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• 1.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
How to Split UL/DL Antennas in Full-DuplexCellular Networks2018In: IEEE International Conference on Communication (ICC’18): ThirdWorkshop on Full-Duplex Communications for Future Wireless Networks, Kansas City, MO, USA: IEEE Communications Society, 2018Conference paper (Refereed)

To further improve the potential of full-duplex com-munications, networks may employ multiple antennas at thebase station or user equipment. To this end, networks thatemploy current radios usually deal with self-interference andmulti-user interference by beamforming techniques. Althoughprevious works investigated beamforming design to improvespectral efficiency, the fundamental question of how to split theantennas at a base station between uplink and downlink infull-duplex networks has not been investigated rigorously. Thispaper addresses this question by posing antenna splitting as abinary nonlinear optimization problem to minimize the sum meansquared error of the received data symbols. It is shown that thisis an NP-hard problem. This combinatorial problem is dealt withby equivalent formulations, iterative convex approximations, anda binary relaxation. The proposed algorithm is guaranteed toconverge to a stationary solution of the relaxed problem with muchsmaller complexity than exhaustive search. Numerical resultsindicate that the proposed solution is close to the optimal in bothhigh and low self-interference capable scenarios, while the usuallyassumed antenna splitting is far from optimal. For large numberof antennas, a simple antenna splitting is close to the proposedsolution. This reveals that the importance of antenna splittingdiminishes with the number of antennas.

• 2.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. Royal Inst Technol, KTH, Stockholm, Sweden..
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
How to Split UL/DL Antennas in Full-Duplex Cellular Networks2018In: 2018 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS), IEEE, 2018Conference paper (Refereed)

To further improve the potential of full-duplex communications, networks may employ multiple antennas at the base station or user equipment. To this end, networks that employ current radios usually deal with self-interference and multi-user interference by beamforming techniques. Although previous works investigated beamforming design to improve spectral efficiency, the fundamental question of how to split the antennas at a base station between uplink and downlink in full-duplex networks has not been investigated rigorously. This paper addresses this question by posing antenna splitting as a binary nonlinear optimization problem to minimize the sum mean squared error of the received data symbols. It is shown that this is an NP-hard problem. This combinatorial problem is dealt with by equivalent formulations, iterative convex approximations, and a binary relaxation. The proposed algorithm is guaranteed to converge to a stationary solution of the relaxed problem with much smaller complexity than exhaustive search. Numerical results indicate that the proposed solution is close to the optimal in both high and low self-interference capable scenarios, while the usually assumed antenna splitting is far from optimal. For large number of antennas, a simple antenna splitting is close to the proposed solution. This reveals that the importance of antenna splitting diminishes with the number of antennas.

• 3.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Hardened registration process for participatory sensing2018In: WiSec 2018 - Proceedings of the 11th ACM Conference on Security and Privacy in Wireless and Mobile Networks, Association for Computing Machinery, Inc , 2018, p. 281-282Conference paper (Refereed)

Participatory sensing systems need to gather information from a large number of participants. However, the openness of the system is a double-edged sword: by allowing practically any user to join, the system can be abused by an attacker who introduces a large number of virtual devices. This poster proposes a hardened registration process for Participatory Sensing to raise the bar: registrations are screened through a number of defensive measures, towards rejecting spurious registrations that do not correspond to actual devices. This deprives an adversary from a relatively easy take-over and, at the same time, allows a flexible and open registration process.

• 4.
KTH.
KTH. KTH. KTH. KTH. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Enterprise Architecture and Agile Development: Friends or Foes?2018Conference paper (Refereed)
• 5.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Optimal Networking in Wirelessly Powered Sensor Networks2018Doctoral thesis, comprehensive summary (Other academic)

Wireless sensor networks (WSNs) are nowadays widely used for the long-term monitoring of small or large regions, such as lakes, forests, cities, and industrial areas. The performance of a WSN typically consists of two aspects: i) the monitoring performance, e.g., the accuracy and the timeliness of the measurements or estimations produced by the sensor nodes of the WSN; and ii) the lifetime, i.e., how long the WSN can sustain such a performance. Naturally, we would like to have the monitoring performance as good as possible, and the lifetime as long as possible. However, in traditional WSNs, the sensor nodes generally have limited resources, especially in terms of battery capacity. If the nodes make measurements and report them frequently for a good monitoring performance, they drain their batteries and  this leads to a severely shortened network lifetime. Conversely, the sensors can have a longer lifetime by sacrificing the monitoring performance. It shows the inherent trade-off between the monitoring performance and the lifetime in WSNs.

We can overcome the limitations of the trade-off described above by wireless energy transfer (WET), where we can provide the sensor nodes with additional energy remotely. The WSNs with WET are called wirelessly powered sensor networks (WPSNs). In a WPSN, dedicated energy sources, e.g., static base stations or mobile chargers, transmit energy via radio frequency (RF) waves to the sensor nodes. The nodes can store the energy in their rechargeable batteries and use it later when it is needed. In so doing, they can use more energy to perform the sensing tasks. Thus, WET is a solution to improve the monitoring performance and lifetime at the same time.  As long as the nodes receive more energy than they consume, it is possible that the WSN be immortal, which is impossible in traditional WSNs.

Although WPSNs can potentially break the trade-off between monitoring performance and lifetime, they also bring many fundamental design and performance analysis challenges. Due to the safety issues, the power that the dedicated energy sources can use is limited. The propagation of the RF waves suffers high path losses. Therefore, the energy received by the sensor nodes is much less than the energy transmitted from the sources. As a result, to have a good WSN performance, we should optimize the energy transmission on the energy source side and the energy consumption on the nodes side. Compared to the traditional WSN scenarios where we can only optimize the sensing and data communication strategies, in WPSNs, we have an additional degree of freedom, i.e., the optimization of the energy transmission strategies. This aspect brings new technical challenges and problems that have not been studied in the traditional WSNs. Several novel research questions arise, such as when and how to transmit the energy, and which energy source should transmit. Such questions are not trivial especially when we jointly consider the energy consumption part.

This thesis contributes to answer the questions above. It consists of three contributions as follows.

In the first contribution, we consider a WPSN with single energy base stations (eBS) and multiple sensor nodes to monitor several separated areas of interest. The eBS has multiple antennas, and it uses energy beamforming to transmit energy to the nodes. Notice that, if we deploy multiple sensor nodes at the same area, these nodes may receive the energy from the eBS at the same time and they can reduce the energy consumption by applying sleep/awake mechanism. Therefore, we jointly study the deployment of the nodes, the energy transmission of the eBS, and the node activation. The problem is an integer optimization, and we decouple the problem into a node deployment problem and a scheduling problem. We provide a greedy-based algorithm to solve the problem, and show its performance in terms of optimality.

The second contribution of the thesis starts by noticing that wireless channel state information (CSI) is important for energy beamforming. The more energy that an eBS spends in channel acquisition, the more accurate CSI it will have, thus improving the energy beamforming performance. However, if the eBS spends too much energy on channel acquisition, it will have less energy for WET, which might reduce the energy that is received by the sensor nodes. We thus investigate how much energy the eBS should spend in channel acquisition, i.e., we study the power allocation problem in channel acquisition and energy beamforming for WPSNs. We consider the general optimal channel acquisition and show that the problem is non-convex. Based on the idea of bisection search, we provide an algorithm to find the optimal solution for the single eBS cases, and a closed-form solution for the case where the eBS uses orthogonal pilot transmission, least-square channel estimation, and maximum ratio transmission for WET. The simulations show that the algorithm converges fast, and the performance is close to the theoretical upper bound.

In the third contribution, we consider a joint energy beamforming and data routing problem for WPSNs. More specifically, we investigate the WPSNs consisting of multiple eBSs, multiple sensor nodes, and a sink node. Based on the received energy, the sensor nodes need to decide how to route their data. The problem aims at maximizing the minimum sensing rate of the sensor nodes while guaranteeing that the received energy of each node is no less than that is consumed. Such a problem is non-convex, and we provide a centralized solution algorithm based on a semi-definite programming transformation. We extend this approach with a distributed algorithm using alternating direction method of multipliers (ADMM). We prove that the centralized algorithm achieves the optimal energy beamforming and routing, and we show by simulation that the distributed one converges to the optimal solution. Additionally, for the cases where the energy beamforming options are pre-determined, we study the problem of finding the energy that should be spent on each vector. We observe that, if the pre-determined beamforming options are chosen wisely, their performance is close to the optimal.

The results of the thesis show that WET can prolong the lifetime of WSNs, and even make them work sufficiently long for general monitoring applications. More importantly, we should optimize the WPSN by considering both the energy provision and the energy consumption part. The studies of the thesis have the potential to be used in many Internet of Things (IoT) systems in smart cities, such as water distribution lines and building monitoring.

• 6.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH Royal Inst Technol, Stockholm, Sweden..
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH Royal Inst Technol, Stockholm, Sweden..
Power Allocation for Channel Estimation and Energy Beamforming in Wirelessly Powered Sensor Networks2018In: 2018 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS), IEEE, 2018Conference paper (Refereed)

Wirelessly powered sensor networks (WPSNs) are becoming increasingly important to monitor many internet-of- things systems. In these WPSNs, dedicated base stations (BSs) with multiple antennas charge the sensor nodes without the need of replacing their batteries thanks to two essential procedures: i) getting of the channel state information of the nodes by sending pilots, and based on this, ii) performing energy beamforming to transmit energy to the nodes. However, the BSs have limited power budget and thus these two procedures are not independent, contrarily to what is assumed in some previous studies. In this paper, we investigate the novel problem of how to optimally allocate the power for channel estimation and energy transmission. Although the problem is non-convex, we provide a new solution approach and a performance analysis in terms of optimality and complexity. We also provide a closed form solution for the case where the channels are estimated based on a least square estimation. The simulations show a gain of approximately 10% in allocating the power optimally, and the importance of improving the channel estimation efficiency.

• 7.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Power Allocation for Channel Estimation and EnergyBeamforming in Wirelessly Powered Sensor Networks2018In: Proceedings of IEEE International Conference on Communications Workshops, 2018Conference paper (Refereed)

Wirelessly powered sensor networks (WPSNs) are becoming increasingly important to monitor many internet-of-things systems. In these WPSNs, dedicated base stations (BSs) with multiple antennas charge the sensor nodes without the need of replacing their batteries thanks to two essential procedures: i)  getting of the channel state information of the nodes by sending pilots, and based on this, ii) performing energy beamforming to transmit energy to the nodes. However, the BSs have limited power budget and thus these two procedures are not independent, contrarily to what  is assumed in some previous studies. In this paper, we investigate the novel problem of how to optimally allocate the power for channel estimation and energy transmission. Although the problem is non-convex, we provide a new solution approach and a performance analysis in terms of optimality and complexity. We also provide a closed form solution for the case where the channels are estimated based on a least square estimation. The simulations show a gain of approximately 10% in allocating the power optimally, and the importance of improving the channel estimation efficiency.

• 8.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
On Maximizing Sensor Network Lifetime by Energy Balancing2018In: IEEE Transactions on Control of Network Systems, ISSN 2325-5870, Vol. 5, no 3Article in journal (Refereed)

Many physical systems, such as water/electricity distribution networks, are monitored by battery-powered wireless-sensor networks (WSNs). Since battery replacement of sensor nodes is generally difficult, long-term monitoring can be only achieved if the operation of the WSN nodes contributes to long WSN lifetime. Two prominent techniques to long WSN lifetime are 1) optimal sensor activation and 2) efficient data gathering and forwarding based on compressive sensing. These techniques are feasible only if the activated sensor nodes establish a connected communication network (connectivity constraint), and satisfy a compressive sensing decoding constraint (cardinality constraint). These two constraints make the problem of maximizing network lifetime via sensor node activation and compressive sensing NP-hard. To overcome this difficulty, an alternative approach that iteratively solves energy balancing problems is proposed. However, understanding whether maximizing network lifetime and energy balancing problems are aligned objectives is a fundamental open issue. The analysis reveals that the two optimization problems give different solutions, but the difference between the lifetime achieved by the energy balancing approach and the maximum lifetime is small when the initial energy at sensor nodes is significantly larger than the energy consumed for a single transmission. The lifetime achieved by energy balancing is asymptotically optimal, and that the achievable network lifetime is at least 50% of the optimum. Analysis and numerical simulations quantify the efficiency of the proposed energy balancing approach.

• 9.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Towards Immortal Wireless Sensor Networks by Optimal Energy Beamforming and Data Routing2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 8, p. 5338-5352Article in journal (Refereed)

The lifetime of a wireless sensor network (WSN) determines how long the network can be used to monitor the area of interest. Hence, it is one of the most important performance metrics for WSN. The approaches used to prolong the lifetime can be briefly divided into two categories: reducing the energy consumption, such as designing an efficient routing, and providing extra energy, such as using wireless energy transfer (WET) to charge the nodes. Contrary to the previous line of work where only one of those two aspects is considered, we investigate these two together. In particular, we consider a scenario where dedicated wireless chargers transfer energy wirelessly to sensors. The overall goal is to maximize the minimum sampling rate of the nodes while keeping the energy consumption of each node smaller than the energy it receives. This is done by properly designing the routing of the sensors and the WET strategy of the chargers. Although such a joint routing and energy beamforming problem is non-convex, we show that it can be transformed into a semi-definite optimization problem (SDP). We then prove that the strong duality of the SDP problem holds, and hence the optimal solution of the SDP problem is attained. Accordingly, the optimal solution for the original problem is achieved by a simple transformation. We also propose a low-complexity approach based on pre-determined beamforming directions. Moreover, based on the alternating direction method of multipliers (ADMM), the distributed implementations of the proposed approaches are studied. The simulation results illustrate the significant performance improvement achieved by the proposed methods. In particular, the proposed energy beamforming scheme significantly out-performs the schemes where one does not use energy beamforming, or one does not use optimized routing. A thorough investigation of the effect of system parameters, including the number of antennas, the number of nodes, and the number of chargers, on the system performance is provided. The promising convergence behaviour of the proposed distributed approaches is illustrated.

• 10.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Wirelessly-powered Sensor Networks: Power Allocation for Channel Estimation and Energy beamformingIn: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248Article in journal (Refereed)

Wirelessly-powered sensor networks (WPSNs) are becoming increasingly important to monitor many internet-of-things systems. We consider a WPSN where a multiple-antenna base station, dedicated for energy transmission, sends pilot signals to estimate the channel state information and consequently shapes the energy beams toward the sensor nodes. Given a fixed energy budget at the base station, in this paper, we investigate the novel problem of optimally allocating the power for the channel estimation and for the energy transmission. We formulate this problem for general channel estimation and beamforming schemes, which turns out to be non-convex. We provide a new solution approach and a performance analysis in terms of optimality and complexity. We also present a closed-form solution for the case where the channels are estimated based on a least square channel estimation and a maximum ratio transmit beamforming scheme. The analysis and simulations indicate a significant gain in terms of the network sensing rate, compared to the fixed power allocation, and the importance of improving the channel estimation efficiency.

• 11.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Optimal Node Deployment and Energy Provision for Wirelessly Powered Sensor Networks2018In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008Article in journal (Refereed)

In a typical wirelessly powered sensor network (WPSN), wireless chargers provide energy to sensor nodes by using wireless energy transfer (WET). The chargers can greatly improve the lifetime of a WPSN using energy beamforming by a proper charging scheduling of energy beams. However, the supplied energy still may not meet the demand of the energy of the sensor nodes. This issue can be alleviated by deploying redundant sensor nodes, which not only increase the total harvested energy, but also decrease the energy consumption per node provided that an efficient  scheduling of the sleep/awake of the nodes is performed. Such a problem of joint optimal sensor deployment, WET scheduling, and node activation is posed and investigated in this paper. The problem is an integer optimization that is challenging due to the binary decision variables and non-linear constraints. Based on the analysis of the necessary condition such that the WPSN be immortal, we decouple the original problem into a node deployment problem and a charging and activation scheduling problem. Then, we propose an algorithm and prove that it achieves the optimal solution under a mild condition. The simulation results show that the proposed algorithm reduces the needed nodes to deploy by approximately 16%, compared to a random-based approach. The simulation also shows if the battery buffers are large enough, the optimality condition will be easy to meet.

• 12.
TU Munich.
TU Munich. Harvard. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Multivariate Unsupervised Machine Learning for Anomaly Detection in Enterprise Applications2019Conference paper (Refereed)
• 13. Enyioha, Chinwendu
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH - Royal Institute of Technology. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
On Variability of Renewable Energy and Online Power Allocation2018In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 33, no 1, p. 451-462Article in journal (Refereed)

As electric power system operators shift from conventional energy to renewable energy sources, power distribution systems will experience increasing fluctuations in supply. These fluctuations present the need to not only design online decentralized power allocation algorithms, but also characterize how effective they are given fast-changing consumer demand and generation. In this paper, we present an online decentralized dual descent (OD3) power allocation algorithm and determine (in the worst case) how much of observed social welfare can be explained by fluctuations in generation capacity and consumer demand. Convergence properties and performance guarantees of the OD3 algorithm are analyzed by characterizing the difference between the online decision and the optimal decision. We demonstrate validity and accuracy of the theoretical results in the paper through numerical experiments using real power generation data.

• 14.
KTH.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Lightweight X.509 Digital Certificates for the Internet of Things2018In: 3rd International Conference on Interoperability in IoT, InterIoT 2017 on conjunction with 4th International Conference on Safety and Security in Internet of Things, SaSeIoT 2017, Springer, 2018, Vol. 242, p. 123-133Conference paper (Refereed)

X.509 is the de facto digital certificate standard used in building the Public Key Infrastructure (PKI) on the Internet. However, traditional X.509 certificates are too heavy for battery powered or energy harvesting Internet of Things (IoT) devices where it is crucial that energy consumption and memory footprints are as minimal as possible. In this paper we propose, implement, and evaluate a lightweight digital certificate for resource-constrained IoT devices. We develop an X.509 profile for IoT including only the fields necessary for IoT devices, without compromising the certificate security. Furthermore, we also propose compression of the X.509 profiled fields using the contemporary CBOR encoding scheme. Most importantly, our solutions are compatible with the existing X.509 standard, meaning that our profiled and compressed X.509 certificates for IoT can be enrolled, verified and revoked without requiring modification in the existing X.509 standard and PKI implementations. We implement our solution in the Contiki OS and perform evaluation of our profiled and compressed certificates on a state-of-the-art IoT hardware.

• 15.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
On the Capacity of Gaussian "Dirty" Z-Interference Channel with Common State2018In: 2018 52ND ANNUAL CONFERENCE ON INFORMATION SCIENCES AND SYSTEMS (CISS), IEEE , 2018Conference paper (Refereed)

A class of Gaussian Z-interference channels with state is investigated in the regime of high state power with two transmitters communicating two independent messages through a "dirty" Z-interference channel with state. Transmitter 1 (primary user) interferes with receiver 2, while transmitter 2 (secondary user) does not interfere with receiver 1. In our model, we assume that both states are the same. Using lattice coding schemes, we obtain achievable rate-regions to characterize the boundary of the capacity region either fully or partially. Surprisingly, we observe that the achievable rate-region under a common state can include some points out of the rate-region when the channel is only corrupted by a state, i.e., when the additional interference is not harmful for the channel.

• 16.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS). City University of Hong Kong. KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Low-Overhead Coordination in Sub-28 Millimeter-Wave Networks2018Conference paper (Refereed)
• 17. Guerreiro, Sérgio
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
A Meta Model for interoperability of Secure Business Transaction using BlockChain and DEMO2017Conference paper (Refereed)

Business transactions executed between organizations and individuals are largely operated on digital environments, conducting to an industrial interoperability challenge demanding secure environments to cooperate safely, therefore increasing credibility, and trust ability between end-users. This paper conceptualizes and prescribes a fine-grained control solution for the execution of business transactions involving critical assets, and using a human-based coordination and interaction design to minimize the negative impacts of security risks, the non-conformable operation and the coarse-grained control. This solution integrates the DEMO-based Enterprise Operating System (EOS) with BlockChain as a way to redesign, and distribute globally, a set of services that are founded in a human-oriented approach, and therefore, offering trust, authenticity, resilience, robustness against fraud and identification and mitigation of risk. The impacts for organizations and individuals are manifold: a security risk-based solution for end-users with budgetary constraints; educate on cyber security issues; and augment the trust for digital business processes environments.

• 18.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Monitoring Water Distribution Network using Machine Learning2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Water is an important natural resource. It is supplied to our home by water distribution network thatis owned and maintained by water utility companies. Around one third of water utilities across the globereport a loss of 40% of clean water due to leakage. The increase in pumping, treatment and operationalcosts are pushing water utilities to combat water loss by developing methods to detect, locate, and xleaks. However, traditional pipeline leakage detection methods require periodical inspection with humaninvolvement, which makes it slow and inecient for leakage detection in a timely manner. An alternativeis on-line, continuous, real-time monitoring of the network facilitating early detection and localization ofthese leakages. This thesis aims to nd such an alternative using various Machine Learning techniques.For a water distribution network, a novel algorithm is proposed based on the concept of dominantnodes from graph theory. The algorithm nds the number of sensors needed and their correspondinglocations in the network. The network is then sub-divided into several leakage zones, which serves as abasis for leak localization in the network. Thereafter, leakages are simulated in the network virtually,using hydraulic simulation software. The obtained time series pressure data from the sensor nodes ispre-processed using one-dimensional wavelet series decomposition by using daubechies wavelet to extractfeatures from the data. It is proposed to use this feature extraction procedure at every sensor nodelocally, which reduces the transmitted data to the central hub over the cloud thereby reducing the energyconsumption for the IoT sensor in real world.For water leakage detection and localization, a procedure for obtaining training data is proposed,which serves as a basis for recognition of patterns and regularities in the data using supervised Machinelearning techniques such as Logistic Regression, Support Vector Machine, and Articial Neural Network.Furthermore, ensemble of these trained model is used to build a better model for leakage detection andits localization. In addition, Random Forest algorithm is trained and its performance is compared tothe obtained ensemble of earlier models. Also, leak size estimation is performed using Support VectorRegression algorithm.It is observed that the sensor node placement using proposed algorithm provides a better leakage localizationresolution than random deployment of sensor. Furthermore, it is found that leak size estimationusing Support Vector Regression algorithm provides a reasonable accuracy. Also, it is noticed that RandomForest algorithm performs better than the ensemble model except for the low leakage scenario. Thus,it is concluded to estimate the leak size rst, based on this estimation for small leakage case ensemblemodels can be applied while for large leakage case only Random Forest can be used.

• 19.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Minimizing age of correlated information for wireless camera networks2018In: INFOCOM 2018 - IEEE Conference on Computer Communications Workshops, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 547-552Conference paper (Refereed)

Freshness of information is of critical importance for a variety of applications based on wireless camera networks where multi-view image processing is required. In this study, we propose to jointly optimize the use of communication and computing resources such that information from multiple views is delivered is obtained in a timely fashion. To this end, we extend the concept of age of information to capture packets carrying correlated data. We consider the joint optimization of processing node assignment and camera transmission policy, so as to minimize the maximum peak age of information from all sources. We formulate the multi-view age minimization problem (MVAM) and prove that it is NP-hard. We provide fundamental results including tractable cases and optimality conditions. To solve the MVAM efficiently, we develop a modular optimization algorithm following a decomposition approach. Numerical results show that, by employing our approach, the maximum peak age is significantly reduced in comparison to a traditional centralized solution with minimum-time scheduling.

• 20.
KTH.
KTH. Uppsala University, Uppsala, Sweden. Uppsala University and RISE SICS, Uppsala and Stockholm, Sweden. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Security on harvested power2018In: WiSec 2018 - Proceedings of the 11th ACM Conference on Security and Privacy in Wireless and Mobile Networks, Association for Computing Machinery, Inc , 2018, p. 296-298Conference paper (Refereed)

Security mechanisms for battery-free devices have to operate under severe energy constraints relying on harvested energy. This is challenging, as the energy harvested from the ambient environment is usually scarce, intermittent and unpredictable. One of the challenges for developing security mechanisms for such settings is the lack of hardware platforms that recreate energy harvesting conditions experienced on a battery-free sensor node. In this demonstration, we present an energy harvesting security (EHS) platform that enables the development of security algorithms for battery-free sensors. Our results demonstrate that our platform is able to harvest sufficient energy from indoor lighting to support several widely used cryptography algorithms.

• 21.
KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
Random forests for resource allocation in 5G cloud radio access networks based on position information2018In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2018, no 1, article id 142Article in journal (Refereed)

Next generation 5G cellular networks are envisioned to accommodate an unprecedented massive amount of Internet of things (IoT) and user devices while providing high aggregate multi-user sum rates and low latencies. To this end, cloud radio access networks (CRAN), which operate at short radio frames and coordinate dense sets of spatially distributed radio heads, have been proposed. However, coordination of spatially and temporally denser resources for larger sets of user population implies considerable resource allocation complexity and significant system signalling overhead when associated with channel state information (CSI)-based resource allocation (RA) schemes. In this paper, we propose a novel solution that utilizes random forests as supervised machine learning approach to determine the resource allocation in multi-antenna CRAN systems based primarily on the position information of user terminals. Our simulation studies show that the proposed learning based RA scheme performs comparably to a CSI-based scheme in terms of spectral efficiency and is a promising approach to master the complexity in future cellular networks. When taking the system overhead into account, the proposed learning-based RA scheme, which utilizes position information, outperforms legacy CSI-based scheme by up to 100%. The most important factor influencing the performance of the proposed learning-based RA scheme is antenna orientation randomness and position inaccuracies. While the proposed random forests scheme is robust against position inaccuracies and changes in the propagation scenario, we complement our scheme with three approaches that restore most of the original performance when facing random antenna orientations of the user terminal.

• 22.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Wireless Communication Networks for Time-critical Industrial Applications2018Licentiate thesis, comprehensive summary (Other academic)

Wireless communication is of paramount importance to enable the vision of Industry 4.0. Compared to mobile communications, industrial communications pose demanding requirements in terms of ultra low latency and high reliability. Currently, for the most time-critical industrial applications, there is no available wireless solutions satisfying these latency requirements. This thesis studies effective techniques to reduce the latency for the time-critical industrial applications, especially from the Physical Layer (PHY) point of view.

The thesis is organized in two main parts. In the first part, the available methods for low latency are surveyed and analyzed in terms of end-to-end latency. It is argued that the enabling techniques should be optimized together to reduce the end-to-end latency while satisfying other requirements such as reliability and throughput. Moreover, the realistic timing constraints of different PHY algorithms, hardware, and mechanisms are derived based on the state-of-art wireless implementations. In the second part, a revision of PHY with an optimized PHY structure is proposed to reduce the latency. It is shown that a PHY with just a short one-symbol preamble and dedicated packet detection and synchronization algorithms for short packets is robust to carrier frequency offsets and false alarms by both theoretical and site experiments.

The investigations of this thesis show that revising the PHY structure/parameters is effective to reduce the packet transmission time, and further improve the latency performance of wireless communication network for time-critical industrial applications. In the future, we include the PHY results of this thesis in the investigation of the Medium Access Control (MAC), for industrial wireless communications with very low latencies.

• 23.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
ABB Corporate Research, Sweden. ABB Corporate Research, Sweden. University of Electronic Science and Technology of China, China. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Fundamental Constraints for Time-slotted MAC Design in Wireless High Performance : the Realistic Perspective of Timing2018Conference paper (Refereed)
• 24.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering. KTH. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Packet Detection by Single OFDM Symbol in URLLC for Critical Industrial Control: a Realistic Study2018In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008Article in journal (Other academic)
• 25.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
A Simplified Interference Model for Outdoor Millimeter-waveNetworks2018In: Mobile Networks and Applications, ISSN 1383-469XArticle in journal (Refereed)

Industry 4.0 is the emerging trend of the industrial automation. Millimeter-wave (mmWave) communication is a prominent technology for wireless networks to support the Industry 4.0 requirements. The availability of tractable accurate interference models would greatly facilitate performance analysis and protocol development for these networks. In this paper, we investigate the accuracy of an interference model that assumes impenetrable obstacles and neglects the sidelobes. We quantify the error of such a model in terms of statistical distribution of the signal to noise plus interference ratio and of the user rate for outdoor mmWave networks under different carrier frequencies and antenna array settings. The results show that assuming impenetrable obstacle comes at almost no accuracy penalty, and the accuracy of neglecting antenna sidelobes can be guaranteed with sufficiently large number of antenna elements. The comprehensive discussions of this paper provide useful insights for the performance analysis and protocol design of outdoor mmWave networks.

• 26.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. Ericsson Research, Kista, Sweden.. Laboratory for Information and Decision Systems, Massachusetts Institute of Technology, Cambridge, MA 02139 USA.. ABB AB, Corporate Research, 721 78 Västerås, Sweden.. Department of Information Engineering, University of Padova, 35131 Padua, Italy.. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Low-Latency Networking: Where Latency Lurks and How to Tame It2018In: Proceedings of the IEEE, ISSN 0018-9219, E-ISSN 1558-2256, p. 1-27Article in journal (Refereed)

While the current generation of mobile and fixed communication networks has been standardized for mobile broadband services, the next generation is driven by the vision of the Internet of Things and mission-critical communication services requiring latency in the order of milliseconds or submilliseconds. However, these new stringent requirements have a large technical impact on the design of all layers of the communication protocol stack. The cross-layer interactions are complex due to the multiple design principles and technologies that contribute to the layers' design and fundamental performance limitations. We will be able to develop low-latency networks only if we address the problem of these complex interactions from the new point of view of submilliseconds latency. In this paper, we propose a holistic analysis and classification of the main design principles and enabling technologies that will make it possible to deploy low-latency wireless communication networks. We argue that these design principles and enabling technologies must be carefully orchestrated to meet the stringent requirements and to manage the inherent tradeoffs between low latency and traditional performance metrics. We also review currently ongoing standardization activities in prominent standards associations, and discuss open problems for future research.

• 27.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
A Meta Language for Threat Modeling and Attack Simulations2018Conference paper (Refereed)
• 28.
KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. SICS.
Can the Common Vulnerability Scoring System be Trusted?: A Bayesian Analysis2018In: IEEE Transactions on Dependable and Secure Computing, ISSN 1545-5971, E-ISSN 1941-0018, Vol. 15, no 6, p. 1002-1015, article id 7797152Article in journal (Refereed)

The Common Vulnerability Scoring System (CVSS) is the state-of-the art system for assessing software vulnerabilities. However, it has been criticized for lack of validity and practitioner relevance. In this paper, the credibility of the CVSS scoring data found in five leading databases – NVD, X-Force, OSVDB, CERT-VN, and Cisco – is assessed. A Bayesian method is used to infer the most probable true values underlying the imperfect assessments of the databases, thus circumventing the problem that ground truth is not known. It is concluded that with the exception of a few dimensions, the CVSS is quite trustworthy. The databases are relatively consistent, but some are better than others. The expected accuracy of each database for a given dimension can be found by marginalizing confusion matrices. By this measure, NVD is the best and OSVDB is the worst of the assessed databases.

• 29.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Decentralized Algorithms for Resource Allocation in Mobile Cloud Computing Systems2018Licentiate thesis, comprehensive summary (Other academic)

The rapid increase in the number of mobile devices has been followed by an increase in the capabilities of mobile devices, such as the computational power, memory and battery capacity. Yet, the computational resources of individual mobile devices are still insufficient for various delay sensitive and computationally intensive applications. These emerging applications could be supported by mobile cloud computing, which allows using external computational resources. Mobile cloud computing does not only improve the users’ perceived performance of mobile applications, but it also may reduce the energy consumption of mobile devices, and thus it may extend their battery life. However, the overall performance of mobile cloud computing systems is determined by the efficiency of allocating communication and computational resources. The work in this thesis proposes decentralized algorithms for allocating these two resources in mobile cloud computing systems. In the first part of the thesis, we consider the resource allocation problem in a mobile cloud computing system that allows mobile users to use cloud computational resources and the resources of each other. We consider that each mobile device aims at minimizing its perceived response time, and we develop a game theoretical model of the problem. Based on the game theoretical model, we propose an efficient decentralized algorithm that relies on average system parameters, and we show that the proposed algorithm could be a promising solution for coordinating multiple mobile devices. In the second part of the thesis, we consider the resource allocation problem in a mobile cloud computing system that consists of multiple wireless links and a cloud server. We model the problem as a strategic game, in which each mobile device aims at minimizing a combination of its response time and energy consumption for performing the computation. We prove the existence of equilibrium allocations of mobile cloud resources, and we use game theoretical tools for designing polynomial time decentralized algorithms with a bounded approximation ratio. We then consider the problem of allocating communication and computational resources over time slots, and we show that equilibrium allocations still exist. Furthermore, we analyze the structure of equilibrium allocations, and we show that the proposed decentralized algorithm for computing equilibria achieves good system performance. By providing constructive equilibrium existence proofs, the results in this thesis provide low complexity decentralized algorithms for allocating mobile cloud resources for various mobile cloud computing architectures.

• 30.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
A Game Theoretic Analysis of Selfish Mobile Computation Offloading2017In: IEEE INFOCOM 2017 - IEEE CONFERENCE ON COMPUTER COMMUNICATIONS, IEEE , 2017Conference paper (Refereed)

Offloading computation to a mobile cloud is a promising approach for enabling the use of computationally intensive applications by mobile devices. In this paper we consider autonomous devices that maximize their own performance by choosing one of many wireless access points for computation offloading. We develop a game theoretic model of the problem, prove the existence of pure strategy Nash equilibria, and provide a polynomial time algorithm for computing an equilibrium. For the case when the cloud computing resources scale with the number of mobile devices we show that all improvement paths are finite. We provide a bound on the price of anarchy of the game, thus our algorithm serves as an approximation algorithm for the global computation offloading cost minimization problem. We use extensive simulations to provide insight into the performance and the convergence time of the algorithms in various scenarios. Our results show that the equilibrium cost may be close to optimal, and the convergence time is almost linear in the number of mobile devices.

• 31.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Decentralized Algorithm for Randomized Task Allocation in Fog Computing SystemsManuscript (preprint) (Other academic)

Fog computing is identified as a key enablerfor using various emerging applications by battery poweredand computationally constrained devices. In this paper, weconsider devices that aim at improving their performanceby choosing to offload their computational tasks to nearbydevices or to a cloud server. We develop a game theoreticalmodel of the problem, and we use variational inequalitytheory to compute an equilibrium task allocation in staticmixed strategies. Based on the computed equilibrium strategy,we develop a decentralized algorithm for allocating thecomputational tasks among nearby devices and the cloudserver. We use extensive simulations to provide insight intothe performance of the proposed algorithm, and we compareits performance with the performance of a myopic bestresponse algorithm that requires global knowledge of thesystem state. Despite the fact that the proposed algorithmrelies on average system parameters only, our results showthat it provides good system performance close to that of themyopic best response algorithm.

• 32.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Decentralized Scheduling for Offloading of Periodic Tasks in Mobile Edge Computing2018In: IFIP NETWORKING 2018, 2018Conference paper (Refereed)

Motivated by various surveillance applications, we consider wireless devices that periodically generate computationally intensive tasks. The devices aim at maximizing their performance by choosing when to perform the computations and whether or not to offload their computations to a cloud resource via one of multiple wireless access points. We propose a game theoretic model of the problem, give insight into the structure of equilibrium allocations and provide an efficient algorithm for computing pure strategy Nash equilibria. Extensive simulation results show that the performance in equilibrium is significantly better than in a system without coordination of the timing of the tasks’ execution, and the proposed algorithm has an average computational complexity that is linear in the number of devices.

• 33.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Privacy Preservation through Uniformity2018In: Proceedings of the ACM Conference on Security and Privacy in Wireless & Mobile Networks (WiSec), Stockholm, Sweden, June 2018., ACM Digital Library, 2018Conference paper (Refereed)

Inter-vehicle communications disclose rich information about vehicle whereabouts. Pseudonymous authentication secures communication while enhancing user privacy thanks to a set of anonymized certificates, termed pseudonyms. Vehicles switch the pseudonyms (and the corresponding private key) frequently; we term this pseudonym transition process. However, exactly because vehicles can in principle change their pseudonyms asynchronously, an adversary that eavesdrops (pseudonymously) signed messages, could link pseudonyms based on the times of pseudonym transition processes. In this poster, we show how one can link pseudonyms of a given vehicle by simply looking at the timing information of pseudonym transition processes. We also propose "mix-zone everywhere": time-aligned pseudonyms are issued for all vehicles to facilitate synchronous pseudonym update; as a result, all vehicles update their pseudonyms simultaneously, thus achieving higher user privacy protection.

• 34.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Privacy preservation through uniformity2018In: WiSec 2018 - Proceedings of the 11th ACM Conference on Security and Privacy in Wireless and Mobile Networks, Association for Computing Machinery, Inc , 2018, p. 279-280Conference paper (Refereed)

Inter-vehicle communications disclose rich information about vehicle whereabouts. Pseudonymous authentication secures communication while enhancing user privacy thanks to a set of anonymized certificates, termed pseudonyms. Vehicles switch the pseudonyms (and the corresponding private key) frequently; we term this pseudonym transition process. However, exactly because vehicles can in principle change their pseudonyms asynchronously, an adversary that eavesdrops (pseudonymously) signed messages, could link pseudonyms based on the times of pseudonym transition processes. In this poster, we show how one can link pseudonyms of a given vehicle by simply looking at the timing information of pseudonym transition processes. We also propose ''mix-zone everywhere'': time-aligned pseudonyms are issued for all vehicles to facilitate synchronous pseudonym update; as a result, all vehicles update their pseudonyms simultaneously, thus achieving higher user privacy protection.

• 35.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Efficient, Scalable, and Resilient Vehicle-Centric Certificate Revocation List Distribution in VANETs2018In: Proceedings of the ACM Conference on Security and Privacy in Wireless & Mobile Networks (WiSec), Stockholm, Sweden, June 2018., 2018Conference paper (Refereed)

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 (50×50 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.

• 36.
KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Modeling Enterprise Authorization: A Unified Metamodel and Initial Validation2016In: Complex Systems Informatics and Modeling Quarterly, ISSN 2255-9922, no 7, p. 1-24Article in journal (Refereed)

Authorization and its enforcement, access control, have stood at the beginning of the art and science of information security, and remain being crucial pillar of security in the information technology and  enterprises operations. Dozens of different models of access control have been proposed. Although Enterprise Architecture as the discipline strives to support the management of IT, support for modeling access policies in enterprises is often lacking, both in terms of supporting the variety of individual models of access control nowadays used, and in terms of providing a unified ontology capable of flexibly expressing access policies for all or the most of the models.This study summarizes a number of existing models of access control, proposes an unified metamodel mapped to ArchiMate, and illustrates its use on a selection of example scenarios and two cases.

• 37.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Automated Probabilistic System Architecture Analysis in the Multi-Attribute Prediction Language (MAPL): Iteratively Developed using Multiple Case Studies2017In: International Journal of Complex Systems Informatics and Modeling Quarterly (CSIMQ), Vol. June/July, no 11, p. 38-68Article in journal (Refereed)

The Multi-Attribute Prediction Language (MAPL), an analysis metamodel for non-functional qualities of system architectures, is introduced. MAPL features automate analysis in five non-functional areas: service cost, service availability, data accuracy, application coupling, and application size. In addition, MAPL explicitly includes utility modeling to make trade-offs between the qualities. The article introduces how each of the five non-functional qualities are modeled and quantitatively analyzed based on the ArchiMate standard for enterprise architecture modeling and the previously published Predictive, Probabilistic Architecture Modeling Framework, building on the well-known UML and OCL formalisms. The main contribution of MAPL lies in the probabilistic use of multi-attribute utility theory for the trade-off analysis of the non-functional properties. Additionally, MAPL proposes novel model-based analyses of several non-functional attributes. We also report how MAPL has iteratively been developed using multiple case studies.

• 38.
Huawei Technol, Ireland Res Ctr, Dublin D01 R3K6 1, Ireland.;Univ Cyprus, KIOS Res & Innovat Ctr Excellence, CY-1678 Nicosia, Cyprus..
Univ Minho, Algoritmi Res Ctr, P-4800058 Guimaraes, Portugal.. Hanyang Univ, Dept Elect Engn, Seoul 04763, South Korea.. Korea Aerosp Res Inst, Nav Res & Dev Div, Daejeon 34133, South Korea.. HERE, Enterprise Indoor Positioning Solut, Tampere 33100, Finland.. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. ..
A Survey of Enabling Technologies for Network Localization, Tracking, and Navigation2018In: IEEE Communications Surveys and Tutorials, ISSN 1553-877X, E-ISSN 1553-877X, Vol. 20, no 4, p. 3607-3644Article in journal (Refereed)

Location information for events, assets, and individuals, mostly focusing on two dimensions so far, has triggered a multitude of applications across different verticals, such as consumer, networking, industrial, health care, public safety, and emergency response use cases. To fully exploit the potential of location awareness and enable new advanced location-based services, localization algorithms need to be combined with complementary technologies including accurate height estimation, i.e., three dimensional location, reliable user mobility classification, and efficient indoor mapping solutions. This survey provides a comprehensive review of such enabling technologies. In particular, we present cellular localization systems including recent results on 5G localization, and solutions based on wireless local area networks, highlighting those that are capable of computing 3D location in multi-floor indoor environments. We overview range-free localization schemes, which have been traditionally explored in wireless sensor networks and are nowadays gaining attention for several envisioned Internet of Things applications. We also present user mobility estimation techniques, particularly those applicable in cellular networks, that can improve localization and tracking accuracy. Regarding the mapping of physical space inside buildings for aiding tracking and navigation applications, we study recent advances and focus on smartphone-based indoor simultaneous localization and mapping approaches. The survey concludes with service availability and system scalability considerations, as well as security and privacy concerns in location architectures, discusses the technology roadmap, and identifies future research directions.

• 39.
ABB Corp Res, S-72226 Vasteras, Sweden.. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. Univ Oslo, Dept Informat, Fog Comp, N-0315 Oslo, Norway.. Linkoping Univ, S-58183 Linkoping, Sweden.;Linkoping Univ, Commun Elect, S-58183 Linkoping, Sweden..
A Taxonomy for the Security Assessment of IP-Based Building Automation Systems: The Case of Thread2018In: IEEE Transactions on Industrial Informatics, ISSN 1551-3203, E-ISSN 1941-0050, Vol. 14, no 9, p. 4113-4123Article in journal (Refereed)

Motivated by theproliferation of wireless building automation systems (BAS) and increasing security-awareness among BAS operators, in this paper, we propose a taxonomy for the security assessment of BASs. We apply the proposed taxonomy to Thread, an emerging native IP-based protocol for BAS. Our analysis reveals a number of potential weaknesses in the design of Thread. We propose potential solutions for mitigating several identified weaknesses and discuss their efficacy. We also provide suggestions for improvements in future versions of the standard. Overall, our analysis shows that Thread has a well-designed security control for the targeted use case, making it a promising candidate for communication in next generation BASs.

• 40. Luvisotto, M.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Physical Layer Design of High-Performance Wireless Transmission for Critical Control Applications2017In: IEEE Transactions on Industrial Informatics, ISSN 1551-3203, E-ISSN 1941-0050, Vol. 13, no 6, p. 2844-2854, article id 7924385Article in journal (Refereed)

The next generations of industrial control systems will require high-performance wireless networks (named WirelessHP) able to provide extremely low latency, ultrahigh reliability, and high data rates. The current strategy toward the realization of industrial wireless networks relies on adopting the bottom layers of general purpose wireless standards and customizing only the upper layers. In this paper, a new bottom-up approach is proposed through the realization of a WirelessHP physical layer specifically targeted at reducing the communication latency through the minimization of packet transmission time. Theoretical analysis shows that the proposed design allows a substantial reduction in packet transmission time, down to 1 $\mu$ s, with respect to the general purpose IEEE 802.11 physical layer. The design is validated by an experimental demonstrator, which shows that reliable communications up to 20 m range can be established with the proposed physical layer.

• 41.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH - Royal Institute of Technology.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Convergence of Limited Communication Gradient Methods2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523Article in journal (Refereed)

Distributed optimization increasingly plays a centralrole in economical and sustainable operation of cyber-physicalsystems. Nevertheless, the complete potential of the technologyhas not yet been fully exploited in practice due to communicationlimitations posed by the real-world infrastructures. This workinvestigates fundamental properties of distributed optimizationbased on gradient methods, where gradient information iscommunicated using limited number of bits. In particular, ageneral class of quantized gradient methods are studied wherethe gradient direction is approximated by a finite quantizationset. Sufficient and necessary conditions are provided on sucha quantization set to guarantee that the methods minimize anyconvex objective function with Lipschitz continuous gradient anda nonempty and bounded set of optimizers. A lower bound on thecardinality of the quantization set is provided, along with specificexamples of minimal quantizations. Convergence rate results areestablished that connect the fineness of the quantization andthe number of iterations needed to reach a predefined solutionaccuracy. Generalizations of the results to a relevant class ofconstrained problems using projections are considered. Finally,the results are illustrated by simulations of practical systems.

• 42.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Harvard Univ, Sch Engn & Appl Sci, Cambridge, MA 02138 USA.. Harvard Univ, Sch Engn & Appl Sci, Cambridge, MA 02138 USA.. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. Harvard Univ, Sch Engn & Appl Sci, Cambridge, MA 02138 USA..
Convergence of Limited Communication Gradient Methods2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, no 5, p. 1356-1371Article in journal (Refereed)

Distributed optimization increasingly plays a central role in economical and sustainable operation of cyber-physical systems. Nevertheless, the complete potential of the technology has not yet been fully exploited in practice due to communication limitations posed by the real-world infrastructures. This work investigates fundamental properties of distributed optimization based on gradient methods, where gradient information is communicated using a limited number of bits. In particular, a general class of quantized gradient methods are studied, where the gradient direction is approximated by a finite quantization set. Sufficient and necessary conditions are provided on such a quantization set to guarantee that the methods minimize any convex objective function with Lipschitz continuous gradient and a nonempty and bounded set of optimizers. A lower bound on the cardinality of the quantization set is provided, along with specific examples of minimal quantizations. Convergence rate results are established that connect the fineness of the quantization and the number of iterations needed to reach a predefined solution accuracy. Generalizations of the results to a relevant class of constrained problems using projections are considered. Finally, the results are illustrated by simulations of practical systems.

• 43.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
VPKIaaS: A Highly-Available and Dynamically-Scalable Vehicular Public-Key Infrastructure2018In: Proceedings of the ACM Conference on Security and Privacy in Wireless & Mobile Networks (WiSec), Stockholm, Sweden, June 2018., ACM Digital Library, 2018Conference paper (Refereed)

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 (and 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. In this extended abstract, we leverage the state-of-the-art VPKI system and enhance its functionality towards a highly-available and dynamically-scalable design; this ensures that the system remains operational in the presence of benign failures or any resource depletion attack, and that it dynamically scales out, or possibly scales in, according to the requests’ arrival rate. Our full-blown implementation on the Google Cloud Platform shows that deploying a VPKI for a large-scale scenario can be cost-effective, while efficiently issuing pseudonyms for the requesters.

• 44.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
VPKIaaS: A highly-available and dynamically-scalable vehicular public-key infrastructure2018In: WiSec 2018 - Proceedings of the 11th ACM Conference on Security and Privacy in Wireless and Mobile Networks, Association for Computing Machinery, Inc , 2018, p. 302-304Conference paper (Refereed)

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 (and 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. In this extended abstract, we leverage the state-of-the-art VPKI system and enhance its functionality towards a highly-available and dynamically-scalable design; this ensures that the system remains operational in the presence of benign failures or any resource depletion attack, and that it dynamically scales out, or possibly scales in, according to the requests' arrival rate. Our full-blown implementation on the Google Cloud Platform shows that deploying a VPKI for a large-scale scenario can be cost-effective, while efficiently issuing pseudonyms for the requesters.

• 45.
KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH. KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Learning-based Pilot Precoding and Combining for Wideband Millimeter-wave Networks2017In: 2017 IEEE 7TH INTERNATIONAL WORKSHOP ON COMPUTATIONAL ADVANCES IN MULTI-SENSOR ADAPTIVE PROCESSING (CAMSAP), IEEE , 2017Conference paper (Refereed)

This paper proposes an efficient channel estimation scheme with a minimum number of pilots for a frequency-selective millimeter-wave communication system. We model the dynamics of the channel's second-order statistics by a Markov process and develop a learning framework that finds the optimal precoding and combining vectors for pilot signals, given the channel dynamics. Using these vectors, the transmitter and receiver will sequentially estimate the corresponding angles of departure and arrival, and then refine the pilot precoding and combining vectors to minimize the error of estimating the small-scale fading of all subcarriers. Numerical results demonstrate near-optimality of our approach, compared to the oracle wherein the second-order statistics (not the dynamics) are perfectly known a priori.

• 46.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Performance Analysis of Opportunistic Content Distribution via Data-Driven Mobility Modeling2018Doctoral thesis, comprehensive summary (Other academic)

An opportunistic network is formed by co-located mobile users in order to exchange data via direct wireless links when their devices are within transmission range, without relying on the use of fixed network infrastructure. In this thesis we investigate the capabilities of opportunistic networks and cover two main areas: data-driven modeling of user mobility and analytic performance evaluation of location-aware opportunistic content distribution.

The first part of the thesis focuses on mobility modeling. We collect a dataset of user associations in the wireless network of the KTH Royal Institute of Technology, and characterize the mobility of users in this dataset both from the network and from the user perspective. From the network perspective, we model the aggregate mobility and access patterns to different parts of the network. To characterize individual mobility, we assess how mobile the users are, and how accurately their movements can be predicted in the near future. Based on these findings, and on the analysis of several other mobility traces, we propose a mobility model for populations with churn, that is specifically tailored for the evaluation of opportunistic content distribution. In the second part of the thesis, we evaluate the performance of opportunistic content distribution in ephemeral, location-aware networks where content is stored only on the user devices within the locale of interest. We develop a framework that allows modeling of the spread of information as a stochastic process and accurate capturing of the stochastic fluctuations in the number of distributed content items. We study the feasibility of opportunistic content distribution and, by means of stochastic stability analysis, assess how the system parameters can be engineered to ensure content persistence. We show that the content persistence strongly depends on the density of users, and that the requirements for user resources are relatively low already for moderate densities.

• 47.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. Tech Univ Munich, Dept Informat, Munich, Germany.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Ensuring Persistent Content in Opportunistic Networks via Stochastic Stability Analysis2018In: ACM Transactions on Modeling and Performance Evaluation of Computing Systems (TOMPECS), ISSN 2376-3639, Vol. 3, no 4, p. 16:1-16:23, article id 16Article in journal (Refereed)

The emerging device-to-device communication solutions and the abundance of mobile applications and services make opportunistic networking not only a feasible solution but also an important component of future wireless networks. Specifically, the distribution of locally relevant content could be based on the community of mobile users visiting an area, if long-term content survival can be ensured this way. In this article, we establish the conditions of content survival in such opportunistic networks, considering the user mobility patterns, as well as the time users keep forwarding the content, as the controllable system parameter.

We model the content spreading with an epidemic process, and derive a stochastic differential equations based approximation. By means of stability analysis, we determine the necessary user contribution to ensure content survival. We show that the required contribution from the users depends significantly on the size of the population, that users need to redistribute content only in a short period within their stay, and that they can decrease their contribution significantly in crowded areas. Hence, with the appropriate control of the system parameters, opportunistic content sharing can be both reliable and sustainable.

• 48.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. Tech Univ Munich, Dept Informat, Munich, Germany.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Predicting the Users’ Next Location From WLAN Mobility Data2018In: 2018 IEEE International Symposium on Local and Metropolitan Area Networks (LANMAN), 2018Conference paper (Refereed)

Accurate prediction of user mobility allows the efficient use of resources in our ubiquitously connected environment. In this work we study the predictability of the users’ next location, considering a campus scenario with highly mobile users. We utilize Markov predictors, and estimate the theoretical predictability limits. Based on the mobility traces of nearly 7400 wireless network users, we estimate that the maximum predictability of the users is on average 82%, and we find that the best Markov predictor is accurate 67% of the time. In addition, we show that moderate performance gains can be achieved by leveraging multi-location prediction.

• 49.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. Tech Univ Munich, Dept Informat, Munich, Germany.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Revisiting the Modeling of User Association Patterns in a University Wireless Network2018In: 2018 IEEE WIRELESS COMMUNICATIONS AND NETWORKING CONFERENCE (WCNC), IEEE , 2018Conference paper (Refereed)

This paper presents an analysis of a large trace of user associations in a university wireless network, which includes around one thousand access points over live campuses. The trace is obtained from RADIUS authentication logs and its merit is in its recency, scale and duration. We propose a methodology for extracting association statistics from these logs, and look at visiting time distributions and processes of user arrivals to access points. We find that a large fraction of the network-around half of all access points-experiences time-varying Poisson arrival process, and association distributions can be modeled by two-stage hyper-exponential distributions at most of the access point. While network associations in campus wireless networks have been extensively studied in the literature, our study reveals changing patterns in user arrival processes and association durations, which seem to be characteristic for networks of predominantly mobile users, and allows the use of tractable network occupancy models.

• 50.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
Interference Model Similarity Index and Its Applications to Millimeter-Wave Networks2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 1, p. 71-85Article in journal (Refereed)

In wireless communication networks, interference models are routinely used for tasks, such as performance analysis, optimization, and protocol design. These tasks are heavily affected by the accuracy and tractability of the interference models. Yet, quantifying the accuracy of these models remains a major challenge. In this paper, we propose a new index for assessing the accuracy of any interference model under any network scenario. Specifically, it is based on a new index that quantifies the ability of any interference model in correctly predicting harmful interference events, that is, link outages. We consider specific wireless scenario of both conventional sub-6 GHz and millimeter-wave networks and demonstrate how our index yields insights into the possibility of simplifying the set of dominant interferers, replacing a Nakagami or Rayleigh random fading by an equivalent deterministic channel, and ignoring antenna sidelobes. Our analysis reveals that in highly directional antenna settings with obstructions, even simple interference models (such as the classical protocol model) are accurate, while with omnidirectional antennas, more sophisticated and complex interference models (such as the classical physical model) are necessary. Our new approach makes it possible to adopt the simplest interference model of adequate accuracy for every wireless network.

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