| 1. |
- Enqvist, Anders
(author)
-
Optimizing Energy Efficiency in Wireless Links Through Reconfigurable Intelligent Surfaces and Optimal Ratios
- 2024
-
Licentiate thesis (other academic/artistic)abstract
- This thesis explores the optimization of energy efficiency (EE) in the radiolink of wireless communication systems, focusing on both the user equipment (UE) and the base station (BS). The first part of the study examines strategies to minimize the energy consumption of the UE when transmitting short data payloads, utilizing a reconfigurable intelligent surface (RIS) controlled by the BS, to improve the channel conditions. The challenge lies in balancing the increased energy consumption due to additional pilot signals needed toconfigure the RIS against the energy savings during data transmission. We propose an innovative approach where the RIS is divided into subarrays of controllable sizes to shorten the pilot length. The analytical results provide a unique energy-minimizing solution in terms of pilot length and power which depends on an interplay between the payload size and path loss conditions between the UE, BS, and RIS. In the second part, the focus shifts to the EE of a multi-antenna BS. A comprehensive power consumption model is employed, accounting for both active and passive components of the transceiver circuitry. By treating the transmit power, bandwidth, and number of antennas as optimization variables, we derive novel closed-form solutions to the optimal value of these variables and propose an algorithm for their joint optimization. This part of the study not only optimizes the variables for maximum EE but also uncovers a new relationship between radiated power and passive transceiver power consumption, offering insights into the trade-offs between using maximum power and bandwidth. Together, these studies provide an updated view of EE optimization in wireless communication systems, offering novel theoretical insights for both UE and BS configurations.
|
|
| 2. |
- Behdad, Zinat
(author)
-
Integrated Sensing and Communication in Cell-Free Massive MIMO
- 2024
-
Licentiate thesis (other academic/artistic)abstract
- Future mobile networks are anticipated to not only enhance communication performance but also facilitate new sensing-based applications. This highlights the essential role of integrated sensing and communication (ISAC) in sixth-generation (6G) and beyond mobile networks. The seamless integration of sensing and communication poses challenges in deployment and resource allocation. Cell-free massive multiple-input multiple-output (MIMO) networks, characterized by multiple distributed access points, offer a promising infrastructure for ISAC implementation. However, the effective realization of ISAC necessitates joint design and resource allocation optimization. In this thesis, we study ISAC within cell-free massive MIMO systems, with a particular emphasis on developing power allocation algorithms under various scenarios.In this thesis, we explore two scenarios: utilizing existing communication signals and incorporating additional sensing signals. We propose power allocation algorithms aiming to maximize the sensing performance while meeting communication and power constraints. In addition, we develop two maximum a posteriori ratio test (MAPRT) target detectors under clutter-free and cluttered scenarios. Results indicate that employing additional sensing signals enhances sensing performance, particularly in scenarios where the target has low reflectivity. Moreover, although the clutter-aware detector requires more advanced processing, it leads to better sensing performance. Furthermore, we introduced sensing spectral efficiency (SE) to measure the effect of resource block utilization, highlighting the integration advantages of ISAC over orthogonal resource sharing approaches. In the next part of the thesis, we study the energy efficiency aspects of ISAC in cell-free massive MIMO systems with ultra-reliable low-latency communications (URLLC) users. We propose a power allocation algorithm aiming to maximize energy efficiency of the system while meeting communication and sensing requirements. We conduct a comparative analysis between the proposed power allocation algorithms and a URLLC-only approach which takes into account only URLLC and power requirements. The results reveal that while the URLLC-only algorithm excels in energy efficiency, it is not able to support sensing requirements. Moreover, we study the impact of ISAC on end-to-end (including radio and processing) energy consumption. Particularly, we present giga-operations per second (GOPS) analysis for both communication and sensing tasks. Two optimization problems are formulated and solved to minimize transmission and end-to-end energy through blocklength and power optimization. Results indicate that while end-to-end energy minimization offers substantial energy savings, its efficacy diminishes with sensing integration due to processing energy requirements.
|
|
| 3. |
- Selvaraju, Shunmuga Priyan, 1992-
(author)
-
Network Management for Dynamic and Heterogeneous Wireless Sensor Networks
- 2022
-
Licentiate thesis (other academic/artistic)abstract
- Wireless Sensor Networks (WSNs) are interconnections of spatially distributed sensor nodes with low-power wireless communication. In comparison with traditional wireless networks, WSNs provide novel features in network architecture, which are known as low-cost networking, rapid formation, widespread arrangement, self-organisation, and ease of deployment. For these reasons, many WSNs are utilised and interconnected to form massive Internet-of-Things (IoT) applications in areas such as e-healthcare, industrial automation, and smart cities, to name a few. Nevertheless, WSN networking is affected by dynamic network topology – nodes’ mobility and varying network density, and heterogeneous networks (hetnets) – coexisting radio technologies. In more detail, mobile nodes create and break network connections as they move around; varying network density causes alterations in the routing graph; and coexisting radios is a scenario when multiple WSNs utilising different communication technologies are located within same physical space, where network interoperability is required for non-obtrusive operations between the co-located networks. These networking constraints must be properly managed, otherwise, they will lead to non-deterministic and erratic behavior in overall IoT applications, causing degraded Quality-of-Service (QoS).In recent literature, several proposals primarily address only one of these aspects; either mobility, density, or coexisting radios. In this thesis, we propose a unified approach to manage dynamic networks and hetnets through the support of network-wide decision-making in the management process. A unified method results in reduction of the overhead cost for system resources and computation complexity with respect to the constrained nature of WSNs, and improvement in decision-making efficiency in network management. The main contributions are modelling of the network management process, proposing an architecture, simulating and implementing the proposed architecture, and evaluating the network performance under network management for WSNs. Performance metrics include latency, throughput, and packet loss rate. Software Defined Networking (SDN), a method for programmable network management, is a suitable solution.The challenges in design and implementation of network management for WSNs have been experimentally studied in the first paper in the thesis. Further, mobility management has been modelled in the second paper with the modular architecture in the third paper. In the third and fourth paper, we implement the proposed architecture and evaluate network performance. In the fifth paper, we have analysed the network performance in different networking architectures. For standardised simulation and evaluations, We used the Contiki and Mininet simulators, and Linux networking simulators, as well as Linux networking concepts on virtualisation. Empirically, simulation results show that the mean latency has improved more than 100 times with network management compared with typical methods using distributed routing protocols, under varying density in hetnets. Also, we observed a smooth-line performance in mobility management with close to zero packet losses under nodes’ mobility with sporadic communication patterns.
|
|
| 4. |
- Topal, Ozan Alp
(author)
-
Millimeter-Wave Communications for Indoor Dense Spaces : Channel Modeling and Network Deployment
- 2023
-
Licentiate thesis (other academic/artistic)abstract
- In the ever-evolving landscape of wireless communication, the deployment of millimeter-wave (mmWave) technology has emerged as a game-changer for indoor environments. As the demand for high-speed, low-latency connectivity continues to surge, especially in densely populated areas, mmWave access point deployment has gained prominence due to its ability to deliver unprecedented data rates thanks to the available wide bandwidths. However, mmWave signals are more prone to blockage by objects and their coverage area is small. Therefore the deployment of mmWave technology is preferred for the cases where a high number of users require high data rates in an environment free of blockages. Indoor dense spaces (IDSs) refer to compact indoor environments with many objects and users within. The main examples of IDS are airplane cabins and high-speed train wagons. On the one hand, due to the dense user existence, IDSs can benefit from mmWave connectivity. On the other hand, the dense blockage in the environment due to the seats and humans would cause significant propagation losses. In this thesis, we investigate the potential of mmWave communications in IDSs. As a first step, we investigate the mmWave signal propagation in IDSs by using ray-tracing (RT) simulations. We provide large-scale fading and spatio-temporal fading characteristics considering the 28, 39, and 60 GHz bands. The results demonstrate that the dielectric characteristics of the environment provide considerable differences in signal propagation, while the geometry and the user denseness are not influential. Furthermore, the coverage area of the IDS is half of the coverage area of the indoor office, demonstrating the severe attenuation in IDS. After analyzing the signal propagation, we investigate the optimal AP deployment for IDSs by minimizing the number of deployed APs while guaranteeing the data rate requirements of the users in the environment. The proposed algorithm jointly allocates time and power resources and selects the optimal locations of the APs considering different levels of AP cooperation. This study shows that R-ZF with C-JT outperforms MRT and NC-JT, providing higher data rates to UEs and reducing the total number of deployed APs. By using 10 times higher bandwidth in the mmWave band compared to sub-6GHz, we can guarantee 9 times higher data rates for users. Later, we investigate the potential of reconfigurable intelligent surfaces (RISs) in extending the coverage of a single mmWave access point. The results of this study show that the coverage area of a single AP can be extended four times by optimally placing the RISs.
|
|
| 5. |
- Meer, Irshad Ahmad
(author)
-
Mobility Management and Localizability for Cellular Connected UAVs
- 2024
-
Licentiate thesis (other academic/artistic)abstract
- Unmanned Aerial Vehicles (UAVs) connected to cellular networks present novel challenges and opportunities in mobility management and localization, distinct from those faced by terrestrial users. This thesis presents an integrated approach, combining two key aspects essential for the integration of UAVs with cellular networks.Firstly, it introduces the mobility management challenges for cellular-connected UAVs, which differ significantly from terrestrial users. While terrestrial mobility management primarily aims to prevent radio link failures near cell boundaries, aerial users experience fragmented and overlapping coverage with line-of-sight conditions involving multiple ground base stations (BSs). Thus, mobility management for UAVs extends beyond link failure avoidance, aiming to minimize unnecessary handovers while ensuring extended service availability, particularly in up-link communication. Line-of-sight conditions from a UAV to multiple BSs increase the likelihood of frequent handovers, resulting in control packet overheads and communication delays. This thesis proposes two approaches to address these challenges: 1) A model-based service availability-aware Mobility Robustness Optimization (MRO) adapting handover parameters to maintain high service availability with minimal handovers, and 2) A model-free approach using Deep Q-networks to decrease unnecessary handovers while preserving high service availability. Simulation results demonstrate that both the proposed algorithms converge promptly and increase the service availability by more than 40 % while the number of handovers is reduced by more than 50% as compared to traditional approaches.Secondly, to assess the ability of a network to support the range-based localization for cellular-connected UAVs, an analytical framework is introduced. The metric B-localizability is defined as the probability of successfully receiving localization signals above a specified Signal-to-Interference plus Noise Ratio (SINR) threshold from at least B ground BSs. The framework, accounting for UAV-related parameters in a three-dimensional environment, provides comprehensive insights into factors influencing localizability, such as distance distributions, path loss, interference, and received SINR. Simulation studies explore the correlation between localizability and the number of participating BSs, SINR requirements, air-to-ground channel characteristics, and network coordination. Additionally, an optimization problem is formulated to maximize localizability, investigating the impact of UAV altitude across different scenarios. Our study reveals that in an urban macro environment, the effectiveness of cellular network-based localization increases with altitude, with localizability reaching 100% above 60 meters. This finding indicates that utilizing cellular networks for UAV localization is a viable option.
|
|
| 6. |
- Azari, Amin, 1988-
(author)
-
Serving IoT Communications over Cellular Networks : Challenges and Solutions in Radio Resource Management for Massive and Critical IoT Communications
- 2018
-
Doctoral thesis (other academic/artistic)abstract
- Internet of Things (IoT) communications refer to the interconnections of smart devices, with reduced human intervention, which enable them to participate more actively in everyday life. It is expected that introduction of a scalable, energy efficient, and reliable IoT connectivity solution can bring enormous benefits to the society, especially in healthcare, wellbeing, and smart homes and industries. In the last two decades, there have been efforts in academia and industry to enable IoT connectivity over the legacy communications infrastructure. In recent years, it is becoming more and more clear that the characteristics and requirements of the IoT traffic are way different from the legacy traffic originating from existing communications services like voice and web surfing, and hence, IoT-specific communications systems and protocols have received profound attention. Until now, several revolutionary solutions, including cellular narrowband-IoT, SigFox, and LoRaWAN, have been proposed/implemented. As each of these solutions focuses on a subset of performance indicators at the cost of sacrificing the others, there is still lack of a dominant player in the market capable of delivering scalable, energy efficient, and reliable IoT connectivity. The present work is devoted to characterizing state-of-the-art technologies for enabling large-scale IoT connectivity, their limitations, and our contributions in performance assessment and enhancement for them. Especially, we focus on grant-free radio access and investigate its applications in supporting massive and critical IoT communications. The main contributions presented in this work include (a) developing an analytical framework for energy/latency/reliability assessment of IoT communications over grant-based and grant-free systems; (b) developing advanced RRM techniques for energy and spectrum efficient serving of massive and critical IoT communications, respectively; and (c) developing advanced data transmission/reception protocols for grant-free IoT networks. The performance evaluation results indicate that supporting IoT devices with stringent energy/delay constraints over limited radio resources calls for aggressive technologies breaking the barrier of the legacy interference-free orthogonal communications.
|
|
