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


Contact:

Robert-Jeron Reifert
robert-.reifert@rub.de

 

Remote sensing technologies such as radar is used for observing different scene of interest. Information about the same scene can be acquired from different types of techniques such as radar, lidar, optical imaging and ultrasound. In addition to that, these techniques can have different configurations such as bandwidth (narrowband, wideband) and different operating frequencies. Such an acquisition is called as “multi modal data acquisition”. The observations from different models can be coupled (data fusion) to achieve a richer description of the phenomenon / scene of interest.

References:

[1] Z. Xu et al., "Photonics-Based Radar-Lidar Integrated System for Multi-Sensor Fusion Applications," in IEEE Sensors Journal, 2020, doi: 10.1109 / JSEN.2020.3011684.

[2] P. Song, X. Deng, JFC Mota, N. Deligiannis, PL Dragotti and MRD Rodrigues, "Multimodal Image Super-Resolution via Joint Sparse Representations Induced by Coupled Dictionaries," in IEEE Transactions on Computational Imaging, 2020, doi : 10.1109 / TCI.2019.2916502.

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.

Im Rahmen dieser Bachelorarbeit soll eine neue Methode zur Extraktion der Vitalparametern aus den Kanalinformationen des WLan-Systems implementiert werden. Die neue Methode nutzt einen Referenzkanal mittels Koax-Kabel zur Synchronisierung um eine hohere Genauigkeit zu erreichen und Hardwareeffekte auszugleichen.
Die Methode ist in [1] im Detail beschrieben. Die neue Implementierung soll unter gleichen Bedingungen gegen das verfügbare System verglichen und ausgewertet werden. Zusätzlich soll der Algorithmus mit einem alternativen Synchronisierungsschema [2], mittels verteiltem LO clock in den Vergleich mit einbezogen werden. Nach der erfolgreichen Implementierung und Test des Algorithmus wird eine Messreihe uber eine Gruppe von Personen durchgeführt, um Trainingsdaten von verschiedensten Atmungszuständen zu erhalten. Mit diesen Trainingsdaten wird erneut ein Classifier zur Detektion trainiert und in der Performance gegen die bestehenden Methoden verglichen.

[1] D. Zhang, Y. Hu, Y. Chen, and B. Zeng, "Breathtrack:Tracking indoor human breath status via commodity WiFi ," IEEE Internet of Things Journal, vol. 6, no. 2, pp. 3899{3911, 2019.

[2] S. Tewes and A. Sezgin, "WS-WiFi: Wired Synchronization for CSI Extraction on COTS-WiFi-Transceivers," in IEEE Internet of Things Journal, vol. 8, no. 11, pp. 9099-9108, 1 June1, 2021, doi: 10.1109/JIOT.2021.3058179.

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.