestacionaris introdueix grans retrassos en les
comunicacions que, afegit al gran número de terminals en servei, limita l’ús de tècniques de retransmissió basades en acknowledgments en cas de pèrdua de paquets. Per tal de sol.lucionar el problema de la pèrdua de paquets, les tècniques més utilitzades son el desplegament de
repetidors terrestres, anomenats gap fillers, l’ús de codis de protecció a nivell de paquet i mecanismes proactius de resolució de col.lisions en el canal de retorn.
En aquesta tesi s’analitzen i s’estudien sol.lucions a problemes en la comunicació per satèl.lit tant en el canal de baixada com el de pujada. En concret, es consideren tres escenaris diferents.
El primer escenari es la transmissió a grans poblacions de terminals mòbils en enorns urbans, que es veuen particularment afectats per la pèrdua de paquets degut a l’obstrucció, per part dels edificis,
de la línia de visió amb el satèl.lit. La sol.lució que considerem consisteix en la utilització de la cooperació entre terminals. Una vegada obtinguda una mesura del guany que es pot assolir mitjançant cooperació en un model bàsic de xarxa, a través del teorema Max-flow Min-cut, proposem un esquema de cooperació compatible amb estàndards de comunicació existents.
El segon escenari que considerem es la transmissió de vídeo, un tipus de tràfic particularment sensible a la pèrdua de paquets i retards endògens als sistemes de comunicació per satèl.lit. Considerem els casos de transmissió en temps real i en diferit, des de la perspectiva de teoria de la informació, i estudiem diferents tècniques de codificació analítica i numèrica. Un dels resultats principals obtinguts es l’extensió del límit assolible de la capacitat ergòdica del canal en cas que el transmissor rebi les dades de manera gradual, enlloc de rebre-les totes a l’inici de la transmissió.
El tercer escenari que considerem es l’accés aleatori al satèl.lit. Desenvolupem un esquema de recuperació dels paquets perduts basat en la codificació de xarxa a nivell físic i en extensions a camps de Galois, amb resultats molt prometedors en termes de rendiment.
També estudiem aspectes relacionats amb la implementació pràctica d’aquest esquema
MULTIMEDIA ON GEOGRAPHIC NETWORK
In this thesis we investigate the topic of the multimedia contents distribution on a geo-
graphic network which is a rarefied and huge field. First of all we have to classify the main
parts necessary in the multimedia distribution on a geographic network. The main aspects
of a geographic network that will be highlighted in this thesis are: the mechanism used to
retrieve the sources of the multimedia content; in the case of the peer-to-peer network on
geographic network one of the most important mechanism is the query flooding protocol.
The kind of overlay network (peer-to-peer) used to distribute the multimedia content. The
usage of this overlay network in a multicast network. The security of the overlay network
over a geographic network.
Therefore the first topic which is investigated in this thesis is the query flooding protocol
that can be used in any kind of query operation on a peer-to-peer network. For this protocol
we achieve an analytical model through a complex analysis of the proxies network. In this
analysis we can see how the proxies permit an improvement in the performance with respect
to the routing operations in a generic network of routers. Moreover we address a simple
formulation and framework about the performance of the network with and without layer
7 (proxy) and we apply them in three different types of scenarios to show the advantages
achieved with the usage of proxies instead of routers.
Through the query flooding operation, each peer of the peer-to-peer network can achieve
the list of the peers that hold the desired multimedia content. In a multimedia content dis-
tribution system, after the previous step in which the list of the peers that hold the desired multimedia content is retrieved, it is necessary to establish the kind of peer-to-peer network
used to distribute this multimedia content to the peers that require it. Therefore the second
aspect analysed in this thesis, is how the peer-to-peer network is built so that it is possible to
provide the multimedia content to the vast majority of peers (that require this content) with
the minimum delay. The construction of the peer-to-peer networks used for the distribution
of the multimedia contents is not a very investigated field. Thus in this thesis we produce
new algorithms used to build peer-to-peer networks in an incremental way on asymmetric
and radio channel and we establish which algorithm is better with respect to the maximum
delay of the network, the maximization of the number of peers accepted in the network and
the minimization of the bit error probability of each peer of the peer-to-peer network.
In this thesis, we propose an usage of the overlay network (peer-to-peer network) in
a multicast network. We introduce an innovative mechanism that exploits the peer-to-peer
network to make reliable a standard unreliable multicast network. Moreover we present an
analytical model for this innovative mechanism.
Finally the last aspect of a geographic network is the security of the communications
among a group of peers. Thus to ensure the maximum level of security with secure commu-
nications among a group of three or more peers, in this thesis we propose a new protocol,
based on the Massey Omura protocol, which can allow the communications among the
peers of a peer-to-peer network in a secure way. Moreover we present the security prob-
lems of this Massey Omura Multiple Users Protocol and how it is possible to avoid these
issues through a specific encryption function and a specific decryption function by chang-
ing the encryption and decryption keys of each peer when the source peer changes. Finally
we present a new cryptography protocol which we use to share the decryption shared key
that is used in the Massey Omura Multiple Users Protocol
Split-Domain TCP-Friendly Protocol For MPEG-4 Adaptive Rate Video Streaming Over 3G Networks
The imminent inception of third-generation (3G) mobile communication networks offers an unprecedented opportunity for the development of video streaming applications through wireless Internet access. Different design challenges exist in implementing video streaming connections spanning both wired and wireless domains. A split-domain TCP-friendly streaming video transmission protocol is presented based on adaptive rate encoding in the MPEG-4 video format. Network simulations are conducted to demonstrate the benefits and viability of such a video streaming scheme over existing options. Further feature enhancements and refinements are necessary for the proposed protocol to achieve its full potential
BEYOND “OVER-THE-TOP” TELEVISION: CIRCUITS OF MEDIA DISTRIBUTION SINCE THE INTERNET
My dissertation analyzes the evolution of contemporary, cross-platform and international circuits of media distribution. A circuit of media distribution refers to both the circulation of media content as well as the underlying ecosystem that facilitates that circulation. In particular, I focus on the development of services for streaming television over the internet. I examine the circulation paths that either opened up or were foreclosed by companies that have been pivotal in shaping streaming economies: Aereo, Netflix, Twitter, Google, and Amazon. I identify the power brokers of contemporary media distribution, ranging from sectors of legacy television—for instance, broadcast networks, cable companies, and production studios—to a variety of new media and technology industries, including social media, e-commerce, internet search, and artificial intelligence. In addition, I analyze the ways in which these power brokers are reconfiguring content access. I highlight a series of technological, financial, geographic, and regulatory factors that authorize or facilitate access, in order to better understand how contemporary circuits of media distribution are constituted. I consider access as a regulatory issue, a foundation of business models, a design concern, and as a function of interoperability that facilitates communication amongst platforms, devices, and other systems of networked technologies.Doctor of Philosoph
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
Network Management and Control for mmWave Communications
Millimeter-wave (mmWave) is one of the key technologies that enables the next wireless
generation. mmWave offers a much higher bandwidth than sub-6GHz communications
which allows multi-gigabit-per-second rates. This also alleviates the scarcity of spectrum
at lower frequencies, where most devices connect through sub-6GHz bands. However new
techniques are necessary to overcome the challenges associated with such high frequencies.
Most of these challenges come from the high spatial attenuation at the mmWave band,
which requires new paradigms that differ from sub-6GHz communications. Most notably
mmWave telecommunications are characterized by the need to be directional in order to
extend the operational range. This is achieved by using electronically steerable antenna
arrays, that focus the energy towards the desired direction by combining each antenna
element constructively or destructively. Additionally, most of the energy comes from
the Line Of Sight (LOS) component which gives mmWave a quasi-optical behaviour
where signals can reflect off walls and still be used for communication. Some other
challenges that directional communications bring are mobility tracking, blockages and
misalignments due to device rotation. The IEEE 802.11ad amendment introduced wireless
telecommunications in the unlicensed 60 GHz band. It is the first standard to address
the limitations of mmWave. It does so by introducing new mechanisms at the Medium
Access Control (MAC) and Physical (PHY) layers. It introduces multi-band operation,
relay operation mode, hybrid channel access scheme, beam tracking and beam forming
among others.
In this thesis we present a series of works that aim to improve mmWave
telecommunications. First we give an overview of the intrinsic challenges of mmWave
telecommunications, by explaining the modifications to the MAC and PHY layers. This
sets the base for the rest of the thesis. Then do a comprehensive study on how mmWave
behaves with existing technologies, namely TCP. TCP is unable to distinguish losses
caused by congestion or by transmission errors caused by channel degradation. Since
mmWave is affected by blockages more than sub-6GHz technologies, we propose a set
of parameters that improve the channel quality even for mobile scenarios. The next job
focuses on reducing the initial access overhead of mmWave by using sub-6GHz information
to steer towards the desired direction. We start this work by doing a comprehensive High Frequency (HF) and Low Frequency (LF) correlation, analyzing the similarity of
the existing paths between the two selected frequencies. Then we propose a beam
steering algorithm that reduces the overhead to one third of the original time. Once
we have studied how to reduce the initial access overhead, we propose a mechanism
to reduce the beam tracking overhead. For this we propose an open platform based
on a Field Programmable Gate Arrays (FPGA) where we implement an algorithm that
completely removes the need to train on the Station (STA) side. This is achieved by
changing beam patterns on the STA side while the Access Point (AP) is sending the
preamble. We can change up to 10 beam patterns without losing connection and we reduce
the overhead by a factor of 8.8 with respect to the IEEE 802.11ad standard. Finally
we present a dual band location system based on Commercial-Off-The-Shelve (COTS)
devices. Locating the STA can improve the quality of the channel significantly, since the
AP can predict and react to possible blockages. First we reverse engineer existing 60
GHz enabled COTS devices to extract Channel State Information (CSI) and Fine Timing
Measurements (FTM) measurements, from which we can estimate angle and distance.
Then we develop an algorithm that is able to choose between HF and LF in order to
improve the overall accuracy of the system. We achieve less than 17 cm of median error
in indoor environments, even when some areas are Non Line Of Sight (NLOS).This work has been supported by IMDEA Networks Institute.Programa de Doctorado en Ingeniería Telemática por la Universidad Carlos III de MadridPresidente: Matthias Hollick.- Secretario: Vincenzo Mancuso.- Vocal: Paolo Casar
TCP performance enhancement in wireless networks via adaptive congestion control and active queue management
The transmission control protocol (TCP) exhibits poor performance when used in error-prone wireless networks. Remedy to this problem has been an active research area. However, a widely accepted and adopted solution is yet to emerge. Difficulties of an acceptable solution lie in the areas of compatibility, scalability, computational complexity and the involvement of intermediate routers and switches.
This dissertation rexriews the current start-of-the-art solutions to TCP performance enhancement, and pursues an end-to-end solution framework to the problem. The most noticeable cause of the performance degradation of TCP in wireless networks is the higher packet loss rate as compared to that in traditional wired networks. Packet loss type differentiation has been the focus of many proposed TCP performance enhancement schemes. Studies conduced by this dissertation research suggest that besides the standard TCP\u27s inability of discriminating congestion packet losses from losses related to wireless link errors, the standard TCP\u27s additive increase and multiplicative decrease (AIMD) congestion control algorithm itself needs to be redesigned to achieve better performance in wireless, and particularly, high-speed wireless networks. This dissertation proposes a simple, efficient, and effective end-to-end solution framework that enhances TCP\u27s performance through techniques of adaptive congestion control and active queue management. By end-to-end, it means a solution with no requirement of routers being wireless-aware or wireless-specific .
TCP-Jersey has been introduced as an implementation of the proposed solution framework, and its performance metrics have been evaluated through extensive simulations. TCP-Jersey consists of an adaptive congestion control algorithm at the source by means of the source\u27s achievable rate estimation (ARE) —an adaptive filter of packet inter-arrival times, a congestion indication algorithm at the links (i.e., AQM) by means of packet marking, and a effective loss differentiation algorithm at the source by careful examination of the congestion marks carried by the duplicate acknowledgment packets (DUPACK).
Several improvements to the proposed TCP-Jersey have been investigated, including a more robust ARE algorithm, a less computationally intensive threshold marking algorithm as the AQM link algorithm, a more stable congestion indication function based on virtual capacity at the link, and performance results have been presented and analyzed via extensive simulations of various network configurations. Stability analysis of the proposed ARE-based additive increase and adaptive decrease (AJAD) congestion control algorithm has been conducted and the analytical results have been verified by simulations. Performance of TCP-Jersey has been compared to that of a perfect , but not practical, TCP scheme, and encouraging results have been observed. Finally the framework of the TCP-Jersey\u27s source algorithm has been extended and generalized for rate-based congestion control, as opposed to TCP\u27s window-based congestion control, to provide a design platform for applications, such as real-time multimedia, that do not use TCP as transport protocol yet do need to control network congestion as well as combat packet losses in wireless networks.
In conclusion, the framework architecture presented in this dissertation that combines the adaptive congestion control and active queue management in solving the TCP performance degradation problem in wireless networks has been shown as a promising answer to the problem due to its simplistic design philosophy complete compatibility with the current TCP/IP and AQM practice, end-to-end architecture for scalability, and the high effectiveness and low computational overhead. The proposed implementation of the solution framework, namely TCP-Jersey is a modification of the standard TCP protocol rather than a completely new design of the transport protocol. It is an end-to-end approach to address the performance degradation problem since it does not require split mode connection establishment and maintenance using special wireless-aware software agents at the routers. The proposed solution also differs from other solutions that rely on the link layer error notifications for packet loss differentiation.
The proposed solution is also unique among other proposed end-to-end solutions in that it differentiates packet losses attributed to wireless link errors from congestion induced packet losses directly from the explicit congestion indication marks in the DUPACK packets, rather than inferring the loss type based on packet delay or delay jitter as in many other proposed solutions; nor by undergoing a computationally expensive off-line training of a classification model (e.g., HMM), or a Bayesian estimation/detection process that requires estimations of a priori loss probability distributions of different loss types.
The proposed solution is also scalable and fully compatible to the current practice in Internet congestion control and queue management, but with an additional function of loss type differentiation that effectively enhances TCP\u27s performance over error-prone wireless networks.
Limitations of the proposed solution architecture and areas for future researches are also addressed
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