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Bachelor- und Masterarbeiten

Auf dieser Seite finden sie eine Auswahl der zur Zeit bei uns am Lehrstuhl verfügbaren Abschlussarbeiten. Für weitere Informationen zu einer Abschlussarbeit schauen sie sich bitte die entsprechenden Tabs an oder kontaktieren sie den Betreuer. Es besteht auch die Möglichkeit ein themenbezogenes Praxisprojekt vor Antritt der Bachelorarbeit abzulegen.

Weitere Themen erfragen Sie bitte direkt bei den wissenschaftichen MitarbeiterInnen am Lehrstuhl.

Bachelorarbeiten

Over-the-Air Computation via Intelligent Reflecting Surfaces

With the introduction of solutions based on the Internet of Things (IoT) on various application areas, such as healthcare, industrial control and more, wireless data aggregation (WDA) becomes a promising solution for data collection from sensors with limited bandwidth. In essence, the superposition property of wireless multiple access channels (MAC) is utilized to accelerate our calculations, by letting the channels do the calculations for us. In practical networks, however, unfavorable signal propagation conditions for WDA prevail. To overcome this problem, an intelligent reflecting surface (IRS) is introduced to the network. The IRS is able to reflect incoming signals, while smartly tuning the phase shift at the individual reflect elements. This enables not only new but also controllable channel links improving the signal propagation conditions for WDA significantly.

References:

[1] T. Jiang and Y. Shi, "Over-the-Air Computation via Intelligent Reflecting Surfaces," 2019 IEEE Global Communications Conference (GLOBECOM), Waikoloa, HI, USA, 2019, pp. 1-6.

Also available at: https://arxiv.org/abs/1904.12475

Die Betreuung kann wahlweise in deutsch oder englisch erfolgen.

Picture of Kevin Weinberger
Kevin Weinberger

Wissenschaftliche Mitarbeiter

Raum: ID 2/352
Tel.: +49234 32-23067
E-Mail: kevin.weinberger@rub.de

Tile-based approach for IRS-assisted Systems

The concept of intelligent reflecting surfaces (IRSs) is considered as a promising technology for increasing the efficiency of mobile wireless networks. This is achieved by employing a vast amount of low-cost individually adjustable passive reflect elements, that are able to apply changes to the reflected signal. To this end, the IRS makes the environment real-time controllable and can be adjusted to significantly increase the received signal quality at the users by passive beamsteering. However, controlling each of the reflect elements individually entails a high computational complexity in practice. In order to alleviate this problem, we utilize the idea of resource bundling: By applying the same phase shifts on a block (tile) of adjacent reflect elements, the complexity of the system can be reduced significantly at the cost of a slight performance degradation.

References:

[1] A. Sezgin, B. Bandemer, A. Paulraj and E. A. Jorswieck, "Tile-based MIMO OFDM systems: The impact of inaccurate channel state information," 2008 42nd Asilomar Conference on Signals, Systems and Computers, 2008, pp. 1326-1329, doi: 10.1109/ACSSC.2008.5074633.

Also available at:  https://www.researchgate.net/publication/224505605_Tsile-based_MIMO_OFDM_systems_The_Impact_of_inaccurate_channel_state_information

[2] K. Weinberger, A. A. Ahmad, and A. Sezgin, “On Synergistic Benefits of Rate Splitting in IRS-assisted Cloud Radio Access Networks,” 2020, submitted to ICC2021

Also available at: https://arxiv.org/abs/2011.14763

Die Betreuung kann wahlweise in deutsch oder englisch erfolgen.

Picture of Kevin Weinberger
Kevin Weinberger

Wissenschaftliche Mitarbeiter

Raum: ID 2/352
Tel.: +49234 32-23067
E-Mail: kevin.weinberger@rub.de

Orthogonalization of Quasi-Orthogonal Space-Time Block Codes

Transmit diversity has been studied extensively as a method of combating detrimental effects in wireless fading channels because of its relative simplicity of implementation. One attractive approach to transmit diversity is space-time block coding (STBC), in which full diversity is achieved. The main characteristic of these codes is their orthogonality property, which comes at the cost of the transmission rate. With the introduction of a quasi-orthogonal design higher transmission rates can be provided while sacrificing the full diversity. In order to alleviate this problem, we aim to utilize an intelligent reflecting surface (IRS), which employs a vast amount of low-cost individually adjustable passive reflect elements, that are able to apply changes to the reflected signal. To this end, we can utilize the IRS to support the quasi-orthogonal design and even orthogonalize the design at the users, potentially achieving both, full diversity and higher transmission rates.

References:

[1] B. Badic, M. Rupp and H. Weinrichter, "Quasi-Orthogonal Space-Time Block Codes: Approaching optimality," 2005 13th European Signal Processing Conference, 2005, pp. 1-8.

Also available at https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.332.4395&rep=rep1&type=pdf

Die Betreuung kann wahlweise in deutsch oder englisch erfolgen.

Picture of Kevin Weinberger
Kevin Weinberger

Wissenschaftliche Mitarbeiter

Raum: ID 2/352
Tel.: +49234 32-23067
E-Mail: kevin.weinberger@rub.de

Channel Estimation for IRS Assisted Wireless Communications

Intelligent Reflective Surfaces (IRS) is a promising technology to improve coverage and energy efficiency through intelligent control of the propagation environment. In practice, however, achieving the expected benefits of IRS requires accurate channel estimation.  Most existing works assume the availability of perfect channel state information (CSI) to design the precoding vectors in the BS and the phase shift matrix in the IRS.  However, it is highly unlikely that this assumption will hold in practice. This is because, unlike conventional communications systems where channels can be estimated by actively transmitting, receiving, and processing pilot symbols, the IRS has no radio resources for transmitting and receiving pilot symbols and no signal processing capability for estimating channels. Therefore, it is challenging to obtain accurate CSI.

References:

[1] Z. Wang, L. Liu and S. Cui, "Channel Estimation for Intelligent Reflecting Surface Assisted Multiuser Communications," 2020 IEEE Wireless Communications and Networking Conference (WCNC), 2020, pp. 1-6, doi: 10.1109/WCNC45663.2020.9120452.

 

Also available at: https://arxiv.org/pdf/2104.01221.pdf

Picture of Chu Li
Chu Li

Wissenschaftliche Mitarbeiter

Raum: ID 2/345
Tel.: +49 (0)234/32-23712
E-Mail: chu.li@rub.de

Enhancing the Properties of Edge Caching: A Proactive Scheme

Beyond the fifth generation (B5G) wireless communication networks are expected to be exposed to unprecedented amounts of data traffic, thanks to the tremendous increase in the number of efficient mobile communication devices. Edge caching in wireless networks brings the content closer to users and promises to be an efficient technique to reduce latency and network congestion, especially during peak-traffic communication.
However, the efficiency of caching depends on the distribution of user's content preferences. The proactive scheme of recommendation is capable of reshaping the content request probabilities of different users.
Through analysis and implementation of the recommendation and caching scheme, a deep understanding of its merits shall be
obtained. Different numerical simulations will give useful insights on the characteristics of the schemes.

References:

[1] Y. Fu, L. Salaün, X. Yang, W. Wen and T. Q. S. Quek, "Caching Efficiency Maximization for Device-to-Device Communication Networks: A Recommend to Cache Approach," in IEEE Transactions on Wireless Communications, doi: 10.1109/TWC.2021.3075278.

 

Also available at https://www.researchgate.net/publication/350983414_Caching_Efficiency_Maximization_for_Device-to-Device_Communication_Networks_A_Recommend_to_Cache_Approach

 

Picture of Robert-Jeron Reifert
Robert-Jeron Reifert

Wissenschaftliche Mitarbeiter

Raum: ID 2/352
Tel.: +49234 32-23067
E-Mail: robert-.reifert@ruhr-uni-bochum.de

Intelligent Surface with Imperfect CSI

In order to achieve high beamforming gains and reconfigurable propagation environments with low-cost and low-power systems, intelligent reflecting surface (IRS) also known as reconfigurable intelligent surface (RIS) has recently been proposed as a promising technology for beyond Fifth Generation (5G) communication systems. A crucial factor in the practical design of IRS-assisted system is the channel state information (CSI) errors, which can severely affect the performance of these systems. This is because the IRS elements are passive and can not transmit/receive pilot symbols. Therefore, channel estimation of all involved channels needs to be performed at the BS, which imposes prohibitive training overhead and can result in high CSI errors. While a vast majority of current works make the perfect CSI assumption, there are a few works that assume imperfect CSI in their system model. Here, the goal is to consider the joint optimization of the stochastic coordinated beamforming (SCB) at the BSs constituting and the reflect beamforming at the IRS with the aim of maximizing the expected minimum fairness subject to power constraints and unit-modulus constraint on IRS elements.

References:
 

[1] Shi, Yuanming, Jun Zhang, and Khaled B. Letaief. "Optimal stochastic coordinated beamforming for wireless cooperative networks with CSI uncertainty." IEEE Transactions on Signal Processing 63.4 (2014): 960-973.

Picture of Hossein Esmaeili
Hossein Esmaeili

Wissenschaftliche Mitarbeiter

Raum: ID 2/346
Tel.: +49 (0)234/32-29850
E-Mail: hossein.esmaeili@rub.de

Blockage and Antenna Misalignment in THz Communication

In order to meet the rapidly increasing data rate demands, migration to Terahertz (THz) frequency bands becomes a key feature of future 6G wireless systems. These high fequency bands offer an ultra-broad bandwidth, however, this comes at a cost of high propagation loss and molecular absorption. Hence, massive MIMO antenna arrays are used to generate very narrow beams (pencil beams) in order to overcome the path loss. This makes the communication susceptible to channel blockage and beam misalignment, which can lead to frequent communication outages. To mitigate these effects and provide a reliable communication, a relay can be deployed, providing an alternative link to the user. In [1], the benefit of such a relaying strategy for joint blockage and beam misalignment mitigation is studied.

In the course of the thesis, an understanding of the model and strategies used in [1] should be obtained, followed by implementation (MATLAB) and performance analysis for different scenarios. The thesis can be done in either English or German.

Reference:

[1] Stratidakis, Giorgos, et al. "Relay-based blockage and antenna misalignment mitigation in THz wireless communications." 2020 2nd 6G Wireless Summit (6G SUMMIT). IEEE, 2020.

Also available at: https://arxiv.org/pdf/2003.03964.pdf

Picture of Yasemin Karacora
Yasemin Karacora

Wissenschaftliche Mitarbeiter

Raum: ID 2/333
Tel.: +49 (0)234/32-29473
E-Mail: yasemin.karacora@rub.de

Impact of Beamforming Strategies on Location Privacy

In 5G networks, the amout of data that can be transmitted has increased significantely due to massive MIMO, larger frequencies and bandwidths and smaller cell areas. With a massive MIMO setup, beamforming strategies can be used to send different signal beams into different directions. In this thesis, it should be investigated how much different beamforming strategies can help in order to keep the location of the user equipment (UE) secret to (a) the base-station (BS) with a (possibly imperfectly) known channel and (b) a randomly-located adversary. Therefore, an according system model has to be implemented in Matlab. Afterwards, different precoding strategies have to be derived mathematically, which will then have to be tested in the simulations and analyzed.

The thesis can be written in English or German.

Literature:

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9171875

Picture of Stefan Roth
Stefan Roth

Wissenschaftliche Mitarbeiter

Raum: ID 2/333
Tel.: +49 (0)234/32-23068
E-Mail: stefan.roth-k21@rub.de

Modeling and Digital Compensation of RF Hardware Impairments

The ever-increasing demand for wireless communication performance forces designers to continuously seek designs with more bandwidth and higher carrier frequency. These trends demand extra performance on RF front-ends, which are being forced to operate beyond their operation boundaries. Consequently, this results in increased imperfections on operation characteristics which is becoming a growing concern for the overall system performance. Some such impairments are power amplifier non-linearity, IQ imbalance, and phase noise of local oscillators.  Characterization and mitigation of such hardware impairments by digital signal processing would be a valuable solution, ensuring reliable operation with low-cost technologies.


The thesis can be written in English.


Literature:
[1] P. Rodríguez-Vázquez, J. Grzyb and U. R. Pfeiffer, "RF Front-End Impairments for Ultra-Broadband Wireless Communication above 200 GHz," 2019 16th International Symposium on Wireless Communication Systems (ISWCS), 2019, pp. 335-339.


[2] T. Schenk, Rf imperfections in high-rate wireless systems impact and digital compensation. Dordrecht: Springer, 2008.

Picture of Furkan Hüseyin Ilgac
Furkan Hüseyin Ilgac

Wissenschaftliche Mitarbeiter

Raum: ID 2/347
Tel.: +49234 32-23063
E-Mail: Furkan.Ilgac@ruhr-uni-bochum.de

Resiliente und Gemischt-Kritische Kommunikationssysteme

Praktische Demonstration Resilienter und Gemischt-Kritischer Kommunikationssysteme mittels Intelligenter Reflektierender Oberflächen

Im Hinblick auf die künftige sechste Generation (6G) von Kommunikationssystemen müssen sicherheitskritische Anwendungen, z. B. fahrerloser Verkehr, modulare Industrie und intelligente Städte, auf natürliche Weise in die Kommunikation einbezogen werden. Solche Anwendungen erfordern hohe Leistungskennzahlen, einen zuverlässigen und fehlertoleranten Betrieb und Autonomie. Dabei müssen 6G-Systeme ein Bewusstsein für die Kritikalität bei verschiedenen funktionalen Sicherheitsanwendungen und ein hohes Maß an Resilienz bieten, was die Fehlertoleranz, Robustheit und Anpassungsfähigkeit der Netze einschließt. Daher werden in diesem Projekt die Konzepte der Resilienz und der gemischten Kritikalität gemeinsam betrachtet.
Während bereits verschiedene Techniken für die Ausfallsicherheit von Netzen in Betracht gezogen werden, besteht ein neuartiger Ansatz darin, intelligente reflektierende Oberflächen (IRS) in das Netz einzubeziehen, um Ausfallsicherheit zu gewährleisten. IRS sind eine vielversprechende Technologie, die das Netz auf vielfältige Weise unterstützen können; allerdings wurde die IRS-gestützte Ausfallsicherheit bisher noch nicht berücksichtigt.

Neben einer Literaturrecherche und dem Verständnis der Konzepte liegt der Schwerpunkt dieses Projekts auf der praktischen Umsetzung eines beispielhaften Kommunikationssystems, das Resilienz für gemischt-kritische Netzwerkteilnehmer bietet. Die Implementierung soll auf USRPs erfolgen und das System wird durch eine IRS unterstützt, die verschiedene Ausfallsicherheitsmechanismen implementiert. Zu diesem Zweck soll eine praktische Demonstration von Kommunikationsnetzen entwickelt werden, die eine gemischte Kritikalität berücksichtigen und ein hohes Maß an Ausfallsicherheit bieten.

Referenz:

[R1] R.-J. Reifert, S. Roth, A. A. Ahmad and A. Sezgin, "Comeback Kid: Resilience for Mixed-Critical Wireless Network Resource Management," 2022.

Auch verfügbar: https://arxiv.org/abs/2204.11878

Picture of Robert-Jeron Reifert
Robert-Jeron Reifert

Wissenschaftliche Mitarbeiter

Raum: ID 2/352
Tel.: +49234 32-23067
E-Mail: robert-.reifert@ruhr-uni-bochum.de

Masterarbeiten