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  • 51.
    Rathi, Vishwambhar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Andersson, Mattias
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Thobaben, Ragner
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Kliewer, Jörg
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Two edge type LDPC codes for the wiretap channel2009Inngår i: Conference Record - Asilomar Conference on Signals, 2009, Vol. Systems and Computers, s. 834-838Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider transmission over a wiretap channel where both the main channel and the wiretapper's channel are Binary Erasure Channels (BEC). We propose a code construction using two edge type LDPC codes based on the method of Thangaraj, Dihidar, Calderbank, McLaughlin and Merolla. The advantage of our construction is that we can easily calculate the threshold over the main channel. Using standard LDPC codes with a given threshold over the BEC we give a construction for a two edge type LDPC code with the same threshold. Since this construction gives a code for the main channel with threshold zero we also give numerical methods to find two edge type LDPC codes with non-zero threshold for the main channel.

  • 52.
    Sandberg, Henrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Dan, György
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektroteknik och datavetenskap (EECS), 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.
    Differentially private state estimation in distribution networks with smart meters2015Inngår i: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2015, s. 4492-4498Konferansepaper (Fagfellevurdert)
    Abstract [en]

    State estimation is routinely being performed in high-voltage power transmission grids in order to assist in operation and to detect faulty equipment. In low- and medium-voltage power distribution grids, on the other hand, few real-time measurements are traditionally available, and operation is often conducted based on predicted and historical data. Today, in many parts of the world, smart meters have been deployed at many customers, and their measurements could in principle be shared with the operators in real time to enable improved state estimation. However, customers may feel reluctance in doing so due to privacy concerns. We therefore propose state estimation schemes for a distribution grid model, which ensure differential privacy to the customers. In particular, the state estimation schemes optimize different performance criteria, and a trade-off between a lower bound on the estimation performance versus the customers' differential privacy is derived. The proposed framework is general enough to be applicable also to other distribution networks, such as water networks.

  • 53.
    Si, Zhongwei
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Andersson, Mattias
    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.
    Rate-compatible LDPC convolutional codes for capacity-approaching hybrid ARQ2011Inngår i: 2011 IEEE Information Theory Workshop (ITW), 2011, s. 513-517Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we construct a family of rate-compatible LDPC convolutional codes for Type-II HARQ systems. For each code family, the codes of lower rates are constructed by successively extending the graph of the high-rate base code. Theoretically, the proposed rate-compatible family includes all rates from 0 to 1. We prove analytically that all LDPC convolutional codes in the family are capacity achieving over the binary erasure channel (BEC). Thus, if applied to an idealized HARQ system over the BEC where the channel parameter stays constant within one complete information delivery, the throughput achieves the capacity of the channel. Moreover, the code construction is realized by regular degree distributions, which greatly simplifies the optimization.

  • 54. Si, Zhongwei
    et al.
    Ma, Junyang
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Coded Cooperation for Multiway Relaying in Wireless Sensor Networks2015Inngår i: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 15, nr 7, s. 15265-15284Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wireless sensor networks have been considered as an enabling technology for constructing smart cities. One important feature of wireless sensor networks is that the sensor nodes collaborate in some manner for communications. In this manuscript, we focus on the model of multiway relaying with full data exchange where each user wants to transmit and receive data to and from all other users in the network. We derive the capacity region for this specific model and propose a coding strategy through coset encoding. To obtain good performance with practical codes, we choose spatially-coupled LDPC (SC-LDPC) codes for the coded cooperation. In particular, for the message broadcasting from the relay, we construct multi-edge-type (MET) SC-LDPC codes by repeatedly applying coset encoding. Due to the capacity-achieving property of the SC-LDPC codes, we prove that the capacity region can theoretically be achieved by the proposed MET SC-LDPC codes. Numerical results with finite node degrees are provided, which show that the achievable rates approach the boundary of the capacity region in both binary erasure channels and additive white Gaussian channels.

  • 55.
    Si, Zhongwei
    et al.
    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.
    A practical approach to adaptive coding for the three-node relay channel2010Inngår i: IEEE Wireless Communications and Networking Conference, 2010, Vol. WCNCKonferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we propose a new adaptive coding scheme for distributed channel coding for the three-node relay channel. In order to make it feasible for application in wireless sensor networks, the distributed code is built from standard components like Turbo and convolutional codes, and adaptation at the relay is obtained by puncturing the input and output of the employed channel code. The proposed code structure includes distributed Turbo codes and distributed serially concatenated codes as special cases. As the results of our optimization show, significant improvements in terms of rate and coverage are obtained. Compared to theoretical limits a decent performance is achieved considering that the focus is on feasibility.

  • 56.
    Si, Zhongwei
    et al.
    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.
    Adaptive channel coding for the three-node relay channel with limited channel-state information2010Inngår i: Final Program and Abstract Book - 4th International Symposium on Communications, Control, and Signal Processing, 2010, Vol. ISCCSP 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We address the design of adaptive channel codes for the three-node relay channel. In order to make the code design feasible for wireless sensor-network (WSN) applications, we focus on the special case where only limited channel-state information is available for code adaptation. For this purpose we design distributed codes which feature a limited set of modes which are optimized to serve a certain range of channel conditions. As the results show, a good performance in terms of coverage and achievable rate is maintained compared to the case with perfect channel-state information. If the target application is spectrum sensing, the proposed scheme provides a feasible solution to improve the sensing performance and to reduce the latency due to its increased data rate compared to standard solutions.

  • 57.
    Si, Zhongwei
    et al.
    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.
    Bilayer LDPC Convolutional Codes for Decode-and-Forward Relaying2013Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, nr 8, s. 3086-3099Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we present bilayer LDPC convolutional codes for half-duplex relay channels. Two types of codes, bilayer expurgated LDPC convolutional codes and bilayer lengthened LDPC convolutional codes, are proposed for decode-and-forward (DF) relaying. In the case of the binary erasure relay channel, we prove analytically that both code constructions achieve the capacities of the source-relay link and the source-destination link simultaneously, provided that the channel conditions are known when designing the codes. Meanwhile, both codes enable the highest transmission rate possible with DF relaying for a wide range of channel parameters. In addition, the regular degree distributions can easily be computed from the channel parameters, which significantly simplifies the code optimization. The code construction and performance analysis are extended to the general binary memoryless symmetric channel, where a capacity-achieving performance is conjectured. Numerical results are provided for both types of codes with finite node degrees over binary erasure channels and binary-input additive white Gaussian noise channels, which verify the aforementioned theoretical analysis.

  • 58.
    Si, Zhongwei
    et al.
    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.
    Bilayer LDPC convolutional codes for half-duplex relay channels2011Inngår i: 2011 IEEE International Symposium on Information Theory Proceedings, ISIT 2011, 2011, s. 1464-1468Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we present regular bilayer LDPC convolutional codes for half-duplex relay channels. For the binary erasure relay channel, we prove that the proposed code construction achieves the capacities for the source-relay link and the source-destination link provided that the channel conditions are known when designing the code. Meanwhile, this code enables the highest transmission rate with decode-and-forward relaying. In addition, its regular degree distributions can easily be computed from the channel parameters, which significantly simplifies the code optimization. Numerical results are provided for the codes with finite node degrees over binary erasure channels. We can observe that the gaps between the decoding thresholds and the Shannon limits are impressively small.

  • 59.
    Si, Zhongwei
    et al.
    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.
    Dynamic decode-and-forward relaying with rate-compatible LDPC convolutional codes2012Inngår i: 5th International Symposium on Communications Control and Signal Processing, ISCCSP 2012, IEEE , 2012, s. 6217841-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Dynamic decode-and-forward (DDF) is an improved decode-and-forward (DF) protocol under which the relay decides based on its received channel-state information (CSI) when to switch from listening mode to transmission mode without knowing the CSI of other links. In this paper we propose to apply rate-compatible LDPC convolutional (RC-LDPCC) codes to the DDF relay channel. The RC-LDPCC codes are constructed by successive graph extensions, and they have been proved analytically to be capacity achieving over the binary erasure channel. In this paper we show that the RC-LDPCC codes fit well with the DDF relaying, and the regularity of degree distributions simplifies the code optimization. Numerical results in terms of bit erasure rate and achievable rate are provided to evaluate the performance of the system. The results show that the RC-LDPCC codes are able to provide high achievable rates for the DDF relay channel.

  • 60.
    Si, Zhongwei
    et al.
    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.
    Instantaneous relaying with bit-interleaved coded modulation: Design and optimization2010Inngår i: 2010 IEEE 6th International Symposium on Turbo Codes and Iterative Information Processing (ISTC), IEEE conference proceedings, 2010, s. 221-225Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we combine bit-interleaved coded modulation (BICM) with instantaneous relaying for the three-node relay channel. We propose a two-step optimization: The first step optimizes the relay functions for different instantaneous relaying strategies like sawtooth (ST) relaying and constellation rearrangement (CR) relaying in order to provide the highest amount of mutual information to the destination. The second step focuses on the bit-to-symbol mapping with the purpose to maximize the achievable gain from iterative demapping/decoding. As our results show, a significant gain can be obtained by using ST and CR relaying with optimized mappings compared with conventional amplify-and-forward and detect-and-forward relaying and compared with standard mappings optimized for point-to-point communications.

  • 61.
    Si, Zhongwei
    et al.
    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.
    ON DISTRIBUTED SERIALLY CONCATENATED CODES2009Inngår i: SPAWC: 2009 IEEE 10TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, NEW YORK: IEEE , 2009, s. 653-657Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we investigate the performance of a new class of distributed codes for the 3-node relay channel, distributed serially concatenated codes (DSCCs). We provide a snap-shot analysis of the iterative DSCC decoder based on extrinsic information transfer characteristics and discuss new design aspects resulting from the extended code structure. Our simulation results show that DSCCs lead to an improved error-floor performance and an increased robustness against decoding errors at the relay compared to conventional distributed parallel concatenated coding schemes.

  • 62.
    Si, Zhongwei
    et al.
    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.
    Rate-Compatible LDPC Convolutional Codes Achieving the Capacity of the BEC2012Inngår i: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 58, nr 6, s. 4021-4029Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we propose a new family of rate-compatible regular low-density parity-check (LDPC) convolutional codes. The construction is based on graph extension, i.e., the codes of lower rates are generated by successively extending the graph of the base code with the highest rate. Theoretically, the proposed rate-compatible family can cover all the rational rates from 0 to 1. In addition, the regularity of degree distributions simplifies the code optimization. We prove analytically that all the LDPC convolutional codes of different rates in the family are capable of achieving the capacity of the binary erasure channel (BEC). The analysis is extended to the general binary memoryless symmetric channel, for which a capacity-approaching performance can be achieved. Analytical thresholds and simulation results for finite check and variable node degrees are provided for both BECs and binary-input additive white Gaussian noise channels. The results confirm that the decoding thresholds of the rate-compatible codes approach the corresponding Shannon limits over both channels.

  • 63.
    Si, Zhongwei
    et al.
    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.
    Oechtering, Tobias
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Bidirectional broadcasting by using multi-edge type LDPC convolutional codes2012Inngår i: Turbo Codes and Iterative Information Processing (ISTC), 2012 7th International Symposium on, IEEE conference proceedings, 2012, s. 91-95Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we propose multi-edge type (MET) LDPC convolutional codes for the bidirectional broadcast channel with common message (BBC-CM). It describes a two-user broadcast channel in which different subsets of the broadcasted messages are a priori known at the receivers. This situation occurs, e.g., in the second transmission phase of a bidirectional relaying protocol. In the proposed scheme, the transmitter broadcasts codewords of an MET LDPC convolutional code. Each user tries then to recover the unknown messages by decoding a two-edge type code which is embedded in the MET code. We prove for each user that the two-edge type LDPC convolutional code has the same properties as a standard LDPC convolutional code, and therefore it is capacity achieving for the binary erasure channel (BEC) and the general binary memoryless symmetric (BMS) channel. Meanwhile, we show that the capacity region of the BBC-CM is achieved. Numerical results with finite node degrees show that the achievable rates approach the channel capacities in both BECs and BI-AWGN channels.

  • 64.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    A new transmitter concept for iteratively-decoded source-channel coding schemes2007Inngår i: 2007 IEEE 8TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, NEW YORK: IEEE , 2007, s. 480-484Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We address the optimization of joint source-channel coding schemes for iterative source-channel decoding (ISCD) of first-order Markov sources. The optimization requires source encoders, providing code words with a minimum Hamming distance d(min) >= 2. Usually, specifically designed variable-length codes (VLCs) are applied for this purpose, leading, however, to an increased complexity of the decoder. In this paper, we propose a novel concept: a single parity-check code is employed for mapping the quantized source symbols to a binary representation. The additional redundancy introduced by this mapping is afterwards compensated by an inner channel code with rate R > 1. Simulation results for the AWGN channel show that the proposed scheme is superior to VLC-based approaches, while leading to a significantly reduced complexity at the same time.

  • 65.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    A Tutorial Introduction to Iterative Source-Channel Decoding2008Inngår i: 2008 ITG Conference on Voice Communication (SprachKommunikation), 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Iterative source-channel decoding has become a standard technique in the field of joint source-channel coding. This paper will therefore provide a tutorial focusing on fundamental principles and design aspects for variable-length codes and fixed-length bit assignments.

  • 66.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    EXIT functions for randomly punctured systematic codes2007Inngår i: 2007 IEEE INFORMATION THEORY WORKSHOP, NEW YORK: IEEE , 2007, s. 24-29Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, the extrinsic information transfer (EXIT) functions of randomly punctured systematic codes (RP-SCs) are analyzed. We consider the systematic encoder to consist of a non-systematic code (NC) and a parallel path for the systematic bits; puncturing of the systematic and the parity bits is then carried out separately. We show that the decoding model for measuring the EXIT characteristics of a RP-SC can be transformed into a decoding model of the underlying NC. For the special case where the a priori/communication channels are modeled by binary erasure channels, it becomes obvious that the EXIT functions of any RP-SC can be analytically derived from the EXIT functions of the underlying NC. This theoretical result is verified by a comparison to simulated EXIT functions.

  • 67.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Joint network/channel coding for bandwidth-efficient multi-user ARQ2009Inngår i: SPAWC: 2009 IEEE 10TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, NEW YORK: IEEE , 2009, s. 419-423Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents a novel bandwidth-efficient joint network/channel coding approach for multi-user ARQ where network coding is employed to combine retransmissions to several users. It features trellis-coded modulation (TCM) and iterative network/channel decoding. We provide guidelines for optimizing the TCM encoder to enable a high throughput and match the network code to the TCM encoder such that convergence of the iterative decoder is achieved. Our results show that the proposed scheme significantly outperforms the conventional ones. At the same time the amount of feedback and the decoding complexity per user are greatly reduced.

  • 68.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Joint Network/Channel Coding for Multi-User Hybrid-ARQ2008Inngår i: 7th International ITG Conference on Source and Channel Coding (SCC), 2008, Institute of Electrical and Electronics Engineers (IEEE), 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We present a novel multi-user hybrid-ARQ scheme for a wireless multiple-unicast scenario where a base station supplies a group of users with individual messages. Considering that all users have access to noisy observations of all transmitted packets, network coding is applied to combine retransmissions to several users. Within this framework, we propose a novel joint network and channel code design which allows the users to perform iterative network/channel decoding. Simulation results for the Rayleigh block-fading channel show a significant increase in throughput compared to separate decoding while the complexity for the users is greatly reduced at the same time.

  • 69.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Non-binary joint network/channel coding for multi-user ARQ2010Inngår i: 5th International ICST Conference on Communications and Networking in China (CHINACOM), 2010, 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We propose a novel joint network and channel coding scheme for multi-user ARQ where network coding is employed to combine retransmissions to several users in a packet-based wireless system. Our approach features a joint design of non-binary network coding and trellis-coded modulation and enables symbol-wise iterative network/channel decoding. Our results based on Monte-Carlo simulations for Rayleigh block-fading channels show an improved performance compared to the conventional separate design while at the same time the amount of feedback and the complexity per user are reduced.

  • 70.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    On Distributed Codes with Noisy Relays2008Inngår i: 2008 42ND ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS / [ed] Matthews MB, 2008, s. 1010-1014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we address the design of distributed schemes for the 3-node relay channel with half-duplex constraint. We first discuss the general problem of optimally re-encoding noisy data at the relay and summarize recently proposed approximations. Based on an analysis of the extrinsic information transfer characteristics of the component codes we investigate the potential of "weak" Turbo or LDPC codes which are employed by the source node in order to increase the reliability of the relay when decoding is not possible. The results show that we can indeed gain from the proposed code design.

  • 71.
    Thobaben, Ragnar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Dán, György
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsnät.
    Sandberg, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Wiretap Codes for Secure Multi-Party Computation2014Inngår i: Globecom Workshops (GC Wkshps), 2014, IEEE conference proceedings, 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we propose a new secret sharing scheme for secure multi-party computation. We present a general framework that allows us to construct efficient secret sharing schemes from channel coding techniques for the wiretap channel. The resulting schemes can be employed to securely calculate linear functions of data that are distributed in a network without leaking any information on the data except the desired result. For the examples considered in this paper, our schemes minimize the communication overhead while keeping the data perfectly secure. Compared to conventional schemes, for which the communication overhead grows quadratically in the number of clients in the considered scenarios, the communication overhead for our approach grows only linearly with the number of clients. This property is maintained even if our secret sharing scheme is set up to introduce redundancy in order to compensate for losses of secret shares. While we only consider the case of passive eavesdroppers and implementations based on nested Reed-Solomon codes in this paper, the proposed framework can also be applied in other cases (e.g., when clients tamper with the data) by taking into account the effects of attacks in the design of the underlying wiretap code.

  • 72.
    Thobaben, Ragnar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Kliewer, J.
    An Efficient Variable-Length Code Construction for Iterative Source-Channel Decoding2009Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 57, nr 7, s. 2005-2013Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a novel variable-length code (VLC) construction which exhibits an inherent error correcting capability due to the exclusive presence of codewords with even Hamming weight. Besides error robustness, the proposed code construction features a similar codeword length distribution as Golomb-Rice codes, and therefore, in particular for sources with exponentially distributed symbols, has good source compression properties at the same time. We show that in a source channel coding framework with outer source encoding, inner channel encoding with a recursive convolutional code, and iterative decoding the proposed VLC construction can. lead to significant performance improvements compared to fixed-length source encoding with optimized mappings. In particular, simulation results for the AWGN channel verify that for Gauss-Markov sources a performance close to the theoretical limit can be achieved.

  • 73.
    Thobaben, Ragnar
    et al.
    University of Kiel.
    Kliewer, J.
    University of Kiel.
    Low-complexity iterative joint source-channel decoding for variable-length encoded Markov sources2005Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 53, nr 12, s. 2054-2064Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we present a novel packetized bit-level decoding algorithm for variable-length encoded Markov sources, which calculates reliability information for the decoded bits in the form of a posteriori probabilities (APPs). An interesting feature of the proposed approach is that symbol-based source statistics in the form of the transition probabilities of the Markov source are exploited as a priori information on a bit-level trellis. This method is especially well-suited for long input blocks, since in contrast to other symbol-based APP decoding approaches, the number of trellis states does not depend on the packet length. When additionally the variable-length encoded source data is protected by channel codes, an iterative source-channel decoding scheme can be obtained in the same way as for serially concatenated codes. Furthermore, based on an analysis of the iterative decoder via extrinsic information transfer charts, it can be shown that by using reversible variable-length codes with a free distance of two, in combination with rate-1 channel codes and residual source redundancy, a reliable transmission is possible even for highly corrupted channels. This justifies a new source-channel encoding technique where explicit redundancy for error protection is only added in the source encoder.

  • 74.
    Thobaben, Ragnar
    et al.
    University of Kiel.
    Kliewer, J
    University of Kiel.
    On iterative source-channel decoding for variable-length encoded Markov sources using a bit-level trellis2003Inngår i: 2003 4TH IEEE WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS - SPAWC 2003, NEW YORK: IEEE , 2003, s. 50-54Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we present a novel bit-level soft-input/softoutput decoding algorithm for variable-length encoded packetized Markov sources transmitted over wireless channels. An interesting feature of the proposed approach is that symbol-based source statistics in form of transition probabilities of the Markov source are exploited as a-priori information on a bit-level trellis. When additionally the variable-length encoded source data is protected by channel codes, an iterative source-channel decoding scheme can be obtained in the same way as for serially concatenated codes. Based on an extrinsic information transfer chart analysis of the iterative decoder computer simulations show for an AWGN channel that by using reversible variable-length codes with free distance greater than one in combination with rate-1 channel codes a reliable transmission is possible even for highly corrupted channels.

  • 75.
    Thobaben, Ragnar
    et al.
    University of Kiel.
    Kliewer, J.
    University of Kiel.
    Robust decoding of variable-length encoded Markov sources using a three-dimensional trellis2003Inngår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 7, nr 7, s. 320-322Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this letter, we present an improved index-based a-posteriori probability (APP) decoding approach for the error-resilient transmission of packetized variable-length encoded Markov sources. The proposed algorithm is based on a novel two-dimensional (2-D) state representation which leads to a three-dimensional trellis with unique state transitions. APP decoding on this trellis is realized by employing a 2-D version of the BCJR algorithm where all available source statistics can be fully exploited in the source decoder. For an additional use of channel codes the proposed approach leads to an increased error-correction performance compared to a one-dimensional state representation.

  • 76.
    Thobaben, Ragnar
    et al.
    University of Kiel.
    Kliewer, Joerg
    University of Kiel.
    Design considerations for iteratively-decoded source-channel coding schemes2006Inngår i: Proceedings of 44th Allerton Conference on Communications, Control, and Computing, 2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We address outer variable-length encoding of afirst-order Markov source in a serially concatenated codingscheme with an inner recursive convolutional code. Decodingis carried out iteratively between the constituent decoders forvariable-length and convolutional code. While variable-lengthcodes are commonly known to be sensitive to transmissionerrors, we show that they can lead to significant performanceimprovements compared to fixed-length source encoding withoptimized mappings. Specifically, we propose a simple variablelengthcode construction with a free distance of two and goodcompression properties at the same time. Numerical resultsshow that the performance gain of the proposed approach alsoholds for precoded ISI channels where iterative joint sourcechannel equalization and decoding is employed at the receiver.

  • 77.
    Thobaben, Ragnar
    et al.
    University of Kiel.
    Kliewer, Joerg
    University of Kiel.
    Robust transmission of variable-length encoded Markov sources using rate-1 channel coding and efficient iterative source-channel decoding2004Inngår i: 12th European Signal Processing Conference (EUSIPCO ’04), 2004, s. 881-884Konferansepaper (Fagfellevurdert)
  • 78.
    Thobaben, Ragnar
    et al.
    University of Kiel.
    Land, I
    University of Kiel.
    Blind quality estimation for corrupted source signals based on A-posteriori probabilities2004Inngår i: 2004 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY, PROCEEDINGS, NEW YORK: IEEE , 2004, s. 304-304Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A novel approach is presented for assessing the quality of transmission systems, comprising quantized source signals and APP source decoders, via Monte-Carlo simulation. A-posteriori probabilities are exploited in order to obtain an unbiased estimate of both the symbol error probability and the expected distortion for the transmission system; knowledge of the transmitted source signal is not necessary. Compared to the conventional method this blind quality estimation has a smaller estimation variance.

  • 79.
    Thobaben, Ragnar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Sensor-network-aided cognitive radio: On the optimal receiver for estimate-and-forward protocols applied to the relay channel2007Inngår i: CONFERENCE RECORD OF THE FORTY-FIRST ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS & COMPUTERS, VOLS 1-5, NEW YORK: IEEE , 2007, s. 777-781Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cognitive radio describes a promising concept for improving the utilization of radio spectrum. It allows secondary users to access licensed radio spectrum in an opportunistic fashion, given that the quality of service for primary users is maintained. In this scenario, the detection of unused radio spectrum is the main obstacle: it requires the recognition of low-power signals in a noisy environment. Therefore, we consider the case where cognitive users are supported by a wireless sensor network (WSN) providing beliefs on the event that the primary user is active. The beliefs provided by the WSN nodes are then combined by the cognitive radio in order to make a final decision. Due to limitations in complexity, power, and bandwidth, the WSN nodes apply the estimate-and-forward protocol to communicate their beliefs and to relay the beliefs of adjacent nodes. For the case where the WSN is subject to noisy communication links, we derive and analyze the optimal receiver which provides the cognitive radio with log-likelihood ratios for the estimated and forwarded hypotheses. The performance of the optimal receiver is compared to the performance of sub-optimal receivers.

  • 80.
    Thobaben, Ragnar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Schmalen, Laurent
    RWTH Aachen, Institute of Communication Systems and Data Processing.
    Vary, Peter
    RWTH Aachen, Institute of Communication Systems and Data Processing.
    Joint Source-Channel Coding with Inner Irregular Codes2008Inngår i: 2008 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY PROCEEDINGS, NEW YORK: IEEE , 2008, s. 1153-1157Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We address the optimization of joint source-channel coding schemes for iterative source-channel decoding of first-order Markov sources. Compared to the traditional design, we propose two novelties: (1) source encoders, providing code words with a minimum Hamming distance distance d(min) >= 2, realized by linear block codes, and (2) irregular channel encoders which are optimized for both the source characteristics and the conditions on the channel. Inner code rates Rc > 1 may be chosen in order to compensate for the additional source redundancy if required. Design examples for the AWGN channel and an overall code rate R=0.66 show that the proposed system is able to establish reliable communication within 0.3 dB of the capacity limit for an interleaver length of approximatively 200000 bits.

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