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  • 151. Bandelow, U.
    et al.
    Schatz, Richard
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP. KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Wunsche, H. -J
    A correct single-mode photon rate equation for multisection lasers1996Ingår i: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 8, s. 614-616Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is shown that not the photon number but photon number divided by the square root of the excess factor of spontaneous emission must be used in the photon rate equation for single-mode lasers when the longitudinal field distribution changes with time. The importance of using the correct dynamic quantity is illustrated with two examples.

  • 152. Bang, I.
    et al.
    Kim, Su Min
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Sung, D. K.
    Opportunistic user selection with adaptive jamming for secure communication in heterogeneous networks2015Ingår i: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, IEEE conference proceedings, 2015, s. 42-46Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we propose an opportunistic user selection criterion to obtain a multiuser diversity gain for secure communication. At the same time, we also propose a strategy for utilizing a small base station in heterogeneous networks as a helper or a jammer adaptively. Our approach is to maximize the secrecy achievable rate based on an analytically derived lower bound instead of the original objective function due to its complexity. Based on a simple proposed user selection criterion considering both macro and small base stations, we propose two jamming strategies according to knowledge of eavesdropper's channel: adaptive jamming and probabilistic jamming strategies. Through simulations in two scenarios, it is shown that our proposed user selection and jamming schemes provide a good performance gain in terms of secrecy achievable rate.

  • 153. Bao, J.
    et al.
    Ma, Z.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Teknisk informationsvetenskap. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Tsiftsis, T. A.
    Zhu, Z.
    Performance analysis of uplink sparse code multiple access with iterative multiuser receiver2017Ingår i: 2017 IEEE International Conference on Communications, ICC 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, artikel-id 7996537Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper investigates the asymptotic performance of bit-interleaved coded modulation (BICM) with iterative multiuser detection and decoding in uplink sparse code multiple access (SCMA) systems. The extrinsic information transfer (EXIT) characteristics analysis of the joint multiuser detector for SCMA is provided, and shows that the average detection reliability for multiple users converges to the single-user case, if ideal feedback from the decoder is available to the detector. We develop a tight analytical bound on the convolutionally encoded bit-error rate (BER) for independent Rayleigh fadings, based on the single-user bound with arbitrary multidimensional constellations. Moreover, we analyze the achievable coding and diversity gains of the SCMA-BICM system with iterative receiver. Simulations are carried out to verify the effectiveness of the analysis.

  • 154.
    Bao, Jinchen
    et al.
    Southwest Jiaotong Univ, Prov Key Lab Informat Coding & Transmiss, Chengdu 611731, Sichuan, Peoples R China..
    Ma, Zheng
    Southwest Jiaotong Univ, Prov Key Lab Informat Coding & Transmiss, Chengdu 611731, Sichuan, Peoples R China..
    Xiao, Ming
    Royal Inst Technol, Dept Commun Theory, S-10044 Stockholm, Sweden..
    Ding, Zhiguo
    Univ Lancaster, Sch Comp & Commun, Lancaster LA1 4YW, England..
    Zhu, Zhongliang
    Southwest Jiaotong Univ, Prov Key Lab Informat Coding & Transmiss, Chengdu 611731, Sichuan, Peoples R China..
    Performance Analysis of Uplink SCMA With Receiver Diversity and Randomly Deployed Users2018Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 67, nr 3, s. 2792-2797Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper considers the performance analysis of sparse code multiple access (SCMA) with receive diversity arrays and randomly deployed users in a cellular uplink scenario. The impact of path loss on the performance of SCMA is characterized, by assuming independent Rayleigh fading and joint maximum likelihood (ML) receivers. A tight upper bound on the probability of symbol detection error is derived, and the achievable diversity and coding gains are investigated. The analytical results are validated by using simulations, and show that a diversity order which is equal to the product of the number of receive antennas and the signal-space diversity can be achieved, and the large-scale path-loss decreases only the coding gain.

  • 155.
    Bao, Lei
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Control over Low-Rate Noisy Channels2009Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Networked embedded control systems are present almost everywhere. A recent trendis to introduce radio communication in these systems to increase mobility and flex-ibility. Network nodes, such as the sensors, are often simple devices with limitedcomputing and transmission power and low storage capacity, so an important prob-lem concerns how to optimize the use of resources to provide sustained overall sys-tem performance. The approach to this problem taken in the thesis is to analyzeand design the communication and control application layers in an integrated man-ner. We focus in particular on cross-layer design techniques for closed-loop controlover non-ideal communication channels, motivated by future control systems withvery low-rate and highly quantized sensor communication over noisy links. Severalfundamental problems in the design of source–channel coding and optimal controlfor these systems are discussed.The thesis consists of three parts. The first and main part is devoted to the jointdesign of the coding and control for linear plants, whose state feedback is trans-mitted over a finite-rate noisy channel. The system performance is measured by afinite-horizon linear quadratic cost. We discuss equivalence and separation proper-ties of the system, and conclude that although certainty equivalence does not holdin general it can still be utilized, under certain conditions, to simplify the overalldesign by separating the estimation and the control problems. An iterative opti-mization algorithm for training the encoder–controller pairs, taking channel errorsinto account in the quantizer design, is proposed. Monte Carlo simulations demon-strate promising improvements in performance compared to traditional approaches.In the second part of the thesis, we study the rate allocation problem for statefeedback control of a linear plant over a noisy channel. Optimizing a time-varyingcommunication rate, subject to a maximum average-rate constraint, can be viewedas a method to overcome the limited bandwidth and energy resources and to achievebetter overall performance. The basic idea is to allow the sensor and the controllerto communicate with a higher data rate when it is required. One general obstacle ofoptimal rate allocation is that it often leads to a non-convex and non-linear problem.We deal with this challenge by using high-rate theory and Lagrange duality. It isshown that the proposed method gives a good performance compared to some otherrate allocation schemes.In the third part, encoder–controller design for Gaussian channels is addressed.Optimizing for the Gaussian channel increases the controller complexity substan-tially because the channel output alphabet is now infinite. We show that an efficientcontroller can be implemented using Hadamard techniques. Thereafter, we proposea practical controller that makes use of both soft and hard channel outputs.

  • 156.
    Bao, Lei
    KTH, Skolan för elektro- och systemteknik (EES).
    Source-channel coding for closed-loop control2006Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Networked embedded control systems are present almost everywhere. A recent trend is to introduce wireless sensor networks in these systems, to take advantage of the added mobility and flexibility offered by wireless solutions. In such networks, the sensor observations are typically quantized and transmitted over noisy links. Concerning the problem of closed-loop control over such non-ideal communication channels, relatively few works have appeared so far. This thesis contributes to this field, by studying some fundamentally important problems in the design of joint source--channel coding and optimal control.

    The main part of the thesis is devoted to joint design of the coding and control for scalar linear plants, whose state feedbacks are transmitted over binary symmetric channels. The performance is measured by a finite-horizon linear quadratic cost function. The certainty equivalence property of the studied systems is utilized, since it simplifies the overall design by separating the estimation and the control problems. An iterative optimization algorithm for training the encoder--decoder pairs, taking channel errors into account in the quantizer design, is proposed. Monte Carlo simulations demonstrate promising improvements in performance compared to traditional approaches.

    Event-triggered control strategies are a promising solution to the problem of efficient utilization of communication resources. The basic idea is to let each control loop communicate only when necessary. Event-triggered and quantized control are combined for plants affected by rarely occurring disturbances. Numerical experiments show that it is possible to achieve good control performance with limited control actuation and sensor communication.

  • 157.
    Bao, Lei
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Encoder-controller design for control over the binary-input Gaussian channel2010Ingår i: IEEE International Symposium on Spread Spectrum Techniques and Applications, IEEE , 2010, s. 23-28Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we consider the problem of the joint optimization of encoder-controller for closed-loop control with state feedback over a binary-input Gaussian channel (BGC). The objective is to minimize the expected linear quadratic cost over a finite horizon. Thisencoder-controller optimization problem is hard in general, mostly because of the curse of dimensionality. The result of this paper is a synthesis technique for a computationally feasible suboptimal controller which exploits both the soft and hard information of thechannel outputs. The proposed controller is efficient in the sense that it embraces measurement quantization, error protection and control over a finite-input infinite-output noisy channel. How to effectively implement this controller is also addressed in the paper. In particular, this is done by using Hadamard techniques. Numerical experiments are carried out to verify the promising gain offered by the combined controller, in comparison to the hard-information-based controller.

  • 158. Barcelo-Ordinas, Jose M.
    et al.
    Casetti, Claudio
    Karlsson, Gunnar
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsnät.
    Sargento, Susana
    Information Mobility: a New Paradigm for Wireless Content Dissemination2009Ingår i: EUWIT: 2009 EUROPEAN WIRELESS TECHNOLOGY CONFERENCE, 2009, s. 100-103Konferensbidrag (Refereegranskat)
    Abstract [en]

    Content distribution networks are nowadays becoming a mature technology. Nevertheless, content delivery research in ad hoc networks has dealt with overlay applications, information querying and data broadcasting techniques. The aim of this paper is to explore and discuss content delivery in wireless ad hoc networks and to state challenges and reference models for this kind of networks. The concept of Information Mobility is introduced to point out that the contents are being stored in mobile nodes and that the contents move and replicate before being accessed. The network considered is a wireless ad hoc network with sparse connectivity and limited infrastructure support.

  • 159.
    Barrios, Carlos A.
    et al.
    Univ Politecn Madrid, ETSI Telecomunicac, ISOM, E-28040 Madrid, Spain..
    Gylfason, Kristinn
    KTH, Skolan för elektro- och systemteknik (EES).
    Sanchez, Benito
    Univ Politecn Valencia, NTC, Valencia 46022, Spain..
    Griol, Amadeu
    Univ Politecn Valencia, NTC, Valencia 46022, Spain..
    Sohlström, Hans
    KTH, Skolan för elektro- och systemteknik (EES).
    Holgado, M.
    Univ Politecn Madrid, Ctr Laser, Madrid 28031, Spain..
    Casquel, R.
    Univ Politecn Madrid, Ctr Laser, Madrid 28031, Spain..
    Slot-waveguide biochemical sensor (vol 32, pg 2080, 2007)2008Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, nr 21, s. 2554-2555Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The group index, instead of the effective index, is used to analyze the performance of a Si(3)N(4)-SiO(2) slot-waveguide microring refractive index sensor [Opt. Lett. 32, 3080 (2007)]. Assuming that the slot is fully filled with liquid, excellent agreement is found between experimental results and calculations.

  • 160.
    Barros da Silva Jr., Jose Mairton
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Fodor, Gabor
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. Ericsson Research.
    Fischione, Carlo
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Distributed Spectral Efficiency Maximization in Full-Duplex Cellular Networks2016Ingår i: IEEE International Conference on Communication (ICC16): Workshop on Novel Medium Access and Resource Allocation for 5G Networks, Kuala Lumpur: IEEE Communications Society, 2016, s. 80-86, artikel-id 7503768Konferensbidrag (Refereegranskat)
    Abstract [en]

    Three-node full-duplex is a promising new transmission mode between a full-duplex capable wireless node and two other wireless nodes that use half-duplex transmission and reception respectively. Although three-node full-duplex transmissions can increase the spectral efficiency without requiring full-duplex capability of user devices, inter-node interference - in addition to the inherent self-interference - can severely degrade the performance. Therefore, as methods that provide effective self-interference mitigation evolve, the management of inter-node interference is becoming increasingly important. This paper considers a cellular system in which a full-duplex capable base station serves a set of half-duplex capable users. As the spectral efficiencies achieved by the uplink and downlink transmissions are inherently intertwined, the objective is to device channel assignment and power control algorithms that maximize the weighted sum of the uplink-downlink transmissions. To this end a distributed auction based channel assignment algorithm is proposed, in which the scheduled uplink users and the base station jointly determine the set of downlink users for full-duplex transmission. Realistic system simulations indicate that the spectral efficiency can be up to 89% better than using the traditional half-duplex mode. Furthermore, when the self-interference cancelling level is high, the impact of the user-to-user interference is severe unless properly managed.

  • 161.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Fodor, Gábor
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. Ericsson Research.
    A Binary Power Control Scheme for D2D Communications2015Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 4, nr 6, s. 669-672Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Binary power control (BPC) is known to maximize the capacity of a two-cell interference limited system and performs near optimally for larger systems. However, when device-to-device (D2D) communication underlaying the cellular layer is supported, an objective function that considers the power consumption is more suitable. We find that BPC remains optimal for D2D communications when the weight of the overall power consumption in the utility function is bounded. Building on this insight, we propose a simple near-optimal extended BPC scheme and compare its performance with a recently proposed utility optimal iterative scheme using a realistic multicell simulator. Our results indicate that a near optimal D2D performance can be achieved without lengthy iterations or complex signaling mechanisms.

  • 162.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Nätverk och systemteknik.
    Sabharwal, Ashutosh
    Fodor, Gabor
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    1-bit Phase Shifters Suffice for Large-Antenna Full-Duplex mmWave Communications2019Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Millimeter-wave using large-antenna arrays is a key technological component forthe future cellular systems, where it is expected that hybrid beamforming along withquantized phase shifters will be used due to their implementation and cost efficiency.In this paper, we investigate the efficacy of full-duplex mmWave communicationwith hybrid beamforming using low-resolution phase shifters, without any analogself-interference cancellation. We formulate the problem of joint self-interferencesuppression and downlink beamforming as a mixed-integer nonconvex joint opti-mization problem. We propose LowRes, a near-to-optimal solution using penaltydual decomposition. Numerical results indicate that LowRes using low-resolutionphase shifters perform within 3% of the optimal solution that uses infinite phaseshifter resolution. Moreover, even a single quantization bit outperforms half-duplextransmissions, respectively by 29% and 10% for both low and high residual self-interference scenarios, and for a wide range of practical antenna to radio-chain ratios.Thus, we conclude that 1-bit phase shifters suffice for full-duplex millimeter-wavecommunications, without requiring any additional new analog hardware.

  • 163. Battiti, R.
    et al.
    Lo Cigno, R.
    Sabel, M.
    Orava, Fredrik
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT. KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Pehrson, Björn
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT. KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Wireless LANs: From WarChalking to open access networks2005Ingår i: Journal on spesial topics in mobile networks and applications, ISSN 1383-469X, E-ISSN 1572-8153, Vol. 10, nr 3, s. 275-287Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work discusses the evolution of W-LANs from their current status of wireless termination of LAN services to a possible global infrastructure where the access networks become open to multiple operators and a vehicle of a win-win scenario, where both users and operators benefit from the new network architecture. The idea of Open Access Networks (OANs) can go beyond wireless HotSpots and be generalized to a generic shared access infrastructure that fosters service operators competition and drastically reduces the cost of last mile coverage. The general concept of Open Access Networks is detailed, highlighting its difference with the more traditional model of vertical integration of the access network into the global service. About the OANs development, it is shown how to support the quick and smooth evolution of the infrastructure toward a widespread and reliable communication support. Business models are discussed by mentioning the different actors, the market organization and the different organization forms. The final part of the paper is devoted to technical challenges such as access control, security, privacy, roaming, resource exploitation and service differentiation. As an example of how to tackle these problems, we discuss a pricing technique devoted to resource management and billing support. In addition we present a simulation on how the OAN concept can speed-up the deployment of broadband access in a real case.

  • 164.
    Baudic, Gwilherm
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Complexity Efficient Decoder Design for Vehicular Communication2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Vehicular communication is currently seen as a key technology for enabling safer and more comfortable driving. In the general effort to reduce the number of casualties and improve the traffic flow despite an increasing number of vehicles, this field has a promising future. IEEE 802.11p has been chosen as the standard for the Physical Layer (PHY) design for wireless vehicular communication. However, the channels encountered in such situations pose several challenges for reliable communications. Time and frequency selectivity caused by dispersive environments and high mobility lead to doubly-selective channels. The systems are expected to conduct proper operation, in spite of these disturbances. In this thesis, we focus on the design of receivers working on the PHY layer, with an emphasis on limited complexity. This poses high constraints on the algorithms, which already have to cope with the limited amount of information provided by the training sequences. The solutions considered all involve joint channel estimation and decoding, characterized by the use of an iterative structure. Such structures allow the channel estimation to benefit from the knowledge brought by the decoder, which ultimately decreases the error rate. Following a previous work, we use algorithms based on Minimum Mean Square Error (MMSE) or Maximum A Posteriori (MAP) estimation. These receivers were modified to operate on full frames instead of individual subcarriers, and various improvements were studied. We provide a detailed analysis of the complexity of the proposed designs, along with an evaluation of their decoding performance. The trade-offs between these two parameters are also discussed. A part of these analyses isused in [10]. Finally, we give an insight into some considerations which may arise when implementing the algorithms on testbeds.

  • 165.
    Baudin, Émilie
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Raptor Codes for Super-Dense Networks2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this project, we investigate the performance of Raptor codes as candidatesfor channel coding for the wireless communication between access nodes.Very high data-rates are used, and processing uses more resources than transmission.Therefore, we need fast encoding and decoding algorithms for thechannel coding. Raptor codes have linear encoding and decoding times, andcan have very small overhead if they are properly designed. Hence, they arepossible candidates.

    We have implemented an encoding and decoding algorithm for Raptorcodes, as well as an environment for simulation. The system requirementsare expressed in terms of delay between the beginning of a transmission andthe successful decoding, and storage required during the transmission and processing.We have evaluated the performance of Raptor codes in terms of delayand storage as a function of system design parameters, in particular the numberof nodes in the network, and the size of the packets. We show that if thesize of the packets is properly chosen, Raptor codes can be useful for the application,and we explain the method for choosing the size of the packets. Wealso provide a way to calculate the delay and the storage for a given systemconfiguration, in order for example to determinate the larger number of nodesor the larger of users such that the delay and the storage are acceptable.

  • 166. Beckman, C.
    et al.
    Eklund, L.
    Karlsson, B.
    Lindmark, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Ribbenfjärd, David
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Wirdemark, P.
    Verifying 3G license requirements when every dB is worth a billion2006Ingår i: Eur Space Agency Spec Publ ESA SP, 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the year 2000, the Swedish Telecom regulator: "Post& Telestyrelsen", PTS, granted in a "beauty contest" four licenses for operations of 3G systems. To verify the coverage and the license requirements, PTS, has developed a test procedure where the field strength of the primary Common Pilot Channel, CPICH, is measured in a drive test. Designing such a test constitutes a number of challenges mainly due to the fact that in 3G the accuracy in the measurement needs to be extremely high since even a small systematic error of ∼1dB could in Sweden have the consequence that each operator would have to build an extra +1000 sites at a staggering cost of ∼1bilion SEK! The present paper gives an overview of the considerations behind the design of the test method used for verification of the 3G licence requirements in Sweden.

  • 167.
    Beckman, Claes
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth. KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Antenna-to-Antenna Isolation Measurements1999Rapport (Övrigt vetenskapligt)
    Abstract [en]

    In this document we show results from measurements of the antenna-to-antenna isolation between different types of base station antenna configurations. The measurements are conducted on antennas for the GSM1800 band. However, since this band is relatively close to the IMT-2000 band it is reasonable to assume similar results for antennas to be used in this band.

    In this report we present measurement results from antennas with both vertical and slanted dual polarisation, and different horizontal beamwidths. The different antennas are shown in Table 1. The isolation is measured with the antennas positioned for some different configurations.

  • 168.
    Beckman, Claes
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, KTH Center för trådlösa system, Wireless@kth.
    Examining the performance of dul band base station antennas: What progress is being made?1996Ingår i: Integrating GSM & DCS 1800: Exploiting the business potential of, London: IIR , 1996Konferensbidrag (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    The recent growth in cellular communications has rapidly created a need for more radio channels. In order to make better use of the available frequency bands new access techniques such as TDMA (Time Division Multiple Access), FDMA (Frequency DMA) and CDMA (Code DMA) have been introduced. Still, the need for new channels is strong and new frequency bands have therefore been allocated for future wireless communication systems. These new communication systems, e.g. the European Personal Communication Network (PCN: 1710-1880MHz) and the North American Personal Communication System (PCS: 1850-1990MHz), use frequencies about twice as high as their predecessors (e.g. AMPS: 824-894MHz and GSM: 880-960MHz). However, at a time when our downtown areas already are littered with basestation antennas, operators are not keen to install more. Therefore, dual-band antennas have gained an increased interest. They would allow the operators to replace two antennas for separate frequency bands with one only, thus, reducing the windload of the towers and perhaps most importantly reducing the cost of installation.

  • 169.
    Beckman, Claes
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Kommunikationssystem, CoS. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, KTH Center för trådlösa system, Wireless@kth.
    Svar till PTS konsultation inför planerad tilldelning av frekvensutrymme i 2,3- och 3,5 GHz-banden samt tilldelning av frekvensutrymme för lokala tillstånd2019Övrigt (Övrig (populärvetenskap, debatt, mm))
    Abstract [sv]

    KTH, Skolan för elektroteknik och datavetenskap (EECS) har beretts möjlighet att ge sin syn på PTS ”Konsultation inför planerad tilldelning av frekvensutrymme i 2,3- och 3,5 GHz-banden samt tilldelning av frekvensutrymme för lokala tillstånd”, PTS DNR 18-8496.

    KTH anser att det är olyckligt att PTS frångår principen om teknikneutrala band. Vi förstår att i detta fall finns inga alternativ men råder PTS att arbeta för att framtida spektrumtilldelning sker på teknikneutral basis då inlåsning av frekvensband till specifika tekniker inte bidrar till innovation.

    TDD medger ett mer effektivt utnyttjande av spektrum i fallet då nedlänkstrafik dominerar. Denna vinst måste dock vägas mot det faktum att co-ordinering och synkronisering av och mellan operatörernas nät hämmar konkurrensen. En möjlig framtida lösning är att 3.5 bandet enbart används för nedlänk och att upplänk sker i annat band (tex 1800 bandet). 

    Slutligen så bör spektrumvillkoren vara oberoende av de nu existerande aktörerna. För att även öppna upp för flera och ev nya operatörer så föreslår vi att hela bandet 3,4 - 3,8GHz bjuds ut vid denna auktion.

  • 170.
    Beckman, Claes
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Verifying 3G License Coverage Requirements2011Ingår i: Advances in Vehicular Networking Technologies / [ed] Miguel Almeida, InTech , 2011, s. 339-356Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    In the beginning of the 21’st century, the 3rd generation mobile phone systems, 3G, were introduced all around the world. In most countries, spectrum for this technology was allocated through some kind of licensing procedure. In Europe, the prevailing approach was to allocatespectrum through auctions, a process which led to a situation where the European operators found themselves committed to pay a staggering 130Bilion Euros for their 3G licenses.However, in most European countries, the fee was not the only obligation put on thelicensee: A coverage, “roll-out” requirement was in many cases also connected to the license(Northstream, 2002). Typically, these coverage requirements required that the licenseescover a certain area at a certain point in time after that the licenses had been awarded.In order for the regulators to verify that the licensees had met the coverage requirement and,hence, complied with the regulation, a method for coverage verification was needed. Suchmethods have therefore since then been developed by several European regulators (e.g. PTS2004; ECC 2007). In this book chapter we describe some general underlying consideration for the verification of radio coverage in UMTS systems and in particular we describe the Swedishmethodology developed by the Swedish Telecom regulator Post & Telestyrelsen (PTS).

  • 171.
    Beckman, Claes
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth. KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Bergek, Martin
    Wireless communication system for moving vehicles2013Patent (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    A wireless communication system for a moving vehicle, such as trains, is disclosed. The system includes at least one router in the moving vehicle for receiving and transmitting wireless voice communication and data communication to and from a stationary communication server outside the moving vehicle through an exterior mobile network. Further, the system includes at least one femtocell provided within the moving vehicle, and being connected to the router for wireless transferring of wireless voice communication and data communication between mobile terminals within the moving vehicle and the router. The at least one femtocell is controlled by a femtocell controller directly or indirectly connected to the communication server outside the moving vehicle.

  • 172.
    Beckman, Claes
    et al.
    Center for RF-Measurement Technology, University of Gävle.
    Belkow, Elena
    Post och Telestyrelsen.
    Eklund, Lars
    Post och Telestyrelsen.
    Landmark, Urban
    Post och Telestyrelsen.
    Wirdemark, Per
    Canaima International.
    Verifying 3G License Requirements: some Preliminary Swedish Results2008Ingår i: The 68th IEEE Vehicular Technology Conference: VTC2008-Fall, IEEE , 2008, s. 1-4Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the year 2000, the Swedish Telecom regulator “Post&Telestyrelsen” (PTS) granted in a “beauty contest” four licenses for operation of 3G mobile networks. Through this process, the licensees committed themselves to cover 8.860.000 inhabitants of the Swedish population. In order to verify the coverage and confirm compliance with the license requirements, PTS, developed a test procedure in close collaboration with the licensees.

    The present paper gives an overview of the considerations behind the design of the test method and presents some preliminary results. Today all Swedish 3G operators comply with the licence requirement and it is concluded that a method for verifying the requirement accepted by the licensees is an important tool for successful licensing of spectrum and fulfilment of licensing obligations.

  • 173.
    Beckman, Claes
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab). KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Karlsson, B.
    The story of Allgon: HF, VHF, cellular and microwave antennas during allmost 60 years2013Ingår i: 2013 7th European Conference on Antennas and Propagation (EuCAP), IEEE , 2013, s. 3171-3173Konferensbidrag (Refereegranskat)
    Abstract [en]

    Allgon, 'The Antenna Specialist', was a leading international design house and manufacturer of antennas for almost 60 years. The company was started in Stockholm in 1947 under the name of 'Antennspecialisten', by the Swedish engineer Torbjörn Cramner and his wife Veronica. In 1951 the company moved to Åkersberga north of Stockholm where its main facilities where located until the late 90's. During its life time the company designed and produced antennas for HF, VHF, Cellular and Microwave frequency bands, and for military, emergency, private and cellular radio systems. The company was in 2004 acquired by the US based company Powerwave but still today many of its original antenna designs are in production and many thousands of its base station antennas for mobile networks are still deployed all around the World.

  • 174.
    Beckman, Claes
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Smith, Gregory
    Shared Networks: Making Wireless Communications Affordable2005Ingår i: IEEE wireless communications, ISSN 1536-1284, E-ISSN 1558-0687, Vol. 12, nr 2, s. 78-85Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the wake of the substantial financial commitments incurred by European and other UMTS network operators in the form of licence fees, licensees have turned to network sharing as a means of reducing the capital requirements needed to bring 3G services to market. The reception from European regulators has been mixed, due to concerns that this inhibits competition, slow buildout, or otherwise result in reduced consumer benefits. The authors believe that the generic product life cycle model provides insights that indicate that network sharing, within an appropriately constructed regulatory framework, is not a threat to vigorous competition in the 3G industry, and in fact is one of the keys to stimulating the development of advanced, ubiquitous, affordable services.

  • 175. Belleschi, Marco
    et al.
    Balucanti, Lapo
    Soldati, Pablo
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Abrardo, Andrea
    Fast power control for cross-layer optimal resource allocation in DS-CDMA wireless networks2009Ingår i: 2009 IEEE International Conference on Communications, 2009, s. 4341-4346Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a novel cross-layer design for joint power and end-to-end rate control optimization in DS-CDMA wireless networks, along with a detailed implementation and evaluation in the network simulator ns-2. Starting with a network utility maximization formulation of the problem, we derive distributed power control, transport rate and queue management schemes that jointly achieve the optimal network operation. Our solution has several attractive features compared to alternatives: it adheres to the natural time-scale separation between rapid power control updates and slower end-to-end rate adjustments, and uses simplified power control mechanisms with reduced signalling requirements. We argue that these features are critical for a successful real-world implementation. To validate these claims, we present a detailed implementation of a crosslayer adapted networking stack for DS-CSMA ad-hoc networks in ns-2. We describe several critical issues that arise in the implementation, but are typically neglected in the theoretical protocol design, and evaluate the alternatives in extensive simulations.

  • 176.
    Belleschi, Marco
    et al.
    Ericsson AB, Sweden.
    Fodor, Gabor
    Ericsson AB, Sweden.
    Della Penda, Demia
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Pradini, Aidilla
    Ericsson AB, Sweden.
    Johansson, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Abrardo, Andrea
    University of Siena, Italy.
    Benchmarking Practical RRM Algorithms for D2D Communications in LTE Advanced2014Ingår i: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 82, nr 2, s. 883-910Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Device-to-device (D2D) communication integrated into cellular networks is an advanced tool to take advantage of the proximity of devices and allow for reusing cellular resources and thereby to increase the user bitrates and the system capacity. However, the introduction of D2D in legacy long term evolution (LTE) cellular spectrum requires to revisit and modify the existing radio resource management and power control (PC) techniques in order to fully realize the potential of the proximity and reuse gains and to limit the interference to the cellular layer. In this paper, we examine the performance of the legacy LTE PC tool box and benchmark it against an utility optimal iterative scheme. We find that the open loop PC scheme of LTE performs well for cellular users both in terms of the used transmit power levels and the achieved signal-to-interference-and-noise-ratio distribution. However, the performance of the D2D users as well as the overall system throughput can be boosted by the utility optimal scheme, by taking better advantage of both the proximity and the reuse gains. Therefore, in this paper we propose a hybrid PC scheme, in which cellular users employ the legacy LTE open loop PC, while D2D users exploits the utility optimizing distributed PC scheme. We also recognize that the hybrid scheme is not only nearly optimal, and can balance between spectral and energy efficiency, but it also allows for a distributed implementation at the D2D users, while preserving the LTE PC scheme for the cellular users.

  • 177. Belqasmi, F.
    et al.
    Fu, C.
    Shashvelayati, Maryamalsadat
    KTH.
    Khlifi, H.
    Glitho, R.
    A peer to peer architecture for enabling a universal presence service2010Ingår i: Proceedings - NGMAST 2010: 4th International Conference on Next Generation Mobile Applications, Services, and Technologies, 2010, s. 90-95Konferensbidrag (Refereegranskat)
    Abstract [en]

    Presence service is used to publish and discover end-users' context information. It is the basis of a wide range of end-user services. It is deployed using a wide range of technologies, which hampers interoperability. This paper proposes a peer to peer infrastructure for enabling a universal presence service, a service that will enable end users with multiple presence accounts in domains with different technologies to publish and discover end-user context information through a single interface. Requirements are derived, an architecture is proposed and implementation aspects are discussed. The architecture is an overlay and the related procedures and protocols are introduced. New software architecture is proposed for the implementation and the related tool kits are identified.

  • 178.
    Ben Slimane, Slimane
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Combined transmitter diversity and multi-level modulation techniques2006Ingår i: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 39, nr 2, s. 215-227Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Orthogonal transmitter diversity such as frequency diversity and time diversity is quite simple to implement and, with optimum signal combining, can take full advantage of fading multipath channels. However, such a scheme has a bandwidth efficiency that decreases inversely with the number of diversity branches making it less attractive in wireless communications applications. This paper considers combined orthogonal transmitter diversity and multi-level linear modulation techniques. The idea is to view the signal constellations of the modulation scheme in an augmented signal space formed by the modulation signal dimension and the number of branches of the transmitter diversity scheme. This augmented signal space provides a good spread for the modulation signal points and can be quite efficient for high-level linear modulation techniques. The obtained results show that this combined scheme, not only improves the system performance on both additive white Gaussian noise and fading multipath channels, but also improves the bandwidth efficiency of orthogonal transmitter diversity.

  • 179.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    A pragmatic approach to multi-user spatial multiplexing2002Ingår i: SAM2002: IEEE SENSOR ARRAY AND MULTICHANNEL SIGNAL PROCESSING WORKSHOP PROCEEDINGS, NEW YORK: IEEE , 2002, s. 130-134Konferensbidrag (Refereegranskat)
    Abstract [en]

    We suggest a new approach for spatial multiplexing in a narrowband system with several access points serving a number of mobile terminals. In contrast to previously suggested algorithms, this approach is formulated based on a systems perspective, generalizing earlier algorithms for jointly optimal beamforming and power control. Since global channel knowledge is required, the algorithm is mainly intended for system simulations where it provides a benchmark for the performance of any spatial multiplexing scheme with equal rate on the spatial channels.

  • 180.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Jointly optimal downlink beamforming and base station assignment2001Ingår i: 2001 IEEE International Conference on Acoustics, Speech, and Signal Processing, 2001. Proceedings (ICASSP '01)  (Volume:5 ), IEEE conference proceedings, 2001, s. 2961-2964Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present an algorithm that jointly determines the optimal downlink beamformers and the optimal assignment of each mobile to a base station. The optimality criterion is based on a systems perspective; provide sufficient quality of service for all users, transmitting as little excess power as possible. Since the algorithm is centralized and requires knowledge about all the channels in the system, it may be infeasible in a practical implementation. However, it provides the ultimate benchmark in system evaluations. Numerical examples show substantial gain compared to ordinary base station assignment.

  • 181.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Multi-User Spatial Multiplexing - A Pragmatic Approach2002Ingår i: RadioVetenskap och Kommunikation (RVK), 2002, s. 724-728Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We suggest a new approach for spatial multiplexing in a narrowband  system with several access points serving a number of mobile  terminals. In contrast to previously suggested algorithms, this  approach is formulated based on a systems perspective, generalizing  earlier algorithms for jointly optimal beamforming and power  control. Since global channel knowledge is required, the algorithm  is mainly intended for system simulations where it provides a  benchmark for the performance of any spatial multiplexing scheme  with equal rate on the spatial channels.

  • 182.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Optimal Transmission Using Smart Antennas2000Ingår i: Proc. IST Mobile Communications Summit, 2000, s. 359-364Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We study the design of beamformers for transmission from a number of base stations to a number of user terminals. Since every transmitted signal will cause interference at all the other user terminals, an optimal beamformer design must be determined jointly for all the beamformers. We review two algorithms that provide an optimal set of downlink beamformers. We also show how to determine not only the beamforming vectors but also the optimal allocation of user terminals to base stations.

  • 183.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Pragmatic multi-user spatial multiplexing with robustness to channel estimation errors2003Ingår i: 2003 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH, AND SIGNAL PROCESSING, VOL IV, PROCEEDINGS: SIGNAL PROCESSING FOR COMMUNICATIONS SPECIAL SESSIONS, 2003, s. 820-823Konferensbidrag (Refereegranskat)
    Abstract [en]

    Using ideas from power control and downlink beamforming, we suggest a pragmatic approach for spatial multiplexing in systems with several access points, each serving one or more mobile terminals. We assume that all channels are known globally, but in the case of fast fading, it is sufficient to know the second order statistics of the channels. Robustness to channel estimation errors is easily incorporated in the algorithm. Since global channel knowledge is required, the algorithm is mainly intended for system simulations where it provides a benchmark for the performance of any spatial multiplexing scheme with equal rate on the spatial channels.

  • 184.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Spatial Interference Suppression for Shared Spectrum2008Ingår i: ICT Mobile and Wireless Communications Summit / [ed] Paul Cunningham and Miriam Cunningham, IIMC International Information Management Corporation , 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider a scenario where a (future generation) cellular system shares the spectrum with a fixed-satellite services (FSS) system or other system that has primary access to the radio spectrum. Normally, the coverage of such a cellular system will have to stay outside an exclusion zone around the FSS ground station, to keep the interference low enough. Here we investigate how spatial interference suppression can be used at a transmitting multi-antenna base station to reduce the exclusion zone and provide downlink coverage closer to the FSS ground station. The study considers both transmit schemes that exploit knowledge about the channel between the base station and mobile station, as well as schemes that only rely on partial or no channel knowledge at all. Numerical examples illustrate that the interference level for the primary system can be reduced by at least 20dB, without a major loss of quality of service within the secondary system.

  • 185.
    Bengtsson, Mats
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Astély, David
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Ottersten, Björn
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Measurements of Spatial Characteristics and Polarization with a Dual Polarized Antenna Array1999Ingår i: Proceedings IEEE Vehicular Technology Conference, IEEE , 1999, s. 366-370Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider antenna arrays equipped with cross-polarized antenna elements. The multipath propagation will affect both the spatial characteristics and the polarization of the received signals which will influence the performance of the system in terms of, for example, bit error rate or direction estimation. In this paper, we present results from field measurement data recorded at the 1800 MHz band, provided by Ericsson Radio Systems AB. The study is divided into two main parts. In the first part we introduce a diversity gain measure related to the BER of an MRC receiver. The polarization diversity introduced by the radio channel is studied, and compared to the spatial diversity. In the second part we use a parameterized model of the received polarized radio waves and illustrate the typical behavior of the estimated polarization parameters

  • 186.
    Bengtsson, Mats
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Bartolomé, Diego
    Vicario, José López
    Centre Tecnològic de Telecom. de Catalunya (CTTC).
    Antón-Haro, Carles
    Centre Tecnològic de Telecom. de Catalunya (CTTC).
    Beamforming and bit-loading strategies for multi-user SDMA with admission control2005Ingår i: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 2005, Vol. 2, s. 842-846Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we address the problem of transmit beamforming, power allocation, bit loading, and admission control in a multi-user scenario, where several single antenna mobile terminals are served by one base station equipped with an antenna array. In particular, we explore the impact of using either optimal or zero-forcing transmit beamforming schemes in combination with different bit allocation strategies, namely the Maximization of the Sum Rate (MSR), the Maximization of the Minimum Rate (MMR) and a modified version of the latter, for a finite set of modulation schemes. The performance evaluation is conducted by means of system-level simulations, using a realistic channel model for urban micro cells, with an emphasis not only on the aggregated cell throughput but also on the associated fairness issues.

  • 187.
    Bengtsson, Mats
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Martin, Cristoff
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Ottersten, Björn
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Ben Slimane, Slimane
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Zetterberg, Per
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Recent Advances on MIMO Processing in the SATURN Project2002Ingår i: Proc. IST Mobile Communications Summit, 2002, s. 309-313Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We highlight some recent results on the theory and algorithms for  MIMO systems, obtained at the Royal Institute of  Technology (KTH) within the SATURN project.   The paper includes a a new approximate expression for the ergodic  channel capacity of a MIMO system with correlated fading, algorithms  for MIMO beamforming under EIRP (equivalent isotropic radiated  power) constraints and a low-complexity algorithm for MIMO channel  estimation in OFDM systems. Also, we show how transmit and  beamformers can be determined in a decentralized fashion without  explicitly estimating the channel response.

  • 188.
    Bengtsson, Mats
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Martin, Cristoff
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Ottersten, Björn
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Slimane, Ben
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Zetterberg, Per
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Recent Advances on MIMO Processing in the SATURN Project2002Ingår i: Proc. IST Mobile Communications Summit, 2002Konferensbidrag (Refereegranskat)
    Abstract [en]

    We highlight some recent results on the theory and algorithmsfor MIMO systems, obtained at the Royal Instituteof Technology (KTH) within the SATURN project.The paper includes a a new approximate expression forthe ergodic channel capacity of a MIMO system with correlatedfading, algorithms for MIMO beamforming underEIRP (equivalent isotropic radiated power) constraintsand a low-complexity algorithm for MIMO channel estimationin OFDM systems. Also, we show how transmitand beamformers can be determined in a decentralizedfashion without explicitly estimating the channel response.

  • 189.
    Bengtsson, Mats
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Ottersten, Björn
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Downlink Beamformer Design Using Semidefinite Optimization1999Ingår i: RadioVetenskap och Kommunikation (RVK), 1999, s. 289-293Konferensbidrag (Övrigt vetenskapligt)
  • 190.
    Bengtsson, Mats
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Ottersten, Björn
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Low Complexity Estimation of Angular Spread with an Antenna Array1997Ingår i: Proceedings of 11th IFAC Symposium on System Identification, 1997, s. 535-540Konferensbidrag (Refereegranskat)
  • 191.
    Bengtsson, Mats
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Ottersten, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Optimal and Suboptimal Transmit Beamforming2001Ingår i: Handbook of Antennas in Wireless Communications / [ed] Lal C. Godara, CRC Press , 2001, s. 18-1-18-33Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 192.
    Bengtsson, Mats
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Ottersten, Björn
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Rooting Techniques for Estimation of Angular Spread with an Antenna Array1997Ingår i: Proceedings of IEEE 47th Vehicular Technology Conference. VTC 97, IEEE , 1997, s. 1158-1162Konferensbidrag (Refereegranskat)
    Abstract [en]

    When antenna arrays are used in mobile communications systems, multipath propagation effects must be taken into account. Local scattering around each signal source causes angular spreading. One important parameter foroptimal transmit and receive algorithms is the width of the angular spread of each scattered source signal. We present a new principle for consistent estimation of direction of arrival as well as angular spread using standardrooting techniques such as root MUSIC, MODE or ESPRIT. The computational complexity is much lower than forpreviously suggested algorithms.

  • 193.
    Bengtsson, Mats
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Ottersten, Björn
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Uplink and Downlink Beamforming for Fading Channels1999Ingår i: Proceedings of SPAWC’99, Signal Processing Advances in Wireless Communications, IEEE , 1999, s. 350-353Konferensbidrag (Refereegranskat)
    Abstract [en]

    We highlight some issues in the design of beamformers for transmission and reception in communications systems with antenna arrays at the base stations. We assume a radio channel characterized by frequency flat Rayleighfading which is correlated (but not coherent) from antenna element to antenna element. Different design criteria are considered and we show the relationship between downlink and uplink formulations and solutions. The resulting beamformers are typically given by quadratically constrained optimization problems which could be expected to give increased robustness to signal cancellation. Unfortunately, signal cancellation is still present, but diagonal loading can be introduced to minimize the problem.

  • 194.
    Bengtsson, Mats
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Svedman, Patrick
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Zetterberg, Per
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Comparison and Cost Analysis of Smart and Opportunistic MIMO OFDM Schemes2006Ingår i: IST Mobile & Wireless Communications Summit 2006, 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper attempts to compare the system downlinkperformance of a smart antenna scheme for OFDMA thatutilizes channel covariance information with an opportunisticmulti-antenna scheme for OFDMA that uses fast limited feedbackof the instantaneous channel condition. The schemes areevaluated by means of simulations in a low load scenario andalso compared to a simple HSDPA-like scheme. The smartantenna method manages to utilize the multiple antennas betterthan the opportunistic scheme. Furthermore, the performanceof the schemes is inserted into a cost model that assumes thatthe receivers are relays that use short-range technologies tocommunicate with user equipments. Also in terms of cost peruser equipment, the smart antenna scheme proves to be moresuitable for the studied scenario.

  • 195.
    Bengtsson, Mats
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Svedman, Patrick
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Zhang, Xi
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Zetterberg, Per
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    System comparison of smart and dumb antennas2005Ingår i: VTC2005-SPRING: 2005 IEEE 61ST VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, PROCEEDINGS, 2005, s. 230-233Konferensbidrag (Refereegranskat)
    Abstract [en]

    Different approaches have been proposed to utilize multiple antennas at both transmitters and receivers of wireless systems. Herein, we provide a system comparison between covariance feedback schemes where a large amount of information is fed back at a low rate and opportunistic beamforming schemes where a small amount of information is fed back at a high rate.

  • 196.
    Bengtsson, Mats
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Völcker, Björn
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    On the estimation of Azimuth distributions and Azimuth Spectra2001Ingår i: IEEE 54TH VEHICULAR TECHNOLOGY CONFERENCE, VTC FALL 2001, 2001, s. 1612-1615Konferensbidrag (Refereegranskat)
    Abstract [en]

    The increased popularity of array antennas for wireless communication, has inspired investigations of the spatio-temporal properties of the radio channel, among others the azimuthal shape of the scattering clusters. Based on a statistical analysis, we show that trying to estimate the shape of the scattering Is an ill-posed problem and that the heavy-tailed Power Azimuth Spectra reported in the literature may be an artifact stemming only from the measurement procedure.

  • 197.
    Bengtsson, Mats
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Yu, Kai
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Ottersten, Björn
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    D523, Part 1. Single and Dual Multi-Sensor Channel Characterisation - Analysis and Models: Stochastic Models2001Rapport (Övrigt vetenskapligt)
  • 198.
    Berg, Miguel
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Hultell, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Access selection in partially Backhaul-limited multi-operator IEEE 802.11 networks2006Ingår i: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, Helsinki, 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    Radio resource management (RRM) across multiple, potentially competing, wireless networks has emerged as a salient feature for future generation system. Besides increased overhead, it will incur more complicated architectures and the question then becomes whether the gains of cooperative RRM (increased throughput, reliability, etc.) can justify these disadvantages. Herein we study potential gains that can be achieved by utilizing sophisticated algorithms in a scenario with two cooperating IEEE 802.11a networks, limited by either the wireless or wired link. Both best-effort (BE) and minimum bitrate (MBR) are treated and throughout the paper we use the rudimentary minimum path-loss (MPL) allocation as reference. Our results indicate that sophisticated access selection methods that besides path-loss, also account for AP load and potential constraints in the wired connection, can increase performance significantly. The maximum gain varies between 30-60% and 100-150% for BE and MBR traffic respectively and is typically obtained when there, on average, is one user per AP. We also studied the case where APs with constrained wired capacity connected (using the MPL criteria) to high-capacity APs in order to reroute traffic. Contrary to the approach in which advanced allocation principles is used, "loose" network integration is sufficient and even though it gave lower gains for BE data, the achievable rates for MBR data could be improved substantially.

  • 199.
    Berg, Miguel
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Hultell, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    On Selfish Distributed Access Selection Algorithms in IEEE 802.11 Networks2006Ingår i: IEEE VTS VEH TECHNOL CONF, 2006, s. 1097-1102Konferensbidrag (Refereegranskat)
    Abstract [en]

    An important question for future wireless networks is whether the prioritization between different accesses should be controlled by the networks or terminals. Herein we evaluate the performance of distributed access-selection algorithms where terminals are responsible for both AP selection and the necessary measurements. In particular, we focus on determining whether selfish distributed algorithms call perform as well as centralized ones (for comparison we include max-sum, max-min, proportional fair and minimum delay allocations). The study is conducted by time-dynamic simulations in a IEEE 802.11a network and its performance measures we use file transfer delay and supportable load at a maximum tolerable delay. Our results show that selfish algorithms can offer similar performance. both in terms of throughput and fairness, as the centralized schemes as long as they account for both path-loss and access point load. This is an important result and it suggests that terminal-controlled algorithms are Just as efficient as centralized schemes, which besides extensive measurements also require that AP exchange information, for improving the efficiency in WLAN networks. Compared with a minimum path-loss selection criteria, which is standard in the IEEE 802.11 family today, our distributed load-aware algorithm increases the maximum supportable load with more than 200 percent even after accounting for measurement time and estimation errors. With fast reselection during ongoing sessions the gains call be further increased with, typically, 20 percent.

  • 200. Berger, Andre
    et al.
    Gross, James
    RWTH Aachen University, Germany.
    Harks, Tobias
    The k–Constrained Bipartite Matching Problem: Approximation Algorithms and Applications to Wireless Networks2010Ingår i: Proceedings IEEE INFOCOM, 2010, IEEE conference proceedings, 2010, s. 1-9Konferensbidrag (Refereegranskat)
    Abstract [en]

    In communication networks, resource assignment problems appear in several different settings. These problems are often modeled by a maximum weight matching problem in bipartite graphs and efficient matching algorithms are well known. In several applications, the corresponding matching problem has to be solved many times in a row as the underlying system operates in a time-slotted fashion and the edge weights change over time. However, changing the assignments can come with a certain cost for reconfiguration that depends on the number of changed edges between subsequent assignments. In order to control the cost of reconfiguration, we propose the k-constrained bipartite matching problem for bipartite graphs, which seeks an optimal matching that realizes at most k changes from a previous matching. We provide fast approximation algorithms with provable guarantees for this problem. Furthermore, to cope with the sequential nature of assignment problems, we introduce an online variant of the k-constrained matching problem and derive online algorithms that are based on our approximation algorithms for the k-constrained bipartite matching problem. Finally, we establish the applicability of our model and our algorithms in the context of OFDMA wireless networks finding a significant performance improvement for the proposed algorithms.

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