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 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 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 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.Item Open Access Un-coordinated multi-user and inter-cell interference alignment based on partial and outdated information for large cellular networks(2016) Aziz, Danish; Speidel, Joachim (Prof. Dr.-Ing.)The cellular networks have gone through rapid evolution during the past decade. However, their performance is still limited due to the problem of interference. Therefore, interference management in current and future cellular networks is still an ongoing research topic. Interference Alignment is one of the techniques to manage the interference efficiently by using "align" and "suppression" strategy. In the first part of this thesis we focus on Coordinated inter cell interference alignment in a large cellular network. We assess the performance of interference alignment based transmit precoding under specific receiver strategies and coordination scenarios by comparing with different state of the art precoding schemes. We continue our assessment by considering imperfect channel state information at the transmitter. The results show that the gains of coordinated alignment based transmission are very sensitive to the receiver strategies and imperfections as compared to the other precoding schemes. However, in case of the availability of good channel conditions with very slow moving users, coordinated interference alignment outperforms the other baselines even with imperfect channel state information. In addition to that, we propose efficient user selection methods to enhance the performance of coordinated alignment. The results of our assessment draws important conclusions about the application of coordinated interference alignment in practical systems. In the second part of the thesis we consider a cellular system where each cell is serving multiple users simultaneously using the same radio resource. In this scenario, we have to manage not only the inter cell interference but also the multi user interference. For this purpose, we propose a novel Uncoordinated transmit precoding scheme for multi user cellular networks which is based on the alignment of multi user interference with partial and outdated inter cell interference. We show analytically that our scheme approaches the performance optimal transmission scheme. With the help of simulations we show that our proposal outperforms the state of the art non-alignment based multi user transmit precoding schemes We further propose user selection methods which exploit the diversity gains and improve the system spectral efficiency. In order to assess the feasibility of our proposal in a real system, we evaluate our scheme with practical constraints like imperfect information at the transmitter and limited feedback in uplink channel. For the proof of concept we also evaluate the performance of our scheme with measured channels using a software defined measurement platform. Finally, we also assess the application of our proposal in future heterogeneous networks. The outcome of our efforts states that as an interference alignment based transmission scheme, our scheme is a good candidate to manage the two dimensional interference in multi user cellular networks. It outperforms the non-alignment baselines in many scenarios even with practical constraints.Item Open Access Coding and modulation for spectral efficient transmission(2010) Muhammad, Nabil Sven; Speidel, Joachim (Prof. Dr.-Ing.)We investigate channel coding and modulation for bandwidth-efficient transmission. For the bit-interleaved coded modulation (BICM) system, we optimize mappings for quadrature amplitude modulation with respect to the resulting symbol and bit error rates at the demapper, and to the achievable BICM and signal set capacities. Further, we design mappings that are most suited for receivers, which exchange information between demapper and decoder in an iterative manner. The mappings are not restricted to certain symbol alphabets, and thus, the optimized mappings outperform similar state-of-the-art schemes. For multi-antenna systems, we examine multidimensional mappings as a means to minimize bit error rates at an iterative receiver. Finally, we derive for block codes over the binary erasure channel closed-form expressions for their transfer characteristics to be used in the extrinsic information transfer chart. Based on that, capacity approaching irregular, i.e., time-varying, codes are suggested.Item Open Access Deep learning for coherent nonlinear optical communications(2025) Uhlemann, Tim; Ten Brink, Stephan (Prof. Dr.-Ing.)Communication, in general, is the transport or exchange of information between two geographically distant points. The higher this distance the more sophisticated methods and materials have to be applied to overcome the same. Current state of the art for long-haul communication are optical fibers, that form the crucial backbone of our global, interlinked and digital society, connecting data-centers, factories and homes. Nevertheless, like all other physical media also the optical fiber induces the ever-present attenuation to the information carrying electromagnetic wave what, finally, limits the achievable throughput. This results in the need for higher input powers provided by (laser) diodes. Over the past decades physical and computational limitations led to an operation of the optical fiber in the linear regime, where attenuation as well as dispersion, and, thus, their compensation, constituted the major challenges. As this has changed recently, the investigation of nonlinearity gained more attraction. This work focuses on the pre-distortion and post-equalization of such nonlinear effects that limit the overall efficiency. Thereby, methods from deep-learning are applied and compared to conventional methods. As those, in general, lack of interpretability, here, the concept of so-called architectural templates is proposed that combines well-known, and, from theory derived, concepts with the ones provided by native deep-learning. This way, the results can be analyzed with proven methods from the field of signal processing. While learning of the receiver is a straight-forward, but still complex, task, even more challenging is learning the transmitter as the optimization, i.e., gradient flow, has to be conducted (backwards) through the optical fiber channel. Here, all learnings and evaluations are performed on an accurate simulation of the optical fiber, what enables an isolation of the investigated nonlinear effects. It results that learning over such accurate nonlinear models is possible as the gradient is preserved and the error can be back-propagated. Further, conventional linear filters for dispersion compensation can be outperformed, when being trained in the nonlinear regime. The extension to a nonlinear architectural template revealed the need for a more sophisticated training procedure proposed in this work. When considering a multi-carrier system the trainable nonlinear template for the transmitter was able to exploit additional information from the neighboring channels.