ES2367013T3 - SYSTEM AND METHOD FOR RELATING QUICK CHANNEL SWITCHING IN A WIRELESS ENVIRONMENT. - Google Patents

Abstract

Method for obtaining fast channel access for a node (24) in a wireless local area network, WLAN (20), characterized in that it comprises the steps of: - determining, in said node, that the WLAN is inactive for a period (56 ) of space between PCF frames, PIFS, in which PCF stands for point coordination function; - transmitting a first management frame during a slot interval after said period (56) PIFS; wherein the transmission of said first management frame in said slot interval provides priority access to said WLAN (20) and in which said first management frame includes guidelines for performing rapid channel switching.

Description

The present invention relates, in general, to wireless local area networks (WLAN). More particularly, the present invention relates to a method and system for providing priority access to a WLAN to perform rapid channel switching.

In a typical wireless local area network (WLAN) based on the 802.11 standard, access to the wireless medium is controlled at the MAC layer through coordination functions. The 802.11 standard provides two coordination functions, the distributed coordination function (DCF), and the point coordination function (PCF). If a contest-free service is required, it can be provided through the point coordination function (PCF), which is built above the DCF. The PCF is an optional part of the 802.11 specification and has not been widely implemented to date. Frame exchanges between STA stations in DCF dominate the currently deployed WLANs. The DCF is based on a scheme of listening before speaking called CSMA / CA (multiple access by carrier detection with collision avoidance) as described by IEEE 15 802.11. A similar access method is described in “A priority scheme for IEEE 802.11 DCF access method” of DENG D.J. et al., published in IEICE transactions on communications.

According to the DCF scheme, before attempting to transmit a frame, each station checks if the medium is inactive. If the medium is not inactive, the stations differ from each other and use an exponential recoil algorithm to avoid transmission collisions.

A drawback with the DCF scheme is that network stations may incur relatively long delays when trying to exchange frames over the wireless medium in the case of high network traffic load.

A consequence of these potential transmission delays is that compliance with the regulatory requirement of dynamic frequency selection (DFS) for operation in the 5 GHz band in Europe may not be met. The DFS regulatory requirement stipulates, among other things, that a wireless STA must (1) quickly suspend transmissions on a current channel within a set time frame and (2) switch channels within a set time frame when a primary user is detected. A primary user can be, for example, a radar tracking system or a satellite system.

Therefore, there is a need for an improved media access scheme, performed at the MAC layer, to provide fast channel access to a wireless medium to quickly perform a channel switching and / or quickly stop transmissions on the current channel to prevent potential interference by performing mission-critical functions by primary users in jointly located systems.

The present invention relates to a method and system for providing fast priority channel access, for sending critical time frames, such as spectrum management action frames, in the MAC layer protocol of a communications system such as, by For example, a wireless communication system based on the 802.11 standard.

A key point of the novelty of the invention is that priority access to the wireless medium is obtained to enable priority transmission of one or more spectrum management frames from a source node (for example, an AP or STA) to perform Fast channel switching. Rapid channel switching, as defined herein, includes the announcement of a channel switching or the suspension of all transmissions on a current operating channel. The present invention encompasses, in one of its aspects, a method for providing fast channel access to a wireless medium. The method generally includes the steps of: determining that the wireless medium has been inactive during a period of space between PCF frames (PIFS), transmitting a first management frame during a slot time after said one PIFS period; wherein the transmission in said slot time substantially guarantees priority access to said wireless medium; and perform rapid channel switching in the network according to the guidelines contained in the management frame. The method may further include the additional step of transmitting one or more additional management frames, the format of which is identical to said first management frame, each additional frame being separated by the space between PIFS frames to provide a higher degree of transmission reliability. . The method is preferably performed at an access point (AP) in an infrastructure network or in an STA of an ad hoc network.

The present invention encompasses, in another of its aspects, a system for providing fast priority channel access to enable transmission with priority of spectrum management action frames, in a MAC protocol of a communications system such as, for example, with respect to a wireless communication system based on the 802.11 standard. The system includes means to determine that the wireless local area network (WLAN) is inactive during a period of space between PCF frames (PIFS); and means for transmitting a first management frame in the slot limit of the PIFS period, in which the transmission of said first management frame in said PIFS slot limit grants said priority node access to said WLAN; means for performing rapid channel switching in the network according to the guidelines contained in a first management frame; and means for transmitting one or more additional management frames after the transmission of said first management frame to provide a higher degree of transmission reliability, in which each additional management frame is separated by the PIFS period of time.

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The foregoing and other objectives, features, aspects and advantages of the present invention will become more apparent from a careful reading of a detailed description provided hereinbelow, with appropriate reference to the attached drawings.

The invention can be understood with reference to the following description, taken in conjunction with the accompanying drawings, in which:

Figure 1 is a diagram of an illustrative communications network that includes an illustrative wireless local area network according to the present invention;

Figure 2 illustrates a simplified block diagram of an access point (AP) and each station (STA) within a cell according to the embodiment of the present invention;

Figure 3 is a timeline illustrating the relationship between the three separations between frames to determine a priority access to a wireless medium; Y

Figure 4 illustrates the transmission of three management frames according to the method of the invention.

The present invention is described below in the context for obtaining priority access to a wireless medium based on the 802.11 standard controlled at the MAC layer that provides main network operations. However, it should be appreciated that the teachings of the invention discussed herein are not limited in this regard. That is, the invention can be applied to other communication systems in which the network stations (for example, mobile or fixed) try to guarantee access to a medium associated with a base station or another access point of the communication system to perform rapid channel switching as defined herein.

In a preferred embodiment, the present invention provides an associated system and method that allows an origin node, which can be an access point (AP) in an infrastructure network or a station (STA) in an ad hoc network to gain access. priority to a wireless medium based on the 802.11 standard to transmit one or more spectrum management frames with priority to perform rapid channel switching (i.e., quickly announce a channel switching and / or suspend all transmissions on the current channel ). Priority access to the wireless medium enables the transmission of management frames at a point in time before the start of the contest with other nodes to avoid widely known network latencies associated with the distributed access contention protocol such as an access delay and an exponential setback.

Figure 1 illustrates a wireless LAN 20 (WLAN) system for implementing the method of the invention. The wireless LAN 20 defines an infrastructure network that includes a plurality of cells 22. Cell 22 includes an access point (AP) 24 (sometimes referred to as a wireless local bridge or base station).

With continued reference to Figure 1, cell 22 may include remote network stations 26 (STA). The access point 24 and the remote STA 26 may be the transmitters and receivers of the system. Each STA 26 can be a mobile, portable or stationary terminal. Each STA 26 can be a desktop workstation, laptop, personal electronic diary, pocket personal computer, computer with pen use, digital personal assistant, portable scanner, data collector, portable printer, etc.

If present, the AP 24 may be an interface for communication between a wireless network 20 and a wired line network. The AP 24 can be configured to provide a communications gateway between the STA 26 and the AP 24 that are in the cell 22 and also between a wired line network and the STA 26. The AP 24 is normally configured to convert the signals between the Wireless and wired line media. The conversion may allow the access point to pass the communication information between the wired line network and the wireless STA 26. The wired line network can be coupled to an external network (for example, PBX, PSTN, Internet, etc.).

Next with reference to Figure 2, both AP 24 and STA 26 may include a screen 30, a CPU 32, a transmitter / receiver 34, an input device 36, a storage module 38, an access memory 40 random (RAM), a read-only memory (42), and a common bus 41. Although the description may refer to terms commonly used in the description of particular computer systems, the description and concepts apply equally to other processing systems, including systems that have different architectures than that shown in Figure 2. The transmitter / receiver 34 it is coupled to an antenna (not shown) to transmit the desired data and its receiver converts the received signals into corresponding digital data. CPU 32 operates under the control of an operating system contained in ROM 42 and uses RAM 40 to perform frequency selection within a wireless local area network (WLAN), allowing the AP in an infrastructure network or a STA In an ad hoc network, provide a new channel or wireless link for all other stations (STA).

In operation, in a typical wireless local area network (WLAN) based on the 802.11 standard, such as a wireless LAN 20 of Figure 1, a plurality of STA 26 can be associated with AP 24 if present. Each STA 26 may have different communication requirements and capabilities. The AP 24 can manage the communication traffic between the STA 26 and the wired line network. The AP 24 can manage the communications traffic by controlling when the frames are transmitted to each remote STA 26 in the cell 22. The communications traffic in the cell 22 may include data frames (eg, signals carrying frames to provide communications of data), voice frames (for example, signals that carry frames to provide voice communications), real-time frames (for example, signals that transport frames to provide real-time communications such as voice or multimedia communications), frames of management (for example, signals that carry frames to provide network management communications), etc.

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To perform rapid channel switching, the method of the present invention requires priority access to the wireless medium. Obtaining priority access to the wireless medium has been previously described in the IEEE 802.11e D3.2 standard.

In general, the 802.11 standard provides two coordination functions to gain access to the wireless medium to exchange communication traffic. The functions are controlled in the MAC layer. The two functions are the distributed coordination function (DCF) and the point coordination function (PCF). As discussed above, the PCF is an optional feature of the 802.11 standard and has not been widely implemented to date. The DCF is a mandatory feature of the 802.11 standard and provides a contention-based service similar to conventional Ethernet that is based on a talk-to-talk scheme called CSMA / CA (multiple access by carrier detection with collision avoidance) such as It is described in the IEEE 802.11 standard. Both the PCF and DCF use the interframe separations to coordinate access to the medium. In particular, the 802.11 standard defines four separations between different frames. Three are used to determine access to the medium.

Referring to Figure 3, a timeline 50 is shown illustrating the relationship between the three separations between frames (ie, SIFS, PIFS, DIFS) used to determine access to the medium. As is widely known in the art, the three separations between frames create different levels of priority for different types of frames over the medium. Different priority levels establish that high priority frames do not have to wait as long as low priority frames after the medium has become inactive. Therefore, if there is any pending high priority frame, such as an acknowledgment frame, it receives access to the network before the low priority frames have an opportunity to do so.

With reference to Figure 3, the wireless medium is initially shown as busy 52. During this busy interval 52, it is assumed that one of the network stations 24 or 26 has obtained control of the wireless medium and is transmitting a frame. During the busy interval 52, all other stations 24, 26 that do not currently have control of the wireless medium must remain silent and differ any intended signal communication. At the end of the busy interval (see point "A"), the medium becomes inactive.

The interval after the occupied interval 52 is defined as an inactive interval 55 within which three separations between frames are shown. Each of the three interframe separations provides a single level of priority for STAs 24 or 26 to access the inactive medium. They are the short interval 54 of interframe space (SIFS), which is used for high priority transmissions. Once the separation interval 54 between SIFS frames in the SIFS slot limit has elapsed (see "B"), high priority transmissions can begin. Once these high-priority transmissions begin, the medium becomes occupied again, so the frames transmitted after the interval 54 between SIFS frames has elapsed have priority over the low-priority frames that can be transmitted only after longer intervals such as the 56 PIFS and 58 DIFS frame separation intervals.

Also shown in Figure 3 is the interval 56 for separation between PCF frames (PIFS) used by STA 24 and AP 26 operating in the PCF service. In a manner similar to that described above with reference to the separation interval 54 between SIFS frames, STA 24 and AP 26 are allowed immediate access to the medium if it is determined that the medium is inactive at the PIFS slot limit (see point "C"). The PIFS frame separation interval 56 is currently only used in the PCF service mode to provide the contention-free service. As stated earlier, the PCF service is rarely incorporated into LAN implementations based on the 802.11 standard, and as such will not be treated further.

With continued reference to Figure 3, the separation interval 58 between DIFS frames is used by STA 24 and AP 26 operating in the DCF service mode based on contention. According to the DCF service, STA 24 and AP 26 are allowed immediate access to the medium if it is determined that the medium is inactive at the DIFS slot limit (see point "D").

A fourth frame separation interval, referred to as the extended frame space (EIFS), is not shown in Figure 3 since it is not a fixed interval, but is used only when there is an error in frame transmission, and It will not be treated further.

As is well known, the contention-based DCF service works by first detecting the wireless medium to determine if it has been inactive during the interval 36 between DIFS frames before transmitting. Once the separation interval 58 between DIFS frames has elapsed, an exponential recoil operation follows. To perform the recoil, a STA 24 generates a random number between zero and a contest window 60. This random number is the number of slots 62 that the STA must wait before transmitting. During periods when the channel is free, the transmission node decreases its recoil counter. When the recoil counter reaches zero, the node transmits the packet. As is evident, the DCF service is subject to latencies such as a backspace and access postponement.

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To perform rapid channel switching according to the principles of the invention, the aforementioned latencies associated with the conventional DCF service described above cannot be tolerated. The present invention, as will be described, overcomes these latency problems by employing a technique for obtaining priority access to the medium to perform functions associated with rapid channel switching in a contention-free manner.

According to one embodiment, to obtain fast channel access, an STA 24 or an AP 26 detects the means to determine if the medium is inactive during the PIFS frame separation interval 56. If the medium remains inactive in the PIFS slot limit (see point "C" in Figure 3), the AP 26 or STA 24 can transmit a management frame in the PIFS slot limit (point "C") to thereby obtain priority access to the channel. The management frame includes guidelines for performing rapid channel switching that may include (1) quickly suspend transmissions on a current channel within a set time frame and (2) quickly switch channels within a set time frame when a primary user is detected .

It is noted that the priority access scheme of the present invention does not replace the service based on conventional contention, but instead serves as a supplementary feature to obtain priority access by AP 26 or STA 24 in those situations in which require to quickly transmit a management plot. It is further noted that, unlike the conventional contention-based service, which includes the "recoil" procedure, as described above, there is no recoil procedure associated with the priority channel access scheme of the present invention. By not including in the method of the invention an associated recoil procedure, contention with other STAs is avoided and priority access is substantially guaranteed.

Next with reference to Figure 4, three management frames are shown that are being transmitted according to the method of the invention. As described above, a single management frame 61 is transmitted in the PIFS slot limit (point "C" in Figure 3). However, a correct reception of the management frame cannot be guaranteed with a single transmission. Therefore, the present invention considers the transmission of additional management frames 63, 65, preferably separated by the PIFS period of time to provide a greater degree of transmission reliability. Three are shown in Figure 4, however, more or less management frames can be used.

Accordingly, modifications such as those suggested above, but not limited to them, should be considered within the scope of the invention.

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Claims (14)

1. Method for obtaining fast channel access for a node (24) in a wireless local area network, WLAN (20), characterized in that it comprises the steps of:

-

 determining, in said node, that the WLAN is inactive during a period (56) of space between PCF frames, PIFS, in which PCF means point coordination function;

-

 transmitting a first management frame during a slot interval after said one period (56) PIFS;

wherein the transmission of said first management frame in said slot interval provides priority access to said WLAN (20) and in which said first management frame includes guidelines for performing rapid channel switching.

2.

Method according to claim 1, wherein said guidelines for performing rapid channel switching include one for switching from a current operating channel to a new operating channel within a set period of time and suspending transmissions on said current operating channel within a set deadline

3.

Method according to claim 1, wherein said node is an access point (24) in an infrastructure WLAN and a wireless station in an ad hoc WLAN.

Four.

Method according to claim 1, wherein said transmission step further comprises transmitting by air from said node to a plurality of associated nodes (26) in said WLAN (20).

5.

Method according to claim 1, wherein said transmission of said first management frame occurs before the start of the contest with a plurality of associated nodes (26) thus providing said priority access to said WLAN, wherein said contest is defined by said plurality of nodes

(26) associates, associated with said WLAN (20) competing for access to said WLAN (20).

6.

Method according to claim 5, wherein said contest with said plurality of associated nodes (26) begins at a slot limit (D) of space between DCF frames (DIFS), said slot limit (D) DIFS being produced at a time after said slot interval after said period (56) PIFS, in which DCF means distributed coordination function.

7.

Method according to claim 1, further comprising the step of transmitting at least one additional management frame after the transmission of said first management frame and before the start of a plurality of associated nodes (26) associated with said WLAN (20 ) competing for access to said WLAN (20).

8.

Method according to claim 7, wherein said first management frame and each of said at least one additional management frame is transmitted having a PIFS interval separation (PIFS) between them.

9.

Node for use in a wireless local area network (WLAN) (20), said node being characterized in that it is configured to:

-

 determine that the WLAN (20) is inactive during a period of space between PCF frames (PEFS); Y

-

 transmitting a first management frame during a slot interval after said one period (56) PIFS;

wherein said transmission of said first management frame in said slot interval provides priority access to said WLAN (20).

10.

Node according to claim 9, wherein said node is one of an access point (24) in an infrastructure network and a STA wireless station in an ad hoc network.

eleven.

Node according to claim 9, wherein said node (24) is further configured to transmit said management frame by air to a plurality of nodes (26) associated in said WLAN (20).

12.

Node according to claim 9, wherein said node (24) is further configured to transmit at least one additional management frame after transmission of said first management frame and before the start of a plurality of associated nodes (26), associated with said WLAN (20) competing for access to said WLAN (20).

13.

Node according to claim 12, wherein said first management frame and each of said at least one additional management frame are transmitted having a separation (56) of PIFS interval between them.

14.

System for granting priority access to a node in a wireless local area network (WLAN) (20),

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the system being characterized because it comprises:

- a memory (40, 42) for storing a computer readable code; Y,

- a processor (32) operatively coupled to said memory (40, 42), said processor being

(32) configured to:

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(1) determine, in said node (24), that the WLAN (20) is inactive during a period (56) of space between

PCF frames (PIFS); Y

(2) transmit a first management frame during the slot after said period (56) PIFS, including

said first management frame guidelines for performing a fast channel switching.

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fifteen. System according to claim 14, further comprising means for transmitting at least one additional management frame before the end of a separation interval between DIFS frames (D) after the first said

management plot.