Network synchronization for dense small cell networks

Although the development of the next generation (i.e., 5G) of wireless networks is in its initial phase, it is widely agreed that some key technologies will play a vital role in the realization of 5G, such as millimeter waves, massive MIMO, small cells, and new radio air interfaces. Among these, densely deployed small cell networks are believed to be one of the most practical solutions to the 5G promise of truly ubiquitous mobile broadband. However, synchronization between densely deployed small cells is the key to the materialization of the benefits a small cell network promises, and is one of the most challenging issues of small cell networks. In this article, we overview the existing network synchronization techniques and address their limitations in small cell network deployment environments. There are two primary synchronization techniques in today's communication networks. GNSS provides the most accurate synchronization accuracy. However, due to environmental and cost limitations, GNSS may not be available in some small cell deployment scenarios (e.g., indoors). Another synchronization technique is IEEE 1588, the accuracy of which depends highly on backhaul conditions. We therefore study the feasibility of a radio-interface- based solution as a practical alternative to the synchronization problem of a dense small cell network with an application to LTE.