Distributed synchronization for beyond 4G indoor femtocells

The exponential growth in indoor data traffic necessitates a massive deployment of small cells, and emphasizes the importance of interference coordination and suppression to realize the full potential of this densification. To be effective however, interference coordination and suppression requires strict time synchronization between the cells. This paper deals with distributed runtime synchronization for Beyond 4G femtocells. A simple random scheduling solution for the clock distribution messages is proposed, as well as different clock update mechanisms. Simulation results for a dense cell scenario with two stripes of apartments show that a `multiplicative clock update' exhibits an initial large time divergence among neighbor cells, but is able to achieve a lower long-term error floor than `additive clock update'. Practical implications of the residual time misalignment on the Beyond 4G system design are also addressed.