High Accuracy Synchronization for Distributed Massive MIMO using White Rabbit

Accurate synchronization is a crucial prerequisite for wireless communication systems and in particular for spatially distributed massive multiple-input multiple-output (MIMO) systems which is also used in the upcoming 5G mobile communication standard. Many applications based on MIMO transmission, such as communication systems or beamforming methods, require synchronization accuracy in the low sub-nanosecond range which surpassed the capabilities of current off-the-shelf system. Furthermore, many of the currently used methods are susceptible to external influences such as temperature or mechanical stress. This paper defines the requirements for such systems and discusses the suitability of some existing synchronization and syn-tonization solutions. The paper further illustrates a measurement setup that allows to evaluate and compare a direct frequency distribution approach over coaxial cables and the White Rabbit timing system using optical fiber. Measurements were conducted under temperature stress to evaluate the performance of the synchronization parameters and their influence on the massive MIMO system. These measurements show that the White Rabbit setup currently meets the requirements for some but not all massive MIMO applications.