| 摘要 |
A method and system is disclosed for clock synchronization in a wireless backhaul network, based on the IEEE1588 Precision Time Protocol (PTP). The network comprises a plurality of hubs, each hub serving one or more remote backhaul modules. Each hub comprises a slave clock, which communicates with a master clock through forward and reverse links. The method comprises, for each hub, estimating the frequency drift {circumflex over (α)} and offset {circumflex over (β)} from the forward and reverse links between the master and slave clock, estimating the accuracy of {circumflex over (α)} and {circumflex over (β)}, determining the least congested link, and adjusting the frequency of the slave clock based on {circumflex over (α)} and {circumflex over (β)} from the least congested link. A fixed or variable time window size is selected to achieve a desired accuracy of {circumflex over (α)} and {circumflex over (β)}. The method may comprise estimating a maximum holdover time for maintaining synchronization with a desired confidence level. |
| 主权项 |
1. A method for clock synchronization in a fixed wireless backhaul network using IEEE1588 Precision Time Protocol (PTP), the wireless backhaul network comprising a plurality of fixed nodes, each node comprising a hub or a Remote Backhaul Module (RBM), wherein each hub serves one or more Remote Backhaul Modules (RBMs), and wherein each hub comprises a slave clock, and each slave clock communicates with a master clock through a forward link (master-to-slave) and a reverse link (slave-to-master), the method comprising, for each slave clock, the steps of:
for a frame rate of Ft and a time window size W, during each time window W, obtaining a plurality of time-stamps, comprising t1 and t2, for the forward link and t3 and t4, for the reverse link, and storing said plurality of time stamps; determining from said stored time stamps, for said time window W, an estimated frequency drift {circumflex over (α)} and estimated offset {circumflex over (β)} for each of the forward and reverse links; determining an estimation error Δ{circumflex over (α)} of the estimated drift frequency drift {circumflex over (α)} and an estimation error Δ{circumflex over (β)} of the estimated offset {circumflex over (β)} for each of the forward and reverse links; determining which of the forward and reverse links is a least congested link; and if the estimation errors Δ{circumflex over (α)} and Δ{circumflex over (β)} of the least congested link are less than or equal to a predefined maximum estimation error, adjusting the slave clock based on said estimated frequency drift {circumflex over (α)} and estimated offset {circumflex over (β)} of the least congested link; otherwise, changing the window size and repeating the preceding steps until the estimation errors Δ{circumflex over (α)} and Δ{circumflex over (β)} of the least congested link are less than or equal to a predefined maximum estimation error, or, declaring loss of synchronization. |
