Generation of Clock Signal From Received Packet Stream

• US 20090225787A1
• Filed: 11/14/2005
• Published: 09/10/2009
• Est. Priority Date: 11/14/2005
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Andre, Tore Mikael
• Granted Patent: US 7,830,922 B2
• Time in Patent Office: Days
• US Class Current: 370/503
• CPC Class Codes: H04J 3/0658 Clock or time synchronisation among packet nodes

Abstract

A receiving unit receiving packets of a packet stream having an evaluating unit for comparing the arrival times of the packets to a generated clock signal. The generated clock signal is used in transmitting information carried in the packets from the receiving unit. From the delays, a signal producing unit determines a characteristic delay value, which is characteristic of or typical of the statistical distribution of the delays. This characteristic delay value may be an average of the smallest delays of the distribution of delays for the latest received packets, and is used for adjusting the frequency of the generated clock signal. The average may be calculated or derived from all of the smallest delays of the distribution obtained for a predetermined share of the latest received packets.

Claims

1. A receiving unit receiving packets including a device for producing, from received packets, a clock signal, the device including:

a clock signal generator for generating a clock signal having a controllable frequency,

a delay determining unit determining the delays of received packets in relation to the clock signal, the delays of most recently received packets forming a delay distribution ranging from a current minimum delay value to larger delay values, and

an evaluating and control signal producing unit for evaluating delays and for producing a control signal provided to the clock signal generator based on the delays, the evaluating and control signal producing unit including means for determining a characteristic delay value, which is characteristic of the delay distribution and for producing the control signal from the characteristic delay value.

2. The receiving unit according to claim 1, wherein the means for determining the characteristic delay value determines the characteristic delay value as an average of the smallest delays of the delay distribution.

3. The receiving unit receiving according to claim 1, wherein the means for determining the characteristic delay value determines the characteristic delay value as an average of all of the smallest delays of the distribution obtained for a predetermined share of received packets.

4. The receiving unit according to claim 3, wherein the evaluating and control signal producing unit includes an evaluating unit including:

a memory or memory cell for holding a variable threshold value,

a comparing unit for comparing the determined delay of a received packet to the threshold value,

an adaptation unit connected to the comparing unit for adjusting the threshold value dependent on the result of the comparing, and

an averaging unit or low pass filter connected to the comparing unit for determining an average or filtered value of delays of selected ones of received packets, the selecting being dependent on the result of the comparing.

5. The receiving unit according to claim 4, wherein the evaluating unit includes:

a memory or memory cell for holding a variable adaptation speed value, wherein

the adaptation unit also adjusts the threshold value dependent on the adaptation speed value.

6. A method of producing a clock signal in a receiving unit receiving packets, said method comprising the steps of:

generating a clock signal having a controllable frequency,

determining delays of received packets in relation to the clock signal, the delays of most recently received packets forming a delay distribution ranging from a current minimum delay value to larger delay values, and

evaluating delays and producing a control signal for controlling the frequency of the clock signal based on the determined delays, by forming a characteristic delay value, which is characteristic of the delay distribution and producing the control signal from the formed characteristic delay value.

7. The method according to claim 6, wherein in forming the characteristic delay value, the characteristic delay value is formed as an average of the smallest delays of the delay distribution.

8. The method according to claim 6, wherein in forming the characteristic delay value, the characteristic delay value is formed as an average of all of the smallest delays of the delay distribution for a predetermined share of received packets.

9. The method according to claim 8, wherein in forming the average the following steps are executed:

determining, for each received packet, the delay of the packet,

comparing the determined delay of each received packet to a variable threshold value,

adjusting the variable threshold value dependent on the result of the comparing,

selecting determined delays dependent on the result of the comparing, and

determining an average of the selected determined delays or a filtered value from the selected determined delays.

10. The method according to claim 9, wherein the step of adjusting the variable threshold value includes adjusting the variable threshold value dependent on a variable adaptation speed value.

11. A method of issuing information from a receiving unit receiving packets, said method comprising the steps of:

generating a clock signal having a controllable frequency,

determining delays of received packets in relation to the clock signal, the delays of most recently received packets forming a delay distribution ranging from a current minimum delay value to larger delay values,

evaluating delays and producing a control signal for controlling the frequency of the clock signal based on the determined delays, by forming a characteristic delay value characteristic of the delay distribution and producing the control signal from the formed characteristic delay value, and

issuing information from the receiving unit based on the generated clock signal.

12. The method according to claim 11, wherein the characteristic delay value is formed as a quantity or signal substantially equivalent to an average of the smallest delays of the delay distribution.

13. The method according to claim 11, wherein the characteristic delay value is formed as a quantity or signal substantially equivalent to an average of all of the smallest delays of the delay distribution for a predetermined share of received packets.

14. The method according to claim 13, wherein in forming the quantity or signal substantially equivalent to said average the following steps are executed:

determining, for each received packet, the delay of the packet,

comparing the determined delay of each received packet to a variable threshold value,

adjusting the variable threshold value dependent on the result of the comparing,

selecting determined delays dependent on the result of the comparing, and

determining an average of the selected determined delays or a filtered value from the selected determined delays.

15. The method according to claim 14, in wherein the step of adjusting the variable threshold value includes adjusting the variable threshold value dependent on a variable adaptation speed value.