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 ...

Operators of cellular networks are hard pressed to provide a seamless wireless connection to their users. Due to the expanded demand not only for coverage but also for increased network capacity, the network architecture needs to be adapted and evolve beyond the classical hexagonal grid. The globally ongoing trend of urbanization leads to more and more users utilizing their wireless devices indoors or in mobile scenarios, when commuting or traveling. These scenarios pose particular challenges to implementing a suitable network in terms of propagation conditions as well as optimal base station (BS) deployment. Therefore, in this thesis, I investigate the potential network-wide average performance of wireless cellular networks particularly in high speed train (HST) environments , as well as of network deployments indoors. An investigation on network scale requires to limit the complexity of the applied system models. This is ...

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 ...

Feedback in wireless communications is tied to a long-standing and successful history, facilitating robust and spectrally efficient transmission over the uncertain wireless medium. Since the application of multiple antennas at both ends of the communication link, enabling multiple-input multiple-output (MIMO) transmission, the importance of feedback information to achieve the highest performance is even more pronounced. Especially when multiple antennas are employed by the transmitter to handle the interference between multiple users, channel state information (CSI) is a fundamental prerequisite. The corresponding multi-user MIMO, interference alignment and coordination techniques are considered as a central part of future cellular networks to cope with the growing inter-cell-interference, caused by the unavoidable densification of base stations to support the exponentially increasing demand on network capacities. However, this vision can only be implemented with efficient feedback algorithms that provide accurate CSI at the transmitter without ...

In order to meet ever-growing needs for capacity in wireless networks, transmission techniques and the system models used to study their performances have rapidly evolved. From single-user single-antenna point-to-point communications to modern multi-cell multi-antenna cellular networks there have been large advances in technology. Along the way, several assumptions are made in order to have either more realistic models, but also to allow simpler analysis. We analyze three aspects of actual networks and try to benefit from them when possible or conversely, to mitigate their negative impact. This sometimes corrects overly optimistic results, for instance when delay in the channel state information (CSI) acquisition is no longer neglected. However, this sometimes also corrects overly pessimistic results, for instance when in a broadcast channel (BC) the number of users is no longer limited to be equal to the number of transmit antennas ...

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 ...

Multi-user multi-antenna wireless communication systems have become essential due to the widespread of smart applications and the use of the Internet. Ultra-dense deployment of small cell networks has been recognized as an effective way to meet the exponentially growing mobile data traffic and to accommodate increasingly diversified mobile applications for beyond 5G and future wireless networks. Small cells using low power nodes are meant to be deployed in hot spots, where the number of users varies strongly with time and between adjacent cells. As a result, small cells are expected to have burst-like traffic, which makes the static time division duplex (TDD) frame configuration strategy, where a common TDD pattern is selected for the whole network, not able to meet the users' requirements and the traffic fluctuations. Dynamic TDD (DTDD) technology which allows the cells to independently adapt their TDD ...

This PhD thesis focuses on system level analysis of Multi-Component Carrier (CC) management for Long Term Evolution (LTE)-Advanced. Cases where multiple CCs are aggregated to form a larger bandwidth are studied. The analysis is performed for both local area and wide area networks. In local area, Time Division Duplexing (TDD) is chosen as the duplexing mode in this study. The performance with different network time synchronization levels is compared, and it is observed that achieving time synchronization significantly improves the uplink performance without penalizing much of the downlink transmission. Next the technique of frequency reuse is investigated. As compared to reuse-1, using different frequency channels in neighboring cells reduces the interference to offer large performance gain. To avoid the frequency planning, several decentralized algorithms are developed for interference reduction. Compared to the case of reuse-1, they achieve a gain of ...

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 ...

This thesis presents the design and application of a Link-to-System (L2S) model capable of predicting the downlink throughput performance of cellular mobile networks based on the 3GPP Long Term Evolution (LTE) standard. The aim of a L2S model is to accurately abstract the physical layer at a fraction of the complexity of detailed link level simulations. Thus, it dramatically reduces the necessary simulation run time and by extension enables the simulation of much more complex scenarios. The thesis is divided in four main parts. First, the basics of the LTE standard are presented, with the link abstraction model being presented afterwards. Extensions for the L2S model for the cases of Hybrid Automatic Repeat reQuest (HARQ) and imperfect channel state information are presented in the third section. In the last chapter, the performance of the application of Fractional Frequency Reuse (FFR) ...

In nowadays communication systems, error correction provides robust data transmission through imperfect (noisy) channels. Error correcting codes are a crucial component in most storage and communication systems – wired or wireless –, e.g. GSM, UMTS, xDSL, CD/DVD. At least as important as the data integrity issue is the recent realization that error correcting codes fundamentally change the trade-offs in system design. High-integrity, low redundancy coding can be applied to increase data rate, or battery life time or by reducing hardware costs, making it possible to enter mass market. When it comes to the design of error correcting codes and their properties, there are two main theories that play an important role in this work. Classical coding theory aims at finding the best code given an available block length. This thesis focuses on the ubiquitous Reed-Solomon codes, one of the major ...

Condition monitoring of machines through vibration analysis has been successfully applied on different types of machines for several decades. However, there are still some mechanical systems where its use has not given the same good results. Epicyclic gearboxes (EG) belong to this group of systems. Due to its special characteristics, EG are used in a wide range of applications within the drive technology, mostly when high power transmission is required. Machines dealing with high power transmission are typically critical, which means that a large part of the process in which they are involved depends on their appropriate operation. Hence, there is a high interest on a solution that can effectively detect failures in EG at an early stage, before they evolve and produce major breakdowns. Probably the most important reason for the deficient results of failure detection on EG through ...

Provisioning of digital video services is a difficult task as it is hard to estimate optimal settings of video parameters, given transmission constraints, while maximizing the overall end-user quality. With Internet streaming services becoming part of our everyday life, end-to-end optimization of such systems is important. On one hand, huge effort is given into subjective or objective evaluation of the end-user perception. High quality audiovisual perception with respect to the minimized costs of the provided service is one of the main interests for the network providers. On the other hand, subjective evaluations to determine best video and audio configurations are often evaluated in controlled test laboratory environments, which have little to do with the real environments in which consumers enjoy such content. Unfortunately, no serious attempts have been made to take into account interactions between quality of the content and ...

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 ...

Wireless communications are important in our highly connected world. The amount of data being transferred in cellular networks is steadily growing, and consequently more capacity is needed. This thesis considers the problem of downlink capacity improvement from the perspective of multicell coordination. By employing multiple antennas at the transmitters and receivers of a multicell network, the inherent spatial selectivity of the users can be exploited in order to increase the capacity through linear precoding and receive filtering. For the coordination between cells, distributed algorithms are often sought due to their low implementation complexity and robustness. In this context, the thesis considers two problem domains: base station clustering and coordinated precoding. Base station clustering corresponds to grouping the cell base stations into disjoint clusters in order to reduce the coordination overhead. This is needed in intermediate-sized to large networks, where the ...