WO2014005461A1

WO2014005461A1 - Virtual access point

Info

Publication number: WO2014005461A1
Application number: PCT/CN2013/074682
Authority: WO
Inventors: Guoxiang XU
Original assignee: Hangzhou H3C Technologies Co., Ltd.
Priority date: 2012-07-06
Filing date: 2013-04-25
Publication date: 2014-01-09
Also published as: CN103533653A

Abstract

In a wireless communication system comprising an access point AP and a plurality of stations STAs, a plurality of virtual APs are configured at the AP for the plurality of STAs. Each virtual AP sends a beacon frame to the associated STA including quiet information for specifying a quiet period during which the associated STA does not access the AP.

Description

Virtual Access Point

[0001] BACKGROUND

[0002] A communication network may be deployed wirelessly as a Wireless Local Area Network (WLAN) by allowing one or more stations (STAs) to access the communication network via an Access Point (AP) . An STA may include any

communication devices such as laptop and tablet computers, PCs and smart phones, etc. Virtual Access Point (virtual AP) technology allows a plurality of logical APs ( irtual access points') to be configured on a single physical AP .

[0003] BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1 is a flow diagram of an example of a method for use in a wireless communication system;

[0005] Figure 2 is a schematic diagram showing an example of the quiet periods of an STA over several beacon

intervals ;

[0006] Figure 3 is a schematic diagram showing an example of the quiet periods of n STAs over one beacon interval; and [0007] Figure 4 is a schematic diagram of an example of a device for performing the method of Figure 1.

[0008] DETAIL DESCRIPTION

[0009] The present disclosure provides examples of a method, and a device configured to carry out the method, for use in a wireless communication system that comprises an Access Point AP and a plurality of stations STAs. In an example of the method, each of the plurality of STAs is provided with its own virtual AP . At each beacon interval, a beacon frame is sent to each STA of the plurality via a respective virtual AP . Each beacon frame of a corresponding STA includes quiet information of the STA, which specifies a quiet period at which the STA does not access the AP via the respective virtual AP .

[0010] It may therefore be possible, using the example above, to schedule periods of time when one or more STAs remain quiet, or do not access the AP, and thus limiting the number of STAs simultaneously accessing the AP . This may help to prevent collision between communications from two different devices trying to access the AP at the same time.

[0011] Although each of a plurality of STAs associated with an AP is able to detect the presence of the AP, an individual STA, for instance STA1, may not be aware of the presence of one or more other STAs associated with the AP . In other words, a hidden node problem occurs in which one or more other STAs may be hidden from STA1 due to distance, obstacles or other reasons. In this case, uplink traffic from STA1 may be affected if STA1 attempts to access the AP while another STA that is hidden from STA1 is also

accessing the AP, which may result in collisions.

[0012] By configuring a separate virtual AP for each station associated with a physical AP, it is possible to limit the number of STAs simultaneously accessing the physical AP . In this way the performance of the network may be improved by reducing the likelihood of collision between communications accessing the physical AP .

Moreover, the above example may be straightforwardly implemented under an IEEE 802.11 standard (incorporated herein by reference) , making its integration with existing networks simple.

[0013] Examples will now be described with reference to the accompanying drawings. In the examples below, the communication network is assumed to be a WLAN, which comprises an AP providing access to the network to two or more STAs. A fit AP provides wireless encryption while the management and policy functions are performed by the Access Controller AC that connects to the fit AP through tunnels. A fit AP may perform functions such as VLAN tagging based on the Service Set Identifier (SSID) that an STA uses to associate with the fit AP . In the examples, the AP may be a fit AP, in which case the method is instructed by the associated AC and carried out through the fit AP . A fat AP is an addressable node in a communication network with its own IP address on its interfaces, and functions like a switch or router in that it provides many of the functions of such devices. In the examples, the AP may be a fat AP, in which case the method may be carried out entirely at the fat AP.

[0014] An example of a method for use in such a wireless communication system to implement quiet periods in the STAs is shown as a flow diagram in Figure 1. [0015] At block S110, a plurality of virtual APs is configured at the physical AP for the plurality of STAs associated with the physical AP, such that each of the created virtual AP corresponds respectively to a single STA. The virtualisation may include configuring a Basic Service Set Identifier (BSSID) for the virtual AP of each STA at the physical AP . In the case of a fit AP, the virtualisation may be instructed by the AC associated with the fit AP . In the case of a fat AP, the virtualisation may be performed at the fat AP independently from the associated AC, or may be instructed by the AC associated with the fat AP . [0016] At block S120, each virtual AP sends a beacon frame to its associated STA. The beacon frame includes quiet information that is specific to the recipient STA and specifies a quiet period at which the STA does not access the AP via its associated virtual AP . The quiet

information may include information of a start time at which the quiet period begins. In particular, the AP may send a beacon frame for each virtual AP using the BSSID of the virtual AP so as to notify the corresponding STA of the types, capacity and other parameters of the service

provided by the AP .

[0017] An example of the quiet information included in a beacon frame directed to a particular STA is shown below:

Element tD Length Quiet I Quiet Quiet Quiet

Count 1 Interval Duration Ofset

Octets: I ^■7 7 [0018] The fields "Element ID" and "Length" respectively identifies the quiet period and indicate the length of the load .

[0019] "Quiet Count" indicates the position of the beacon interval after the received beacon frame in which the quiet period of the STA is carried out. A beacon interval (T_B) is the time interval between two consecutive beacon frames. This will be explained in more detail below.

[0020] "Quiet Interval" indicates a periodic interval (I_Q) between two consecutive quiet periods of the STA, which may be indicated in units of a beacon interval.

[0021] "Quiet Duration" indicates the duration of time (T_Q) for which the quiet period of the STA continues, or in other words, the duration of time over which the STA does not access the AP . [0022] "Quiet Offset" indicates an offset (T_off) in time relative to the start time of the beacon frame at which the quiet period of the STA begins.

[0023] Figure 2 schematically shows an example with two quiet periods of the STA over three beacon intervals separated by beacons Bl to B4. As shown in Figure 2, if the quiet information in the beacon frame Bl received by the STA indicates a Quiet Count of 1, the STA is required to carry out its quiet period (i.e. to remain quiet and not access the AP) during the first beacon interval after the beacon frame Bl (between Bl and B2) . The quiet period is carried out according to the parameters Quiet Interval I_Q, Quiet Duration T_Q and Quiet Offset (explained in more detail below) as specified in the quiet information. In the next beacon frame B2, if the quiet information

indicates a Quiet Count of 2, the STA is required to carry out its quiet period in the second beacon interval after the beacon frame B2, therefore in the interval T_B between B3 and B4. [0024] When there is a plurality of STAs, it may be desirable for only a fixed number of STAs to access the AP at any given time during each beacon interval. In this case, the values of these parameters may be set in the quiet information, based on the total number of STAs and the number of STAs allowed to access the AP at the same time, so as to limit the number of STAs accessing the AP at any given time.

[0025] At block S130, each of the plurality of STAs receives a beacon frame from its respective virtual AP, and based on the quiet information in the beacon frame, carry out their respective quiet periods during a beacon

interval. In this way, at any given time during a beacon interval, only some of the plurality of STAs may access the AP, thus reducing the likelihood of collision, and

improving the performance of the communication network.

[ 0026 ] In an example, each physical AP may be optimally accessed by a particular number of STA. For an AP of present technology, the optimal number is around 4 to 8 STAs at any one time. If the number of STAs accessing the AP at a given time is less than this number, this results in some time slots being left unused and creating waste. If too many STAs are accessing the AP at a given time, this increases the likelihood of collisions. The specific number of STAs that can simultaneously access an AP may be determined by actual channel parameters, such as noise, interference, and channel use rate. [ 0027 ] In an example, in order to ensure that each STA has a quiet period during each beacon interval, the Quiet Count and Quiet Interval of the quiet information may be set to 1 for every STA.

[ 0028 ] If the number of STAs associated with a physical AP is n, and the optimal number of STAs that may access the AP at any one time is m, the Quiet Duration may be determined by :

Quiet Duration = (1-m/n) ^χ beacon interval

[ 0029 ] If a beacon interval is considered to be divided in n equal portions, then in each of the n portions, only m number of STAs may access the AP . Using "0" to indicate that an STA cannot access the AP and "1" to indicate that an STA can access the AP, each STA is then arranged to have (n-m) number of O's in a beacon interval in order to allow m number of STAs to access the AP in each of the n portions of the beacon interval . [0030] An example of arrangements of the quiet periods is shown in Figure 3 for n STAs, STA(l), STA(2), STA(n-l), STA(n), using the "0" and "1" representation. As can be seen in the figure, the quiet period of STA(l) begins at the start of a beacon interval T_B. On the other hand, the quiet period of STA(2) is offset from the start of the beacon interval by 1/n of T_B, and the quiet period of

STA(3) is offset from the start of the beacon interval by 2/n of T_B. These offsets may be specified in the Quiet Offset field of the quiet information.

[0031] For an STA whose "0" positions are not continuous within a beacon interval, for example STA(n) as shown by the last (n^th) row in Figure 3, the transmission time of a beacon frame by the virtual AP to this STA may be shifted. In the example of STA(n), the virtual AP may be configured to shift the transmission of a beacon frame to STA(n) to a later time with respect to the transmission time of other STAs, such that, for example, a beacon interval of STA(n) begins with a series of l's followed by a continuous series of O's.

[0032] It may be possible to avoid a hidden node problem by centralizing channel accesses in Point Coordination Function PCF mode in which the AP sends a CF-Poll frame to a PCF-capable STA to permit it to transmit a frame. In Distributed Coordination Function DCF mode, an optional virtual carrier sense mechanism may be used in which

Request-to-send (RTS) and Clear-to-send (CTS) frames are exchanged between source and destination STAs during the intervals between the data frame transmissions. However, conventional STAs generally do not support PCF mode or the RTS/CTS mechanism. Thus, in particular examples, the implementation of the method is based on DCF and does not require PCF-supports in the STAs or the use of the RTS/CTS mechanism. Nevertheless, it is to be understood that the examples described above are equally applicable to an AP and STAs that support PCF and/or the RTS/CTS mechanism. [0033] An example of a device for performing the method above in a wireless communication system comprising the device and a plurality of stations STAs is schematically shown in Figure 4.

[0034] The device comprises a virtualization module 410 for configuring one or more virtual APs at a physical AP with which a plurality of STAs associates, for example to provide each of the plurality of STAs with its own virtual AP, and a sending module 420 for sending via a respective virtual AP a beacon frame to each STA. As described above, the beacon frame includes quiet information for specifying a quiet period during which the STA does not access the physical AP via its virtual AP . The quiet information may include information of a start time at which the quiet period begins.

[0035] In an example, the virtualization module 410 configures the one or more virtual APs by configuring each virtual AP with a respective BSSID.

[0036] In an example, when the AP used in the

communication system is a fit AP, the virtualization module 410 may be provided at the AC that is associated with the fit AP, such that the fit AP receives configuration

instructions from the virtualization module 410 of the AC, while the sending module 420 may be provided at the fit AP .

[0037] In another example, when the AP used in the

communication system is a fat AP, the device may be

provided at the fat AP . [ 0038 ] Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted.

[ 0039 ] The above examples can be implemented by hardware, software, firmware, or a combination thereof. For example, the various methods and functional modules described herein may be implemented by a processor (the term processor is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, or programmable gate array etc.) . The methods and functional modules may all be performed by a single processor or divided amongst several processers. The methods and functional modules may be implemented as machine readable instructions executable by one or more processors, hardware logic circuitry of the one or more processors, or a combination thereof. Further, the

teachings herein may be implemented in the form of a software product, the computer software product being stored in a storage medium and comprising a plurality of instructions for making a computer device (e.g. a personal computer, a server or a network device such as a router, switch, access point etc.) implement the method recited in the examples of the present disclosure.

[ 0040 ] It should be understood that embodiments of the method and device described above are implementation examples only, and do not limit the scope of the invention. Numerous other changes, substitutions, variations,

alternations and modifications may be ascertained by those skilled in the art, and it is intended that the present disclosure encompass all such changes, substitutions, variations, alterations and modifications as falling within the spirit and scope of the appended claims.

Claims

1. A method for use in a wireless communication system comprising an access point AP and a plurality of stations STAs, the method comprises:

configuring at the AP a plurality of virtual APs each of which is associated with one of the plurality of STAs; whereby each STA is associated with a different virtual AP; and

sending via each virtual AP a beacon frame to the associated STA, the beacon frame including quiet

information for specifying a quiet period during which the associated STA is not to access the AP .

2. The method of claim 1, wherein the configuring

includes configuring each virtual AP with a respective basic service set identifier BSSID.

3. The method of claim 1, wherein the quiet information further includes a start time at which the quiet period begins, and a quiet duration which is the duration of time for which the quiet period continues, and the start time corresponds to the start time of the quiet duration.

4. The method of claim 1, further comprising specifying in the quiet information that the quiet period is to be shorter than a beacon interval, the beacon interval being an interval between two consecutive beacon frames sent by a virtual AP, and specifying the start time in the quiet information of at least two STAs to be different from each other .

5. The method of claim 1, wherein the quiet information of an STA of the plurality comprises:

a quiet interval for indicating a periodic interval between two consecutive quiet periods of the STA, the quiet interval being in units of a beacon interval that is an interval between two consecutive beacon frames;

a quiet duration for indicating the duration of time for which the quiet period continues; and

a quiet offset for indicating an offset in time relative to a transmission time of the beacon frame at which the quiet period of the STA begins.

6. The method of claim 5, wherein the quiet information further comprises:

a quiet count for indicating a number of beacon interval counting from the beacon frame during which the quiet period of the STA begins.

7. The method of claim 5, wherein the quiet interval is set to 1 to indicate that the periodic interval between two consecutive quiet periods corresponds to one beacon

interval, the quiet duration of the STA at each quiet interval is set to be the same, and, if the quiet period of the STA is not continuous within the beacon interval, the method further comprises shifting a transmission time of the beacon frame via the associated virtual AP so that the quiet period of the STA becomes continuous within the shifted beacon interval.

8. A device for use in a wireless communication system comprising an access point AP and a plurality of stations STAs, the device comprising:

a virtualization module to configure at the AP a plurality of virtual APs, each virtual AP to associate with a respective one of the plurality of STAs; and

a sending module to send via each virtual AP a beacon frame to the associated STA, the beacon frame including quiet information for specifying a quiet period during which the associated STA does not access the AP .

9. The device of claim 8, wherein the virtualization module is to configure each virtual AP with a respective basic service set identifier BSSID.

10. The device of claim 8, wherein the sending module is to include in the quiet information a start time at which the quiet period begins, and a quiet duration which is the duration of time for which the quiet period continues, and the start time corresponds to the start time of the quiet duration .

11. The device of claim 8, wherein the sending module is to specify in the quiet information that the quiet period is to be shorter than a beacon interval, the beacon interval being an interval between two consecutive beacon frames sent by a virtual AP, and to specify the start time in the quiet information of at least two STAs to be different from each other.

12. The device of claim 8, wherein the sending module is to include in the quiet information of an STA of the plurality : a quiet interval for indicating a periodic interval between two consecutive quiet periods of the STA, the quiet interval being in units of a beacon interval that is an interval between two consecutive beacon frames;

13. The device of claim 12, wherein the sending module further includes in the quiet information:

14. The device of claim 12, wherein the quiet interval is set to 1 to indicate that the periodic interval between two consecutive quiet periods corresponds to one beacon

interval, the quiet duration of the respective STA at each quiet interval is set to be the same, and, if the quiet period of the STA is not continuous within the beacon interval, the sending module is to shift a transmission time of the beacon frame via the associated virtual AP so that the quiet period of the STA becomes continuous within the shifted beacon interval.

15. An access point AP for use in a wireless communication system comprising the AP, an access controller AC

associated with the AP and a plurality of stations STAs, the AP is to configure a plurality of virtual APs according to configuration instructions received from the AC, each of the plurality of virtual AP being associated with a single one of the plurality of STAs, and the AP comprises a sending module to send via each virtual AP a beacon frame to the associated STA, the beacon frame including quiet information for specifying a quiet period during which the associated STA does not access the AP .