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| 2. |
- Gundlegård, David
(författare)
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Generating Road Traffic Information Based on Cellular Network Signaling
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cellular networks of today generate a massive amount of signalling data. A large part of this signalling is generated to handle the mobility of subscribers, irrespective of the subscriber actively uses the terminal or not. Hence it contains location information that can be used to fundamentally change our understanding of human travel patterns.This thesis aims to analyse the potential and limitations of using this signalling data in the context of road traffic information, i.e. how we can estimate the road network traffic state based on standard signalling data already available in cellular networks. This is achieved by analytical examination and experiments with signalling data and measurements generated by standard cell phones.The thesis describes the location data that is available from signalling messages in GSM, GPRS and UMTS networks, both in idle mode and when engaged in a telephone call or a data session. The signalling data available in a ll three networks is useful to estimate traffic information, although the resolution in time and space will to a large extent depend on in which mode the terminal is operating.Spatial analysis of handover signalling data has been performed for terminals engaged in telephone calls. The analysis indicates that handover events from both GSM and UMTS networks can be used as efficient input to systems for travel time estimation, given that route classification and filtering of non -vehicle terminals can be solved.By analysing signalling data and received signal strength (RSS) measur ements from cell phones, it can be seen the route classification problem in the context of estimating travel times based on handover events is non -trivial even for highway environments. However, it is presented that the problem can be sa tisfactory solved for highway environments by using basic classification methods, like for example Bayesian classification.Furthermore the thesis points out that the new era of smartphones can be an enabler for road traffic information from cellular networks in the close future. By examining measurements collected by a smartphone client, it is illu strated how the radio map for cell phone positioning can be built by participatory sensing. It is also shown that the location accuracy of RSS-based cell phone positioning is accurate enough to p rovide both travel time and OD-matrix estimation.
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| 3. |
- Kuiper, Erik, 1973-
(författare)
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Geographic Routing in Intermittently-connected Mobile Ad Hoc Networks : Algorithms and Performance Models
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Communication is a key enabler for cooperation. Thus to support efficient communication humanity has continuously strived to improve the communication infrastructure. This infrastructure has evolved from heralds and ridden couriers to a digital telecommunication infrastructures based on electrical wires, optical fibers and radio links. While the telecommunication infrastructure efficiently transports information all over the world, there are situations when it is not available or operational. In many military operations, and disaster areas, one cannot rely on the telecommunication infrastructure to support communication since it is either broken, or does not exist. To provide communication capability in its absence, ad hoc networking technology can be used to provide a dynamic peer-based communication mechanism. In this thesis we study geographic routing in intermittently connected mobile ad hoc networks (IC-MANETs).For routing in IC-MANETs we have developed a beacon-less delay-tolerant geographic routing protocol named LAROD (location aware routing for delay-tolerant networks) and the delay-tolerant location service LoDiS (location dissemination service). To be able to evaluate these protocols in a realistic environment we have used a military reconnaissance mission where unmanned aerial vehicles employ distributed coordination of their monitoring using pheromones. To be able to predict routing performance more efficiently than by the use of simulation, we have developed a mathematical framework that efficiently can predict the routing performance of LAROD-LoDiS. This framework, the forward-wait framework, provides a relationship between delivery probability, distance, and delivery time. Provided with scenario specific data the forward-wait framework can predict the expected scenario packet delivery ratio.LAROD-LoDiS has been evaluated in the network simulator ns-2 against Spray and Wait, a leading delay-tolerant routing protocol, and shown to have a competitive edge, both in terms of delivery ratio and overhead. Our evaluations also confirm that the routing performance is heavily influenced by the mobility pattern. This fact stresses the need for representative mobility models when routing protocols are evaluated.
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| 4. |
- Lei, Lei
(författare)
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From Orthogonal to Non-orthogonal Multiple Access : Energy- and Spectrum-Efficient Resource Allocation
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The rapid pace of innovations in information and communication technology (ICT) industry over the past decade has greatly improved people’s mobile communication experience. This, in turn, has escalated exponential growth in the number of connected mobile devices and data traffic volume in wireless networks. Researchers and network service providers have faced many challenges in providing seamless, ubiquitous, reliable, and high-speed data service to mobile users. Mathematical optimization, as a powerful tool, plays an important role in addressing such challenging issues.This dissertation addresses several radio resource allocation problems in 4G and 5G mobile communication systems, in order to improve network performance in terms of throughput, energy, or fairness. Mathematical optimization is applied as the main approach to analyze and solve the problems. Theoretical analysis and algorithmic solutions are derived. Numerical results are obtained to validate our theoretical findings and demonstrate the algorithms’ ability of attaining optimal or near-optimal solutions.Five research papers are included in the dissertation. In Paper I, we study a set of optimization problems of consecutive-channel allocation in single carrier-frequency division multiple access (SCFDMA) systems. We provide a unified algorithmic framework to optimize the channel allocation and improve system performance. The next three papers are devoted to studying energy-saving problems in orthogonal frequency division multiple access (OFDMA) systems. In Paper II, we investigate a problem of jointly minimizing energy consumption at both transmitter and receiver sides. An energy-efficient scheduling algorithm is developed to provide optimality bounds and near-optimal solutions. Next in Paper III, we derive fundamental properties for energy minimization in loadcoupled OFDMA networks. Our analytical results suggest that the maximal use of time-frequency resources can lead to the lowest network energy consumption. An iterative power adjustment algorithm is developed to obtain the optimal power solution with guaranteed convergence. In Paper IV, we study an energy minimization problem from the perspective of scheduling activation and deactivation of base station transmissions. We provide mathematical formulations and theoretical insights. For problem solution, a column generation approach, as well as a bounding scheme are developed. Finally, towards to 5G communication systems, joint power and channel allocation in non-orthogonal multiple access (NOMA) is investigated in Paper V in which an algorithmic solution is proposed to improve system throughput and fairness.
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| 5. |
- Tatino, Cristian, 1988-
(författare)
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Analysis and Optimization for Robust Millimeter-Wave Communications
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Spectrum scarcity is a longstanding problem in mobile telecommunications networks. Specifically, accommodating the ever-growing data rate and communications demand in the extensively used spectrum between 800 MHz and 6 GHz is becoming more challenging. For this reason, in the last years, communications in the millimeterwave (mm-wave) frequency range (30-300 GHz) have attracted the interest of many researchers, who consider mm-wave communications a key enabler for upcoming generations of mobile communications, i.e., 5G and 6G. However, the signal propagation in the mm-wave frequency range is subject to more challenging conditions. High path loss and penetration loss may lead to short-range communications and frequent transmission interruptions when the signal path between the transmitter and the receiver is blocked. In this dissertation, we analyze and optimize techniques that enhance the robustness and reliability of mm-wave communications. In the first part, we focus on approaches that allow user equipment (UE) to establish and maintain connections with multiple access points (APs) or relays, i.e., multi-connectivity (MC) and relaying techniques, to increase link failure robustness. In such scenarios, an inefficient link scheduling, i.e., over or under-provisioning of connections, can lead to either high interference and energy consumption or unsatisfied user’s quality of service (QoS) requirements. In the first paper, we propose a novel link scheduling algorithm for network throughput maximization with constrained resources and quantify the potential gain of MC. As a complementary approach, in the second paper, we solve the problem of minimizing allocated resources while satisfying users’ QoS requirements for mm-wave MC scenarios. To deal with the channel uncertainty and abrupt blockages, we propose a learning-based solution, of which the results highlight the tradeoff between reliability and allocated resource. In the third paper, we perform throughput and delay analysis of a multi-user mm-wave wireless network assisted by a relay. We show the benefits of cooperative networking and the effects of directional communications on relay-aided mm-wave communications. These, as highlighted by the results, are characterized by a tradeoff between throughput and delay and are highly affected by the beam alignment duration and transmission strategy (directional or broadcast). The second part of this dissertation focuses on problems related to mm-wave communications in industrial scenarios, where robots and new industrial applications require high data rates, and stringent reliability and latency requirements. In the fourth paper, we consider a multi-AP mm-wave wireless network covering an industrial plant where multiple moving robots need to be connected. We show how the joint optimization of robots’ paths and the robot-AP associations can increase mm-wave robustness by decreasing the number of handovers and avoiding coverage holes. Finally, the fifth paper considers scenarios where robot-AP communications are assisted by an intelligent reflective surface (IRS). We show that the joint optimization of beamforming and trajectory of the robot can minimize the motion energy consumption while satisfying time and communication QoS constraints. Moreover, the proposed solution exploits a radio map to prevent collisions with obstacles and to increase mm-wave communication robustness by avoiding poorly covered areas.
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| 6. |
- He, Qing
(författare)
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A Comprehensive Analysis of Optimal Link Scheduling for Emptying a Wireless Network
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless communications have become an important part of modern life. The ubiquitous wireless networks and connectivities generate exponentially increasing data traffic. In view of this, wireless network optimization, which aims at utilizing the limited resource, especially spectrum and energy, as efficiently as possible from a network perspective, is essential for performance improvement and sustainable development of wireless communications.In the dissertation, we focus on a fundamental problem of wireless network optimization, link scheduling, as well as its subproblem, link activation. The problem type arises because of the nature of wireless media and hence it is of relevance to a wide range of networks with multiple access. We freshen these classic problems up by novel extensions incorporating new technologies of interference management or with new performance metrics. We also revisit the problems in their classic setup to gain new theoretical results and insights for problem-solving. Throughout the study, we consider the problems with a general setup, such that the insights presented in this dissertation are not constrained to a specific technology or network type. Since link activation and scheduling are key elements of access coordination in wireless communications, the study opens up new approaches that significantly improve network performance, and eventually benefit practical applications.The dissertation consists of five research papers. The first paper addresses maximum link activation with cooperative transmission and interference cancellation. Papers II and III investigate the minimum-time link scheduling problem in general and a particular class of networks, respectively. In Paper IV, we consider the scheduling problem of emptying a network in its broad form and provide a general optimality condition. In Paper V, we study the scheduling problem with respect to age of information.
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| 7. |
- Modarres Razavi, Sara, 1981-
(författare)
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Planning and Optimization of Tracking Areas for Long Term Evolution Networks
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Along with the evolution of network technologies, user’s expectations on performance and mobile services are rising rapidly. To fulfill the customer demands the operators are facing a great amount of network signaling overhead in terms of Location Management (LM), which tracks and pages User Equipments (UEs) in the network. Hence, sustaining a reliable and cost-efficient LM system for future mobile broadband networks has become one of the major challenges in mobile telecommunications. Tracking Area (TA) in Long Term Evolution (LTE), is a logical grouping of cells, that manages and represents the locations of UEs. This dissertation deals with planning and optimization of TAs.TA design must be revised over time in order to adapt to changes and trends in UE location and mobility patterns. Re-optimization of a once-optimized design subject to different cost budgets is one of the problems considered in this dissertation. By re-optimization, the design is successively improved by re-assigning some cells to TAs other than their original ones. For solving the resulting problem, an algorithm based on repeated local search is developed.The next topic of research is the trade-off between the performance in terms of the total signaling overhead of the network and the reconfiguration cost. This trade-off is modeled as a bi-objective optimization problem to which the solutions are characterized by Pareto-optimality. Solving the problem delivers a host of potential trade-offs among which the selection can be based on the preferences of a decision-maker. An integer programming model and a genetic algorithm heuristic are developed for solving the problem in large-scale networks.In comparison to previous generations of cellular networks, LTE systems allow for a more flexible configuration of TA design by means of Tracking Area List (TAL). How to utilize this flexibility in applying TAL to large-scale networks is still an open problem. In this dissertation, three approaches for allocating and assigning TALs are presented, and their performances are compared with each other, as well as with the conventional TA scheme. Moreover, a linear programming model is developed to minimize the total signaling overhead of the network based on overlapping TALs.In this dissertation, the problem of mitigating signaling congestion is thoroughly studied both for the specific train scenario and also for the general network topology. For each signaling congestion scenario, a related linear programming model based on minimizing the maximum signaling due to tracking area update or paging is developed. As a major advantage of the modified overlapping TAL scheme for signaling congestion avoidance, information of individual UE mobility is not required.Automatic reconfiguration of LM is an important element in LTE. The network continuously collects UE statistics, and the management system adapts the network configuration to changes in UE distribution and demand. In this dissertation an evaluation of dynamic configuration of TA design, including the use of overlapping TAL for congestion mitigation, is performed and compared to the static configuration by using a case study.
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| 8. |
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| 9. |
- Ahani, Ghafour
(författare)
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Optimal Scheduling for Timely Information in Communication Systems
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The explosive growth of data in information society poses significant challenges in the timely delivery of information in the context of communication networks. Hence, optimal utilization of scarce network resources is crucial. This dissertation contributes to several aspects related to the timely delivery of information, including scheduling of data flows between sources and destinations in a network, scheduling of content caching in a base station of mobile networks, and scheduling of information collection. Two important metrics, namely, delivery deadline and information freshness, are accounted for. Mathematical models and tailored solution approaches are developed via tools from optimization.Five research papers are included in the dissertation. Paper I studies a flow routing and scheduling problem with delivery deadline. This type of problem arises in many applications such as data exchange in scientific projects or data replication in data centers where large amounts of data need to be timely distributed across the globe. Papers II, III, and IV investigate content caching along time in a base station. Content caching at the network’s edge has recently been considered a costefficient way of providing users with their requested information. In Paper II, the schedule for updating the cache is optimized with respect to the content requests of users and the popularity of contents over time. Paper III, as an extension of Paper II, addresses the question of how to keep the cache information fresh, as all contents can not be updated due to the limited capacity of the backhaul link. The freshness of information is quantified via the notion of age of information (AoI). Paper IV investigates joint optimization of content caching as well as recommendation; the latter contributes to satisfying content requests in case of a cache miss. Paper V studies optimal scheduling of information collection from a set of sensor nodes via an unmanned aerial vehicle. The objective is to keep the overall AoI as small as possible.In these studies, analysis of problem complexity is provided, and timeefficient solution algorithms based on column generation, Lagrangian decomposition, and graph labeling are developed. The algorithms also yield a bound of global optimum, that can be used to assess the performance of any given solution. The effectiveness of the algorithms in obtaining nearoptimal solutions is demonstrated via extensive simulations.
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| 10. |
- Chen, Lei, 1981-
(författare)
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Coverage Planning and Resource Allocation in Broadband Cellular Access : Optimization Models and Algorithms
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The last two decades have witnessed a booming in the use of cellular communication technologies. Billions of people are now enjoying the benefits of mobile communications. This thesis deals with planning and optimization of broadband cellular access network design and operation. The problem types considered include coverage planning, power optimization, and channel assignment. Mathematical modeling and optimization methods have been used to approach the problems.Coverage planning is a classical problem in cellular network deployment. A minimum-power covering problem with overlap constraints between cell pairs is considered. The objective is to minimize the total power consumption for coverage, while maintaining a necessary level of overlap to facilitate handover. For this coverage planning problem, the thesis develops two integer programming models and compares the models' strength in approaching global optimality. In addition, a tabu search algorithm has been developed for solving the problem in large-scale networks.For High Speed Downlink Packet Access (HSDPA) networks, transmission power is a crucial factor to performance. Minimizing the power allocated for coverage enables significant power saving that can be used for HSDPA data transmission, thus enhancing the HSDPA performance. Exploring this potential power saving, a mathematical model targeting cell-edge HSDPA performance has been developed. In determining the optimal coverage pattern for maximizing power saving, the model also allows for controlling the degree of soft handover for Universal Mobile Telecommunications System (UMTS) Release 99 services. In addition to the mathematical model, heuristic algorithms based on local search and repeated local search are developed.For Orthogonal Frequency Division Multiple Access (OFDMA), which is used in Long Term Evolution (LTE) networks, inter-cell interference control is a key performance engineering issue. The aspect is of particular importance to cell-edge throughput. Frequency reuse schemes for mitigating inter-cell interference at cell-edge areas have received an increasing amount of research attention. In the thesis, a generalization of the standard Fractional Frequency Reuse (FFR) scheme is introduced. The generalization addresses OFDMA networks with irregular cell layout. Optimization algorithms using local search have been proposed to find the frequency reuse pattern of generalized FFR that maximizes the cell-edge area performance.For the problems considered in the thesis, computational experiments of the optimization models and algorithms using data sets representing realistic planning scenarios have been carried out. The experimental results demonstrate the effectiveness of the proposed solution approaches.
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