EP1815644A1

EP1815644A1 - Method and apparatus for disassociating a wireless station in a wireless network

Info

Publication number: EP1815644A1
Application number: EP05803091A
Authority: EP
Inventors: Javier Del Prado Pavon
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2004-11-16
Filing date: 2005-11-14
Publication date: 2007-08-08
Also published as: CN101061674A; JP2008521271A; WO2006054232A1

Abstract

A method of wireless communication includes setting an association time-out (AT) period (207) for each of a plurality of wireless stations (102,103) in a wireless network (100). The method also includes probing (209) each of the stations at least once after the AT expires; and if, after probing, a reply is not received from one of the stations (103), disassociating the one station (103) from the network. A wireless network is also described.

Description

METHOD AND APPARATUS FOR DISASSOCIATING A WIRELESS STATION IN A WIRELESS NETWO_RK

The wireless communication bandwidth has significantly 5 increased with advances of channel modulation techniques, making the wireless medium a viable alternative to wired and optical fiber solutions. As such, the use of wireless connectivity in data and voice communications continues to increase. These devices include mobile telephones, portable

10 computers in wireless networks (e.g., wireless local area networks (WLANS) , stationary computers in wireless networks, portable handsets, to name only a few.

Each wireless network includes a number of layers and sub-layers. The Medium Access Control (MAC) sub-layer and

15 the Physical (PHY) layer are two of these layers. The MAC layer is the lower of two sublayers of the Data Link layer in the Open System Interconnection (OSI) stack. The MAC layer provides coordination between many users that require simultaneous access to the same wireless medium.

20 The MAC layer protocol includes a number of rules governing the access to the broadcast medium that is shared by the users within the network. As is known, several different multiple access technologies (often referred to as MAC protocols) have been defined to work within the protocols

25 that govern the MAC layer. These include, but are not limited, to Carrier Sensing Multiple Access (CSMA) , Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA) .

While standards and protocols have provided for

30 significant improvement in the control of voice and data traffic, the continued increase in the demand for network access at increased channel rates while supporting quality- of-service (QoS) requirements have required a continuous evaluation of protocols and standards and changes thereto. Illustratively, in a wireless network governed by the IEEE 802.11, a centralized MAC is associated with an access point AP, which governs the transmission and reception of traffic by and between the wireless stations (STAs) within its network. As can be appreciated, in such a network, a wireless station (STA) may need to ^λleave' the network. This departure may be in the form of a physical departure from the communication limits of the network, or loss of power, to name only a few possibilities.

The departure of an STA, if unaccounted for by the AP, can be detrimental to the overall efficiency of the network. For example, transmissions from the AP and other STAs of the network to the departed STA will be lost. These transmissions may cause the transmitting STA or AP to await a response, further adding to the inefficiency. Moreover, the AP continues to allocate bandwidth and other network resources to the STA that has departed its network. Thus, vital network resources, which could be allocated to the remaining STAs, continue to be allocated to the STA that has departed from the network. In addition, additional STAs may wish to access the network, but may be denied access because of network resource constraints. One attempt to address the problems presented by the departure of an STA has been included in IEEE 802.11- 04/106r0. This proposal requires each STA to be associated with an AP, and when an STA leaves the network, it must communicate its disassociation of the existing association. While this may address some issues presented by the disassociation of an STA, there are clear shortcomings. For example, in many instances, the STA does not have information in advance that it is to disassociate. One clear instance is the loss of power by the STA, or loss of connection with the AP for some other reason. If this were to occur, the STA would not be able to inform the AP of its disassociation. What is needed, therefore, is a method of addressing the departure of an STA from a network that overcomes at least the shortcomings of the known methods referred to above.

In accordance with an example embodiment, a method of wireless communication includes setting an association time- out (AT) period for each of a plurality of wireless stations in a network. The method also includes probing the each of the stations at least once after the AT expires; and if, after probing, a reply is not received from one of the stations, disassociating the one station from the network. In accordance with another example embodiment, a method of wireless communication includes setting an association time-out (AT) period for each of a plurality of wireless stations associated with a wireless network. If, during its respective AT period, a reply is not received from one of the stations, or during its respective AT period, a communication from one of the stations to another station in the network is not monitored by an access point, disassociating the one station from the network.

In accordance with another example embodiment, a wireless communication network includes an access point. The apparatus also includes a plurality of wireless stations associated with the network, wherein the access point is adapted to set an association time-out (AT) period for each of the wireless stations and to disassociate any of the wireless stations if, during the its respective AT period, a reply is not received from the station, or during its respective AT period, a communication from the stations to another station in the network is not monitored by an access point.

The invention is best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion.

Fig. 1 is a diagram representative of wireless communication network sharing a medium in accordance with an example embodiment.

Fig. 2a is a time line of a wireless network, including an association timeout in accordance with an example embodiment. Fig. 2b is a flow chart of a method of disassociating an STA from a wireless network in accordance with an example embodiment.

In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of the example embodiments. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods, systems and protocols may be omitted so as to not obscure the description of the present invention. Nonetheless, such devices, methods, systems and protocols that are within the purview of one of ordinary skill in the art may be ^'used in accordance with the example embodiments. Finally, wherever practical, like reference numerals refer to like features.

Briefly, in accordance with illustrative embodiments, a wireless network includes a plurality of STAs. The wireless network is adapted to create a disassociation with a station, if the station becomes non-responsive. In an illustrative embodiment, a probe is transmitted to the STA, and if a reply is not received, the disassociation is created. In an example embodiment, the network may be an AP, which includes an association timeout (AT) for each STA after the termination of communication from the STA. If, after the termination of the AT the STA is non-responsive to a probe frame transmitted by the AP, the AP transmits a disassociation frame (DF) . The DF is transmitted to the network and informs all remaining STAs that the non- responsive STA is no longer associated with the AP, and thus the network.

It is noted that in the illustrative embodiments described herein, the network may be a wireless network with a centralized architecture. Illustratively, the network may^¬ be one which functions under the IEEE 802.11 standard or any of its progeny. Moreover, the network may function in accordance with a known protocol useful in centralized architectures. These include, but are not limited to: cellular networks; wireless local area networks (WLAN) ; time division multiple access (TDMA) protocol; CSMA; CSMA with collision avoidance (CSMA/CA) ; and frequency division multiple access (FDMA) . It is emphasized that these protocols are merely illustrative and that protocols other than those specifically mentioned may be used without departing from the example embodiments. It is further noted that the networks of the example embodiments are not necessarily centralized. To this end, as will become clearer as the present description continues, the wireless networks of the example embodiments effect the disassociation function by first creating an association with the STAs of the network. Normally, the association is created by the AP of the centralized network. However, it is emphasized that networks other than centralized networks create can create such associations. As such, it is not essential that the networks of the example embodiments be centralized.

Fig. 1 is a schematic diagram of a wireless network 100 in accordance with an example embodiment. The wireless network 100 includes a centralized MAC layer within an AP (HOST) 101, which illustratively operates according to one of the plurality of illustrative protocols referenced above. The AP 101 services a number of STAs (wireless devices) 102 according to the chosen protocol. Illustratively, the first network 100 is a WLAN, a wide area network (WAN) or mobile telephone network, and the STAs (devices) 102 are computers, mobile telephones, personal digital assistants (PDA) , or similar device that typically operates in such networks. As indicated by the two-way arrows, the devices 102 may communicate bilaterally; and the host 101 and devices 102 may communicate bilaterally.

It is noted that according to certain MAC layer protocols, communication from one device 102 to another device 102 is not direct; rather such communications pass through the host 101, which then transmits the communications (using known scheduling methods) to the correct recipient device 102. It is further noted that while only a few STAs 102 are shown, this is merely for simplicity of discussion. Clearly, many other devices 102 may be used. Finally, it is noted that the devices 102 are not necessarily the same. In fact a plethora of different devices that function under the chosen protocol may be used within the first network 100.

Fig. 2a is a timeline 200 in accordance with the example embodiment, and is best understood when reviewed in conjunction with the illustrative embodiments of Fig. 1. At selected intervals the AP 101 of the first (centralized) network 100 sends a beacon 201. As is known, the beacons define the beginning of a service interval. The beacon 201 is received within the range of the network 100; and upon receipt by the devices 102, requests for service are made by the devices 102. As can be appreciated, this process continues while one or more of the devices remain in the range of the host 101. Upon termination of a first service interval, another beacon 201 is transmitted indicating the commencement of a second service interval. During a service interval, the STAs 102 communicate with one another, or with the AP 101, or both. In keeping with the example embodiments, when the AP 101 receives a transmission (for example, voice or data) from a station, the AP sets an AT for the STA. Additionally, the AP 101 may monitor transmissions from one station to another and set the AT for the transmitting. The AT is internally maintained and measured by the AP 101 using an internal clock. The AT is normally a fixed time period that is uniform for each STA. However, the duration of the AT is necessarily fixed in relation to a characteristic temporal period of the network 100. For example, the time-out does not need to be a fixed number of services intervals. In fact, the time-out may be relatively long (e.g., on the order of seconds or minutes) or relatively short (on the order of one or more beacon periods), or some duration therebetween. As will be appreciated by one of ordinary skill in the art, a long timeout may cause inefficiencies in the network due to unnecessary transmissions attempts to the departing STA, but a short timeout may cause unnecessary transmissions of probe frames.

In the example embodiment of Fig.l, STA 103 is shown as a departing STA (dashed lines) . At the last transmission of the STA 103, the AP 101 sets an AT. If during the AT a communication is received by the AP 101 or a communication from the STA 103 to another STA 102 is monitored, the AP 101 sets/resets a new AT for STA 103. However, if a transmission is not received from STA 103 by the termination of the AT for the STA 103, the AP 101 issues at least one Probe Request Frame (PRF) 202 for STA 103.

The PRF 202 may be repeated at certain intervals of time, and thus, in keeping with the settings of the AP 101, a number, n, of PRFs 202 may be issued. The PRF 202 seeks an acknowledgement transmission from the STA 103 indicating the desire to maintain the association with the network 100.

If the acknowledgement is not received within a set time interval after the transmission of the PRF 202, the AP 101 will transmit a disassociation frame (DF) 203 to the STA 103 and all STAs 102 of the network 100 that indicates that STA 103 is no longer associated with the network. Thereby, the STAs 102 and the AP 101 will no longer attempt to communicate with STA 103. It is noted that the DF 204 may be transmitted at a set time within a service interval or at the next beacon interval. For example, the DF 204 may be transmitted at a certain time after the last PRF was sent, assuming no acknowledgement was received from STA 103.

In accordance with another example embodiment, the probing by the AP 101 is optional. To wit, if communication from the particular STA (e.g., STA 103) is not received by the AP, or no communications from the STA 103 and another STA 102 in the network 100 are monitored by the AP 101, the AP may then transmit a DF 204. As such, in the present example where the STA 103 is non-communicative with the AP 101 or stations in the network, the AP disassociates the STA 103 without probing.

Fig. 2b is a flow-chart of a method of controlling a wireless network 205 in accordance with an example embodiment. The method 205 includes many features described in connection with the example embodiments described in connection with Figs. 1 and 2a. Many of these features are not repeated so as to not obscure the illustrative method.

At step 206, an association is created by an AP with an STA(s) in a wireless network. This association is created , within the requirements of the protocol of the MAC layer of the AP. After reception of a transmission from the STA of step 206, the AP sets an AT at step 207. Step 208 is a decision point of the method. If by the termination of the AT, a communication is not received by the AP or a communication between the STA and another STA of the network is not monitored, the method 205 continues with step 209. If a communication is received from the AP or is monitored by the AP at any time before the termination of the AT, a new AT is begun at step 207. At step 209, a PRF is issued. As described previously, a number of successive PRFs may be sent by the AP. Step 210 is another decision point in the method 205. Like step 208, if a communication is received or monitored by the AP, a new AT commences at step 207, and the sequence of the method 205 continues. If, however, no communication from the STA is received or monitored, the AP transmits a DF at a predetermined time (e.g., at the next beacon frame) .

It is noted that in keeping with the example embodiment described above wherein no PRF is issued by the AP, steps 209 and 210 are omitted. To wit, if the AP does not receive communication from the STA in question during an AT; or if the AP does not monitor communications from the subject STA at step 208, the probing is foregone and the method proceeds directly to step 211.

As can be appreciated, the method 205 is effected in parallel for each STA of a wireless network of the example embodiments. Beneficially, the method improves the efficiency of the network by informing each STA of the STAs currently associated with the network. Additionally, the network resources may be allocated in accordance with the STAs that are still associated with the network. Still further benefits will be readily apparent to one skilled in the wireless communication arts upon review of the present disclosure.

In view of this disclosure it is noted that the various methods and devices described herein can be implemented in hardware and software. Further, the various methods and parameters are included by way of example only and not in any limiting sense. In view of this disclosure, those skilled in the art can implement the various example devices and methods in determining their own techniques and needed equipment to effect these techniques, while remaining within the scope of the appended claims.

Claims

Claims :

1. A method of wireless communication, the method comprising: setting an association time-out (AT) period (207) for each of a plurality of wireless stations (102,103) in a network (100) ; probing (209) each of the stations at least once after the AT expires; and if, after the probing, a reply is not received from one of the stations (103) , disassociating the station from the network.

2. The method of claim 1, wherein the method is effected in parallel for all of the plurality of wireless stations associated with the network.

3. The method of claim 2, wherein, the network is a centralized network.

4. The method of claim 2, wherein the disassociating further comprises transmitting (211) a disassociation frame (203) to the plurality of stations in the network.

5. The method as recited in claim 2, wherein, if during the probing of the plurality of wireless stations, a communication is received from any of the plurality of stations, another AT period is commenced for each of the stations from which communication is received.

6. The method as recited in claim 2, wherein if during its respective AT period, a communication from one of the plurality of stations to another of the plurality of stations is monitored by an access point, another AT period is commenced for the one station.

7. The method as recited in claim 2, wherein, if during the probing of any of the plurality of wireless stations, a communication from one of the stations to another of the stations is monitored by an access point, another AT period is commenced for the one station.

8. The method as recited in claim 1, wherein the probing is effected a plurality of times.

9. The method as recited in claim 1, wherein each of the AT periods has a duration extending over at least one superframe.

10. The method as recited in claim 1, wherein the probing is effected by an access point.

11. The method as recited in claim 1, wherein, if during its respective AT period, a communication is received by an access point from one of the plurality of stations, or during its respective AT period, a communication from one of the stations to another station in the network is monitored by an access point, the probing is not effected; and another AT period is commenced for the one station.

12. A method of wireless communication, the method comprising: setting an association time-out (AT) period (207) for each of a plurality of wireless stations (102,103) associated with a wireless network; and if, during its respective AT period, a reply is not received from one of the stations (103) , or during its respective AT period, a communication from one of the stations (103) to another station (102) in the network is not monitored by an access point (101), disassociating the station from the network.

13. A wireless communication network, comprising: an access point (101); a plurality of wireless stations (102) associated with the network, wherein the access point is adapted to set an association time-out (AT) period (207) for each of the wireless stations and to disassociate any of the wireless stations if, during the its respective AT period, a reply is not received from the station, or during its respective AT period, a communication from the station to another station in the network is not monitored by an access point.

14. The wireless communication apparatus of claim 13, wherein the access point is adapted to commence another AT period for each of the wireless stations after receiving a communication from the station, or after monitoring a communication between the station and another wireless station.

15. The wireless communication apparatus of claim 14, wherein the access point is adapted to commence another AT period for each of the plurality of wireless stations after receiving a communication from the wireless station, or after monitoring a communication between the station and another wireless station.

16. The wireless communication apparatus as recited in claim 13, wherein the access point is adapted to probe each of the plurality of wireless stations.

17. The wireless communication apparatus as recited in claim 16, wherein the access point probes each of the plurality of wireless stations at least once, and if no reply is received from the station after the probing, the access point disassociates the station from the network.

18. The wireless communication apparatus as recited in claim 17, wherein if during its respective AT period a communication is received by an access point from one of the plurality of wireless stations, or during its respective AT period a communication from one of the plurality of wireless stations to another station in the network is monitored by an access point, the probing is not effected; and another AT period is commenced for the one wireless station.

19. The wireless communication apparatus as recited in claim 16, wherein the access point is adapted to probe each of the stations a plurality of times.

20. The wireless communication apparatus as recited in claim 1, wherein the access point is adapted to set an AT period for each of the plurality of stations in parallel.