Protograph Design for Spatially-Coupled Codes to Attain an Arbitrary Diversity Order

This work focuses on the design of SC-LDPC codes for transmission over non-ergodic, block-fading channels. Our main contribution is an algorithm, allowing to start from a (J,K )-regular, uncoupled LDPC ensemble, from which one can recursively build up a protograph-based SC-LDPC ensemble having any target diversity order d. The diversity order is achieved assuming a low-complexity iterative decoding algorithm. The increase of d comes at the cost of increasing the memory constraint (i.e., the coupling parameter) of the SC-LDPC ensemble

On Cyclic Polar Codes and the Burst Erasure Performance of Spatially-Coupled LDPC Codes

In this thesis, we produce our work on two of the state-of-the-art techniques in modern coding theory: polar codes and spatially-coupled LDPC codes. Polar codes were introduced in 2009 and proven to achieve the symmetric capacity of any binary-input discrete memoryless channel under low-complexity successive cancellation decoding. Since then, finite length (non-asymptotic) performance has been the primary concern with respect to polar codes. In this work, we construct cyclic polar codes based on a mixed-radix Cooley-Tukey decomposition of the Galois field Fourier transform. The main results are: we can, for the first time, construct, encode and decode polar codes that are cyclic, with their blocklength being arbitrary; for a given target block erasure rate, we can achieve significantly higher code rates on the erasure channel than the original polar codes, at comparable blocklengths; on the symmetric channel with only errors, we can perform much better than equivalent rate Reed-Solomon codes with the same blocklength, by using soft-decision decoding; and, since the codes are subcodes of higher rate RS codes, a RS decoder can be used if suboptimal performance suffices for the application as a trade-o_ for higher decoding speed. The programs developed for this work can be accessed at https://github.com/nrenga/cyclic_polar. In 2010, it was shown that spatially-coupled low-density parity-check (LDPC) codes approach the capacity of binary memoryless channels, asymptotically, with belief-propagation (BP) decoding. In our work, we are interested in the finite length average performance of randomly coupled LDPC ensembles on binary erasure channels with memory. The significant contributions of this work are: tight lower bounds for the block erasure probability (PB) under various scenarios for the burst pattern; bounds focused on practical scenarios where a burst affects exactly one of the coupled codes; expected error floor for the bit erasure probability (Pb) on the binary erasure channel; and, characterization of the performance of random regular ensembles, on erasure channels, with a single vector describing distinct types of size-2 stopping sets. All these results are verified using Monte-Carlo simulations. Further, we show that increasing variable node degree combined with expurgation can improve PB by several orders of magnitude in the number of bits per coupled code

Lattice-Based Coding Schemes for Wireless Relay Networks

Compute-and-forward is a novel relaying paradigm in wireless communications in which relays in a network directly compute or decode functions of signals transmitted from multiple transmitters and forward them to a central destination. In this dissertation, we study three problems related to compute-and-forward. In the first problem, we consider the use of lattice codes for implementing a compute-and-forward protocol in wireless networks when channel state information is not available at the transmitter. We propose the use of lattice codes over Eisenstein integers and we prove the existence of a sequence of lattices over Eisenstein integers which are good for quantization and achieve capacity over an additive white Gaussian noise (AWGN) channel. Using this, we show that the information rates achievable with nested lattice codebooks over Eisenstein integers are higher than those achievable with nested lattice codebooks over integers considered by Nazer and Gastpar in [6] in the average sense. We also propose a separation-based framework for compute-and-forward that is based on the concatenation of a non-binary linear code with a modulation scheme derived from the ring of Eisenstein integers, which enables the coding gain and shaping gain to be separated, resulting in significantly higher theoretically achievable computation rates. In the second problem, we construct lattices based on spatially-coupled low-density parity check (LDPC) codes and empirically show that such lattices can approach the Poltyrev limit very closely for the point-to-point unconstrained AWGN channel. We then employ these lattices to implement a compute-and-forward protocol and empirically show that these lattices can approach the theoretically achievable rates closely. In the third problem, we present a new coding scheme based on concatenating a newly introduced class of lattice codes called convolutional lattice codes with LDPC codes, which we refer to as concatenated convolutional lattice codes (CCLS) and study their application to compute-and-forward (CF). The decoding algorithm for CCLC is based on an appropriate combination of the stack decoder with a message passing algorithm, and is computationally much more efficient than the conventional decoding algorithm for convolutional lattice codes. Simulation results show that CCLC can approach the point-to-point uniform input AWGN capacity very closely with soft decision decoding. Also, we show that they possess the required algebraic structure which makes them suitable for recovering linear combinations (over a finite field) of the transmitted signals in a multiple access channel. This facilitates their use as a coding scheme for the compute-and-forward paradigm. Simulation results show that CCLC can approach theoretically achievable rates very closely when implemented for the compute-and-forward

Compute-and-Forward Relay Networks with Asynchronous, Mobile, and Delay-Sensitive Users

We consider a wireless network consisting of multiple source nodes, a set of relays and a destination node. Suppose the sources transmit their messages simultaneously to the relays and the destination aims to decode all the messages. At the physical layer, a conventional approach would be for the relay to decode the individual message one at a time while treating rest of the messages as interference. Compute-and-forward is a novel strategy which attempts to turn the situation around by treating the interference as a constructive phenomenon. In compute-and-forward, each relay attempts to directly compute a combination of the transmitted messages and then forwards it to the destination. Upon receiving the combinations of messages from the relays, the destination can recover all the messages by solving the received equations. When identical lattice codes are employed at the sources, error correction to integer combination of messages is a viable option by exploiting the algebraic structure of lattice codes. Therefore, compute-and-forward with lattice codes enables the relay to manage interference and perform error correction concurrently. It is shown that compute-and-forward exhibits substantial improvement in the achievable rate compared with other state-of-the-art schemes for medium to high signal-to-noise ratio regime. Despite several results that show the excellent performance of compute-and-forward, there are still important challenges to overcome before we can utilize compute-and- forward in practice. Some important challenges include the assumptions of \perfect timing synchronization "and \quasi-static fading", since these assumptions rarely hold in realistic wireless channels. So far, there are no conclusive answers to whether compute-and-forward can still provide substantial gains even when these assumptions are removed. When lattice codewords are misaligned and mixed up, decoding integer combination of messages is not straightforward since the linearity of lattice codes is generally not invariant to time shift. When channel exhibits time selectivity, it brings challenges to compute-and-forward since the linearity of lattice codes does not suit the time varying nature of the channel. Another challenge comes from the emerging technologies for future 5G communication, e.g., autonomous driving and virtual reality, where low-latency communication with high reliability is necessary. In this regard, powerful short channel codes with reasonable encoding/decoding complexity are indispensable. Although there are fruitful results on designing short channel codes for point-to-point communication, studies on short code design specifically for compute-and-forward are rarely found. The objective of this dissertation is threefold. First, we study compute-and-forward with timing-asynchronous users. Second, we consider the problem of compute-and- forward over block-fading channels. Finally, the problem of compute-and-forward for low-latency communication is studied. Throughout the dissertation, the research methods and proposed remedies will center around the design of lattice codes in order to facilitate the use of compute-and-forward in the presence of these challenges

Cellular, Wide-Area, and Non-Terrestrial IoT: A Survey on 5G Advances and the Road Towards 6G

The next wave of wireless technologies is proliferating in connecting things among themselves as well as to humans. In the era of the Internet of things (IoT), billions of sensors, machines, vehicles, drones, and robots will be connected, making the world around us smarter. The IoT will encompass devices that must wirelessly communicate a diverse set of data gathered from the environment for myriad new applications. The ultimate goal is to extract insights from this data and develop solutions that improve quality of life and generate new revenue. Providing large-scale, long-lasting, reliable, and near real-time connectivity is the major challenge in enabling a smart connected world. This paper provides a comprehensive survey on existing and emerging communication solutions for serving IoT applications in the context of cellular, wide-area, as well as non-terrestrial networks. Specifically, wireless technology enhancements for providing IoT access in fifth-generation (5G) and beyond cellular networks, and communication networks over the unlicensed spectrum are presented. Aligned with the main key performance indicators of 5G and beyond 5G networks, we investigate solutions and standards that enable energy efficiency, reliability, low latency, and scalability (connection density) of current and future IoT networks. The solutions include grant-free access and channel coding for short-packet communications, non-orthogonal multiple access, and on-device intelligence. Further, a vision of new paradigm shifts in communication networks in the 2030s is provided, and the integration of the associated new technologies like artificial intelligence, non-terrestrial networks, and new spectra is elaborated. Finally, future research directions toward beyond 5G IoT networks are pointed out.Comment: Submitted for review to IEEE CS&

Proceedings of the 23rd International Congress of Byzantine Studies : Thematic Sessions of Free Communications

This volume contains the abstracts of the free communications sessions from the 23rd International Congress of Byzantine Studies, taking the form of one hundred and seventeen thematic sessions and twenty poster presentations. The success of forty three sessions should be attributed above all to the conveners who designed and realised them in cooperation with other participants, and then presided over them at the Congress. This type of sessions was the organisers’ response to the challenge posed by a large number of high-quality proposals for round table discussion. Since it was not possible to implement all the received proposals into the round table sessions, the proposers were encouraged to present their ideas as Thematic Sessions of Free Communications. The remaining seventy-four sessions were selected by the organizer out of approximately six hundred abstracts submitted. Stanoje Bojanin (The Institute for Byzantine Studies) created the initial classification of abstracts according to thematic compatibility, and the final form of the sessions was determined by Vujadin Ivanišević (The Institute of Archeology), Srđan Pirivratić, Dejan Dželebdžić, Ljubomir Milanović and Miloš Živković (The Institute for Byzantine Studies). Tamara Matović and Miloš Cvetković (The Institute for Byzantine Studies), prepared the abstracts for the Congress website, and then for this publication. Bojana Pavlović (The Institute for Byzantine Studies) made a significant contribution to organizing the sessions by taking on the bulk of the correspondence with the participants. In principle, all the abstracts in this book are published in the form they were submitted to the organizer, but certain minor, sometimes unavoidable alterations were made to the headings. The index of the participant’s names, which is customary and necessary in printed publications, has been omitted from this searchable electronic book. We believe that the main purpose of this book is to present in one place the wide range of topics featured at the Congress, which accurately reflects contemporary trends in Byzantine Studies. We present this book to the public in the hope that the larger part of the communications read at the Congress will find their way into published research papers

Proceedings of the 23rd International Congress of Byzantine Studies : Thematic Sessions of Free Communications

This volume contains the abstracts of the free communications sessions from the 23rdInternational Congress of Byzantine Studies, taking the form of one hundred and seventeen thematic sessions and twenty poster presentations. The success of forty three sessions should be attributed above all to the conveners who designed and realised them in cooperation with other participants, and then presided over them at the Congress. This type of sessions was the organisers’ response to the challenge posed by a large number of high-quality proposals for round table discussion. Since it was not possible to implement all the received proposals into the round table sessions, the proposers were encouraged to present their ideas as Thematic Sessions of Free Communications.The remaining seventy-four sessions were selected by the organizer out of approximatelysix hundred abstracts submitted. Stanoje Bojanin (The Institute for Byzantine Studies) createdthe initial classification of abstracts according to thematic compatibility, and the final form of thesessions was determined by Vujadin Ivanišević (The Institute of Archeology), Srđan Pirivratić,Dejan Dželebdžić, Ljubomir Milanović and Miloš Živković (The Institute for Byzantine Studies).Tamara Matović and Miloš Cvetković (The Institute for Byzantine Studies), prepared the abstractsfor the Congress website, and then for this publication. Bojana Pavlović (The Institute for Byzantine Studies) made a significant contribution to organizing the sessions by taking on the bulk of the correspondence with the participants.In principle, all the abstracts in this book are published in the form they were submitted tothe organizer, but certain minor, sometimes unavoidable alterations were made to the headings.The index of the participant’s names, which is customary and necessary in printed publications, has been omitted from this searchable electronic book.We believe that the main purpose of this book is to present in one place the wide range oftopics featured at the Congress, which accurately reflects contemporary trends in Byzantine Studies. We present this book to the public in the hope that the larger part of the communications read at the Congress will find their way into published research papers

Proceedings of the 23rd International Congress of Byzantine Studies : Round Tables

Following the 23rd International Congress of Byzantine Studies, the Organizing Committee decided to produce an online publication of Proceedings from the Round Tables. According to the official title of the congress, Byzantium - a World of Changes, AIEB together with the Organizing Committee, have decided to implement some changes to the concept of the Round Tables. The aim of these changes were to encourage discussion at the Round Tables by presenting preliminary papers at the website in advance. The idea was to introduce the topic and papers of the individual Round Tables that would be discussed, first between the participants, and then with the public present. Therefore, the conveners of the Round Tables were asked to create Round Tables with no more than 10 participants. They collected the papers, which were to be no longer than 18,000 characters in one of the official languages of the Congress and without footnotes or endnotes. Conveners provided a general statement on the goal of each roundtable and on the content of the papers. The present volume contains papers from 49 Round Tables carefully selected to cover a wide range of topics, developed over the last five years since the previous Congress. The topics show diversity within fields and subfields, ranging from history to art history, archeology, philosophy, literature, hagiography, and sigillography. The Round Tables displayed current advances in research, scholarly debates, as well as new methodologies and concerns germane to all aspects of international Byzantine studies. The papers presented in this volume were last sent to the congress organizers in the second week of August 2016 and represent the material that was on hand at that time and had been posted on the official website; no post-congress revisions have occurred. We present this volume in hope that it will be an initial step for further development of Round Tables into collections of articles and thematic books compiled and published following the Congress, in collaboration with other interested institutions and editors. With this volume, the organizers signal their appreciation of the efforts of more than 1600 participants who contributed, both to the Round Tables and to the Congress in general