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  • 201.
    Jia, Shi
    et al.
    Tech Univ Denmark, DTU Foton, DK-2800 Lyngby, Denmark..
    Lo, Mu-Chieh
    Univ Carlos III Madrid, Madrid 28911, Spain..
    Zhang, Lu
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Optical Network Laboratory (ON Lab).
    Ozolins, Oskars
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Fotonik.
    Udalcovs, Aleksejs
    Res Inst Sweden AB, NETLAB, S-16425 Kista, Sweden..
    Kong, Deming
    Tech Univ Denmark, DTU Foton, DK-2800 Lyngby, Denmark..
    Pang, Xiaodan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Optical Network Laboratory (ON Lab).
    Yu, Xianbin
    Xiao, Shilin
    Shanghai Jiao Tong Univ, Sch SE IEE, Shanghai 200240, Peoples R China..
    Popov, Sergei
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Fotonik.
    Chen, Jiajia
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Optical Network Laboratory (ON Lab).
    Carpintero, Guillermo
    Univ Carlos III Madrid, Madrid 28911, Spain..
    Morioka, Toshio
    Tech Univ Denmark, DTU Foton, DK-2800 Lyngby, Denmark..
    Hu, Hao
    Tech Univ Denmark, DTU Foton, DK-2800 Lyngby, Denmark..
    Oxenlowe, Leif K.
    Tech Univ Denmark, DTU Foton, DK-2800 Lyngby, Denmark..
    Integrated Dual-DFB Laser for 408 GHz Carrier Generation Enabling 131 Gbit/s Wireless Transmission over 10.7 Meters2019Inngår i: 2019 OPTICAL FIBER COMMUNICATIONS CONFERENCE AND EXHIBITION (OFC), Optica Publishing Group , 2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A monolithically integrated dual-DFB laser generates a 408 GHz carrier used for demonstrating a record-high single-channel bit rate of 131 Gbit/s transmitted over 10.7 m. 16-QAM-OFDM modulation and specific nonlinear equalization techniques are employed.

  • 202.
    Jia, Shi
    et al.
    Zhejiang Univ, Coll Informat Sci & Elect Engn, Hangzhou 310027, Zhejiang, Peoples R China.;Tech Univ Denmark, DTU Fotonik, Dept Photon Engn, DK-2800 Lyngby, Denmark..
    Zhang, Lu
    Zhejiang Univ, Coll Informat Sci & Elect Engn, Hangzhou 310027, Zhejiang, Peoples R China.;Zhejiang Lab, Hangzhou 310000, Zhejiang, Peoples R China..
    Wang, Shiwei
    Zhejiang Univ, Coll Informat Sci & Elect Engn, Hangzhou 310027, Zhejiang, Peoples R China..
    Li, Wei
    Zhejiang Univ, Coll Informat Sci & Elect Engn, Hangzhou 310027, Zhejiang, Peoples R China..
    Qiao, Mengyao
    Zhejiang Univ, Coll Informat Sci & Elect Engn, Hangzhou 310027, Zhejiang, Peoples R China..
    Lu, Zijie
    Zhejiang Univ, Coll Informat Sci & Elect Engn, Hangzhou 310027, Zhejiang, Peoples R China..
    Idrees, Nazar Muhammad
    Zhejiang Univ, Coll Informat Sci & Elect Engn, Hangzhou 310027, Zhejiang, Peoples R China..
    Pang, Xiaodan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Optical Network Laboratory (ON Lab).
    Hu, Hao
    Tech Univ Denmark, DTU Fotonik, Dept Photon Engn, DK-2800 Lyngby, Denmark..
    Zhang, Xianmin
    Zhejiang Univ, Coll Informat Sci & Elect Engn, Hangzhou 310027, Zhejiang, Peoples R China..
    Oxenlowe, Leif K.
    Tech Univ Denmark, DTU Fotonik, Dept Photon Engn, DK-2800 Lyngby, Denmark..
    Yu, Xianbin
    Zhejiang Univ, Coll Informat Sci & Elect Engn, Hangzhou 310027, Zhejiang, Peoples R China.;Zhejiang Lab, Hangzhou 310000, Zhejiang, Peoples R China..
    2 x 300 Gbit/s Line Rate PS-64QAM-OFDM THz Photonic-Wireless Transmission2020Inngår i: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 38, nr 17, s. 4715-4721Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The proliferation of wireless broadband services have significantly raised the demand for high data rates. Due to the limited bandwidth of radio frequency (RF) bands that are currently in use for communication purposes, the choice of the 'Terahertz (THz) frequency region' (0.3-10 THz) is getting favored thanks to its merits of bringing together wireless and optical communications with photonics technologies. We report on an experimental demonstration of a hybrid THz photonic-wireless transmission based on a THz orthogonal polarization dual-antenna scheme. Probabilistic shaped 64-ary quadrature amplitude modulation based orthogonal frequency division multiplexing (64QAM-OFDM) modulation format is used to realize high transmission rate. A potential total system throughput of 612.65 Gbit/s (around 2 x 300 Gbit/s line rate) with an average net spectral efficiency of 4.445 bit/s/Hz per antenna is successfully achieved.

  • 203.
    Jiang, Tao
    et al.
    Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Natl Engn Lab Next Generat Internet Access Syst, Wuhan, Hubei, Peoples R China..
    Chen, Jiajia
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Lin, Rui
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Tang, Ming
    Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Natl Engn Lab Next Generat Internet Access Syst, Wuhan, Hubei, Peoples R China..
    Network Performance Analysis of Spatial Division Multiplexing enabled Packet Switching Networks2018Inngår i: 2018 ASIA COMMUNICATIONS AND PHOTONICS CONFERENCE (ACP), IEEE , 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We propose a mathematical model based on queue theory to quantify how fferent spatial division multiplexing (SDM) transmission paradigms pact optical packet switching, providing an insightful guideline for sign of SDM networks.

  • 204.
    Jin, Hongyu
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Cooperative Privacy and Security for Mobile Systems2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The growing popularity of powerful mobile devices, along with increased computation and storage of computing infrastructure, opened possibilities for versatile mobile system applications. Users, leveraging sensing capabilities of the devices, can collect rich data and exchange the data with diverse Service Providers (SPs) or their close neighboring devices. Provision of such user status awareness to the involved system entities, can facilitate customized user experience for system participants.

    Nonetheless, the open and decentralized nature of mobile systems raise concerns on both security and privacy of users and the system infrastructure. Sensitive user data could be exposed to honest-but-curious entities, which can further process data to profile users. At the same time, compromised system entities can feed faulty data to disrupt system functionalities or mislead users. Such issues necessitate secure and privacy-enhancing mobile systems, while not compromising the quality of service the systems provide to their users. More specifically, the solutions should be efficient and scale as the system grows, and resilient to both external and internal adversaries. This thesis considers two mobile system instances: Location-based Services (LBSs) and Vehicle-to-Vehicle (V2V) safety applications. We address security and privacy in a cooperative manner, relying on cooperation among the users to protect themselves against the adversaries. Due to the reliance on peers, input from the peers should be examined, in order to ensure the reli- ability of the applications. We adapt pseudonymous authentication, designed for Vehicular Communication (VC) systems, and integrate it with LBSs. This protects user privacy and holds users accountable for their actions, which are non-repudiable. At the same time, our scheme prevents malicious nodes from aggressively passing on bogus data. We leverage redundancy of shared data from multiple cooperating nodes to detect potential conflicts. Any conflict triggers proactive checking on the data with the authoritative entity that reveals the actual misbehaving users. For V2V safety applications, we extend safety beacons, i.e., Cooperative Awareness Messages (CAMs), to share signature verification effort, for more efficient message verification. Similarly to the LBSs, redundancy of such piggybacked claims is also key for remedying malicious nodes that abuse this cooperative verification. In addition, the extended beacon format facilitates verification of event-driven messages, including Decentralized Environmental Notification Messages (DENMs), leveraging proactive authenticator distribution.

    We qualitatively and quantitatively evaluate achieved security and privacy protection. The latter is based on extensive simulation results. We propose a location privacy metric to capture the achieved protection for LBSs, taking into consideration the pseudonymous authentication. The performance of the privacy-enhancing LBS is experimentally evaluated with the help of an implementation on a small scale automotive computer testbed. We embed processing delays and queue management for message processing in simulations of V2V communication, to show scalability and efficiency of the resilient V2V communication scheme. The results confirm the resilience to both internal and external adversaries for the both systems.

    Fulltekst (pdf)
    fulltext
  • 205.
    Jin, Hongyu
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Papadimitratos, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS. RISE SICS, Stockholm, Sweden .
    Resilient Privacy Protection for Location-Based Services through Decentralization2019Inngår i: ACM Transactions on Privacy and Security (TOPS), ISSN 2471-2566, Vol. 22, nr 4, s. 1-36, artikkel-id 21Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Location-Based Services (LBSs) provide valuable services, with convenient features for mobile users. However, the location and other information disclosed through each query to the LBS erodes user privacy. This is a concern especially because LBS providers can be honest-but-curious, collecting queries and tracking users’ whereabouts and infer sensitive user data. This motivated both centralized and decentralized location privacy protection schemes for LBSs: anonymizing and obfuscating LBS queries to not disclose exact information, while still getting useful responses. Decentralized schemes overcome disadvantages of centralized schemes, eliminating anonymizers, and enhancing users’ control over sensitive information. However, an insecure decentralized system could create serious risks beyond private information leakage. More so, attacking an improperly designed decentralized LBS privacy protection scheme could be an effective and low-cost step to breach user privacy. We address exactly this problem, by proposing security enhancements for mobile data sharing systems. We protect user privacy while preserving accountability of user activities, leveraging pseudonymous authentication with mainstream cryptography. We show our scheme can be deployed with off-the-shelf devices based on an experimental evaluation of an implementation in a static automotive testbed.

    Fulltekst (pdf)
    fulltext
  • 206.
    Jin, Hongyu
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Papadimitratos, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Scalable and DoS-resilient Secure Vehicular CommunicationManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Vehicular Communication (VC) provides vehicles with real-time “sensing” of their surrounding environment: high-rate broadcasted beacons carry vehicle status information, and event-driven messages report traffic- or road-related events with different levels of criticality. Paramount to vehicle safety, these messages must be secured. Pseudonymous authentication is used to secure messages while preserving privacy. Vehicles become aware of and keep track of their pseudonymized neighbors. However, attackers can exploit this dynamicity and need for timely verification: a clogging Denial of Service (DoS) attack can severely delay or even deny benign vehicle message verification and thus severely degrade awareness. We address the problem by extending the traditional pseudonymous authentication with cooperative message verification and symmetric-key based authentication. We remedy the vulnerability of cooperative verification with probabilistic signature checking and cross-checking across multiple validators. Our scheme trades off higher communication overhead for lower verification latency and thus improved robustness of transportation safety applications. Our scheme is resilient to both DoS attacks and malicious nodes. Even when vehicles are saturated by high-rate bogus beacons and event messages, our scheme achieves an average waiting time of 50ms with an expiration ratio less than 1% for beacons, and 80% of event message acceptance ratio with latency less than 200ms on the average. This is a huge improvement over the current standard, the baseline scheme, which would suffer, having from 50% to almost 100% received benign messages expiring. In spite of its collaborative operation, our scheme drastically detects internal adversaries that attempt to exploit the cooperative verification itself.

  • 207. Jocevski, Milan
    et al.
    Mardinoglu, Adil
    KTH, Centra, Science for Life Laboratory, SciLifeLab. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Proteinvetenskap, Systembiologi.
    Gurov, Dilian
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Teoretisk datalogi, TCS.
    Mohammadat, Tage
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektronik och inbyggda system.
    Monti, Paolo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Optical Network Laboratory (ON Lab).
    Harmonized Supervision of Degree Project Work2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Background and purposeEffective supervision practices are vital for the educational and professional development of students,for continuous growth of supervisors, as well as for the development of respective scientific fields. In lightof different learning styles (Taylor & Beasley 2005) and having in mind the time resource constraints ofsupervisors, it is not easy to point out the best pedagogical approach to supervision that maximizes thelearning experience. In addition to the traditional individual supervision (IS) style there are other options(e.g., group supervision (GS) and peer supervision (PS)), which offer certain advantages. These threestyles do not exclude each other, but can rather be combined to complement each other’s strengths.In order to maximize the effectiveness of combining multiple approaches, it is essential to understand itsadvantages and disadvantages. Based on a survey of different experiences among supervisors andstudents collected from different Swedish education institutions, our paper suggests ways to optimizethe supervision processes. Moreover, we call it harmonized supervision, and belive that it would savetime and effort for the supervisors, and help students to overcome the individual limitations of eachsupervision style. 

    Work done/work in progressIn order to study the preferences of students and supervisors with respect to IS, GS, and PS weconducted a survey among faculty members as well as former students at four higher educationinstitutions (HEIs), where our goal was to aggregate their experiences and learnings. The sampling wasdone in two-stages. First, we selected the HEIs. Due to convenience and connections to specific departments at given HEIs that the authors had, we then sent e-mail invitations to both students andsupervisors at these HEIs. In the second stage, through a voluntary process, respondents from bothgroups took part in the survey. Questions in the survey were inspired by the previous experiences of theauthors, and traditional supervision approaches of the affiliated institutions. We asked informants abouttheir experiences, and what they believed were advantages and disadvantages of each of theexperienced supervision styles. Finally, data was analyzed using descriptive statistics and qualitativeanalysis of open-ended questions. Basically, we looked into which style was used the most and in whichsituations, as well as compared different answers that spoke in favor and against each style.Results/observations/lessons learnedIt is interesting to note that supervisors and students had similar views with respect to IS, GS, and PS. Interms of IS “lack of different perspective” and “limited flows of new idea/opinions” are among thedrawbacks highlighted by both supervisors and students. Interestingly enough, a solution to these issuesis readily available among the benefits of GS and PS, i.e., “New ideas for solving problems” and“Diverse feedback”. This observation leads us to conclude that combining IS, GS, and PS in aharmonized supervision approach. By harmonized supervision we refer to an approach where GS andPS are used as the basis, and where IS is used only when needed.Take-home messageRegardless of the choice of the supervision method, one can note that a mixture of style is moreeffective depending on the learner’s phase, which can be broken down in two main stages. In theinitial phase, the supervisor exercises a more structural and contractual style. For instance, thesupervisor acts as a teacher explaining the research method and the student performs it on a step-bystep basis. The next stage is the training phase, where the supervisor can give the student moreformative assessment support and feedback to develope student's skills until a certain autonomy qualityis achieved. Lastly, the learner becomes a master of the thesis topic and therefore becomes moreindependent. When considering supervision it is important to think about different levels of intellectualdevelopment and the social component of the learning process. At the second phase, i.e. trainingphase, the supervisor can adopt group or peer supervision. Engaging the students in peer and groupsupervision may be conducive to the creation of a more secure learning environment. However, it isessential to provide a constructive group constellation and complementing instructions for peers tomaximize the learning outcomes in an efficient manner.

    Fulltekst (pdf)
    fulltext
  • 208.
    Karapantelakis, Athanasios
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab). Ericsson Research.
    Fersman, Elena
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    A Deep-Q Learning Approach to Mobile Operator Collaboration2020Inngår i: Journal of Communications and Networks, ISSN 1229-2370, E-ISSN 1976-5541, Vol. 22, nr 6, s. 455-466Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Next-generation mobile connectivity services include a large number of devices distributed across vast geographical areas. Mobile network operators will need to collaborate to fulfill service requirements at scale. Existing approaches to multioperator services assume already-established collaborations to fulfill customer service demand with specific quality of service (QoS). In this paper, we propose an agent-based architecture, where establishment of collaboration for a given connectivity service is done proactively, given predictions about future service demand. We build a simulation environment and evaluate our approach with a number of scenarios and in context of a real-world use case, and compare it with existing collaboration approaches. Results show that by learning how to adapt their collaboration strategy, operators can fulfill a greater part of the service requirements than by providing the service independently, or through pre-established, intangible service level agreements.

    Fulltekst (pdf)
    fulltext
  • 209.
    Karapantelakis, Athanasios
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Markendahl, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Challenges for ICT Business Development in Intelligent Transport Systems2017Inngår i: 2017 JOINT 13TH CTTE AND 10TH CMI CONFERENCE ON INTERNET OF THINGS - BUSINESS MODELS, USERS, AND NETWORKS / [ed] Falch, M, Institute of Electrical and Electronics Engineers (IEEE), 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Intelligent Transportation Systems (ITS) are a product of convergence of Information and Communication Technology (ICT) and transport industries, with an aim to improve safety, mobility and efficiency of transportation. Ubiquitous, fast and inexpensive wireless communication and increasing vehicle computation, storage and sensing capabilities, are technological enablers for ITS. Notwithstanding technological maturity, the real challenge rises from the change the ITS market brings to the business of ICT players, as development of ITS services requires cooperation of multiple actors across industries. For ICT players, this signifies a departure from rigid telecom-era business models to a more networked structure of collaboration with other players. In this paper, we identify key business challenges that ICT players face in ITS market, by analysis of two ITS use cases.

  • 210.
    Karlsson, Örn Arnar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Design and implementation of a data acquisition system with filter quality evaluation2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Particulate matter is a growing health concern that is considered to contribute to many diseases. To develop appropriate air filtration systems, we need to understand how particulate matter affects air filters. In this project, we implement an automated data acquisition system for an air filter test rig. The data acquisition system allows us to gather empirical data on how particle matter affects air filters over time. Although the quality of the air filters does not reach critical levels, there is a measurable degradation. The collected data is used to train and validate a machine learning model that can evaluate air filter quality. This machine learning proved to be a powerful tool in air filter evaluation and performs with 99% accuracy on test data. The result of this project is a fully functioning data acquisition system along with a user interface that considerably reduces the number of man-hours needed to perform tests of filters. In addition, the automated data acquisition system can notify the operator when the rig needs a change of filter or when certain faults occur. Unfortunately, the project did not reach its original goal of being able to automatically determine when the test rig needs maintenance or re-calibration.

    Fulltekst (pdf)
    fulltext
  • 211.
    Kathiravelu, Pradeeban
    et al.
    Univ Lisbon, Inst Super Tecn, INESC ID Lisboa, Lisbon, Portugal.;Catholic Univ Louvain, Louvain, Belgium..
    Chiesa, Marco
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Marcos, Pedro
    UFRGS FURG, Porto Alegre, RS, Brazil..
    Canini, Marco
    KAUST, Thuwal, Saudi Arabia..
    Veiga, Luis
    Univ Lisbon, Inst Super Tecn, INESC ID Lisboa, Lisbon, Portugal..
    Moving Bits with a Fleet of Shared Virtual Routers2018Inngår i: 2018 IFIP NETWORKING CONFERENCE (IFIP NETWORKING) AND WORKSHOPS / [ed] Stiller, B, IEEE , 2018, s. 352-360Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The steady decline of IP transit prices in the past two decades has helped fuel the growth of traffic demands in the Internet ecosystem. Despite the declining unit pricing, bandwidth costs remain significant due to ever-increasing scale and reach of the Internet, combined with the price disparity between the Internet's core hubs versus remote regions. In the meantime, cloud providers have been auctioning underutilized computing resources in their marketplace as spot instances for a much lower price, compared to their on-demand instances. This state of affairs has led the networking community to devote extensive efforts to cloud-assisted networks - the idea of offloading network functionality to cloud platforms, ultimately leading to more flexible and highly composable network service chains. We initiate a critical discussion on the economic and technological aspects of leveraging cloud-assisted networks for Internet-scale interconnections and data transfers. Namely, we investigate the prospect of constructing a large-scale virtualized network provider that does not own any fixed or dedicated resources and runs atop several spot instances. We construct a cloud-assisted overlay as a virtual network provider, by leveraging third-party cloud spot instances. We identify three use case scenarios where such approach will not only be economically and technologically viable but also provide performance benefits compared to current commercial offerings of connectivity and transit providers.

  • 212.
    Katsikas, Georgios P.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab). RISE SICS.
    NFV Service Chains at the Speed of the Underlying Commodity Hardware2018Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Link speeds in networks will in the near-future reach and exceed 100 Gbps. While available specialized hardware can accommodate these speeds, modern networks have adopted a new networking paradigm, also known as Network Functions Virtualization (NFV), that replaces expensive specialized hardware with open-source software running on commodity hardware. However, achieving high performance using commodity hardware is a hard problem mainly because of the processor-memory gap. This gap suggests that only the fastest memories of today’s commodity servers can achieve the desirable access latencies for high speed networks. Existing NFV systems realize chained network functions (also known as service chains) mostly using slower memories; this implies a need for multiple additional CPU cores or even multiple servers to achieve high speed packet processing. In contrast, this thesis combines four contributions to realize NFV service chains with dramatically higher performance and better efficiency than the state of the art.

    The first contribution is a framework that profiles NFV service chains to uncover reasons for performance degradation, while the second contribution leverages the profiler’s data to accelerate these service chains by combining multiplexing of system calls with scheduling strategies. The third contribution synthesizes input/output and processing service chain operations to increase the spatial locality of network traffic with respect to a system’s caches. The fourth contribution combines the profiler’s insights from the first contribution and the synthesis approach of the third contribution to realize NFV service chains at the speed of the underlying commodity hardware. To do so, stateless traffic classification operations are offloaded into available hardware (i.e., programmable switches and/or network cards) and a tag is associated with each traffic class. At the server side, input traffic classes are classified by the hardware based upon the values of these tags, which indicate the CPU core that should undertake their stateful processing, while ensuring zero inter-core communication.

    With commodity hardware, this thesis realizes Internet Service Provider-level service chains and deep packet inspection at a line-rate 40 Gbps and stateful service chains at the speed of a 100 GbE network card on a 16 core single server. This results in up to (i) 4.7x lower latency, (ii) 8.5x higher throughput, and (iii) 6.5x better efficiency than the state of the art. The techniques described in this thesis are crucial for realizing future high speed NFV deployments.

    Fulltekst (pdf)
    fulltext
  • 213.
    Katsikas, Georgios P.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Barbette, Tom
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Chiesa, Marco
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Kostic, Dejan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Maguire Jr., Gerald Q.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Programvaruteknik och datorsystem, SCS.
    What you need to know about (Smart) Network Interface Cards2021Inngår i: Proceedings Passive and Active Measurement - 22nd International Conference, PAM 2021 / [ed] Springer International Publishing, Springer Nature , 2021Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Network interface cards (NICs) are fundamental componentsof modern high-speed networked systems, supporting multi-100 Gbpsspeeds and increasing programmability. Offloading computation from aserver’s CPU to a NIC frees a substantial amount of the server’s CPU resources, making NICs key to offer competitive cloud services.

    Therefore, understanding the performance benefits and limitations of offloading anetworking application to a NIC is of paramount importance.In this paper, we measure the performance of four different NICs fromone of the largest NIC vendors worldwide, supporting 100 Gbps and200 Gbps. We show that while today’s NICs can easily support multihundred-gigabit throughputs, performing frequent update operations ofa NIC’s packet classifier — as network address translators (NATs) andload balancers would do for each incoming connection — results in adramatic throughput reduction of up to 70 Gbps or complete denial ofservice. Our conclusion is that all tested NICs cannot support high-speednetworking applications that require keeping track of a large number offrequently arriving incoming connections. Furthermore, we show a variety of counter-intuitive performance artefacts including the performanceimpact of using multiple tables to classify flows of packets.

    Fulltekst (pdf)
    fulltext
  • 214.
    Katsikas, Georgios P.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Barbette, Tom
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Kostic, Dejan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Maguire Jr., Gerald Q.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Steinert, Rebecca
    RISE, Sweden.
    Metron: High-Performance NFV Service Chaining Even in the Presence of Blackboxes2021Inngår i: ACM Transactions on Computer Systems, ISSN 0734-2071, E-ISSN 1557-7333, Vol. 38, nr 1-2, s. 1-45, artikkel-id 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Deployment of 100 Gigabit Ethernet (GbE) links challenges the packet processing limits of commodity hardware used for Network Functions Virtualization (NFV). Moreover, realizing chained network functions (i.e., service chains) necessitates the use of multiple CPU cores, or even multiple servers, to process packets from such high speed links.

    Our system Metron jointly exploits the underlying network and commodity servers' resources: (i) to offload part of the packet processing logic to the network, (ii) by using smart tagging to setup and exploit the affinity of traffic classes, and (iii) by using tag-based hardware dispatching to carry out the remaining packet processing at the speed of the servers' cores, with zero inter-core communication. Moreover, Metron transparently integrates, manages, and load balances proprietary "blackboxes" together with Metron service chains.

    Metron realizes stateful network functions at the speed of 100 GbE network cards on a single server, while elastically and rapidly adapting to changing workload volumes. Our experiments demonstrate that Metron service chains can coexist with heterogeneous blackboxes, while still leveraging Metron's accurate dispatching and load balancing. In summary, Metron has (i) 2.75-8× better efficiency, up to (ii) 4.7× lower latency, and (iii) 7.8× higher throughput than OpenBox, a state-of-the-art NFV system.

    Fulltekst (pdf)
    fulltext
  • 215.
    Katsikas, Georgios P.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Barbette, Tom
    Kostic, Dejan
    Steinert, R.
    Maguire Jr., Gerald Q.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Metron: NFV service chains at the true speed of the underlying hardware2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we present Metron, a Network Functions Virtualization (NFV) platform that achieves high resource utilization by jointly exploiting the underlying network and commodity servers’ resources. This synergy allows Metron to: (i) offload part of the packet processing logic to the network, (ii) use smart tagging to setup and exploit the affinity of traffic classes, and (iii) use tag-based hardware dispatching to carry out the remaining packet processing at the speed of the servers’ fastest cache(s), with zero intercore communication. Metron also introduces a novel resource allocation scheme that minimizes the resource allocation overhead for large-scale NFV deployments. With commodity hardware assistance, Metron deeply inspects traffic at 40 Gbps and realizes stateful network functions at the speed of a 100 GbE network card on a single server. Metron has 2.75-6.5x better efficiency than OpenBox, a state of the art NFV system, while ensuring key requirements such as elasticity, fine-grained load balancing, and flexible traffic steering

  • 216.
    Katsikas, Georgios P.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab). RISE SICS.
    Barbette, Tom
    University of Liege.
    Kostic, Dejan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Steinert, Rebecca
    RISE SICS.
    Maguire Jr., Gerald Q.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Metron: NFV Service Chains at the True Speed of the Underlying Hardware2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we present Metron, a Network Functions Virtualization (NFV) platform that achieves high resource utilization by jointly exploiting the underlying network and commodity servers’ resources. This synergy allows Metron to: (i) offload part of the packet processing logic to the network, (ii) use smart tagging to setup and exploit the affinity of traffic classes, and (iii) use tag-based hardware dispatching to carry out the remaining packet processing at the speed of the servers’ fastest cache(s), with zero inter-core communication. Metron also introduces a novel resource allocation scheme that minimizes the resource allocation overhead for large-scale NFV deployments. With commodity hardware assistance, Metron deeply inspects traffic at 40 Gbps and realizes stateful network functions at the speed of a 100 GbE network card on a single server. Metron has 2.75-6.5x better efficiency than OpenBox, a state of the art NFV system, while ensuring key requirements such as elasticity, fine-grained load balancing, and flexible traffic steering.

    Fulltekst (pdf)
    fulltext
  • 217.
    Khodaei, Mohammad
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    The Key to Intelligent Transportation Systems: Identity and Credential Management for Secure and Privacy-Preserving Vehicular Communication Systems2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Vehicular Communication (VC) systems can greatly enhance road safety and transportation efficiency and enable a variety of applications providing traffic efficiency, environmental hazards, road conditions and infotainment. Vehicles are equipped with sensors and radars to sense their surroundings and external environment, as well as with an internal Controller Area Network (CAN) bus. Hence, vehicles are becoming part of a large-scale network, the so-called Internet of Vehicles (IoV). Deploying such a large-scale VC system cannot materialize unless the VC systems are secure and do not expose their users’ privacy. On the one hand, vehicles could be compromised or their sensors become faulty, thus disseminating erroneous information across the network. Therefore, participating vehicles should be held accountable for their actions and credentials (their Long Term Certificates (LTCs) and their pseudonyms) can be efficiently revoked and disseminated in a timely manner throughout a large-scale (multi-domain) VC system. On the other hand, user privacy is at stake: according to standards, vehicles should disseminate spatio-temporal information frequently, e.g., location and velocity. Due to the openness of the wireless communication, an observer can eavesdrop the vehicular communication to infer users’ sensitive information, and possibly profile users based on different attributes, e.g., trace their commutes and identify home/work locations. The objective is to secure the communication, i.e., prevent malicious or compromised entities from affecting the system operation, and ensure user privacy, i.e., keep users anonymous to any external observer but also for security infrastructure entities and service providers. This is not very straightforward because accountability and privacy, at the same time, appear contradictory. 

    In this thesis, we first focus on the identity and credential management infrastructure for VC systems, taking security, privacy, and efficiency into account. We begin with a detailed investigation and critical survey of the standardization and harmonization efforts, along with industrial projects and proposals. We point out the remaining challenges to be addressed in order to build a central building block of secure and privacy-preserving VC systems, a Vehicular Public-Key Infrastructure (VPKI). Towards that, we provide a secure and privacy-preserving VPKI design that improves upon existing proposals in terms of security and privacy protection and efficiency. More precisely, our scheme facilitates multi-domain operations in VC systems and enhances user privacy, notably preventing linking of pseudonyms based on timing information and offering increased protection in the presence of honest-but-curious VPKI entities. We further extensively evaluate the performance, i.e., scalability, efficiency, and robustness, of the full-blown implementation of our VPKI for a large-scale VC deployment. We provide tangible evidence that it is possible to support a large area of vehicles by investing in modest computing resources for the VPKI entities. Our results confirm the efficiency, scalability and robustness of our VPKI.

    As a second main contribution of this thesis, we focus on the distribution of Certificate Revocation Lists (CRLs) in VC systems. The main challenges here lie exactly in (i) crafting an efficient and timely distribution of CRLs for numerous anonymous credentials, pseudonyms, (ii) maintaining strong privacy for vehicles prior to revocation events, even with honest-but-curious system entities, (iii) and catering to computation and communication constraints of on-board units with intermittent connectivity to the infrastructure. Relying on peers to distribute the CRLs is a double-edged sword: abusive peers could "pollute" the process, thus degrading the timely CRLs distribution. We propose a vehicle-centric solution that addresses all these challenges and thus closes a gap in the literature. Our scheme radically reduces CRL distribution overhead: each vehicle receives CRLs corresponding only to its region of operation and its actual trip duration. Moreover, a "fingerprint" of CRL ‘pieces’ is attached to a subset of (verifiable) pseudonyms for fast CRL ‘piece’ validation (while mitigating resource depletion attacks abusing the CRL distribution). Our experimental evaluation shows that our scheme is efficient, scalable, dependable, and practical: with no more than 25 KB/s of traffic load, the latest CRL can be delivered to 95% of the vehicles in a region (15x15 KM) within 15s, i.e., more than 40 times faster than the state-of-the-art. Overall, our scheme is a comprehensive solution that complements standards and can catalyze the deployment of secure and privacy-protecting VC systems. 

    As the third main contribution of the thesis, we focus on enhancing location privacy protection: vehicular communications disclose rich information about the vehicles and their whereabouts. Pseudonymous authentication secures communication while enhancing user privacy. To enhance location privacy, cryptographic mix-zones were proposed to facilitate vehicles covertly transition to new ephemeral credentials. The resilience to (syntactic and semantic) pseudonym linking (attacks) highly depends on the geometry of the mix-zones, mobility patterns, vehicle density, and arrival rates. Our experimental results show that an eavesdropper could successfully link 73% of pseudonyms (during non-rush hours) and 62% of pseudonyms (during rush hours) after vehicles change their pseudonyms in a mix-zone. To mitigate such inference attacks, we present a novel cooperative mix-zone scheme that enhances user privacy regardless of the vehicle mobility patterns, vehicle density, and arrival rate to the mix-zone. A subset of vehicles, termed relaying vehicles, are selected to be responsible for emulating non-existing vehicles. Such vehicles cooperatively disseminate decoy traffic without affecting safety-critical operations: with 50% of vehicles as relaying vehicles, the probability of linking pseudonyms (for the entire interval) drops from 68% to 18%. On average, this imposes 28 ms extra computation overhead, per second, on the Roadside Units (RSUs) and 4.67 ms extra computation overhead, per second, on the (relaying) vehicle side; it also introduces 1.46 KB/sec extra communication overhead by (relaying) vehicles and 45 KB/sec by RSUs for the dissemination of decoy traffic. Thus, user privacy is enhanced at the cost of low computation and communication overhead.

    Fulltekst (pdf)
    dissertation-fulltext
  • 218.
    Khodaei, Mohammad
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Jin, Hongyu
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Papadimitratos, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    SECMACE: Scalable and Robust Identity and Credential Management Infrastructure in Vehicular Communication Systems2018Inngår i: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016, Vol. 19, nr 5, s. 1430-1444Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several years of academic and industrial research efforts have converged to a common understanding on fundamental security building blocks for the upcoming vehicular communication (VC) systems. There is a growing consensus toward deploying a special-purpose identity and credential management infrastructure, i.e., a vehicular public-key infrastructure (VPKI), enabling pseudonymous authentication, with standardization efforts toward that direction. In spite of the progress made by standardization bodies (IEEE 1609.2 and ETSI) and harmonization efforts [Car2Car Communication Consortium (C2C-CC)], significant questions remain unanswered toward deploying a VPKI. Deep understanding of the VPKI, a central building block of secure and privacy-preserving VC systems, is still lacking. This paper contributes to the closing of this gap. We present SECMACE, a VPKI system, which is compatible with the IEEE 1609.2 and ETSI standards specifications. We provide a detailed description of our state-of-the-art VPKI that improves upon existing proposals in terms of security and privacy protection, and efficiency. SECMACE facilitates multi-domain operations in the VC systems and enhances user privacy, notably preventing linking pseudonyms based on timing information and offering increased protection even against honest-but-curious VPKI entities. We propose multiple policies for the vehicle-VPKI interactions and two large-scale mobility trace data sets, based on which we evaluate the full-blown implementation of SECMACE. With very little attention on the VPKI performance thus far, our results reveal that modest computing resources can support a large area of vehicles with very few delays and the most promising policy in terms of privacy protection can be supported with moderate overhead.

    Fulltekst (pdf)
    secmace-tits
  • 219.
    Khodaei, Mohammad
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Noroozi, Hamid
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Papadimitratos, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Scaling Pseudonymous Authentication for Large Mobile Systems2019Inngår i: WiSec 2019 - Proceedings of the 2019 Conference on Security and Privacy in Wireless and Mobile Networks, Miami, FL, USA, 2019, s. 174-185Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The central building block of secure and privacy-preserving Vehicular Communication (VC) systems is a Vehicular Public-Key Infrastructure (VPKI), which provides vehicles with multiple anonymized credentials, termed pseudonyms. These pseudonyms are used to ensure message authenticity and integrity while preserving vehicle (thus passenger) privacy. In the light of emerging large-scale multi-domain VC environments, the efficiency of the VPKI and, more broadly, its scalability are paramount. By the same token, preventing misuse of the credentials, in particular, Sybil-based misbehavior, and managing “honest-but-curious” insiders are other facets of a challenging problem. In this paper, we leverage the state-of-the-art VPKI system and enhance its functionality towards a highly-available, dynamically-scalable, and resilient design; this ensures that the system remains operational in the presence of benign failures or resource depletion attacks, and that it dynamically scales out, or possibly scales in, according to request arrival rates. Our full-blown implementation on the Google Cloud Platform shows that deploying large-scale and efficient VPKI can be cost-effective.

    Fulltekst (pdf)
    fulltext
  • 220.
    Khodaei, Mohammad
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Papadimitratos, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS. Networked Systems Security group.
    Cooperative Location Privacy in Vehicular Networks: Why Simple Mix-zones are not Enough2021Inngår i: IEEE Internet of Things Journal, ISSN 2327-4662, s. 1-1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Vehicular communications disclose rich information about the vehicles and their whereabouts. Pseudonymous authentication secures communication while enhancing user privacy. To enhance location privacy, cryptographic mix-zones were proposed to facilitate vehicles covertly transition to new ephemeral credentials. The resilience to (syntactic and semantic) pseudonym linking (attacks) highly depends on the geometry of the mix-zones, mobility patterns, vehicle density, and arrival rates. We introduce a tracking algorithm for linking pseudonyms before and after a cryptographically protected mix-zone. Our experimental results show that an eavesdropper, leveraging standardized vehicular communication messages and road layout, could successfully link ≈73% of pseudonyms during non-rush hours and ≈62% of pseudonyms during rush hours after vehicles change their pseudonyms in a mix-zone. To mitigate such inference attacks, we present a novel cooperative mix-zone scheme that enhances user privacy regardless of the vehicle mobility patterns, vehicle density, and arrival rate to the mix-zone. A subset of vehicles, termed relaying vehicles, are selected to be responsible for emulating non-existing vehicles. Such vehicles cooperatively disseminate decoy traffic without affecting safety-critical operations: with 50% of vehicles as relaying vehicles, the probability of linking pseudonyms (for the entire interval) drops from ≈68% to ≈18%. On average, this imposes 28 ms extra computation overhead, per second, on the Road-Side Units (RSUs) and 4.67 ms extra computation overhead, per second, on the (relaying) vehicle side; it also introduces 1.46 KB/sec extra communication overhead by (relaying) vehicles and 45 KB/sec by RSUs for the dissemination of decoy traffic. Thus, user privacy is enhanced at the cost of low computation and communication overhead. 

    Fulltekst (pdf)
    cooperative-mix-zones-iot-fulltext.pdf
  • 221.
    Khodaei, Mohammad
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Papadimitratos, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Cooperative Location Privacy in Vehicular Networks: Why Simple Mix-zones are not EnoughInngår i: Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Vehicular communications disclose rich information about the vehicles and their whereabouts. Pseudonymous authentication secures communication while enhancing user privacy. To enhance location privacy, cryptographic mix-zones were proposed to facilitate vehicles covertly transition to new ephemeral credentials. The resilience to (syntactic and semantic) pseudonym linking (attacks) highly depends on the geometry of the mix-zones, mobility patterns, vehicle density, and arrival rates. Our experimental results show that an eavesdropper could successfully link 73% of pseudonyms (during non-rush hours) and 62% of pseudonyms (during rush hours) after vehicles change their pseudonyms in a mix-zone. To mitigate such inference attacks, we present a novel cooperative mix-zone scheme that enhances user privacy regardless of the vehicle mobility patterns, vehicle density, and arrival rate to the mix-zone. A subset of vehicles, termed relaying vehicles, are selected to be responsible for emulating non-existing vehicles. Such vehicles cooperatively disseminate decoy traffic without affecting safety-critical operations: with 50% of vehicles as relaying vehicles, the probability of linking pseudonyms (for the entire interval) drops from 68% to 18%. On average, this imposes 28 ms extra computation overhead, per second, on the Roadside Units (RSUs) and 4.67 ms extra computation overhead, per second, on the (relaying) vehicle side; it also introduces 1.46 KB/sec extra communication overhead by (relaying) vehicles and 45 KB/sec by RSUs for the dissemination of decoy traffic. Thus, user privacy is enhanced at the cost of low computation and communication overhead.

    Fulltekst (pdf)
    cooperative-mix-zones
  • 222.
    Khodaei, Mohammad
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Papadimitratos, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Scalable & Resilient Vehicle-Centric Certificate Revocation List Distribution in Vehicular Communication Systems2021Inngår i: IEEE Transactions on Mobile Computing, ISSN 1536-1233, E-ISSN 1558-0660, Vol. 20, nr 7, s. 2473-2489Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In spite of progress in securing Vehicular Communication (VC) systems, there is no consensus on how to distribute Certificate Revocation Lists (CRLs). The main challenges lie exactly in (i) crafting an efficient and timely distribution of CRLs for numerous anonymous credentials, pseudonyms, (ii) maintaining strong privacy for vehicles prior to revocation events, even with honest-but-curious system entities, (iii) and catering to computation and communication constraints of on-board units with intermittent connectivity to the infrastructure. Relying on peers to distribute the CRLs is a double-edged sword: abusive peers could "pollute" the process, thus degrading the timely CRLs distribution. In this paper, we propose a vehicle-centric solution that addresses all these challenges and thus closes a gap in the literature. Our scheme radically reduces CRL distribution overhead: each vehicle receives CRLs corresponding only to its region of operation and its actual trip duration. Moreover, a "fingerprint" of CRL 'pieces' is attached to a subset of (verifiable) pseudonyms for fast CRL 'piece' validation (while mitigating resource depletion attacks abusing the CRL distribution). Our experimental evaluation shows that our scheme is efficient, scalable, dependable, and practical: with no more than 25 KB/s of traffic load, the latest CRL can be delivered to 95% of the vehicles in a region (15 x 15 KM) within 15s, i.e., more than 40 times faster than the state-of-the-art. Overall, our scheme is a comprehensive solution that complements standards and can catalyze the deployment of secure and privacy-protecting VC systems.

    Fulltekst (pdf)
    crl-dis-vanet-tmc-fulltext
  • 223.
    Khodaei, Mohammad
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Papadimitratos, Panos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Poster: Mix-Zones Everywhere: A Dynamic Cooperative Location Privacy Protection Scheme2018Inngår i: 2018 IEEE Vehicular Networking Conference, (VNC) / [ed] Altintas, O Tsai, HM Lin, K Boban, M Wang, CY Sahin, T, IEEE, 2018, artikkel-id 8628340Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Inter-vehicle communications disclose rich information about vehicle whereabouts. Pseudonymous authentication secures communication while enhancing user privacy. To enhance location privacy, cryptographic mix-zones are proposed where vehicles can covertly update their credentials. But, the resilience of such schemes against linking attacks highly depends on the geometry of the mix-zones, mobility patterns, vehicle density, and arrival rates. In this poster, we propose "mix-zones everywhere",a cooperative location privacy protection scheme to mitigate linking attacks during pseudonym transition. Time-aligned pseudonyms are issued for all vehicles to facilitate synchronous pseudonym updates. Our scheme thwarts Sybil-based misbehavior, strongly maintains user privacy in the presence of honest-but-curious system entities, and is resilient against misbehaving insiders.

    Fulltekst (pdf)
    fulltext
  • 224.
    Khorsandmanesh, Yasaman
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Hardware Distortion-Aware Beamforming for MIMO Systems2024Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In the upcoming era of communication systems, there is an anticipated shift towards using lower-grade hardware components to optimize size, cost, and power consumption. This shift is particularly beneficial for multiple-input multiple-output (MIMO) systems and internet-of-things devices, which require numerous components and extended battery lifes. However, using lower-grade components introduces impairments, including various non-linear and time-varying distortions affecting communication signals. Traditionally, these distortions have been treated as additional noise due to the lack of a rigorous theory. This thesis explores new perspective on how distortion structure can be exploited to optimize communication performance. We investigate the problem of distortion-aware beamforming in various scenarios. 

    In the first part of this thesis, we focus on systems with limited fronthaul capacity. We propose an optimized linear precoding for advanced antenna systems (AAS) operating at a 5G base station (BS) within the constraints of a limited fronthaul capacity, modeled by a quantizer. The proposed novel precoding minimizes the mean-squared error (MSE) at the receiver side using a sphere decoding (SD) approach. 

    After analyzing MSE minimization, a new linear precoding design is proposed to maximize the sum rate of the same system in the second part of this thesis. The latter problem is solved by a novel iterative algorithm inspired by the classical weighted minimum mean square error (WMMSE) approach. Additionally, a heuristic quantization-aware precoding method with lower computational complexity is presented, showing that it outperforms the quantization-unaware baseline. This baseline is an optimized infinite-resolution precoding which is then quantized. This study reveals that it is possible to double the sum rate at high SNR by selecting weights and precoding matrices that are quantization-aware. 

    In the third part and final part of this thesis, we focus on the signaling problem in mobile millimeter-wave (mmWave) communication. The challenge of mmWave systems is the rapid fading variations and extensive pilot signaling. We explore the frequency of updating the combining matrix in a wideband mmWave point-to-point MIMO under user equipment (UE) mobility. The concept of beam coherence time is introduced to quantify the frequency at which the UE must update its downlink receive combining matrix. The study demonstrates that the beam coherence time can be even hundreds of times larger than the channel coherence time of small-scale fading. Simulations validate that the proposed lower bound on this defined concept guarantees no more than 50 \% loss of received signal gain (SG).

    Fulltekst (pdf)
    fulltext
  • 225.
    Khorsandmanesh, Yasaman
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Björnson, Emil
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Jaldén, Joakim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Teknisk informationsvetenskap.
    Fronthaul Quantization-Aware MU-MIMO Precoding for Sum Rate Maximization2023Inngår i: ICC 2023 - IEEE International Conference on Communications: Sustainable Communications for Renaissance, Institute of Electrical and Electronics Engineers (IEEE) , 2023, s. 1332-1337Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper considers a multi-user multiple-input multiple-output (MU-MIMO) system where the precoding matrix is selected in a baseband unit (BBU) and then sent over a digital fronthaul to the transmitting antenna array. The fronthaul has a limited bit resolution with a known quantization behavior. We formulate a new sum rate maximization problem where the precoding matrix elements must comply with the quantizer. We solve this non-convex mixed-integer problem to local optimality by a novel iterative algorithm inspired by the classical weighted minimum mean square error (WMMSE) approach. The precoding optimization subproblem becomes an integer least-squares problem, which we solve with a new algorithm using a sphere decoding (SD) approach. We show numerically that the proposed precoding technique vastly outperforms the baseline of optimizing an infinite-resolution precoder and then quantizing it. We also develop a heuristic quantization-aware precoding that outperforms the baseline while having comparable complexity.

  • 226.
    Khorsandmanesh, Yasaman
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Björnson, Emil
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Jaldén, Joakim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Teknisk informationsvetenskap.
    Optimized Precoding for MU-MIMO With Fronthaul Quantization2023Inngår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 22, nr 11, s. 7102-7115Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the first widespread uses of multi-user multiple-input multiple-output (MU-MIMO) is in 5G networks, where each base station has an advanced antenna system (AAS) that is connected to the baseband unit (BBU) with a capacity-constrained fronthaul. In the AAS configuration, multiple passive antenna elements and radio units are integrated into a single box. This paper considers precoded downlink transmission over a single-cell MU-MIMO system. We study optimized linear precoding for AAS with a limited-capacity fronthaul, which requires the precoding matrix to be quantized. We propose a new precoding design that is aware of the fronthaul quantization and minimizes the mean-squared error at the receiver side. We compute the precoding matrix using a sphere decoding (SD) approach. We also propose a heuristic low-complexity approach to quantized precoding. This heuristic is computationally efficient enough for massive MIMO systems. The numerical results show that our proposed precoding significantly outperforms quantization-unaware precoding and other previous approaches in terms of the sum rate. The performance loss for our heuristic method compared to quantization-aware precoding is insignificant considering the complexity reduction, which makes the heuristic method feasible for real-time applications. We consider both perfect and imperfect channel state information (CSI).

  • 227.
    Khorsandmanesh, Yasaman
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Björnson, Emil
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Jaldén, Joakim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Teknisk informationsvetenskap.
    Lindoff, Bengt
    Beam Coherence Time Analysis for Mobile Wideband mmWave Point-to-Point MIMO ChannelsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Multi-Gbps data rates are achievable in millimeter-wave (mmWave) bands, but a prominent issue is the tiny wavelength that results in rapid fading variations and significant pilot signaling for channel estimation. In this letter, we recognize that the angles of scattering clusters seen from the user equipment (UE) vary slowly compared to the small-scale fading. We characterize the \emph{beam coherence time}, which quantifies how frequently the UE must update its downlink receive combining matrix. The exact beam coherence time is derived in the single-cluster case, and an achievable lower bound is proposed for the multi-cluster case. These values are determined so that at least half of the received signal gain is maintained in between the combining updates. We demonstrate how the beam coherence time can be hundreds of times larger than the channel coherence time of the small-scale fading.

  • 228.
    Khosravi, Sara
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Petrova, Marina
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS. Mobile Communications and Computing, RWTH Aachen University, Germany.
    Beam Selection Using Trajectory Information in Mobile Millimeter-wave Networks2023Inngår i: Artikkel i tidsskrift (Fagfellevurdert)
  • 229.
    Khosravi, Sara
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Location-aided Beam Alignment and Handover in Millimeter-wave Networks2023Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Ever-increasing data rate demands in mobile networks and the spectrum scarcity at the microwave bands have resulted in the exploration of millimeter-wave (mmWave) frequencies for the next generation of wireless networks. While mmWave frequencies offer large bandwidth, communication at these frequencies is not straightforward due to the challenging propagation characteristics. One approach to overcome the propagation challenge is the use of directional communication with narrow beams at the base station and the user to prepare a link with sufficient received power. Hence, communications with narrow beams pose a new challenge in link establishment and channel estimation based on fine angular scanning. Current mmWave systems apply analog phase arrays that can scan one angle at a time, resulting in high latency and overhead during link establishment. Moreover, mmWave links are sensitive to blockages that lead to the high probability of beam misalignment and the frequent updating of beam scanning, especially in mobile scenarios. Hence, it is desirable to design a low overhead beam selection by exploiting the unique properties of the mmWave channel. Furthermore, to provide adequate coverage and capacity, the density of the base stations in mmWave networks is usually higher than the conventional sub-6 GHz network. This leads to frequent handovers and establishing and maintaining the mmWave links more challenging. Therefore, fast base station discovery (finding the target base station in the handover process), and efficient handover execution techniques, will be required to use the full promise of mmWave cellular networks.

    Motivated by the mentioned challenges, this thesis considers the beam alignment and handover problems. Specifically, in the first thread of the thesis, inspired by the unique properties of the spatial channel response of mmWave links, we propose a location-aided beam alignment method based on dividing the user trajectory into regions and storing a set of candidate beams for each region in mobile mmWave networks. Our analysis reveals that our proposed method can achieve a high signal-to-noise ratio, and low overhead while being more robust to the location information accuracy compared with some location-aided baselines in the literature.

    In the second thread of the thesis, we focus on the handover problem. To this end, we formulate the association problem that maximizes the aggregate data rate along the trajectory while guaranteeing a predefined data rate threshold. We also consider the effect of choosing beam tracking or handover when the serving link quality drops on the user throughput along the trajectory. We apply reinforcement learning to learn whether and when the handover and beam tracking should be performed and choose the target base stations. We evaluate the proposed methods through numerical simulations and show promising results in terms of the achieved rate and throughput compared with the comparable methods in the literature.

    In the third thread of the thesis, we focus on joint link configuration and resource allocation in a multi-user mobile scenario. We consider two kinds of link configuration: base station selection and beamwidth optimization in the case of handover. We apply reinforcement learning to approximate the solution of the association problem. In general, the main objective of our proposed method is to maximize the aggregate throughput of all the users along trajectories and ensure that their throughput in each location is higher than a threshold. Our numerical results demonstrate that the improved policy obtained from joint link configuration and resource allocation significantly outperforms other baseline policies in both throughput and achieved rate.

    Fulltekst (pdf)
    fulltext
  • 230.
    Khosravi, Sara
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Seamless Millimeter-wave Connectivity via Efficient Beamforming and Handover2021Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Extremely high data rate demands, and the spectrum scarcity at the microwave bands, make the millimeter wave (mmWave) band a promising solution to satisfy the high data rate demands in wireless networks. The main advantage of moving to the mmWave spectrum is the availability of large bandwidth. Moreover, due to an order of magnitude smaller wavelength of mmWave signals in compared to the conventional bands, many antenna elements can be incorporated in a small size chip to provide high directivity gain both at the transmitter and the receiver sides.Millimeter wave links experience severe vulnerability to the obstacles compared to the conventional sub-6 GHz networks for two main reasons. First, due to the tiny wavelength, mmWave signals can easily be blocked by obstacles in the environment and this causes severe loss. Second, due to the use of directional communications to compensate for the high path-loss (the distance-dependent component of the attenuation), mmWave links are sensitive to blockages that leads to the high probability of beam misalignment and the frequent updating of beamforming vectors. These issues are more challenging in mobile scenarios, in which mobility of the users and obstacles cause frequent re-execution of the beamforming process. Therefore, the tradeoff between the latency of the beamforming process (which latency increases with the number of the re-execution of the beamforming process) and instantaneous user rate is a significant design challenge in mmWave networks. Moreover, to provide adequate coverage and capacity, the density of the base stations in mmWave networks is usually higher than the conventional sub-6 GHz network. This leads to frequent handovers that make maintaining and establishing the mmWave links more challenging.

    Motivated by the mentioned challenges, this thesis considers the beamforming and handover problems and proposes lightweight joint beamforming and handover methods to guarantee a certain data rate along user trajectory. Specifically, in the first thread of the thesis, inspired by the fundamental properties of the spacial channel response of mmWave links, we propose a beamforming method in mobile mmWave networks. Our analysis reveals that our proposed method is efficient in terms of signaling and computation complexity, power consumption, and throughput in compared to the benchmark. 

    In the second thread of the thesis, we focus on the handover problem. We formulate the association problem that maximizes the trajectory rate while guarantees a predefined data rate threshold. We then extend our problem to the multi-user dense scenario that the density of the users is higher than the base stations and consider the resource allocation in the association optimization problem. We apply reinforcement learning in order to approximate the solution of the association problem. In general, the main objective of our proposed method is to maximize the sum rates of all the users and minimize the number of the handovers and reduce the probability of the events in which the users' rate becomes less than a predefined threshold. Simulation results confirm that our proposed handover method provides a reliable connection along a trajectory in compared to the benchmarks. 

    Fulltekst (pdf)
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    Fulltekst (pdf)
    Khosravi errata to thesis
  • 231.
    Khosravi, Sara
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    S. Ghadikolaei, Hossein
    Ericsson research.
    Zander, Jens
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Petrova, Marina
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS. Mobile Communications and Computing, RWTH Aachen University, Germany.
    Reinforcement Learning-based Joint Handover and Beam Tracking in Millimeter-wave Networks2023Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we develop an algorithm for jointhandover and beam tracking in millimeter-wave (mmWave)networks. The aim is to provide a reliable connection in terms ofthe achieved throughput along the trajectory of the mobile userwhile preventing frequent handovers. We model the associationproblem as an optimization problem and propose a reinforcementlearning-based solution. Our approach learns whether and whenbeam tracking and handover should be performed and choosesthe target base stations. In the case of beam tracking, wepropose a tracking algorithm based on measuring a small spatialneighbourhood of the optimal beams in the previous time slot.Simulation results in an outdoor environment show the superiorperformance of our proposed solution in achievable throughputand the number of handovers needed in comparison to a multiconnectivity baseline and a learning-based handover baseline.

    Fulltekst (pdf)
    fulltext
  • 232.
    Khosravi, Sara
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Shokri Ghadikolaei, Hossein
    Ericsson research.
    Zander, Jens
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Petrova, Marina
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS. Mobile Communications and Computing, RWTH Aachen University, Germany.
    Beam Alignment Using Trajectory Information in Mobile Millimeter-wave Networks2023Inngår i: ICC 2023 - IEEE International Conference on Communications, Institute of Electrical and Electronics Engineers (IEEE) , 2023Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Millimeter-wave and terahertz systems rely on beam-forming/combining codebooks to determine the best beam directions during the initial access and data transmission. Existing approaches suffer from large codebook sizes and high beam searching overhead in the presence of mobile devices. To address this issue, we utilize the similarity of the channel in adjacent locations to divide the user trajectory into a set of separate regions and maintain a set of candidate beams for each region in a database. Due to the tradeoff between the number of regions and the signalling overhead, i.e., the greater number of regions results in a higher signal-to-noise ratio (SNR) but also a larger signalling overhead for the database, we propose an optimization framework to find the minimum number of regions based on the trajectory of a mobile device. Using a ray tracing tool, we demonstrate that the proposed method provides high SNR while being more robust to the location information accuracy in comparison to the lookup table baseline and fixed size region baseline.

    Fulltekst (pdf)
    fulltext
  • 233.
    Khosravi, Sara
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Shokri-Ghadikolaei, Hossein
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Petrova, Marina
    Efficient Beamforming for Mobile mmWave Networks2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We design a lightweight beam-searching algorithmfor mobile millimeter-wave systems. We construct and maintaina set of path skeletons, i.e., potential paths between a user and theserving base station to substantially expedite the beam-searchingprocess. To exploit the spatial correlations of the channels, wepropose an efficient algorithm that measures the similarity ofthe skeletons and re-executes the beam-searching procedure onlywhen the old one becomes obsolete. We identify and optimizeseveral tradeoffs between: i) the beam-searching overhead andthe instantaneous rate of the users, and ii) the number of usersand the update overhead of the path skeletons. Simulation resultsin an outdoor environment with real building map data show thatthe proposed method can significantly improve the performanceof beam-searching in terms of latency, energy consumption andachievable throughout.

  • 234.
    Khosravi, Sara
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Shokri-Ghadikolaei, Hossein
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Petrova, Marina
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Learning-based Handover in Mobile Millimeter-wave Networks2021Inngår i: IEEE Transactions on Cognitive Communications and Networking, E-ISSN 2332-7731, Vol. 7, nr 2, s. 663-674Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Millimeter-wave (mmWave) communication is considered as a key enabler of ultra-high data rates in the future cellular and wireless networks. The need for directional communication between base stations (BSs) and users in mmWave systems, that is achieved through beamforming, increases the complexity of the channel estimation. Moreover, in order to provide better coverage, dense deployment of BSs is required which causes frequent handovers and increased association overhead. In this paper, we present an approach that jointly addresses the beamforming and handover problems. Our solution entails an efficient beamforming method with a few number of pilots and a learning-based handover method supporting mobile scenarios. We use reinforcement learning algorithm to learn the optimal choices of the backup BSs in different locations of a mobile user. We show that our method provides an almost constant rate and reliability in all locations of the user’s trajectory with a small number of handovers. Simulation results in an outdoor environment based on narrow band cluster mmWave channel modeling and real building map data show the superior performance of our proposed solution in achievable instantaneous rate and trajectory rate. 

  • 235.
    Khosravi, Sara
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Shokri-Ghadikolaei, Hossein
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Petrova, Marina
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Learning-based Load Balancing Handover in Mobile Millimeter Wave Networks2020Inngår i: 2020 IEEE Global Communications Conference, GLOBECOM 2020 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2020, artikkel-id 9322601Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Millimeter-wave (mmWave) communication is a promising solution to the high data rate demands in the upcoming 5G and beyond communication networks. When it comes to supporting seamless connectivity in mobile scenarios, resource and handover management are two of the main challenges in mmWave networks. In this paper, we address these two problems jointly and propose a learning-based load balancing handover in multi-user mobile mm Wave networks. Our handover algorithm selects a backup base station and allocates the resource to maximize the sum rate of all the users while ensuring a target rate threshold and preventing excessive handovers. We model the user association as a non-convex optimization problem. Then, by applying a deep deterministic policy gradient (DDPG) method, we approximate the solution of the optimization problem. Through simulations, we show that our proposed algorithm minimizes the number of the events where a user's rate is less than its minimum rate requirement and minimizes the number of handovers while increasing the sum rate of all users.

    Fulltekst (pdf)
    fulltext
  • 236.
    Khosravi, Sara
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Zander, Jens
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Petrova, Marina
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS. Mobile Communications and Computing, RWTH Aachen University, Germany.
    Reinforcement Learning-based Joint Link Configuration and Resource Allocation in Millimeter-wave NetworksInngår i: Artikkel i tidsskrift (Fagfellevurdert)
  • 237. Kim, D.
    et al.
    Sung, Ki Won
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Koh, J.
    Kang, J.
    On the benefit of inter-operator cooperation in C-RAN2021Inngår i: IET Communications, ISSN 1751-8628, E-ISSN 1751-8636, Vol. 15, nr 2, s. 191-199Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cooperation of co-located mobile network operators can provide potential benefits for the capacity expansion without further densification of radio nodes. However, such benefits need to be scrutinised for coexisting cloud radio access network (C-RAN) operators because the inter-operator cooperation may compromise the superb interference coordination capability that each C-RAN has. Furthermore, altering C-RAN infrastructure for the cooperation incurs a high investment cost. In this paper, quantitative gain of inter-operator coordination strategies is evaluated to provide the C-RAN operators with a guideline on their cooperation decisions. The coordination strategies encompass dynamic user association and the spectrum sharing which aim at maximising the total user throughput. A heuristic algorithm is proposed that reduces the computational burden of the coordination significantly. Numerical results suggest that the inter-operator cooperation is beneficial particularly when the network size of each operator tends to be highly asymmetric. It is also verified that the users who belong to smaller network attain more coordination gains. 

  • 238.
    Kim, Donggu
    et al.
    Korea Adv Inst Sci & Technol, Sch Elect Engn, Daejeon 34141, South Korea..
    Yang, Yanpeng
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Sung, Ki Won
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Kang, Joonhyuk
    Korea Adv Inst Sci & Technol, Sch Elect Engn, Daejeon 34141, South Korea..
    Cooperation Strategies for Partly Wireless C-RAN2018Inngår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 22, nr 6, s. 1248-1251Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This letter presents a variant of cloud radio access network (C-RAN) architecture, which we term partly wireless C-RAN (PW-CRAN). It is characterized by extra radio nodes connected through the existing remote radio heads. Because of the newly connected nodes and the consequent additional delay, the operation of PW-CRAN requires different approaches compared with that of the typical C-RAN. Specifically, the effect of delayed channel state information on the suitability of network cooperation should be identified. To tackle this problem, we introduce two representative cooperation strategies and evaluate the performance with regard to the delay via simulations. Numerical results suggest that it is better to exclude the extra nodes from cooperation if they incur excess delay. Furthermore, whether the delay is deemed excessive depends on the interference environment. Hence, we provide quantified guidelines on the cooperation strategy of PW-CRAN.

  • 239. Kim, Jongyul
    et al.
    Jang, Insu
    Reda, Waleed
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Im, Jaeseong
    Canini, Marco
    Kostic, Dejan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Kwon, Youngjin
    Peter, Simon
    Witchel, Emmett
    LineFS: Efficient SmartNIC Offload of a Distributed File System with Pipeline Parallelism2021Inngår i: ACM SIGOPS 28th Symposium on Operating Systems Principles, 2021Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In multi-tenant systems, the CPU overhead of distributed file systems (DFSes) is increasingly a burden to application performance. CPU and memory interference cause degraded and unstable application and storage performance, in particular for operation latency. Recent client-local DFSes for persistent memory (PM) accelerate this trend. DFS offload to SmartNICs is a promising solution to these problems, but it is challenging to fit the complex demands of a DFS onto simple SmartNIC processors located across PCIe.

    We present LineFS, a SmartNIC-offloaded, high-performance DFS with support for client-local PM. To fully leverage the SmartNIC architecture, we decompose DFS operations into execution stages that can be offloaded to a parallel datapath execution pipeline on the SmartNIC. LineFS offloads CPU-intensive DFS tasks, like replication, compression, data publication, index and consistency management to a Smart-NIC. We implement LineFS on the Mellanox BlueField Smart-NIC and compare it to Assise, a state-of-the-art PM DFS. LineFS improves latency in LevelDB up to 80% and throughput in Filebench up to 79%, while providing extended DFS availability during host system failures.

    Fulltekst (pdf)
    fulltext
  • 240.
    Kokkalis, Andreas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    On-demand virtual laboratory environments for Internetworking e-learning: A first step using docker containers2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Learning Management Systems (LMSs) are widely used in higher education to improve the learning, teaching, and administrative tasks for both students and instructors. Such systems enrich the educational experience by integrating a wide range of services, such as on-demand course material and training, thus empowering students to achieve their learning outcomes at their own pace.

    Courses in various sub-fields of Computer Science that seek to provide rich electronic learning (e-learning) experience depend on exercise material being offered in the forms of quizzes, programming exercises, laboratories, simulations, etc. Providing hands on experience in courses such as Internetworking could be facilitated by providing laboratory exercises based on virtual machine environments where the student studies the performance of different internet protocols under different conditions (such as different throughput bounds, error rates, and patterns of changes in these conditions). Unfortunately, the integration of such exercises and their tailored virtual environments is not yet very popular in LMSs.

    This thesis project investigates the generation of on-demand virtual exercise environments using cloud infrastructures and integration with an LMS to provide a rich e-learning in an Internetworking course. The software deliverable of this project enables instructors to dynamically instantiate virtual laboratories without incurring the overhead of running and maintaining their own physical infrastructure. This sets the foundations for a virtual classroom that can scale in response to higher system utilization during specific periods of the academic calendar.

    Fulltekst (pdf)
    fulltext
  • 241. Kolpakov, S.
    et al.
    Sergeyev, S. V.
    Udalcovs, Aleksejs
    KTH.
    Pang, Xiaodan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Optical Network Laboratory (ON Lab). KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Fotonik.
    Ozolins, Oskars
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Fotonik.
    Schatz, Richard
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Fotonik.
    Popov, Sergei
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Fotonik.
    Polarization dynamics of coupled raman lasers2020Inngår i: International Conference on Transparent Optical Networks, IEEE Computer Society , 2020Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We experimentally demonstrated a new mechanism of generation of random pulses with the anomalous statistics (optical rogue waves) in a system of coupled Raman lasers. The pump laser with a linear cavity and wavelength of 1550 nm was coupled to a random laser generating nearby 1670 nm. These rogue waves appeared as a result of the interactions between Raman cascades and a coupling of the orthogonal states of polarization (SOPs). The desynchronization of SOPs caused by polarization instability led to chaotic oscillations. Due to the antiphase dynamics in two cascades, these chaotic oscillations were transformed into anomalous spikes satisfying rogue waves criteria.

  • 242.
    Kuvaja Rabhi, Karim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Automatisering av aktiv lyssnare processen inom examensarbetesseminarium: En utökning av lärplattformen Canvas2019Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    I dagsläget när studenter från Kungliga Tekniska Högskolan (KTH) ska genomföra en examensarbetspresentation ska det finnas aktiva lyssnare på plats. Aktiva lyssnare är andra studenter som också utför examensarbeten och som lyssnar på presentationen och ställer frågor. Detta är ett obligatoriskt moment som alla studenter genomför under sina examensarbeten. Problemet med detta moment är att det inte genomförs på ett smidigt sätt, för att få sitt deltagande godkänt får man en underskrift på ett papper av examinatorn på plats som bevis på delaktighet. Skulle detta papper tappas bort finns inga bevis på delaktighet.

    I detta examensarbete ska närvaroprocessen göras smidigare, både för studenter och för examinatorer, med hjälp av digitalisering. Som student ska det vara enkelt att ställa frågor till presentatören, dessa frågor kommer vara en del av grunden för närvarokontrollen. För examinatorer ska närvarokontrollen av aktiv lyssnare deltagandet förenklas.

    Med hjälp av lärplattformen Canvas, som KTH använder sig av, ska det bli lättare för examinatorer att ta närvaro på studenter. Studenter ska med hjälp av en gruppfunktion i Canvas kunna välja vilken presentation de vill delta i genom att gå med i en grupp som representerar en vald presentationen. Canvas har också en diskussionsfunktion som gör det möjligt för aktiva lyssnare att ställa sina frågor om presentationen, frågorna kommer sedan vara ett underlägg för närvaro och deltagande under presentationen. Canvas kan med sitt applikationsprogrammeringsgränssnitt användas med programmeringsspråket Ruby, vilket är tänkta ska användas, för att digitalisera och förenkla aktiv lyssnare processen.

    Detta projekt har tagit fram en process som endast använder Canvas för bevis på närvaro och delaktighet som aktiv lyssnare under en presentation. Som aktiv lyssnare behöver man endast gå med i en grupp som representerar en presentation och publicera en fråga i en diskussionstråd i gruppen för att få delmomentet godkänt. Med denna process behöver varken studenter eller examinatorer hantera osmidigt pappersarbete. Resultatet är fullt fungerande och har testats på en fiktiv Canvasdomän och skulle i teorin kunna användas på KTH.

    Fulltekst (pdf)
    fulltext
  • 243.
    Kwon, Younggap
    et al.
    Yonsei Univ, Sch Elect & Elect Engn, Seoul 120749, South Korea.;Agcy Def Dev, Daejeon 305600, South Korea..
    Park, Hyunsung
    Yonsei Univ, Sch Elect & Elect Engn, Seoul 120749, South Korea..
    Oh, Jintaek
    Yonsei Univ, Sch Elect & Elect Engn, Seoul 120749, South Korea..
    Miao, Guowang
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Hwang, Taewon
    Yonsei Univ, Sch Elect & Elect Engn, Seoul 120749, South Korea..
    Energy-Efficient Routing and Link Adaptation for 2D Wireless Relay Networks in the Wideband Regime2018Inngår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, nr 11, s. 7325-7339Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We discuss the globally optimal energy-efficient design of a 2D relay network. Different from the existing routing protocols on energy saving, which finds the minimal energy route for a given data rate, the proposed algorithm jointly optimizes routing and data rate to maximize energy efficiency (EE) defined as the achievable data rate per power consumption. We propose a low-complexity algorithm to circumvent the huge complexity of the exhaustive search for the network EE maximization and prove its global optimality. Moreover, the proposed algorithm is implemented in a distributed fashion because each relay needs to send its routing information only to the relays in its adjacent tiers, which significantly reduces the signaling overhead of the centralized implementation. Our analysis on the worst-case complexity in a fading channel shows that the complexity of the proposed algorithm increases linearly while that of the exhaustive search increases exponentially as the tier index increases. Simulation results confirm that the proposed algorithm outperforms the existing routing protocols on energy saving and achieves the globally optimal network EE at a significantly lower complexity than the exhaustive search.

  • 244.
    Lau, Chun Pong
    et al.
    King Abdullah Univ Sci & Technol, Comp Elect & Math Sci Engn Div, Thuwal 239556900, Saudi Arabia. abbasi, Abdulrahman.
    Alabbasi, Abdulrahman
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Shihada, Basem
    An Efficient Content Delivery System for 5G CRAN Employing Realistic man Mobility2019Inngår i: IEEE Transactions on Mobile Computing, ISSN 1536-1233, E-ISSN 1558-0660, Vol. 18, nr 4, s. 742-756Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Today's modern communication technologies such as cloud radio access and software defined networks are key candidate technologies for enabling 5G networks as they incorporate intelligence for data-driven networks. Traditional content caching in the last mile access point has shown a reduction in the core network traffic. However, the radio access network still does not fully leverage such solution. Transmitting duplicate copies of contents to mobile users consumes valuable radio spectrum resources and unnecessary base station energy. To overcome these challenges, we propose huManmObility-based cOntent Distribution (MOOD) system. MOOD exploits urban scale users' mobility to allocate radio resources spatially and temporally for content delivery. Our approach uses the broadcast nature of wireless communication to reduce the number of duplicated transmissions of contents in the radio access network for conserving radio resources and energy. Furthermore, a human activity model is presented and statistically analyzed for simulating people daily routines. The proposed approach is evaluated via simulations and compared with a generic broadcast strategy in an actual existing deployment of base stations as well as a smaller cells environment, which is a trending deployment strategy in future 5G networks. MOOD achieves 15.2 and 25.4 percent of performance improvement in the actual and small-cell deployment, respectively. 

  • 245.
    Laya, Andrés
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Markendahl, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Solutions based on digital connected devices for social care and well-being2019Inngår i: Digital Transformation and Public Services: Societal Impacts in Sweden and Beyond, Taylor and Francis , 2019, s. 127-140Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    This chapter deals with two aspects of the development of solutions for social care and well-being in Sweden. First, we investigate the business challenges preventing the development and uptake of new digital solutions. Second, we discuss the implication of those challenges in terms of the emerging development patterns. The analysis is based on a number of interviews with technology providers and municipalities. The findings revolve around three main themes discussing possible strategies for both public actors and technology providers to handle these challenges: 1) in a digitalized home care environment, governmental actors need stronger cooperation with private companies to provide new services, 2) local governments should develop clear development guidelines related to procurement and also how to change the role of different actors, and 3) focus on well-being for innovation in order to avoid unclear regulation/public procurement if you are a small company. 

  • 246.
    Laya, Andrés
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Markendahl, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Lundberg, Stefan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Ergonomi.
    Network-centric business models for health, social care and wellbeing solutions in the internet of things2018Inngår i: Scandinavian Journal of Management, ISSN 0956-5221, E-ISSN 1873-3387, Vol. 34, nr 2, s. 103-116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this multiple case study we analyze solutions based on connected devices in the context of health, social care and wellbeing. Based on the consideration that a solution is a combination of services and products, we build on the notion that business models can be studied at a firm-level and also at a network-level. The network-level analysis is used to motivate the reasons why solutions emerging at the intersection of the healthcare and the ICT industries benefit from collaboration among different actors. We conclude that the firm- and the network-level development of business models provide alignment in the business network and are useful to establish the relation that technological component have with overall solutions. Our findings suggest that some component bring novelty in the final offer without affecting the ongoing operation, while other component aim at improving the internal working processes, with minimal effects on the final offer to end users. We discuss the benefits of a network-level perspective for each case.

  • 247.
    Le, Mai T. P.
    et al.
    Univ Danang, Univ Sci & Technol, Da Nang 550000, Vietnam..
    Sanguinetti, Luca
    Univ Pisa, Dipartimento Ingn Informaz, I-56122 Pisa, Italy..
    Björnson, Emil
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS. Linköping Univ, Dept Elect Engn, S-58183 Linköping, Sweden..
    Di Benedetto, Maria-Gabriella
    Univ Roma La Sapienza, I-00184 Rome, Italy..
    Code-Domain NOMA in Massive MIMO: When Is It Needed?2021Inngår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 70, nr 5, s. 4709-4723Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In overloaded Massive MIMO (mMIMO) systems, wherein the number K of user equipments (UEs) exceeds the number of base station antennas M, it has recently been shown that non-orthogonal multiple access (NOMA) can increase the sum spectral efficiency. This paper aims at identifying cases where code-domain NOMA can improve the spectral efficiency of mMIMO in the classical regime where K < M. Novel spectral efficiency expressions are provided for the uplink and downlink with arbitrary spreading signatures and spatial correlation matrices. Particular attention is devoted to the planar arrays that are currently being deployed in pre-5G and 5G networks (in sub-6 GHz bands), which are characterized by limited spatial resolution. Numerical results show that mMIMO with such planar arrays can benefit from NOMA in scenarios where the UEs are spatially close to each other. A two-step UE grouping scheme is proposed for NOMA-aided mMIMO systems that is applicable to the spatial correlation matrices of the UEs that are currently active in each cell. Numerical results are used to investigate the performance of the algorithm under different operating conditions and types of spreading signatures (orthogonal, sparse and random sets). The analysis reveals that orthogonal signatures provide the highest average spectral efficiency.

  • 248.
    Lee, Jong-Ho
    et al.
    Soongsil Univ, Sch Elect Engn, Seoul, South Korea..
    Choi, Jeongsik
    Intel Corp, Intel Labs, Santa Clara, CA USA..
    Lee, Woong-Hee
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Song, Jiho
    Univ Ulsan, Sch Elect Engn, Ulsan, South Korea..
    Array pattern synthesis using semidefinite programming and a bisection method2019Inngår i: ETRI Journal, ISSN 1225-6463, E-ISSN 2233-7326, Vol. 41, nr 5, s. 619-625Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we propose an array pattern synthesis scheme using semidefinite programming (SDP) under array excitation power constraints. When an array pattern synthesis problem is formulated as an SDP problem, it is known that an additional rank-one constraint is generated inevitably and relaxed via semidefinite relaxation. If the solution to the relaxed SDP problem is not of rank one, then conventional SDP-based array pattern synthesis approaches fail to obtain optimal solutions because the additional rank-one constraint is not handled appropriately. To overcome this drawback, we adopted a bisection technique combined with a penalty function method. Numerical applications are presented to demonstrate the validity of the proposed scheme.

  • 249.
    Lee, Jong-Ho
    et al.
    Soongsil Univ, Sch Elect Engn, Seoul 06978, South Korea..
    Choi, Jeongsik
    Intel Corp, Intel Labs, Santa Clara, CA 95054 USA..
    Lee, Woonghee
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Song, Jiho
    Univ Ulsan, Sch Elect Engn, Ulsan 44610, South Korea..
    Exploiting Array Pattern Synthesis for Physical Layer Security in Millimeter Wave Channels2019Inngår i: Electronics, E-ISSN 2079-9292, Vol. 8, nr 7, artikkel-id 745Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we propose a beamformer design scheme for wireless physical layer security using partial channel state information (CSI) in millimeter wave channels. The partial CSI used in this work is the range of angle-of-departure (AOD). Assuming that the AOD range of each node is available, we design a transmit beamformer using semidefinite programming based on array pattern synthesis. Numerical results are presented to verify the secrecy rates achieved by the proposed scheme.

  • 250.
    Lee, Woong-Hee
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS.
    Lee, Jong-Ho
    Soongsil Univ, Sch Elect Engn, Seoul 06978, South Korea..
    Sung, Ki Won
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Geometric Sequence Decomposition With k-Simplexes Transform2021Inngår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 69, nr 1, s. 94-107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a computationally efficient technique for decomposing non-orthogonally superposed k geometric sequences. The method, which is named as geometric sequence decomposition with k-simplexes transform (GSD-ST), is based on the concept of transforming an observed sequence to multiple k-simplexes in a virtual k-dimensional space and correlating the volumes of the transformed simplexes. Hence, GSD-ST turns the problem of decomposing k geometric sequences into one of solving a k-th order polynomial equation. Our technique has significance for wireless communications because sampled points of a radio wave comprise a geometric sequence. This implies that GSD-ST is capable of demodulating randomly combined radio waves, thereby eliminating the effect of interference. To exemplify the potential of GSD-ST, we propose a new radio access scheme, namely non-orthogonal interference-free radio access (No-INFRA). Herein, GSD-ST enables the collision-free reception of uncoordinated access requests. Numerical results show that No-INFRA effectively resolves the colliding access requests when the interference is dominant.

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