Disputation i kommunikationsteknologi

Ashkan Sheikhi improved wireless systems

Describe your research in a popular science way

It has been more than two decades since we passed the point when the majority of earth's population connected to the internet and gained full access to mobile communications. The number of connected devices, however, has been constantly and rapidly growing due to the emerging applications and services, such as smart vehicles, smart homes, self-controlled robot workers, remote-controlled machinery, and so on. During recent years, not only has the number of connected devices increased rapidly, but also the amount of information transmitted by each device over the wireless networks. Therefore, the demands on the network are increasing significantly daily and the advancements in wireless technology are constantly struggling to keep up with the level of users demands.
 
Massive MIMO (Multiple-Input Multiple-Output) and LIS (Large Intelligent Surface) are two of the major key technologies in the recent wave of advancements in 5G and 6G wireless networks. The performance gain from deploying these systems highly depends on the possibility of increasing the number of transmissions and having antennas receive up to hundreds or thousands of elements. While in theory there can be infinite gain from scaling up these systems, deploying hundreds to thousands of transceiver chains with high-end hardware components limits the scalability of massive MIMO in terms of cost efficiency. Reducing the requirements on hardware components quality while maintaining the system performance is of great importance to enable the scalability of massive MIMO for future wireless networks. In this thesis, we focus on scaling up massive MIMO and beyond with imperfect transceivers. In particular, we study the performance of massive MIMO and LIS systems with imperfect hardware components to analyze the scalability of these systems in practice. We also propose solutions to optimize the system performance while considering the non-ideal effects in hardware components. We propose compensations schemes to mitigate the effects of imperfect transceivers, and we show that by adopting the proposed schemes, we can improve the overall systems efficiency, which paves the way for scaling up massive MIMO systems to meet the increasing demands in future wireless networks.
 
What made you want to pursue a PhD?

I think research is fun simply because it involves a lot of creativity and imagination. Researchers have the possibility to learn new useful things everyday which I find enjoyable. After finishing a master's degree in wireless communications, I wanted to work as a researcher in this field, and doing a PhD in Sweden was the perfect choice for me. The PhD journey has a lot of ups and downs, more than you can imagine, but it is well worth it.

Do you believe some results from your research will be applied in practice eventually? And if so, how / how?

One of the main motivations of this work is to facilitate the implementation of massive MIMO and LIS systems for future wireless networks. In general, the thesis focuses on analysing and compensating the effect of deploying non-ideal hardware components in practical wireless transceivers for massive MIMO and beyond. Therefore, this thesis directly aims to bridge the gap between theory and practice. As an example, one of the key ideas in the thesis has been selected by Ericsson company in Sweden to file a patent application, which is recently granted. I hope the content of the thesis can bring more insight into practical implementation of massive MIMO and LIS for 5G and 6G.

Länk till avhandlingen (på engelska, Lunds universitets forskningsportal)