Frame synchronisation in a radio access network

A method of optimizing the timing offsets with which data frames are transmitted over the Iur/Iub interfaces of a UMTS Terrestrial Radio Access Network, UTRAN, the method comprising:

• for a given Iur/Iub interface or set of Iur/Iub interfaces over which identical user plane data is to be sent, defining a duration of a data frame receiving window for use by one or more receiving node(s);
• transmitting data frames from a sending node with an initial timing offset;
• reducing the initial timing offset using a first relatively small timing offset value α until a report is received that a transmitted data frame is outside of the data frame receiving window;
• in response to the report, increasing the reduced timing offset using a second relatively large timing offset adjustment value β;
• at the one or more receiving nodes, collecting and/or computing time of arrival statistics for received data frames;
• reporting said statistics to the sending node;
• and
• adjusting the timing offset at the sending node on the basis of the received statistics, wherein β=kα and k is a constant greater than 1.

A node for use in a UMTS Terrestrial Radio Access Network, UTRAN, where for a given Iur/Iub interface or set of Iur/Iub interfaces over which identical user plane data is to be sent, there is a data frame receiving window having a defined duration, the node comprising:

• a transmitter for transmitting data frames to one or more receiving nodes via lub/lur interfaces with an initial timing offset;
• electronic control circuitry arranged to:
• reduce by an amount a the timing offset in a stepwise manner, and
• adjust the timing offset by increasing an amount β, reduced timing offset in response to the receipt of one or more late time of arrival error reports, wherein the relatively small step value a is smaller than the relatively large adjustment value β, and wherein β=kα and k is a constant greater than 1.

A node for use in a UMTS Terrestrial Radio Access Network, UTRAN, the node comprising:

• means for transmitting data frames to one ore more receiving nodes via lub/lur interfaces with an initial timing offset;
• means for reducing the initial timing offset using a first relatively small timing offset value α until a report is received that a transmitted data frame is outside of a data frame receiving window;
• means, in response to the report, for increasing the reduced timing offset using a second relatively large timing offset adjustment value β;
• wherein β=kα and k is a constant greater than 1, and
• means for receiving statistical data sent periodically from the or each receiving node and relating to the times of arrival of data frames at respective receiving nodes and for adjusting the timing offset on the basis of the received statistics.