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  • 251.
    Grant, Alex J.
    et al.
    University of South Australia.
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Iterative Techniques2009Ingår i: Advances in Multiuser Detection / [ed] Michael Honig, John Wiley & Sons, 2009, 1, s. 47-126Kapitel i bok, del av antologi (Refereegranskat)
  • 252.
    Grosjean, Leefke
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Practical Anytime Codes2016Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    The demand of an increasingly networked world is well reflected in modern industrial control systems where communication between the different components of the system is more and more taking place over a network. With an increasing number of components communicating and with hardware devices of low complexity, the communication resources available per communication link are however very limited. Yet, despite limited resources, the control signals transmitted over the link are still required to meet strict real-time and reliability constraints. This requires entirely new approaches in the intersection of communication and control theory. In this thesis we consider the problem of stabilizing an unstable linear-quadratic-Gaussian (LQG) plant when the communication link between the observer and the controller of the plant is noisy. Protecting the data transmitted between these components against transmission errors by using error control schemes is essential in this context and the main subject to this thesis. We propose novel error-correcting codes, so-called anytime codes, for this purpose and show that they asymptotically fulfill the reliability requirements known from theory when used for transmission over the binary erasure channel (BEC). We identify fundamental problems when the messages to be transmitted are very short and/or the communication channel quality is very low. We propose a combinatorial finite-length analysis which allows us to identify important parameters for a proper design of anytime codes. Various modifications of the basic code structure are explored, demonstrating the flexibility of the codes and the capability of the codes to be adapted to different practical constraints. To cope with communication channels of low quality, different feedback protocols are proposed for the BEC and the AWGN channel that together with the error-correcting codes ensure the reliability constraints at short delays even for very short message lengths. In the last part of this thesis, we integrate the proposed anytime codes in an automatic control setup. We specify the different components necessary for this and determine the control cost when controlling an unstable LQG plant over a BEC using either the anytime codes proposed in this thesis or block codes. We detail the relation between parameters such as channel quality, code rate, plant instability and resources available and highlight the advantage of using anytime codes in this context.Throughout the thesis, the performance of the anytime codes is evaluated using asymptotic analysis, finite-length analysis and/or simulation results.

  • 253.
    Grosjean, Leefke
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Rasmussen, Lars K.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Systematic LDPC Convolutional Codes: Asymptotic and Finite-Length Anytime Properties2014Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, ISSN 0090-6778, Vol. 62, nr 12, s. 4165-4183Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Here we propose an ensemble of non-terminated systematic LDPC convolutional codes with increasing memory, and show that over the binary erasure channel (BEC) these codes achieve anytime reliability asymptotically when decoded with an expanding-window message-passing decoder. The corresponding anytime exponents are determined through protograph-based extrinsic information transfer charts. Fundamental complications arising when transmitting with finite block lengths are identified and a combinatorial performance analysis, when transmitting over a static BEC with a fixed number of erasures per codeword block, is developed. Based on the performance analysis we explore the use of feedback for achieving anytime behavior with constraints on block length. To meet complexity constraints, with or without feedback, the code memory can be limited at the cost of an error floor emerging with a delay proportional to the memory constraint. Although the analysis is developed for a static BEC we show numerically that we can design efficient low-complexity finite-length codes with anytime properties even for the conventional BEC.

  • 254.
    Grosjean, Leefke
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Rasmussen, Lars K.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Variable-rate anytime transmission with feedback2016Ingår i: IEEE Vehicular Technology Conference, IEEE, 2016, artikel-id 7881963Konferensbidrag (Refereegranskat)
    Abstract [en]

    A generalization of the ensemble of non-terminated systematic LDPC convolutional codes developed in our previous work is proposed that allows us to design codes with lower rates than the original structure. We show that over the BEC, the modified codes have improved asymptotic and finite-length behavior and we determine the operational anytime exponent. Having shown the advantages of lowering the rate of the code, we propose a feedback protocol that permits encoder and decoder to operate at a variable rate. The rate is set on-the-fly and depends on the decoding success of the decoder. We describe the construction of the variable rate code structure and demonstrate by simulations the superiority of the variable rate scheme as compared to a scheme using a fixed rate.

  • 255.
    Gross, James
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Alvarez, Pablo
    Wolisz, Adam
    The Signaling Overhead in Dynamic OFDMA Systems: Reduction by Exploiting Frequency Correlation2007Ingår i: Communications, 2007. ICC '07. IEEE International Conference on, IEEE conference proceedings, 2007, s. 5143-5148Konferensbidrag (Refereegranskat)
    Abstract [en]

    Dynamic OFDMA systems provide a significant performance gain compared to static OFDM approaches. In reality this gain is reduced by an overhead due to signaling. Previous work has shown that this loss is particularly high if the number of sub-carriers is large. In this paper we present two approaches to reduce this overhead by exploiting the correlation in frequency. These two schemes are shown to provide a significant reduction of the signaling overhead.

  • 256.
    Gross, James
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Emmelmann, Marc
    Punyal, Oscar
    Wolisz, Adam
    Dynamic Single-User OFDM Adaptation for IEEE 802.11 Systems2007Ingår i: Proceedings of ACM/IEEE International Symposium on Modeling, Analysis and Simulation of Wireless and Mobile Systems 2007 (MSWIM 2007), 2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    Earlier paper have demonstrated that the achievable throughput of OFDM systems can benefit significantly from individual modulation/transmit power selection on a per sub-carrier basis according to the actual gain of individual sub-carriers (so called dynamic OFDM scheme). Usage of such approach requires, however, providing support for additional functionality like: acquisition of the subcarrier gains, signaling of the used modulation types between the sender and receiver, etc. Therefore dynamic OFDM is actively pursued for future radio interfaces, rather then considered as extension of existing OFDM based standards. In this paper we present for the first time a proposal how the widely accepted IEEE 802.11a/g systems might be extended to support the dynamic OFDM in a singleuser (point-to-point) setting while assuring backward compatibility. We address these issues by a) presenting a set of protocol modifications; and b) a performance evaluation of the suggested extension (referred further on to as single-user 802.11 DYN mode) demonstrating the potential of performance improvement.

  • 257.
    Gross, James
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Karl, Holger
    Fitzek, Frank
    Wolisz, Adam
    Comparison of Heuristic and Optimal Subcarrier Assignment Algorithms2003Ingår i: Proc. of the 2003 International Conference on Wireless Networks ICWN'03, June 2003, 2003, s. 249-255Konferensbidrag (Refereegranskat)
    Abstract [en]

    Wireless multi carrier approaches can support the simultaneous transmissions to several wireless terminals,each one getting only some of the available subcarriers. Judiciously assigning subcarriers to terminals can be used to, e.g., increase the capacity of a wireless cell; however, the resulting assignment problem is difficult. The first subproblem is to decide the number of carriers assigned to each terminal. Then, carriers have to be assigned to individual terminals. For this assignment problem, we present in this paper an optimal but impractical algorithm as well as two new heuristic ones, which have a considerably lower complexity and can be used in real systems. We show that the performance of even the simple heuristic algorithm is comparable with that of the optimal algorithm. The advanced heuristic increases the performance further, at a modest increase in complexity. Both heuristics are at most 5% off from the optimal algorithm’s performance.

  • 258.
    Gross, James
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Punyal, Oscar
    RWTH Aachen University.
    Pereira, Carlos
    University of Porto.
    Aguiar, Ana
    University of Porto.
    Experimental Characterization and Modeling of RF Jamming Attacks on VANETs2015Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 64, nr 2, s. 524-540Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, we evaluate the performance of 802.11p-based vehicular communications in the presence of RF jamming attacks. Specifically, we characterize the transmission success rate of a car-to-car link subject to constant, periodic, and reactive RF jamming. First, we conduct extensive measurements in an anechoic chamber, where we study the benefits of built-in techniques for interference mitigation. In addition, we identify that the periodic transmission of preamblelike jamming signals can hinder successful communication despite being up to five orders of magnitude weaker than the signal of interest. We further provide the rationale behind this remarkably high jammer eectiveness. Additionally, we quantify the impact of reaction delay and interference signal length on the eectiveness of the reactive jammer. Next, by means of outdoor measurements, we evaluate the suitability of the indoor measurements for being used as a model to characterize the performance of car-to-car communications in the presence of RF jamming. Finally, we conduct outdoor measurements emulating a vehicular platoon and study the threats that RF jamming poses to this VANET application. We observe that constant, periodic, but also reactive jammer can hinder communication over large propagation areas, which would threaten road safety.

  • 259. Gómez-Cuba, F.
    et al.
    Du, Jinfeng
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Médard, M.
    Erkip, E.
    Bandwidth occupancy of non-coherent wideband fading channels2015Ingår i: IEEE International Symposium on Information Theory - Proceedings, IEEE, 2015, s. 2351-2355Konferensbidrag (Refereegranskat)
    Abstract [en]

    Peaky and non-peaky signaling schemes have long been considered species apart in non-coherent wideband fading channels, as the first approaches asymptotically the linear-in-power capacity of a wideband AWGN channel with the same SNR, whereas the second reaches a nearly power-limited peak rate at some finite critical bandwidth and then falls to zero as bandwidth grows to infinity. In this paper it is shown that this distinction is in fact an artifact of the limited attention paid in the past to the product between the bandwidth and the fraction of time it is in use. This fundamental quantity, that is termed bandwidth occupancy, measures average bandwidth usage over time. The two types of signaling in the literature are harmonized to show that, for any type of signals, there is a fundamental limit - a critical bandwidth occupancy. All signaling schemes with the same bandwidth occupancy approach the capacity of wideband AWGN channels with the same asymptotic behavior as the bandwidth occupancy grows to its critical value. For a bandwidth occupancy above the critical, rate decreases to zero as the bandwidth occupancy goes to infinity.

  • 260.
    Gómez-Cuba, Felipe
    et al.
    University of Vigo, Spain.
    Du, Jinfeng
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. Research Lab of Electronics, MIT.
    Médard, Muriel
    MIT.
    Erkip, Elza
    NYU Polytechnic School of Engineering, USA.
    Unified Capacity Limit of Non-Coherent Wideband Fading Channels2015Ingår i: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Peaky and non-peaky signaling schemes have long been considered species apart in non-coherent wideband fading channels, as the first approaches asymptotically the linear-in-power capacity of a wideband AWGN channel with the same SNR, whereas the second reaches a nearly power-limited peak rate at some finite critical bandwidth and then falls to zero as bandwidth grows to infinity. In this paper it is shown that this distinction is in fact an artifact of the limited attention paid in the past to the product between the bandwidth and the fraction of time it is in use. This fundamental quantity, that is termed bandwidth occupancy, measures average bandwidth usage over time. As it turns out, a peaky signal that transmits in an infinite bandwidth but only for an infinitesimal fraction of the time may only have a small bandwidth occupancy, and so does a non-peaky scheme that limits itself to the critical bandwidth even though more spectrum is available, so as to not degrade rate. The two types of signaling in the literature are harmonized to show that, for any type of signals, there is a fundamental limit---a critical bandwidth occupancy. All signaling schemes with the same bandwidth occupancy approach the linear-in-power capacity of wideband AWGN channels with the same asymptotic behavior as the bandwidth occupancy approaches its critical value. For a bandwidth occupancy above the critical value, rate decreases to zero as the occupancy goes to infinity. This unified analysis not only recovers previous results on capacity bounds for (non-)peaky signaling schemes, but also reveals the fundamental tradeoff between accuracy and convergence when characterizing the maximal achievable rate.

  • 261.
    Helgason, Olafur Ragnar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Karlsson, Gunnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsnät.
    On the effect of cooperation in wireless content distribution2008Ingår i: 2008 FIFTH ANNUAL CONFERENCE ON WIRELESS ON DEMAND NETWORK SYSTEMS AND SERVICES, NEW YORK: IEEE , 2008, s. 141-148Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we propose continuous time Markov chain models that capture the dynamics of content spreading in a disruption tolerant wireless content distribution system. We use our models to study the effect of cooperation among the mobile nodes and how limited node resources, such as battery lifetime and confined storage, affect the content distribution process. Based on our models and numerical results we deduce that limiting the number of times a node shares each content entry is a good method to conserve energy while at the same time only slightly reducing system performance. Our study also suggests that the effect of assisting nodes is greatest for content channels with few subscribers. For promoting fairness in distributing channels and giving new channels a chance to spread, assisting nodes should therefore solicit and help in spreading less popular channels.

  • 262.
    Henter, Gustav Eje
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Probabilistic Sequence Models with Speech and Language Applications2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Series data, sequences of measured values, are ubiquitous. Whenever observations are made along a path in space or time, a data sequence results. To comprehend nature and shape it to our will, or to make informed decisions based on what we know, we need methods to make sense of such data. Of particular interest are probabilistic descriptions, which enable us to represent uncertainty and random variation inherent to the world around us.

    This thesis presents and expands upon some tools for creating probabilistic models of sequences, with an eye towards applications involving speech and language. Modelling speech and language is not only of use for creating listening, reading, talking, and writing machines---for instance allowing human-friendly interfaces to future computational intelligences and smart devices of today---but probabilistic models may also ultimately tell us something about ourselves and the world we occupy.

    The central theme of the thesis is the creation of new or improved models more appropriate for our intended applications, by weakening limiting and questionable assumptions made by standard modelling techniques. One contribution of this thesis examines causal-state splitting reconstruction (CSSR), an algorithm for learning discrete-valued sequence models whose states are minimal sufficient statistics for prediction. Unlike many traditional techniques, CSSR does not require the number of process states to be specified a priori, but builds a pattern vocabulary from data alone, making it applicable for language acquisition and the identification of stochastic grammars. A paper in the thesis shows that CSSR handles noise and errors expected in natural data poorly, but that the learner can be extended in a simple manner to yield more robust and stable results also in the presence of corruptions.

    Even when the complexities of language are put aside, challenges remain. The seemingly simple task of accurately describing human speech signals, so that natural synthetic speech can be generated, has proved difficult, as humans are highly attuned to what speech should sound like. Two papers in the thesis therefore study nonparametric techniques suitable for improved acoustic modelling of speech for synthesis applications. Each of the two papers targets a known-incorrect assumption of established methods, based on the hypothesis that nonparametric techniques can better represent and recreate essential characteristics of natural speech.

    In the first paper of the pair, Gaussian process dynamical models (GPDMs), nonlinear, continuous state-space dynamical models based on Gaussian processes, are shown to better replicate voiced speech, without traditional dynamical features or assumptions that cepstral parameters follow linear autoregressive processes. Additional dimensions of the state-space are able to represent other salient signal aspects such as prosodic variation. The second paper, meanwhile, introduces KDE-HMMs, asymptotically-consistent Markov models for continuous-valued data based on kernel density estimation, that additionally have been extended with a fixed-cardinality discrete hidden state. This construction is shown to provide improved probabilistic descriptions of nonlinear time series, compared to reference models from different paradigms. The hidden state can be used to control process output, making KDE-HMMs compelling as a probabilistic alternative to hybrid speech-synthesis approaches.

    A final paper of the thesis discusses how models can be improved even when one is restricted to a fundamentally imperfect model class. Minimum entropy rate simplification (MERS), an information-theoretic scheme for postprocessing models for generative applications involving both speech and text, is introduced. MERS reduces the entropy rate of a model while remaining as close as possible to the starting model. This is shown to produce simplified models that concentrate on the most common and characteristic behaviours, and provides a continuum of simplifications between the original model and zero-entropy, completely predictable output. As the tails of fitted distributions may be inflated by noise or empirical variability that a model has failed to capture, MERS's ability to concentrate on high-probability output is also demonstrated to be useful for denoising models trained on disturbed data.

  • 263.
    Henter, Gustav Eje
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Frean, Marcus R.
    School of Engineering and Computer Science, Victoria University of Wellington, New Zealand.
    Kleijn, W. Bastiaan
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Gaussian process dynamical models for nonparametric speech representation and synthesis2012Ingår i: Acoustics, Speech and Signal Processing (ICASSP), 2012 IEEE International Conference on, IEEE , 2012, s. 4505-4508Konferensbidrag (Refereegranskat)
    Abstract [en]

    We propose Gaussian process dynamical models (GPDMs) as a new, nonparametric paradigm in acoustic models of speech. These use multidimensional, continuous state-spaces to overcome familiar issues with discrete-state, HMM-based speech models. The added dimensions allow the state to represent and describe more than just temporal structure as systematic differences in mean, rather than as mere correlations in a residual (which dynamic features or AR-HMMs do). Being based on Gaussian processes, the models avoid restrictive parametric or linearity assumptions on signal structure. We outline GPDM theory, and describe model setup and initialization schemes relevant to speech applications. Experiments demonstrate subjectively better quality of synthesized speech than from comparable HMMs. In addition, there is evidence for unsupervised discovery of salient speech structure.

  • 264.
    Henter, Gustav Eje
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. The University of Edinburgh, United Kingdom.
    Kleijn, W. Bastiaan
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. Victoria University of Wellington, New Zealand.
    Minimum Entropy Rate Simplification of Stochastic ProcessesManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We propose minimum entropy rate simplification (MERS), an information-theoretic, representation-independent framework for simplifying generative models of stochastic processes. Applications include improving model quality for sampling tasks by concentrating the probability mass on the most characteristic and accurately described behaviors while de-emphasizing the tails, and obtaining clean models from corrupted data (nonparametric denoising). This is the opposite of the smoothing step commonly applied to classification models. Drawing on rate-distortion theory, MERS seeks the minimum entropy-rate process under a constraint on the dissimilarity between the original and simplified processes. We particularly investigate the Kullback-Leibler divergence rate as a dissimilarity measure, where, compatible with our assumption that the starting model is disturbed or inaccurate, the simplification rather than the starting model is used for the reference distribution of the divergence. This leads to analytic solutions for stationary and ergodic Gaussian processes and Markov chains. The same formulas are also valid for maximum entropy smoothing under the same divergence constraint. In experiments, MERS successfully simplifies and denoises Markov models from text, speech, and meteorology.

  • 265.
    Henter, Gustav Eje
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. The University of Edinburgh, United Kingdom.
    Leijon, Arne
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Kleijn, W. Bastiaan
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. Victoria University of Wellington, New Zealand.
    Kernel Density Estimation-Based Markov Models with Hidden StateManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We consider Markov models of stochastic processes where the next-step conditional distribution is defined by a kernel density estimator (KDE), similar to certain time-series bootstrap schemes from the economic forecasting literature. The KDE Markov models (KDE-MMs) we discuss are nonlinear, nonparametric, fully probabilistic representations of stationary processes with strong asymptotic convergence properties. The models generate new data simply by concatenating points from the training data sequences in a context-sensitive manner, with some added noise. We present novel EM-type maximum-likelihood algorithms for data-driven bandwidth selection in KDE-MMs. Additionally, we augment the KDE-MMs with a hidden state, yielding a new model class, KDE-HMMs. The added state-variable enables long-range memory and signal structure representation, complementing the short-range correlations captured by the Markov process. This is compelling for modelling complex real-world processes such as speech and language data. The paper presents guaranteed-ascent EM-update equations for model parameters in the case of Gaussian kernels, as well as relaxed update formulas that greatly accelerate training in practice. Experiments demonstrate increased held-out set probability for KDE-HMMs on several challenging natural and synthetic data series, compared to traditional techniques such as autoregressive models, HMMs, and their combinations.

  • 266. Hithnawi, A.
    et al.
    Li, S.
    Shafagh, H.
    Duquennoy, S.
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Poster abstract: Cross-layer optimization for low-power wireless coexistence2015Ingår i: SenSys 2015 - Proceedings of the 13th ACM Conference on Embedded Networked Sensor Systems, ACM Digital Library, 2015, s. 443-444Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a system that leverages physical layer features to combat Cross-Technology Interference (CTI) in low-power wireless networks. Our system incorporates: (i) a lightweight interference detection mechanism for low-power radios that recognizes the type of interference in the received signal, (ii) a lightweight error detection mechanism to estimate and characterize error patterns within interfered packets, and (iii) a CTI-aware protocol that dynamically adapts transmission and recovery mode to the current interference patterns. We implement a prototype of our system for the lowpower IEEE 802.15.4 in software defined radios (SDR). Our early results of the system components demonstrate that we can achieve a high accuracy in error detection and interference type identification. Moreover, we observed a significant performance improvement compared to the standard 802.15.4 systems without interference-awareness.

  • 267.
    Hithnawi, Anwar
    et al.
    ETH Zurich.
    Su, Li
    ETH Zurich.
    Shafagh, Hossein
    ETH Zurich.
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Duquennoy, Simon
    SICS.
    CrossZig: Combating Cros-Technology Interference in Low-Power Wireless Networks2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    Low-power wireless devices suffer notoriously from Cross- Technology Interference (CTI). To enable co-existence, researchers have proposed a variety of interference mitigation strategies. Existing solutions, however, are designed to work with the limitations of currently available radio chips. In this paper, we investigate how to exploit physical layer properties of 802.15.4 signals to better address CTI. We present CrossZig, a cross-layer solution that takes advantage of physical layer information and processing to improve low-power communication under CTI. To this end, CrossZig utilizes physical layer information to detect presence of CTI in a corrupted packet and to apply an adaptive packet recovery which incorporates a novel cross-layer based packet merging and an adaptive FEC coding. We implement a prototype of CrossZig for the low-power IEEE 802.15.4 in a software-defined radio platform. We show the adaptability and the performance gain of CrossZig through experimental evaluation considering both micro-benchmarking and system performance under various interference patterns. Our results demonstrate that CrossZig can achieve a high accuracy in error localization (94.3% accuracy) and interference type identification (less than 5% error rate for SINR ranges below 3 dB). Moreover, our system shows consistent performance improvements under interference from various interfering technologies.

  • 268.
    Holzapfel, Gerhard A.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Collagen in arterial walls: Biomechanical aspects2008Ingår i: Collagen: Structure and Mechanics, Springer-Verlag New York, 2008, s. 285-324Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    This chapter is written with an emphasis on the biomechanical role of collagen in normal and diseased arterial walls, its structural quantification and its consideration in material models including phenomena such as growth and remodeling. Collagen is the ubiquitous load-bearing and reinforcing element in arterial walls and thus forms an important structural basis. The structural arrangement of collagen leads to the characteristic anisotropic behavior of the arterial wall and its respective layers. The organization of collagen fibers, and the tension within, maintains the function, integrity and strength of arteries. This chapter starts by reviewing the structure of the arterial wall and the biomechanical properties of the individual wall layers. Subsequently, structural quantifications of the collagen fabric are discussed with focus on polarized light microscopy, small-angle X-ray scattering and computer vision analysis. A basic building block for soft collagenous tissues in which the material is reinforced by one family of collagen fibers is next presented. On this basis, a structural model for arteries with an ideal alignment of collagen fibers is reviewed, and subsequently extended to consider collagen crimping and the dispersion of collagen fiber orientations. In order to capture structural modifications such as collagen reorientation, phenomenologically based microstructural and continuum models are presented which consider stress-modulated collagen remodeling. Finally, a constitutive model in which continuous remodeling of collagen is responsible for the growth of saccular cerebral aneurysms is outlined. All of the provided models have been implemented in finite element codes, and have proven to be efficient in the computational analysis of clinically relevant problems. This chapter is by no means complete, but it might help to grasp the most important biomechanical aspects of collagen in arterial tissues, and may serve as the basis for a more intense study of this fascinating topic

  • 269. Hu, Bin
    et al.
    Land, Ingmar
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Piton, Romain
    Fleury, Bernard H.
    A divergence minimization approach to joint multiuser decoding for coded CDMA2008Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 26, nr 3, s. 432-445Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, a theoretical framework of divergence minimization (DM) is applied to derive iterative receiver algorithms for coded CDMA systems. The DM receiver obtained performs joint channel estimation, multiuser decoding, and noisecovariance estimation. While its structure is similar to that of many ad-hoc receivers in the literature, the DM receiver is the result of applying a formal framework for optimization without further simplifications,namely the DM approach with a factorizable auxiliary model distribution. The well-known expectation-maximization (EM) algorithm and space-alternating generalized expectation-maximization (SAGE) algorithm are special cases of degenerate model distributions within the DM framework. Furthermore, many ad-hoc receiver structures from literature are shown to represent approximations of the proposed DM receiver. The DM receiver has four interesting properties that all result directly from applying the formal framework: (i) The covariances of all estimates involved are taken into account. (ii) The residual interference after interference cancellation is handled by the noise-covariance estimation as opposed to by LMMSE filters in other receivers. (iii) Posterior probabilities of the code symbols are employed rather than extrinsic probabilities. (iv) The iterative receiver is guaranteed to converge in divergence. The theoretical insights are illustrated by simulation results.

  • 270. Hu, H.
    et al.
    Taghia, Jalil
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Sang, J.
    Mohammadiha, Nasser
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Azarpour, M.
    Dokku, R.
    Wang, S.
    Lutman, M. E.
    Bleeck, S.
    Speech enhancement via combination of Wiener filter and blind source separation2011Ingår i: Proceedings of the Sixth International Conference on Intelligent Systems and Knowledge Engineering, Shanghai, China  (ISKE2011), 2011, s. 485-494Konferensbidrag (Refereegranskat)
    Abstract [en]

    Automatic speech recognition (ASR) often fails in acoustically noisy environments. Aimed to improve speech recognition scores of an ASR in a real-life like acoustical environment, a speech pre-processing system is proposed in this paper, which consists of several stages: First, a convolutive blind source separation (BSS) is applied to the spectrogram of the signals that are pre-processed by binaural Wiener filtering (BWF). Secondly, the target speech is detected by an ASR system recognition rate based on a Hidden Markov Model (HMM). To evaluate the performance of the proposed algorithm, the signal-to-interference ratio (SIR), the improvement signal-to-noise ratio (ISNR) and the speech recognition rates of the output signals were calculated using the signal corpus of the CHiME database. The results show an improvement in SIR and ISNR, but no obvious improvement of speech recognition scores. Improvements for future research are suggested.

  • 271.
    Hu, Yuanyang
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Proof-of-Concepts of Distributed Detection with Privacy2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Konceptetdistribuerad detektering ar en fundamental metod inom statistiskinferenssomhar manga tillampningar i praktiken. Informationen som sands mellansensorerna och fusionsnoden ar daremot inte alltid saker. Pa grund av dettahar konceptet utvidgats till att inkludera en tjuvlyssnare i systemkongurationen.Det overgripande malet med avhandlingen ar attskapa ett bevis bakom teorindistribuerad detektering och sakerhet. Detta har gjorts genom att anvandadatansom givits av HVAC systemet, som utvecklats pa andra vaningen av Qbyggnaden pa KTH. Tva modeller som beskriver sensormatningen (observationerna)relaterade till den behandlade hypotesen foreslas.Resultaten visar att modellerna ar rimliga. Malet med projektet ar darmeduppfyllt. Forbattringar samt forslag pa framtida arbeten namns dessutom.

  • 272. Hu, Yulin
    et al.
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    On the Outage Probability and Effective Capacity of Multiple Decode-and-forward Relay System2012Ingår i: Wireless Days (WD), 2012 IFIP, 2012, s. 1-8Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper investigates the quality-of-service performance of multiple decode-and-forward relay system. In particular, we study the outage probability and effective capacity performance of the system based on average channel gain. First, a closed-form expression of outage probability is derived which is more concise than the previous work. Second, we introduce four retransmission strategies and derive the effective capacities of the multi-relay system under these strategies. By means of simulation, we provide the numerical verification of our formula derivation. The simulation results illustrate perfect agreement for our theoretical analysis. In addition, we evaluate the system queue behavior under the strategies. The simulation shows that relay can significantly improve the system queue behavior and that the combined signal processing only pays off under relay-driven retransmission strategies.

  • 273.
    Hu, Yulin
    et al.
    RWTH Aachen University.
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Schmeink, Anke
    RWTH Aachen University.
    On the Capacity of Relaying with Finite Blocklength2015Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, nr 99Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the relaying performance is studied under the finite blocklength regime. The overall error probability of relaying is derived. Moreover, we investigate the Blocklength- Limited capacity (BL-capacity) of relaying. We prove that the BL-capacity of relaying is quasiconcave in the overall error probability. Therefore, the BL-capacity has a global maximum value which can be achieved by choosing an appropriate error probability. Through numerical investigations, we validate our analytical model and compare the performance of relaying under the finite blocklength regime versus the Shannon capacity regime.

  • 274.
    Hu, Yulin
    et al.
    RWTH Aachen University.
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Schmeink, Anke
    RWTH Aachen University.
    On the Performance Advantage of Relaying under the Finite Blocklength Regime2015Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 19, nr 5, s. 779-782Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider a two-phase relaying system with finite blocklengths. We study the performance difference of relaying under the finite blocklength regime as well as under the Shannon capacity regime. Most importantly, we are interested in the conditions that lead to a higher performance of relaying under the finite blocklength regime. We find that these situations are characterized by error probabilities of relaying, e.g., the overall error probability of relaying and the error probability of the bottleneck link of relaying. We identify scenarios where relaying outperforms direct transmission under the finite blocklength regime even if their performances are similar under the Shannon capacity regime. Moreover, we prove that under these scenarios the performance advantage of relaying is more significant with short blocklengths. Finally, numerical results are provided and discussed.

  • 275.
    Hu, Yulin
    et al.
    RWTH Aachen University.
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Schmeink, Anke
    RWTH Aachen University.
    QoS-Constrained Energy Efficiency of Cooperative ARQ in Multiple DF Relay Systems2015Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, s. 848-859Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we study the higher-layer performance as well as the "throughput, delay, energy consumption" tradeoff problem for multi-relay assisted cooperative automatic repeat request (C-ARQ) protocols. We study a practical scenario where only the average channel state information is available at the source and relays. We consider four multi-relay C-ARQ protocols, and derive closed-form expressions for the transmission delay distribution, the energy consumption and the higherlayer queuing performance. Furthermore, we analyze the QoSconstrained energy efficiency performances of the protocols. Our analysis is validated by simulations. In addition, we evaluate the system performance under these C-ARQ protocols and for different topologies. We conclude several guidelines for the design of efficient C-ARQ protocols. Finally, a simple extension of the studied C-ARQ protocols is proposed, which improves the QoSconstrained energy efficiency by 4%.

  • 276. Hu, Yulin
    et al.
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Schmeink, Anke
    Wang, Tong
    Maximizing energy efficiency for multiple DF relay system with QoS constraint2013Ingår i: Proceedings of the Tenth International Symposium on Wireless Communication Systems (ISWCS 2013), IEEE conference proceedings, 2013, s. 419-423Konferensbidrag (Refereegranskat)
    Abstract [en]

    Multiple relays assisted transmission is an effective way to enhance the reliability of wireless communication network. However multiple relays joining in the transmission costs more energy and may reduce the energy efficiency of the system. In this paper, we investigate the energy efficiency performance of multiple decode-and-forward relays system under a quality of service constraint. In particular, we study a feedback-limited scenario where only the knowledge of average channel gain is available at the source. First, we define a tradeoff factor and based on it design a tradeoff mechanism between energy efficiency and outage probability. Second, we prove that the energy efficiency of the system is a piecewise strictly monotonic function of our tradeoff factor and has only one extreme value which is the global maximum. Third, by means of simulation we show that the numerical results perfectly match our theoretical analysis. In addition, we show that energy efficiency can achieve the extreme value under the loose QoS constraint.

  • 277.
    Hu, Yulin
    et al.
    RWTH Aachen University.
    Schmeink, Anke
    RWTH Aachen University.
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Blocklength-Limited Performance of Relaying under Quasi-Static Rayleigh Channels2016Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, nr 7, s. 4548-4558, artikel-id 7434063Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the blocklength-limited performance of a relaying system is studied, where channels are assumed to experience quasi-static Rayleigh fading while at the same time only the average channel state information (CSI) is available at the source. Both the physical-layer performance (blocklength-limited throughput) and the link-layer performance (effective capacity) of the relaying system are investigated. We propose a simple system operation by introducing a factor based on which we weight the average CSI and let the source determine the coding rate accordingly. In particular, we show that both the blocklengthlimited throughput and the effective capacity are quasi-concave in the weight factor. Through numerical analysis, we investigate the relaying performance with average CSI while considering perfect CSI scenario and direct transmission as contrasts. We observe that relaying is more efficient than direct transmission in the finite blocklength regime. Moreover, this performance advantage of relaying under the average CSI scenario is more significant than under the perfect CSI scenario. Finally, the speed of convergence (between the blocklength-limited performance and the performance with infinite blocklengths) in relaying system is faster in comparison to the direct transmission under both the average CSI scenario and the perfect CSI scenario.

  • 278.
    Hu, Yulin
    et al.
    RWTH Aachen University.
    Schmeink, Anke
    RWTH Aachen University.
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Outage Probability of a Multi-Relay Cognitive Network with an Uncertain Number of Forwarding Relays2014Ingår i: Wireless Communications Systems (ISWCS), 2014 11th International Symposium on, IEEE conference proceedings, 2014, s. 350-354Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we focus on a Cognitive Relay Network (CRN) where only the information of the average channel gains is available at the secondary source. A distributed multiple relay selection scheme is proposed for the secondary transmission. Since the secondary source does not fully control the selection but lets each secondary relay decide by itself, it doesn't know which and how many relays will participate in the forwarding. This brings a serious uncertainty in the number of forwarding relays. We analyze this uncertainty and derive the closed-form expression of the outage probability of the secondary transmission under the uncertainty. Finally, we evaluate the proposed relay selection scheme by means of simulation. The simulation shows the appropriateness of our analytical model. In addition, although having lower interference constraint at each relay, the performances of the proposed multi-relay CRN scheme are shown to be strictly superior to the single relay CRN. Moreover, the simulation results suggest that it is necessary to spend the general overhead for secondary networks on knowing the exact QoS requirement of the primary user (i.e. the interference violation probability) to apply our proposed relay selection scheme with the statistical total interference constraint.

  • 279. Hu, Yulin
    et al.
    Schmeink, Anke
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Relaying with Finite Blocklength: Challenge vs. Opportunity2016Ingår i: Sensor Array and Multichannel Signal Processing Workshop (SAM), 2016 IEEE, IEEE conference proceedings, 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we study the performance of a system with multiple decode-and-forward (DF) relays under the finite blocklength (FBL) regime. We derive the FBL-Throughput under both perfect CSI and average CSI scenarios while the corresponding throughputs under an infinite blocklength assumption (IBL-throughput) are discussed as performance references. Through numerical analysis, we evaluate the system performance. We show a higher throughput under the FBL assumption than under the IBL assumption under the perfect CSI scenario.

  • 280.
    Huang, Sheng
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Linear Coding, Applications and Supremus Typicality2015Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [sv]

    Detta arbete börjar med att presentera en kodningssats gällande linjärkodning över ändliga ringar för kodning av korrelerade diskretaminneslösa källor. Denna sats inkluderar som specialfall motsvarandeuppnåbarhetssatser från Elias och Csiszár gällande linjär kodning överändliga kroppar. Dessutom visas det att för varje uppsättning av ändligakorrelerade diskreta minneslösa källor, så finns alltid en sekvens avlinjära kodare över vissa ändliga icke-kropp-ringar som uppnårdatakompressionsgränsen bestämd av Slepian-Wolf-regionen. Därmed slutervi problemet med linjär kodning över ändlig icke-kropps-ringar föri.i.d. datakomprimering med positiv bekräftelse gällande existens.

    Vi studerar också kodning av funktioner, där avkodaren är intresseradav att återskapa en diskret mappning av data som genererats av flerakorrelerade i.i.d. källor och som kodats individuellt. Vi föreslårlinjär kodning över ändliga ringar som en alternativ lösning på dettaproblem. Vi visar att linjär kodning över ändliga ringar presterarbättre än sin ändliga-kropp-motsvarighet, liksom dessutomSlepian-Wolf-kodning, i termer av att uppnå bättre kodningshastigheterför kodning av flera diskreta funktioner.

    För att generalisera ovannämnda genomförbarhetssatser, både gällandedatakompression och funktionskodningsproblemet, till Markov-källor(homogena irreducerbara Markov-källor), så introducerar vi ett nyttkoncept gällande klassificering av typiska sekvenser, benämndSupremus-typiska sekvenser. Den asymptotiska likafördelningsprincipensamt en generaliserad version av typiskhets-hjälpsatsen förSupremus-typiska sekvenser bevisas. Jämfört med traditionell (stark ochsvag) typiskhet, så tillåter Supremus-typiskhet oss att härleda bättretillgängliga verktyg och resultat, som låter oss bevisa att linjärkodning över ringar är överlägsen andra metoder. I motsats härtillmisslyckas argument baserade på den traditionella versionen antingen medatt nå liknande resultat eller så är de härledda resultaten svåra attanalysera på grund av en utmanande utvärdering av entropitakt.

    För att ytterligare undersöka den grundläggande skillnaden mellantraditionell typiskhet och Supremus-typiskhet och dessutom göra våraresultat än mer allmänt gällande, så betraktar vi ävenasymptotiskt medelvärdesstationära ergodiska källor. Våra resultat visaratt en inducerad transformation med avseende på en ändligt mätbar mängdöver ett rekurrent asymptotiskt medelvärdesstationärt dynamiskt systemmed ett sigma-ändlig sannolikhetsmått är asymptotisktmedelvärdesstationär. Följaktligen så gällerShannon-McMillan-Breiman-teoremet, liksom Shannon-McMillan-teoremet, föralla reducerade processer härledda ur rekurrenta asymptotisktmedelvärdesstationära stokastisk processer. Alltså ser vi att dettraditionella typiskhetkonceptet endast realiserarShannon-McMillan-Breiman-teoremet i ett globalt hänseende, medanSupremus-typiskhet leder till att resultatet håller samtidigt även föralla härledda reducerade sekvenser.

  • 281.
    Huang, Sheng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Computing polynomial functions of correlated sources: Inner bounds2012Ingår i: 2012 International Symposium on Information Theory and its Applications (ISITA), IEEE conference proceedings, 2012, s. 160-164Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper considers the problem of source coding for computing functions of correlated i.i.d. random sources. The approach of combining standard and linear random coding for this problem was first introduced by Ahlswede and Han, in the special case of computing the modulo-two sum. In this paper, making use of an adapted version of that method, we generalize their result to more sophisticated scenarios, where the functions to be computed are polynomial functions. Since all discrete functions are fundamentally restrictions of polynomial functions, our results are universally applied.

  • 282.
    Huang, Sheng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Induced transformations of recurrent a.m.s. dynamical systems2015Ingår i: Stochastics and Dynamics, ISSN 0219-4937, Vol. 15, nr 02Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This note proves that an induced transformation with respect to a finite measure set of a recurrent asymptotically mean stationary dynamical system with a sigma-finite measure is asymptotically mean stationary. Consequently, the Shannon–McMillan–Breiman theorem, as well as the Shannon–McMillan theorem, holds for all reduced processes of any finite-state recurrent asymptotically mean stationary random process.

    As a by-product, a ratio ergodic theorem for asymptotically mean stationary dynamical systems is presented.

  • 283.
    Huang, Sheng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Linear source coding over rings and applications2012Ingår i: 2012 Swedish Communication Technologies Workshop, Swe-CTW 2012, IEEE , 2012, s. 1-6Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper studies linear coding (LC) techniques in the setting of computing functions of correlated memoryless sources. Instead of linear mappings over finite fields, we consider using linear mappings over finite rings as encoders. It is shown that generally the region c×R, where c ≥ 1 is a constant and R is the Slepian-Wolf (SW) region, is achievable with LC over ring (LCoR) when the function to compute is the identity function. c = 1 if the ring used is a field. Hence, LCoR could be suboptimal in terms of achieving the best coding rates (the SW region) for computing the identity function. In spite of that, the ring version shows several advantages. It is demonstrated that there exists a function that is neither linear nor can be linearized over any finite field. Thus, LC over field (LCoF) does not apply directly for computing such a function unless the polynomial approach [1], [2] is used. On the contrary, such a function is linear over some ring. Using LCoR, an achievable region containing the SW region can be obtained for computing this function. In addition, the alphabet sizes of the encoders are strictly smaller than using LCoF. More interestingly, LCoF is not useful if some special requirement is imposed.

  • 284.
    Huang, Sheng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    On achievability of linear source coding over finite rings2013Ingår i: IEEE International Symposium on Information Theory: Proceedings, IEEE conference proceedings, 2013, s. 1984-1988Konferensbidrag (Refereegranskat)
    Abstract [en]

    We propose using linear mappings over finite rings as encoders in the Slepian-Wolf and the source coding for computing problems. It is known that the arithmetic of many finite rings is substantially easier to implement than the one of finite fields. Hence, one of the advantages of using linear mappings over rings, instead of its field counterparts, is reducing implementation complexity. More importantly, the ring version dominates the field version in terms of achieving strictly better coding rates with strictly smaller alphabet size in the source coding for computing problem [1]. This paper is dedicated to proving an achievability theorem of linear source coding over finite rings in the Slepian-Wolf problem. This result includes those given by Elias [2] and Csiszár [3] saying that linear coding over finite fields is optimal, i.e. achieves the Slepian-Wolf region. Although the optimality issue remains open, it has been verified in various scenarios including particularly many cases use non-field rings [1], [4].

  • 285.
    Huang, Sheng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    On Existence of Optimal Linear Encoders over Non-field Rings for Data Compression with Application to Computing2013Ingår i: 2013 IEEE Information Theory Workshop, ITW 2013, IEEE , 2013, s. 6691314-Konferensbidrag (Refereegranskat)
    Abstract [en]

    This note proves that, for any finite set of correlated discrete i.i.d. sources, there always exists a sequence of linear encoders over some finite non-field rings which achieves the data compression limit, the Slepian-Wolf region. Based on this, we address a variation of the data compression problem which considers recovering some discrete function of the data. It is demonstrated that linear encoder over non-field ring strictly outperforms its field counterpart for encoding some function in terms of achieving strictly larger achievable region with strictly smaller alphabet size.

  • 286.
    Huang, Sheng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    On linear coding over finite rings and applications to computing2017Ingår i: Entropy, ISSN 1099-4300, E-ISSN 1099-4300, Vol. 19, nr 5, artikel-id 233Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a coding theorem for linear coding over finite rings, in the setting of the Slepian-Wolf source coding problem. This theorem covers corresponding achievability theorems of Elias (IRE Conv. Rec. 1955, 3, 37-46) and Csiszár (IEEE Trans. Inf. Theory 1982, 28, 585-592) for linear coding over finite fields as special cases. In addition, it is shown that, for any set of finite correlated discrete memoryless sources, there always exists a sequence of linear encoders over some finite non-field rings which achieves the data compression limit, the Slepian-Wolf region. Hence, the optimality problem regarding linear coding over finite non-field rings for data compression is closed with positive confirmation with respect to existence. For application, we address the problem of source coding for computing, where the decoder is interested in recovering a discrete function of the data generated and independently encoded by several correlated i.i.d. random sources. We propose linear coding over finite rings as an alternative solution to this problem. Results in Körner-Marton (IEEE Trans. Inf. Theory 1979, 25, 219-221) and Ahlswede-Han (IEEE Trans. Inf. Theory 1983, 29, 396-411, Theorem 10) are generalized to cases for encoding (pseudo) nomographic functions (over rings). Since a discrete function with a finite domain always admits a nomographic presentation, we conclude that both generalizations universally apply for encoding all discrete functions of finite domains. Based on these, we demonstrate that linear coding over finite rings strictly outperforms its field counterpart in terms of achieving better coding rates and reducing the required alphabet sizes of the encoders for encoding infinitely many discrete functions.

  • 287.
    Huang, Sheng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Polynomials and computing functions of correlated sources2012Ingår i: Information Theory Proceedings (ISIT), 2012 IEEE International Symposium on, IEEE , 2012, s. 771-775Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider the source coding problem of computing functions of correlated sources, which is an extension of the Slepian - Wolf coding problem. We observe that all the discrete functions are in fact restrictions of polynomial functions over some finite field. Based on this observation, we demonstrate how to use Elias' Lemma to enlarge the coding rate region (compared to the Slepian - Wolf region) for a certain class of polynomial functions. We present a classification result about polynomial functions regarding this coding problem. The result is conclusive in the two-sources scenario and, in fact, gives another interpretation of a result by Han and Kobayashi [1, Theorem 1].

  • 288.
    Huang, Sheng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Supremus typicality2014Ingår i: 2014 IEEE International Symposium on Information Theory (ISIT), IEEE , 2014, s. 2644-2648Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper investigates a new type of typicality for sequences, termed Supremus typical sequences, in both the strong and the weak senses. It is seen that Supremus typicality is a condition stronger than classic typicality in both the strong and the weak senses. Even though Supremus typical sequences form a (often strictly smaller) subset of classic typical sequences, the Asymptotic Equipartion Property is still valid for Supremus typical sequences. Furthermore, Supremus typicality leads to a generalized typicality lemma that is more accessible and easier to analyze than its classic counterpart.

  • 289.
    Hussain, Iqbal
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Analysis and Design of Rateless Codes2014Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    The invention of turbo codes and the re-discovery of sparse graph codes constitute a milestone in error-correction codes designed for communication and storage systems. Sparse graph codes such as low-density parity-check codes can offer a performance that approaches the previously elusive Shannon capacity with reasonable practical computational complexity. Fountain codes have emerged in the realm of sparse graph codes, and  have shown excellent performance for multicast and broadcast transmission without channel state information at the transmitter. A fountain code is inherently rateless, and as a consequence, such codes may potentially generate an unlimited number of encoded symbols on the fly. Thus due to the rateless property, these codes are suitable for transmission over time varying channels. The results presented in this thesis aim at providing insight into the fundamental design of rateless codes, which could serve as a guideline for the optimal design of rateless codes in real-world applications.

    The thesis is divided into two parts. The first part considers the analysis and design of rateless codes for point-to-point communication. To this end, we commence by considering the concatenation of Luby transform (LT) codes, which were the first practical realization of rateless codes, with differential modulators to exploit the inherent coding gain of differential modulations. An algorithm is developed based on the extrinsic information transfer (EXIT) chart to obtain optimized degree distributions of LT coded differential modulator systems in terms of convergence performance. Then, we delve deeper into the characteristics of LT codes with the objective of improving the error floor performance over noisy channels. An encoding scheme is proposed, which is subsequently used to reduce the error floor. To observe the consequences of the modified encoding scheme, the convergence behavior of the proposed LT code is analyzed using EXIT charts, and shown to be similar to the convergence performance of conventional LT codes. This idea is then extended to LT codes for transmission over erasure channels and a design framework is developed to jointly improve the transmission efficiency and erasure floor performance. For complexity-constrained applications, we construct low-complexity LT codes and devise a reduced-complexity LT decoder for transmission over noisy channels.

    The second part of the thesis deals with the analysis and design of rateless codes for multi-point communication. To address the shortcomings of existing distributed LT (DLT) codes, we introduce buffer-based DLT codes for a multi-source and multi-relay network to virtually convert lossy source-relay links to corresponding lossless links. We optimize the proposed DLT codes in terms of transmission efficiency; thus exhibiting better performance as compared to their conventional counterparts at the expense of increased computational complexity. The idea is then extended to a multi-way relay network where a linear-programming design framework is outlined for optimizing degree distributions in terms of transmission efficiency. Finally, a design framework is provided for DLT coding schemes, to jointly improve the transmission efficiency and erasure floor performance.

  • 290.
    Hussain, Iqbal
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Land, I.
    Chan, T.H.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Rasmussen, Lars K.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    A new design framework for LT codes over noisy channels2014Ingår i: 2014 IEEE International Symposium on Information Theory (ISIT), IEEE , 2014, s. 2162-2166Konferensbidrag (Refereegranskat)
    Abstract [en]

    Luby transform (LT) codes are a class of rateless codes that automatically adapt their rate to the quality of the communication channel. In the original LT codes, fixed check-node degree distributions are used to combine variable nodes uniformly at random to extend the code graph and produce code bits. Here we propose a different approach: we design a sequence of rate-compatible degree distributions, and develop an algorithm that produces code bits in a manner such that the resulting degree distributions follow the designed sequence. Using this new design framework, we develop low-complexity LT codes suitable for time-varying noisy channels. Performance and complexity of the proposed LT codes are measured in terms of bit error rate and average number of edges per information and coded bit, respectively. Numerical examples illustrate the resulting trade-off between performance and complexity of the designed LT codes.

  • 291.
    Hussain, Iqbal
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Rasmussen, Lars
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Design of LT Codes with Equal and Unequal Erasure Protection over Binary Erasure Channels2013Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 17, nr 2, s. 261-264Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The erasure floor performance of Luby Transform (LT) codes is mainly determined by the minimum variable-node degree. Thus we propose a modified encoding scheme that maximizes the minimum variable-node degree for transmission over binary erasure channels. The proposed scheme leads to an almost-regular variable-node degree distribution. The encoding process is generalized to accommodate arbitrary variable-node degree distributions for additional improved performance. The asymptotic performance is investigated using density evolution and compared with a conventional LT code. The scheme is further extended to enable a higher level of unequal erasure protection.

  • 292.
    Hussain, Iqbal
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Rasmussen, Lars
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Design of Spatially-Coupled Rateless Codes2012Ingår i: 2012 IEEE 23rd International Symposium on Personal, Indoor and Mobile Radio Communications - (PIMRC), IEEE , 2012, s. 1913-1918Konferensbidrag (Refereegranskat)
    Abstract [en]

    We investigate the design and performance of spatially-coupled rateless codes. A modified encoding process is introduced for spatially-coupled Luby Transform (SCLT) codes which leads to an almost regular variable-node degree distribution at the encoding graph. The proposed SCLT codes outperform its counterparts significantly over binary erasure channels, particularly in the erasure floor region. To further improve the erasure floor performance, the approach of spatial coupling is then extended to Raptor codes by concatenating a high-rate pre-coder to the SCLT codes. It is shown that the spatial coupling improves the convergence threshold of Raptor codes. Different ensembles of spatially-coupled Raptor codes are constructed depending on whether pre-coders and/or LT codes are spatially-coupled. The performance of different ensembles of spatially-coupled Raptor codes is then evaluated and compared based on density evolution, leading to an improved spatially-coupled Raptor code in terms of convergence threshold and lower complexity.

  • 293.
    Hussain, Iqbal
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Rasmussen, Lars K.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Buffer-Based Distributed LT Codes2014Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 62, nr 11, s. 3725-3739Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We focus on the design of distributed Luby transform (DLT) codes for erasure networks with multiple sources and multiple relays, communicating to a single destination. The erasure-floor performance of DLT codes improves with the maximum degree of the relay-degree distribution. However, for conventional DLT codes, the maximum degree is upper-bounded by the number of sources. An additional constraint is that the sources are required to have the same information block length. We introduce a D-bit buffer for each source-relay link, which allows the relay to select multiple encoded bits from the same source for the relay-encoding process; thus, the number of sources no longer limits the maximum degree at the relay. Furthermore, the introduction of buffers facilitates the use of different information block sizes across sources. Based on density evolution we develop an asymptotic analytical framework for optimization of the relay-degree distribution. We further integrate techniques for unequal erasure protection into the optimization framework. The proposed codes are considered for both lossless and lossy source-relay links. Numerical examples show that there is no loss in erasure rate performance for transmission over lossy source-relay links as compared to lossless links. Additional delays, however, may occur. The design framework and our contributions are demonstrated by a number of illustrative examples, showing the improvements obtained by the proposed buffer-based DLT codes.

  • 294.
    Hussain, Iqbal
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Rasmussen, Lars K.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Rateless Codes for the Multiway Relay Channel2014Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 3, nr 5, s. 457-460Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider distributed Luby transform (DLT) codes for efficient packet transmission in a multi-way relay network, where the links are modeled as erasure channels. Density evolution is applied for asymptotic performance analysis, and subsequently used in a linear-programming design framework for optimizing the degree distribution at the relay in terms of overhead. Moreover a buffer is introduced at the relay to enable efficient downlink transmission even if packets are lost during uplink transmission. Performance losses in terms of delay and/or erasure rates caused by link erasures during uplink transmission are thus alleviated. The proposed DLT codes provide significant improvements in overhead and decoded erasure rates. Numerical results for finite-length codes follow closely the asymptotic analysis. Our results demonstrate that the proposed buffer-based DLT codes outperform its counterparts for lossy uplink transmission.

  • 295.
    Hussain, Iqbal
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Rasmussen, Lars K.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Reduced-complexity decoding of LT codes over noisy channels2013Ingår i: 2013 IEEE Wireless Communications and Networking Conference (WCNC), IEEE Communications Society, 2013, s. 3856-3860Konferensbidrag (Refereegranskat)
    Abstract [en]

    We propose an adaptive decoding scheme for Luby Transform (LT) codes over noisy channels which exhibits lower complexity as compared to the conventional LT decoder. The corresponding modified degree distributions have been derived for the low-complexity LT decoder. The complexity and performance comparison demonstrate that the decoding complexity can be reduced with negligible degradation in bit error rate performance.

  • 296.
    Hussain, Iqbal
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Rasmussen, Lars K.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Regularized Variable-Node LT Codes with Improved Erasure Floor Performance2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider the use of extrinsic information transfercharts for the design of Luby Transform (LT) codes over thebinary erasure channel (BEC). In particular, we formulate anoptimization problem to determine asymptotically good check-node degree distributions in terms of decoder overhead. Wefurther propose a modified encoding scheme that maximizes theminimum variable-node degree, thus optimizing the erasure-floorperformance at the expense of decoder overhead, and resultingin a regularized variable-node degree distribution. The two ap-proaches are combined to jointly improve decoder overhead anddecoder erasure floor by incorporating the proposed encodingstrategy into the convex optimization problem. The performanceof the proposed schemes is investigated for transmission over theBEC through density evolution and numerical simulations. Theoptimized codes compare favorably to conventional LT codes,and are further extended to enable improved performance forunequal erasure protection.

  • 297.
    Hussain, Iqbal
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Rasmussen, Lars K.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Unequal error protection of LT codes over noisy channels2012Ingår i: 2012 Swedish Communication Technologies Workshop, Swe-CTW 2012, IEEE , 2012, s. 19-24Konferensbidrag (Refereegranskat)
    Abstract [en]

    We propose a new unequal error protection (UEP) scheme for Luby Transform (LT) codes over additive white Gaussian noise (AWGN) channels. In contrast to the state-of-the-art UEP scheme for LT codes where the effective code rates are exploited for UEP, we characterize the variable-node degree distribution to achieve UEP for LT codes. For performance analysis, we compare the lower bounds on bit error rate for our proposed scheme and a conventional UEP-based LT codes over AWGN channels for various parameters. Moreover, it is demonstrated through numerical examples that our proposed UEP scheme has better performance than the conventional UEP-based LT codes over a wide range of code rates and channel conditions.

  • 298.
    Hussain, Iqbal
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Rasmussen, Lars Kildehoj
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. University of South Australia, Australia.
    Erasure Floor Analysis of Distributed LT Codes2015Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, nr 8, s. 2788-2796Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the erasure floor performance of distributed Luby transform (DLT) codes for transmission within a multi-source, single-relay, and single-destination erasure-link network. In general, Luby transform (LT) codes exhibit a high erasure floor due to poor minimum-distance properties, which can be improved by maximizing the minimum variable-node degree. The same behavior is observed for DLT codes, and therefore a new combining scheme at the relay is proposed to maximize the minimum variable-node degree in the decoding graph. Furthermore, the encoding process at the sources and the combining scheme at the relay are coordinated to improve the transmission overhead. To characterize the asymptotic performance of the proposed DLT codes, we derive closed-form density-evolution expressions, considering both lossless and lossy source-relay channels, respectively. To support the asymptotic analysis, we evaluate the performance of the proposed DLT codes by numerical examples and demonstrate that the numerical results correspond closely to the analysis. Significant improvements in both the erasure floor and transmission overhead are obtained for the proposed DLT codes, as compared to conventional DLT codes.

  • 299.
    Hussain, Iqbal
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Error floor Analysis of LT Codes over the Additive White Gaussian Noise Channel2011Ingår i: 2011 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE (GLOBECOM 2011) , IEEE , 2011, s. 6133650-Konferensbidrag (Refereegranskat)
    Abstract [en]

    We investigate the error floor performance of Luby Transform (LT) codes over the additive white Gaussian noise channel. We first derive a lower bound on the bit error rate for an LT code, which we subsequently use to show that the corresponding error floor is predominantly caused by low-degree variable nodes. Based on this observation, we propose a modified encoding scheme for LT codes that provides a lower error floor with no increase in encoding and decoding complexities. The convergence behavior of the proposed scheme is analyzed using extrinsic information transfer charts, and shown to be similar to the original LT code. Numerical examples demonstrate the improvements of the modified LT code as a stand-alone code and as a component code of a Raptor code.

  • 300.
    Hussain, Iqbal
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    LT coded MSK over AWGN channels2010Ingår i: 6th International Symposium onTurbo Codes and Iterative Information Processing (ISTC) 2010, 2010, s. 289-293Konferensbidrag (Refereegranskat)
    Abstract [en]

    We investigate the design of Luby Transform (LT) codes with minimum-shift-keying (MSK) modulation over additive white Gaussian noise (AWGN) channels. Both systematic and nonsystematic LT codes are considered from the perspectives of decoding threshold and bit error rate. Using systematic LT codes, coding complexity can be reduced by eliminating the need for decoder-doping, and less parity bits are required as compared to the nonsystematic LT codes. In addition, systematic LT codes exhibit better performance than their nonsystematic counterparts for low fixed code rates. To evaluate the performance of the LT coded MSK system, we consider a family of rate-compatible fixed-rate codes, which allows us to use extrinsic information transfer (EXIT) charts for analysis and design. We observe that systematic LT codes have a better decoding threshold than their corresponding nonsystematic counterparts for all tested rates up to R = 0.59 bits per symbol. Furthermore, with the use of EXIT charts, we propose a new degree distribution function for the LT code, which leads to improved decoding thresholds for all examined code rates, as compared to codes using existing degree distributions optimized for binary erasure and AWGN channels. Numerical results confirm our EXIT chart analysis and conclusions.

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