05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Equalization and blind signal combining algorithms for mobile television broadcast reception(2016) Ahmed, Rana; Speidel, Joachim (Prof. Dr.-Ing.)Item Open Access Channel estimation and precoding in closed-loop distributed multi-antenna systems(2015) Wild, Thorsten; Speidel, Joachim (Prof. Dr.-Ing.)Today’s wireless cellular systems are limited by inter-cell interference. Coordinated multi-point transmission and reception (CoMP) is a promising approach to cope with this problem. Here, multiple base stations act as a distributed antenna system, exchanging coordination information and potentially user data via backhaul in order to reduce this interference, increasing spectral efficiency and generating a more homogeneous user experience throughout the entire cell, especially at the currently weak cell edges. This dissertation aims at enabling coordinated multi-point systems by dealing with its current realization challenges. Accurate channel knowledge is required both at transmitter and receiver side in order to realize the CoMP gains. Hence, practical channel estimation algorithms are investigated and developed in order to get as accurate channel knowledge as possible with manageable computational complexity under realistic system operation points. Especially the often neglected obtainment of statistical parameter knowledge is included here, which is challenging under dynamic user scheduling conditions. A multi-user multi-cell channel estimator is provided which, even for larger number of coordinated cells, can get receiver performance fairly close to performance with perfect channel knowledge. Furthermore, different downlink precoding and receive combining strategies are compared against each other under imperfect channel knowledge. As the number of coordinated cells - the cluster size - is limited in practice, mobiles at cluster edges suffer from inter-cluster interference. A novel patented precoding and control signaling scheme is introduced in order to deal with the inter-cluster interference.Item Open Access Low-complexity adaptive digital equalizers for electronic dispersion compensation in optical fiber links(2022) Efinger, Daniel; Speidel, Joachim (Prof. Dr.-Ing.)This thesis addresses electronic equalization of intersymbol interference caused by chromatic and polarization mode dispersion in intensity-modulated optical communication links with direct detection. The simple and cost-efficient system setup is, even at high bit rates of 40 Gbit/s and beyond, of interest for short-haul optical links in metropolitan, aggregation or local area networks. Therefore, this thesis investigates preferably simple and low-complexity equalizer structures, which are able to compensate well for the nonlinear characteristics and influences of the intensity-modulated optical communication link with direct detection. Starting with system modeling and the introduction to different equalization methods, we identify low-complexity feed-forward and decision-feedback equalizers in the first part of this thesis. We further put their chromatic and polarization mode dispersion compensation performance to the broader context by comparison to maximum likelihood sequence estimation. Finally, we come to the investigation of adaptation algorithms for equalizer coefficient adjustment, which accounts for the time-variant nature of polarization mode dispersion, while still targeting preferably simple and efficient realization.Item Open Access Spectrally efficient transmitter diversity scheme for optical satellite feeder links(2024) Mustafa, Ahmad; Ten Brink, Stephan (Prof. Dr.-Ing.)There is an ever-growing demand for increasing the data traffic in the order of Tb/s to the geostationary (GEO) satellites. It will help connect numerous users on the ground who do not have access to internet service. This high throughput can be achieved using multiple laser beams in the uplink and combining them with the dense wavelength division multiplexing technique. However, optical signals propagating through the turbulent atmosphere to GEO satellites suffer from the intensity and phase fluctuations. Additionally, atmospherically induced beam wander leads to pointing errors at the satellite resulting in deep fades, hence loss of signal power which can fall below the receiver sensitivity making the communication impossible. The problem of photon scarcity can be tackled by using advanced power-efficient coherent modulation formats which are highly sensitive, but they come at the expense of increased system complexity. Therefore, in this thesis, only an intensity modulation and direct detection scheme called non-return-to-zero on-off keying is considered, which is relatively easier to implement in free-space optical communications. To mitigate the atmospheric fades, a transmitter diversity technique called MISO is considered for GEO feeder links for reliable signal reception at the satellite. It requires multiple laser beams to propagate through uncorrelated channels, which can be achieved by having a physical separation between the transmitting telescopes greater than the atmospheric coherence length. This thesis is divided into two main parts: The first part includes the quantitative analysis of the MISO scheme with no spectral overlapping between the neighboring signals. Here, the fading consists of log-normal scintillation and residual beam pointing jitter. The bit error rate (BER) for the single-input single-output and MISO systems is obtained using the fading statistics of the atmosphere and considering the receiver model of a commercially available 10Gb/s photoreceiver with an avalanche photodiode. For the given atmospheric conditions and residual beam pointing jitter, the transmit power of each beam is optimized to minimize the overall power scintillation index and maximize the BER gain. The second part of the thesis aims at increasing the spectral efficiency of the transmission system where SSB signals are generated using optical filters to achieve the desired BER performance. A laboratory experiment with a 32Gb/s system is performed in a back-to-backup setup to optimize the SSB signals using a passive filtering technique. Here, the filter bandwidth and the center frequency from the carrier are optimized to get the error-free performance. Finally, simulations are performed where the optimized upper sideband and lower sideband from the respective double-sideband signals are obtained, and then they are propagated through the atmospheric channel, which consists of log-normal scintillation effects and phase piston. The carrier separation between the two signals is selected such to emulate constructive and destructive interference due to the slowly varying phase piston. A diversity gain of 2.3dB is achieved, which shows the efficacy of using transmitter diversity in a GEO uplink channel.Item Open Access Digital pre- and post-equalizers for in-car data transmission over plastic optical fibers(2014) Voigt, Yixuan; Speidel, Joachim (Prof. Dr.-Ing. )Lately, a hot topic in the automobile industry is the development of the in-vehicle infotainment communication network based on the media oriented system transport (MOST) standard, where a cost-effective optical physical layer composed of light emitting diodes (LED), plastic optical fibers (POF) and positive-intrinsic-negative photodiodes (PIN PD) is used by the in-car network. The latest MOST150 standard has specified a transmission speed of 150 Mbit/s, while the next MOST generation is targeted at multi-Gbit/s. Obviously, the very limited bandwidth of the current physical layer will weigh on the future MOST generations. However, it is important to evaluate the potential of the current physical layer, for the reason that the car-manufacturers may continue using the low-cost and easily operable POFs and LEDs. The objective of this dissertation is to increase the data-rate for the next MOST generation from 150 Mbit/s to 2 ∼ 3 Gbit/s, based upon the current MOST150 optical physical layer. The main emphasis lies in investigating electronic signal processing techniques to detect the multi-level pulse-amplitude modulated (MPAM) signal transmitted through the noisy dispersive POF-based optical channel. To be specific, four different transmission schemes are studied respectively: the post-equalization scheme using either linear or decision-feedback equalizer, the joint pre- and post-equalization scheme, the non-linear Tomlinson-Harashima precoding (THP) scheme, and the bidirectional decision feedback equalization (BiDFE) scheme. In the BiDFE scheme, a novel trellis-based BiDFE (TB-BiDFE) equalizer is proposed. Their performances are investigated by means of theoretical analysis and computer simulations. As will be shown, with the help of electronic equalizers and error-correcting code, the final bitrate is able to reach 3 Gbit/s over a 10 m standard step-index POF, despite the use of a low-cost LED transmitter.Item Open Access Die digitale Zukunft - mobil und multimedial(2000) Speidel, JoachimDie Informations- und Kommunikationstechnik durchdringt alle Lebensbereiche des modernen Menschen. Neue Entwicklungen schreiten kräftig voran. Das Telefon mit Wählscheibe ist schon Geschichte, das Kabel hindert unseren Bewegungsdrang. Lautlos sind die Netze und Systeme der Telekommunikation zur Grundlage für die Internationalisierung und Globalisierung des modernen Wirtschaftens geworden. „E-Commerce “ und „E-Business “ heißen die Zauberworte dieser Tage, welche die Börsen der Welt zu Höhenflügen anregen. Für solche Unternehmen reichen Telefon und Telefax schon lange nicht mehr. Internet, das „Netz der Netze “, verschafft uns Zugang zu vielerlei Informationen. Es kostet uns leider noch viel Zeit – oft zu viel Zeit. Durch Kommunikationssysteme sehr hoher Bitraten wird das „World Wide Wait “ bald zum wirklichen World Wide Web (www).Item Open Access Performance analysis of rate adaptive wireless communication system with regenerative relaying using low density parity check codes(2019) Chaoudhry, Bushra Bashir; Speidel, Joachim (Prof. Dr.-Ing.)Item Open Access Investigations of the error resilient rate distortion optimization for H.264 video transport over packet lossy channels(2010) Zeng, Hao; Speidel, Joachim (Prof. Dr.-Ing.)This dissertation first presents a rigorous analysis of the rate-distortion optimization (RDO) framework in H.264 and other similar video coding standards. The analysis is based on the rate-distortion theory and provides a deep theoretical insight into the RDO practice. In the analysis, the crucial assumptions and models on which the RDO is based, are formulated and discussed. Then the validity of deploying the RDO in error resilient video encoding is analyzed. Finally, the dissertation proposes and investigates two modification schemes to the error resilient RDO (ER-RDO) framework in the H.264 reference codec. The schemes are inspired by the aforementioned analyses and seek to find better complexity-performance balance points. The simulation results suggest that the performance of the existing H.264 ER-RDO framework has already been highly optimized. On the other side, algorithm complexity reduction is still possible using one of the proposed schemes.Item Open Access Trends in picture communication(1993) Speidel, JoachimIn the past years significant progress was made with digital transmission of audiovisual services and most interesting trends are visible for the future. Such applications encompass interactive services, like videoconferencing, ISDN-videophone, storage of moving video and audio in computers or on CD, e.g. for multimedia applications. For distribution services, there is an unbroken trend from TV to HDTV. Strong emphasis is on compressed digital video even for transmission to the home.Item Open Access Decentralized interference coordination for the downlink of fully loaded heterogeneous wireless networks(2019) Bleicher, Zarah M. L.; Speidel, Joachim (Prof. Dr.-Ing.)The relentless evolution towards an overwhelming increase of mobile data traffic, where mobile phone subscribers demand the highest data rates and comprehensive coverage presents current and future mobile communication networks with demanding requirements. Previous homogeneous networks were mostly designed to optimize the sum capacity and peak data rates rather than take the individual user experience into account, and therefore failed to meet these requirements. Multi-layer networks, also known as heterogeneous networks, can improve the coverage and capacity of the cellular network and bring the network closer to the user. Moreover, the introduction of the smaller cells into the macro cellular network can improve the performance, especially in hotspots and indoors, which results in a better user experience. Frequency spectrum is rare and valuable, thus solely adding further bandwidth does not meet the demand. However, when reusing the bandwidth, inter-cell interference from neighboring cells leads to performance degradations, in particular for users located at the cell edges. Within a multi-layer network, additional and even more dynamic interference is present, caused by different kinds of cells, like macro-, pico-, femtocells, and relays. Therefore, addressing the interference issue is essential. This thesis examines suitable interference coordination algorithms and introduces an advanced interference coordination technique for heterogeneous networks. Whereas current techniques require significant communication between base stations, reduce the available bandwidth notably or do not consider interference between the small cells, the advanced technique is located in the small cells with only marginal information exchange. Its performance is investigated by means of computer simulations for fully loaded heterogeneous networks on the system layer. As a result, the proposed technique reduces the impact on the surrounding cells significantly, making in-home communication services attractive, leading to a tremendous advantage for service providers as well as the end-user.