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  • 151.
    Du, Rong
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Fischione, Carlo
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Lifetime Maximization for Sensor Networks with Wireless Energy Transfer2016Inngår i: 2016 IEEE International Conference on Communications, ICC 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, s. 20-25, artikkel-id 7510602Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In Wireless Sensor Networks (WSNs), to supply energy to the sensor nodes, wireless energy transfer (WET) is a promising technique. One of the most efficient procedures to transfer energy to the sensor nodes consists in using a sharp wireless energy beam from the base station to each node at a time. A natural fundamental question is what is the lifetime ensured by WET and how to maximize the network lifetime by scheduling the transmissions of the energy beams. In this paper, such a question is addressed by posing a new lifetime maximization problem for WET enabled WSNs. The binary nature of the energy transmission process introduces a binary constraint in the optimization problem, which makes challenging the investigation of the fundamental properties of WET and the computation of the optimal solution. The sufficient condition for which the WET makes WSNs immortal is established as function of the WET parameters. When such a condition is not met, a solution algorithm to the maximum lifetime problem is proposed. The numerical results show that the lifetime achieved by the proposed algorithm increases by about 50% compared to the case without WET, for a WSN with a small to medium size number of nodes. This suggests that it is desirable to schedule WET to prolong lifetime of WSNs having small or medium network sizes.

  • 152.
    Du, Rong
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Fischione, Carlo
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Poster: On the Immortality of Wireless Sensor Networks by Wireless Energy Transfer - A Node Deployment Perspective2017Inngår i: Proceedings of International Conference on Embedded Wireless Systems and Networks, 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The lifetime of wireless sensor networks (WSNs) can be substantially extended by transferring energy wirelessly to the sensor nodes. In this poster, a wireless energy transfer (WET) enabled WSN is presented, where a base station transfers energy wirelessly to the sensor nodes that are deployed in several regions of interest, to supply them with energy to sense and to upload data. The WSN lifetime can be extended by deploying redundant sensor nodes, which allows the implementation of duty-cycling mechanisms to reduce nodes' energy consumption. In this context, a problem on sensor node deployment naturally arises, where one needs to determine how many sensor nodes to deploy in each region such that the total number of nodes is minimized, and the WSN is immortal. The problem is formulated as an integer optimization, whose solution is challenging due to the binary decision variables and a non-linear constraint. A greedy-based algorithm is proposed to achieve the optimal solution of such deployment problem. It is argued  that such scheme can be used in monitoring systems in smart cities, such as smart buildings and water lines.

  • 153.
    Du, Rong
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Gkatzikis, Lazaros
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Fischione, Carlo
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Xiag, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Energy Efficient Sensor Activation for Water Distribution Networks Based on Compressive Sensing2015Inngår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 33, nr 12, s. 2997-3010Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The recent development of low cost wireless sensors enables novel internet-of-things (IoT) applications, such as the monitoring of water distribution networks. In such scenarios, the lifetime of the wireless sensor network (WSN) is a major concern, given that sensor node replacement is generally inconvenient and costly. In this paper, a compressive sensing-based scheduling scheme is proposed that conserves energy by activating only a small subset of sensor nodes in each timeslot to sense and transmit. Compressive sensing introduces a cardinality constraint that makes the scheduling optimization problem particularly challenging. Taking advantage of the network topology imposed by the IoT water monitoring scenario, the scheduling problem is decomposed into simpler subproblems, and a dynamic-programming-based solution method is proposed. Based on the proposed method, a solution algorithm is derived, whose complexity and energy-wise performance are investigated. The complexity of the proposed algorithm is characterized and its performance is evaluated numerically via an IoT emulator of water distribution networks. The analytical and numerical results show that the proposed algorithm outperforms state-of-the-art approaches in terms of energy consumption, network lifetime, and robustness to sensor node failures. It is argued that the derived solution approach is general and it can be potentially applied to more IoT scenarios such as WSN scheduling in smart cities and intelligent transport systems.

  • 154.
    Du, Rong
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Gkatzikis, Lazaros
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Fischione, Carlo
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Energy efficient monitoring of water distribution networks via compressive sensing2015Inngår i: 2015 IEEE International Conference on Communications (ICC), IEEE conference proceedings, 2015, Vol. 2015, s. 6681-6686Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The recent development of low cost wireless sensors enables water monitoring through dense wireless sensor networks (WSN). Sensor nodes are battery powered devices, and hence their limited energy resources have to be optimally managed. The latest advancements in compressive sensing (CS) provide ample promise to increase WSNs lifetime by limiting the amount of measurements that have to be collected. Additional energy savings can be achieved through CS-based scheduling schemes that activate only a limited number of sensors to sense and transmit their measurements, whereas the rest are turned off. The ultimate objective is to maximize network lifetime without sacrificing network connectivity and monitoring performance. This problem can be approximated by an energy balancing approach that consists of multiple simpler subproblems, each of which corresponds to a specific time period. Then, the sensors that should be activated within a given period can be optimally derived through dynamic programming. The complexity of the proposed CS-based scheduling scheme is characterized and numerical evaluation reveals that it achieves comparable monitoring performance by activating only a fraction of the sensors.

  • 155.
    Dössel, 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.
    Anytime reliability of systematic LDPC convolutional codes2012Inngår i: Communications (ICC), 2012 IEEE International Conference on, IEEE , 2012, s. 2171-2175Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We propose a LDPC Convolutional Code ensemble together with an expanding-window message-passing decoder that asymptotically have anytime properties when used for streaming transmission on the binary erasure channel. We show analytically that the decoding erasure probability of these codes decays exponentially over decoding delay and determine the corresponding anytime exponents.

  • 156.
    Ebri Mars, David
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Multi-View Vocabulary Trees for Mobile 3D Visual Search2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Mobile Visual Search (MVS) is a research field which focuses on the recognition of real-world objects by using mobile devices such as smart phones or robots. Current mobile visual search solutions achieve search results based on the appearance of the objects in images captured by mobile devices. It is suitable for planar structured objects such as CD cover images, magazines and art works. However, these solutions fail if different real objects appear similar in the captured images. To solve this problem, the novel solution captures not only the visual appearance of the query object, but uses also the underlying 3D geometry.

    Vocabulary Tree (VT) methods have been widely used to efficiently find the match for a query in the database with a large volume of data. In this thesis, we study the vocabulary tree in the scenario of multi-view imagery for mobile visual search. We use hierarchically structured multi-view features to construct a multi-view vocabulary trees which represent the 3D geometric information of the objects. Relevant aspects of vocabulary trees such as the shaping of trees, tf-idf weighting and scoring functions have been studied and incorporated in the multi-view scenario. The experimental results show that our multi-view vocabulary trees improve the matching and ranking performance of mobile visual search.

  • 157.
    Ebri Mars, David
    et al.
    KTH, Skolan för elektro- och systemteknik (EES).
    Wu, Hanwei
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Li, Haopeng
    KTH, Skolan för elektro- och systemteknik (EES).
    Flierl, Markus
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    GEOMETRY-BASED RANKING FOR MOBILE 3D VISUAL SEARCH USING HIERARCHICALLY STRUCTURED MULTI-VIEW FEATURES2015Inngår i: 2015 IEEE INTERNATIONAL CONFERENCE ON IMAGE PROCESSING (ICIP), IEEE Computer Society, 2015, s. 3077-3081Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper proposes geometry-based ranking for mobile 3D visual search. It utilizes the underlying geometry of the 3D objects as well as the appearance to improve the ranking results. A double hierarchy has been embedded in the data structure, namely the hierarchically structured multi-view features for each object and a tree hierarchy from multi-view vocabulary trees. As the 3D geometry information is incorporated in the multi-view vocabulary tree, it allows us to evaluate the consistency of the 3D geometry at low computational complexity. Thus, a cost function is proposed for object ranking using geometric consistency. With that, we devise an iterative algorithm that accomplishes 3D geometry-based ranking. The experimental results show that our 3D geometry-based ranking improves the recall-datarate performance as well as the subjective ranking results for mobile 3D visual search.

  • 158. Emadi, M. J.
    et al.
    Khormuji, M. N.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Aref, M. R.
    The generalized MAC with partial state and message cooperation2014Inngår i: IWCIT 2014 - Iran Workshop on Communication and Information Theory, 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider a two-user state-dependent generalized multiple access channel (GMAC) with correlated channel state information (CSI). It is assumed that the CSI is partially known at each encoder noncausally. We first present an achievable rate region using multi-layer Gelfand-Pinsker coding with partial state and message cooperation between the encoders. We then specialize our result to a Gaussian GMAC with additive interferences that are known partially at each encoder. We show that the proposed scheme can remove the common part known at both encoders and also mitigate a significant part of the independent interference via state cooperation when the feedback links are strong. Thus, the proposed scheme can significantly improve the rate region as compared to that with only message cooperation.

  • 159. Emadi, M. J.
    et al.
    Khormuji, Majid Nasiri
    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.
    Aref, M. R.
    Multi-layer Gelfand-Pinsker strategies for the generalized multiple-access channel2013Inngår i: 2013 Iran Workshop on Communication and Information Theory, IWCIT 2013, 2013, s. 6555750-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We study a two-user state-dependent generalized multiple-access channel (GMAC) with correlated states. It is assumed that each encoder noncausally knows partial channel state information. We develop an achievable rate region by employing rate-splitting, block Markov encoding, Gelfand-Pinsker multicoding, superposition coding and jointly typical decoding. In the proposed scheme, the encoders use a partial decoding strategy to collaborate in the next block, and the receiver uses a backward decoding strategy with a joint unique decoding at each stage. Our achievable rate region includes several previously known rate regions proposed in the literature for different scenarios of multiple-access and relay channels. We finally consider a Gaussian GMAC with an additive interference which is known noncausally at both of the encoders and construct a multi-layer Costa precoding scheme that removes completely the effect of the interference.

  • 160. Emadi, M. J.
    et al.
    Nasiri Khormuji, Majid
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Aref, M. R.
    On the achievable rate region of a state-dependent MAC with cooperating encoders2012Inngår i: 2012 Swedish Communication Technologies Workshop, Swe-CTW 2012, IEEE , 2012, s. 48-52Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The two-user discrete memoryless state-dependent multiple-access channel with cooperating encoders is considered. It is assumed that the channel is controlled with two independent states such that each of the channel state information is noncausally available at one encoder. Moreover, based on the intrinsic characteristic of wireless networks, it is assumed that each encoder strictly causally receive a noisy version of the transmitted signal of the other encoder. Hence, the encoders can cooperate in transmitting the message to the receiver. An achievable rate region for the channel is derived by use of rate splitting, block Markov encoding and Gelfand-Pinsker multilevel encoding along with partial decoding at the encoders and backward decoding at the receiver. Finally, for a Gaussian channel model the proposed achievable rate region is evaluated and discussed.

  • 161. Emadi, Mohammad Javad
    et al.
    Khormuji, Majid Nasiri
    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.
    Aref, Mohammad Reza
    Multi-layer Gelfand-Pinsker strategies for the generalised multiple-access channel2014Inngår i: IET Communications, ISSN 1751-8628, Vol. 8, nr 8, s. 1296-1308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The authors study a two-user state-dependent generalised multiple-access channel (GMAC) with correlated states. It is assumed that each encoder has non-causal' access to channel state information (CSI). They develop an achievable rate region by employing rate-splitting, block Markov encoding, Gelfand-Pinsker multicoding, superposition coding and joint typicality decoding. In the proposed scheme, the encoders use a partial decoding strategy to collaborate in the next block, and the receiver uses a backward decoding strategy with joint unique decoding at each stage. The author's achievable rate region includes several previously known regions proposed in the literature for different scenarios of multiple-access and relay channels. Then, they consider two Gaussian GMACs with additive interference. In the first model, they assume that the interference is known non-causally at both of the encoders and construct a multi-layer Costa precoding scheme that removes completely' the effect of the interference. In the second model, they consider a doubly dirty Gaussian GMAC in which each of interferences is known non-causally only at one encoder. They derive an inner bound and analyse the achievable rate region for the latter model and interestingly prove that if one of the encoders knows the full CSI, there exists an achievable rate region which is independent' of the power of interference.

  • 162.
    Fanny, Roche
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Evaluation of Audio FeatureExtraction Techniques to ClassifySynthesizer Sounds2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    After many years focused on speech signal processing, the research in audio processing started to investigate the field of music processing. Music Information Retrieval is a very new topic steadily growing since a few years as music is more and more part of our daily life, particularly thanks to the new technologies like mp3 players and smartphones. Moreover, with the development of electronic music and the huge improvements in computational power, new instruments have appeared such as virtual instruments, bringing with them new needs concerning the availability of sounds. One main necessity which came with these novel technologies is to have a user friendly system to make it easy for the users to have access to the whole range of sounds the device can offer.  In this thesis, the purpose is to implement a smart automatic classification of synthesizer sounds based on audio descriptors without any human influence. Hence the study first focus on what is a musical sound and what are the main characteristics of synthesizer sounds that need to be extracted using wisely chosen audio descriptors extraction. Then the interest moves to a classifier system based on the Self-Organizing Map model using unsupervised learning to match with the main purpose to avoid any human bias and use only objective parameters for the sounds classification. Finally the evaluation of the system is done, showing that it gives good results both in terms of accuracy and time efficiency.

  • 163. Farhadi, H.
    et al.
    Atai, J.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Nadimi, E. S.
    Pahlavan, K.
    Tarokh, V.
    An adaptive localization technique for wireless capsule endoscopy2016Inngår i: International Symposium on Medical Information and Communication Technology, ISMICT, IEEE Computer Society, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Wireless capsule endoscopy (WCE) is an emerging technique to enhance Gastroenterologists information about the patient's gastrointestinal (G.I.) tract. Localization of capsule inside human body in this case is an active area of research. This can be thought of as a sub-domain of micro and bio-robotics fields. If capsule and micro-robot localization problem in human body is solved, then it may potentially lead to less invasive treatments for G.I. diseases and other micro-robot assisted medical procedures. Several approaches have been investigated by the researchers to estimate capsule location. The proposed solutions are mainly static and thus prone to the changes in the propagation medium. We propose an adaptive algorithm based on expectation maximization technique for capsule localization. The proposed algorithm adaptively updates the estimated location based on the received radio frequency (RF) signal measurements.

  • 164.
    Farhadi, Hamed
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Coordinated Transmission for Wireless Interference Networks2014Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Wireless interference networks refer to communication systems in which multiple source–destination pairs share the same transmission medium, and each source’s transmission interferes with the reception at non-intended destinations. Optimizing the transmission of each source–destination pair is interrelated with that of the other pairs, and characterizing the performance limits of these networks is a challenging task. Solving the problem of managing the interference and data communications for these networks would potentially make it possible to apply solutions to several existing and emerging communication systems. Wireless devices can carefully coordinate the use of scarce radio resources in order to deal effectively with interference and establish successful communications. In order to enable coordinated transmission, terminals must usually have a certain level of knowledge about the propagation environment; that is, channel state information (CSI). In practice, however, no CSI is a priori available at terminals (transmitters and receivers), and proper channel training mechanisms (such as pilot-based channel training and channel state feedback) should be employed to acquire CSI. This requires each terminal to share available radio resources between channel training and data transmissions. Allocating more resources for channel training leads to an accurate CSI estimation, and consequently, a precise coordination. However, it leaves fewer resources for data transmissions. This creates the need to investigate optimum resource allocation. This thesis investigates an information-theoretic approach towards the performance analysis of interference networks, and employs signal processing techniques to design transmission schemes for achieving these limits in the following scenarios. First, the smallest interference network with two single-input single-output (SISO) source–destination pairs is considered. A fixed-rate transmission is desired between each source–destination pair. Transmission schemes based on point-to-point codes are developed. The transmissions may not always attain successful communication, which means that outage events may be declared. The outage probability is quantified and the ε-outage achievable rate region is characterized. Next, a multi-user SISO interference network is studied. A pilot-assisted ergodic interference alignment (PAEIA) scheme is proposed to conduct channel training, channel state feedback, and data communications. The performance limits are evaluated, and optimum radio resource allocation problems are investigated. The analysis is extended to multi-cell wireless interference networks. A low-complexity pilot-assisted opportunistic user scheduling (PAOUS) scheme is proposed. The proposed scheme includes channel training, one-bit feedback transmission, user scheduling and data transmissions. The achievable rate region is computed, and the optimum number of cells that should be active simultaneously is determined. A multi-user MIMO interference network is also studied. Here, each source sends multiple data streams; specifically, the same number as the degrees of freedom of the network. Distributed transceiver design and power control algorithms are proposed that only require local CSI at terminals.

  • 165.
    Farhadi, Hamed
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Interference alignment and power control for wireless interference networks2012Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    This thesis deals with the design of efficient transmission schemes forwireless interference networks, when certain channel state information(CSI) is available at the terminals.In wireless interference networks multiple source-destination pairsshare the same transmission medium for the communications. The signalreception at each destination is affected by the interference from unintendedsources. This may lead to a competitive situation that each sourcetries to compensate the negative effect of interference at its desired destinationby increasing its transmission power, while it in fact increasesthe interference to the other destinations. Ignoring this dependency maycause a significant waste of available radio resource. Since the transmissiondesign for each user is interrelated to the other users’ strategies, anefficient radio resource allocation should be jointly performed consideringall the source-destination pairs. This may require a certain amount ofCSI to be exchanged, e.g. through feedback channels, among differentterminals. In this thesis, we investigate such joint transmission designand resource allocation in wireless interference networks.We first consider the smallest interference network with two sourcedestinationpairs. Each source intends to communicate with its dedicateddestination with a fixed transmission rate. All terminals have the perfectglobal CSI. The power control seeks feasible solutions that properly assigntransmission power to each source in order to guarantee the successfulcommunications of both source-destination pairs. To avoid interference,the transmissions of the two sources can be orthogonalized. They canalso be activated non-orthogonally. In this case, each destination maydirectly decode its desired signals by treating the interference signals asnoise. It may also perform decoding of its desired signals after decodingand subtracting the interference signals sent from the unintendedsources. The non-orthogonal transmission can more efficiently utilize the 

    available channel such that the power control problem has solutions withsmaller transmission power in comparison with the orthogonal transmission.However, due to the randomness of fading effects, feasible powercontrol solutions may not always exist. We quantify the probability thatthe power control problem has feasible solutions, under a Rayleigh fadingenvironment. A hybrid transmission strategy that combines the orthogonaland non-orthogonal transmissions is then employed to use the smallesttransmission power to guarantee the communications in the consideredtwo-user interference network.The network model is further extended to the general K-user interferencenetwork, which is far more complicated than the two-user case. Thecommunication is conducted in a time-varying fading environment. Thefeedback channel’s capacity is limited so that each terminal can obtainonly quantized global CSI. Conventional interference management techniquestend to orthogonalize the transmissions of the sources. However,we permit them to transmit non-orthogonally and apply an interferencealignment scheme to tackle inter-user interference. Ideally, the interferencealignment concept coordinates the transmissions of the sources insuch a way that at each destination the interference signals from differentunintended sources are aligned together in the same sub-space which isdistinguishable from the sub-space for its desired signals. Hence, eachdestination can cancel the interference signals before performing decoding.Nevertheless, due to the imperfect channel knowledge, the interferencecannot be completely eliminated and thus causes difficulties to theinformation recovery process. We study efficient resource allocation intwo different classes of systems. In the first class, each source desires tosend information to its destination with a fixed data rate. The powercontrol problem tends to find the smallest transmission powers to guaranteesuccessful communications between all the source-destination pairs.In another class of systems where the transmission power of each sourceis fixed, a rate adaptation problem seeks the maximum sum throughputthat the network can support. In both cases, the combination of interferencealignment and efficient resource allocation provides substantialperformance enhancement over the conventional orthogonal transmissionscheme.When the fading environment is time-invariant, interference alignmentcan still be realized if each terminal is equipped with multiple antennas.With perfect global CSI at all terminals, the interference signalscan be aligned in the spatial dimension. If each terminal has only localCSI, which refers to the knowledge of channels directly related to 

    the terminal itself, an iterative algorithm can be applied to calculate thenecessary transmitter-side beamformers and receiver-side filters to properlyalign and cancel interference, respectively. Again, due to the lack ofperfect global CSI, it is difficult to completely eliminate the interferenceat each destination. We study the power control problem in this caseto calculate the minimum required power that guarantees each source tosuccessfully communicate with its destination with a fixed transmissionrate. In particular, since only local CSI is available at each terminal, wepropose an iterative algorithm that solves the joint power control andinterference alignment design in a distributed fashion. Our results showthat a substantial performance gain in terms of required transmissionpower over the orthogonalizing the transmissions of different sources canbe obtained.

  • 166.
    Farhadi, Hamed
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Ghauch, Hadi
    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.
    Pilot-assisted opportunistic user scheduling for wireless multi-cell networks2015Inngår i: IEEE International Conference on Communications, IEEE , 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider downlink transmission in multi-cell wireless networks where in each cell one base station is serving multiple mobile terminals. There is no a priori channel state information (CSI) available at base stations and mobile terminals. We propose a low-complexity pilot-assisted opportunistic user scheduling (PAOUS) scheme. The proposed scheme operates in four subsequent phases: channel training; feedback transmission; user scheduling; and data transmission. We deploy an orthogonal pilot-assisted channel training scheme for acquiring CST at mobile terminals. Consequently, each mobile terminal obtains a noisy estimation of the corresponding local CST (i.e. channel gains from base stations to the mobile terminal). Then, it makes a local decision based on the estimated channel gains of the interfering links (i.e. the links between base stations in neighboring cells and the mobile terminal) and sends a one-bit feedback signal to the base station of the corresponding cell. Each base station schedules one mobile terminal for communication. We compute the achievable rate region and the achievable degrees of freedom (DoF) of the proposed transmission scheme. Our results show that in a multi-cell network with K base stations and coherence time T, the total DoF K-opt (1 - K-opt/T) is achievable given that the number of mobile terminals in each cell scales proportional to signal-to-noise-ratio. Since limited radio resources are available, only a subset of base stations should be activated, where the optimum number of active base stations is K-opt = min {K, T/2}. This recommends that in large networks (K > T/2), select only a subset of the base stations to be active and perform the PAOUS scheme within the cells associated to these base stations. Our results reveal that, even with single antenna at base stations and no a priori CSI at terminals, a non-trivial DoF gain can be achieved. We also investigate the power allocation between channel training and data transmission phases. Our study shows that in large networks (many base stations) more power should be allocated to channel training while in dense networks (many mobile terminals in each cell) more power should be allocated for data transmission.

  • 167.
    Farhadi, Hamed
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Nasiri Khormuji, Majid
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Pilot-assisted ergodic interference alignment for wireless networks2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper considers the ergodic block fading multi-user Gaussian interference channel (IC) in which each source desires to communicate to an intended destination. We assume that there is no CSI a priori available at terminals. We develop achievable rate results and compute the associated degrees of freedom by using a pilot-assisted interference alignment scheme. In this scheme, each source first sends known pilot symbols via which the destinations estimate channel gains,  and the destinations then broadcast the estimated channel gains via orthogonal feedback channels. The estimated channel gains are used to perform interference alignment for data transmission. The pilot transmission power can be different from the data transmission power. By allocating more power to pilot transmission, channel gains can be estimated more accurately which implies less power left for data transmission. We find the optimum power allocation to pilot symbols and data symbols. Our study recommends, in large networks, to allocate more power to channel training instead of data transmission. In addition, our results reveal that for a K-user ergodic IC with a coherence time T, the total degrees of freedom 1/2Kopt(1-Kopt/T) is achievable, where Kopt=min{K,T/2} is the optimum number of users selected to be active in the network. This recommends to perform a user selection in large networks (K>T/2), and apply channel training and interference alignment within the set of selected users.

  • 168.
    Farhadi, Hamed
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Nasiri Khormuji, Majid
    Wang, Chao
    Tongji University, P.R. China.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Ergodic interference alignment with noisy channel state information2013Inngår i: 2013 IEEE International Symposium on Information Theory Proceedings (ISIT), IEEE conference proceedings, 2013, s. 584-588Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We investigate the multi-user time-varying Gaussian interference channel (IC) in which each source desires to communicate to an intended destination. For the ergodic time-varying IC with global perfect CSI at all terminals, it is known that with an interference alignment technique each source-destinationpair can communicate at half of the interference-free achievable rate. In practice, the channel gains are estimated by transmitting known pilot symbols from the sources, and the channel estimation procedure is hence prone to errors. In this paper, we model the channel estimation error at the destinations by an independent additive Gaussian noise and study the behavior of the ergodic interference alignment scheme with the global noisy CSI at all terminals. Toward this end, we present a closed-form innerbound on the achievable rate region by which we conclude that the achievable degrees of freedom with global perfect CSI is preserved, if the variance of channel estimation error is proportional to the inverse of the transmitted power.

  • 169.
    Farhadi, Hamed
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Wang, Chao
    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.
    Distributed interference alignment and power control for wireless MIMO interference networks2013Inngår i: 2013 IEEE Wireless Communications and Networking Conference (WCNC), IEEE Communications Society, 2013, s. 3077-3082Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper considers joint transceiver design and power control for K-user multiple-input multiple-output (MIMO) interference networks. Each source intends to communicate with its corresponding destination at a fixed data rate. Only local channel side information (i.e. knowledge related to the channels directly connected to a terminal) is available at each terminal. We propose iterative algorithms to perform power control to guarantee successful communication while designing transmitter beamforming matrices and receiver filtering matrices according to the interference alignment concept. The proposed algorithms can exhibit a substantial performance improvement compared to the conventional orthogonal transmission schemes.

  • 170.
    Farhadi, Hamed
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Wang, Chao
    Tongji University.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Distributed Transceiver Design and Power Control for Wireless MIMO Interference Networks2015Inngår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, nr 3, s. 1199-1212, artikkel-id 7055983Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper considers distributed transceiver design and power control for K-user multiple-input-multiple-output interference networks. Each source intends to send multiple independent data streams to its corresponding destination where the number of data streams coincides with the degrees of freedom of the network. Each data stream is encoded at a fixed data rate, whereas different streams can be encoded at possibly different rates. We assume that only local channel side information (i.e., knowledge related to channels directly connected to a terminal) can be acquired by each terminal. We propose iterative algorithms to perform both power control and transceiver design. Transmitter beamforming matrices and receiver filtering matrices are designed to maximize signal-to-interference-plus-noise ratio corresponding to each stream, and a power control scheme is performed to assign the minimum power to each encoded data stream such that successful communication can be guaranteed. The proposed algorithms exhibit a substantial performance improvement compared with the conventional orthogonal transmission schemes.

  • 171.
    Farhadi, Hamed
    et al.
    Chalmers University of Technology, Gothenburg, Sweden.
    Wang, Chao
    Tongji University, Shanghai, China.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Ergodic Interference Alignment with Limited Feedback: Power Control and Rate Adaptation2015Inngår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 4, nr 12, s. 6679-6694Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Considering the time-varying K-user single-antenna interference channel (IC), it has been shown that, when terminals have perfect global channel state information (CSI) and they can tolerate asymptotically long delay, applying an ergodic interference alignment (EIA) scheme can achieve half of the interference-free achievable rate. However, in practice obtaining such CSI is challenging, and only a limited delay is acceptable. This paper addresses data transmission over the IC by taking these concerns into account. Specifically, we consider the case that each transmitter attains only quantized CSI via limited feedback signals. This causes imperfect interference alignment and a degraded performance. We propose adaptive schemes to compensate the impact of the CSI uncertainties. We first study a power control problem which concerns how to communicate at fixed rates using minimum transmit powers. A power control algorithm is used to reach the solution. Next, we address a throughput maximization problem when the transmit powers are fixed. Through the analysis of system outage probability, we propose a rate adaptation scheme to maximize throughput. Finally, we quantify the throughput loss in delay-limited systems. Our results show that, even with limited feedback, performing the EIA scheme with proper power control or rate adaptation strategies can still outperform conventional orthogonal transmission approaches.

  • 172.
    Farhadi, Hamed
    et al.
    Chalmers University of Technology.
    Wang, Chao
    KTH, Skolan för elektro- och systemteknik (EES). Tongji University.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Fixed-rate Transmission over Fading Interference Channels Using Point-to-Point Gaussian Codes2015Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, nr 10, s. 3633-3644Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates transmission schemes for fixed-rate communications over a Rayleigh block-fading interference channel. There are two source-destination pairs where each source, in the presence of a short-term power constraint, intends to communicate with its dedicated destination at a fixed data rate. It encodes its messages using a point-to-point Gaussian codebook. The two users' transmissions can be conducted orthogonally or non-orthogonally. In the latter case, each destination performs either direct decoding by treating the interference as noise, or successive interference cancellation (SIC) to recover its desired message. For each scheme, we seek solutions of a power control problem to efficiently assign power to the sources such that the codewords can be successfully decoded at destinations. However, because of the random nature of fading, the power control problem for some channel realizations may not have any feasible solution and the transmission will be in outage. Thus, for each transmission scheme, we first compute a lower bound and an upper bound on the outage probability. Next, we use these results to find an outer bound and an inner bound on the epsilon-outage achievable rate region, i.e., the rate region in which the outage probability is below a certain value epsilon

  • 173.
    Farhadi, Hamed
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Wang, Chao
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    On the Throughput of Wireless Interference Networks with Limited Feedback2011Inngår i: 2011 IEEE International Symposium on Information Theory Proceedings (ISIT), IEEE , 2011, s. 762-766Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Considering a single-antenna M-user interferencechannel with symmetrically distributed channel gains, when thechannel state information (CSI) is globally available, applyingthe ergodic interference alignment scheme, each transmitterreceiverpair achieves a rate proportional to 1⁄2 of a single user’sinterference-free achievable rate. This is substantially higher thanthe achievable rate of the conventional orthogonal transmissionschemes such as TDMA. Since the rigid requirement on theCSI may be difficult to realize in practice, in this paper weinvestigate the performance of applying the ergodic interferencealignment scheme when the estimation of each channel gain ismade globally known through exploiting only a limited feedbacksignal from the associated receiver of that channel. Under a blockfading environment, we provide a lower bound on the achievableaverage throughput of the network. Our results imply that thebetter performance of interference alignment over TDMA maystill exist even without the assumption of perfect CSI. Also, thetrade off between allocating feedback rate of each receiver tothe desired channel or the interference channels at deferent SNRregion investigated.

  • 174.
    Farhadi, Hamed
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Wang, Chao
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Power Control in Wireless Interference Networks with Limited Feedback2012Inngår i: International Symposium on Wireless Communication Systems (ISWCS), 2012, IEEE conference proceedings, 2012, s. 671-675Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper addresses a power control problem in a wireless time-varying K-user interference network. Each transmitter intends to communicate to its desired receiver at afixed rate. Quantized channel gains are globally available through limited feedback signals. To eliminate multi-user interference, interference alignment scheme is performed based on the imperfect channel knowledge. The communication quality is affected by the channel quantization errors and interference leakage. We proposea power control algorithm, aiming to guarantee successful transmissions of each user while minimizing the transmission powerof the network. Our results show that even with limited number of feedback bits, by performing power control the considered interference alignment scheme can outperform the conventional time-division-multiple-access scheme.

  • 175.
    Farhadi, Hamed
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Zaidi, Ali
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Fischione, Carlo
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Wang, Chao
    School of Electronics and Information Engineering, Tongji University, Shanghai, China.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Distributed Interference Alignment and Power Control for Wireless MIMO Interference Networks with Noisy Channel State Information2013Inngår i: 2013 First International Black Sea Conference on Communications and Networking (BlackSeaCom), IEEE conference proceedings, 2013, s. 23-27Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper considers a multi-input multi-output(MIMO) interference network in which each transmitter intendsto communicate with its dedicated receiver at a certain fixed rate. It is known that when perfect CSI is available at each terminal, the interference alignment technique can be applied to align theinterference signals at each receivers in a subspace independent of the desired signal subspace. The impact of interference canhence be eliminated. In practice, however, terminals in general can acquire only noisy CSI. Interference alignment cannot be perfectly performed to avoid interference leakage in the signal subspace. Thus, the quality of each communication link dependson the transmission power of the unintended transmitters. Tosolve this problem, we propose an iterative algorithm to performstochastic power control and transceiver design based on onlynoisy local CSI. The transceiver design is conducted based on the interference alignment concept, and the power control seeks solutions of efficiently assigning transmit powers to provide successful communications for all transmitter-receiver pairs.

  • 176.
    Farokhi, Farhad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Shirazinia, Amirpasha
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Networked Estimation Using Sparsifying Basis Prediction2013Inngår i: IFAC Proceedings Volumes, 2013, s. 174-181Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We present a framework for networked state estimation, where systems encode their (possibly high dimensional) state vectors using a mutually agreed basis between the system and the estimator (in a remote monitoring unit). The basis sparsifies the state vectors, i.e., it represents them using vectors with few non-zero components, and as a result, the systems might need to transmit only a fraction of the original information to be able to recover the non-zero components of the transformed state vector. Hence, the estimator can recover the state vector of the system from an under-determined linear set of equations. We use a greedy search algorithm to calculate the sparsifying basis. Then, we present an upper bound for the estimation error. Finally, we demonstrate the results on a numerical example.

  • 177. Faundez-Zanuy, M.
    et al.
    Nilsson, Mattias
    KTH, Skolan för datavetenskap och kommunikation (CSC), Tal, musik och hörsel, TMH, Tal-kommunikation.
    Kleijn, Bastiaan
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    On the relevance of bandwidth extension for speaker identification2015Inngår i: European Retail Research, ISSN 1782-1029, E-ISSN 2219-5491, European Signal Processing Conference, ISSN 2219-5491, artikkel-id 7072183Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we discuss the relevance of bandwidth extension for speaker identification tasks. Mainly we want to study if it is possible to recognize voices that have been bandwith extended. For this purpose, we created two different databases (microphonic and ISDN) of speech signals that were bandwidth extended from telephone bandwidth ([300, 3400] Hz) to full bandwidth ([100, 8000] Hz). We have evaluated different parameterizations, and we have found that the MELCEPST parameterization can take advantage of the bandwidth extension algorithms in several situations.

  • 178. Fei, Zesong
    et al.
    Cao, Congzhe
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Hussain, Iqbal
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Kuang, Jingming
    Improved Luby transform codes in low overhead regions for binary erasure channels2014Inngår i: Transaction on Emerging Telecommunications Technologies, ISSN 2161-3915Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study improved degree distribution for Luby transform (LT) codes, which exhibits improved bit error rates particularly in low overhead regions. We construct the degree distribution by modifying robust soliton distribution. The performance of our proposed LT codes is evaluated and compared with the conventional LT codes via And-Or tree analysis. Then we propose a transmission scheme based on our proposed degree distribution to improve the frame error rate in full recovery regions. Furthermore, the improved degree distribution is applied to distributed multi-source relay networks and unequal error protection. It is shown that our schemes achieve better performance and reduced complexity especially in low overhead regions, compared with conventional schemes.

  • 179. Fei, Zesong
    et al.
    Yuan, Jinhong
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Bai, Baoming
    Zhang, Shengli
    Lin, Dengsheng
    RECENT DEVELOPMENT OF ERROR CONTROL CODES FOR FUTURE COMMUNICATION AND STORAGE SYSTEMS2017Inngår i: China Communications, ISSN 1673-5447, Vol. 14, nr 8, s. III-VArtikkel i tidsskrift (Annet vitenskapelig)
  • 180. Flam, J. T.
    et al.
    Zachariah, Dave
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    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.
    The linear model under mixed gaussian inputs: Designing the transfer matrix2013Inngår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 61, nr 21, s. 5247-5259Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Suppose a linear model Y = Hx+n, where inputs x, n are independent Gaussian mixtures. The problem is to design the transfer matrix so as to minimize the mean square error (MSE) when estimating x from . This problem has important applications, but faces at least three hurdles. Firstly, even for a fixed H, the minimum MSE (MMSE) has no analytical form. Secondly, theMMSE is generally not convex in . Thirdly, derivatives of the MMSEw.r.t. are hard to obtain. This paper casts theproblemas a stochastic program and invokes gradient methods. The study is motivated by two applications in signal processing. One concerns the choice of error-reducing precoders; the other deals with selection of pilot matrices for channel estimation. In either setting, our numerical results indicate improved estimation accuracy-markedly better than those obtained by optimal design based on standard linear estimators. Some implications of the non-convexities of the MMSE are noteworthy, yet, to our knowledge, not well known. For example, there are cases in which more pilot power is detrimental for channel estimation. This paper explains why.

  • 181.
    Flierl, Markus
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Girod, Bernd
    Stanford University.
    Vandergheynst, Pierre
    EPFL.
    Image transform for video coding2006Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    A method is disclosed for decomposing a set of even and odd pictures into low-band and high-band pictures respectively in a image decomposing unit, in which the even picture is used by at least two prediction motion compensators on which the output signal of each prediction motion compensator is scaled according to the number of prediction motion compensators. The method includes calculating the high-band picture by subtracting from the odd picture the scaled motion-compensated signals and using the high-band picture in the at least two update motion compensators, the output signal of each update motion compensator being scaled according to the number of update motion compensators. Finally, the low-band picture is calculated by adding the scaled update motion-compensated signals to the even picture.

  • 182. Floor, P. A.
    et al.
    Kim, A.
    Ramstad, T.
    Balasingham, I.
    Wernersson, N.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Transmitting multiple correlated gaussian sources over a Gaussian MAC using delay-free mappings2011Inngår i: ISABEL '11 Proceedings of the 4th International Symposium on Applied Sciences in Biomedical and Communication Technologies, 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we study the problem of communicating multiple correlated Gaussian memoryless sources over a Gaussian Multiple Access Channel (GMAC). We focus on distributed delay-free, low complexity, joint source-channel coding (JSCC) solutions to the problem. Theoretical performance bounds are derived and linear and nonlinear JSCC schemes are evaluated. The main contribution is a nonlinear hybrid discrete-analog mapping based on distributed quantization and a linear continuous mapping named Distributed Quantizer Linear Coder (DQLC). The proposed scheme shows promising performance which improve with increasing correlation and is robust against variations in noise level.

  • 183.
    Floor, P. A.
    et al.
    NTNU.
    Kim, A.
    NTNU.
    Wernersson, Niklas
    Ericsson Research.
    Ramstad, Tor
    NTNU.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    DISTRIBUTED ZERO-DELAY JOINT SOURCE-CHANNEL CODING FOR ABI-VARIATE GAUSSIAN ON A GAUSSIAN MAC2011Inngår i: 19th European Signal Processing Conference (EUSIPCO 2011), 2011, s. 2084-2088Konferansepaper (Fagfellevurdert)
  • 184. Floor, P. A.
    et al.
    Ramstad, T. A.
    Wernersson, Niklas
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Power constrained channel optimized vector quantizers used for bandwidth expansion2007Inngår i: Proceedings of 4th IEEE Internatilonal Symposium on Wireless Communication Systems 2007, ISWCS, New York: IEEE , 2007, s. 667-671Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper deals with algorithms for determining well performing bandwidth expanding joint source-channel coding (JSCC) systems. The JSCC systems are realized as direct source-channel mappings. The algorithms presented are "Power Constrained Channel Optimized Vector Quantizers" (PCCOVQ). The PCCOVQ algorithm is a modified generalized Lloyd algorithm. Theory on PCCOVQ is presented, with the emphasis on bandwidth expansion. Examples and results concerning bandwidth expansion by a factor of 2 and 3 are given.

  • 185. Floor, Pal Anders
    et al.
    Kim, Anna N.
    Ramstad, Tor A.
    Balasingham, Ilangko
    Wernersson, Niklas
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    On Joint Source-Channel Coding for a Multivariate Gaussian on a Gaussian MAC2015Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, nr 5, s. 1824-1836Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, nonlinear distributed joint source-channel coding (JSCC) schemes for transmission of multivariate Gaussian sources over a Gaussian multiple access channel are proposed and analyzed. The main contribution is a zero-delay JSCC named Distributed Quantizer Linear Coder (DQLC), which performs relatively close the information theoretical bounds, improves when the correlation among the sources increases, and does not level off as the signal-to-noise ratio (SNR) becomes large. Therefore it outperforms any linear solution for sufficiently large SNR. Further an extension of DQLC to an arbitrary code length named Vector Quantizer Linear Coder (VQLC) is analyzed. The VQLC closes in on the performance upper bound as the code length increases and can potentially achieve the bound for any number of independent sources. The VQLC leaves a gap to the bound whenever the sources are correlated, however. JSCC achieving the bound for arbitrary correlation has been found for the bivariate case, but that solution is significantly outperformed by the DQLC/VQLC when there is a low delay constraint. This indicates that different approaches are needed to perform close to the bounds when the code length is high and low. The VQLC/DQLC also apply for bandwidth compression of a multivariate Gaussian transmitted on point-to-point links.

  • 186. Floor, Pål Anders
    et al.
    Kim, Anna N.
    Wernersson, Niklas
    Ramstad, Tor A.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Balasingham, Ilangko
    Zero-Delay Joint Source-Channel Coding for a Bivariate Gaussian on a Gaussian MAC2012Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 60, nr 10, s. 3091-3102Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, delay-free, low complexity, joint source-channel coding (JSCC) for transmission of two correlated Gaussian memoryless sources over a Gaussian Multiple Access Channel (GMAC) is considered. The main contributions of the paper are two distributed JSCC schemes: one discrete scheme based on nested scalar quantization, and one hybrid discrete-analog scheme based on a scalar quantizer and a linear continuous mapping. The proposed schemes show promising performance which improves with increasing correlation and are robust against variations in noise level. Both schemes also exhibit a constant gap to the performance upper bound when the channel signal-to-noise ratio gets large.

  • 187. Flåm, John
    et al.
    Björnson, Emil
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Chatterjee, Saikat
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Pilot design for MIMO channel estimation: An alternative to the Kronecker structure assumption2013Inngår i: ICASSP IEEE Int Conf Acoust Speech Signal Process Proc, IEEE conference proceedings, 2013, s. 5061-5064Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This work seeks to design a pilot signal, under a power constraint, such that the channel can be estimated with minimum mean square error. The procedure we derive does not assume Kronecker structure on the underlying covariance matrices, and the pilot signal is obtained in three main steps. Firstly, we solve a relaxed convex version of the original minimization problem. Secondly, its solution is projected onto the feasible set. Thirdly we use the projected solution as starting point for an augmented Lagrangian method. Numerical experiments indicate that this procedure may produce pilot signals that are far better than those obtained under the Kronecker structure assumption.

  • 188. Flåm, John
    et al.
    Vehkaperä, Mikko
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Zachariah, Dave
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Tsakonas, Efthymios
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Mean square error reduction by precoding of mixed Gaussian input2012Inngår i: 2012 International Symposium on Information Theory and Its Applications, ISITA 2012, 2012, s. 81-85Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Suppose a vector of observations y = Hx + n stems from independent inputs x and n, both of which are Gaussian Mixture (GM) distributed, and that H is a fixed and known matrix. This work focuses on the design of a precoding matrix, F, such that the model modifies to z = HFx + n. The goal is to design F such that the mean square error (MSE) when estimating x from z is smaller than when estimating x from y. We do this under the restriction E[(Fx)TFx] ≤ PT, that is, the precoder cannot exceed an average power constraint. Although the minimum mean square error (MMSE) estimator, for any fixed F, has a closed form, the MMSE does not under these settings. This complicates the design of F. We investigate the effect of two different precoders, when used in conjunction with the MMSE estimator. The first is the linear MMSE (LMMSE) precoder. This precoder will be mismatched to the MMSE estimator, unless x and n are purely Gaussian variates. We find that it may provide MMSE gains in some setting, but be harmful in others. Because the LMMSE precoder is particularly simple to obtain, it should nevertheless be considered. The second precoder we investigate, is derived as the solution to a stochastic optimization problem, where the objective is to minimize the MMSE. As such, this precoder is matched to the MMSE estimator. It is derived using the KieferWolfowitz algorithm, which moves iteratively from an initially chosen F0 to a local minimizer F*. Simulations indicate that the resulting precoder has promising performance.

  • 189.
    Forssell, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Energy Efficiency of Heterogeneous LTE Networks2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Awareness of climate change and our environment is affecting the field of mobile communications. The challenge of reducing the carbon footprint and operating expenditures, while the demand for coverage and capacity is growing exponen-tially, is driving the trend of studying energy efficiency of mobile networks. Providing services in a resource efficient way have benefits both for the operator and the environment, which is why requirements on energy performance will be a part of the specifications of future 5G networks. In long term evolution (LTE) networks, indoor small cells are deployed inlarge volume to improve performance in areas with poor macro coverage or high traffic demand. This type of network topology, that consists of several types of access nodes, is called a heterogeneous network (HetNet). In this master thesis we study the energy efficiency of various HetNet deployments in a dense urban environment. The small cells deployments investigated are pico base stations and micro distributed antenna systems. Dense and sparse deployment strategies with varying transmit powers are compared. Furthermore, we investigate the potential for energy savings by setting the small cells into a low power sleep state under certain conditions. Both short sleep periods between transmissions, called discontineous transmission (DTX), and longer sleep cycles during periods of low activity is investigated.This thesis was carried out as a project at Ericsson Systems & Technology in Kista, Stockholm 2015. To be able to evaluate the energy consumption at network level, realistic models for the power consumption of various base station types had to be implemented into a static radio network simulator. Results show good performance of the considered HetNets but at a cost ofhigher power consumption than a macro only network. For example, a pico HetNet with twice the macro capacity consume 75% more energy over one day. However, results show that with DTX and sleep modes enabled, the daily energy consumption of the same HetNets is only 30% higher than the macro only network. Therefore, the main conclusion is that energy saving techniques will be of great importance for improving capacity without increasing network energyconsumption.

  • 190.
    Forssell, Henrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Gross, James
    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.
    Feature-Based Multi-User Authentication for Parallel Uplink Transmissions2016Inngår i: 2016 9TH INTERNATIONAL SYMPOSIUM ON TURBO CODES AND ITERATIVE INFORMATION PROCESSING (ISTC), IEEE, 2016, s. 355-359Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We study a multi-user up-link scenario where an attacker tries to impersonate the legitimate transmitters. We present a new framework for deriving a posteriori attack probabilities from the channel observations at the access point, which enables fast intrusion detection and authentication at the physical layer and can be exploited to reduce the security overhead by offtoading higher-layer authentication schemes. This is highly relevant for delay-sensitive applications that are targeted in 5G where the security overhead may limit the real-time performance. We take a factor-graph approach that can easily be extended to take into account other features, channel models, and radio access schemes. While related works only consider single-link scenarios, the multi-user approach in this paper allows us to exploit the cross-channel correlation of the large-scale fading parameters that is due to the propagation environment for improving the detection performance. As numerical results show, especially for slowly changing channels with high correlation our approach provides significant performance gains.

  • 191. Fouillot, P.
    et al.
    Le Martret, C. J.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Adaptive relaying strategies for collaborative spectrum sensing2010Inngår i: 2010 Proceedings of the 5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications, CROWNCom 2010, 2010, s. 5577676-Konferansepaper (Fagfellevurdert)
  • 192.
    Gabry, Frederic
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Cooperation for Secrecy in Wireless Networks2012Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    The growth of wireless networks has been considerable over the last decades. Due to the broadcast nature of these networks, security issues have taken a critical role in today’s communications. A promising direction towards achieving secure communications is information theoretic secrecy, which is an approach exploiting the randomness of the channels to ensure secrecy. Based on this approach, there has been a recent surge of interest in a potential cooperation between users to enhance the secrecy of communications. In this thesis we investigate the interaction between cooperation and secrecy. In particular the contributions of the thesis can be divided into two parts.

    In the first part, we study cooperative strategies for secrecy for wireless channels. Our goal is to evaluate the effect of fading and limited CSI on the eavesdropper’s channels. In that purpose we consider a scenario where a helper aims at increasing the secrecy of the communication between a source and destination in the presence of an eavesdropper. Several strategies are discussed for the helper, namely decode-and-forward, amplify-and-forward, and cooperative jamming. We introduce the secrecy outage probability, the conditional secrecy outage probability and the secure throughput as secrecy measures. For each measure, we investigate and compare the secrecy performance of cooperation. We furthermore elaborate a system optimization in terms of strategy selection, node positioning, power allocation and rate design.

    In the second part, we consider cooperation in the 4-node scenario against a more sophisticated adversary: an active eavesdropper, which can either passively eavesdrop, or jam the transmission. A game-theoretic perspective is a natural way to analyze the competitive interaction between the helper and the eavesdropper. Therefore we define several secrecy games, for which we find the Nash and Stackelberg equilibria as well as the corresponding secrecy rate outcomes. Another important consideration in this scenario is the interaction between the source and the helper, which we model and solve as a Stackelberg game, and we illustrate its impact on the achievable secrecy rates.

  • 193.
    Gabry, Frederic
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Secrecy in Cognitive Radio Networks2014Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    With the considerable growth of wireless networks in recent years, the issue of network security has taken an important role in the design of communication devices and protocols. Indeed, due to the broadcast nature of these networks, communications can potentially be attacked by malicious parties, and therefore, the protection of transmitted data has become a main concern in today's communications. On the other hand the cooperation of nodes overhearing the transmission may potentially lead to a better performance. In this thesis we combine both fundamental concepts of cooperation and secrecy in wireless networks. In particular we investigate the cooperation between transmitters in a cognitive radio network where the secondary receiver is treated as a potential eavesdropper to the primary transmission. We study this novel model focusing on several fundamental aspects.

    First we derive achievable rate regions for different transmission schemes, such as cooperative jamming and relaying, with and without primary message knowledge at the secondary transmitter. For these schemes, we formulate and solve three relevant power allocation problems: the maximization of the achievable primary and secondary rates, and the minimization of the secondary transmitting power. We model the interaction between the transmitting users as a Stackelberg game corresponding to a more realistic power allocation problem. We solve the game and illustrate its impact on the achievable rates.

    Secondly we generalize our system model by introducing the multi-phase clean relaying (CR) scheme, which takes into account the message-learning constraint at the secondary transmitter, and we derive the achievable rate region for this scheme. We compare our CR scheme to other transmission strategies such as dirty paper coding, interference neutralization, and pure cooperative jamming.

     Thirdly we extend our model to the generalized scenario where multiple secondary transmitter-receiver pairs wish to access the spectrum. For this scenario, we define and study several types of games between the primary network and the secondary pairs, such as Stackelberg games, power control games, and auction games. We derive the equilibrium of each game considered, which allows us to predict the behavior of the users in the cognitive radio network with multiple secondary pairs.

    Moreover we consider the important concept of energy efficiency (EE) for the performance of the cognitive radio network and we derive the power allocation and power splitting maximizing the secondary transmitter's energy efficiency. An important EE Stackelberg game between the two transmitters is formulated, and the impact of the game theoretic interaction is analyzed.

     Finally we motivate and investigate information theoretic secrecy using key agreement techniques in wireless networks. In particular we derive achievable secret key rate regions for two different key agreement schemes in Gaussian channels using several transmission strategies such as power control and cooperative jamming. The interaction between transmitting users is analyzed from a game theoretic perspective using non-cooperative game theory.

    For every fundamental perspective considered for the analysis of the model studied in the thesis, our results are illustrated through numerical examples based on a geometrical setup, highlighting the impact of the node geometry on the achievable rates, the optimal strategies, the games' equilibria and the impact of the game theoretic interaction between transmitters on the system performance.

  • 194.
    Gabry, Frederic
    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), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Outage Performance and Power Allocation for Decode-and-Forward Relaying and Cooperative Jamming for the Wiretap Channel2011Inngår i: 2011 IEEE International Conference on Communications Workshops, ICC 2011 Workshops, IEEE , 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we investigate the wiretap channel in the presence of a cooperative helping node. We derive a closed-form expression for the secrecy outage probability for the decode-and-forward (DF) relaying and cooperative jamming (CJ) strategies for the Rayleigh slow fading channel. We investigate the power allocation at the source and helping node, and compare the secrecy outage performance of the two schemes.

  • 195.
    Gabry, Frederic
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Thobaben, Ragnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Cooperation for secrecy in presence of an active eavesdropper: A game-theoretic analysis2011Inngår i: 8th International Symposium on Wireless Communication Systems (ISWCS), 2011, 2011, s. 281-285Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we investigate a four single-antenna node network, constituted of a transmitter, a receiver, a cooperative node and a wiretapper. The wiretapper has the ability to eavesdrop the communication or disrupt the transmission by jamming. This results in both cases in the decrease of the secrecy rate. The cooperative node on the other hand aims to improve secrecy by either relaying or jamming. We investigate the secrecy performance of the decode-and-forward and cooperative jamming strategies against this kind of adversary. To model the interaction between the helper and the wiretapper, we define an extensive form game, for which we derive the pure and mixed strategies equilibria. Finally, we compare the performance of the schemes and we analyze the equilibrium outcomes through simulation results.

  • 196.
    Gabry, Frederic
    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), 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.
    Outage Performances for Amplify-and-Forward, Decode-and-Forward and Cooperative Jamming Strategies for the Wiretap Channel2011Inngår i: 2011 IEEE Wireless Communications and Networking Conference, WCNC 2011, IEEE , 2011, s. 1328-1333Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we investigate the wiretap channel in the presence of a cooperative relay node. We analyze and compare the outage performance of three cooperatives schemes: cooperative jamming (CJ), decode-and-forward (DF), and amplify-and-forward (AF) for the Rayleigh slow fading channel. In particular, we derive a closed-form expression for the outage probability for the DF and CJ strategies, which allows an optimal strategy selection in terms of outage performance. We compare the three cooperative schemes through numerical simulations.

  • 197. Gabry, Frederic
    et al.
    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.
    Secrecy Games In Cognitive Radio Networks with Multiple Secondary Users2015Inngår i: 2015 IEEE CONFERENCE ON COMMUNICATIONS AND NETWORK SECURITY (CNS), 2015, s. 143-148, artikkel-id 7346822Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we investigate secrecy games in cognitive radio networks with multiple secondary pairs and secrecy constraints. We consider the cognitive channel model with multiple secondary pairs where the secondary receivers are treated as eavesdroppers with respect to the primary transmission. For this novel network model, we derive achievable rate regions when secondary pairs are allowed to use the channel simultaneously. We then investigate the spectrum sharing mechanisms using several game theoretic models, namely 1) a single-leader multiple-follower Stackelberg game with the primary transmitter as the leader and the secondary transmitters as followers; 2) a non-cooperative power control game between the secondary transmitters if they can access the channel simultaneously; and 3) an auction between a primary auctioneer and secondary bidders which allows the primary transmitter to exploit the competitive interaction between the secondary transmitters. We illustrate through numerical simulations the equilibrium outcomes of the analyzed games and the impact of the competition between the secondary transmitters on the utility performance of every node in the cognitive radio network.

  • 198.
    Gabry, Frédéric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Li, Nan
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Schrammar, Nicolas
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Girnyk, Maksym
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Karipidis, Eleftherios
    Thobaben, Ragnar
    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.
    Larsson, Erik G.
    Skoglund, Mikeal
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Secure Broadcasting in Cooperative Cognitive Radio Networks2012Inngår i: 2012 Future Network and Mobile Summit, FutureNetw 2012, IIMC , 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper explores the trade-off between cooperation and secrecy in cognitive radio networks. We consider a scenario consisting of a primary and a secondary system. In the simplest case, each system is represented by a pair of transmitter and receiver. We assume a secrecy constraint on the transmission in the sense that the message of the primary transmitter has to be concealed from the secondary user. Both situations where the secondary transmitter is aware and unaware of the primary message are investigated and compared. Furthermore, we extend our results to the scenario where the secondary system comprises multiple users. For each case we sketch the derivation of the rates that are achievable from an information theoretic perspective. We then investigate the findings by numerical simulations. Our main result is that, in spite of the secrecy constraint, cooperation is beneficial in terms of the achievable rates. The secondary transmitter has the two contradicting tasks of helping the primary system and transmitting its own message. Our results show that both tasks can be accomplished simultaneously, improving both systems' performance. In particular, the secondary system can achieve a significant rate without decreasing the primary rate below the benchmark rate achievable without the help of the secondary transmitter. In the case of multiple secondary users, the rate region reduces, which results in a lower individual rate. However, the linear increase in sumrate counterbalances this effect.

  • 199.
    Gabry, Frédéric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Li, Nan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Elektroniksystem. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Schrammar, Nicolas
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Girnyk, Maksym
    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.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    On the Optimization of the Secondary Transmitter's Strategy in Cognitive Radio Channels with Secrecy2014Inngår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 32, nr 3, s. 451-463Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates cooperation for secrecy in cognitive radio networks. In particular, we consider a four-node cognitive scenario where the secondary receiver is treated as a potential eavesdropper with respect to the primary transmission. The cognitive transmitter can help the primary transmission, and it should also ensure that the primary message is not leaked to the secondary user. We consider two cognitive scenarios depending on whether the secondary transmitter knows the primary message or not. In the first case, the secondary transmitter is unaware of the primary transmitter's message and acts as a helping interferer to enhance the secrecy of the primary transmission, whereas in the second case, relaying of the primary message is also within its capabilities. First, we find achievable rate regions for these two scenarios in the case of AWGN channels. We then investigate three different optimization problems: the maximization of the primary rate, the maximization of the secondary rate and the minimization of the secondary transmit power. For these optimization problems, we find closed-form expressions in important special cases. Furthermore, we analyze the cooperation between the primary and secondary transmitters from a game-theoretic perspective. We model their interaction as a Stackelberg game, for which we define and find the Stackelberg equilibrium. Finally, we use numerical examples to illustrate the rate regions, the three optimizations, and the impact of the Stackelberg game on the achievable rates and on the transmission strategies of the secondary transmitter.

  • 200.
    Gabry, Frédéric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Salimi, Somayen
    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.
    High SNR performance of amplify-and-forward relaying in Rayleigh fading wiretap channels2013Inngår i: 2013 Iran Workshop on Communication and Information Theory, IWCIT 2013, IEEE , 2013, s. 6555771-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper investigates amplify-and-forward (AF) relaying for secrecy in quasi-static Rayleigh fading channels. We consider a four-node network where a helping node intends to enhance secrecy of the transmission between the source and the destination in presence of a passive eavesdropper. In this scenario, the common assumption of full CSI on the eavesdropper's channels is not realistic, and thus, we study the performance of cooperation from an outage perspective. Starting from the secrecy outage probability, we introduce a novel measure, the conditional secrecy outage probability to analyze the performance of AF. In particular, we derive closed-form expressions for AF for these two secrecy measures under a high SNR assumption. Moreover, we use numerical examples to illustrate our results and to characterize the effect of the nodes' geometry. We also show numerically how AF improves the secrecy performance in comparison to direct transmission in terms of outage probability and secure throughput.

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