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.

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.

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.

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

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

 

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.

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

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

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.

Privacy Violation Over the Air: Intelligent Reflecting Surfaces for Adversarial Wireless Sensing (Master thesis only)

Abstract:
Wireless connectivity drives digital innovation and is becoming increasingly ubiquitous. However, a downside of this trend is the burgeoning of new types of privacy concerns: The radio wave propagation underlying the wireless communication gives away sensitive information to adversaries – regardless of cryptographic measures. Such types of attacks are known as adversarial wireless sensing. For example, adversaries can launch remote surveillance attacks by simply observing the wireless traffic of Wi-Fi devices. Previous work has already demonstrated practical motion detection attacks based on employing physical layer channel information. In this work, we seek to investigate the potential of Intelligent Reflecting Surfaces (IRS) to aid such attacks. The IRS is a new type of wireless infrastructure, essentially a digitally configurable reflector towards radio waves. In your thesis, you will first conduct practical wireless reconnaissance attacks and then try to improve them by utilizing an IRS.

This thesis is a follow-up to our previous work IRShield [1] which we presented at the IEEE Symposium on Security and Privacy (S&P) in 2022. We are looking for a highly motivated candidate, ideally with experience in Python and C programming and with basic knowledge of wireless systems or signal processing. The thesis will have strong focus on practical aspects, including real-world implementation and experimentation. As part of the thesis, there is potential for a joint scientific publication. The thesis is offered in cooperation by the Max Planck Institute for Security and Privacy (MPI-SP) and the RUB chairs Digital Communication Systems (DKS) and Systems Security (SysSec).

[1] https://doi.ieeecomputersociety.org/10.1109/SP46214.2022.9833676

Contact:
If you are interested in the topic, please send an email to paul.staat@rub.de, together with a recent transcript of records (i.e. Grunddatenblatt).

Titel: Dezentrales Funkressourcenmanagement für Digital Twins und Sub-Metaverses: Synchronisation in Multi-Cloud und Multi-MEC Netzwerken

Ziel der Masterarbeit ist ein detailliertes Verständnis der Multi-Cloud/Multi-MEC Kommunikations- und Berechnungsarchitektur, des Konzeptes der Digital Twins und des Metaverses, und der Netzwerkdezentralisierung. Methodisch sollte zunächst eine Literaturrecherche der beiden Referenzen [1], [2] und weiterer relevanter Arbeiten erfolgen. Technisch sollte zunächst die User-to-cloud association aus [2] mit der Metaverse and DT association aus [1] verglichen werden. Das Systemmodell aus [2] sollte um die Konzepte Metaverse und Digital Twin (Synchronization, computation, etc.) erweitert werden. Da die Arbeit [1] allerdings nach der association aufhört, wird das erweiterte Systemmodell aus [2] um ein dezentralisiertes Radio-Ressourcenmanagement erweitert. Die Performance der entwickelten Methoden soll in verschiedenen numerischen Simulationen validiert werden.

Die Arbeit an diesem Thema geht so über den aktuellen Stand der Forschung hinaus. Das Ergebnis der Masterarbeit ist ein erweitertes Systemmodell, welches Konzepte aus [1] und [2] kombiniert, und ein Forschungsbeitrag zum Thema des dezentralisierten Ressourcenmanagements für Digital Twins und Sub-Metaverses.

Referenzen:

[1] O. Hashash et. al., 'Towards a Decentralized Metaverse: Synchronized Orchestration of Digital Twins and Sub-Metaverses,' 2023. [Online] https://arxiv.org/abs/2211.14686.

[2] R.-J. Reifert et. al., 'Distributed Resource Management in Downlink Cache-Enabled Multi-Cloud Radio Access Networks,' 2022. [Online] https://ieeexplore.ieee.org/document/9847048.