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  • 2251.
    Zhao, Xueqian
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Elektronik och Inbyggda System.
    Network on Chip: Performance Bound and Tightness2015Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Featured with good scalability, modularity and large bandwidth, Network-on-Chip (NoC) has been widely applied in manycore Chip Multiprocessor (CMP) and Multiprocessor System-on-Chip (MPSoC) architectures. The provision of guaranteed service emerges as an important NoC design problem due to the application requirements in Quality-of-Service (QoS).

    Formal analysis of performance bounds plays a critical role in ensuring guaranteed service of NoC by giving insights into how the design parameters impact the network performance. The study in this thesis proposes analysis methods for delay and backlog bounds with Network Calculus (NC). Based on xMAS (eXecutable Micro-Architectural Specification), a formal framework to model communication fabrics, the delay bound analysis procedure is presented using NC. The micro-architectural xMAS representation of a canonical on-chip router is proposed with both the data flow and control flow well captured. Furthermore, a well-defined xMAS model for a specific application on an NoC can be created with network and flow knowledge and then be mapped to corresponding NC analysis model for end-to-end delay bound calculation. The xMAS model effectively bridges the gap between the informal NoC micro-architecture and the formal analysis model. Besides delay bound, the analysis of backlog bound is also crucial for predicting buffer dimensioning boundary in on-chip Virtual Channel (VC) routers. In this thesis, basic buffer use cases are identified with corresponding analysis models proposed so as to decompose the complex flow contention in a network. Then we develop a topology independent analysis technique to convey the backlog bound analysis step by step. Algorithms are developed to automate this analysis procedure.

    Accompanying the analysis of performance bounds, tightness evaluation is an essential step to ensure the validity of the analysis models. However, this evaluation process is often a tedious, time-consuming, and manual simulation process in which many simulation parameters may have to be configured before the simulations run. In this thesis, we develop a heuristics aided tightness evaluation method for the analytical delay and backlog bounds. The tightness evaluation is abstracted as constrained optimization problems with the objectives formulated as implicit functions with respect to the system parameters. Based on the well-defined problems, heuristics can be applied to guide a fully automated configuration searching process which incorporates cycle-accurate bit-accurate simulations. As an example of heuristics, Adaptive Simulated Annealing (ASA) is adopted to guide the search in the configuration space. Experiment results indicate that the performance analysis models based on NC give tight results which are effectively found by the heuristics aided evaluation process even the model has a multidimensional discrete search space and complex constraints.

    In order to facilitate xMAS modeling and corresponding validation of the performance analysis models, the thesis presents an xMAS tool developed in Simulink. It provides a friendly graphical interface for xMAS modeling and parameter configuring based on the powerful Simulink modeling environment. Hierarchical model build-up and Verilog-HDL code generation are essentially supported to manage complex models and conduct simulations. Attributed to the synthesizable xMAS library and the good extendibility, this xMAS tool has promising use in application specific NoC design based on the xMAS components.

  • 2252. Zhao, Ying
    et al.
    Deng, Lei
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Yu, Xianbin
    Zheng, Xiaoping
    Zhang, Hanyi
    Monroy, Idelfonso Tafur
    Digital predistortion of 75–110 GHz W-band frequency multiplier for fiber wireless short range access systems2011Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, nr 26, s. 18-25Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a W-band fiber-wireless transmission system based on a nonlinear frequency multiplier for high-speed wireless short range access applications. By implementing a baseband digital signal predistortion scheme, intensive nonlinear distortions induced in a sextuple frequency multiplier can be effectively pre-compensated. Without using costly W-band components, a transmission system with 26km fiber and 4m wireless transmission operating at 99.6GHz is experimentally validated. Adjacent-channel power ratio (ACPR) improvements for IQ-modulated vector signals are guaranteed and transmission performances for fiber and wireless channels are studied. This W-band predistortion technique is a promising candidate for applications in high capacity wireless-fiber access systems.

  • 2253. Zhao, Ying
    et al.
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Deng, Lei
    Othman, Maisara B
    Yu, Xianbin
    Zheng, Xiaoping
    Zhang, Hanyi
    Monroy, Idelfonso T
    Experimental demonstration of 5-Gb/s polarization-multiplexed fiber-wireless MIMO systems2011Ingår i: 2011 IEEE International Topical Meeting on Microwave Photonics - Jointly Held with the 2011 Asia-Pacific Microwave Photonics Conference, MWP/APMP 2011, 2011, s. 13-16, artikel-id 6088657Konferensbidrag (Refereegranskat)
    Abstract [en]

    We experimentally demonstrate a 5-Gb/s fiber-wireless transmission system combining optical polarization-division-multiplexing (PDM) and wireless multiple-input, multiple-output (MIMO) spatial multiplexing technologies. The optical-wireless channel throughput is enhanced by achieving a 4b/s/Hz spectral efficiency. Based on the implementation of constant modulus algorithm (CMA), the 2x2 MIMO wireless channel is characterized and adaptively equalized for signal demodulation. The performance of the CMA-based channel adaptation is studied and it is revealed that the algorithm is particularly advantageous to the MIMO wireless system due to the inter-channel delay insensitivity. The hybrid transmission performance of 26km fiber and up to 2m wireless MIMO is investigated.

  • 2254. Zhao, Ying
    et al.
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Deng, Lei
    Yu, Xianbin
    Zheng, Xiaoping
    Monroy, Idelfonso Tafur
    Ultra-Broadband Photonic Harmonic Mixer Based on Optical Comb Generation2012Ingår i: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 24, nr 1, s. 16-18, artikel-id 6045319Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a novel photonic harmonic mixer operating at frequencies up to the millimeter-wave (MMW) band. By combining a broadband fiber-wireless signal with high-order harmonics of a fundamental local oscillator in an optical frequency comb generator, frequency down-conversion can be implemented without using a costly ultra-broadband photodiode. It is theoretically shown that the down-conversion efficiency and the bandwidth of the mixer is highly dependent on the optical modulation indices and the fundamental frequency of comb lines. Down-conversion of a W-band (75-110 GHz) fiber-wireless signal is experimentally demonstrated. Moreover, the error vector magnitude (EVM) performance of a multigigabit quadrature phase-shift-keying (QPSK) signal at 62.5-, 82.5-, and 102.5-GHz carrier frequencies is studied to evaluate the down-conversion efficiency. The proposed photonic harmonic mixer can be a candidate for applications in high capacity fiber-wireless communication systems.

  • 2255. Zhao, Ying
    et al.
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Deng, Lei
    Yu, Xianbin
    Zheng, Xiaoping
    Zhou, Bingkun
    Monroy, Idelfonso Tafur
    High accuracy microwave frequency measurement based on single-drive dual-parallel Mach-Zehnder modulator2011Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, nr 26, s. 681-686Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel approach for broadband microwave frequency measurement by employing a single-drive dual-parallel Mach-Zehnder modulator is proposed and experimentally demonstrated. Based on bias manipulations of the modulator, conventional frequency-to-power mapping technique is developed by performing a two-stage frequency measurement cooperating with digital signal processing. In the experiment, 10GHz measurement range is guaranteed and the average uncertainty of estimated microwave frequency is 5.4MHz, which verifies the measurement accuracy is significantly improved by achieving an unprecedented 10(-3) relative error. This high accuracy frequency measurement technique is a promising candidate for high-speed electronic warfare and defense applications.

  • 2256.
    Zhao, Zhengjian
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Mediating updates using a web based service2007Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Den Europeiska kommissionen antog 2006 en ny bestämmelse för informationsspridning av kemikalier, Registration, Evaluation, and Authorization of Chemicals (REACH), och den kommer att tas i bruk från första juni 2007. Bestämmelsen innebär ett starkt ökat skydd för användare av kemikalier, men den ställer även till problem för både tillverkare och användare. Exempelvis, de måste generera och distribuera betydligt fler materialsäkerhetsföreskrifter, Material Safety Data Sheets (MSDS), än tidigare. Detta arbete är krävande för de flesta företag eftersom arbetet ofta sker manuellt. Den nya bestämmelsen kräver mycket effektivare metoder att generera och distribuera MSDS.

    Det här examensarbetet fokuserar på problemet att automatiskt distribuera MSDS och den korresponderande metadatat. Rapporten presenterar den underliggande teknologin för examensarbetet. Därutöver ges en kort introduktion till examensarbetet, den underliggande teknologin, tillsammans med de metoderna som används för att skicka relevanta och aktuella materialsäkerhetsföreskrifter.

    Som avslutning väljs en HTTP Web applikationslösning för att lösa problemet. Den lösningen kan effektivt underrätta en användare att det finns en nyare MSDS och sedan skicka den korresponderande filen och dess metadata. Den är data driven, vilket gör att en användare inte måste kontrollera för uppdateringar varje dag, utan kommer att bli informerad när det finns en ny tillgänglig.

  • 2257. Zheng, G.
    et al.
    Li, J.
    Wong, K. -K
    Petropulu, A. P.
    Ottersten, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Using simple relays to improve physical-layer security2012Ingår i: Communications in China (ICCC), 2012 1st IEEE International Conference on, IEEE , 2012, s. 329-333Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper studies different uses of two cooperating relays to improve the secrecy rate of a wiretap channel. These two relays are assumed to perform only simple functions: either amplify-and-forward (AF) or jamming. Complex functions such as decode-and-forward (DF) are not considered. We study three modes of cooperation: i) cooperative jamming (CJ), ii) AF-aided beamforming and iii) mixed AF-aided beamforming and CJ, all with individual relay power constraints. While i) is known in the literature, our efforts are spent on ii) and iii). In particular, for iii), we assume that the jamming signals in two communication stages are correlated, giving rise to improved performances. We also propose a heuristic approach for selecting the appropriate cooperating mode. Simulation results illustrate the performance gain of each scheme under different channel conditions and the effectiveness of the proposed mode selection method.

  • 2258.
    Zheng, Gan
    et al.
    Department of Electrical and Electronic Engineering, University College London, UK.
    Wong, Kai-Kit
    Department of Electrical and Electronic Engineering, University College London, UK.
    Paulraj, Arogyasvsami
    Information Systems Laboratory, Stanford University, US.
    Ottersten, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Collaborative-Relay Beamforming with Perfect CSI: Optimum and Distributed Implementation2009Ingår i: IEEE Signal Processing Letters, ISSN 1070-9908, E-ISSN 1558-2361, Vol. 16, nr 4, s. 257-260Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This letter studies the collaborative use of amplify-and-forward (AF) relays to form a virtual multiple-input single-output (MISO) beamforming system with the aid of perfect channel state information (CSI) in a flat-fading channel. In particular, we optimize the relay weights jointly to maximize the received signal-to-noise ratio (SNR) at the destination terminal with both individual and total power constraints at the relays. We show that the optimal collaborative-relay beamforming (CRB) solution achieves the full diversity of a MISO antenna system. Another main contribution of this letter is a distributed algorithm that allows each individual relay to learn its own weight, based on the Karush-Kuhn-Tucker (KKT) analysis.

  • 2259.
    Zheng, Gan
    et al.
    Department of Electrical and Electronic Engineering, University College London, London, WC1E 7JE, UK..
    Wong, Kai-Kit
    Department of Electrical and Electronic Engineering, University College London, London, WC1E 7JE, UK..
    Paulraj, Arogyasvsami
    Information Systems Laboratory, Stanford University, US.
    Ottersten, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Robust and distributed beamforming2009Ingår i: 2009 International Conference on Wireless Communications and Signal Processing, 2009, Vol. WCSP 2009, s. 1629-1633Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper studies the use of amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst-case signal-to-noise ratio (SNR) at the destination terminal is studied under a bounded spherical region for the norm of CSI error vector. We show that under a condition on the estimated CSI quality, the robust-optimal collaborative-relay beamforming (CRBF) can be obtained by S-Procedure and rank relaxation techniques. In addition, a distributed algorithm is proposed by examining the structure of the optimal CRBF.

  • 2260.
    Zheng, Gan
    et al.
    Department of Electrical and Electronic Engineering, University College London.
    Wong, Kai-Kit
    Department of Electrical and Electronic Engineering, University College London.
    Paulraj, Arogyasvsami
    Information Systems Laboratory, Stanford University, US.
    Ottersten, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Robust Collaborative-Relay Beamforming2009Ingår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 57, nr 8, s. 3130-3143Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Relay communications is a promising technique to extend the range of wireless communications by forwarding the message from the sender to the intended destination. While fixed or variable-power relays have been previously investigated, this paper addresses the collaborative use of variable-phase variable-power amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst-case signal-to-noise ratio (SNR) at the destination terminal is studied under a bounded spherical region for the norm of the CSI error vector from the relays to the destination. Our main contribution is that we prove, under a condition on the quality of the estimated CSI, the robust-optimal collaborative-relay beamforming (CRBF) can be obtained by S-Procedure and rank relaxation techniques. In addition, a distributed algorithm is developed by examining the structure of the optimal CRBF solution. Results demonstrate a significant gain of CRBF over non-robust approaches.

  • 2261.
    Zheng, Li-Rong
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Elektronik- och datorsystem, ECS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    Intelligent paper and packaging - Integration of microelectronics technologies into paper and packaging products2007Ingår i: International Paperworld IPW, ISSN 1615-1720, nr 11, s. 56-58Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    The integration of microelectronics technologies and intelligent packaging into the paper and packaging products are creating new business opportunities. Intelligent and interactive packaging aims to make traditional food packaging smart, active and user-friendly. he printed optical code or integrated radio-frequency identification (RFID) chips will allow the customers to link the products directly to mobile Internet through the camera or near field communication. The paper can be used as a paper-based biochip for biochemical analysis by integrating biochemical sensors or a sensor array. VINN Excellence iPack Center has been established with the focus on ubiquitous intelligence in paper and packaging. The center will establish collaborations between the forest products industry, the electronics industry and the biomedical industry in the area of intelligent paper and packaging for biomedical applications.

  • 2262.
    Zhou, Jia
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Adding bandwidth specification to a AAA Sever2008Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Authentication, authorization, and accounting (AAA) are key elements in network security. In many networks, clients can use resources only after they have been authenticated by an authentication server and authorized to use these resources. In some cases the server will also maintain accounting records in order for an operator (a provider of resources) to charge the account/subscriber for using the service. There are four main AAA protocols being used today. Of these RADIUS is the mostly widely used.

    This thesis starts with an introduction to AAA protocols, and then goes in the details of RADIUS. In order to perform a practical evaluation of how the AAA could be improved, FreeRADIUS was selected as the base code for this project; because this implementation is one of the most widely used RADIUS servers. A proposal for how to improve AAA performance is introduced and the implementation steps needed to realize these improvements are shown. Additionally, some experiments have been conducted to show both the correct functioning of the resulting implementation and to examine if there is a performance improvement. Following this some conclusions are drawn based upon a comparison with a traditional AAA server.

    A key element of the change in AAA which is proposed is the use of a non-binary IEEE 802.1x process. This new non-binary solution introduces a new type of AAA server and requires the re-thinking of a number of traditional AAA design decisions. It is expected that this change will have a significant impact, but will require some time for exposure, implementation by others, and a more extensive evaluation that was possible during the period of this thesis project.

    One of the most important conclusions drawn during this thesis is the difficulty of making a change in authentication and authorization, because of the large amount of interaction between both the various protocols and the standards which have been developed for these protocols. Thus one of the difficult aspects of the task is how to introduce a change in a protocol while maintaining backward compatibility for others who have not adopted this change -- without requiring the addition of a protocol version field.

    A second important conclusion is that doing this implementation in three separate parts with different students being responsible for the different parts revealed just how complex the interaction of protocol design decisions are. While a working version of the entire set of changes proved to be impossible, it was observed that the different parts could be decoupled more than initially expected.

  • 2263.
    Zhu, Kun
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Industriella informations- och styrsystem.
    Nordström, Lars
    KTH, Skolan för elektro- och systemteknik (EES), Industriella informations- och styrsystem.
    Hammouri, A.
    Jordan University of Science and Technology .
    Examination of data delay and packet loss for wide-area monitoring and control systems2012Ingår i: 2012 IEEE International Energy Conference and Exhibition, ENERGYCON 2012, IEEE , 2012, s. 927-934Konferensbidrag (Refereegranskat)
    Abstract [en]

    Timely and synchronized phasor data at high resolutions holds a great promise for more responsible and advanced power grid operations. It is expected that the combined effort of developing new application paradigms and the supporting Information and Communication Technology (ICT) will enable the evolutionary change for future transmission grid operation. This paper addresses the design of the supporting ICT system for Wide-Area Monitoring and Control applications considering system performance. The major contribution that distinguishes this paper from previous research efforts in the same area is that this study quantifies the end-to-end data delay and the received packet rate with considerations of different levels of data concentrations. The analysis performed in this paper is not merely limited to the performance issues caused by communication networks but also provides means to view and analyze the overall data delay of the entire supporting ICT system.

  • 2264.
    Zhu, Wanning
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Multipoint Relay flooding: Network coding improvements2009Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Network coding is a new research area with potential to reduce network resources. With network coding, intermediate nodes forward packets that are linear combinations of previously received packets.

    The type of networks we consider are vehicle mounted mobile tactical radio networks. Tactical communication may be required in areas where pre-deployed base stations are unavailable. Mobile ad hoc networks satisfy this requirement. Due to low antenna heights, network resources are scarce inmobile networks without base stations. Broadcast traffic, which disseminates information network-wide, is very important in tactical mobile networks. Multipoint relay flooding is a well-known technique for efficient distribution of broadcast traffic. It is therefore interesting to evaluate how much network coding can reduce the number of transmissions in a mobile ad hoc network. In this thesis we show that it is possible to further reduce the number of transmissions for Multipoints Relay flooding by using network coding. However, this improvement is largely theoretical - there has been no effort to evaluate this approach in practice.

  • 2265. Zhu, Xuncheng
    et al.
    Ding, Zhizhong
    Punyal, Oscar
    Gross, James
    Design and Implementation of Baseband Algorithms for OFDM-based Wireless Communication Systems2011Ingår i: 7th International Conference on Wireless Communications, Networking and Mobile Computing (WiCOM), 2011, IEEE conference proceedings, 2011, s. 1-5Konferensbidrag (Refereegranskat)
    Abstract [en]

    Orthogonal frequency-division multiplexing (OFDM) is an appropriate solution to combat inter-symbol interference (ISI) caused by multi-path propagation in wireless communications. OFDM-based wireless communication systems become more and more popular and the base-band algorithm is one of the significant parts of the systems. In this paper, we present the design and implementation of base-band algorithms for OFDM-based wireless communication systems. The results show that the designed algorithms are effective for implementation of the system.

  • 2266. Zibar, Darko
    et al.
    Caballero, Antonio
    Yu, Xianbin
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Dogadaev, Anton K
    Monroy, I Tafur
    Hybrid optical fibre-wireless links at the 75–110 GHz band supporting 100 Gbps transmission capacities2011Ingår i: 2011 IEEE International Topical Meeting on Microwave Photonics - Jointly Held with the 2011 Asia-Pacific Microwave Photonics Conference, MWP/APMP 2011, 2011, s. 445-449, artikel-id 6088767Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a photonic generation and down-conversion method for realizing a 40Gbps wireless link at the 75-110 GHz band exploiting the recent advances in photonic coherent detection technologies and digital signal processing. Furthermore, we analyze the capacities of hybrid optical fiber-wireless links at the 75-110GHz band, and propose several approaches to overcome the challenges towards 100Gbps wireless capacity.

  • 2267.
    Zografos, Alexandros
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Wireless Sensor-based Agricultural Monitoring System2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Idag när energiresurser blir allt knappare och knappare blir de även mer värdefulla. I samband med befolkningstillväxten under förra århundradet har behovet av att hitta nya, mer effektiva och hållbara metoder inom jordbruket och livsmedelsproduktion blivit av allt större vikt. . För att underlätta denna process har vi designat, byggt och utvärderat ett system för precisionsjordbruk som ger bönder mer användbara data om jorden, vattenförsörjning och det allmänna tillståndet i sina områden på ett användarvänligt och lättillgängligt sätt. Vårt system syftar till att göra odling och bevattning effektivare då bonden kan fatta bättre underbyggda beslut och därmed spara tid och resurser.

    Mångfalden av läget och jordbrukets klimatpåverkan, tillsammans med andra miljöparametrar över tiden gör bondens beslutsprocess mer komplicerad än tidigare och kräver ytterligare empirisk kunskap. Att tillämpa trådlösa sensornätverk för övervakning av dessa parametrar och att presentera? denna information med en användarvänlig skräddarsydd webbtjänst kan göra det möjligt för jordbrukare att utnyttja på ett effektivt sätt nåde bästa resultaten från sitt jordbruk. Systemet kan skala utifrån varje bondes krav och den insamlade data kan utgöra en värdefull resurs för ett framtida jordbruk, utöver dess användning för dagens bondes beslut. Utformningen av systemet för precisionsjordbruk innehåller en prototyplösning avseende sensorplattformen och en anpassningsbar tjänst som kan användas på olika sätt och av flera enheter.

  • 2268.
    Zou, Zhenhua
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Deadline-constrained maximum reliability packet forwarding with limited channel state information2013Ingår i: 2013 IEEE Wireless Communications and Networking Conference (WCNC), New York: IEEE Communications Society, 2013, s. 1721-1726Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper considers real-time packet forwarding over wireless multi-hop networks with lossy and bursty links. Our objective is to maximize the probability that individual packets reach their destination before a hard deadline. The loss processes on links are modeled by finite-state Markov chains. While the parameters of the Markov chains are assumed to be known, the instantaneous channel states are not accessible but have to be estimated from observations of successes and failures of actual packet transmissions. We formulate the forwarding problem as a partially observable Markov decision process and derive the optimal forwarding policy. A novel technique, based on maximum-volume inscribed ellipsoids, for computing approximate solutions with reduced implementation complexity is proposed. We further discuss structural properties of the value function and the optimal actions. Finally, numerical examples illustrate the power of the developed techniques.

  • 2269.
    Zou, Zhuo
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Elektroniksystem.
    Impulse Radio UWB for the Internet-of-Things: A Study on UHF/UWB Hybrid Solution2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This dissertation investigates Ultra-Wideband (UWB) techniques for the next generation Radio Frequency Identification (RFID) towards the Internet-of-Things (IoT). In particular, an ultra-high frequency (UHF) wireless-powered UWB radio (UHF/UWB hybrid) with asymmetric links is explored from system architecture to circuit implementation.

    Context-aware, location-aware, and energy-aware computing for the IoT demands future micro-devices (e.g., RFID tags) with capabilities of sensing, processing, communication, and positioning, which can be integrated into everyday objects including paper documents, as well as food and pharmaceutical packages. To this end, reliable-operating and maintenance-free wireless networks with low-power and low-cost radio transceivers are essential. In this context, state-of-the-art passive RFID technologies provide limited data rate and positioning accuracy, whereas active radios suffer from high complexity and power-hungry transceivers. Impulse Radio UWB (IR-UWB) exhibits significant advantages that are expected to overcome these limitations. Wideband signals offer robust communications and high-precision positioning; duty-cycled operations allow link scalability; and baseband-like architecture facilitates extremely simple and low-power transmitters. However, the implementation of the IR-UWB receiver is still power-hungry and complex, and thus is unacceptable for self-powered or passive tags.

    To cope with μW level power budget in wireless-powered systems, this dissertation proposes an UHF/UWB hybrid radio architecture with asymmetric links. It combines the passive UHF RFID and the IR-UWB transmitter. In the downlink (reader-tag), the tag is powered and controlled by UHF signals as conventional passive UHF tags, whereas it uses an IR-UWB transmitter to send data for a short time at a high rate in the uplink (tag-reader). Such an innovative architecture takes advantage of UWB transmissions, while the tag avoids the complex UWB receiver by shifting the burden to the reader. A wireless-powered tag providing -18.5 dBm sensitivity UHF downlink and 10 Mb/s UWB uplink is implemented in 180 nm CMOS. At the reader side, a non-coherent energy detection IR-UWB receiver is designed to pair the tag. The receiver is featured by high energy-efficiency and flexibility that supports multi-mode operations. A novel synchronization scheme based on the energy offset is suggested. It allows fast synchronization between the reader and tags, without increasing the hardware complexity. Time-of-Arrival (TOA) estimation schemes are analyzed and developed for the reader, which enables tag localization. The receiver prototype is fabricated in 90 nm CMOS with 16.3 mW power consumption and -79 dBm sensitivity at 10 Mb/s data rate. The system concept is verified by the link measurement between the tag and the reader. Compared with current passive UHF RFID systems, the UHF/UWB hybrid solution provides an order of magnitude improvement in terms of the data rate and positioning accuracy brought by the IR-UWB uplink.

  • 2270. Zu, L.
    et al.
    Ji, Y.
    Wang, Liping
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsnät.
    Zhong, L.
    Liu, F.
    Wang, P.
    Xu, J.
    Joint optimization in multi-user MIMO-OFDMA relay-enhanced cellular networks2011Ingår i: 2011 IEEE Wireless Communications and Networking Conferenc, 2011, s. 13-18Konferensbidrag (Refereegranskat)
    Abstract [en]

    MIMO, OFDMA and cooperative relaying are the key technologies in future wireless communication systems. However, under the usage of these technologies, resource allocation becomes a more crucial and challenging task. In multi-user MIMO-OFDMA relay-enhanced cellular networks, we formulate the optimal instantaneous resource allocation problem including user group selection, path selection, power allocation, and subchannel scheduling to maximize system capacity. We first propose a low-complex resource allocation algorithm named CP-CP under constant uniform power allocation and then use a water-filling method named CP-AP to allocate power among transmitting antennas. Moreover, we solve the original optimization problem efficiently by using the Jensen's inequality and propose a modified iterative water-filling algorithm named AP-CP. Based on AP-CP, the AP-AP algorithm is proposed to allocate power adaptively not only among subchannels but also among multiple transmitting. Finally, we compare the performance of the four schemes. Our results show that allocating power among subchannels is more effective than among transmitting antennas if the average signal-to-noise radio of users is low, and vice versa. Furthermore, the AP-AP algorithm achieves the highest throughout especially for users near the cell edge.

  • 2271.
    Åhman, Stefan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Wallstersson, Marcus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    EVH2 protocol: Performance analysis and Wireshark dissector development2012Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    EVH2 är ett proprietärt applikationslagerprotokoll utvecklat av Aptilo Networks som används i deras mjukvaruprodukt. För närvarande kan EVH2-trafik endast inspekteras med deras egenutvecklade applikation. Denna applikation har inte något stöd för att inspektera annan trafik än EVH2. Eftersom Aptilo kontinuerligt utvecklar detta protokollet är det viktigt att kunna se hur förändringar i protokollet påverkar dess prestanda. Detta examenarbete undersöker möjliga sätt att underlätta användningen och utvecklingen av protokollet.

    För att kunna inspektera EVH2-trafik tillsammans med trafik från andra protokoll behövs en annan lösning än den nuvarande. Wireshark är en applikation som har stöd för att inspektera flera protokoll samtidigt där protokollpaketen avkodas med dissectors (dissektorer översatt till svenska). I detta examensarbete beskrivs och utvärderas utvecklingen av ett Wireshark dissector plugin för inspektion av EVH2-trafik.

    Genom att prestandatesta EVH2 kan prestandaskillnader påvisas vid förändringar i protokollet. Detta examensarbete tar fram en plattform för prestandautvärdering genom att introducera en testsvit för prestandatestning. Den utvecklade testsviten användes för att utföra prestandtestning av EVH2.

  • 2272.
    Åkervik, Mattias
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Network Gaming: Performance and Traffic Modeling2006Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Det finns idag en stor mängd datorspel som spelas i flerspelarläge över nätverk. De spel som från ett hårdvaru- och nätverksperspektiv ställer högst krav är realtidsbaserade flerspelarspel. Slutanvändare av dessa realtidsspel både förutsätter och tar för givet att interaktionen sker i så nära realtid som möjligt samtidigt som dessa spel ofta stödjer ett stort antal samtidiga användare. De flesta nätverk är i första hand anpassade för rösttrafik (som första och andra generationens mobilnät) eller datatrafik (som trådade datanätverk). Det står inte klart huruvida någon av dessa nätverk kan garantera tillräcklig prestanda för att en acceptabel spelkvalité skall uppnås för slutanvändaren. Kärnan i denna rapport utreder vilka krav som dagens mest krävande realtidsbaserade flerspelarspel ställer på nätverken de spelas över samt kopplingen mellan brister i dessa nätverk och den upplevda spelkvalitén för användarna. Trafik genererad av realtidsbaserade flerspelarspel särskiljer sig från annan trafik både när det gäller generell karaktäristik och när det gäller de krav som de ställer på nätverken. Det är viktigt att ha en förståelse kring den trafik som dessa spel skapar, kraven de ställer, samt de konsekvenser ett misslyckande av upprätthållande av sådana krav medför. Denna förståelse är av yttersta vikt när man designar nya nätverk för att kunna erbjuda en passande Quality of Service för denna typ av interaktiva multimediatjänster.

  • 2273.
    Ålemark, Niklas
    KTH, Tidigare Institutioner, Teleinformatik.
    Specification and development of animage acquisition and processing systemwith IR communications capabilities1996Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The GSM network has experienced a fast growth after its introduction in 1992. A large number of users in several countries in the word now have access to a standardised digital cellular network. This fact has lead to that the network is being used for several other things than voice communications. One such application is the transfer of pictures. This requires a unit that can digitise pictures and adapt the digital image information to the characteristics of the GSM network.

    This report describes the specification and development of an image acquisition and processing system with IR communications capabilities. It also outlines some of the possible applications for such a system.

  • 2274.
    Åman, Erik
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    A Distributed Cachefor Very Large Objects2001Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Within a few years’ time, the Internet is expected to be used to transfer highquality video material and other bandwidth-demanding objects to a much larger extent than today. Users would prefer to be able to access such very large objects at an arbitrary point in time without any kind of preparation or advance planning. Offering such services on a large scale puts high demands on the network.

    Using a caching Web proxy server may increase the bandwidth and reliability perceived by the users while reducing the load on the network. This can be done transparently to the users.

    This thesis presents the principles for a caching Web proxy server better adapted to this expected traffic pattern. The bandwidth usage and transfer rate can be improved by taking advantage of the longer persistence of connections and by assuming that comparatively few objects will be popular at any given time. An experimental implementation has been developed in order to test the main principles. The new server is designed to operate in a distributed fashion by employing several cooperating servers at strategic points in the network. The system optimizes reliability and throughput by dynamically selecting from where to download objects based on current traffic and previous statistics.

  • 2275.
    Ótão Pereira, Pedro Miguel
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Dimarogonas, Dino V.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Family of controllers for attitude synchronization in S22016Ingår i: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2016, s. 6761-6766Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we study a family of controllers that guarantees attitude synchronization for a network of elements in the unit sphere domain, i.e., S2. We propose distributed continuous controllers for elements whose dynamics are controllable (i.e., control with torque as command), and which can be implemented by each individual agent without the need of a common global orientation frame among the network, i.e., it requires only local information that can be measured by each individual agent from its own orientation frame. The controllers are specified according to arbitrary distance functions in S2, and we provide conditions on those distance functions that guarantee that i) a synchronized network of agents is locally asymptotically stable for an arbitrary connected network topology; ii) a synchronized network can be achieved for almost all initial conditions in a tree graph network. We also study the equilibria configurations that come with specific types of network graphs. The proposed strategies can be used in attitude synchronization of swarms of fully actuated rigid bodies, such as satellites.

  • 2276.
    Ögren, Niklas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Selecting/realization of Virtual Private Networks with Multiprotocol Label Switching or Virtual Local Area Networks2002Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Many reports have been written about the techniques behind Virtual Private Networks (VPN) and Multi Protocol Label Switching (MPLS). They usually deal with the low level design of the software implementing a specific technique. The initial products are usually not mature enough to run in a large network or have to be adjusted in some way to fit.

    This report investigates the different ways of implementing strict layer 2 Virtual Private Networks in an existing nation-wide Gigabit Ethernet. The infrastructure in use, as well as the hardware, has to be used without major changes. Since 1998/1999, when MPLS first started in the laboratories, development has continued. Today it is possible to introduce MPLS or tunneled national virtual local area network into an existing network. This requires high speed, fault tolerant, and stable hardware and software.

    Going beyond the separation of traffic at layer 3 using Virtual Private Networks, i.e., IPSec, we can tunnel layer 2 traffic through a network. Although the first layer 3 VPN products are already in use, layer 2 VPNs still need to be evaluated and brought into regular use. There are currently two ways of tunneling VLANs in a core network: tunneled VLANs (or as Extreme Networks calls them, VMANs) and MPLS.

    This project showed that it is possible to start with a VLAN-only solution, and then upgrade to MPLS to solve scalability issues. The VMAN solution can not be used at Arrowhead, since there are too many disadvantages in the way Extreme Networks has implemented it. However, a mix of tunneling VMAN in a VLAN core is possible, and enables customer tagging of VLANs in a Layer 2 VPN. Furthermore, the testing of EAPS and per-VLAN Spanning Tree Protocol turned out well, and showed that EAPS should not be used when there is more than one loop.

  • 2277.
    Östermark, Filip
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Performance Optimization of Virtualized Packet Processing Function for 5G RAN2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Med den annalkande femte generationen av mobila nätverk (5G) följer en rad utmaningar för att uppnå de krav som ställs av kommande standarder. Den femte generationens Radioaccessnätverk (RAN) har flera funktioner som måste vara väloptimerade för att prestera enligt ökade krav. En sådan funktion är Packet Processing-funktionen (PPF), vilken måste kunna bearbeta paket med hög genomströmning och låg latens. En avgörande faktor i jakten på högre genomströmning och lägre latens är anpassningsbarhet hos 5Gteknologin.  Ericsson har därför utvecklat en prototyp av en PPF för 5G RAN som en virtuell nätverksfunktion (VNF) med hjälp av DPDK:s Eventdev-ramverk, som kan köras på en dator avsedd för allmän användning. I detta projekt optimeras genomströmningen och latensen hos Ericssons 5G RAN PPF-prototyp med hjälp av ett antal verktyg för prestandamätning och kodprofilering för att hitta flaskhalsar i pakethanteringsvägen, och därefter minska flaskhalsarnas negativa effekt på PPFens prestanda genom att ändra dess konfiguration.

    I experimenten användes IxNetwork för att generera 2 flöden med GTP-u/UDP/IPv4-paket som bearbetades av PPFen. IxNetwork användes även för att mäta genomströmning och latens.

    Resultaten visade att den maximala genomströmningen kunde ökas med 40.52% med en genomsnittlig latens på 97.59% jämfört med den ursprungliga PPF-prototypkonfigurationen i testfallet, genom att omfördela processorkärnor, sammanslå paketbearbetningssteg, och att patcha RSS-funktionen hos mottagardrivaren.

  • 2278.
    Östlund, Pontus
    KTH, Tidigare Institutioner, Teleinformatik.
    Integration of an optical network element in a TMN system1999Självständigt arbete på avancerad nivå (masterexamen), 12 poäng / 18 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The objective of this thesis project was to investigate how to control a new type of hardware, an optical add-drop multiplexer, and integrate it into a management system. One section of the report covers the design of this control/management system. The hardware for the optical add-drop multiplexer is also described.

  • 2279.
    Östman, Fredrik
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Automated Interface Switching for Wireless PDAs2001Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Mobility has become one of the major driving forces behind the Internet research effort for the last couple of years. Many large computer companies have begun to shift their focus and are trying to converge into the telecommunications and computing market. With the huge potential market of mobile/cellular phones to build on, hybrids between cellular phones and computers are a very lucrative and relatively new area. Recent efforts to bring traditional telecommunications closer to an IP based environment (for example the development and deployment of GPRS) have created new possibilities for the future of mobile systems. Personal Digital Assistants (PDAs) have been around for a couple of years, and they are getting ever more advanced and powerful. Considering how it will soon be very easy to connect these PDAs to the Internet (or any inter-, intranet), using faster and less expensive carriers and technology than ever before, and the new services that can be offered as a result, the market for - and usage of - PDAs have the potential to grow even more rapidly than before.

    This Master of Science Thesis will investigate the current and near future development of wireless PDAs, give an analysis of the most suitable technologies and discuss the new capabilities they can provide to consumers. Software for Microsoft Windows CE will be developed which manages the network interface selection for a PDA. The software, which will be integrated with Microsoft Windows CE, will automatically select the best interface for internetworking when two or more networks are available.

  • 2280.
    Östman, Thomas
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Parkvall, Stefan
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Ottersten, Björn
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    An Improved MUSIC Algorithm for Estimation of Time Delays in Asynchronous DS-CDMA Systems1999Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, Vol. 47, nr 11, s. 1628-1631Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The problem of near–far resistant time-delay estimation in an asynchronous direct-sequence code-division multipleaccess system is considered, and by better exploiting the structureof the problem, estimators superior to previously known techniques are obtained. For a typical numerical example, a gain insignal-to-noise ratio of approximately 3 dB is obtained.

  • 2281.
    Özger, Mustafa
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Vondra, Michal
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Cavdar, Cicek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Towards Beyond Visual Line of Sight Piloting of UAVs with Ultra Reliable Low Latency Communication2018Ingår i: 2018 IEEE Global Communications Conference, GLOBECOM 2018 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2018, artikel-id 8647652Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we propose a model for beyond visual line of sight (BVLOS) operation for remote piloting of unmanned aerial vehicles (UAVs), which utilizes different technologies such as mobile edge computing and augmented reality. Ultra reliable low latency communication (URLLC) is a key service of 5G that enables safe BVLOS operation. Since message size of piloting signal is finite and communication channel is altitude dependent, we study reliability and latency under finite blocklength regime for different altitudes. In our numerical study, we find that for message sizes 30 and 50 bits, coded packet size, i.e., blocklength, should be in the range of 200 and 300 bits to enable BVLOS operation. We also found that minimum distance between UAVs to avoid any crash should be around 0.2 m for 15 m/s UAV speed and different altitudes ranging from 1.5 m to 120 m. According to our study, BVLOS operation of UAVs can be realized by URLLC by providing error probability in the vicinity of 10(-3), and latency on the order of milliseconds for downlink communication with blocklength of tens to hundred bits.

  • 2282.
    Özyagci, Ali
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Selfish Dynamic Spectrum Access in Multichannel Wireless Networks: Complete and incomplete information analysis2011Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The increasing popularity and widespread deployment of wireless data systems fuel the increasing demand for more spectrum. On the other hand, various studies measuring spectrum utilization show that there is a huge variation in spectrum utilization at different times and locations. In view of this, various dynamic spectrum access (DSA) methods have been proposed in order to achieve more efficient utilization of spectrum resources by virtue of exploiting the variations in spectrum demand over time and space. Implementing DSA systems in a centralized way can lead to complexity and scalability problems due to the extensive control signaling involved. Therefore distributed implementations of DSA systems in which the users can access the system resources at their own discretion have been proposed. These distributed mechanisms typically incorporate cognitive radio systems which act as agents on behalf of users to measure the radio environment and make decisions based on these measurements. On the other hand, the freedom of the users in distributed systems to form their actions can lead each user to try to maximize its benefit from the system without regard the overall performance of the DSA system. Therefore, selfish behavior can prevail in distributed systems, which is likely to degrade the system performance.In this thesis we investigate the implications of selfish decision making in dynamic spectrum access systems. To address this broad problem, we focus our analysis on a particular system which can represent the essential properties of DSA systems and thus can shed light on the performance of the broad class of DSA systems with selfish users. Specifically, we model a DSA system as a multichannel random access system which uses ALOHA for medium access, and we analyze the behavior of the selfish users by modeling the system as a non-cooperative game. In this analysis we incorporate the effect of channel state information on the decision making of the users; we consider both cases when the users act on global (complete) and on local (incomplete) information. We determine the behavior of the selfish users at the Nash equilibria of the non-cooperative game and measure the performance of the system in terms of sum and individual utilities for various user loads and amount of available resources. We try to identify how the performance of the DSA system with selfish users compares with its cooperative counterpart. By performing these analyses we provide insights into the broader question of whether selfish users can utilize spectrum resources in a DSA system as well as cooperative users.

  • 2283.
    Özyagci, Ali
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Ileri, Ömer
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Zander, Jens
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Distributed multichannel random access networks with selfish users2010Ingår i: Proceedings of the Fifth International Conference on Cognitive Radio Oriented Wireless Networks Communications (CROWNCOM), 2010, 2010, s. 5577687-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Dynamic spectrum access (DSA) schemes allow the users to share spectrum resources by taking advantage of the variations in spectrum demand over time and space. Carrying out dynamic spectrum allocation centrally, however, can be a complex task. For this reason, distributed schemes in which users can access the available channels independently may be preferable to centralized DSA schemes. Cognitive radio systems, which enable user terminals to sense their environment and form their action accordingly, are particularly well-suited for distributed systems. On the other hand, the freedom in distributed schemes gives the users the option to act selfishly, which has decisive effects on system performance. In this paper we consider a distributed multichannel wireless random access system where users selfishly access the channels in the system. We analyze the behavior of the selfish users by modeling the system as a non-cooperative game and we identify all stable operating points (Nash equilibria) of this game. We then compare the performance of this system with a number of cooperative distributed DSA schemes in terms of user utilities. Our results show that the performance of the selfish multichannel random access system can be comparable to cooperative schemes.

  • 2284.
    Özyagci, Ali
    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.
    Sung, Ki Won
    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.
    Zander, Jens
    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.
    Effect of propagation environment on area throughput of dense WLAN deployments2013Ingår i: 9th IEEE Broadband wireless access workshop (BWA 2013), IEEE Computer Society, 2013, s. 333-338Konferensbidrag (Refereegranskat)
    Abstract [en]

    Indoor wireless LAN deployments have become ubiquitous. As WLAN deployments become increasingly dense, WLANs start to cause more and more contention and interference to each other, to the point that they cause significant throughput degradation to other WLANs. Since WLANs are one of the most commonplace solutions to provide indoor broadband data access, it is crucial to assess the throughput limits of WLANs in order to understand at what demand level novel broadband access mechanisms will be critically needed. The amount of contention and interference that coexisting WLANs create on each other is influenced by the indoor propagation environment such as existence of walls or clutter. Although the indoor propagation environment has a significant impact on the interaction between WLANs, and consequently on the area throughput, the relationship between the indoor propagation environment and achievable area throughput has not received much attention. In this paper, we investigate the area throughput of densely deployed WLANs in different indoor propagation environments by conducting detailed MAC layer simulations using OPNET. The results show that the propagation conditions have a profound impact on achievable area throughput; as much as several tens of times increase in highly cluttered environments compared to open areas.

  • 2285.
    Özyagci, Ali
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Zander, Jens
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Distributed Dynamic Spectrum Access in Multichannel Random Access Networks with Selfish Users2010Ingår i: Wireless Communications and Networking Conference (WCNC), 2010 IEEE, IEEE , 2010, s. 1-6Konferensbidrag (Refereegranskat)
    Abstract [en]

    Dynamic spectrum allocation schemes enable users to share spectrum resources by exploiting the variations in spectrum demand over time and space. Performing dynamic spectrum allocation centrally can be prohibitively complex. Therefore distributed schemes in which users can access the available channels independently may be preferable to centralized allocation. However, in distributed dynamic spectrum access, the lack of central coordination makes it difficult to utilize the system resources efficiently. Furthermore, if some or all of the users decide to deviate selfishly from the commonly agreed access procedure, this may have a decisive effect on system performance. In this paper we investigate the effect of incomplete information and selfish behavior on system performance in wireless access systems. We extend previous work by studying a distributed multichannel wireless random access system. Using a game-theoretic approach, we analyze the behavior of users in the selfish system and derive the transmission strategies at the Nash equilibrium. Our results show that lack of information leads to substantial degredation in performance of cooperative systems. We also show that there is a large incentive for selfish behavior in such cooperative systems. Selfish behavior of all users, however, causes further performance degradation, particularly in high load settings.

  • 2286.
    Özyagci, Ali
    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.
    Zander, Jens
    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.
    Selfish multi-channel random access in heterogeneous channelsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We analyze the behavior of selfish users in a multichannel random access system in which the propagation characteristics of the available channels in the system exhibit different statistics. We formulate the behavior of the selfish users as a Bayesian game and identify the transmission strategies at the Nash equilibria. Following this, we propose a simple iterative algorithm to obtain the transmission probabilities of the selfish uses at the Nash equilibria and investigate the convergence properties of this algorithm. Using the transmission probabilities of the selfish users at the Nash equilibria, we analyze the performance of the MRA system with selfish users in terms of sum and per-user utilities and compare this system with its cooperative and scheduling system counterparts. We find that selfish behavior results in significant performance loss compared to scheduling and cooperative systems, which increases as the system load increases.

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