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  • 301.
    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.

  • 302.
    Ibrahim, Bilal
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Interference Management for Stabilization of Dynamical Systems over Wireless Channels2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In networked control systems, dynamical systems are stabilized by actions of remotely placed controllers. This involves communication between plants and controllers over wireless channel(s). The communication channel(s) are subjected to interfering signals, caused by some external radio devices in the neighborhood or by the other wireless components within the same networked control system. Interference in the communication channel is a major problem which drastically affects performance of the dynamical systems that are to be controlled over the wireless channels. This thesis in particular focuses on such a problem; it aims to improve stabilizability of linear systems by managing interference in the wireless channels. We propose an idea of using dedicated sensor nodes in a networked control system whose sole purpose is to manage interferences. Such a dedicated sensor node is termed as a relay node in this thesis, as it relays its received information to the other components in networked control system.

    We assume first order linear time invariant plants with arbitrary distributed initial state and model all the communication links as white Gaussian channels. We study two related setups. In the first setup, we study the remote stabilization of a first order linear plant over a wireless channel in which the communication between the plant’s sensor (state encoder) and controller is disturbed by an independent interference signal. The relay node observes this interference information and sends it to the state encoder and the controller, which then utilize this information to mitigate interference. In the second setup, we consider two separate plants that communicate with two separate controllers using a shared spectrum. Due to the common communication medium, the signals transmitted by the state encoders of the two plants interfere with each other. In this setup, the relay node observes the signals transmitted by the encoders of both plants. It then assists by communicating its observations to the two controllers. The fundamental difference between the two setups is that in the former, the interference is independent of the signal transmitted by the encoder, whereas in the later, the interference becomes correlated with the signals transmitted by the encoders of the two plants. In both setups, we use delay-free linear sensing and control schemes. By employing these schemes, we derive sufficient conditions for mean square stability. We show that the achievable stability region significantly enlarges with the relay assisted interference cancelation schemes.

  • 303.
    Imtiaz, Sahar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Teknisk informationsvetenskap.
    Ghauch, Hadi
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Ur Rahman, M. M.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Koudouridis, Georgios
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsnät. Huawei Technologies Sweden R&D Center.
    Gross, James
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Learning-based resource allocation scheme for TDD-based 5G CRAN system2016Inngår i: MSWiM 2016 - Proceedings of the 19th ACM International Conference on Modeling, Analysis and Simulation of Wireless and Mobile Systems, ACM Press, 2016, s. 176-185Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Provision of high data rates with always-onconnectivity to high mobility users is one of the motivations for design of fifth generation (5G) systems. High system capacity can be achieved by coordination between large number of antennas, which is done using the cloud radio access network (CRAN) design in 5G systems. In terms of baseband processing, allocation of appropriate resources to the users is necessary to achieve high system capacity, for which the state of the art uses the users' channel state information (CSI); however, they do not take into account the associated overhead, which poses a major bottleneck for the effective system performance. In contrast to this approach, this paper proposes the use of machine learning for allocating resources to high mobility users using only their position estimates. Specifically, the 'random forest' algorithm, a supervised machine learning technique, is used to design a learning-based resource allocation scheme by exploiting the relationships between the system parameters and the users' position estimates. In this way, the overhead for CSI acquisition is avoided by using the position estimates instead, with better spectrum utilization. While the initial numerical investigations, with minimum number of users in the system, show that the proposed learning-based scheme achieves 86% of the efficiency achieved by the perfect CSI-based scheme, if the effect of overhead is factored in, the proposed scheme performs better than the CSI-based approach. In a realistic scenario, with multiple users in the system, the significant increase in overhead for the CSI-based scheme leads to a performance gain of 100%, or more, by using the proposed scheme, and thus proving the proposed scheme to be more efficient in terms of system performance.

  • 304.
    Jaldén, Joakim
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Oechtering, Tobias J.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Distributed Bayesian detection for the butterfly network2013Inngår i: 2013 IEEE 14th Workshop on Signal Processing Advances in Wireless Communications (SPAWC), IEEE , 2013, s. 61-65Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider a distributed detection problem where two nodes, or decision makers, observe a common source and aim to decide on one of several hypotheses. Before making their individual decisions, the nodes are allowed to communicate over rate-constrained links, through a bidirectional relay. We show that if the rate of the common relay-to-node link is greater than or equal to the rate of the individual node-to-relay links, and the individual decisions are not coupled by the cost metric, then network coding at the relay allows the overall problem to decouple into two separate two-node distributed detection problems over serial networks; and the two serial networks can be designed independently. However, if the rate of the relay-to-node link is strictly less than the node-to-relay links, no such decoupling can be assumed in general, and the overall detection network needs to be jointly designed.

  • 305.
    Jalil, Taghia
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Arne, Leijon
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Variational Inference for Watson Mixture ModelInngår i: IEEE Transaction on Pattern Analysis and Machine Intelligence, ISSN 0162-8828, E-ISSN 1939-3539Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    This paper addresses modelling data using the multivariate Watson distributions. The Watson distribution is one of thesimplest distributions for analyzing axially symmetric data. This distribution has gained some attention in recent years due to itsmodeling capability. However, its Bayesian inference is fairly understudied due to difficulty in handling the normalization factor. Recentdevelopment of Monte-Carlo Markov chain (MCMC) sampling methods can be applied for this purpose. However, these methods canbe prohibitively slow for practical applications. A deterministic alternative is provided by variational methods that convert inferenceproblems into optimization problems. In this paper, we present a variational inference for Watson mixture model. First, the variationalframework is used to side-step the intractability arising from the coupling of latent states and parameters. Second, the variational freeenergy is further lower bounded in order to avoid intractable moment computation. The proposed approach provides a lower bound onthe log marginal likelihood and retains distributional information over all parameters. Moreover, we show that it can regulate its owncomplexity by pruning unnecessary mixture components while avoiding over-fitting. We discuss potential applications of the modelingwith Watson distributions in the problem of blind source separation, and clustering gene expression data sets.

  • 306. Janda, Carsten Rudolf
    et al.
    Wiese, Moritz
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Noetzel, Janis
    Boche, Holger
    Jorswieck, Eduard A.
    Wiretap-Channels under Constrained Active and Passive Attacks2015Inngår i: 2015 IEEE CONFERENCE ON COMMUNICATIONS AND NETWORK SECURITY (CNS), Institute of Electrical and Electronics Engineers (IEEE), 2015, s. 16-21, artikkel-id 7346805Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, the pessimistic multi letter common randomness assisted secrecy capacity for the Arbitrarily Varying Wiretap Channel (AVWC) under input and state constraints is derived.

  • 307.
    Johansson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Design, prototype and evaluation of a Geocast Enabler Architecture for the IP Multimedia Subsystem2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The evolution from the traditional Internet to the Internet of Things (IoT) is in full progress. Since some of the objects are moving, e.g. vehicles, geoinformation is the key for various distributed application and networking aspects. A Geocast Enabler operating in the IP Multimedia Subsystem (IMS) has been identified in order to allow a real-time transmission of information to objects in a specific region. The IMS has in combination with Web 2.0 technology lowered the barrier for developers to incorporate regular telecommunications technology in their applications. The driving force behind these Web 2.0 technologies are simple techniques such as Ajax. A Geocast Enabler Architecture is presented that enables third-party developers to send Geocasted messages to mobile phones and other handheld devices with an HTTP request. The Enabler consists of a server part, deployed in the operators network, and a client part, installed on the device. A third-party creates a sending part that communicates with the server and a receiving part that communicates with the client on the device. Messages are pushed to the receiving part with HTTP using a Comet Service. It is shown that pushing messages this way results in a low latency which is important for time critical services. A hurdle for network operators is a signalling overhead which is very common in newer smartphone application. The Geocast Enabler takes care of keeping signalling traffic to a minimum by using light UDP datagrams, and communicating sparingly.

  • 308.
    Jorswieck, Eduard A.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Multiuser gaussianity and constellation randomization for the MIMO multiple access channel: A unified view2007Inngår i: 2007 IEEE 8th Workshop On Signal Processing Advances In Wireless Communications, Vols 1 And 2, IEEE , 2007, s. 126-130Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In recent analyses of multiuser MIMO systems and their capacity achieving transmit strategies, Gaussian codebooks; are usually used. For the case in which the input signals are constrained to belong to a finite constellation, we study and explain two effects, namely Multiuser Gaussianity (MuG) and constellation randomization (CoRa). MuG means that the more users transmit simultaneously, the higher is the similarity of the received density to the optimal Gaussian one. Hence, the instantaneous mutual information is increased by MuG. This leads to a tradeoff between multiuser diversity and MuG. On the other hand, CoRa is done by linear precoding by random unitary matrices. Based on the observations from MuG, we explain why the outage capacity is increased by CoRa. The effects are illustrated by various numerical simulations.

  • 309.
    Juntti, Markku
    et al.
    Department of Electrical and Information Engineering, University of Oulu.
    Vehkaperä, Mikko
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Leinonen, Jouko
    Li, Zexian
    Tujkovic, Djordje
    Tsumura, Shigehiko
    Hara, Shinsuke
    Graduate School of Engineering, Osaka City University .
    MIMO MC-CDMA communications for future cellular systems2005Inngår i: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 43, nr 2, s. 118-124Artikkel i tidsskrift (Fagfellevurdert)
  • 310.
    Jöngren, George
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Ottersten, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Space-Time Block Coding Using Channel Side Information2005Inngår i: Smart Antennas - State-of-the-Art / [ed] Kaiser, Thomas, Hindawi Publishing Corporation , 2005, s. 375-399Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 311.
    Kabashima, Yoshiyuki
    et al.
    Department of Computational Intelligence and Systems Science, Tokyo Institute of Technology.
    Vehkaperä, Mikko
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Chatterjee, Saikat
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Typical l(1)-recovery limit of sparse vectors represented by concatenations of random orthogonal matrices2012Inngår i: Journal of Statistical Mechanics: Theory and Experiment, ISSN 1742-5468, E-ISSN 1742-5468, Vol. 2012, nr 12, s. P12003-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider the problem of recovering an N-dimensional sparse vector x from its linear transformation y = Dx of M (<N) dimensions. Minimization of the l(1)-norm of x under the constraint y = Dx is a standard approach for the recovery problem, and earlier studies report that the critical condition for typically successful l(1)-recovery is universal over a variety of randomly constructed matrices D. To examine the extent of the universality, we focus on the case in which D is provided by concatenating T = N/M matrices O-1, O-2,O- ... ,O-T drawn uniformly according to the Haar measure on the M x M orthogonal matrices. By using the replica method in conjunction with the development of an integral formula to handle the random orthogonal matrices, we show that the concatenated matrices can result in better recovery performance than that predicted by the universality when the density of non-zero signals is not uniform among the T matrix modules. The universal condition is reproduced for the special case of uniform non-zero signal densities. Extensive numerical experiments support the theoretical predictions.

  • 312.
    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.

  • 313. Kansanen, K.
    et al.
    Kim, A. N.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Karlsson, Johannes
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Low complexity bandwidth compression mappings for sensor networks2010Inngår i: Final Program and Abstract Book: 4th International Symposium on Communications, Control and Signal Processing, Limassol, 2010, Vol. ISCCSP 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Compressive (2:1) joint source-channel coding using direct mappings from source to channel symbol space is considered. To enable the use of prior information due to e.g. correlated samples at the receiver, or statistical knowledge of the source, minimum mean square error decoding is considered. The prior information is incorporated in the form of the a-priori distribution in the decoding. Four mapping methods are presented and evaluated using the generic Bayesian minimum mean square error estimator. The schemes are evaluated for transmitting a memoryless Gaussian source over additive white Gaussian noise channel with a quadratic distortion measure. The simplicity of implementation and applicability to a wider variety of sources is discussed.

  • 314. Karam, Lina J.
    et al.
    Kleijn, W. Bastiaan
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    MacLean, Karon
    Perception-Based Media Processing2013Inngår i: Proceedings of the IEEE, ISSN 0018-9219, E-ISSN 1558-2256, Vol. 101, nr 9, s. 1900-1904Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    The articles in this special issue provide a timely reviewof the state of the art in the areas of perception-based audio, visual, and haptic processing.

  • 315.
    Karlsson, Johannes
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Low-delay sensing and transmission in wireless sensor networks2008Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    With the increasing popularity and relevance of ad-hoc wireless sensor networks, cooperative transmission is more relevant than ever. In this thesis, we consider methods for optimization of cooperative transmission schemes in wireless sensor networks. We are in particular interested in communication schemes that can be used in applications that are critical to low-delays, such as networked control, and propose suitable candidates of joint source-channel coding schemes. We show that, in many cases, there are significant gains if the parts of the system are jointly optimized for the current source and channel. We especially focus on two means of cooperative transmission, namely distributed source coding and relaying.

    In the distributed source coding case, we consider transmission of correlated continuous sources and propose an algorithm for designing simple and energy-efficient sensor nodes. In particular the cases of the binary symmetric channel as well as the additive white Gaussian noise channel are studied. The system works on a sample by sample basis yielding a very low encoding complexity, at an insignificant delay. Due to the source correlation, the resulting quantizers use the same indices for several separated intervals in order to reduce the quantization distortion.

    For the case of relaying, we study the transmission of a continuous Gaussian source and the transmission of an uniformly distributed discrete source. In both situations, we propose design algorithms to design low-delay source-channel and relay mappings. We show that there can be significant power savings if the optimized systems are used instead of more traditional systems. By studying the structure of the optimized source-channel and relay mappings, we provide useful insights on how the optimized systems work. Interestingly, the design algorithm generally produces relay mappings with a structure that resembles Wyner-Ziv compression.

  • 316.
    Karlsson, Johannes
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Gattami, Ather
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Oechtering, Tobias J.
    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.
    Iterative Source-Channel Coding Approach to Witsenhausen's Counterexample2011Inngår i: Proceedings of the American Control Conference, NEW YORK: IEEE , 2011, s. 5348-5353Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In 1968, Witsenhausen introduced his famous counterexample where he showed that even in the simple linear quadratic static team decision problem, complex nonlinear decisions could outperform any given linear decision. This problem has served as a benchmark problem for decades where researchers try to achieve the optimal solution. This paper introduces a systematic iterative source-channel coding approach to solve problems of the Witsenhausen Counterexample-character. The advantage of the presented approach is its simplicity. Also, no assumptions are made about the shape of the space of policies. The minimal cost obtatined using the introduced method is 0.16692462, which is the lowest known thus far.

  • 317.
    Karlsson, Johannes
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Analog Distributed Source-Channel Coding Using Sinusoids2009Inngår i: 2009 6TH INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATION SYSTEMS: (ISWCS 2009), NEW YORK: IEEE , 2009, s. 279-282Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In a wireless sensor network, it is likely that the measurements of the sensors are correlated. Distributed source coding can be used to reduce transmission rate or mitigate the effects of the channel noise in the case of analog transmission. In this paper, we propose a novel scheme for implementing distributed source-channel coding based on analog mappings. We assume that an analog source is to be transmitted to a receiver that has access to correlated side information, as in the Wyner-Ziv problem. From the Cramer-Rao lower bound, we observe general properties of analog distributed source-channel mappings. It is especially clear how the stretch factor influences the performance. From this observation we propose two different mappings based on sinusoidal waveforms. The proposed transmission scheme is numerically evaluated and shown to perform well, particularly in the low-SNR regime. Furthermore, it requires no encoding or decoding delay, making it suitable for delay-critical applications in wireless sensor networks.

  • 318.
    Karlsson, Johannes
    et al.
    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.
    Design and performance of optimized relay mappings2010Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, nr 9, s. 2718-2724Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We look at the three-node relay channel and the transmission of an information symbol from the source node to the destination node. We let the relay be a memoryless function and formulate necessary conditions for the optimality of the relay mapping and the detector. Based on these, we propose a design algorithm to find relay mappings such that the symbol error rate at the destination is minimized. The optimized relay mappings are illustrated for different scenarios and the dependency between the relay mapping and the link qualities is discussed in detail. Furthermore, the performance is compared with existing schemes, such as detect-and-forward, amplify-and-forward, and estimate-and-forward. It is shown that there is a significant gain in terms of decreased symbol error rate if the optimized relay mapping is used.

  • 319.
    Karlsson, Johannes
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    DESIGN AND PERFORMANCE OF OPTIMIZED RELAY MAPPINGS2008Inngår i: 2008 5TH INTERNATIONAL CONFERENCE ON BROADBAND COMMUNICATIONS, NETWORKS AND SYSTEMS: (BROADNETS 2008), NEW YORK: IEEE , 2008, s. 2-7Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We look at the three-node relay channel and the transmission of an information symbol from the source node to the destination node. We let the relay be a memoryless function and formulate necessary conditions for the optimality of the relay mapping and the detector. Based on these, we propose a design algorithm to find relay mappings such that the symbol error rate at the destination is minimized. The optimized relay mappings are illustrated for different scenarios and the dependency between the relay mapping and the link qualities is discussed in detail. Furthermore, the performance is compared to the existing schemes detect-and-forward, amplify-and-forward, and estimate-and-forward. It is shown that there is a significant gain in terms of decreased symbol error rate if the optimized relay mapping is used.

  • 320.
    Karlsson, Johannes
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Joint source-channel mappings for the relay channel2008Inngår i: 2008 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING, 2008, s. 2953-2956Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The three-node relay channel with a Gaussian source is studied for transmission subject to a low-delay constraint. A joint source-channel coding design algorithm is proposed and numerically evaluated. The designed system is compared to a reference system, based on modular source and channel coding, and the distortion-rate function for the Gaussian source, using known achievable rates on the relay channel. The structure of the source encoder and the relay mapping is visualized and discussed in order to gain understanding of how the system works. The relay mapping gets a structure that resembles a Wyner-Ziv code.

  • 321.
    Karlsson, Johannes
    et al.
    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.
    Lattice-based source-channel coding in wireless sensor networks2011Inngår i: IEEE International Conference on Communications (ICC), Kyoto, Japan, June 5-9, 2011, IEEE conference proceedings, 2011, s. 1-5Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider the problem of gathering measurements in a wireless sensor network consisting of a large number of sensor nodes. A practical joint source–channel coding scheme is proposed and evaluated. The scheme uses lattices to extend apreviously proposed scheme to higher dimensions. The key ideais to use conventional point-to-point communication for a subset of the sensor nodes and side-information aware transmission for the remaining sensor nodes. The selection of sensors is based on their instantaneous channel quality. It is shown that by expanding from one to eight dimensions, a gain of about 1 dB is achievable. The overall transmission delay of the scheme is still very low and it is therefore suitable to use in delay-sensitive applications.

  • 322.
    Karlsson, Johannes
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Optimized low-delay source-channel-relay mappings2010Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, nr 5, s. 1397-1404Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The three-node relay channel with a Gaussian source is studied for transmission subject to a low-delay constraint. A joint source-channel coding design algorithm is proposed and numerically evaluated. The designed system is compared with reference systems, based on modular source and channel coding, and the distortion-rate function for the Gaussian source using known achievable rates for the relay channel. There is a significant gain, in terms of decreased power, in using the optimized systems compared with the reference systems. The structure of the resulting source encoder and the relay mapping is visualized and discussed in order to gain understanding of fundamental properties of optimized systems. Interestingly, the design algorithm generally produces relay mappings with a structure that resembles Wyner-Ziv compression.

  • 323.
    Karlsson, Johannes
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Wernersson, Niklas
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Distributed scalar quantizers for noisy channels2007Inngår i: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, 2007, s. 633-636Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Sensor nodes in wireless sensor networks should preferable be both cheap and energy efficient. To cope with these requirements an algorithm for designing distributed scalar quantizers optimized for noisy channels is proposed and evaluated. Applying the algorithm results in locally optimal systems. It is demonstrated that the correlation between the sources can be used to reduce the quantization distortion when the channel is close to error-free. If, on the other hand, there are a lot of disturbances on the channel the correlation can be used to introduce protection against channel errors.

  • 324.
    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.

  • 325. Khormuji, Majid N.
    et al.
    Oechtering, Tobias J.
    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.
    Capacity Region of the Bidirectional Broadcast Channel with Causal Channel State Information2013Inngår i: Proceedings of the Tenth International Symposium on Wireless Communication Systems (ISWCS 2013), IEEE Computer Society, 2013, s. 274-278Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider the broadcast channel with one transmitter and two receivers such that the transmitter wishes to convey two independentmessages to each receiver, respectively. When each receiver knows the intended message for the other one, as a side information the channel is referred to as the bidirectional broadcast channel. In this work, we establish the capacity region of the discrete memoryless bidirectional broadcast channel with state whose knowledge is causally known at the encoder. Further, we present an Ariomoto-Blahut-like algorithm to compute the capacity region numerically.

  • 326.
    Khormuji, Majid N.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Rizvi, Umar H.
    Janssen, Gerard J. M.
    Ben Slimane, Slimane
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Rotation optimization for MPSK/MQAM signal constellations over rayleigh fading channels2006Inngår i: 2006 10th IEEE Singapore International Conference on Communication Systems, Vols 1 and 2, 2006, s. 671-675Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The performance of uncoded phase-shift-keying (PSK) and quadrature amplitude modulation (QAM) schemes over fading channels can be improved by using coded modulation techniques. Improvement is due to the coding gain coupled with interleaving and depends on the complexity of the code. Recently, it was shown that constellation rotation coupled with interleaving can be used to improve the performance of QPSK modulation over block-fading single-input-single-output (SISO) wireless communication channels. This paper considers the use of such a scheme with higher order constellation sets such as 8PSK and 16QAM. A framework is then presented for the calculation of the optimum rotation angle for MPSK/MQAM schemes. A simple cost function based on the union bound of the symbol error probability (SEP) is defined. The optimum rotation angle is then found by minimizing the cost function using the gradient search algorithm. The obtained simulation results show considerable improvement over the conventional unrotated system.

  • 327.
    Khormuji, Majid N.
    et al.
    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.
    Instantaneous Forwarding Strategies for Relay Channels with Known Interference2009Inngår i: ITW: 2009 IEEE INFORMATION THEORY WORKSHOP ON NETWORKING AND INFORMATION THEORY  , NEW YORK: IEEE , 2009, s. 42-46Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider a Gaussian relay channel, with the source and relay operating in different frequency bands. Hence, the received signals at the destination are orthogonal. We also assume that the source reuses the frequency band in which the relay is operating, to communicate with another destination. This results in a scenario that can be modeled in such a way that the relay-destination link suffers from an additive interference which is non-causally known at the source. We present different achievable rates for this model, focusing on instantaneous relaying, i.e., the relay output depends solely on the current received signal at the relay. The main conclusion of our work is that to achieve high rates, one should resort to joint design of precoding with non-linear relaying.

  • 328.
    Khormuji, Majid N.
    et al.
    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.
    Noisy network coding approach to the relay channel with a random state2011Inngår i: 2011 45th Annual Conference on Information Sciences and Systems, CISS 2011, 2011, s. 1-5Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider the three-node relay channel with a random state. We assume that noncausal knowledge of the random state is partially known at the nodes. We present an achievable rate based on the noisy network coding (NNC) and the Gelfand-Pinsker random binning strategies. We then compare the achievable rate of NNC with that of compress-and-forward.

  • 329.
    Khormuji, Majid N.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    The Relay Channel with Partial Causal State Information2008Inngår i: 2008 International Symposium on Information Theory and its Applications, ISITA2008, NEW YORK: IEEE , 2008, s. 1392-1397Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We investigate the relay channel with a random parameter whose causal knowledge is available partially at the source, the relay and the destination. We define four different classes of this scenario and establish lower and upper bounds on the resulting capacity. We also show that the bounds axe tight in some cases.

  • 330.
    Khormuji, Majid N.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Two-Hop Transmission with Second-Hop Channel State Information2008Inngår i: 2008 INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY AND ITS APPLICATIONS, VOLS 1-3, NEW YORK: IEEE , 2008, s. 678-682Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider a two-hop relay channel with a random parameter in the second hop. We present two main strategies for the case when the random parameter is known non-casually at the source. We then introduce the Gaussian two-hop channel with known interference as one instance of the general model, and present achievable-rate results.

  • 331.
    Khormuji, Majid Nasiri
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    On the capacity of molecular communication over the AIGN channel2011Inngår i: 2011 45th Annual Conference on Information Sciences and Systems, CISS 2011, 2011, s. 5766248-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We study a memoryless molecular communication channel with an additive inverse Gaussian noise (AIGN). We assume that information are encoded in the release time of molecules and the arrival time of the transmitted molecules at the receiver is the release time plus a propagation delay. Motivated by the Brownian motion, the propagation delay is modelled as an inverse Gaussian random variable. Lower- and upper bounds on the capacity are presented. In particular, we develop simple capacity expressions for cases either when the molecules have a high drift velocity or when the medium has a low diffusion coefficient.

  • 332.
    Khormuji, Majid Nasiri
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Symmetric Capacity of the Gaussian Two-Way Relay Channel to Within 1/4e [nat]2013Inngår i: 2013 Information Theory And Applications Workshop (ITA), New York: IEEE , 2013, s. 278-282Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The problem of reliable communication over the Gaussian two-way relay channel is considered and a new achievable rate region by combining structured lattice-and random Gaussian codes is presented. It is then demonstrated that the new bound can outperform previously known rate regions. In particular, having found the optimal time-sharing and power allocation policies, it is established that the proposed strategy achieves the symmetric capacity to within 1/4e approximate to 0.092 [nat] approximate to 0.133 [bit], which improves on earlier bounds.

  • 333.
    Khormuji, Majid Nasiri
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    El Gamal, Abbas
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    State-Dependent Relay Channel: Achievable Rate and Capacity of a Semideterministic Class2013Inngår i: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 59, nr 5, s. 2629-2638Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper considers the problem of communicating over a relay channel with state when noncausal state information is partially available at the nodes. We first establish a lower bound on the achievable rates based on noisy network coding and Gelfand-Pinsker coding, and show that it provides an alternative characterization of a previously known bound. We then introduce the class of state-decoupled relay channels and show that our lower bound is tight for a subclass of semideterministic channels. We also compute the capacity for two specific examples of this subclass-a channel with multiplicative binary fading and a channel with additive Gaussian interference. These examples are not special cases of previous classes of semideterministic relay channels with known capacity.

  • 334.
    Khormuji, Majid Nasiri
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    Finite-SNR Analysis and Optimization of Decode-and-Forward Relaying Over Slow-Fading Channels2009Inngår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 58, nr 8, s. 4292-4305Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We provide analytical results on the finite signal-to-noise ratio (SNR) outage performance of packet-based decode-and-forward relaying over a quasi-static fading channel, with different types of transmitter channel state information (CSI). At the relay, we consider repetition coding (RC) and parallel coding (PC). At the destination, we consider receivers based on selection combining (SC), code combining (CC), and maximum-ratio combining (MRC) (the latter only for the case of RC at the relay). Based on available CSI, we optimize the number of channel uses consumed by the source and by the relay for each packet. In doing so, we consider three different protocols that make use of different combinations of long-term CSI, 1-bit CSI, and complete CSI, respectively, at the source node. Several interesting observations emerge. For example, we show that for high SNRs, SC and CC provide the same outage probabilities when the source has perfect CSI.

  • 335.
    Khormuji, Majid Nasiri
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    Rate-optimized constellation rearrangement for the relay channel2008Inngår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 12, nr 9, s. 618-620Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the. instantaneous relay channel where the relay's output only depends on the current received signal at the relay. We propose a novel forwarding strategy for this class of relay channels which can outperform amplify-and-forward, detect-and-forward and estimate-and-forward. The proposed scheme is based on a remapping of the signal constellation at the relay.

  • 336.
    Khormuji, Majid Nasiri
    et al.
    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.
    Capacity achieving instantaneous relaying2011Inngår i: Wireless Communication Systems (ISWCS), 2011 8th International Symposium on, IEEE , 2011, s. 814-818Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A class of semi-deterministic relay channels is introduced and it is shown that for channels in the class capacity can be achieved using an instantaneous relaying scheme. Applications to Gaussian channels are then discussed.

  • 337.
    Khormuji, Majid Nasiri
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Capacity of Two Semideterministic Classes of Multiple-Access Relay Channels2012Inngår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 16, nr 10, s. 1529-1531Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate memoryless multiple-access relay channels (MARCs) and establish the capacity of two semideterministic classes of such channels: MARCs with orthogonal receive components and state-decoupled MARCs. For both cases, the achievability and converse are proved using the noisy network coding lower bound and the cutset upper bound, respectively. Finally, the capacity of a MARC with additive Gaussian interference is quantified.

  • 338.
    Khormuji, Majid Nasiri
    et al.
    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.
    Hybrid Digital-Analog Noisy Network Coding2011Inngår i: 2011 International Symposium on Network Coding, NETCOD 2011 - Proceedings, 2011, s. 5979088-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We investigate noisy network coding strategies for the two-way Gaussian relay channel. We present three hybrid digital-analog noisy network coding schemes. The schemes are constructed by combination of linear analog noisy network coding, Wyner-Ziv- based compress-and-forward, and noisy network coding as proposed by Lim et al. We show that our proposed schemes outperform existing protocols for this problem.

  • 339.
    Khormuji, Majid Nasiri
    et al.
    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.
    Noisy analog network coding for the two-way relay channel2011Inngår i: Information Theory Proceedings (ISIT), 2011 IEEE International Symposium on, 2011, s. 2065-2069Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An achievable rate region based on Shannon’s inner bound is given for the two-way relay channel. The relaying scheme operates on noisy received signals and generates new analog values to be transmitted to a destination. The scheme is therefore referred to as noisy analog network coding. The achievable rates are then optimized for a Gaussian two-way relay channel, when the relay is memoryless (this type of relaying is also known as instantaneous relaying). For one particular instance of the channel when the received signal at the relay is noiseless, it is shown that instantaneous noisy analog network coding can be optimal. For the noisy case, a numerical optimization algorithm is presented in order to optimize the instantaneous coding strategy. The optimized analog mapping turns out to be nonlinear and periodic. Finally, it is demonstrated that the achievable rates associated with optimized mappings can outperform those achieved by linear relaying, compress-and-forward, and can operate close to the recently proposed noisy network coding scheme.

  • 340.
    Khormuji, Majid Nasiri
    et al.
    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 Cooperative Downlink Transmission with Frequency Reuse2009Inngår i: IEEE International Symposium on Information Theory - Proceedings, NEW YORK: IEEE , 2009, s. 849-853Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We study a three-node Gaussian relay channel with interference which is non-causally known at the source. It is assumed that the interference affects only the relay destination link. This model is motivated by a downlink scenario, where the source (base station), communicates with two destinations. We present several transmission strategies for this class of relay channels. Our proposed relaying schemes can be divided into two main categories: instantaneous relaying and causal relaying. In the former, the relay functionality is restricted to a memoryless, symbol-by-symbol mapping (linear as well as non-linear). While in the latter, the relay has an infinite memory and utilizes past received blocks to cooperate in the present block. For causal relaying, we investigate decode-and-forward (DF), compress-and-forward (CF), and combined DF and CF. To utilize the knowledge of the interference at the source, superposition coding at the source and Costa encoding at the relay are employed. One interesting observation is that instantaneous relaying can achieve higher rates than those achieved with causal relaying.

  • 341.
    Khormuji, Majid Nasiri
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    On Instantaneous Relaying2010Inngår i: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 56, nr 7, s. 3378-3394Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Gaussian, three-node relay channel with orthogonal receive components (i.e., the transmitted signals from the source and the relay do not interfere with each other) is investigated. For such channels, linear relaying is a suboptimal strategy in general. This is because a linear scheme merely repeats the received noisy signal and does not utilize the available degrees of freedom efficiently. At this background, nonlinear, symbol-wise (as opposed to block-wise) relaying strategies are developed to compensate for the shortcomings of the linear strategy. Optimal strategies are presented for two special cases of the general scenario, and it is shown that memoryless relaying can achieve the capacity. Furthermore, for the general Gaussian relay channel, a parametric piecewise linear (PL) mapping is proposed and analyzed. The achievable rates obtained by the PL mapping are computed numerically and optimized for a certain number of design parameters. It is concluded that optimized PL relaying always outperforms conventional instantaneous linear relaying (amplify-and-forward). It is also illustrated that the proposed PL relaying scheme can improve on sophisticated block Markov encoding (i.e., decode-and-forward) when the source-relay link is ill-conditioned (relative to other links). Furthermore, PL relaying can work at rates close to those achieved by side-information encoding (i.e., compress-and-forward), but at a much lower complexity.

  • 342.
    Kim, Su Min
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Do, Tan Tai
    Oechtering, Tobias J.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Peters, Gunnar
    On the Entropy Computation of Large Complex Gaussian Mixture Distributions2015Inngår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 63, nr 17, s. 4710-4723Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The entropy computation of Gaussian mixture distributions with a large number of components has a prohibitive computational complexity. In this paper, we propose a novel approach exploiting the sphere decoding concept to bound and approximate such entropy terms with reduced complexity and good accuracy. Moreover, we propose an SNR region-based enhancement of the approximation method to reduce the complexity even further. Using Monte-Carlo simulations, the proposed methods are numerically demonstrated for the computation of the mutual information including the entropy term of various channels with finite constellation modulations such as binary and quadratic amplitude modulation (QAM) inputs for communication applications.

  • 343.
    Kim, Su Min
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Do, Tan Tai
    KTH, Skolan för elektro- och systemteknik (EES).
    Oechtering, Tobias J.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Peters, Gunnar
    Huawei Technologies Sweden AB.
    Sphere decoding inspired approximation method to compute the entropy of large Gaussian mixture distributions2014Inngår i: IEEE Workshop on Statistical Signal Processing Proceedings, 2014, s. 264-267Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The computation of mutual informations of large scale systems with finite input alphabet and Gaussian noise has often prohibitive complexities. In this paper, we propose a novel approach exploiting the sphere decoding concept to bound and approximate such mutual information term with reduced complexity and good accuracy. Using Monte-Carlo simulations, the method is numerically demonstrated for the computation of the mutual information of a frequency- and time-selective channel with QAM modulation.

  • 344. Kim, T.
    et al.
    Choudhury, S.
    Doppler, K.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Simultaneous polling mechanism with uplink power control for low power sensor nodes2013Inngår i: 2013 IEEE 77th Vehicular Technology Conference (VTC Spring), IEEE , 2013, s. 6692755-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Collecting sensory data at access point (AP) from large number of sensor nodes with low latency is a critical issue. In Wi-Fi, prior to uplink data delivery, AP typically needs to poll large number of sensor nodes sequentially and allocate channel resources to individual node resulting in large latency. An efficient method to reduce the latency and power consumption in wireless sensor networks is to parallelize the polling operation so that multiple nodes can concurrently respond to the poll request of an AP by sending orthogonal sequences with uplink power control. In this paper, we present a conceptually simple uplink power control scheme for the parallel polling operation between AP and low power sensor nodes. We formulate the uplink power control problem as a sequence design problem and show that uplink channel state information (CSI) required to achieve a given target receive SNR can be significantly reduced by carefully designing sequences. We further develop a low complexity instantaneous (fast) power control scheme in order to reduce the number of computations required by the low power sensor node. We also analyze and compare the detection performance of the instantaneous (fast) and average (slow) power control schemes in terms of diversity gain.

  • 345. Kim, Taejoon
    et al.
    Love, David J.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Jin, Zhong-Yi
    An Approach to Sensor Network Throughput Enhancement by PHY-Aided MAC2015Inngår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, nr 2, s. 670-684Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Low power sensor networks with communication enabled by WiFi are expected to be widely deployed. A major challenge is collecting event-driven uplink data from a large number of low-power sensors with low latency. In WiFi, the access point (AP) typically polls nodes individually to schedule uplink transmission times, resulting in a large latency. In this paper, we present a physical (PHY) layer-aided medium access control (MAC) framework to enhance the uplink throughput of sensor data traffic. In the approach, the acknowledgements from the sensor nodes to the poll message are parallelized. By detecting the parallel acknowledgement, the AP knows which nodes have data to send and allocates channel resources by sending a pull message. This approach is referred to as the probe and pull MAC (PPMAC) mechanism. Our scheme is based on maximizing the achievable throughput of PPMAC by optimizing the PHY layer components. More precisely, we investigate the parallel acknowledgement detector design problem and develop a non-convex optimization framework that maximizes the PPMAC throughput by optimizing the parallel acknowledgement detection statistics. Numerical examples illustrate that PPMAC outperforms the point coordination function (PCF) and distributed coordination function (DCF) mechanisms, standardized in IEEE 802.11, in terms of the achievable throughput and the overhead.

  • 346.
    Kim, Thanh Tung
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. 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.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Combining long-term and low-rate short-term channel state information over correlated MIMO channels2008Inngår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 7, nr 7, s. 2409-2414Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A simple structure to exploit both long-term and partial short-term channel state information at the transmitter (CSIT) over a family of correlated multiple-antenna channels is proposed. Partial short-term CSIT in the form of a weighting matrix is combined with a unitary transformation based on the long-term channel statistics. The heavily quantized feedback link is directly optimized to maximize the expected achievable rate under different power constraints, using vector quantization and convex optimization techniques on a sample channel distribution. Robustness against errors in the feedback link is also pursued with tools in channel optimized vector quantization. Simulations indicate the benefits of the proposed scheme.

  • 347.
    Kim, Thanh Tung
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Combining short-term and long-term channel state information over correlated MIMO channels2006Inngår i: 2006 IEEE International Conference on Acoustics, Speech, and Signal Processing, 2006, s. 13-16Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A simple structure to exploit both long-term and partial short-term channel state information at the transmitter (CSIT) over a family of correlated multiple-antenna channels is proposed. Partial short-term CSIT in the form of a weighting matrix is obtained via a resolution-constrained feedback link, combined with a unitary transformation based on the long-term channel statistics. The feedback link is optimized to maximize the expected achievable rate under different power constraints, using vector quantization techniques. Simulations indicate the benefits of the proposed scheme in all scenarios considered.

  • 348.
    Kim, Thanh Tung
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Quantized feedback design for MIMO broadcast channels2007Inngår i: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, 2007, s. 1-4Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Low-rate feedback design for multiple-input multiple-output broadcast channels is studied under a vector quantization framework. Iterative algorithms are proposed to design the partial feedback link, the scheduler, and the linear precoding code-book. It is demonstrated that the gain due to multi-user diversity can be significant even with heavily quantized channel state information at the transmitter. Our results highlight the potential of multi-user diversity, even with simple schemes and extremely-low-rate feedback.

  • 349.
    Kim, Thanh Tung
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Caire, Giuseppe
    Diversity Gains of Power Control With Noisy CSIT in MIMO Channels2009Inngår i: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 55, nr 4, s. 1618-1626Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A multiantenna channel with partial channel state information at the transmitter (CSIT) is studied. The partial CSIT takes the form of the channel matrix corrupted by additive white Gaussian noise (AWGN) with a variance that is assumed to decay as a power of the signal-to-noise ratio (SNR). It is shown that under a long-term power constraint and in the regime of asymptotically high SNR, a large diversity gain over the channel can be achieved by using rarely a high power at the transmitter that compensates for bad channel realizations. Examples relating the diversity gain of the systems with the channel Doppler bandwidth are discussed.

  • 350.
    Kim, Thanh Tung
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Caire, Giuseppe
    USC.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Decode-and-forward relaying with quantized channel state feedback: An outage exponent analysis2008Inngår i: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 54, nr 10, s. 4548-4564Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The problem of resource allocation to maximize the outage exponent over a fading relay channel using the decode-and-forward protocol with quantized channel state feedback (CSF) is studied. Three different scenarios are considered: relay-to-source, destination-to-relay, and destination-to-source-and-relay CSF. In the relay-to-source CSF scenario, it is found that using merely one bit of CSF to control the source transmit power is sufficient to achieve the multiantenna upper bound in a range of multiplexing gains. In the destination-to-relay CSF scenario, the systems slightly outperform dynamic decode-and-forward (DDF) at high multiplexing gains, even with only one bit of feedback. Finally, in the destination-to-source-and-relay CSF scenario, if the source-relay channel gain is unknown to the feedback quantizer at the destination, the diversity gain only grows linearly in the number of feedback levels, in sharp contrast to an exponential growth for multiantenna channels. In this last scenario, a simple scheme is shown to perform close to the corresponding upper bound.

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