Network Time-Synchronization in TDD Based LTE-Advanced Systems

In Frequency Division Duplex (FDD) systems or Time Division Duplex (TDD) systems with perfect Uplink (UL)/Downlink (DL) alignment, all UL transmissions receive interference only from other UL links and vice versa. However, take into consideration one of the most important benefits that TDD offers, i.e., dynamic UL/DL switching points, the UL and DL transmission can be misaligned. This means UL might be corrupted by DL, and vice versa. The loss of network time-synchronization among different cells makes things even more complicated for TDD systems. Many techniques are developed to achieve network synchronization, e.g., GPS based or IEEE 1588 based techniques. In this paper, the effect that different synchronization and UL/DL switching points introduce to the system performance is studied. The purpose is to find out the benefit that synchronization can offer. Based on the observations, it is suggested to achieve at least loose network synchronization.