9 research outputs found
Exponential bounds on error probability with Feedback
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 95-97).Feedback is useful in memoryless channels for decreasing complexity and increasing reliability; the capacity of the memoryless channels, however, can not be increased by feedback. For fixed length block codes even the decay rate of error probability with block length does not increase with feedback for most channel models. Consequently for making the physical layer more reliable for higher layers one needs go beyond the framework of fixed length block codes and consider relaxations like variable-length coding, error- erasure decoding. We strengthen and quantify this observation by investigating three problems. 1. Error-Erasure Decoding for Fixed-Length Block Codes with Feedback: Error-erasure codes with communication and control phases, introduced by Yamamoto and Itoh, are building blocks for optimal variable-length block codes. We improve their performance by changing the decoding scheme and tuning the durations of the phases, and establish inner bounds to the tradeoff between error exponent, erasure exponent and rate. We bound the loss of performance due to the encoding scheme of Yamamoto-Itoh from above by deriving outer bounds to the tradeoff between error exponent, erasure exponent and rate both with and without feedback. We also consider the zero error codes with erasures and establish inner and outer bounds to the optimal erasure exponent of zero error codes. In addition we present a proof of the long known fact that, the error exponent tradeoff between two messages is not improved with feedback. 2. Unequal Error Protection for Variable-Length Block Codes with Feedback: We use Kudrayashov's idea of implicit confirmations and explicit rejections in the framework of unequal error protection to establish inner bounds to the achievable pairs of rate vectors and error exponent vectors. Then we derive an outer bound that matches the inner bound using a new bounding technique. As a result we characterize the region of achievable rate vector and error exponent vector pairs for bit-wise unequal error protection problem for variable-length block codes with feedback. Furthermore we consider the single message message-wise unequal error protection problem and determine an analytical expression for the missed detection exponent in terms of rate and error exponent, for variable-length block codes with feedback. 3. Feedback Encoding Schemes for Fixed-Length Block Codes: We modify the analysis technique of Gallager to bound the error probability of feedback encoding schemes. Using the encoding schemes suggested by Zigangirov, D'yachkov and Burnashev we recover or improve all previously known lower bounds on the error exponents of fixedlength block codes.by Bariş Nakiboḡlu.Ph.D
Scalable Video Streaming with Prioritised Network Coding on End-System Overlays
PhDDistribution over the internet is destined to become a standard approach for live broadcasting
of TV or events of nation-wide interest. The demand for high-quality live video
with personal requirements is destined to grow exponentially over the next few years. Endsystem
multicast is a desirable option for relieving the content server from bandwidth bottlenecks
and computational load by allowing decentralised allocation of resources to the users
and distributed service management. Network coding provides innovative solutions for a
multitude of issues related to multi-user content distribution, such as the coupon-collection
problem, allocation and scheduling procedure. This thesis tackles the problem of streaming
scalable video on end-system multicast overlays with prioritised push-based streaming.
We analyse the characteristic arising from a random coding process as a linear channel
operator, and present a novel error detection and correction system for error-resilient decoding,
providing one of the first practical frameworks for Joint Source-Channel-Network
coding. Our system outperforms both network error correction and traditional FEC coding
when performed separately. We then present a content distribution system based on endsystem
multicast. Our data exchange protocol makes use of network coding as a way to
collaboratively deliver data to several peers. Prioritised streaming is performed by means
of hierarchical network coding and a dynamic chunk selection for optimised rate allocation
based on goodput statistics at application layer. We prove, by simulated experiments, the
efficient allocation of resources for adaptive video delivery. Finally we describe the implementation
of our coding system. We highlighting the use rateless coding properties, discuss
the application in collaborative and distributed coding systems, and provide an optimised
implementation of the decoding algorithm with advanced CPU instructions. We analyse
computational load and packet loss protection via lab tests and simulations, complementing
the overall analysis of the video streaming system in all its components
Channel Coding in Molecular Communication
This dissertation establishes and analyzes a complete molecular transmission system from
a communication engineering perspective. Its focus is on diffusion-based molecular communication
in an unbounded three-dimensional fluid medium. As a basis for the investigation
of transmission algorithms, an equivalent discrete-time channel model (EDTCM) is developed
and the characterization of the channel is described by an analytical derivation, a
random walk based simulation, a trained artificial neural network (ANN), and a proof of
concept testbed setup. The investigated transmission algorithms cover modulation schemes
at the transmitter side, as well as channel equalizers and detectors at the receiver side.
In addition to the evaluation of state-of-the-art techniques and the introduction of orthogonal
frequency-division multiplexing (OFDM), the novel variable concentration shift
keying (VCSK) modulation adapted to the diffusion-based transmission channel, the lowcomplex
adaptive threshold detector (ATD) working without explicit channel knowledge,
the low-complex soft-output piecewise linear detector (PLD), and the optimal a posteriori
probability (APP) detector are of particular importance and treated. To improve the
error-prone information transmission, block codes, convolutional codes, line codes, spreading
codes and spatial codes are investigated. The analysis is carried out under various
approaches of normalization and gains or losses compared to the uncoded transmission are
highlighted. In addition to state-of-the-art forward error correction (FEC) codes, novel line
codes adapted to the error statistics of the diffusion-based channel are proposed. Moreover,
the turbo principle is introduced into the field of molecular communication, where extrinsic
information is exchanged iteratively between detector and decoder. By means of an extrinsic
information transfer (EXIT) chart analysis, the potential of the iterative processing is
shown and the communication channel capacity is computed, which represents the theoretical
performance limit for the system under investigation. In addition, the construction of an
irregular convolutional code (IRCC) using the EXIT chart is presented and its performance
capability is demonstrated. For the evaluation of all considered transmission algorithms the
bit error rate (BER) performance is chosen. The BER is determined by means of Monte
Carlo simulations and for some algorithms by theoretical derivation
Progressive Source-Channel Coding for Multimedia Transmission over Noisy and Lossy Channels with and without Feedback
Rate-scalable or layered lossy source-coding is useful for
progressive transmission of multimedia sources, where the receiver can
reconstruct the source incrementally.
This thesis considers ``joint source-channel'' schemes
for such a progressive transmission, in the presence of
noise or loss, with and without the use of a feedback link.
First we design image communication schemes for memoryless and finite
state channels using limited and explicitly constrained use of
the feedback channel in the form of a variable incremental redundancy
Hybrid ARQ protocol. Constraining feedback allows a direct
comparison with schemes without feedback. Optimized feedback based
systems are shown to have useful gains.
Second, we develop a controlled Markov chain approach for constrained feedback Hybrid ARQ protocol design.
The proposed methodology allows the protocol to be chosen from a collection of signal flow graphs, and
also allows explicit control over the tradeoffs in throughput, reliability and complexity.
Next we consider progressive image transmission in
the absence of feedback. We assign unequal error protection to the bits of
a rate-scalable source-coder using rate compatible
channel codes. We show that, under the framework, the source and
channel bits can be ``scheduled'' in a single bitstream in such a way
that operational optimality is retained for different transmission
budgets, creating a rate-scalable joint source-channel coder.
Next we undertake the design of a joint source-channel decoder that
uses ``distortion aware'' ACK/NACK feedback generation. For
memoryless channels, and Type-I HARQ, the design of optimal ACK/NACK
generation and decoding by packet combining is cast and solved as a
sequential decision problem. We obtain dynamic programming based
optimal solutions and also propose suboptimal, lower complexity
distortion-aware decoders and feedback generation rules which
outperform conventional BER based rules such as
CRC-check.
Finally we design operational rate-distortion optimal ACK/NACK
feedback generation rules for transmitting a tree structured quantizer
over a memoryless channel. We show that the optimal feedback
generation rules are embedded, that is, they allow incremental
switching to higher rates during the transmission. Also, we
obtain the structure of the feedback generation rules in terms
of a feedback threshold function that simplifies the implementation
Advanced Trends in Wireless Communications
Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics
Méthodes de codage et d'estimation adaptative appliquées aux communications sans fil
Les recherches et les contributions présentées portent sur des techniques de traitement du signal appliquées aux communications sans fil. Elles s’articulent autour des points suivants : (1) l’estimation adaptative de canaux de communication dans différents contextes applicatifs, (2) la correction de bruit impulsionnel et la réduction du niveau de PAPR (Peak to Average Power Ratio) dans un système multi-porteuse, (3) l’optimisation de schémas de transmission pour la diffusion sur des canaux gaussiens avec/sans contrainte de sécurité, (4) l’analyse, l’interprétation et l’amélioration des algorithmes de décodage itératif par le biais de l’optimisation, de la théorie des jeux et des outils statistiques. L’accent est plus particulièrement mis sur le dernier thème