Particularly in wireless mobile communications, link errors severely affect the quality of the services due to the high error probability and the specific error characteristics (burst errors) in the radio access part of the network. In this thesis it is shown that a thorough analysis and the appropriate modeling of the radiolink error behaviour is essential not only to evaluate and optimize the higher layer protocols and services. It is also the basis for finding network-aware cross-layer processing algorithms which are capable of exploiting the specific properties of the link error statistics (e.g. the predictability). This thesis presents the analysis of the radio link errors based on measurements in live UMTS (Universal Mobile Telecommunication System) radio access networks. It is shown that due to the link error characteristics basically two scenarios have to be distinguished: static and dynamic (regardless of ...

Allocating resources to variable bitrate (VBR) teletraffic sources is not a trivial task because the impact of such sources on a buffered switch is diffcult to predict. This problem has repercussions for call admission control (CAC) on asynchronous transfer mode (ATM) networks. In this thesis we report on investigations into the nature of several types of VBR teletraffic. The purpose of these investigations is to identify parameters of the traffic that may assist in the development of CAC algorithms. As such we concentrate on the correlation structure and marginal distribution: the two aspects of a teletraffic source that affect its behaviour through a buffered switch. The investigations into the correlation structure consider whether VBR video is self-similar or non-stationary. This question is signicant as the exponent of self-similarity has been identied as being useful for characterising VBR teletraffic. Although results ...

The fourth and fifth generation wireless communication systems (4G and 5G) use a physical layer (PHY) based on multicarrier modulations for data transmission using high bandwidth. This type of modulations has shown to provide high spectral efficiency while allowing low complexity radio channel equalization. These systems use OFDMA as a mechanism for distributing the available radio resources among different users. This allocation is done by assigning a subset of subcarriers to each user in a given instant of time. This provides great flexibility to the system that allows it to adapt to both the quality of service requirements of users and the radio channel state. The media access layer (MAC) of these systems is in charge of configuring the multiple OFDMA PHY layer parameters, in addition to managing the data flows of each user, transforming the higher layer packets into ...

Over the last few years multimedia and data-based services experienced a non-stopping growth. Unlike before, people do not use the services only from a static location, but they are continuously on the move between different scenarios, using their mobile devices to access data-based services. In parallel, commuter traffic from rural areas is also rising, since most of work places are in and around cities. During transportation, people intensively employ mobile devices to work, access to social networks, or as an entertainment means. Internet access is required for most of these services. Currently, GSM for Railways (GSM-R), which is based on the Global System for Mobile Communications (GSM), is the most widely used communication system between trains and the elements involved in operation, control, and intercommunication within the railway infrastructure. However, GSM-R is not well suited for supporting advanced services such ...

VIDEO streaming over cellular networks has been made possible in the last years by better performing video codecs and wireless cellular networks oriented to data transmission. The interaction between two heterogeneous worlds, the telecommunication infrastructure and the coding video software, calls for advanced optimization mechanisms. The actors involved in the optimization process are the cellular system's access network, UMTS and HSDPA, the wireless transmission channel and the fi nal user equipped with a mobile device capable of decoding video sequences. The knowledge and characterization of each of the building blocks allow the optimization of each element to the specifi c needs of the others. This doctoral thesis discusses three main contributions. In the fi rst part, the e ffects of transmission errors on video streams are analyzed. Incorrectly received video packets are usually discarded by the lower layers and not ...

For the provisioning of video streaming services it is essential to provide a required level of customer satisfaction, given by the perceived video stream quality. It is therefore important to choose the compression parameters as well as the network settings so that they maximize the end-user quality. Due to video compression improvements of the newest video coding standard H.264/AVC, video streaming for low bit and frame rates is possible while preserving its perceptual quality. This is especially suitable for video applications in 3G wireless networks. Mobile video streaming is characterized by low resolutions and low bitrates. The commonly used resolutions are Quarter Common Intermediate Format (QCIF,176x144 pixels) for cell phones, Common Intermediate Format (CIF, 352x288 pixels) and Standard Interchange Format (SIF or QVGA, 320x240 pixels) for data-cards and palmtops (PDA). The mandatory codec for Universal Mobile Telecommunications System (UMTS) streaming ...

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 third generation of mobile systems brought higher data rates that allow for provisioning of multimedia services containing also video. The real-time services like video call, conferencing, and streaming are particularly challenging for mobile communication systems due to the wireless channel quality variations. The mechanism for video compression utilizes a hybrid of temporal and spatial prediction, transform coding and variable length coding. The combination of these methods provides high compression gain, but at the same time makes the encoded stream more prone to errors. In this thesis, techniques for error resilient transmission of video streaming over wireless mobile networks are investigated. Focus is given to the recent H.264/AVC standard, although the ma jority of the proposed method apply to other video coding standards, too. The first part is dedicated to exploiting the residual redundancy of the received video stream at ...

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 ...

During the last decades, information is being gathered and processed at an explosive rate. This fact gives rise to a very important issue, that is, how to effectively and precisely describe the information content of a given source signal or an ensemble of source signals, such that it can be stored, processed or transmitted by taking into consideration the limitations and capabilities of the several digital devices. One of the fundamental principles of signal processing for decades is the Nyquist-Shannon sampling theorem, which states that the minimum number of samples needed to reconstruct a signal without error is dictated by its bandwidth. However, there are many cases in our everyday life in which sampling at the Nyquist rate results in too many data and thus, demanding an increased processing power, as well as storage requirements. A mathematical theory that emerged ...

Currently, the telecommunications market has brought changes to the design of the old model of the telecommunications network. The emergence of new technologies for higher speed access was inevitable in order to meet the requirements of the appearance of the multimedia services (VoD, online gaming etc.). The latest technologies for broadband access over telephone pairs are Digital Subscriber Lines or DSL. This set of xDSL technologies allow the transfer of binary high speed over telephone twisted pair by using a suitable type of line codes. They allow a flow of high-speed information both asymmetrical and symmetrical over the telephone loop. This thesis presents the state of the art of Dynamic Spectrum Management (DSM) technologies suggested to improve the performance of DSL systems and proposes a new approach to this issue. The main contributions of this thesis includes extended bandwidth channel ...

Packet delay is among the most important characteristics of networks, since it directly impacts the user satisfaction. Accordingly, it is often used for benchmarking networks. Modern mobile cellular networks handle data streams with complex algorithms, in order to maximize the achievable throughput. Considering that, two question arise: (i) How can latency be measured in such networks? (ii) Are respective concepts from wired networks directly applicable to wireless networks? This thesis provides a self-contained guide on how to measure packet delay in mobile cellular networks. Covered aspects reach from timekeeping on tracing hardware to the design of measurement processes. Measurements in operational networks have evidenced them to be reactive; namely, the experienced latency depends on the injected traffic pattern (including the respective history). Accordingly, involved actions are required to obtain fair delay benchmarks, as outlined in this thesis. Thereby, the design ...

The major contribution of this thesis is on the problem of transmit beamforming to multiple cochannel multicast groups. Two viewpoints are considered: i) minimizing total transmission power while guaranteeing a prescribed minimum signal-to-interference-plus-noise ratio (SINR) at each receiver; and ii) a "fair" approach maximizing the overall minimum SINR under a total power budget. The core problem is a multicast generalization of the multiuser downlink beamforming problem; the difference is that each transmitted stream is directed to multiple receivers, each with its own channel. Such generalization is relevant and timely, e.g., in the context of the emerging WiMAX and UMTS-LTE wireless networks. The joint multicast beamforming problem is in general NP-hard, motivating the pursuit of computationally efficient quasi-optimal solutions. In chapter 1, it is shown that semidefinite relaxation coupled with suitable randomization / cochannel multicast power control yield computationally efficient high-quality ...

Localization, separation and tracking of acoustic sources are ancient challenges that lots of animals and human beings are doing intuitively and sometimes with an impressive accuracy. Artificial methods have been developed for various applications and conditions. The majority of those methods are centralized, meaning that all signals are processed together to produce the estimation results. The concept of distributed sensor networks is becoming more realistic as technology advances in the fields of nano-technology, micro electro-mechanic systems (MEMS) and communication. A distributed sensor network comprises scattered nodes which are autonomous, self-powered modules consisting of sensors, actuators and communication capabilities. A variety of layout and connectivity graphs are usually used. Distributed sensor networks have a broad range of applications, which can be categorized in ecology, military, environment monitoring, medical, security and surveillance. In this dissertation we develop algorithms for distributed sensor networks ...

This thesis proposes and discusses aspects of a low-cost wireless network called “Hopscotch” as a potential solution to the rural broadband problem. Providing broadband internet access to rural locations is challenging due to the long distances between internet backbone and households, the sparse population density and difficult terrain. Hopscotch uses a network of renewable powered base stations, termed “WindFi”, connected by point-to-point links, to deliver internet access to rural communities. A combination of frequency bands are used within Hopscotch. Standard IEEE 802.11 5GHz WiFi access technology is used for high capacity links, and an ultra high frequency TV “white space” spectrum overlay in the 600-800 MHz band provides long distance coverage. The advantages of “white space” spectrum are demonstrated for a rural wireless scenario; reducing the number of base stations required to cover a community and decreasing the transmit power ...