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  • 51.
    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 Techniques2009Inngår i: Advances in Multiuser Detection / [ed] Michael Honig, John Wiley & Sons, 2009, 1, s. 47-126Kapittel i bok, del av antologi (Fagfellevurdert)
  • 52.
    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 Properties2014Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, ISSN 0090-6778, Vol. 62, nr 12, s. 4165-4183Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 53.
    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 feedback2016Inngår i: IEEE Vehicular Technology Conference, IEEE, 2016, artikkel-id 7881963Konferansepaper (Fagfellevurdert)
    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.

  • 54.
    Guo, Dongning
    et al.
    National University of Singapore.
    Rasmussen, Lars Kildehöj
    National University of Singapore.
    Linear parallel interference cancellation using fixed weighting factors for long-code CDMA2000Inngår i: IEEE International Symposium on Information Theory, 2000, s. 332-332Konferansepaper (Fagfellevurdert)
  • 55.
    Guo, Dongning
    et al.
    National University of Singapore.
    Rasmussen, Lars Kildehöj
    National University of Singapore.
    Lim, Teng Joon
    National University of Singapore.
    Linear parallel interference cancellation in long-code CDMA multiuser detection1999Inngår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 17, nr 12, s. 2074-2081Artikkel i tidsskrift (Fagfellevurdert)
  • 56.
    Guo, Dongning
    et al.
    National University of Singapore.
    Rasmussen, Lars Kildehöj
    National University of Singapore.
    Lim, Teng Joon
    National University of Singapore.
    MMSE-based parallel interference cancellation for long-code CDMA2000Inngår i: International Zurich Seminar on Broadband Communications, 2000, s. 31-38Konferansepaper (Fagfellevurdert)
  • 57.
    Guo, Dongning
    et al.
    National University of Singapore.
    Rasmussen, Lars Kildehöj
    National University of Singapore.
    Sun, S M
    National University of Singapore.
    Lim, Teng Joon
    National University of Singapore.
    A matrix-algebraic approach to linear parallel interference cancellation in CDMA2000Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 48, nr 1, s. 152-161Artikkel i tidsskrift (Fagfellevurdert)
  • 58.
    Guo, Dongning
    et al.
    Princeton University.
    Verdu, Sergio
    Princeton University.
    Rasmussen, Lars Kildehöj
    Chalmers University of Technology.
    Asymptotic normality of linear multiuser detection outputs2001Inngår i: IEEE International Symposium on Information Theory, 2001, s. 307-307Konferansepaper (Fagfellevurdert)
  • 59.
    Guo, Dongning
    et al.
    Princeton University.
    Verdu, Sergio
    Princeton University.
    Rasmussen, Lars Kildehöj
    University of South Australia.
    Asymptotic normality of linear multiuser receiver outputs2002Inngår i: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 48, nr 12, s. 3080-3095Artikkel i tidsskrift (Fagfellevurdert)
  • 60.
    Hong, Yi
    et al.
    University of South Australia.
    Rasmussen, Lars Kildehöj
    University of South Australia.
    Iterative switched decoding for interleave-division multiple-access systems2008Inngår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 57, nr 3, s. 1939-1944Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we consider an interleave-division multiple-access (IDMA) system with multiple users transmitting over a shared additive white Gaussian noise channel. In an IDMA system, the information sequence of each user is encoded by a low-rate serially concatenated code consisting of a convolutional code and a repetition code. To reduce decoding complexity, it has been proposed to only decode the inner repetition code for the first few iterations before including the full concatenated code constraints into the decoding process. Here, we characterize this concept of switched decoding as the parallel decoding of two complementary punctured codes and propose a systematic design procedure based on the extrinsic information transfer chart and trajectory analyses, leading to the best decoding convergence-complexity tradeoffs.

  • 61.
    Hu, Bin
    et al.
    Aalborg University, Denmark.
    Kocian, Alexander
    Aalborg University, Denmark.
    Piton, Romain
    Aalborg University, Denmark.
    Hviid, A.
    Aalborg University, Denmark.
    Fleury, Bernard H.
    Aalborg University, Denmark.
    Rasmussen, Lars Kildehöj
    University of South Australia.
    Iterative joint channel estimation and successive interference cancellation using a SISO-SAGE algorithm for coded CDMA2004Inngår i: ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS & COMPUTERS, 2004, s. 622-626Konferansepaper (Fagfellevurdert)
    Abstract [en]

    n this paper we propose an extension of the space alternating generalized expectation maximization (SAGE) algorithm that accepts as input and provides as output soft information. This so-called soft-input soft-output (SISO) SAGE algorithm is applied to joint successive interference cancellation and channel estimation and combined with SISO single-user decoders in an iterative CDMA receiver. Monte Carlo simulations in flat Rayleigh fading channel show that this receiver is robust against channel estimation errors and can support a high system load.

  • 62. 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 CDMA2008Inngår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 26, nr 3, s. 432-445Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 63.
    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 channels2014Inngår i: 2014 IEEE International Symposium on Information Theory (ISIT), IEEE , 2014, s. 2162-2166Konferansepaper (Fagfellevurdert)
    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.

  • 64.
    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 Channels2013Inngår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 17, nr 2, s. 261-264Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 65.
    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 Codes2012Inngår i: 2012 IEEE 23rd International Symposium on Personal, Indoor and Mobile Radio Communications - (PIMRC), IEEE , 2012, s. 1913-1918Konferansepaper (Fagfellevurdert)
    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.

  • 66.
    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 Codes2014Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 62, nr 11, s. 3725-3739Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 67.
    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 Channel2014Inngår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 3, nr 5, s. 457-460Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 68.
    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 channels2013Inngår i: 2013 IEEE Wireless Communications and Networking Conference (WCNC), IEEE Communications Society, 2013, s. 3856-3860Konferansepaper (Fagfellevurdert)
    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.

  • 69.
    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 Performance2013Konferansepaper (Fagfellevurdert)
    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.

  • 70.
    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 channels2012Inngår i: 2012 Swedish Communication Technologies Workshop, Swe-CTW 2012, IEEE , 2012, s. 19-24Konferansepaper (Fagfellevurdert)
    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.

  • 71.
    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 Codes2015Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, nr 8, s. 2788-2796Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 72.
    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 Channel2011Inngår i: 2011 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE (GLOBECOM 2011) , IEEE , 2011, s. 6133650-Konferansepaper (Fagfellevurdert)
    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.

  • 73.
    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 channels2010Inngår i: 6th International Symposium onTurbo Codes and Iterative Information Processing (ISTC) 2010, 2010, s. 289-293Konferansepaper (Fagfellevurdert)
    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.

  • 74.
    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.
    Serially concatenated LT code with DQPSK modulation2011Inngår i: Wireless Communications and Networking Conference (WCNC), 2011 IEEE, 2011, s. 1811-1816Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider serial concatenation of a Luby Transform (LT) code with a differential quadrature phase-shift-keying (DQPSK) modulator for transmission over an additive white Gaussian noise (AWGN) Channel. Assuming a target average rate for the operation of the rateless LT DQPSK scheme, the degree distribution of the LT code is optimized in terms of convergence threshold using extrinsic information transfer (EXIT) charts. From the EXIT chart analysis, we show that the proposed LT DQPSK scheme has a similar convergence performance, but lower complexity, as compared to a Raptor code with differential modulation, and a LDPC code optimized for DQPSK. The EXIT chart analysis framework is also applied to evaluate the throughput performance for the three schemes in terms of the average code rate as a function of the signal-to-noise ratio. The comparison demonstrates that the proposed structure is well-suited for adaptive-rate transmission over a wide range of rates.

  • 75.
    Kambhampati, Sri Krishna
    et al.
    University of South Australia.
    Lechner, Gottfried
    University of South Australia.
    Chan, Terence
    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.
    Check Splitting of Root-Check LDPC Codes over ARQ Block-Fading Channels2010Inngår i: 2010 Australian Communications Theory Workshop, New York: IEEE , 2010, s. 123-127Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we extend the concept of check splitting to root-check LDPC codes, thus providing an incremental redundancy code construction specifically for the ARQ blockfading channel. By construction, the proposed coding scheme achieves a high level of diversity and effectively adapts the transmission rate to the instantaneous channel conditions.

  • 76.
    Khabbazibasmenj, Arash
    et al.
    University of Alberta.
    Girnyk, Maksym
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Vorobyov, Sergiy
    Aalto Univeristy.
    Vehkaperä, Mikko
    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.
    On the Optimal Precoding for MIMO Gaussian Wire-Tap Channels2013Inngår i: Proc. Int. Symp. Wireless Commun. (ISWCS) 2013, VDE Verlag GmbH, 2013, s. 356-359Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider the problem of finding secrecy rate ofa multiple-input multiple-output (MIMO) wire-tap channel. Atransmitter, a legitimate receiver, and an eavesdropper are allequipped with multiple antennas. The channel states from thetransmitter to the legitimate user and to the eavesdropper areassumed to be known at the transmitter. In this contribution,we address the problem of finding the optimal precoder/transmitcovariance matrix maximizing the secrecy rate of the given wiretapchannel. The problem formulation is shown to be equivalentto a difference of convex functions programming problem andan efficient algorithm for addressing this problem is developed.

  • 77.
    Land, Ingmar
    et al.
    University of South Australia.
    Graell i Amat, Alexandre
    Telecom Bretagne, France.
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Bounding of MAP Decode and Forward Relaying2010Inngår i: 2010 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY, 2010, s. 938-942Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We formulate the maximum a posteriori (MAP) rule for the decode-and-forward transmission strategy operating with a noisy relay. From the MAP rule we derive an analytical bound on the error probability, taking into account decoding errors at the relay. We further determine a practical close-to-MAP decoding scheme based on a convenient error model for the decoding operation at the relay. This error model allows for a trellis representation of the code described jointly by the encoding process at the source and the re-encoding process at the relay. Numerical results demonstrate a close agreement between our analytical results and monte carlo simulations.

  • 78.
    Land, Ingmar
    et al.
    University of South Australia.
    Lechner, Gottfried
    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.
    Adaptive Decoding of LDPC Codes with Binary Messages2009Inngår i: 2009 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORYIEEE International Symposium on Information Theory - Proceedings, NEW YORK: IEEE , 2009, s. 2146-2150Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A novel adaptive binary decoding algorithm for LDPC codes is proposed, which reduces the decoding complexity while having a comparable or even better performance than corresponding non-adaptive alternatives. In each iteration the variable node decoders use the binary check node decoders multiple times; each single use is referred to as a sub-iteration. To process the sequences of binary messages in each iteration, the variable node decoders employ pre-computed look-up tables. These look-up tables as well as the number of sub-iterations per iteration are dynamically adapted during the decoding process based on the decoder state, represented by the mutual information between the current messages and the syndrome bits. The look-up tables and the number of sub-iterations per iteration are determined and optimized using density evolution. The performance and the complexity of the proposed adaptive decoding algorithm is exemplified by simulations.

  • 79.
    Land, Ingmar
    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.
    Grant, Alex
    University of South Australia.
    Shaping EXIT functions of turbo codes2008Inngår i: 2008 AUSTRALIAN COMMUNICATIONS THEORY WORKSHOP, NEW YORK: IEEE , 2008, s. 119-124Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper investigates the shaping of the extrinsic information transfer (EXIT) functions of parallel turbo codes, when the turbo code is used as an outer code in a serially concatenated scheme. As opposed to other work, we consider the overall EXIT function of the turbo decoder and not the EXIT chart for the component codes. Three methods for shaping are investigated: (i) individual puncturing of the systematic part and the two parity parts of the turbo codes, (ii) puncturing of the overall turbo code, and (iii) repetition of the overall turbo code. For each case, the EXIT function of the resulting turbo code is computed from the EXIT function of its component codes. Exact results are obtained for the binary erasure channel.

  • 80.
    Larsson, Peter
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Al-Zubaidy, Hussein
    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.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Effective Capacity of Retransmission Schemes: A Recurrence Relation Approach2016Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, nr 11, s. 4817-4835Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider the effective capacity performance measure of persistent-and truncated-retransmission schemes that can involve any combination of multiple transmissions per packet, multiple communication modes, or multiple packet communication. We present a structured unified analytical approach, based on a random walk model and recurrence relation formulation, and give exact effective capacity expressions for persistent hybrid automatic repeat request (HARQ) and for truncated-retransmission schemes. For the latter, effective capacity expressions are given for systems with finite (infinite) time horizon on an algebraic (spectral radius-based) form of a special block companion matrix. In contrast to prior HARQ models, assuming infinite time horizon, the proposed method does not involve a non-trivial per case modeling step. We give effective capacity expressions for several important cases that have not been addressed before, e.g., persistent-HARQ, truncated-HARQ, network-coded ARQ, two-mode-ARQ, and multilayer-ARQ. We propose an alternative quality-of-service-parameter (instead of the commonly used moment generating function parameter) that represents explicitly the target delay and the delay violation probability. This also enables the closed-form expressions for many of the studied systems. Moreover, we use the recently proposed matrix-exponential distributed modeling of wireless fading channels to provide the basis for numerous new effective capacity results for HARQ.

  • 81.
    Larsson, Peter
    et al.
    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.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Throughput Analysis of ARQ Schemes in Gaussian Block Fading Channels2014Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 62, nr 7, s. 2569-2588Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper examines throughput performance, and its optimization, for lossless and truncated automatic repeat request (ARQ) schemes in Gaussian block fading channels. Specifically, ARQ, repetition redundancy, and in part also incremental redundancy-hybrid ARQ, are considered with various diversity schemes. We propose a parameterization-based method that allows (semi-) closed-form expressions, linking optimized throughput, optimal rate, and mean SNR, to be derived for any ARQ and repetition redundancy-HARQ method even when a non-parameterized closed-form does not exist. We derive numerous throughput and optimal throughput expressions for various ARQ schemes and diversity scenarios, potentially useful for benchmarking purposes or as design guidelines.

  • 82.
    Larsson, Peter
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Rasmussen, Lars Kildehoj
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Throughput Analysis of Hybrid-ARQ -A Matrix Exponential Distribution Approach2016Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, nr 1, s. 416-428Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a novel performance analysis framework for lossless- and truncated-hybrid automatic repeat request (HARQ) that enables neat, general, closed-form throughput expressions in a matrix exponential (ME) distribution form. This approach is applicable to all HARQ schemes for which the probability density function of the effective channel can be characterized by a rational Laplace transform, or equivalently, an ME-distribution. This includes, for example, repetition redundancy HARQ in ME distributed channels. Throughput expressions are also given for the K-truncated-HARQ N-fold diversity, ARQ N-fold diversity, and lossless-HARQ 2-fold diversity cases in the ME distributed channel. Schemes with effective channels of non-rational Laplace transforms, such as IR-HARQ, are explored using truncated continued fractions. A novel integration trick is developed for the integration of ME distributions with singular matrices and yields the simple throughput expression of lossless-HARQ. We also give general analytical expressions for the optimal throughput and optimal rate point that benefit from the compact ME-distribution form proposed.

  • 83.
    Larsson, Peter
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    The Golden Quantizer: The Complex Gaussian Random Variable Case2018Inngår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 7, nr 3, s. 312-315Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The problem of quantizing a circularly symmetric complex Gaussian random variable is considered. For this purpose, we design two non-uniform quantizers, a high-rate- and a Lloyd-Max-quantizer, that are both based on the (golden angle) spiral-phyllotaxis packing principle. We find that the proposed schemes have lower mean-square error distortion compared to (non)-uniform polar/rectangular-quantizers, and near-identical to the best performing trained vector quantizers. The proposed quantizer scheme offers a structured design, a simple natural index ordering, and allows for any number of centroids.

  • 84.
    Lechner, Gottfried
    et al.
    University of South Australia.
    Land, Ingmar
    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.
    Decoding of LDPC Codes with Binary Vector Messages and Scalable Complexity2008Inngår i: 2008 5TH INTERNATIONAL SYMPOSIUM ON TURBO CODES AND RELATED TOPICS, NEW YORK: IEEE , 2008, s. 350-355Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, an iterative decoder for LDPC codes, suitable for high-speed processing, is proposed and analyzed. The messages exchanged between the nodes are binary vectors, where the information is conveyed by the number of ones rather than their positions in the vector. Regarding this aspect, the approach exhibits some similarities to stochastic decoding techniques. The check node decoders perform simple bit-wise modulo-2 additions, whereas the variable node decoders perform more complex processing tasks, making the resulting structure attractive for high-speed hardware implementation. By selecting the length of the binary vector messages between one and infinity, the complexity and the performance of the decoder can be scaled between that of the original binary message passing algorithm and that of the sum-product algorithm. Density evolution is developed for the proposed decoding algorithm, and decoding thresholds are determined as functions of the length of the binary vector messages. Simulation results exemplify the performance for finite-length codes.

  • 85. Lechner, Gottfried
    et al.
    Nguyen, Khoa D.
    Guillen i Fabregas, Albert
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Optimal Power Control for LDPC Codes in Block-Fading Channels2011Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 59, nr 7, s. 1759-1765Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the error probability of LDPC codes in delay-limited block-fading channels with channel state information (CSI) at the transmitter and the receiver. We derive the optimal power allocation algorithms for LDPC codes with specific degree distributions using multi-edge-type density evolution error boundaries. The resulting performance approaches the outage probability for a number of power constraints. Furthermore, we adapt the algorithm for finite-length codes and show that the proposed algorithm enables gains larger than 10 dB over uniform power allocation. The method is valid for general, possibly correlated, fading distributions. This represents the first analysis of specific LDPC codes over block-fading channels with full CSI.

  • 86.
    Li, Nan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Rasmussen, Lars Kildehöj
    Xiao, Ming
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Performance Analysis of Cognitive User Cooperation Using Binary Network Coding2018Inngår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 67, nr 8, s. 7355-7369Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider a cognitive radio network where a primary and a secondary transmitter, respectively, communicate a message to their primary and secondary receivers over a packet-based wireless link, using a joint automatic-repeat-request (ARQ) error control scheme. The secondary transmitter assists in the retransmission of the primary message, which improves the primary performance, and as a reward it is granted limited access to the transmission resources. Conventional ARQ, as well as two network-coding schemes are investigated for applications in the retransmission phase; namely the static network-coding scheme and the adaptive network-coding scheme. For each scheme we analyze the transmission process by investigating the distribution of the number of transmission attempts. We divide every frame into three transmission sessions and in each session we discover that the number of transmission attempts follows a certain negative binomial distribution, in which case can be further approximated by a normal distribution. Considering both the cases of an adaptive frame size and a truncated frame size, we derive analytical results on system performances and discuss the comparison of three schemes. Besides, the approximation method greatly reduces the complexity of transmission analysis, especially in the truncated frame-size case. Numerical results show that our analysis are valid and closely match the simulations.

  • 87.
    Li, Nan
    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.
    Cooperation-based Network Coding in Cognitive Radio Networks2014Inngår i: 2014 IEEE 80th Vehicular Technology Conference (VTC Fall), IEEE , 2014, s. 1-5Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider a scenario consisting of a primary and asecondary system, each represented by a pair of a transmitter anda receiver. The secondary transmitter assists in the retransmission of the primary message, which prevents the primary performance from being degraded by allowing the secondary system to access the transmission resources. Two network coding schemes applied in retransmission phase are investigated, the stationary network coding (SNC) scheme and the adaptive network coding(ANC) scheme. For each scheme we derive analytical results on packet throughput and infer that the ANC scheme outperforms the SNC scheme. We then provide a numerical performance comparison and a numerical optimization of the secondary packet throughput. Our main result shows cooperation can provide a significant performance improvement through effective network coding.

  • 88.
    Li, Nan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Xiao, Ming
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Rasmussen, Lars Kildehöj
    Diverse Communication Modes in Cooperative Downlink Non-Orthogonal Multiple Access - Invited Paper2018Inngår i: IEEE Vehicular Technology Conference, Institute of Electrical and Electronics Engineers Inc. , 2018, s. 1-5Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider cooperation in downlink non-orthogonal multiple access (NOMA) in a network supporting diverse communication modes. One user (UE2) exists as a potential relay between a base station (BS) and another user (UE1). With relaying the signal for UE1, UE2 obtains the opportunity for its own transmission to UE3 in D2D mode, meanwhile maintaining the transmission efficiency for UE1. On the basis of supporting different communication modes, we propose a NOMA-based cooperation scheme at UE2 to combine the relay message with its own. We derive achievable rate regions for two cases depending on the status of the Rayleigh fading channel of the UE2. We find solutions based on experiments through the transmit power allocation strategy at the UE2 and(/or) the BS. We show the impacts of our cooperative scheme and the corresponding user geometry on the achievable rates and the resource sharing strategies. © 2018 IEEE.

  • 89.
    Li, Nan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Xiao, Ming
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Optimized Cooperative Multiple Access in Industrial Cognitive Networks2018Inngår i: IEEE Transactions on Industrial Informatics, ISSN 1551-3203, E-ISSN 1941-0050, Vol. 14, nr 6, s. 2666-2676Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider optimized cooperation in joint orthogonal multiple access and nonorthogonal multiple access in industrial cognitive networks, in which lots of devices may have to share spectrum and some devices (e.g., those for critical control devices) have higher transmission priority, known as primary users. We consider one secondary transmitter (less important devices) as a potential relay between a primary transmitter and receiver pair. The choice of cooperation scheme differs in terms of use cases. With decode-and-forward relaying, the channel between the primary and secondary users limits the achievable rates especially when it experiences poor channel conditions. To alleviate this problem, we apply analog network coding to directly combine the received primary message for relaying with the secondary message. We find achievable rate regions for these two schemes over Rayleigh fading channels. We then investigate an optimization problem jointly considering orthogonalmultiple access and nonorthogonal multiple access, where the secondary rate is maximized under the constraint of maintaining the primary rate. We find both analytical solutions as well as solutions based on experiments through the time sharing strategy between the primary and secondary system and the transmit power allocation strategy at the secondary transmitter. We show the performance improvements of exploiting analog network coding and the impacts of cooperative schemes and user geometry on achievable rates and resource sharing strategies.

  • 90.
    Li, Nan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Xiao, Ming
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Spectrum Sharing With Network Coding for Multiple Cognitive Users2019Inngår i: IEEE Internet of Things Journal, ISSN 2327-4662, Vol. 6, nr 1, s. 230-238Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, an intelligently cooperative communication network with cognitive users is considered, where in a primary system and a secondary system, respectively, a message is communicated to their respective receiver over a packet-based wireless link. The secondary system assists in the transmission of the primary message employing network coding, on the condition of maintaining or improving the primary performance, and is granted limited access to the transmission resources as a reward. The users in both systems exploit their previously received information in encoding and decoding the binary combined packets. Considering the priority of legitimate users, a selective cooperation mechanism is investigated and the system performance based on an optimization problem is analyzed. Both the analytical and numerical results show that the condition for the secondary system accessing the licensed spectrum resource is when the relay link performs better than the direct link of the primary transmission. We also extend the system model into a network with multiple secondary users and propose two relay selection algorithms. Jointly considering the related link qualities, a best relay selection and a best relay group selection algorithm are discussed. Overall, it is found that the throughput performance can be improved with multiple secondary users, especially with more potential users cooperating in the best relay group selection algorithm.

  • 91.
    Lim, Teng Joon
    et al.
    National University of Singapore.
    Rasmussen, Lars Kildehöj
    National University of Singapore.
    Adaptive symbol and parameter estimation in asynchronous multiuser CDMA detectors1997Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 45, nr 2, s. 213-220Artikkel i tidsskrift (Fagfellevurdert)
  • 92.
    Lim, Teng Joon
    et al.
    National University of Singapore.
    Rasmussen, Lars Kildehöj
    National University of Singapore.
    Sugimoto, Hiroki
    OKI Techno Center, Singapore.
    An asynchronous multiuser CDMA detector based on the Kalman filter1998Inngår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 16, nr 9, s. 1711-1722Artikkel i tidsskrift (Fagfellevurdert)
  • 93.
    Lim, Teng Joon
    et al.
    National University of Singapore.
    Rasmussen, Lars Kildehöj
    National University of Singapore.
    Sugimoto, Hiroki
    OKI Techno Center, Singapore.
    Multi-user code division multiple access receiver1997Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    A receiver and method for receiving a code-division multiple-access (CDMA) signal combining symbol values spread by a plurality of spreading codes, which method comprises the steps of:(a) converting the CDMA signal to a baseband signal; (b) recognizing symbol boundaries in every multipath for every user in the baseband signal to produce a delay estimate; (c) estimating an attenuation and phase rotation impressed on the signal by each multipath to produce channel estimates; (d) generating new symbol estimates for every user at a sampling rate that is greater than a symbol rate of the signal; (e) generating an estimate of the received signal using said symbol estimates and channel estimates; (f) comparing the received signal with its estimate and feeding estimation error back to a means for estimating the transmitted symbols; (g) sampling the symbol estimates at the estimated symbol boundaries of each user to obtain final symbol estimates; and(h) repeating steps (b) through (g) with every new sample.

  • 94.
    Lim, Teng Joon
    et al.
    National University of Singapore.
    RasmussenS, Lars Kildehöj
    National University of Singapore.
    Sugimoto, Hiroki
    OKI Techno Center, Singapore.
    Relative performance of BPSK and QPSK in the presence of complex multiuser CDMA interference2000Inngår i: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 13, nr 3, s. 237-256Artikkel i tidsskrift (Fagfellevurdert)
  • 95.
    Lin, Tao
    et al.
    University of South Australia.
    Rasmussen, Lars Kildehöj
    University of South Australia.
    Application of maximal ratio combining for iterative multiuser decoding2004Inngår i: 2004 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY, PROCEEDINGS, 2004, s. 531-531Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we apply the concept of recursive maximal ratio combining over iterations in an iterative multiuser decoder. The principle can be applied to any multiuser estimator that does not exploit information across iterations.

  • 96.
    Lin, Tao
    et al.
    University of South Australia.
    Rasmussen, Lars Kildehöj
    University of South Australia.
    Iterative multiuser decoding with maximal ratio combining2004Inngår i: Australian Communication Theory Workshop, 2004, s. 42-46Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we apply the concept of recursive maximal ratio combining over iterations in an iterative multiuser decoder. The principle can be applied to any multiuser estimator that does not exploit information across iterations. Here, we have applied the concept to a previously suggested iterative linear minimum mean squared error filter, improving the load in terms of number of supported users at single-user-performance by 20%, making this structure a strong linear alternative.

  • 97.
    Lin, Tao
    et al.
    University of South Australia.
    Rasmussen, Lars Kildehöj
    University of South Australia.
    Truncated maximal ratio combining for iterative multiuser decoding2005Inngår i: Proceedings 6th Australian Communications Theory Workshop 2005, IEEE , 2005, s. 35-41Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, the concept of information combining is investigated for iterative multiuser decoding. This is done by applying recursive maximal ratio combining (MRC) over iterations to interference cancellation based multiuser detectors. Here, we show that combining over all iterations may not be appropriate as correlations build up. Numerical results show that applying MRC only over the first few iterations can improve the bit error rate performance with only a modest increase in complexity, as compared to no combining.

  • 98.
    Liu, Dong
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Cavarec, Baptiste
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Yue, Jing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    On Dominant Interference in Random Networks and Communication Reliability2019Inngår i: ICC 2019 - 2019 IEEE International Conference on Communications (ICC), Institute of Electrical and Electronics Engineers (IEEE), 2019, artikkel-id 8761613Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we study the characteristics of dominant interference power with directional reception in a random network modelled by a Poisson Point Process. Additionally, the Laplace functional of cumulative interference excluding the n dominant interferers is also derived, which turns out to be a generalization of omni-directional reception and complete accumulative interference. As an application of these results, we study the impact of directional receivers in random networks in terms of outage probability and error probability with queue length constraint.

  • 99.
    Liu, Dong
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Fodor, Viktória
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Will Scale-Free Popularity Develop Scale-Free Geo-Social Networks?2019Inngår i: IEEE Transactions on Network Science and Engineering, Vol. 6, nr 3, s. 587-598Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Empirical results show that spatial factors such as distance, population density and communication range affect our social activities, also reflected by the development of ties in social networks. This motivates the need for social network models that take these spatial factors into account. Therefore, in this paper we propose a gravity-low-based geo-social network model, where connections develop according to the popularity of the individuals, but are constrained through their geographic distance and the surrounding population density. Specifically, we consider a power-law distributed popularity, and random node positions governed by a Poisson point process. We evaluate the characteristics of the emerging networks, considering the degree distribution, the average degree of neighbors and the local clustering coefficient. These local metrics reflect the robustness of the network, the information dissemination speed and the communication locality. We show that unless the communication range is strictly limited, the emerging networks are scale-free, with a rank exponent affected by the spatial factors. Even the average neighbor degree and the local clustering coefficient show tendencies known in non-geographic scale-free networks, at least when considering individuals with low popularity. At high-popularity values, however, the spatial constraints lead to popularity-independent average neighbor degrees and clustering coefficients.

  • 100.
    Liu, Dong
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Vu, Minh Thành
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Chatterjee, Saikat
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Rasmussen, Lars Kildehöj
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    ENTROPY-REGULARIZED OPTIMAL TRANSPORT GENERATIVE MODELS2019Inngår i: 2019 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING (ICASSP), IEEE , 2019, s. 3532-3536Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We investigate the use of entropy-regularized optimal transport (EOT) cost in developing generative models to learn implicit distributions. Two generative models are proposed. One uses EOT cost directly in an one-shot optimization problem and the other uses EOT cost iteratively in an adversarial game. The proposed generative models show improved performance over contemporary models on scores of sample based test.

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