WO2008067123A2

WO2008067123A2 - Base station, system and method for notifying the presence of a first non-conforming device between beacon signal transmissions

Info

Publication number: WO2008067123A2
Application number: PCT/US2007/083916
Authority: WO
Inventors: Kaberi Banerjee
Original assignee: Nxp B.V.
Priority date: 2006-11-07
Filing date: 2007-11-07
Publication date: 2008-06-05
Also published as: WO2008067123A3; CN101536421A; EP2103045A2

Abstract

A base station, system and method for notifying the presence of a first non-conforming device in a wireless communication system between beacon signal transmissions uses an announcement signal regarding the presence of the non-conforming device in the system, which is transmitted from the base station to at least one conforming device before the transmission of the next beacon signal from the base station so that the conforming device can implement a protection mechanism for transmissions.

Description

BASE STATION, SYSTEM AND METHOD FOR NOTIFYING THE

PRESENCE OF A FIRST NON-CONFORMING DEVICE BETWEEN

BEACON SIGNAL TRANSMISSIONS

The evolving IEEE 820.1 In standard allows transmission of one of three different types of Preambles in order to synchronize the physical layer function in both non-High Throughput (HT) and HT devices. These Preambles include non-HT Preamble, HT Mixed Mode Preamble and HT Greenfield Preamble. The non-HT Preamble includes the following fields, which are listed in the time order of non- HT transmission: non-HT Short Training field - 8 microseconds long; non-HT Long Training field - 8 microseconds long; and non-HT Signal field - 4 microseconds long. The HT Mixed Mode Preamble includes the following fields, which are also listed in the time order of transmission: non-HT Preamble as defined above - 20 microseconds long; HT Signal field - 8 microseconds long; HT Short Training field - 4 microseconds long; a variable number of Data HT Long Training fields (based on the number of supported Space Time streams) - 4 microseconds long (each); and a variable number of Extension HT Long Training fields - 4 microseconds long. The Greenfield Preamble includes the following fields, which are also listed in the time order of transmission: HT Greenfield Short Training field - 8 microseconds long; First HT Long Training field - 8 microseconds long; HT Signal field - 8 microseconds long; a variable number of Data HT Long Training fields (based on the number of supported Space Time streams) - 4 microseconds long (each); and Extension HT Long Training field - 4 microseconds long.

While the non-HT and the HT Mixed Mode Preambles allow non-HT devices in the network to synchronize to HT transmissions, non-HT and non-Greenfield HT devices do not recognize the Greenfield Preamble. In order to allow Greenfield (GF) HT devices, non-GF HT devices and non-HT devices to coexist in a base service set (BSS), the 802.1 In standard specifies a GF protection mechanism. By this mechanism, it will be necessary for all devices to employ a protection mechanism before the transmission of frames that are compliant with the GF mode. Specifically, a device that is about to perform GF transmission will have to initially reserve the medium via the Virtual Carrier Sense mechanism using an RTS/CTS for example. This operation is performed in a non-GF mode such that all devices, including non-GF devices, would be able to decode these protection frames and set their Network Allocation Vector (NAV). The GF protection mechanism is necessary the moment a non-GF device is associated with a GF- only BSS (i.e., a BSS that consists of only GF devices).

However, the 802.1 In standard allows an access point (AP) to announce to the GF devices in the BSS, the presence of a non-GF device in the BSS via HT Information Element in beacon frames, which are transmitted intermittently or periodically. Thus, if the time between beacon frames is long, then there may be a significant period of time when a non-GF device is associated with a BSS but the presence of a non-GF device is not known to the GF devices in the BSS. During this period, the GF devices would not be using the GF protection mechanism for transmission since the GF devices do not know about the non-GF device that has been recently admitted into the BSS.

A similar situation can occur when there is a change in state of the BSS for Reduced Interframe Spacing (RIFS) protection. When a non-HT device or HT device incapable of conforming to RIFS timing is associated with a BSS that consists of only HT devices that use RIFS timing, it is expected that the HT devices will apply a RIFS protection mechanism while performing their transmissions. However, during a period when the HT devices do not know about the associated non-HT or RIFS incapable HT device, the HT devices would not be using the RIFS protection mechanism.

Thus, there is a need for notifying the presence of a non-GF device in a BSS currently supporting only GF devices and/or the presence of a non-HT or RIFS incapable HT device in a BSS currently supporting only HT devices, between beacon transmissions so that GF and/or RIFS protection mechanisms can be employed.

A base station, system and method for notifying the presence of a first non- conforming device in a wireless communication system between beacon signal transmissions uses an announcement signal regarding the presence of the non- conforming device in the system, which is transmitted from the base station to at least one conforming device before the transmission of the next beacon signal from the base station so that the conforming device can implement a protection mechanism for transmissions. The use of the announcement signal allows the conforming devices to implement the protection mechanism earlier so that problems associated with not implementing the protection mechanism when needed are avoided.

A method for notifying the presence of a first non-conforming device in a wireless communication system between beacon signal transmissions in accordance with an embodiment of the invention comprises transmitting a beacon signal from a base station to at least one conforming device of the wireless communication system, receiving an association request signal from the non-conforming device at the base station after transmission of the beacon signal, transmitting an association response signal from the base station to the non-conforming device, and transmitting an announcement signal from the base station to the at least one conforming device of the presence of the non-conforming device in the wireless communication system before the transmission of the next beacon signal from the base station so that the at least one conforming device can implement a protection mechanism for transmissions.

A base station of a wireless communication system in accordance with an embodiment of the invention comprises at least one antenna for transmitting and receiving signals, a transmitter connected to the at least one antenna to transmit outgoing signals, a receiver connected to the at least one antenna to receive incoming signals, and a control module operatively coupled to the transmitter and the receiver. The control module is configured to transmit a beacon signal to at least one conforming device of the wireless communication system. The control module is further configured to transmit an association response signal to a non- conforming device in response to an association request signal from the non- conforming device after transmission of the beacon signal. The control module is further configured to transmit an announcement signal to the at least one conforming device of the presence of the non-conforming device in the wireless communication system before the transmission of the next beacon signal from the base station so that the at least one conforming device can implement a protection mechanism for transmissions. A wireless communication system in accordance with an embodiment of the invention comprises at least one conforming device configured to operate in a wireless environment, a non-conforming device configured to operate in the wireless environment, and a base station configured to operate in the wireless environment. The base station comprising at least one antenna for transmitting and receiving signals, a transmitter connected to the at least one antenna to transmit outgoing signals, a receiver connected to the at least one antenna to receive incoming signal, and a control module operatively coupled to the transmitter and the receiver. The control module is configured to transmit a beacon signal to the at least one conforming device of the wireless communication system. The control module is further configured to transmit an association response signal to the non-conforming device in response to an association request signal from the non-conforming device after transmission of the beacon signal. The control module is further configured to transmit an announcement signal to the at least one conforming device of the presence of the non-conforming device in the wireless communication system before the transmission of the next beacon signal from the base station so that the at least one conforming device can implement a protection mechanism for transmissions. Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention. Fig. 1 is a diagram of a wireless communication system in accordance with an embodiment of the invention. Fig. 2 is a block diagram showing some of the components of a base station (BS) and one of user equipments (UEs) of the wireless communication system in accordance with an embodiment of the invention.

Fig. 3 is a diagram of an announcement signal transmitted by the BS when the first non-conforming device is associated with the BSS supported by the BS in accordance with an embodiment of the invention. Fig. 4 is a timing diagram showing the operation related to notifying the presence of the first non-conforming UE to the conforming UEs between beacon signal transmissions in accordance with an embodiment of the invention. Fig. 5 is a process flow diagram of a method for notifying the presence of a non- conforming device between beacon signal transmissions in accordance with an embodiment of the invention.

With reference to Fig. 1, a wireless communication system 100 in accordance with an embodiment of the invention is described. The wireless communication system 100 includes a base station (BS) 102 and a number of user equipments (UEs) 104 and 106. The UEs 104 and 106 are wireless devices, which may be mobile stations, cellular phone, laptop computers, personal digital assistants (PDAs) or any other wireless devices that can operate in a wireless environment. The BS 102 may be an access point (AP), an evolved Node B (eNB) or any other type of wireless central device that can operate in a wireless environment. Although only a single BS and four UEs are shown in Fig. 1, the wireless communication system 100 may include any number of BSs and UEs. In the illustrated embodiment, the wireless communication system 100 is capable of transmitting data in accordance with IEEE 802.1 In standard. However, in other embodiments, the wireless communication system 100 may be capable of transmitting data in accordance with other standards or protocols. The UEs 104 are conforming devices, which do not require a special protection mechanism to coexist in the BSS with other conforming devices. In an embodiment, the UEs 104 are Greenfield (GF) devices, which can recognize transmissions with GF preambles, and the special protection mechanism is the GF protection mechanism. Thus, the UEs 104 will sometimes be referred to herein as GF devices. Some of these UEs 104 may be High Throughput (HT) devices. The UE 106 is a non- conforming device, which requires the special protection mechanism to coexist in the BSS with the conforming devices. In this embodiment, the UE 106 is a non- GF device, which cannot recognize transmissions with GF preambles. Thus, the UE 106 will sometimes be referred to herein as a non-GF device. The UE 106 may be a non-HT device or a non-GF HT device, which can operate in accordance with IEEE 802.1 la/b/g/n standard. As described in more detail below, the wireless communication system 100 is configured so that GF devices, such as the GF devices 104, in the base service set (BSS) of the BS 102 are notified when the first non-GF device, such as the non- GF device 106, is associated with the BSS before transmission of the next beacon signal from the BS 102. Beacon signals are intermittently or periodically transmitted from the BS 102 to the UEs in the BSS, such as the GF devices 104, to provide various information, including whether a non-GF device, such as the non- GF device 104, has been associated with the BSS for the first time. Thus, the GF devices 104 in the BSS can initiate GF protection mechanism for the non-GF device 106 before the next beacon signal is transmitted from the BS 102. Some of the components of the BS 102 and one of the UEs 104 are illustrated in a block diagram of Fig. 2. As shown in Fig. 2, the BS 102 includes at least one antenna 206, a transmitter 208, a receiver 210, a processor 212 and a control module 214. The transmitter 208 and the receiver 210 are connected to the antenna 206. The transmitter 208 is configured to transmit outgoing signals to the UEs 104 and 106 using the antenna 206. The receiver 210 is configured to receive incoming signals from the UEs 104 and 106 using the antenna 206. Although the BS 102 is illustrated with a single antenna 206, the BS 102 may include any number of antennas. In an embodiment, the BS 102 may support Multi-User Multi-Input Multi-Output (MU-MIMO) communications. The control module 214 operates with the processor 212 to perform operations related to transmission of beacon signals and accepting requests from UEs to associate with the BSS supported by the BS 102. The control module 214 is configured to periodically transmit a beacon signal to announce the presence of the BS 102 and relay information, such as timestamp, service set identifier (SSID), and other parameters regarding the BS to UEs that are within range of the BS, including whether there are any non-GF devices in the BSS. The beacon signal is transmitted in the form of a particular type of frame, which is one of the types of management frames used in the wireless communication system 100. The time interval between beacon transmissions may vary depending on various parameters.

The control module 214 is also configured to control the association of UEs with the BSS so that the UEs can properly operate in the BSS. In response to an association request signal from a UE, the control module 214 transmits an association response signal containing an acceptance or rejection notice to the requesting UE. In an embodiment, the association response signal may be one of the types of management frames used in the wireless communication system 100. The control module 214 is also configured to send out an announcement signal of the presence of a first non-conforming device, e.g., the non-GF device 106, when the first non-conforming device is associated with the BSS so that the conforming devices in the BSS, e.g., the GF devices 104, can employ a required protection mechanism before the transmission of the next beacon signal. Thus, the conforming devices in the BSS can employ the required protection mechanism soon after the first non-conforming device is associated with the BSS without having to wait for the next beacons signal. Consequently, there is no significant period of time when the required protection mechanism is not employed by the conforming devices after the first non-conforming device is associated with the BSS. If only the beacon signals are used to notify the conforming devices in the BSS when the first non-conforming device is associated with the BSS, there could be a significant period of time when the required protection mechanism is not employed even though the first non-conforming device is associated with the BSS. This time period is between the time when the first non-conforming device is associated with the BSS and the time when the next beacon signal is transmitted from the BS 102 to the conforming devices in the BSS. The announcement signal reduces the time period between the time when the first non-conforming device is associated with the BSS and the time when the conforming devices are notified to employ the required protection mechanism.

In the embodiment in which the conforming devices are GF devices and the non- conforming devices are non-GF devices, the required protection mechanism is GF protection mechanism. In this embodiment, the announcement signal is used to notify the GF devices in the BSS supported by the BS 102 the presence of the first non-GF device in the BSS when the non-GF device is associated with the BSS. In an embodiment, as illustrated in Fig. 3, the announcement signal is a management action frame 302 in which GF protection announcement information is embedded in the HT Information Element 304 of the management action frame. In a specific implementation, the GF protection announcement information is a bit of digital data in the thirty- fourth bit location 306 in the HT Information Element 304 of the management action frame 302.

The control module 214 may be implemented in the BS 102 as software, hardware and/or firmware. In some embodiments, the control module 214 is a program being executed by the processor 212, and thus, the functions of the control module 214 are performed by the processor 212. The processor 212 can be any type of a signal processor. The BS 102 includes other conventional components commonly found in a wireless BS, which are not described herein so as to not obscure the inventive features of the BS 102.

As shown in Fig. 2, the UE 104 includes at least one antenna 216, a transmitter 218, a receiver 220, a processor 222, an association module 224 and a protection mechanism module 226. The transmitter 218 and the receiver 220 are connected to the antenna 216. The transmitter 218 is configured to transmit outgoing signals to the BS 102 using the antenna 216. The receiver 220 is configured to receive incoming signals from the BS 102 using the antenna 218. Although the UE 104 is shown with a single antenna 216, the UE 104 may include any number of antennas. The association module 224 operates with the processor 222 to perform operations related to associating with the BSS supported by the BS 102. The association module 224 is configured to send an association request signal to the BS 102 in order for the UE 104 to associate with the BSS. In an embodiment, the association request signal is a data frame, which may be one of the types of management frames used in the wireless communication system 100. The association module 224 is also configured to process the association response signal from the BS 102 in response to the transmitted association request signal to determine whether the request has been accepted or rejected by the BS. The protection mechanism module 226 operates with the processor 222 to perform operations related to implementing a protection mechanism so that different types of UEs can coexist in the BSS supported by the BS 102. In this embodiment in which the UEs 104 are GF devices and the UE 106 is a non-GF device, the protection mechanism module 226 performs operations related to implementing GF protection mechanism, which may involve reserving the medium in a non-GF mode via the Virtual Carrier Sense mechanism using an RTS/CTS for example before the transmission of frames that are compliant with the GF mode. The protection mechanism module 226 implements the GF protection mechanism in response to a GF protection announcement signal from the BS 102 or a beacon signal from the BS indicating that the first non-GF device has been associated with the BSS.

The association module 224 and the protection mechanism module 226 may be implemented in the UE 104 as software, hardware and/or firmware. In some embodiments, one or both of the association module 224 and the protection mechanism module 226 are programs being executed by the processor 222, and thus, the functions of the association module and/or the protection mechanism module are performed by the processor 222. The processor 222 can be any type of a signal processor. The UE 104 includes other conventional components, which are not described herein so as to not obscure the inventive features of the UE.

The UE 106 is similar in structure and function to the UE 104. However, the UE 106 does not include the protection mechanism module 226 since the UE 106 is a different type of device than the UEs 104, e.g., the UE 106 is a non-GF device and the UEs 104 are GF devices.

The operation related to notifying the presence of the first non-conforming UE, e.g., the UE 106, to the conforming UEs in a BSS, e.g., the UEs 104, between beacon signal transmissions so that the conforming UEs can implement a special protection mechanism for transmissions due to the presence of the non- conforming UE in accordance with an embodiment of the invention is described with reference to a timing diagram of Fig. 4. Before t=tl, it is assumed that the BSS supported by the BS 102 includes only the UEs 104, which in this embodiment are GF devices. At t=tl, a beacon signal 402 is transmitted from the BS 102 to the UEs 104 in the BSS during the target beacon transmission time (TBTT) for that beacon signal, announcing that there are no non-GF devices in the BSS. At t=t-2, an association request signal from the UE 106, which in this embodiment is a non-GF device, is received by the BS 102. In response to the received association request signal, the BS 102 processes the request signal and transmits an association response signal to the UE 104, at t=t3. In this example, it is assumed that the association response signal is an acceptance of the requested association from the UE 106.

At t=t4, an announcement signal 404 is transmitted from the BS 102 to the UEs 104 to notify the UEs 104 of the association of the UE 106 with the BSS. In an embodiment, the announcement signal is a signal to instruct the UEs 104, which are GF devices, to implement GF protection for GF transmissions due to the association of the UE 106, which is a non-GF device, with the BSS. Thus, after t=t4, the UEs 104 will implement GF protection for GF transmissions. The transmission start time of the announcement signal 404, i.e., t=t4, may be selected to minimize the duration between t=t3 and t=t4 so that the notification regarding the admitted UE 106 is expedited and provided to the UE 104 in essentially real time. In an embodiment, the duration between t=t3 and t=t4 may be equivalent to Short Interframe Spacing (SIFS) or Reduced Interframe Spacing (RIFS). If the UE 106 is not capable of supporting RIFS, then the BS 102 will send the announcement signal 404 only after SIFS. However, if the UE 106 is capable of supporting RIFS, then the BS 102 can transmit the announcement signal 404 within RIFS time. At t=t5, the next beacon signal 406 is transmitted from the BS 102 to the UEs 104 in the BSS during the target beacon transmission time (TBTT) for the beacon signal 406, announcing that there are non-GF devices in the BSS. If the announcement signal was not transmitted by the BS 102 shortly after the UE 106 has been associated with the BSS, the UEs 104 will know the presence of the UE 104 only after receiving the beacon 406. Thus, without the announcement signal 404, the UEs 104 will not employ the needed protection mechanism during t=t3 to t5, which will cause problems in the wireless communication system 100. However, with the use of the announcement signal 404, the UEs 104 will be notified of the presence of the UE 106 earlier, i.e., soon after t=t4, and consequently, will implement the needed protection mechanism earlier, thereby eliminating the problems associated with not using the needed protection mechanism.

In another embodiment, the technique described above can be used for Reduced Interframe Spacing (RIFS) protection. In this embodiment, the conforming devices 104 are RIFS-capable HT devices, i.e., HT devices that are capable of supporting RIFS and the non-conforming device 106 is a non-HT device or a non- RIFS-capable HT device, i.e., a HT device that is not capable of supporting RIFS. When the non-HT or non-RIFS-capable HT device 106 is associated with the BSS supported by the BS 102, an announcement signal will be transmitted from the BS to the RIFS-capable HT devices 104 to notify these devices of the presence of the non-HT or non-RIFS-capable HT device before the transmission of the next beacon signal from the BS. Thus, the RIFS-capable HT devices 104 will implement a RIFS protection mechanism while performing their transmissions before the next beacon signal. The technique for RIFS protection may be used in conjunction with the technique for GF protection using same or different announcement signals from the BS 102.

A method for notifying the presence of a first non-conforming device in a wireless communication system between beacon signal transmissions in accordance with an embodiment of the invention is described with reference to a process flow diagram of Fig. 5. At block 502, a beacon signal is transmitted from a base station to at least one conforming device of the wireless communication system. Next, at block 504, an association request signal from the non-conforming device is received at the base station after transmission of the first beacon signal. Next, at block 506, an association response signal from the base station is transmitted to the non-conforming device. Next, at block 508, an announcement signal is transmitted from the base station to the at least one conforming device of the presence of the non-conforming device in the wireless communication system before the transmission of the next beacon signal from the base station so that the at least one conforming device can implement a protection mechanism for transmissions.

The use of announcement signals between beacon transmissions to notify conforming devices, e.g., the UE 104, in a BSS populated with only the conforming devices regarding the entry of non-conforming devices, e.g., the UE 106, into the BSS may allow the beacon transmission intervals to be increased, which will result in saved power for the devices in the BSS since there will be fewer beacon signals to be processed.

Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is to be defined by the claims appended hereto and their equivalents.

Claims

CLAIMS:

1. A method for notifying the presence of a first non-conforming device in a wireless communication system between beacon signal transmissions, the method comprising: transmitting a beacon signal from a base station to at least one conforming device of the wireless communication system; receiving an association request signal from the non-conforming device at the base station after transmission of the first beacon signal; transmitting an association response signal from the base station to the non-conforming device; and transmitting an announcement signal from the base station to the at least one conforming device of the presence of the non-conforming device in the wireless communication system before the transmission of the next beacon signal from the base station so that the at least one conforming device can implement a protection mechanism for transmissions.

2. The method of claim 1 wherein the at least one conforming device includes a Greenfield device and the non-conforming device is a non-Greenfield device, and wherein the protection mechanism is a Greenfield protection mechanism.

3. The method of claim 1 wherein the transmitting the announcement signal includes transmitting a management action frame with information regarding the presence of the non-conforming device.

4. The method of claim 3 wherein the information regarding the presence of the non-conforming device is included in a HT Information Element of the management action frame.

5. The method of claim 4 wherein the information regarding the presence of the non-conforming device includes a protection announcement in the HT Information Element of the management action frame.

6. The method of claim 5 wherein the protection announcement in the Additional HT Information Element of the management action frame is a bit of data included in the thirty- forth bit location of the HT Information Element.

7. The method of claim 1 wherein the at least one conforming device includes a High Throughput (HT) device that is capable of supporting Reduced Interframe Spacing (RIFS) and the non-conforming device is a non-HT device or a HT device that is not capable of supporting RIFS, and wherein the protection mechanism is a RIFS protection.

8. A base station of a wireless communication system, the base station comprising: at least one antenna for transmitting and receiving signals; a transmitter connected to the at least one antenna to transmit outgoing signals; a receiver connected to the at least one antenna to receive incoming signals; and a control module operatively coupled to the transmitter and the receiver, the control module being configured to transmit a beacon signal to at least one conforming device of the wireless communication system, the control module being further configured to transmit an association response signal to a non-conforming device in response to an association request signal from the non- conforming device after transmission of the beacon signal, the control module being further configured to transmit an announcement signal to the at least one conforming device of the presence of the non-conforming device in the wireless communication system before the transmission of the next beacon signal from the base station so that the at least one conforming device can implement a protection mechanism for transmissions.

9. The base station of claim 8 wherein the at least one conforming device includes a Greenfield device and the non-conforming device is a non-Greenfield device, and wherein the protection mechanism is a Greenfield protection mechanism.

10. The base station of claim 8 wherein the announcement signal includes a management action frame with information regarding the presence of the non- conforming device.

11. The base station of claim 10 wherein the information regarding the presence of the non-conforming device is included in a HT Information Element of the management action frame.

12. The base station of claim 11 wherein the information regarding the presence of the non-conforming device includes a protection announcement in the HT Information Element of the management action frame.

13. The base station of claim 12 wherein the protection announcement in the HT Information Element of the management action frame is a bit of data included in the thirty-forth bit location of the HT Information Element.

14. The base station of claim 8 wherein the at least one conforming device includes a High Throughput (HT) device that is capable of supporting Reduced Interframe Spacing (RIFS) and the non-conforming device is a non-HT device or a HT device that is not capable of supporting RIFS, and wherein the protection mechanism is a RIFS protection.

15. A wireless communication system comprising: at least one conforming device configured to operate in a wireless environment; a non-conforming device configured to operate in the wireless environment; and a base station configured to operate in the wireless environment, the base station comprising: at least one antenna for transmitting and receiving signals; a transmitter connected to the at least one antenna to transmit outgoing signals; a receiver connected to the at least one antenna to receive incoming signals; and a control module operatively coupled to the transmitter and the receiver, the control module being configured to transmit a beacon signal to the at least one conforming device of the wireless communication system, the control module being further configured to transmit an association response signal to the non-conforming device in response to an association request signal from the non-conforming device after transmission of the beacon signal, the control module being further configured to transmit an announcement signal to the at least conforming device of the presence of the non-conforming device in the wireless communication system before the transmission of the next beacon signal from the base station so that the at least one conforming device can implement a protection mechanism for transmissions.

16. The system of claim 15 wherein the at least one conforming device includes a Greenfield device and the non-conforming device is a non-Greenfield device, and wherein the protection mechanism is a Greenfield protection mechanism.

17. The system of claim 16 wherein the announcement signal includes a management action frame with information regarding the presence of the non- conforming device.

18. The system of claim 17 wherein the information regarding the presence of the non-conforming device is included in a HT Information Element of the management action frame.

19. The system of claim 18 wherein the information regarding the presence of the non-conforming device includes a protection announcement in the HT Information Element of the management action frame.

20. The system of claim 15 wherein the at least one conforming device includes a High Throughput (HT) device that is capable of supporting Reduced Interframe Spacing (RIFS) and the non-conforming device is a non-HT device or a HT device that is not capable of supporting RIFS, and wherein the protection mechanism is a RIFS protection.