METHODS AND SYSTEMS FOR PROVIDING EFFICIENT OPERATION OF MULTIPLE MODES IN A WLAN SYSTEM

• US 20070171858A1
• Filed: 12/29/2006
• Published: 07/26/2007
• Est. Priority Date: 01/04/2006
• Status: Active Grant

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Sammour, Mohammed, Levy, Joseph, Grandhi, Sudheer
• Granted Patent: US 8,014,818 B2
• Time in Patent Office: Days
• US Class Current: 370/328
• CPC Class Codes: H04W 72/20 Control channels or signalling for resource management
• CPC Class Codes: H04W 74/002 Transmission of channel access control information
• CPC Class Codes: H04W 74/0816 with collision avoidance
• CPC Class Codes: H04W 74/0833 Random access procedures, e.g. with 4-step access
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A method and system applies MAC transmission opportunity (TXOP) protection for multiple mode operation in a WLAN system. In particular, MAC mechanisms are defined to support multiple mode CTS frames, and multiple mode CF-End frames sent by the AP, each in a format appropriate for the corresponding mode which also applies to a single mode as a trivial case. MAC mechanisms permit truncation of TXOP duration for releasing the unused portion of the TXOP when no further data for transmission is available. Release of unused protected TXOP is possible for both protected AP transmissions and STA transmissions.

Claims

1. A method for multiple mode operation in a wireless network having an access point and at least one station (STA) where a mode is defined by the STA'"'"'s network link, comprising:

sending a respective beacon by the access point for each mode supported by the system in a format suitable to the respective mode;

supporting multiple clear to send (CTS) frames in mode formats corresponding to the respective modes; and

sending a multicast/broadcast data for each mode supported by the network.

2. The method as in claim 1, in which one of the several beacons transmitted is identified as a primary beacon by a primary beacon field or bit in a high throughput (HT) information element sent by the AP.

3. The method as in claim 1, wherein the beacons include secondary beacons that are identified by a secondary beacon field or bit in a HT information element sent by the AP.

4. The method as in claim 3, in which the secondary beacons are transmitted with a time offset with reference to a time reference.

5. The method as in claim 4, in which the time reference is related to the primary beacon.

6. The method as in claim 4, in which the time offset is determined based on system considerations.

7. The method as in claim 4, in which the time offset is a configurable system parameter dynamically changeable by the AP.

8. The method as in claim 4, in which fields in the secondary beacon are identical to the corresponding fields in the primary beacon except for a timestamp field which is unique to the secondary beacon.

9. The method as in claim 1, in which the multicast/broadcast data transmitted after a secondary beacon is identical to the multicast and broadcast data sent after the primary beacon.

10. The method as in claim 3, in which the secondary beacon includes fields that are unique to its mode.

11. The method as in claim 1, further comprising indicating that the network supports multiple mode operation and protection for multiple mode operation by a multiple clear-to-send (CTS) protection bit sent by the AP in a high throughput (HT) information element (included in the beacons)in medium access control (MAC).

12. The method according to claim 11, further comprising:

starting a transmission opportunity (TXOP) by the STA with a request to send (RTS) frame transmitted to the AP.

13. The method as in claim 11, in which the RTS frame is sent as the first frame by an initiating station in a network link and a CTS frame from the AP is addressed to the initiating station in the same mode, further comprising:

AP sending the CTS-to-Self frame in all modes except in the mode being used for the TXOP protected by the STA; and

protecting a TXOP by the STA

14. The method as in claim 13, further comprising:

sending a response from the AP that includes multiple CTS frames.

15. The method as in claim 14, in which the AP sends CTS-to-Self frames in respective mode formats.

16. The method of claim 15, wherein the relative order of the CTS-to-self frames are arbitrary.

17. The method as in claim 15, in which the AP sends multiple CTS-to-Self frames corresponding to respective multiple modes supported by the system and the relative order of the CTS-to-Self frames are determined based on priority assigned to modes.

18. The method as in claim 15, in which the CTS frames are in formats that correspond to the respective mode, including a modulation or a link configuration.

19. A method for multiple mode operation in an IBSS wireless network having multiple STAs operating in multiple modes that are defined by a STA'"'"'s link, comprising:

a first STA sending CTS-to-Self frames for each mode of operation to indicate protection of a TXOP in one mode for the first STA or one other STA; and

sending an End-of-data frame by the STA having TXOP protected once there is no more data for transmission; and

releasing the remainder of the TXOP for access by any STA.

20. A method for transmission in a wireless network including at least one access point (AP) and at least one station (STA) where a mode is defined by the STA'"'"'s network link, the method comprising:

the STA obtaining a transmission opportunity (TXOP);

the STA transmitting data; and

the STA sending an indication of its completion or truncation of its TXOP when the STA does not have any further data to send.

21. The method as in claim 20, wherein dual clear-to-send (CTS) protection is enabled in the network characterized by two modes, the first mode using STBC CTS frames and the second mode using non-STBC CTS frames.

22. The method as in claim 21, wherein the STA indicates the completion or truncation of its TXOP by sending a contention free (CF)-End frame in a modulation that the STA is using if the remaining TXOP duration is sufficient to allow it.

23. The method as in claim 20, wherein the STA indicates the completion or truncation of its TXOP by sending a QoS-Null frame.

24. The method as in claim 20, wherein the STA indicates the completion or truncation of its TXOP by sending any type of medium access control (MAC) frame.

25. The method as in claim 20, wherein the indication of completion or truncation of the TXOP is interpreted by the other STAs as a network allocation vector (NAV) reset.

26. The method as in claim 20, further comprising:

upon receipt of the indication of completion or truncation of the TXOP, the AP sending multiple CF-End frames in all supported modes.

27. The method of claim 26, wherein the multiple modes consist of an STBC mode and a non-STBC mode, further comprising the AP receiving a CF-End frame from the STA matching its BSSID, wherein the AP'"'"'s multiple CF-End frames consist of a STBC CF-End frame and a Non-STBC CF-End Frame.

28. The method of claim 26, further comprising the STA with protected TXOP determining if sufficient TXOP duration is available for truncation by assessing whether the remaining TXOP duration is greater than the sum of an End-of-data frame or CF-End frame duration used by the STA for the truncation indication plus all of the AP'"'"'s CF-End frames and any interframe spacing durations inserted between the CF-end frames.

29. The method as in claim 26, wherein a single mode is being used in a system capable of supporting multiple modes, further comprising the AP sending a CF-end frame upon receiving the indication of the truncation of the TXOP.

30. The method as in claim 26, wherein one space time block code (STBC) CF-End frame and one non-STBC CF-End frame are sent by the AP and each of the CF-End frames are separated by a short interframe spacing (SIFS) duration.

31. The method as in claim 28, wherein each of the CF-End frames are separated by a reduced interframe spacing (RIFS) duration.

32. The method as in claim 28, wherein the AP sends an acknowledgement (ACK) before sending the CF-End frames.

33. A method for multiple mode operation in a wireless network including at least one access point (AP) and at least one station (STA) where a mode is defined by the STA'"'"'s network link, the method comprising:

the AP obtaining a transmission opportunity (TXOP);

the AP transmitting data; and

the AP sending an indication of end of transmission when the AP does not have any data to send.

34. The method as in claim 33 wherein the indication of end of transmission is multiple CF-End frames in all supported modes.

35. The method as in claim 34 wherein the AP sends one STBC CF-End frame and one non-STBC CF-End frame, which form a dual CF-End frame.

36. The method as in claim 33, wherein each of the CF-End frames are separated by a short interframe spacing (SIFS) duration.

37. The method as in claim 33, wherein the CF-End frames are sent in a reduced interframe spacing (RIFS) duration.

38. The method as in claim 33, wherein the order of the CF-End frames is determined arbitrarily.

39. The method as in claim 33, wherein the CF-End frame in the same modulation used for transmissions in the transmission opportunity (TXOP) is transmitted first.

40. The method as in claim 33, wherein dual CTS protection is enabled in the network.

41. A method for multiple mode operation in a wireless network including at least one access point (AP) and at least one station (STA) where a mode is defined by the STA'"'"'s network link, the method comprising:

the AP or the STA obtaining a transmission opportunity (TXOP) while using a long network allocation vector (NAV);

the AP or the STA transmitting data; and

the AP or the STA sending a contention free (CF)-End frame when the AP or the STA does not have any data to send.

42. The method as in claim 41, wherein the AP sends dual CF-End frames including one STBC CF-End frame and one non-STBC CF-End frame after a SIFS duration.

43. The method as in claim 42, wherein the remaining TXOP duration allows for sending the dual CF-End frames.

44. The method as in claim 43, further comprising determining that the remaining TXOP duration allows for sending dual CF-End frames by at least one of the following means:

if the remaining duration of the TXOP is greater than the sum of CF-End frame duration, a STBC CF-End frame duration, a non-STBC CF-End frame at a known basic rate, and two SIFS durations.

49. The system of claim of 41 wherein the STA sends the CF-End frame in a modulation that the STA is using.

50. The system of claim 41, wherein the STA indicates the end of transmission by sending a QoS-Null frame.

51. The system of claim of 50 wherein the STA sends the QoS-Null frame in a modulation that the STA is using.

52. The system of claim 41, wherein the STA indicates the end of transmission by sending any type of MAC frame.

53. The system as in claim 41, wherein the indication of end of transmission is interpreted by the other STAs as a network allocation vector (NAV) reset.

54. The system as in claim 41, wherein the AP sends multiple CF-End frames in all supported modes upon receipt of the indication of end of transmission.

55. The system as in claim 41, wherein the CF-End frames are separated by a short interframe spacing (SIFS) duration.

56. The system as in claim 41, wherein the CF-End frames are sent in a reduced interframe spacing (RIFS) duration.

57. The system as in claim 41, wherein the AP sends an acknowledgement (ACK) before sending the CF-End frames.

58. The system of claim 41 wherein the AP sends one STBC CF-End frame and one non-STBC CF-End frame.

45. A wireless communication system configured with MAC mechanisms to support protection of TXOP for multiple modes of operation, comprising:

a plurality of stations (STAs) operating in two or more supported modes; and

an access point (AP) configured to send multiple clear-to-send (CTS) frames, each corresponding with a respective mode supported by the system.

46. The system of claim 45 wherein the CTS frames are sent in response to a request-to-send (RTS) frame by a STA.

47. The system as in claim 45, wherein the STA is configured to indicate the end of transmission when there is no data to send.

48. The system of claim 47 wherein the STA sends a contention free (CF)-End frame for the indication.

59. A method for controlling medium usage during multiple mode operation in a wireless network having an access point (AP) and at least one station (STA), comprising:

sending by the AP multiple Contention Free End (CF-End) frames in a medium access control (MAC) layer, the CF-End frames with transmission formats corresponding to the modes supported by the AP.

60. The method as in claim 59, further comprising:

releasing unused TXOP after receiving an End-of-Data MAC signal from a STA that initiated the TXOP.

61. The method as in claim 60, in which unused TXOP is released after the AP detects unused TXOP using carrier sensing and the AP does not have any data to send.

62. The method as in claim 60, in which unused TXOP is released after the AP recovers the medium and sends CF-End frames to allow stations to access the medium.

63. The method as in claim 60, in which unused TXOP is released where the AP initiated the TXOP and is done with downlink transmission and does not expect any uplink transmissions.

64. The method as in claim 60, in which unused TXOP is released where the AP initiated the TXOP in EDCA and is done with downlink transmission and does not expect any further uplink transmissions.

65. The method as in claim 60, in which unused TXOP is released where the AP initiated the TXOP in HCCA with a CF-Poll and is done with downlink transmission and does not expect any uplink transmissions.

66. The method as in claim 60, in which unused TXOP is released where the AP initiated the TXOP in HCCA with a CF-Poll and receives an End-of-Data MAC signal from the STA.

67. The method as in claim 60, in which the multiple CF-End frames are sent by the AP when they can be sent before the current TXOP expires.

68. The method as in claim 60, in which the multiple CF-End frames are sent by the AP to the extent that as many as can be sent before the current TXOP expires.

69. The method as in claim 60, in which the multiple CF-End frames are sent by the AP where all or some of the multiple CF-End frames cannot be sent before the current TXOP expires, all or some of them are sent outside the TXOP.

70. The method as in claim 60, in which multiple CF-End frames are sent by the AP to release unused TXOP is in an order of priority as determined by the network configuration.

71. The method as in claim 70, where the order is dynamically changed.

72. The method as in claim 70, where the priority corresponds to that assigned to the modes supported by the network.

73. The method as in claim 70, where the first CF-End frame corresponds to the mode of the current TXOP and the rest of the CF-End frames correspond to the priority of the modes.

74. The method as in claim 70, where the order of the multiple CF-End frames corresponding to the modes supported in the system is arbitrary.

75. The method as in claim 60, where one CF-End frame is in a format corresponding to the mode of the current TXOP such that the medium is opened up to all stations operating in that mode until the protection for that mode expires.

76. The method as in claim 60, where the network is a dual mode network using an extended range mode and a normal range mode, in which one CF-End frame is sent in space time block code (STBC) modulation for the extended range mode and the other CF-End frame is sent in non-STBC modulation for the normal range mode.

77. The method as in claim 60, further comprising:

a STA receiving the CF-End frame; and

the STA updating its network allocation vector (NAV) in response to the received CF-End frame.

78. The method as in claim 77, where the CF-End frame includes a basic service set identification (BSSID), in which the STA updates its NAV after verifying that the BSSID corresponds to its basic service set that is controlled by the AP with which the STA is associated.

79. The method as in claim 77, where the CF-End frame includes a basic service set identification (BSSID), in which the STA updates its NAV regardless of whether the BSSID corresponds to its basic service set that is controlled by the AP with which the STA is associated.