Apparatus And Method For Determining Timing For Transmissions

Abstract

A communication network element ( 536 ) comprises a transmitter ( 535 ) for transmitting at least one timing data packet to at least one further network element ( 524 ) over both a first communication link and a second communication link and a receiver ( 537 ) for receiving two timing data packets from the at least one further network element ( 524 ) over the second communication link. The communication network element ( 536 ) further comprises signal processing logic ( 538 ) operably coupled to the transmitter and receiver and arranged to calculate a transit delay of the at least one timing data packet over the first communication link based on the received two timing data packets from the at least one further network element ( 524 ) over the second communication link, wherein the signal processing logic ( 538 ) is capable of scheduling at least one transmission across the first communication link to the at least one further network element ( 524 ) in response thereto.

1 . A communication network element comprising:
 a transmitter for transmitting at least one timing data packet to at least one further network element over both a first communication link and a second communication link;   a receiver for receiving two timing data packets from the at least one further network element over the second communication link; and   signal processing logic operably coupled to the transmitter and receiver, wherein the signal processing logic is operable to calculate a transit delay of the at least one timing data packet over the first communication link based on the two timing data packets, and   wherein the signal processing logic is further operable to schedule at least one transmission across the first communication link to the at least one further network element in response to the calculated transit delay.   
     
     
         2 . The communication network element of  claim 1  wherein the signal processing logic is operable to calculate a worst case transmit delay for transmissions to a plurality of further network elements. 
     
     
         3 . The communication network element of  claim 1  wherein the signal processing logic is operable to add a first transmit timestamp (T 1 ) to the at least one timing data packet over at least one of the first communication link and the second communication link. 
     
     
         4 . The communication network element of  claim 3  wherein the at least one further network element is operable to add a receive timestamp (T 2 ) indicating a time that the timing signal is received, and further operable to add a second transmit timestamp (T 3 ) when transmitting a timing data packet to the communication network element. 
     
     
         5 . The communication network element of  claim 1  wherein the signal processing logic is operable to receive the two timing signals from the at least one further network element over the second communication link in response to the respective transmissions over the first and second communication links. 
     
     
         6 . The communication network element of  claim 1  wherein the calculation of a transit delay of the at least one timing data packet by the signal processing logic comprises calculating a round-trip time for the at least one timing data packet over the first communication link and second communication link. 
     
     
         7 . The communication network element of  claim 1  wherein the first communication link is a unidirectional multicast link. 
     
     
         8 . The communication network element of  claim 7  wherein the second communication link is a bidirectional link and the signal processing logic is operable to calculate a transit delay of the at least one timing data packet over the first communication link by subtracting half of a calculated round-trip time of the at least one timing data packet over the second communication link from a calculated round-trip time for the at least one timing data packet transmitted out over the first communication link and back via the second communication link. 
     
     
         9 . The communication network element of  claim 1  wherein the communication network element is operable to support communication of a Forward Access Channel (FACH) Frame Protocol using multicast delivery. 
     
     
         10 . The communication network element of  claim 1  wherein the communication network element is operable to support communication in a 3rd Generation Partnership Project (3GPP) cellular communication network over at least one of:
 a Multimedia Broadcast Multicast Service (MBMS) with soft combining; 
 MBMS over a Single Frequency Network (MBSFN); 
 Iub communication over a satellite communication link; or 
 Iub communication over a terrestrial communication link. 
 
     
     
         11 . The communication network element of  claim 10  wherein the communication network element is operable to transmit a downlink Node Synchronisation message over at least one of the first and second communication links, and in response to the downlink Node Synchronisation message, the communication network element is further operable to transmit an UL Node Synchronisation message over the second communication link. 
     
     
         12 . The communication network element of  claim 1  wherein the communication network element is one of: a radio network controller or a base station controller. 
     
     
         13 . A communication system comprising a communication network element; the communication network element comprising:
 a transmitter for transmitting at least one timing data packet to at least one further network element over both a first communication link and a second communication link;   a receiver for receiving two timing data packets from the at least one further network element over the second communication link; and   signal processing logic operably coupled to the transmitter and receiver, wherein the signal processing logic is operable to calculate a transit delay of the at least one timing data packet over the first communication link based on receiving two timing data packets from the at least one further network element over the second communication link, and the signal processing logic is further operable to schedule at least one transmission across the first communication link to the at least one further network element in response thereto.   
     
     
         14 . A method for determining a timing of multicast transmissions from a network element, the method comprising:
 transmitting at least one timing data packet to at least one further network element over both a first communication link and a second communication link;   receiving two timing data packets from the at least one further network element over the second communication link;   calculating a transit delay of the at least one timing data packet over the first communication link based on receiving two timing data packets from the at least one further network element over the second communication link; and   scheduling at least one transmission across the first communication link to the at least one further network element in response thereto.   
     
     
         15 . Logic for determining a timing of multicast transmissions from a network element, wherein the logic comprises:
 logic for transmitting at least one timing data packet to at least one further network element over both a first communication link and a second communication link;   logic for receiving two timing data packets from the at least one further network element over the second communication link;   logic for calculating a transit delay of the at least one timing data packet over the first communication link based on receiving two timing data packets from the at least one further network element over the second communication link; and   logic for scheduling at least one transmission across the first communication link to the at least one further network element in response thereto.   
     
     
         16 . A communication network element comprising:
 a receiver for receiving at least one timing data packet from a network controller element over both a first communication link and a second communication link;   a transmitter for transmitting two timing data packets from the communication network element to the network controller element over the second communication link; such that the network controller element is operable to calculate a transit delay of the at least one timing data packet over the first communication link based on the two timing data packets,   wherein the communication network element is operable to receive at least one scheduled transmission across the first communication link from the network controller element based on a calculated transit delay.   
     
     
         17 . The communication network element of  claim 16  wherein the communication network element is a Node B of a third generation communication system.