MIMO transmission based communication systems require accurate synchronization in the low sub-nanosecond range, which surpassed the capabilities of current off-the-shelf system. In the traditional/co-localized antenna array, it is straightforward to make phase-coherent transmissions over the different antenna elements. Nevertheless, in a distributed MIMO system such as a cell-free massive MIMO system, timing errors between transmissions from different access points (APs) affect the phase-coherency and thereby the system performance.   

We assume inexpensive APs connected the central unit (CU) via a traditional wired fronthaul/backhaul capable of transmitting accurately data at sufficient speed from/to CU, but not able to distribute a common clock (i.e., timing information) to the APs due to the physical distance between them.  Since each AP is driven by its own individual clock, differences between local times in the different APs give rise to the timing errors. 

The main goal of this internship is to study synchronization procedures that can realize accurate phase-coherent transmissions in a distributed massive MIMO system. Solutions should be scalable to enable large-scale MIMO in a distributed system. 

The internship will be conducted as follows:

-        Study the impact of timing errors on the performance of cell-free massive MIMO systems

-        Study a scalable synchronization scheme that can be implemented in a distributed manner.

-        Implementation of the developed method with a cell-free massive MIMO system 

The candidate should have diverse skills including signal processing dedicated to digital communications, optimization and machine learning.