"Distributed massive MIMO" technology is a candidate for future "beyond 5G" and "6G" mobile networks. By getting several base station transceivers, distributed across building facades or even across multiple buildings, to cooperate, the reliability and the performance of a mobile communications network can be significantly improved compared to a traditional cellular architecture. Furthermore, a network with distributed base station antennas could provide additional services such as end user localization, potentially enhancing or, in some applications, even replacing satellite-based localization systems like GPS.
As one can imagine, getting distributed base station antennas to cooperate in a meaningful way is challenging, especially when it comes to time synchronization. After all, when transmitting at wavelengths of a few centimeters, synchronization offsets of a few picoseconds can cause the entire system to fail.
In a practical experiment with a distributed channel sounder called Distributed Channel Sounder by University of Stuttgart (DICHASUS), INUE researchers have demonstrated that synchronization is possible using an over-the-air reference signal and a set of well-know beacon transmitter locations. This work has been summarized in a paper entitled Channel Sounder with Over-the-Air Antenna Synchronization: Absolute Phase and Timing Calibration Using Known Transmitter Locations, which covers the basic principle of synchronization and potential algorithms. The paper was presented at the European Conference on Networks and Communications (EuCNC 2022) in Grenoble, France.
A tutorial on the topic of time and phase offset calibration in the context of DICHASUS datasets is available on the DICHASUS website.