In this work, a realistic physical layer performance evaluation of High Speed Downlink Packet Access (HSDPA) as well as IEEE 802.16-2004, commonly referred to as Worldwide Inter-operability for Microwave Access (WiMAX), is provided. The performance evaluation is carried out in two measurement campaigns that took place in an alpine and an urban environment. Both, WiMAX and HSDPA use adaptive modulation and coding to adapt the channel coding rate and the size of the symbol alphabet to the current channel conditions. Additionally, both systems allow for multiple transmit and multiple receive antennas to increase the spectral efficiency and the reliability of the transmission. While WiMAX utilizes multiple transmit antennas by simple Alamouti space-time coding, HSDPA implements a closed-loop system with channel adaptive spatial precoding. The necessary, quantized channel information is fed back from the user equipment to the base station. The ...

In the last two decades, multicarrier modulations have emerged as a low complexity solution to combat the effects of the multipath in wireless communications. Among them, Orthogonal Frequency Division Multiplexing (OFDM) is possibly the most studied modulation scheme, and has also been widely adopted as the foundation of industry standards such as WiMAX or LTE. However, OFDM is sensitive to time-selective channels, which are featured in mobility scenarios, due to the appearance of Inter-Carrier Interference (ICI). Implementation of hardware equipment for the end user is usually implemented in dedicated chips, but in research environments, more flexible solutions are preferred. One popular approach is the so-called Software Defined Radio (SDR), where the signal processing algorithms are implemented in reconfigurable hardware such as Digital Signal Processors (DSPs) and Field Programmable Gate Arrays (FPGAs). The aim of this work is two-fold. On the ...

To enable a new level of connectivity among machines as well as between people and machines, future wireless applications will demand higher requirements on data rates, response time, and reliability from the communication system. This will lead to a different system design, comprising a wide range of deployment scenarios. One important aspect is the evolution of physical layer (PHY), specifically the waveform modulation. The novel generalized frequency division multiplexing (GFDM) technique is a prominent proposal for a flexible block filtered multicarrier modulation. This thesis introduces an advanced GFDM concept that enables the emulation of other prominent waveform candidates in scenarios where they perform best. Hence, a unique modulation framework is presented that is capable of addressing a wide range of scenarios and to upgrade the PHY for 5G networks. In particular, for a subset of system parameters of the modulation ...

Broadband wireless communication is a very fast growing communication area. Multicarrier modulation techniques like Orthogonal Frequency Division Multiplexing (OFDM), Biorthogonal Frequency Division Multiplexing (BFDM), Pulse Shaping (PS) and Multi-Carrier Spread Spectrum (MCSS) have recently been introduced as robust techniques against intersymbol interference (ISI) and noise, compared to single carrier communication systems over fast fading multipath communication channels. Therefore, multicarrier modulation techniques have been considered as a candidate for new generation, high data rate broadband wireless communication systems and have been adopted as the related standards. Several examples are the European digital audio broadcasting (DAB) and digital video broadcasting (DVB), the IEEE standands for wireless local area networks (WLAN), 802.11a, and wireless metropolitan area networks (WMAN), 802.16a. However, Doppler frequency shifts, phase offset, local oscillator frequency shifts, and multi-path fading severely degrade the performance of multicarrier communication systems. For fast-varying channels, ...

Relaying, i.e., multihop communication via so-called relay nodes, has emerged as an advanced technology for economically realizing long transmission ranges and high data rates in wireless systems. The focus of this thesis is on multihop multiuser systems where signals are modulated with orthogonal frequency-division multiplexing or multiple access, i.e., OFDM(A), and relays are infrastructure-based network nodes. In general, the thesis contributes by investigating how to operate relay links optimally under spectrum, transmit power and processing capability limitations, as well as how to improve signal processing in relays by exploiting other advanced concepts such as multiantenna techniques, spectrum reuse, transmit power adaptation, and new options for multicarrier protocol design. The first theme is the design and analysis of duplexing modes which define how a relay link reuses allocated frequency bands in each hop. Especially, the full-duplex relaying mode is promoted as ...

The thriving development of wireless communications calls for innovative and advanced signal processing techniques targeting at an enhanced performance in terms of reliability, throughput, robustness, efficiency, flexibility, etc.. This thesis addresses such a compelling demand and presents new and intriguing progress towards fulfilling it. We mainly concentrate on two advanced multi-dimensional signal processing challenges for wireless systems that have attracted tremendous research attention in recent years, multi-carrier Multiple-Input Multiple-Output (MIMO) systems and multi-dimensional harmonic retrieval. As the key technologies of wireless communications, the numerous benefits of MIMO and multi-carrier modulation, e.g., boosting the data rate and improving the link reliability, have long been identified and have ignited great research interest. In particular, the Orthogonal Frequency Division Multiplexing (OFDM)-based multi-user MIMO downlink with Space-Division Multiple Access (SDMA) combines the twofold advantages of MIMO and multi-carrier modulation. It is the essential element ...

The goal of this Ph.D. dissertation is to address a number of challenges encountered in the digital baseband design of modern and future wireless communication systems. The fast and continuous evolution of wireless communications has been driven by the ambitious goal of providing ubiquitous services that could guarantee high throughput, reliability of the communication link and satisfy the increasing demand for efficient re-utilization of the heavily populated wireless spectrum. To cope with these ever-growing performance requirements, researchers around the world have introduced sophisticated broadband physical (PHY)-layer communication schemes able to accommodate higher bandwidth, which indicatively include multiple antennas at the transmitter and receiver and are capable of delivering improved spectral efficiency by applying interference management policies. The merging of Multiple Input Multiple Output (MIMO) schemes with the Orthogonal Frequency Division Multiplexing (OFDM) offers a flexible signal processing substrate to implement ...

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) ...

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 ...

Filter bank based multicarrier is an evolution with many advantages over the widespread OFDM multicarrier scheme. The author of the thesis stands behind this statement and proposes various solutions for practical physical layer problems based on filter bank processing of wireless communications signals. Filter banks are an evolved form of subband processing, harnessing the key advantages of original efficient subband processing based on the fast Fourier transforms and addressing some of its shortcomings, at the price of a somewhat increased implementation complexity. The main asset of the filter banks is the possibility to design very frequency selective subband filters to compartmentalize the overall spectrum into well isolated subbands, while still making very efficient use of the assigned bandwidth. This thesis first exploits this main feature of the filter banks in the subband system configuration, in which the analysis filter bank ...

Base station cooperation is recognized as a key technology for future wireless cellular communication networks. Considering antennas of distributed base stations and those of multiple terminals within those cells as a distributed multiple-input multiple-output (MIMO) system, this technique has the potential to eliminate inter-cell interference by joint signal processing and to enhance spectral efficiency in this way. Although the theoretical gains are meanwhile well-understood, it still remains challenging to realize the full potential of such cooperative schemes in real-world systems. Among other factors, such as the limited overhead for pilot symbols and for the feedback and backhaul, these performance limitations are related to channel and synchronization impairments, such as channel estimation, feedback quantization and channel aging, as well as imperfect carrier and sampling synchronization among the base stations. Because of these impairments, joint data precoding results to be mismatched with ...

The ever increasing demand for mobility calls for new mobile communication systems that deal more efficiently with the very limited bandwidth available. While such systems do exist and work well in computer simulations, little is known about their performance under real world conditions. Little is also known about how to best determine and compare the throughput performance of such wireless communication schemes in specific, realistic outdoor scenarios. The range of effective answers spans from performing numerical simulations to building prototypes. In recent years we have determined that a cost, time, and manpower efficient ---as well as effective--- method is that of carrying out quasi-realtime testbed measurements. In this approach, all possible transmit data is generated off-line in Matlab, but only the required data is then transmitted over a wireless channel which is altered by moving the receive antennas. The for ...

The wireless communication industry has experienced rapid growth in recent years, and digital cellular systems are currently designed to provide high data rates at high terminal speeds. High data rates give rise to intersymbol interference (ISI) due to so-called multipath fading. Such an ISI channel is called frequency selective. On the other hand, due to terminal mobility and/or receiver frequency offset the received signal is subject to frequency shifts (Doppler shifts). Doppler shift induces time-selectivity characteristics. The Doppler effect in conjunction with ISI gives rise to a so-called doubly selective channel (frequency- and time-selective). In addition to the channel effects, the analog front-end may suffer from an imbalance between the I and Q branch amplitudes and phases as well as from carrier frequency offset. These analog front-end imperfections then result in an additional and significant degradation in system performance, especially ...

From the perspective of increasingly data rate requirements in mobile communications, it is deemed necessary to do further research so that the future goals can be reached. To that end, the radio-based communications are resorting to multicarrier modulations and spatial diversity. Until today, the orthogonal frequency division multiplexing (OFDM) modulation is regarded as the dominant technology. On one hand, the OFDM modulation is able to accommodate multiantenna configurations in a very straightforward manner. On the other hand, the poor stopband attenuation exhibited by the OFDM modulation, highlights that a definitely tight synchronization is required. In addition, the cyclic prefix (CP) has to be sufficiently long to avoid inter-block interference, which may substantially reduce the spectral efficiency. In order to overcome the OFDM drawbacks, the filter bank multicarrier modulation based on OQAM (FBMC/OQAM) is introduced. This modulation does not need any ...

The aim of this dissertation is the investigation of the key issues encountered in the development of wideband radio air-interfaces. Orthogonal frequency-division multiplexing (OFDM) is considered as the enabling technology for transmitting data at extremely high rates over time-dispersive radio channels. OFDM is a transmission scheme, which splits up the data stream, sending the data symbols simultaneously at a drastically reduced symbol rate over a set of parallel sub-carriers. The first part of this thesis deals with the modeling of the time-dispersive and frequency-selective radio channel, utilizing second order Gaussian stochastic processes. A novel channel measurement technique is developed, in which the RMS delay spread of the channel is estimated from the level-crossing rate of the frequency-selective channel transfer function. This method enables the empirical channel characterization utilizing simplified non-coherent measurements of the received power versus frequency. Air-interface and multiple ...