This thesis consists in developing distributed mechanisms for resource allocation in next-generation cellular networks. In the first part of this thesis, the technical and economic challenges for the implementation of distributed storage policies in small cell networks are addressed. In particular, a proactive storage approach is proposed enabling the small base stations to exploit the information extracted from online social networks to estimate the local popularity of the files. Another optimized storage approach is proposed for ultra-dense cellular networks while accounting for the instantaneous variations of the state of the storage units. To facilitate the deployment of these storage solutions, new economic mechanisms are developed to motivate content providers to cooperate with network operators and store their files within the operators' small base stations. In the second part of this thesis, the problem of spectrum management is studied in cache-enabled ...

Device-to-Device (D2D) is one of the important proposed solutions to increase the capacity, offload the traffic, and improve the energy effciency in next generation cellular networks. D2D communication is known as a direct communication between two users without using cellular infrastructure networks. Despite of large expected bene fits in terms of capacity in D2D, the coexistence of D2D and cellular networks in the same spectrum creates new challenges in interference management and network design. To limit the interference power control schemes on cellular networks and D2D networks are typically adopted. Even though power control is introduced to limit the interference level, it does not prevent cellular and D2D users from experiencing coverage limitation when sharing the same radio resources. Therefore, the design of such networks requires the availability of suitable methods able to properly model the eff ect of interference ...

The envisioned rapid and exponential increase of wireless data traffic demand in the next years imposes rethinking current wireless cellular networks due to the scarcity of the available spectrum. In this regard, three main drivers are considered to increase the capacity of today's most advanced (4G systems) and future (5G systems and beyond) cellular networks: i) use more bandwidth (more Hz) through spectral aggregation, ii) enhance the spectral efficiency per base station (BS) (more bits/s/Hz/BS) by using multiple antennas at BSs and users (i.e. MIMO systems), and iii) increase the density of BSs (more BSs/km2) through a dense and heterogeneous deployment (known as dense heterogeneous cellular networks). We focus on the last two drivers. First, the use of multi-antenna systems allows exploiting the spatial dimension for several purposes: improving the capacity of a conventional point-to-point wireless link, increasing the number ...

With the rapidly growing of the customers’ data traffic demand, improving the system capacity and increasing the user throughput have become essential concerns for the future fifth-generation (5G) wireless communication network. In this context, device-to-device (D2D) communication and in-band full-duplex (FD) are proposed as potential solutions to increase the spatial spectrum utilization and the user rate in a cellular network. D2D allows two nearby devices to communicate without base station (BS) participation or with limited participation. On the other hand, FD communication enables simultaneous transmission and reception in the same frequency band. Due to the short distance property of D2D links, exploiting the FD technology in D2D communication is an excellent choice to further improve the cellular spectrum efficiency and the users’ throughput. However, practical FD transceivers add new challenges for D2D communication. For instance, the existing FD devices cannot ...

The number of mobile devices and the amount of traffic generated by them has grown at a tremendous pace in the last years and it is expected to continue growing. This growth contrasts with the limited bandwidth that needs to be shared among users. Network densification has been proposed as a promising technique to satisfy the previous demands over a shared bandwidth. This is realized by increasing the density of base stations deployed. Although network densification can improve the signal-to-interference-plus-noise ratio (SINR) of the users located close to the serving base station, it can also increase the inter-cell interference received by other users. In current cellular networks, base stations deal with inter-cell interference by splitting the bandwidth in two parts. The first one is assigned to users with low interference (typically in the cell center) and it is reused in ...

The level of automation in our society is ever increasing. Technologies like self-driving cars, virtual reality, and fully autonomous robots, which all were unimaginable a few decades ago, are realizable today, and will become standard consumer products in the future. These technologies depend upon autonomous localization and situation awareness where careful processing of sensory data is required. To increase efficiency, robustness and reliability, appropriate models for these data are needed. In this thesis, such models are analyzed within three different application areas, namely (1) magnetic localization, (2) extended target tracking, and (3) autonomous learning from raw pixel information. Magnetic localization is based on one or more magnetometers measuring the induced magnetic field from magnetic objects. In this thesis we present a model for determining the position and the orientation of small magnets with an accuracy of a few millimeters. This ...

The cumulative impact of co-channel interferers, commonly referred to as aggregate network interference, is one of the main performance limiting factors in today’s mobile cellular networks. Thus, its careful statistical description is decisive for system analysis and design. A system model for interference analysis is required to capture essential network variation effects, such as base station deployment- and signal propagation characteristics. Furthermore it should be simple and tractable so as to enable first-order insights on design fundamentals and rapid exchange of new ideas. Interference modeling has posed a challenge ever since the establishment of traditional macro cellular deployments. The recent emergence of heterogeneous network topologies complicates matters by contesting many established aspects of time-honored approaches. This thesis presents user-centric system models that enable to investigate scenarios with an asymmetric interference impact. The first approach simplifies the interference analysis in a ...

Nowadays, with a worldwide market penetration of over 50% in the mobile telecommunications sector, there is also an unrelenting demand from the subscribers for ever increasing transmission rates and availability of broadband-like experience on the handset. Due to this, research in next-generation networks is rife. Such systems are expected to achieve peak data rates of up to 1 Gbps through the use of innovative technologies such as multiple-input and multiple- output (MIMO) and orthogonal frequency division multiple access (OFDMA). Two more ways of boosting capacity have also been identified: shrinking cell sizes and greater reuse of resources in the same area. This forms the foundation of the research presented in this thesis. For operators, the costs involved with planning and deploying additional network infrastructure to provide a dense coverage of small, high capacity cells cannot be justified. Femto-cells, however, promise ...

Cellular wireless networks have become a commodity. We use our cellular devices every day to connect to others, to conduct business, for entertainment. Strong demand for wireless access has made corresponding parts of radio spectrum very valuable. Consequently, network operators and their suppliers are constantly being pressured for its efficient use. Unlike the first and second generation cellular networks, current generations do not therefore separate geographical sites in frequency. This universal frequency reuse, combined with continuously increasing spatial density of the transmitters, leads to challenging interference levels in the network. This dissertation collects several contributions to analysis and mitigation of interference in cellular wireless networks. The contributions are categorized and set in the context of prior art based on key characteristics, then they are treated one by one. The first contribution encompasses dynamic signaling that measures instantaneous interference situations and ...

THE task of modeling data traffic in networks is as old as the first commercial telephony systems. In the recent past in mobile telephone networks the focus has moved from voice to packetswitched services. The new cellular mobile networks of the third generation (UMTS) and the evolved second generation (GPRS) offer the subscriber the possibility of staying online everywhere and at any time. The design and dimensioning is well known for circuit switched voice systems, but not for mobile packet-switched systems. The terms user expectation, grade of service and so on need to be defined. To find these parameters it is important to have an accurate traffic model that delivers good traffic estimates. In this thesis we carried out measurements in a live 3G core network of an Austrian operator, in order to find appropriate models that can serve as ...

The use of multiple antennas at base stations and user devices is a key component in the design of cellular communication systems that can meet the capacity demands of tomorrow. The downlink transmission from base stations to users is particularly limiting, both from a theoretical and a practical perspective, since user devices should be simple and power-efficient, and because many applications primarily create downlink traffic (e.g., video streaming). The potential gain of employing multiple antennas for downlink transmission is well recognized: the total data throughput increases linearly with the number of transmit antennas if the spatial dimension is exploited for simultaneous transmission to multiple users. In the design of practical cellular systems, the actual benefit of multiuser multiantenna transmission is limited by a variety of factors, including acquisition and accuracy of channel information, transmit power, channel conditions, cell density, user ...

Advances in wearable electrocardiogram (ECG) monitoring devices have allowed for new cardiovascular applications to emerge beyond diagnostics, such as stress and fatigue detection, athletic performance assessment, sleep disorder characterization, mood recognition, activity surveillance, biometrics, and fitness tracking, to name a few. Such devices, however, are prone to artifacts, particularly due to movement, thus hampering heart rate and heart rate variability measurement and posing a serious threat to cardiac monitoring applications. To address these issues, this thesis proposes the use of a spectro-temporal signal representation called “modulation spectrum”, which is shown to accurately separate cardiac and noise components from the ECG signals, thus opening doors for noise-robust ECG signal processing tools and applications. First, an innovative ECG quality index based on the modulation spectral signal representation is proposed. The representation quantifies the rate-of-change of ECG spectral components, which are shown to ...

This thesis aims at contributing to overcome two of the main challenges for the deployment of highly dense wireless M2M networks in data collection scenarios for the Internet of Things: the management of massive numbers of end-devices that attempt to get access to the wireless channel; and the need to extend the network lifetime to reduce maintenance costs. In order to solve these challenges, two complementary strategies are considered. Firstly, the thesis focuses on the design, analysis and performance evaluation of random and hybrid access protocols that can handle abrupt transitions in the traffic load and minimize the energy consumption devoted to communications. And secondly, the use of energy harvesting (EH) is considered in order to provide the network with unlimited lifetime. To this end, the second part of the thesis focuses on the design and analysis of EH-aware MAC ...

Developing realistic channel models is one of the greatest challenges for describing wireless communications. Their quality is crucial for accurately predicting the performance of a wireless system. While on the one hand, channel models have to be accurate in describing the physical properties of wave propagation, on the other hand, they have to be as least complex as possible. With the recent emergence of antennas with a massive amount of elements as a promising technology for a further enhancement of spectral efficiency, new channel models that characterize the propagation environment in both azimuth and elevation become necessary. While standardization bodies such as 3rd Generation Partnership Project (3GPP) and International Telecommunications Unit (ITU) have introduced a 3-dimensional (3D) geometry-based stochastic channel model, a system-level modeling has been missing to serve the purpose of further analysis and evaluations. Furthermore, with such a ...

Advances in compression techniques, decreasing cost of storage, and high-speed transmission have facilitated the way videos are created, stored and distributed. As a consequence, videos are now being used in many applications areas. The increase in the amount of video data deployed and used in today's applications reveals not only the importance as multimedia data type, but also led to the requirement of efficient management of video data. This management paved the way for new research areas, such as indexing and retrieval of video with respect to their spatio-temporal, visual and semantic contents. This thesis presents work towards a unified framework for semi-automated video indexing and interactive retrieval. To create an efficient index, a set of representative key frames are selected which capture and encapsulate the entire video content. This is achieved by, firstly, segmenting the video into its constituent ...