Method and system for accurate clock synchronization through interaction between communication layers and sub-layers for communication systems

• US 9,392,565 B2
• Filed: 12/31/2010
• Issued: 07/12/2016
• Est. Priority Date: 03/05/2010
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd. (Samsung Group)
• Original Assignee: Samsung Electronics Co. Ltd. (Samsung Group)
• Inventors: Shao, Huai-Rong, Hsu, Ju-Lan, Ngo, Chiu
• Primary Examiner(s): Kao, Jutai
• Application Number:
  US12/983,208
• Publication Number:
  US 20110216747A1
• Time in Patent Office: 2,020 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: H04J 3/0685 Clock or time synchronisation in a node; Intranode synchronisation
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 56/005 compensating for timing error by adjustment in the receiver
• CPC Class Codes: H04W 56/0065 using measurement of signal travel time

Abstract

Time synchronization in a wireless communication system comprises transmitting a synchronization frame from a transmitter to a receiver over a wireless communication medium. The synchronization frame includes a timestamp indicating the transmitter local time when a symbol at a predefined position of the synchronization frame is placed on the wireless communication medium for transmission. The synchronization frame is received at the receiver which determines a receiving time comprising the receiver local time when said symbol of the synchronization frame was received at the physical layer of the receiver. Time synchronizing is performed by determining a difference between said timestamp and said receiving time, and adjusting the receiver local time based on said difference to time synchronize the receiver with the transmitter.

Claims

1. A method of time synchronization in a wireless communication system, comprising:

transmitting a synchronization frame from a wireless transmitter to a wireless receiver over a wireless communication medium, wherein the synchronization frame includes a timestamp comprising a transmitting time indicating the wireless transmitter local time when a symbol at a predefined position of the synchronization frame is placed on the wireless communication medium for transmission, said predefined position is set to a particular point of one of a preamble and a header of the synchronization frame based on the wireless transmitter determining actual local time when said symbol at said predefined position is transmitted on the wireless communication medium using a particular time information parameter that carries a time value for said predefined position, and the parameter is transmitted at a physical medium dependent (PMD) sub-layer of a physical (PHY) layer of the wireless transmitter;

receiving the synchronization frame at a PHY layer of the wireless receiver;

determining a receiving time comprising the wireless receiver local time when said symbol of the synchronization frame was received from the wireless communication medium at the PHY layer of the wireless receiver;

time synchronizing the wireless receiver with the wireless transmitter by;

determining a difference between said timestamp and said receiving time; and

adjusting the wireless receiver local time based on said difference to time synchronize the wireless receiver with the wireless transmitter,

wherein a media access control (MAC) layer of the wireless transmitter determines the actual local time based on communication from a PHY layer convergence procedure (PLCP) sub-layer of the wireless transmitter PHY layer.

2. The method of claim 1, further comprising:

providing the received synchronization frame to a higher communication layer at the wireless receiver, wherein the synchronization frame arrives at said higher communication layer at an arriving time indicating a receiver local time at which the synchronization frame arrived at said higher communication layer;

wherein time synchronizing the wireless receiver with the wireless transmitter comprises;

using said timestamp of the received synchronization frame to determine a difference between said timestamp and said receiving time;

determining a revised local time based on a combination of said arriving time and said difference; and

updating the receiver local time based on the revised local time to time synchronize the wireless receiver with the wireless transmitter.

3. The method of claim 1, further comprising:

reading a transmitter local clock to obtain the actual local time when said symbol at said predefined position of the synchronization packet is placed on the wireless communication medium for transmission to the wireless receiver; and

reading a receiver local clock to obtain the local time when said symbol at said predefined position of the synchronization packet is received on the wireless communication medium from the wireless transmitter.

4. The method of claim 1, wherein time synchronizing the wireless receiver with the wireless transmitter comprises:

adjusting the wireless receiver local time by adding a processing delay at the wireless receiver PHY layer and a processing delay between the wireless receiver PHY layer and said higher communication layer.

5. The method of claim 1, wherein:

said timestamp comprises a transmitting time estimating the wireless transmitter local time when said symbol at said predefined position of the synchronization frame is placed on the wireless communication medium for transmission.

6. The method of claim 1, wherein:

said timestamp comprises a transmitter local time when said symbol at said predefined position of the synchronization frame is placed on the wireless communication medium for transmission.

7. The method of claim 1, wherein:

wireless communication system comprises a wireless local area network; and

the wireless receiver further comprises a MAC layer for wireless communication, and said higher communication layer of the wireless receiver comprises the MAC layer.

8. The method of claim 7, wherein:

said predefined position is set to a starting point of a preamble of the synchronization frame.

9. The method of claim 8, wherein:

the MAC layer of the wireless transmitter determines the actual local time when said symbol at said predefined position is transmitted on the wireless communication medium using the particular time information parameter, after the PLCP sub-layer of the wireless transmitter PHY layer issuing a PHY_TXSTART.confirmation (TXSTATUS) primitive to the wireless transmitter MAC layer, and the particular time information parameter comprises a TIME_OF_DEPARTURE parameter; and

the TIME_OF_DEPARTURE parameter carries the time value for the starting point of the preamble.

10. The method of claim 9, further comprising:

the MAC layer of the wireless receiver obtaining the estimated time that the PHY layer of the wireless receiver commenced receiving said preamble of the synchronization packet, using a RX_START_OF_FRAME_OFFSET parameter within a RXVECTOR, after a PLCP sub-layer of the wireless receiver PHY layer issues the PHY_RXSTART.indication (RXVECTOR) primitive to the wireless receiver MAC layer;

wherein the RX_START_OF_FRAME_OFFSET parameter carries the estimated time offset from the point in time at which the start of the synchronization frame preamble arrived at the wireless receiver PHY layer, to the point in time at which the PHY_RXSTART.indication primitive is issued to the wireless receiver MAC layer.

11. The method of claim 7, wherein said predefined position is set to a starting point of the PLCP header of the synchronization frame.

12. The method of claim 11, further comprising:

the MAC layer of the wireless transmitter determining the actual local time when said symbol at said predefined position is transmitted on the wireless communication medium since a PHY_TXSTART.confirmation is issued to the wireless transmitter MAC layer at the start of the PLCP header.

13. The method of claim 12, further comprising:

the PMD sub-layer of the wireless receiver PHY layer issuing a PM_DATA.ind to a PLCP sub-layer of the wireless receiver PHY layer, at the beginning of the PLCP header;

determining when the beginning of the PLCP header is received at the PMD sub-layer of the PHY layer; and

issuing PHY_RXSTART.indication (RXVECTOR) to the wireless receiver MAC layer at the end of PLCP header.

14. The method of claim 13, further comprising:

providing a RX_START_TIME_OF_PLCP_HEADER parameter in the RXVECTOR to record the time when the PMD_DATA. ind is issued to the PLCP sub-layer of the wireless receiver PHY layer;

wherein the RX_START_TIME_OF_PLCP_HEADER parameter indicates the time that the beginning of the PLCP header is received at the PMD sub-layer of the wireless receiver PHY layer.

15. The method of claim 7, wherein said predefined position is set to an end point of the PLCP header of the synchronization frame.

16. The method of claim 15, further comprising:

providing a PHY_TXPLCPEND.indication primitive;

the wireless transmitter obtaining local time directly using the primitive PHY_TXPLCPEND.indication issued to the transmitter MAC layer when the transmission of PLCP header is completed at the wireless transmitter PHY layer.

17. The method of claim 16, further comprising:

the wireless transmitter MAC layer obtaining the local time when transmission of the PLCP header is completed at the PHY layer, by recording the time when the PHY_TXPLCPEND.indication primitive is received from the PLCP sub-layer of the wireless transmitter PHY layer.

18. The method of claim 17, further comprising:

issuing PH_RXSTART.indication (RXVECTOR) to the wireless receiver MAC layer at the end of PLCP header; and

the wireless receiver MAC layer obtaining local time since the PHY_RXSTART.indication is issued to the wireless receiver MAC layer at the end of the PLCP header.

19. The method of claim 1, wherein the wireless communication system comprises a wireless local area network.

20. The method of claim 19, wherein the wireless local area network comprises a millimeter wave wireless local area network.

21. The method of claim 20, wherein the wireless transmitter and the wireless receiver include wireless radios operating in a 60 GHz and the wireless communication medium comprises a wireless radio frequency channel.

22. The method of claim 21, wherein:

the wireless transmitter comprises an access point; and

the synchronization packet comprises a broadcast beacon from transmitted by the access point over the wireless radio frequency channel.

23. The method of claim 1, wherein said predefined position is set to one of a starting point of the synchronization frame, staring point of the PLCP header of the synchronization frame, or an end point of the PLCP header of the synchronization frame.

24. A wireless communication system, comprising:

a wireless transmitter; and

a wireless receiver;

the wireless transmitter comprising a synchronization interface configured to transmit a synchronization frame to the wireless receiver over a wireless communication medium, the synchronization frame including a timestamp comprising a transmitting time indicating the wireless transmitter local time when a symbol at a predefined position of the synchronization frame is placed on the wireless communication medium for transmission, wherein said predefined position is set to a particular point of one of a preamble and a header of the synchronization frame based on the wireless transmitter determining actual local time when said symbol at said predefined position is transmitted on the wireless communication medium using a particular time information parameter that carries a time value for said predefined position, and the parameter is transmitted at a physical medium dependent (PMD) sub-layer of a physical (PHY) layer of the wireless transmitter;

the wireless receiver comprising a synchronization interface configured to determine a receiving time comprising the wireless receiver local time when said symbol of the synchronization frame was received from the wireless communication medium at a PHY layer of the wireless receiver, and to provide the received synchronization frame to a higher communication layer at the wireless receiver, wherein the synchronization frame arrives at said higher communication layer at an arriving time indicating a wireless receiver local time at which the synchronization frame arrived at said higher communication layer;

the wireless receiver synchronization interface is configured to time synchronize the wireless receiver with the wireless transmitter by being configured to;

determine a difference between said timestamp and said receiving time; and

adjust the wireless receiver local time with said difference to time synchronize the wireless receiver with the wireless transmitter,

wherein a media access control (MAC) layer of the wireless transmitter determines the actual local time based on communication from a PHY layer convergence procedure (PLCP) sub-layer of the wireless transmitter PHY layer.

25. The system of claim 24, wherein the wireless receiver synchronization interface time synchronizes the wireless receiver with the wireless transmitter based on the wireless receiver being configured to:

use said timestamp of the received synchronization frame to determine a difference between said timestamp and said receiving time;

determine a revised local time based on a combination of said arriving time and said difference; and

update the wireless receiver local time based on the revised local time.

26. The system of claim 24, wherein:

the wireless transmitter synchronization interface is configured to read a transmitter local clock to obtain the local time when said symbol at said predefined position of the synchronization packet is placed on the wireless communication medium for transmission to the wireless receiver; and

the wireless receiver synchronization interface is configured to read a receiver local clock to obtain the local time when said symbol at said predefined position of the synchronization packet is received on the wireless communication medium from the wireless transmitter.

27. The system of claim 24, wherein the wireless receiver synchronization interface is configured to adjust the wireless receiver local time by adding a processing delay at the wireless receiver layer and a processing delay between the wireless receiver PHY layer and said higher communication layer.

28. The system of claim 24, wherein said timestamp comprises a transmitting time estimating the wireless transmitter local time when said symbol at said predefined position of the synchronization frame is placed on the wireless communication medium for transmission.

29. The system of claim 24, wherein:

the wireless communication system comprises a wireless local area network;

the wireless receiver further comprises a MAC layer for wireless communication; and

said higher communication layer of the receiver comprises wireless receiver MAC layer.

30. The system of claim 29, wherein:

said predefined position is set to a starting point of a preamble of the synchronization frame.

31. The system of claim 30, wherein:

the wireless transmitter synchronization interface includes the wireless transmitter MAC layer for determining the actual local time when said symbol at said predefined position is transmitted on the wireless communication medium using the particular time information parameter, after the PLCP sub-layer of the wireless transmitter PHY layer issues a PHY_TXSTART. confirmation (TXSTATUS) primitive to the transmitter MAC layer, wherein the particular time information parameter comprises a TIME_OF_DEPARTURE parameter; and

the TIME_OF_DEPARTURE parameter carries the time value for the starting point of the preamble.

32. The system of claim 31, wherein:

the wireless receiver synchronization interface includes the wireless receiver MAC layer that is configured to obtain the estimated time that the PHY layer of the wireless receiver commenced receiving said preamble of the synchronization packet, using a RX_START_OF_FRAME_OFFSET parameter within a RXVECTOR, after a PLCP sub-layer of the wireless receiver PHY layer issues the PHY_RXSTART. indication (RXVECTOR) primitive to the wireless receiver MAC layer; and

the RX_START_OF_FRAME_OFFSET parameter carries the estimated time offset from the point in time at which the start of the synchronization frame preamble arrived at the wireless receiver PHY layer, to the point in time at which the PHY_RXSTART. indication primitive is issued to the wireless receiver MAC layer.

33. The system of claim 29, wherein said predefined position is set to a starting point of the PLCP header of the synchronization frame.

34. The system of claim 33, wherein:

the wireless transmitter synchronization interface includes the wireless transmitter MAC layer for determining the actual local time when said symbol at said predefined position is transmitted on the wireless communication medium since a PHY_TXSTART.confirmation is issued to the wireless transmitter MAC layer at the start of the PLCP header.

35. The system of claim 34, wherein:

the PMD sub-layer of the wireless receiver PHY layer is configured to issue a PM_DATA.ind to the PLCP sub-layer of the wireless receiver PHY layer, at the beginning of the PLCP header;

the wireless receiver synchronization interface is configured to determine when the beginning of the PLCP header is received at the PMD sub-layer of the PHY layer; and

the wireless receiver PHY layer is configured to issue a PHY_RXSTART.indication (RXVECTOR) to the wireless receiver MAC layer at the end of the PLCP header.

36. The system of claim 35, wherein:

a RX_START_TIME_OF_PLCP_HEADER parameter is provided in the RXVECTOR and is configured to record the time when the PMD_DATA. ind is issued to the PLCP sub-layer of the wireless receiver PHY layer; and

the RX_START_TIME_OF_PLCP_HEADER parameter indicates the time that the beginning of the PLCP header is received at the PMD sub-layer of the wireless receiver PHY layer.

37. The system of claim 29, wherein said predefined position is set to an end point of the PLCP header of the synchronization frame.

38. The system of claim 37, wherein:

a PHY_TXPLCPEND.indication primitive is provided; and

the wireless transmitter obtains local time directly using the primitive PHY_TXPLCPEND.indication issued to the wireless transmitter MAC layer when the transmission of PLCP header is completed at the wireless transmitter PHY layer.

39. The system of claim 38, wherein:

the wireless transmitter MAC layer obtains the local time when transmission of the PLCP header is completed at the PHY layer, by recording the time when the PHY_TXPLCPEND.indication primitive is received from a PHY layer convergence procedure (PLCP) sub-layer of the wireless transmitter PHY layer.

40. The system of claim 39, wherein:

a PHY_RXSTART.indication (RXVECTOR) is issued to the wireless receiver MAC layer at the end of the PLCP header; and

the wireless receiver MAC layer obtains local time since the PHY_RXSTART.indication is issued to the wireless receiver MAC layer at the end of the PLCP header.

41. The system of claim 24, wherein:

the wireless communication system comprises a millimeter wave wireless local area network and the wireless communication medium comprises a wireless radio frequency channel;

the wireless transmitter comprises an access point; and

the synchronization packet comprises a broadcast beacon transmitted by the access point over the wireless radio frequency channel.

42. A wireless receiver, comprising:

a wireless receiver physical (PHY) layer configured to perform wireless communication to receive a synchronization frame over a wireless communication medium, the synchronization frame including a timestamp comprising a transmitting time indicating a wireless transmitter local time when a symbol at a predefined position of the synchronization frame is placed on the wireless communication medium for transmission to the wireless receiver, wherein said predefined position is set to a particular point of one of a preamble and a header of the synchronization frame based on the wireless transmitter determining actual local time when said symbol at said predefined position is received, from a physical medium dependent (PMD) sub-layer of a wireless transmitter physical (PHY) layer, on the wireless communication medium using a particular time information parameter that carries a time value for said predefined position; and

a synchronization interface configured to determine a receiving time comprising the wireless receiver local time when said symbol of the synchronization frame was received from the wireless communication medium at the PHY layer of the wireless receiver, and to provide the received synchronization frame to a higher communication layer at the wireless receiver, wherein the synchronization frame arrives at said higher communication layer at an arriving time indicating a wireless receiver local time at which the synchronization frame arrived at said higher layer;

the wireless receiver synchronization interface is configured to time synchronize the wireless receiver with the wireless transmitter by being configured to;

determine a difference between said timestamp and said receiving time; and

adjust the wireless receiver local time with said difference to time synchronize the wireless receiver with the wireless transmitter,

wherein a media access control (MAC) layer of the wireless transmitter obtains the actual local time based on communication from a PHY layer convergence procedure (PLCP) sub-layer of the wireless transmitter PHY layer.

43. The wireless receiver of claim 42, wherein the wireless receiver synchronization interface time synchronizes the wireless receiver based on the wireless receiver being configured to:

use said timestamp of the received synchronization frame to determine a difference between said timestamp and said receiving time;

determine a revised local time based on a combination of said arriving time and said difference; and

update the wireless receiver local time based on the revised local time.

44. The wireless receiver of claim 42, wherein:

the wireless receiver synchronization interface is configured to read a receiver local clock to obtain the local time when said symbol at said predefined position of the synchronization packet is received on the wireless communication medium.

45. The wireless receiver of claim 42, wherein the wireless receiver synchronization interface is configured to adjust the wireless receiver local time by adding a processing delay at the wireless receiver PHY layer and a processing delay between the wireless receiver PHY layer and said higher communication layer.

46. The wireless receiver of claim 42, wherein said timestamp comprises a transmitting time estimating a wireless transmitter local time when said symbol at said predefined position of the synchronization frame is placed on the wireless communication medium for transmission.

47. The wireless receiver of claim 42, wherein:

the wireless communication medium comprises a wireless local area network; and

said higher communication layer of the wireless receiver comprises a media access control (MAC) layer.

48. The wireless receiver of claim 47, wherein:

said predefined position is set to a starting point of a preamble of the synchronization frame.

49. The wireless receiver of claim 48, wherein:

the wireless receiver synchronization interface includes the wireless receiver MAC layer for obtaining the estimated time that the PHY layer of the wireless receiver commenced receiving said preamble of the synchronization packet, using a RX_START_OF_FRAME_OFFSET parameter within a RXVECTOR, after the PLCP sub-layer of the wireless receiver PHY layer issues the PHY_RXSTART.indication (RXVECTOR) primitive to the wireless receiver MAC layer;

the RX_START_OF_FRAME_OFFSET parameter carries the estimated time offset from the point in time at which the start of the synchronization frame preamble arrived at the wireless receiver PHY layer, to the point in time at which the PHY_RXSTART.indication primitive is issued to the wireless receiver MAC layer;

the particular time information parameter comprises a TIME_OF_DEPARTURE parameter; and

the TIME_OF_DEPARTURE parameter carries the time value for the starting point of the preamble, to be transmitted at the PMD sub-layer of the transmitter PHY layer.

50. The wireless receiver of claim 47, wherein said predefined position is set to a starting point of the PLCP header of the synchronization frame.

51. The wireless receiver of claim 50, wherein:

the PMD sub-layer of the wireless receiver PHY layer is configured to issue a PM_DATA.ind to the PLCP sub-layer of the wireless receiver PHY layer, at the beginning of the PLCP header;

the wireless receiver synchronization interface is configured to determine when the beginning of the PLCP header is received at the PMD sub-layer of the wireless receiver PHY layer; and

the wireless receiver PHY layer is configured to issue a PHY_RXSTART.indication (RXVECTOR) to the wireless receiver MAC layer at the end of PLCP header.

52. The wireless receiver of claim 51, wherein:

a RX_START_TIME_OF_PLCP_HEADER parameter is provided in the RXVECTOR to record the time when the PMD_DATA.ind is issued to the PLCP sub-layer of the wireless receiver PHY layer; and

the RX_START_TIME_OF_PLCP_HEADER parameter indicates the time that the beginning of the PLCP header is received at the PMD sub-layer of the wireless receiver PHY layer.

53. The wireless receiver of claim 47, wherein said predefined position is set to an end point of the PLCP header of the synchronization frame.

54. The wireless receiver of claim 53, wherein:

a PHY_RXSTART.indication (RXVECTOR) is issued to the wireless receiver MAC layer at the end of the PLCP header; and

the wireless receiver MAC layer obtains local time since the PHY_RXSTART.indication is issued to the wireless receiver MAC layer at the end of the PLCP header.

55. The wireless receiver of claim 42, wherein:

the wireless communication system comprises a millimeter wave wireless local area network;

the wireless communication medium comprises a wireless radio frequency channel; and

the synchronization packet comprises a broadcast beacon received from an access point over the wireless radio frequency channel.