| 1. |
- Chang, Peiliang, 1987-
(författare)
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Cross-Layer Energy-Efficient Mobile Network Design
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To assure the sustainable development of mobile networks, it is crucial to improve their energy efficiency. This thesis is devoted to the design of energy-efficient mobile networks. A cross-layer design approach is adopted. The resource management at the MAC layer, the network layer as well as the service layer are optimized to improve the energy efficiency of mobile networks. The problem of optimizing the MAC-layer resource allocation of the downlink transmission in multi-carrier NOMA systems to maximize the system energy efficiency while satisfying users’ QoS requirements is firstly considered. The optimal power allocation across sub-carriers and across users sharing one sub-carrier are proposed. Furthermore, exploiting the structure of the optimal power allocation across users sharing one sub-carrier, a sub-optimal solution for sub-carrier assignment, which greedily minimizes the required power to serve all users with required QoS, is developed. Besides optimizing the channel assignment and power allocation within a single cell, the link scheduling in the multi-cell scenario to deal with inter-cell interference is also studied. A scalable distributed link scheduling solution is proposed to orchestrate the transmission and DTX micro-sleep of multiple base stations such that both the inter-cell interference and the energy consumption are reduced. At the network layer, the operation of base station sleeping is optimized to improve the energy efficiency of mobile networks without deteriorating users’ QoS. The spectral and energy efficiency of mobile networks, where base stations are enabled with DTX, under different traffic load is firstly studied. It shows that as the networks are more loaded, the link spectral efficiency reduces while the network spectral efficiency increases. Regarding the network energy efficiency, it will either firstly increase and then decrease or always increase when the network load gets higher. The optimal network load to maximize the network energy efficiency depends on the power consumption of base stations in DTX sleep mode. Based on the findings of the above study, the joint optimization of cell DTX and deep sleep to maximize the network energy efficiency is investigated. A scaling law of transmit power, which assures that the distribution of the received power remains unchanged as more base stations are switched into deep sleep, is proposed. Then the average resource utilization and overload probability of non-deep-sleep base stations are derived. Based on these results, the feasible range of the percentage of deep-sleep base stations is obtained. Finally, the optimal percentage of deep-sleep base stations to maximize the network energy efficiency while satisfying users’ QoS requirements is derived. Lastly, the service-layer resource provision of edge computing in mobile networks is optimized to improve the energy efficiency. With this work, the trade-offs on service latency and energy consumption between the computation and the communication subsystems are studied. It is shown that the load of the communication subsystem and that of the computation subsystem should be balanced. Increasing the resource of the highly loaded subsystem can significantly reduce the required resource of the other subsystem. An algorithm is proposed to find out the optimal processing speed and the optimal number of active base stations that minimizes the overall energy consumption while assuring the requirements on the mean service latency.
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| 2. |
- Ganjalizadeh, Milad
(författare)
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Ultra-Reliable and Resilient Communication Service for Cyber-Physical Systems
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cyber-Physical Systems (CPSs) are becoming ubiquitous in modern society, enabling new applications that rely on the seamless interaction between computing, communication, and physical processes. In this context, ultra-reliable low-latency communications (URLLC) emerges as a crucial element, reliably allowing the real-time exchange of critical data.In wireless networks, reliability is commonly evaluated based on the percentage of packets delivered successfully, with timeliness sometimes considered. Nevertheless, in CPSs, performance is typically assessed by operational metrics such as availability (as the ability to provide service at any given time) and reliability (as the ability to maintain consistent service over an extended period). To bridge the gap between these two domains, we study the CPSs performance in terms of wireless communications and derive a mapping function between the well-known network metrics (such as packet error ratio) and operational metrics (namely communication service availability and reliability) for deterministic traffic arrivals. This thesis then deals with wireless system orchestration techniques that aim to facilitate URLLC for CPSs, factoring in spectrum and energy efficiency. It investigates two scenarios: i) a single service, where the focus is only on URLLC, and ii) mixed services, where other services simultaneously run on the same network as URLLC.In the first part, we assume that the impact of other nearby services on URLLC service is negligible. Accordingly, we concentrate on diversity techniques and power control as primary methods to enhance communication service availability and reliability at the cost of redundant transmissions and excessive resource usage. Thus, we devise a deep reinforcement learning (DRL) orchestrator that optimizes the number of hybrid automatic repeat request retransmissions and transmission power to enhance these metrics. We use a deep Q-network framework along with a branching soft actor-critic (BSAC) framework to address scalability issues in per-device orchestration. Our 3GPP-compliant simulations show that our approach achieves significant gains in computational time and memory requirements compared to the state-of-the-art. Besides, our approach requires substantially less energy or spectrum to achieve the target metrics. Additionally, we offer valuable insights into the practical implementation of DRL solutions for URLLC service in real-world wireless communication systems.In the second part, we examine mixed services with an emphasis on distributed learning as a coexistent service. We consider 5G-NR's quality of service mechanisms to prioritize URLLC traffic and develop models to characterize distributed training workflow in terms of training delay, model size, and convergence. This leads to an optimization problem that uses device selection to minimize distributed learning convergence time, while meeting URLLC availability requirements. We transform this coexistence problem into a DRL problem and tackle it with our adjusted BSAC framework. Our simulations reveal that our approach achieves URLLC service availability performance comparable to the scenario where all communication resources are solely dedicated to URLLC service, and significantly higher than the performance achieved using a static slicing approach with unvarying dedicated resources to slices. Finally, we propose a hierarchical reinforcement learning architecture for dynamic resource slicing on a large timescale, thereby enhancing network flexibility, scalability, and profitability.
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| 3. |
- Khosravi, Sara, 1987-
(författare)
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Seamless Millimeter-wave Connectivity via Efficient Beamforming and Handover
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Extremely high data rate demands, and the spectrum scarcity at the microwave bands, make the millimeter wave (mmWave) band a promising solution to satisfy the high data rate demands in wireless networks. The main advantage of moving to the mmWave spectrum is the availability of large bandwidth. Moreover, due to an order of magnitude smaller wavelength of mmWave signals in compared to the conventional bands, many antenna elements can be incorporated in a small size chip to provide high directivity gain both at the transmitter and the receiver sides.Millimeter wave links experience severe vulnerability to the obstacles compared to the conventional sub-6 GHz networks for two main reasons. First, due to the tiny wavelength, mmWave signals can easily be blocked by obstacles in the environment and this causes severe loss. Second, due to the use of directional communications to compensate for the high path-loss (the distance-dependent component of the attenuation), mmWave links are sensitive to blockages that leads to the high probability of beam misalignment and the frequent updating of beamforming vectors. These issues are more challenging in mobile scenarios, in which mobility of the users and obstacles cause frequent re-execution of the beamforming process. Therefore, the tradeoff between the latency of the beamforming process (which latency increases with the number of the re-execution of the beamforming process) and instantaneous user rate is a significant design challenge in mmWave networks. Moreover, to provide adequate coverage and capacity, the density of the base stations in mmWave networks is usually higher than the conventional sub-6 GHz network. This leads to frequent handovers that make maintaining and establishing the mmWave links more challenging.Motivated by the mentioned challenges, this thesis considers the beamforming and handover problems and proposes lightweight joint beamforming and handover methods to guarantee a certain data rate along user trajectory. Specifically, in the first thread of the thesis, inspired by the fundamental properties of the spacial channel response of mmWave links, we propose a beamforming method in mobile mmWave networks. Our analysis reveals that our proposed method is efficient in terms of signaling and computation complexity, power consumption, and throughput in compared to the benchmark. In the second thread of the thesis, we focus on the handover problem. We formulate the association problem that maximizes the trajectory rate while guarantees a predefined data rate threshold. We then extend our problem to the multi-user dense scenario that the density of the users is higher than the base stations and consider the resource allocation in the association optimization problem. We apply reinforcement learning in order to approximate the solution of the association problem. In general, the main objective of our proposed method is to maximize the sum rates of all the users and minimize the number of the handovers and reduce the probability of the events in which the users' rate becomes less than a predefined threshold. Simulation results confirm that our proposed handover method provides a reliable connection along a trajectory in compared to the benchmarks.
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| 4. |
- Markendahl, Jan, 1955-
(författare)
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Mobile Network Operators and Cooperation : A Tele-Economic Study of Infrastructure sharing and Mobile Payment Services
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mobile network operators are currently faced with a number of challenges at the market. The revenues from voice services have decreased the last couple of years. Mobile broadband access services are being adopted and the demand is increasing. The increasing traffic volumes require investments in order to increase the network capacity. This development leads to a large interest in network solutions that can offer high capacity and low cost. Besides the use of more efficient radio access technology mobile network operators use strategies for network deployment and operation involving other market actors. Operators share networks with competitors or outsource network deployment and operation to other companies, e.g. suppliers of network equipment. In these examples the mobile operators cooperate about the networks, the relations to end-users are the same as if the operator would operate the network on its own. However, in other areas other actors enter the market for mobile services where mobile operators traditionally have been the dominant player. Handset manufacturers and Internet companies offer value added services and applications to the end-users. They also establish relations with customers of the mobile operators. Hence, mobile operators look into new technical solutions and services in order to reduce costs and find new services and sources of revenues. Many of the networking solutions and services require that the operator cooperates with some other actor. In this PhD thesis cooperation strategies of mobile network operators are analyzed including cooperation with competitors, customers and different types of partners. The partner can be a provider of a non-telecom service like public transportation, financial institutes or third parties taking intermediary roles. The main research questions in the thesis revolves around why and how mobile operators cooperate. The drivers for cooperation and the way the cooperation is organized is analyzed for a number of cases. Three types of services and markets are analyzed: - Public mobile broadband access services - Services and solutions for indoor wireless access - Mobile payment, ticketing and contactless services A number of technical solutions, business concepts and different types of cooperation and business scenarios have been investigated. Two overall research questions that are applicable for all cases of cooperation are identified for the analysis. - What are the main drivers for a specific type of cooperation? - In what ways can the actors organize the cooperation?
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| 5. |
- Tavana, Morteza
(författare)
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RF Energy Harvesting for Zero-Energy Devices and Reconfigurable Intelligent Surfaces
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The growth of Internet of Things (IoT) networks has made battery replacement in IoT devices increasingly challenging. This issue is particularly pronounced in scenarios with a large number of IoT devices, in locations where IoT devices are difficult to access, or when frequent replacement is necessary. The risk of losing or forgetting some IoT devices also exists, leading to a risk of hazardous chemical leakage and e-waste in nature. Radio Frequency(RF) wireless power transfer (WPT) offers an alternative solution for powering these devices. Moreover, it has been observed that the receivers absorb less than one-millionth of the transmitter energy while surrounding objects absorb the remainder. This situation opens up the possibility of leveraging existing wireless infrastructures, such as base stations (BSs), to charge IoT devices. In this thesis, we focus on analyzing the feasibility and limitations of battery-less operation of IoT devices using RF WPT technology, along with energy harvesting (EH) from existing wireless communication infrastructure. We explore both indoor and outdoor scenarios for powering IoT devices. Initially, we consider an outdoor environment where an IoT device periodically harvests energy from existing BSs and transmits a data packet related to sensor measurement. We analyze the coverage range of energy harvesting from a BS for powering IoT devices, which shows a tradeoff between the coverage range and the rate of sensor measurements. Additionally, we compare the operational domain in terms of the range and measurement rate for WPT and battery-powered technologies. Furthermore, we consider the coverage probability for a multi-site scenario, which is the likelihood that a randomly allocated IoT device harvests enough power to enable its operation. We derive an expression for this probability at a random location in terms of harvesting sufficient power for IoT device operation at a given measurement rate. Next, we consider the remote powering of IoT devices inside an aircraft. Wired sensors add weight and maintenance costs to the aircraft. Although replacing data cables with wireless communication reduces costs and simplifies deployment, providing power cables for the sensors remains challenging. We assume fixed locations for IoT devices inside an aircraft. The goal is to minimize the number of WPT transmitters for a given cabin geometry and IoT device duty cycles. We address WPT system design under channel uncertainties through robust optimization. Following this, we turn our attention to energy harvesting at a reconfigurable intelligent surface (RIS). The potential benefits of using RIS compared to traditional relays when it comes to improving wireless coverage have been debated in previous works, under the assumption that both technologies have a wired power supply. The comparison would be entirely different if the RIS can become self-sustaining, which is not possible for relays. Therefore, we explore energy harvesting for RIS, proposing an algorithm for phase adjustment to maximize energy harvesting from RF sources based on power measurements. Lastly, we explore the charging of zero-energy devices (ZEDs) via a RIS. Mitigating the path loss in WPT requires large antenna arrays, which leads to increased hardware complexity, as it demands an RF chain per antenna element. Alternatively, RIS offers high beamforming gain with simpler hardware. Therefore, we consider RIS-assisted RF charging of ZEDs. We develop dynamic algorithms for battery-aware and queue-aware scenarios, adjusting RIS phases and transmission power to meet the requirements.
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| 6. |
- Ahmed, Ashraf Awadelkarim Widaa
(författare)
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Towards Affordable Provisioning Strategies for Local Mobile Services in Dense Urban Areas : A Techno-economic Study
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The future mobile communication networks are expected to cope with growing local usage patterns especially in dense urban areas at more affordable deployment and operation expenses. Beyond leveraging small cell architectures and advanced radio access technologies; more radio spectrum are expected to be required to achieve the desired techno-economic targets. Therefore, the research activity has been directed towards discussing the benefits and needs for more flexible and local spectrum authorization schemes. This thesis work is meant to be a contribution to this ongoing discussion from a techno-economic perspective. In chapter three, the engineering value of the different flexible authorization options are evaluated from the perspective of established mobile network operators using the opportunity cost approach. The main results in chapter three indicate the economic incentives to deploy more small cells based on flexible spectrum authorization options are subject to the potential saving in the deployment and operation costs. Nonetheless; high engineering value can be anticipated when the density of small cells is equal or larger than the active mobile subscribers’ density. While in chapter four, the possible local business models around different flexible authorization options are investigated from the perspective of emerging actors with limited or ’no’ licensed spectrum resources. In this context, dependent or independent local business can be identified according to surrounding spectrum regulations. On possible independent local business models for those emerging actors is to exploit the different flexible spectrum authorization options to provision tailored local mobile services. Other viable dependent local business models rest with the possibility to enter into different cooperation agreements to deploy and operate dedicated local mobile infrastructure on behalf established mobile network operators.
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| 7. |
- Azari, Amin, 1988-
(författare)
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Energy Efficient Machine-Type Communications over Cellular Networks : A Battery Lifetime-Aware Cellular Network Design Framework
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Internet of Things (IoT) refers to the interconnection of uniquely identifiable smart devices which enables them to participate more actively in everyday life. Among large-scale applications, machine-type communications (MTC) supported by cellular networks will be one of the most important enablers for the success of IoT. The existing cellular infrastructure has been optimized for serving a small number of long-lived human-oriented communications (HoC) sessions, originated from smartphones whose batteries are charged in a daily basis. As a consequence, serving a massive number of non-rechargeable machine-type devices demanding a long battery lifetime is a big challenge for cellular networks.The present work is devoted to energy consumption modeling, battery lifetime analysis, and lifetime-aware network design for massive MTC services over cellular networks. At first, we present a realistic model for energy consumption of machine devices in cellular connectivity, which is employed subsequently in deriving the key performance indicator, i.e. network battery lifetime. Then, we develop an efficient mathematical foundation and algorithmic framework for lifetime-aware clustering design for serving a massive number of machine devices. Also, by extending the developed framework to non-clustered MTC, lifetime-aware uplink scheduling and power control solutions are derived. Finally, by investigating the delay, energy consumption, spectral efficiency, and battery lifetime tradeoffs in serving coexistence of HoC and MTC traffic, we explore the ways in which energy saving for the access network and quality of service for HoC traffic can be traded to prolong battery lifetime for machine devices.The numerical and simulation results show that the proposed solutions can provide substantial network lifetime improvement and network maintenance cost reduction in comparison with the existing approaches.
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| 8. |
- Hossain, Mohammad Istiak, 1987-
(författare)
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Cellular-Internet-of-Things Enablers: : A Techno-Economic Study of Wide Area Networks Connectivity and Platform Solutions
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Internet of Things (IoT) services are gradually attaining the expected service growth rate estimated by market actors. New connectivity paradigms, like the low-power wide-area network (LPWAN), have emerged to address the immediate challenges of IoT connectivity service. In addition, a plethora of new connectivity and application platforms have been developed to support IoT services. Until now, the majority of IoT services have been small scale deployments or trials. The overall cost-effectiveness and scalability aspects of IoT service provisioning are still not well understood. Hence, the growth of IoT services requires attention from a multidisciplinary perspective to address the cost-efficient scalability of IoT communication and service platforms.The technical part of this thesis focuses on the impact of multiplicity on the physical random access channel (PRACH) performance. We investigate the performance limitations of the initial access resource allocation, considering the multiplicity effect on physical layer signature detection to ensure uniform accessibility of devices. The performance evaluation reveals that MAC-protocol designed for PRACH needs to consider the realistic impact of multiplicity on signature detection. Then, we propose an efficient algorithm to detect multiplicity with a higher confidence factor. We also investigate the trade-off of random-access collision and resource allocation utilisation to meet the IoT resource utilisation requirements. We propose a pool-based resource allocation procedure that uses supervised learning to optimise the performance of early data transmission (EDT). Our analysis suggests that with this approach, EDT can handle delay constraint IoT services efficiently.The economic part of the thesis addresses the cost-structure and scalability aspects of both connectivity and platform solutions. The overall research question is: "What factors are driving the costs of IoT connectivity and platform services and why?" We have developed a framework for cost structure analysis of IoT services. We present cost structure breakdown analysis for both IoT connectivity and IoT platform services. The evaluation results discuss conditions when a platform service provider should choose a platform as a service (PaaS), and when on-premises platform deployment is viable.The technical study contributes to shaping the assessment metrics of the random-access algorithm selection. This study proposes solutions to support heterogeneous IoT solutions in cellular-IoT systems. Furthermore, the study demonstrates the potential of supervised learning to optimise resource allocation. The proposed algorithm assures service scalability in terms of user density for massive-IoT, and delay constraint IoT use cases.The economic study is helpful for telecom managers and IoT service providers to understand the cost breakdown of IoT connectivity and platform solutions under a different scenario. The cost driver of different IoT communication technologies like LPWAN, LPLAN, and C-IoT can be estimated at a high level. The framework provides a comparison base which is helpful for the actors in the IoT domain to analyse and compare different service provisioning options.
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| 9. |
- Hultell, Johan, 1978-
(författare)
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Cooperative and non-cooperative wireless access : Resource and infrastructure sharing regimes
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Future wireless networks will combine multiple radio technologies and subsystems, possibly managed by competing network providers. For such systems it may be advantageous to let the end nodes (terminals) make some or all of the resource management decisions. In addition to reducing complexity and costs, increasing redundancy, and facilitating more timely decisions; distributed resource sharing regimes can decouple the individual subsystems. Decoupled subsystems could be desirable both because competing operators can be business-wise separated and because it allows new technologies to be added (removed) in a modular fashion. However, distributed regimes can also lead to “selfish” wireless nodes who only try to maximize their own performance. The first part of this dissertation studies if selfish nodes can make efficient use of wireless resources, using multiaccess and network layers as examples. The related problems are formulated as noncooperative games between nodes. To maintain tractability nodes are confined to simple strategies that neither account for future payoffs nor allow for coordination. Yet, it is demonstrated that selfish nodes can achieve comparable performance to traditional protocols. These results should be interpreted as an argument in favor of distributed regimes. The second part of this dissertation evaluates the effects of multi-provider network architectures where users can roam freely across all networks. From a supply side perspective the benefits are improved path gain statistics and the fact that different networks may have non-overlapping busy hours. Several network configurations are analyzed and it is shown that cooperation between symmetric providers can yield significant capacity gains for both downlink and uplink; even if the providers have nearly collocated sites. When the providers have different site densities the gains from cooperation are reduced and the provider with a sparse network always gains more from cooperating. This suggests that initially, voluntary cooperation may be limited to some special cases. Lastly, the architecture is analyzed in a context where the providers compete for users on a per session basis by offering access at different prices. Although such architectures currently only exist in a few special cases, they could emerge in domestic markets where the costs to switch and search for new networks are low. Based on a game theoretic formulation it is shown that a competitive market for wireless access can be advantageous for both users and providers. The results presented suggest that the advantages of cooperation of competing providers occur in more than just a few cases.
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| 10. |
- Kang, Du Ho
(författare)
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Interference Coordination for Low-cost Indoor Wireless Systems in Shared Spectrum
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mobile broadband services have become a big success over the last several years. Innovative, smart handsets have caused explosive traffic growth which has led to a severe capacity shortage. Since the majority of traffic originates from indoor locations or hotspots, significant invest- ment in indoor wireless infrastructure is predicted in order to resolve the capacity problem. While existing public operators mainly focus on high-mobility wide-area services, non-traditional local access providers (LAPs) such as facility owners are more and more interested in high data rate indoor services for their employees or customers. An obstacle is that they do not have access to dedicated spectrum. One proposal is spectrum sharing between LAPs. In shared spectrum, interference management emerges as a key technical challenge, and this becomes more critical as indoor systems become increasingly dense.This thesis concentrates on the interference management problem when spectrum is shared between high-density indoor wireless systems. There are two different design directions which require different system architectures. A Wi-Fi or femtocell system works in a fully uncoordinated manner without any inter-cell signaling. This allows high network scalability with cheap devices but leads to poor performance. Alter- natively, advanced interference coordination can be used. It certainly improves the performance; however, it usually requires expensive infras- tructure for real-time information exchange. A key question asked in this thesis is if the interference coordination gives sufficient economic gain to a LAP in terms of a total deployment cost. In order to answer this question, we first develop a conceptual framework to define and compare various levels of coordination. Then, we measure the re- quired number of access points (APs) at a given area capacity demand to estimate the economic gain.The coordination decision problem for a LAP is divided into two. Firstly, the LAP needs to choose the right level of coordination within its own network. Secondly, it determines whether or not to cooperate with neighboring LAPs for coordinating interference across the net- works. Regarding the intra-network decision, the comparison ranges from uncoordinated CSMA/CA to ideal interference cancellation. We find the total deployment cost of the uncoordinated CSMA/CA network soars when an area capacity requirement exceeds a certain threshold. The performance gain of the ideal coordination does not pay off the cost of high-speed backhaul because walls effectively suppress interference. Therefore, the most viable approach in a typical indoor environment is using dynamic coordination schemes via existing backhauls, for example Ethernet or xDSL. As for the cooperation decision, our major finding is that non-cooperative spectrum sharing is feasible provided that the transmit power of the APs is properly regulated. Although cooperation with advanced inter-network coordination schemes brings about cost savings, it is not sufficient to overcome practical barriers to a cooperation agreement especially when the capacity demand is high.
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