Ultra-wideband (UWB) communication systems use radio signals with a bandwidth in the range of some hundred MHz to several GHz. Radio channels with dense multipath propagation achieve high multipath diversity, which can be used to improve the robustness and capacity of the communication channel. Furthermore the large bandwidth allows to transmit signals with a small power spectral density such that the interference to other radio signals will be negligible, even if they lie within the same frequency band. In this work the focus is on low-complexity receiver architectures for communication systems in presence of multiple-access interference (MAI). The main objective of this thesis is to develop and to study a framework for communications for transmitted reference (TR) UWB systems and energy detection UWB systems. First, we study the hybrid matched-filter (HMF) receiver for TR UWB systems, which employs matched filters ...

The aim of this thesis is to investigate key issues encountered in the design of transmission schemes and receiving techniques for Ultra Wideband (UWB) communication systems. Based on different data rate applications, this work is divided into two parts, where energy efficient and robust physical layer solutions are proposed, respectively. Due to a huge bandwidth of UWB signals, a considerable amount of multipath arrivals with various path gains is resolvable at the receiver. For low data rate impulse radio UWB systems, suboptimal non-coherent detection is a simple way to effectively capture the multipath energy. Feasible techniques that increase the power efficiency and the interference robustness of non-coherent detection need to be investigated. For high data rate direct sequence UWB systems, a large number of multipath arrivals results in severe inter-/intra-symbol interference. Additionally, the system performance may also be deteriorated by ...

In a multipath dominated environment, ultra-wideband (UWB) systems that transmit trains of subnanosecond duration pulses exhibit the desirable property of fine resolution in time of the received paths, which as a result of the impulsive form of the transmitted signal go through fewer amplitude fluctuations than those emanating from systems with narrower bandwidths. Being distributed over a large number of resolvable paths, UWB signal energy is typically collected by the rake receiver. In this thesis, achievable information rates of time-hopping M-ary pulse position modulation UWB systems using either soft- or hard-decision outputs are calculated first, where one distinguishing characteristic observed for the hard-output systems is that increasing the constellation size is advantageous only at sufficiently large values of the code rate. Next, it is shown that with time division duplex UWB systems, for which channel information is available at the ...

It is well known that Ultra WideBand (UWB) transmission is inherently robust against small-scale-fading (SSF) that arises in multipath scattering environments, due to its large signal bandwidth. However, no model with a physical interpretation exists that relates the variations of received signal strength to the signal bandwidth and general channel parameters, like e.g. the average channel power delay profile. Such a model would be of relevance for e.g. system designers, who have to make tradeoffs between system aspects, like complexity and energy efficiency on one hand, and robustness against small-scale fading on the other hand. In this thesis, a model is presented that allows for such a tradeoff analysis, relating the average power delay profile parameters and signal bandwidth to the statistical properties of the SSF. Additionally, it is shown how the uncoded and coded BER of BPSK modulation can ...

This thesis investigates noncoherent multi-channel ultra-wideband receivers. Noncoherent ultra-wideband receivers promise low power consumption and low processing complexity as they, in contrast to coherent receiver architectures, relinquish the need of complex carrier frequency and phase recovering. Unfortunately, their peak data rate is limited by the delay spread of the multipath radio channel. Noncoherent multi-channel receivers can break this rate limit due to their capability to demodulate multi-carrier signals. Such receivers use an analog front-end to separate the received signals into their sub-channels. In this work, the modeling and optimization of realistic front-end components is addressed and their impact on the system performance of noncoherent multi-channel ultra-wideband receivers is analyzed. With a proposed generalized mathematical framework, it is shown that there exists a variety of noncoherent multi-channel receiver types with similar system performance which differ only in their front-end filters. It ...

In multiuser ultra-wideband (UWB) systems, a large number of multipath components (MPCs) are introduced by the channel. One of the main challenges for the receiver is to effectively suppress the interference with affordable complexity. In this thesis, we focus on the linear adaptive interference suppression algorithms for the direct-sequence ultrawideband (DS-UWB) systems in both time-domain and frequency-domain. In the time-domain, symbol by symbol transmission multiuser DS-UWB systems are considered. We first investigate a generic reduced-rank scheme based on the concept of joint and iterative optimization (JIO) that jointly optimizes a projection vector and a reduced-rank filter by using the minimum mean-squared error (MMSE) criterion. A low-complexity scheme, named Switched Approximations of Adaptive Basis Functions (SAABF), is proposed as a modification of the generic scheme, in which the complexity reduction is achieved by using a multi-branch framework to simplify the structure ...

Indoor location has experienced a major boost in recent years. location based services (LBS), which until recently were restricted to outdoor scenarios and the use of GPS, have also been extended into buildings. From large public structures such as airports or hospitals to a multitude of industrial scenarios, LBS has become increasingly present in indoor scenarios. Of the various technologies that can be used to achieve this indoor location, the ones based on ultra- wideband (UWB) signals have become ones of the most demanded due primarily to their accuracy in position estimation. Additionally, the appearance in the market of more and more manufacturers and products has lowered the prices of these devices to levels that allow to think about their use for large deployments with a contained budget. By their nature, UWB signals are very resistant to the multi-path phenomenon, ...

In this thesis novel implementation approaches for standardized and non-standardized ultra wide-band (UWB) systems are presented. These implementation approaches include signal processing algorithms to achieve processing of UWB signals in transceiver front-ends and in digital back-ends. A parallelization of the transceiver in the frequency-domain has been achieved with hybrid filterbank transceivers. The standardized MB-OFDM signaling scheme allows par- allelization in the frequency domain by distributing the orthogonal multicarrier modulation onto multiple units. Furthermore, the channel’s response to wideband signals has been parallelized in the frequency domain and the effects of the parallelization have been investi- gated. Slight performance decreases are observed, where the limiting effects are truncated sidelobes and filter mismatches in analog front-ends. Measures for the performance loss have been defined. For UWB signal generation, a novel broadband signal generation approach is presented. For that purpose, multiple digital-to-analog converters ...

In the last decades, ranging systems have benefited from advances in the wireless communication field, as multiple access techniques or near-far mitigation algorithms. In CDMA- based (Code-Division Multiple-Access) ranging systems, the properties of the spreading sequence used play a key role on the development of high-precision ranging measurements. This thesis proposes novel efficient generation/correlation architectures of Complement- ary Sets of Sequences (CSS) and sequences derived from them, as Loosely Synchronized (LS) and Generalized Pairwise Complementary (GPC) sequences. We consider the term efficient applicable whether the proposed architectures requires less operations per input sample in comparison with a straighforward implementation (a Tapped-Delay Line implementation). The contributions of the thesis can be divided into two stages: Firstly, we generalize the efficient generation/correlation architectures for binary CSS, derived in previous works, to the multilevel (real-valued) alphabet by using multilevel Hadamard matrices. This approach ...

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 ...

Wireless communication systems rely on a multiple-access technique, i.e., a mechanism to divide the common transmission medium among di erent users. Code-division multiple-access (CDMA) is a multiple-access technique that has received considerable attention in recent years. In a CDMA system, each user spreads his information-bearing signal into a wideband signal, using speci c code information. All users then transmit their wideband signal within the same frequency and time channel. This thesis deals with the development of receivers for various CDMA systems. Digital signal processing plays a central role in this development. In recent literature, so-called multi-user receivers have become very popular. These receivers take into account the full structure of the multi-user interfer- ence (MUI), i.e., the interference originating from the other users. However, they have a rather high computational complexity. In the rst part of this the- sis, we ...

The implementation of wireless transceivers on a single chip in a single technology requires digital realizations of traditional analog building blocks such as phase-locked loops (PLLs). All-digital PLLs (ADPLLs) utilize the zero crossings of signals instead of their amplitudes to realize the frequency synthesizer entirely in digital CMOS technology. This thesis analyzes ADPLLs and highlights the system-level signal processing aspects. A z-domain model and a mixed-signal model are used to develop signal processing algorithms, to perform high-level simulations, and to evaluate the performance of ADPLLs. The impact of imperfections on the output phase noise spectrum are analytically described and compared to event-driven simulation outcomes. Oscillator noise, frequency quantization noise with sigma-delta noise shaping, and reference clock jitter raise the output phase noise level, whereas phase quantization and injection pulling manifest themselves as spurs in the output phase noise spectrum. Furthermore, ...

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 radio frequency spectrum for commercial wireless communications has become an expensive commodity. Consequently, radio access techniques are required which enable the efficient exploitation of these resources. This, however, is a difficult task due to an increasing diversity of wireless services. Hence, in order to achieve acceptable spectrum efficiency a flexible air– interface is required. It has been demonstrated that code division multiple access (CDMA) provides flexibility by enabling efficient multi user access in a cellular environment. In addition, time division duplex (TDD) as compared to frequency division duplex (FDD) represents an appropriate method to cater for the asymmetric use of a duplex channel. However, the TDD technique is subject to additional interference mechanisms in particular if neighbouring cells require different rates of asymmetry. If TDD is combined with an interference limited multiple access technique such as CDMA, the additional ...

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 ...