ES2644481T3 - Procedures for implementing a dynamic frequency selection (DFS) and a time channel selection feature for WLAN devices - Google Patents

Description

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DESCRIPTION

Procedures for implementing a dynamic frequency selection (DFS) and a time channel selection feature for WLAN devices

RELATED APPLICATION

[0001] This application is a continuation in part (CIP) of US Patent Application Serial No. 10/406 049, entitled "Procedures for the Implementation of a Dynamic Frequency Selection Feature (DFS) for Devices WLAN ", filed on April 2, 2003 by Atheros Communications, Inc.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] The present invention relates to wireless local area network devices (WLAN) devices and in particular to techniques in WLAN devices for performing radar start scans, identification of support channels for a channel change, and so Efficient channel change in the case of radar detection in the operating channel.

Description of the related technique

[0003] Wireless local area network (WLAN) devices operating in the 5 GHz spectrum coexist with radar systems. Several regulatory standards (for example, the draft of the European Telecommunications Standards Institute (ETSI) EN 301 893, version V1.2.1, published in July 2002) require that a dynamic frequency selection (DFS) feature be incorporated into devices 5 GHz WLAN. This DFS function must change the operating channels in the presence of a co-channel radar and a uniform propagation operation across a wide frequency range.

[0004] Regulatory standards usually provide simple guidelines for the detection and / or avoidance of co-channel radar. For example, current European regulatory standards require that a 60-second scan of each allowed channel be completed before the operation begins. In addition, after the detection of a radar signal in the current operating channel, the WLAN device (ie an access point or a station) must interrupt the communication in a short time period, for example, from 0.2 to 1.0 second Please note that pending revisions of European regulatory standards may require that the additional transmission time of an access point or station be limited to a total of 260 ms counting from the moment a radar is detected. Other regulatory domains have proposed similar guidelines. For example, an IEEE 802.11h specification draft (which adapts the 802.11a standard to European standards) suggests that stations respond to a channel change announcement frame from an access point ceasing data transmission, thereby avoiding data transmission. harmful interference to the co-channel radar system.

[0005] However, these regulatory standards do not provide specific application details. Therefore, several patented solutions have been proposed. For example, United States Patent Application 10 / XXX XXX (hereinafter McFarland), entitled "Radar Detection And Dynamic Frequency Selection For Wireless Local Area Networks" (Radar Detection and Dynamic Frequency Selection for Local Area Networks) wireless), presented on December 6, 2001 by Atheros Communications, Inc., teaches how to efficiently detect co-channel radar.In McFarland, signal pulses are received as detected events.All detected events that correspond to the network traffic At this point, any event not eliminated can be examined to determine if it corresponds to radar signals.This test may include the identification of pulse repetition frequency, a pulse period or a number of pulses in a period of time. predefined time.

[0006] McFarland also teaches a technique to cease transmissions between an access point and its associated stations after radar detection. In this technique, a point coordination function (PCF), which is provided in the IEEE 802.11 standard, can be used to control which stations transmit and when they transmit. Specifically, a PCF beacon, which is sent by an access point, announces the beginning of a drilling period, in which all stations must wait until they are polled by that access point before transmitting. During the interval between the PCF beacon and the probing of the next station, the access point can perform a radar detection cycle. At the end of the radar detection cycle, the access point can continue with the normal PCF survey.

[0007] Other implementation techniques related to DFS are currently being developed. These techniques should include defining the specific algorithms for performing radar start scans, determining an acceptable support channel for a possible channel change and changing the channel efficiently in the case of radar detection in the operating channel. Preferably, these techniques should also include a mechanism by which legacy stations, that is, those stations that have not implemented DFS functionality,

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they can be easily controlled by the access point during a channel change operation and, more often than not, they can operate on the new channel. Another example of the prior art is disclosed in EP 1 248 477.

SUMMARY OF THE INVENTION

[0008] Several regulatory and regulatory bodies enact standards to define how wireless devices should operate in certain frequency bands. The 5 GHz frequency band is of particular importance for regulatory authorities due to radar systems operating in parts of this band. Radar systems could be used by military, aviation, meteorological and other government agencies. Therefore, due to the importance of these radar systems, wireless devices operating in the 5 GHz frequency bands must be able to detect radar and avoid any frequency used by radar systems. Radar detection and avoidance is a key feature of the capacity called dynamic frequency selection (DFS). In accordance with one aspect of the present invention, techniques are provided for performing radar start scans, determining an acceptable support channel for a possible channel change and changing channels efficiently in the case of radar detection in the channel operational These techniques advantageously comply with the current regulatory standards that govern DFS while minimizing delays at the start of the network and interrupting users during a radar detection event.

[0009] The startup routine of a wireless device typically depends a lot on time. Specifically, stations (and their human users) might think that a long startup routine is a product failure. Access points can be restarted in response to an inefficient start scan of the available channels, which significantly reduces the usability and availability of a wireless network. Some regulatory domains require relatively long time periods to verify that a channel is without radar. For example, European regulations require that each channel be scanned for 60 seconds to determine if it is without radars. Therefore, this requirement must be met while minimizing the time spent on the startup routine.

[0010] According to one aspect of the invention, the access point fills a short list of support channels (eg one or two) during initial startup and stores this short list during normal operation. The support channels can be advantageously used to make a fast and non-disruptive channel change in case radar is detected on the current channel. The use of this short list of channels, which have been pre-scanned for the radar by the required period (for example, 60 seconds), eliminates a start-up routine that is otherwise long (for example, up to 19 X 60 channels) seconds = 19 minutes).

[0011] During startup, the access point can quickly scan multiple radar channels. In one embodiment, normal operation can begin on the first channel without radar. During normal operation, the access point or one or more stations at the request of the access point may perform short background scans to identify additional channels without radar. The scanning process can continue until one or two channels are found without support radar. At this point, the channel (s) without radar can be stored at the access point for use during a future channel change event.

[0012] Fortunately, the timing of these scans will vary advantageously, thereby avoiding the possibility that the radar in the support channel is transmitting radar bursts with a timing exactly coincident with the short periods during which the access point or Station is not performing short channel scans. It is important to note that multiple short background scans performed during normal operation on a selected support channel effectively result in a full scan (for example, 60 seconds) for radars, as required by some regulatory standards.

[0013] Note that the radar can transmit significant energy on multiple adjacent channels (ie, both higher and lower) to the current channel of the WLAN device. Therefore, according to a feature of the invention, the selection of the support channels can be made to reduce the probability that the new channel is adjacent in frequency to the current channel. This selection process also advantageously satisfies the European requirement for a uniform propagation of operating channels. In addition, because many legacy stations will not be able to operate in some parts of the 5 GHz spectrum, that is, the 5470-5725 MHz subband, the selection process can be weighted in such a way that most or all of the Stations currently associated with the access point are able to operate on the new channel.

[0014] For example, in an embodiment of the invention, the access point may construct a list of support channels by choosing a channel of each sub-band at 5 GHz (ie 5150-5250 MHz, 5250-5350 MHz and 5470-5725 MHz). It is important to note that the random choice of the channels distributed within each subband (as opposed to the random choice of the channels using the full range of channels) results in a pseudo-random list of the support channels weighted towards the lower end of the spectrum (i.e. 5150-5350 MHz). Because many legacy stations are not able to operate in the 54705725 MHz subband, an access point that minimizes channel selection in this large subband may increase the likelihood of compatibility with such legacy devices.

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[0015] Advantageously, few, or none, radars operating in certain target regional domains (eg, Europe) will be found in the 5150-5250 MHz sub-band. Therefore, both US and European regulatory requirements exempt The devices search for radars in this sub-band. In addition, relatively few radars are expected to be found in the 5250-5350 MHz sub-band. Instead, the larger 5470-5725 MHz sub-band is expected to be occupied by meteorological radars commonly deployed in many countries. Therefore, this weighting also reduces the probability of finding radar in the candidate support channels.

[0016] According to another aspect of the invention, the access point may also consider the presence of other WLAN devices that already operate in certain bands. In one embodiment, a list of channels without BSS is filled from a list of allowed channels of the current regional domain. Preferably, the access point chooses its support channels from this list of channels without BSS. However, if the number of support channels is too low, then the access point may better choose its support channels from the list of allowed channels to continue complying with the channel propagation rules.

[0017] When radar is detected in the current operating channel, the access point may choose its support channel from a list of channels without radar that are, in general, farther in frequency (ie, above or below) of the current channel on which the radar was detected. In one embodiment, the channel change process can advantageously prioritize the selection of support channel in the 5150-5350 MHz sub-band, which, as indicated above, are less likely to contain radar energy and They are more likely to allow legacy stations to operate. For example, if the current channel is in the 5250-5350 MHz sub-band and at least one support channel is in the 5150-5250 MHz sub-band, then the access point can set the new channel to the more channel Low on the list of channels without radar. On the contrary, if the current channel is in the 5250-5350 MHz sub-band and there is no support channel in the 5150-5250 MHz sub-band, then the access point can set the new channel to the highest channel in the list of channels without radar. Finally, if the current channel is in the 5470-5725 MHz sub-band, then the access point can set the new channel to the lowest channel in the list of channels without radar. This channel change operation in combination with the selection of support channel (i.e., fill in the list of channels without radar) advantageously minimizes network interruption to legacy and non-inherited station devices and significantly improves wireless network operation in comparison with a completely random channel change.

[0018] After radar detection in the current operating channel, the access point can broadcast a channel change frame to all stations, thereby ensuring that all stations capable of interpreting this message will cease data transmission. immediately. At this point, the access point can broadcast an additional control frame, that is to say, a de-authentication frame, to all stations. This de-authentication frame, which is understood by all stations, immediately stops the transmission of data to the access point and returns to a start state.

[0019] It is important to note that the deauthentication frame is sent after the designated channel change time. Without this synchronization, most if not all 802.11h-compatible stations would respond to the de-authentication frame by immediately interrupting communication with the access point, thus losing the ability to make the desired non-disruptive channel change initiated by the change process. channel. By sending the deauthentication frame at a designated time after a channel change frame, any 802.11 h compatible station that received, understood and accepted the channel change frame will pass from the current operating channel before the access point sends the deauthentication plot. In addition, any station not compatible with 802.11h (i.e. inherited) will cease its operation quickly, thereby reducing harmful interference to co-channel radars as well as reducing the time needed to detect that the access point has left the channel and initiate recovery procedures

[0020] A procedure for carrying out a start-up operation for an access point in a regulatory domain is also provided. Note that the regulatory domain has a frequency propagation requirement and the access point can only communicate using the channels allowed in a spectrum. In this procedure, a list of allowed channels can be filled in with the allowed channels. A list of channels without BSS can be filled in with any allowed channel that has acceptable levels of current WLAN transmission on it. A list of channels without radar can then be filled in using the list of channels without BSS and the list of allowed channels.

[0021] A first channel can be randomly selected from the list of channels without radar. If the first channel is in a first sub-band and the regulatory domain exempts scanning in the first sub-band, then the first channel can be designated as the current channel, a support channel can be selected from the list of channels without radar in the first sub-band without scanning, and the operation of the access point can begin with the first channel.

[0022] On the other hand, if the first channel is not in the first sub-band and the regulatory domain exempts scanning in the first sub-band, then a radar scan can be performed on each channel in the list of channels without

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radar, except any channel in the first subband. Similarly, if the first channel is in the first subband and the regulatory domain requires scanning in the first subband, then a radar scan can be performed on each channel in the list of channels without radar. In these two cases, you can delete any channel with radar in the list of channels without radar. The above steps can be repeated until a predetermined number of channels remain in the list of channels without radar. At this point, a first channel can be chosen in the list of channels without radar and the normal operation of the access point can start with the first channel.

[0023] In some regulatory domains, when radar is detected, the access point may advantageously select a new channel from the list of channels without radar for operation without additional radar scanning. In other regulatory domains, for example, the United States regulatory domain, an access point should perform a 60-second radar scan "immediately" before operation on a non-radar-free channel (that is, a channel that requires radar detection). Therefore, radar scans performed during startup and update may not meet this requirement. A continuous 60-second radar scan that begins after radar detection on the current channel would undesirably result in the operation of interrupting the access point with its current associated stations. In other words, a rapid channel change (without loss of association with stations) would not be possible since it is necessary that the access point and the stations undo the channel in 10 seconds and the access point therefore could not broadcast the channel. Quick channel change information to the stations if you were trying any 60 second scan on a candidate channel at this time.

[0024] Therefore, according to an aspect of the invention, after a channel change operation initiated due to the radar detection in the current channel, if the new selected channel is in a radar-free sub-band, then the access point can immediately start the operation again in this new channel. In other words, regardless of the interpretation of the regulatory domain of the channel availability check, the 60-second scan is not necessary to start operation in a radar-free sub-band. Note that the new channel is selected using a pseudo-random channel algorithm and, therefore, also complies with the uniform propagation rules.

[0025] On the other hand, if the new selected channel is in a non-radar-free sub-band, then the access point may select a new temporary channel in a radar-free sub-band. In one embodiment, the new time channel can be selected randomly. In another embodiment, at the beginning, the access point can store information related to the traffic of the channel and the access point can select the radar-free channel with the lowest traffic. Normal operation can continue on this new temporary channel until the access point has completed a total background radar scan of the previously selected new channel. If radars are detected on the previous new channel, then the access point can select another channel from the list of channels without radar and perform another total background scan. If radars are not detected during total background radar scanning, then the access point can quickly change from the new temporary channel to the previous new channel. Using this channel change technique, network users do not experience any service interruption advantageously, because only fast channel changes and background scanning are used to comply with applicable regulatory requirements.

BRIEF DESCRIPTION OF THE DRAWINGS.

[0026]

Figure 1 illustrates an exemplary process for channel selection during the start / restart of an access point.

Figures 2A, 2B and 2C illustrate an exemplary process for filling in a list of channels without radar based on a list of allowed channels and a list of channels without BSS.

Figure 3A illustrates an exemplary radar scanning procedure that can be performed by an access point during normal operation.

Figure 3B illustrates an embodiment for selecting a new channel after a radar is detected in the current channel.

Figures 4A and 4B illustrate an example channel selection technique that can be performed by an access point. In this channel change technique, if the new selected channel is not in a radar-free sub-band, then the access point can temporarily perform a fast channel change operation of the access point and the stations associated with a channel within a radar-free subband and immediately start a total background radar scan on the new selected channel. After confirming that the new selected channel is without radar, the access point can perform a second fast channel change operation to switch to the new selected channel.

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Figure 5 illustrates an embodiment of a channel change process in a station. This channel change process allows the station to remain compatible with the IEEE 802.11h standard, remain compatible with non-802.11h access points, and comply with the mandatory European requirements.

Figures 6A and 6B illustrate another exemplary start operation in which an access point can request associated stations to assist in the radar detection function.

Figure 7 illustrates another exemplary procedure for channel selection during the start / restart of an access point.

DETAILED DESCRIPTION OF THE DRAWINGS

[0027] In accordance with various aspects of the present invention now described in detail, the techniques for performing radar start scans, the determination of an acceptable support channel for a channel change, and the change efficiently of channels in the case of radar detection in the operating channel advantageously comply with the current regulatory standards governing DFS, while minimizing network start delays and interruption for users during a radar event.

Channel selection during the start / restart of the access point

[0028] Figure 1 illustrates an exemplary procedure for the selection of support channel during the start / restart of an access point. In step 101, an access point can search for the channels allowed by the regulatory domain in which the access point will be operating. In one embodiment, the access point can access a search table (LUT) that includes known regulatory domains and associated allowed operating channels. If the regulatory domain is Europe, then the allowed channels are within the following frequency ranges (also called subbands in this document): 5150-5250 MHz (4 channels), 5250-5350 MHz (4 channels) and 5470 -5725 MHz (11 channels). These allowed channels can be added to a list of allowed channels. In this document, this process is called "filling in" a list.

[0029] In step 102, the access point can perform a start scan for the basic service sets (BSS) in the list of allowed channels. A BSS is a set of IEEE 802.11 compatible devices that function as a fully connected wireless network. In one embodiment, this start scan can take 200 ms per channel. Therefore, assuming that all subbands are allowed, this start scan will last no more than 200 ms X 19 channels = 4 s. At this point, the access point can fill in a list of channels without BSS of allowed channels that are currently without transmission or have an acceptable level of current WLAN transmission.

[0030] In step 103, the access point may fill in a list of channels without radar using a process described in reference to Figure 2. In the embodiment described in Figures 2A and 2B, two or three candidate channels are included in the list of channels without radar. Note that at this point, these candidate channels have not yet been tested for radar.

[0031] In step 104, the access point can perform a radar scan on each candidate channel in the list of channels without radar. In one embodiment, this radar scan conforms to the current European standard of 60 seconds for each channel. After this radar scanning operation, the access point can erase any channel on which radar signals were detected from the list of channels without radar. Typically, at this point, the list of channels without radar will have 0, 1, 2 or 3 channels.

[0032] In step 105, if the list of channels without radar contains two or more channels, then the access point may randomly choose a channel from the list of channels without radar and establish that channel as the current operating channel in the step 106. At this point, the access point can delete the current channel from the list of channels without radar, thus leaving one or two support channels in this list. The access point can retain the list of channels without radar for support in case radar is detected on the current channel. In step 107, the access point can begin to perform beacons and perform normal operations on the current channel. In one embodiment, the list of channels without BSS can be discarded after step 106 to preserve the valuable storage area.

[0033] On the other hand, referring again to step 105, if the list of channels without radar contains less than two (ie, 0 or 1) channels, then the access point may send a console message indicating that an insufficient number of channels without radars has been found. Then, the process can return to step 101 to repeat the start operation.

[0034] For regulatory domains that enforce the regulatory requirement where WLAN devices must not occupy a channel on which radar was detected (for example, nominally during a period of at least 30 minutes after radar is detected), a additional protection In this case, the device

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WLAN can store the channel number (s) in which the radar was detected along with a time stamp of the radar event associated with the channels. In one embodiment, this information can be stored in a non-volatile memory. During normal operation, the timestamp can be updated periodically to count the required period (for example, 30 minutes), at which time the non-reoccupation indicator can be eliminated. After a restart of the WLAN device, the list of candidate radar channels (according to Figure 1, step 103) can be compared with the number (s) of channel (s) stored in non-volatile memory and can be deleted the appropriate channels. This list of non-reoccupation channels can be eliminated in the 2nd subsequent restart of the WLAN device using an independent useful life time indicator (which could also be stored and reduced in a non-volatile memory) that counts the number of restarts since it was stored non-reoccupation channel numbers.

[0035] An alternative implementation of the non-reoccupation list that does not require real-time clock or timestamp of individual channels in the list can be implemented as follows. The non-occupancy channel list can be compiled as described above and the new channels can be stored in non-volatile memory immediately after the radar is detected. The complete list of non-occupancy channels only restarts after 30 minutes from the moment any channel is added to the list. If the device restarts or returns to operation as a result of radar detection or other causes, the list of non-reoccupation existing at startup is checked and a new 30-minute timer is started. Only after a 30-minute continuous period has elapsed (during which no new channels are added to the list), the list stored in non-volatile memory will be deleted. In this way, no time stamp of individual channels or real time clock is used. Please note that periods of more than 30 minutes may elapse before certain eligible channels are removed from the list. This elimination technique will probably have a minimal impact on the operation and / or availability of the wireless network due to the significant number of total channels as well as sub-bands that are not subject to the requirements of radar detection (and, therefore, , are typically available for operation, regardless of radar activity in the area). To take full advantage of the short support channel list (for example, a faster start and less damaging update of the support channels), the list of channels without radar should be filled in step 103 taking into account certain considerations. Specifically, the selection of the support channels should reduce the risk of a channel change operation that results in the access point moving to a channel in which the radar continues to operate. At present, regulatory requirements do not require that a 5 GHz WLAN device take specific measures to prevent the passage to a new radar-occupied channel after radar is detected in the current channel, except the requirement that the new channel be Check beforehand on speed cameras during the start scan.

[0036] It is important to note that radars can operate across transmission bandwidths wider than the WLAN device. In addition, some radars, called agile frequency radars, may intentionally change the operation across multiple adjacent frequencies in a spectrum band. In addition, other radars, such as transportable, airborne or even fixed radars, can operate intermittently or with a long and irregular directional scanning sequence (a meteorological radar, for example). In addition, due to high spurious out-of-band emissions from nearby radars accessing WLAN receivers with finite out-of-band rejection, WLAN devices located near radars will receive significant energy in channels adjacent to the current operating channel. Therefore, unfortunately, moving to a channel in which radar energy is still present is absolutely possible in the real world.

[0037] Therefore, a list of conventional support channels, even if updated according to regulatory requirements (described in reference to Figure 3A), may not protect against the access point that makes a channel change to a support channel that has a radar or may be undesirably close in frequency to a radar channel. Such a change of channel may require another change of channel with its associated interruption of network operation. This problem can be further complicated by the regulatory requirement to extend the operation of WLAN devices across the entire spectrum spectrum available.

[0038] According to a feature of the invention, the selection of support channel (ie, filling in the list of channels without radar) can be weighted to provide a wide range of channel frequencies in the 5 GHz spectrum, keeping the at the same time the randomness required to achieve the extension of operation for WLAN devices. In addition, the weighting can increase the likelihood that legacy stations can continue to function when an access point makes a channel change.

[0039] Figures 2A, 2B and 2C illustrate an example weighted process for filling in a list of channels without radar. In one embodiment, the access point can fill in the list of channels without radar using the list of allowed channels and the list of channels without BSS. Preferably, two or three channels weighted towards the lower end of the spectrum can be chosen, thereby significantly improving the support of the inherited device.

[0040] In step 201, if the list of allowed channels includes channels having frequencies between 5150-5250 MHz, 5250-5350 MHz, as well as 5470-5725 MHz, then the access point determines whether the list of channels without BSS has less than two channels in step 204. In other words, if two or more channels currently do not have (or

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they have an acceptable level of) transmission from other sets of basic services, then said channels would preferably be used for support channels in case a radar is detected in the current channel. If the list of channels without BSS does not have less than two channels, that is, two or more channels are in the list of channels without BSS, then the process can determine whether the list of channels without BSS includes at least one channel in each one of the 5150-5250 MHz, 5250-5350 MHz and 5470-5725 MHz subbands in step 206. If the list of channels without BSS includes at least one channel in each of the 5150-5250 subbands MHz, 5250-5350 MHz and 5470-5725 MHz, then the access point can pseudo-randomly select three channels from the list of channels without BSS in step 207. In one embodiment, one channel can be chosen from each of the 5150-5250 MHz, 5250-5350 MHz and 5470-5725 MHz subbands (hence the selection is considered to be "pseudo-random").

[0041] On the other hand, if the list of channels without BSS has less than two channels or if the list of channels without BSS does not include at least one channel in each of the sub-bands of 5150-5250 MHz, 5250-5350 MHz and 5470-5725 MHz, then the access point may select three channels from the list of channels allowed in step 207 pseudo-randomly. In one embodiment, one channel can be selected from each sub-band, that is, 5150-5250 MHz, 5250-5350 MHz and 5470-5725 MHz.

[0042] In step 202, if the list of allowed channels includes channels that have frequencies only between 5150-5250 MHz and 5250-5350 MHz, then the access point determines whether the list of channels without BSS has less than two channels in step 208. If not, the process can determine whether the list of channels without BSS includes at least two channels in the 5150-5250 MHz sub-band and at least one channel in the 5250-5350 MHz sub-band in step 210. If the list of channels without BSS includes at least two channels in the 5150-5250 MHz sub-band and at least one channel in the 5250-5350 MHz sub-band, the access point may choose pseudo - Randomly three channels from the list of channels without BSS in step 211. In one embodiment, two channels of the 5150-5250 MHz subband can be chosen and one channel of the 5250 subband can be chosen -5350 MHz

[0043] On the other hand, if the list of channels without BSS has less than two channels or the list of channels without BSS does not contain at least two channels in the 5150-5250 MHz sub-band and one channel in 5250-5350 MHz, then the access point can choose pseudo-randomly three channels from the list of channels allowed in step 209. In one embodiment, two channels of the frequency range 5150-5250 MHz can be selected and one can be selected frequency range channel 5250-5350 MHz.

[0044] In step 203, if the list of allowed channels includes channels that have frequencies only between 5150-5250 MHz, then the access point determines whether the list of channels without BSS has less than two channels in step 212. Yes it is not so, then the access point can randomly choose two channels from the list of channels without BSS in step 214. On the other hand, if the list of channels without BSS has less than two channels, then the access point can choose Randomly two channels from the list of channels allowed in step 213. In the case of the list of allowed channels that includes frequencies only between 5150-5250 MHz, the choice of only two channels (steps 211/212) is adequate and desirable because to the less likely presence of radar signals in this subband. In addition, reducing the number of channels in the list of channels without radar from three to two channels can advantageously reduce the start times while maintaining the required channel propagation.

[0045] In an embodiment mode in which the channels must be chosen from the list of allowed channels due to the shortage of channels in the list of channels without BSS, the above steps can be modified to take into account the relative level of activity BSS on busy channels. In this embodiment, the access point can construct a histogram of received signal strength levels (RSSI) and traffic levels from BSS signals received on each allowed channel. Those channels with combined RSSI and traffic levels that constitute the lowest values can fill in the list of channels without BSS. In this way, the list of channels without BSS can still be used to fill in the list of channels without radar even in cases where there is some BSS traffic in most or all allowed channels. This procedure advantageously reduces the probability that the access point will operate in a channel with heavy co-channel BSS traffic. In another embodiment, a single absolute RSSI threshold value may be used instead of a histogram of values. Therefore, allowed channels that are seen to contain minimum and / or acceptable levels of BSS traffic can fill in the list of channels without BSS. In other words, the BSS traffic below a minimum RSSI value will have no real impact on the functioning of the access point and, therefore, can be safely ignored.

Radar scanning performed by an access point under normal operating conditions

[0046] Figures 3A and 3B illustrate a mode of performing a radar scan that can be performed by an access point during normal operation. According to one aspect of the invention, continuous radar scanning of the current channel is required. This scan is performed during normal operation on the current channel through step 301 to ensure compliance with regulatory requirements. If radar is detected on the current channel, as determined in step 302, then the process continues to step 311, which is explained with reference to Figure 3B.

[0047] If radar is not detected on the current channel, then the access point determines whether a

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update time in step 303. The update time refers to a period of time during which the support channels in the list of channels without radar should be rechecked for radar. Specifically, some regulatory specifications require that a WLAN device rescan any channel in the list of channels without radar, otherwise the access point cannot change to that support channel during a channel change operation. A 24-hour period is typical for this update period. According to European requirements, the access point must perform another 60 second scan for the radar on each support channel during the update period. If the update time is not reached in step 303, then the access point returns to step 301 and continues to perform periodic radar scanning on the current channel. If the update time is reached, then the access point pauses normal operation and rescan the support channels in the list of channels without radar in step 304.

[0048] The update scan is preferably performed at certain times instead of trying to update in the unpredictable time of a channel change due to radar detection in the current channel. Specifically, the sending of a channel change announcement and the cessation of operation in a channel can be performed in a period of time much shorter than the 60 seconds necessary to perform a scan of each support channel. Therefore, to save time during the channel change and reduce network interruption, scanning must be updated during normal operation. However, interrupting the operation of the wireless network (even if it is scheduled for more hours than normal) for a 60-second update operation on even one of the support channels could result in all stations losing communication with protocols. and higher layer applications as well as possible data loss or other unacceptable interruptions.

[0049] Therefore, an exemplary update operation includes the access point that uses background scanning of short time periods (eg, 2-5 s) of each support channel to comply with the total scan time of 60 seconds, thus complying with the regulatory requirements and minimizing the impact of the network and the user. In another embodiment, one or more associated stations can be used to perform a periodic background scan of short time perfumes of each support channel (see, for example, Figure 6B). According to a feature of the invention, the identification of a short support list with 1 or 2 channels can advantageously guarantee that the updating of the support channels is significantly faster compared to the updating of a larger list. In addition, the use of short time update update scanning can dramatically reduce or even eliminate disruption of network operation.

[0050] If radar is detected on one or more support channels during the update scan by step 305, then any radar channel is deleted from the list of channels without radar in step 306 and the complete full scan is performed. leave for those channels immediately after radar detection. In another embodiment, the access point may attempt a revalidation of a deleted channel in a predetermined interval (eg, 30 min). If a radar is not found during revalidation, then that channel can be added back to the list of channels without radar. If at least one support channel remains in the list of channels without radar (as determined in step 307) or if a radar is not detected in step 305, then the access point can resume normal operation on the current channel in step 308 and reset the update time in step 309. At this point, the access point can return to step 301 to scan for radar on the current channel.

[0051] If there are no channels in the list of channels without radar (step 307), then the access point can be dissociated with all stations in step 310. At this point, the access point can return to step 101 for a start scan (or restart). In another embodiment, the access point can perform background scanning (e.g., periodic scanning in 200 ms increments) of any channel allowed in step 320 until a channel without radar is identified and entered. to the list of channels without radar. Then, the process proceeds to step 308. In one embodiment, if a channel cannot be found without radar, then the process could proceed to step 310, that is, that is, dissociation of all stations.

[0052] Figure 3B illustrates an exemplary selection process for a new channel after a radar is detected in the current channel. In step 311 of this process, the access point ceases the current transmission on that channel and rejects new association requests. At this point, the access point can characterize the current channel according to the sub-band (eg 5150-5250 MHz, 5250-5350 MHz and 5470-5725 MHz) and respond based on this characterization.

[0053] Specifically, as noted above, certain regulatory domains may not require radar scanning in predetermined subbands that have few or no radar. For example, regulatory domains in the United States and Europe do not currently require radar scanning in the 5150-5250 MHz subband. The United States does not require radar scanning in the 5725-5850 MHz subband. Sub-band that does not require radar scanning is referred to herein as the radar-exempt sub-band. Therefore, if radar is detected on a channel in step 302, then the current transmission may be in the 5250-5350 MHz or 5470-5725 MHz sub-band.

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[0054] Because short-distance radars can cause a WLAN to receive significant energy on multiple channels adjacent to the current channel, the establishment of a new channel with the farthest possible frequency from the current channel can advantageously reduce the probability of That the new channel has radar. For example, if the current channel is in the 5250-5350 MHz sub-band and at least one channel in the list of channels without radar is in the 5150-5250 MHz sub-band, as determined in step 314, then the access point can advantageously set its new channel to the lowest channel in the list of channels without radar in step 315. In contrast, if the current channel is in the 5250-5350 MHz sub-band and no channel in the list of channels without radar is in the sub-band of 5150-5250 MHz, as determined in step 316, then the access point can set its new channel to the highest channel in the list of channels without radar in step 317 Finally, if the current channel is in the 5470-5725 MHz sub-band, as determined in step 318, then the access point may establish its new channel to the lowest channel in the list of channels without radar in the step 319. After adjusting your new channel, the access point can proceed to a channel change technique described in n reference to figures 4A and 4B.

The selection of temporary channel guarantees the continuity of the transmission

[0055] In some regulatory domains, when radar is detected, the access point can advantageously select a channel from the list of channels without radar for operation without additional radar scanning. US Patent Application Serial No. 10 / 406,049 discusses this type of channel change technique in more detail. In other regulatory domains, for example, the United States regulatory domain, an access point should perform a 60-second radar scan "immediately" before operation on a non-radar-free channel (that is, a channel that requires radar detection). Therefore, radar scans performed during startup (step 104) and update (step 304) may not meet this requirement. As indicated above, a continuous 60-second radar scan will undesirably result in the operation of interrupting the access point with its current associated stations.

[0056] Therefore, in reference to Figure 4A, if the new selected channel is in a radar-free sub-band, for example 5150-5250 MHz or 5725-5850 MHz, as determined in step 401, then the access point can immediately restart operation on this new channel. In other words, regardless of the interpretation of the regulatory domain of the channel availability check, the 60-second scan is not necessary to start operation in a radar-free sub-band. Note that the new channel is selected using a pseudo-random channel algorithm and, therefore, also complies with the uniform propagation rules.

[0057] If the new selected channel is in a non-radar-free sub-band, then step 402 may select a new temporary channel in a radar-free sub-band (eg 5150-5250 MHz or 5725-5850 MHz) In one embodiment, the new time channel can be selected randomly. In another embodiment, at the beginning, the access point may store information related to the traffic of the channel and step 402 may include the selection of the radar-free channel with the least traffic. Normal operation can continue in this new time channel until the access point has completed a radar scan of the new channel previously selected (i.e. the new channel selected by one of steps 315, 316 and 317), as described below in the reference to figure 4B.

[0058] Note that in one embodiment, if the regulatory domain does not require frequency propagation, then the new time channel can be used as the new channel and it is not necessary to perform the change steps described in Figure 4B.

Access point operation during channel change

[0059] After detecting a radar, the access point can transmit control and / or management frames, up to a maximum movement time (MaxMoveTime) (for example 10.24 s) in accordance with current regulations. However, to reduce the impact on latency-sensitive applications, the access point must make the channel change as quickly as possible (that is, on the order of less than 3 s).

[0060] In one embodiment, the access point can quickly dissociate with stations not compatible with 802.11h because they are not able to act on a channel change frame broadcast by the access point. The access point can advantageously maintain the association with most of the 802.11h compatible stations in a new channel through a channel change technique described in reference to steps 403-410. Specifically, in step 403, the access point can broadcast a channel change frame to its associated stations. It is important to note that the 802.11h compatible stations, upon receiving the channel change frame, should respond by ceasing the normal data transmissions and changing their transmission channel to the new channel at the time of the channel change designated in the change frame channel. However, some 802.11h-compatible stations may be disabled or otherwise lose the channel change frame (for example, due to interference from continuous co-channel radar pulses or system malfunction).

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[0061] In step 404, the access point determines whether a channel change time has expired. If the channel change time has not expired, then the access point may repeat the broadcast of the channel change frame in step 405 to the MaxMoveTime, but typically for a duration of less than 3 seconds. If the channel change time has expired, then the access point may broadcast a de-authentication frame to any remaining station in the old channel in step 406. The broadcasting authentication frame, which silences all stations and results in the Dissociation with the access point is sent only after the expiration of a channel change time. This synchronization prevents the 802.11h compatible stations from receiving the de-authentication frame (which otherwise results in said stations being immediately disconnected from the access point instead of performing the less harmful channel change procedure). Note that any resulting dissociation does not contradict the IEEE 802.11h standard or regulatory requirements. Advantageously, upon losing contact with the access point, a station is programmed to interrupt the transmission of data before 1 second, thus causing a limited or no impact on any radar system. Note that these dissociated stations can quickly re-associate with the access point (analyzed in reference to step 409) in the new channel or associate with a new access point in another channel.

[0062] In step 407, the access point is moved to the new channel and the beacon shipment on this new channel begins. In step 408, the access point can restart communication with the 802.11h compatible stations that successfully moved to the new channel. In step 409, the access point can be associated with any station that has dissociated during the change of channel and / or with any new station requesting association. The access point can continue its normal operation in step 410.

[0063] Step 420 determines whether the new operating channel is temporary. If it is not, the process returns to step 301 to perform a radar scan (if necessary) on the channel. If the new channel is temporary, then step 421 can perform a background channel check on the previous channel chosen by the pseudo-random weighted algorithm (for example, steps 317 or 319). In particular, this background channel check can use a total scan time to meet the 60 second scan requirement. This background channel check can be performed only by the access point or with the help of any available station that responds positively to a request to make a part of this 60-second scan.

[0064] If the total 60 second background scan does not show radar presence, as determined in step 422, then step 425 can remove the designation of a new time channel and return to step 403 to initiate a second change. Fast channel using the new previous channel. In this way, after performing steps 403-408, you will start operation again on this newly scanned channel. Advantageously, since only fast channel changes and background scanning are used to comply with applicable regulatory requirements, network users will not experience service interruption.

[0065] Because this channel has already undergone a continuous 60-second radar scan during the start of the access point and perhaps even a total 60-second background scan during an update cycle (see step 304 ), there is a high probability that the background scan performed in step 422 will not find radars. However, if radars are detected, then step 423 can mark that channel for non-occupancy and choose another channel from the list of channels without radar. At this point, step 424 can perform a total 60 second radar scan on this new channel. The procedure can then return to step 422. Note that until the channel passes through the background scan, the access point can advantageously continue to operate normally in the time channel.

DFS implementation for a WLAN station

[0066] Figure 5 illustrates an example channel change process that can be performed in a WLAN station. This channel change process advantageously allows the station to remain compatible with the IEEE 802.11h standard, remains compatible with non-802.11h access points and, at the same time, conforms to the mandatory European requirements.

[0067] In step 501, the station determines whether a channel change or a de-authentication frame has been received from an access point. If a channel change frame is received, then the station ceases the entire transmission and responds with a confirmation in step 502. If the station supports the new channel, as determined in step 503, then the station establishes its operation for the new channel in step 504. In one embodiment, it is not necessary to re-authenticate the station in step 504.

[0068] At this point, the station is ready to listen to signals (ie beacons) from the access point in the new channel. In one embodiment, the appropriate time to wait to hear the access point in step 505 includes the time necessary for an access point to change the channels plus the time for a predetermined number of beacons (for example seven beacons) be sent by that access point. Note that several timers within the station can be frozen during this channel change, either using this or a different timing.

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[0069] If the station listens to the access point on the new channel at step 505, then the station can start operation again on the new channel at step 507. On the other hand, if the station does not hear the access point in the new channel, then the station can begin a normal passive scanning sequence in all the channels allowed in step 506. If the station receives a frame of disengagement of an access point, then the station immediately ceases all transmission in the step 509. This cessation in general is not preceded by a confirmation by the station to the access point. Note that the deauthentication frame can be transmitted when a non-802.11h access point (i.e. an inherited access point) responds to radar detection or when the station has lost a channel change frame from an 802.11 access point h (remember that the access point sends a deauthentication frame before leaving the channel). Once the deauthentication frame is received, the station can initiate scanning sequences in the channels allowed in step 506.

[0070] The station may also be configured with a relatively recently lost beacon timer (for example, 1 second beacon interval X 2 lost beacons) to further protect the radars in the situation where the station receives not even a frame of misunderstanding Not a channel change frame. In this case, within 2 seconds after the access point leaves the current channel due to a radar event, the station would stop transmitting. Shorter values for the lost beacon timer may result in degraded station performance with marginal links to the access point.

[0071] Note that if the station is not capable of detecting a radar, the station can be configured to deactivate ad hoc communication using any 5 GHz channel and to force passive scanning in step 506. This configuration ensures that the station does not it will transmit on any 5 GHz channel until after an access point has checked the radars and the beacon shipment begins. Specifically, the regulatory requirements allow stations that are not capable of detecting a radar to remain under the control of a "main" device, for example, an access point, which is responsible for checking radar before and during use. of any channel. The embodiment described in Figure 5 allows station devices with no radar detection feature to comply with regulatory requirements while maintaining efficient startup and continuous operation when operating in regions where DFS is required. On the other hand, if the station is capable of detecting radar, then the station can be configured to enable ad hoc communication and to perform an active scan in step 506, although said station is not required to do either. In this way, even the stations capable of detecting radar could be configured to perform passive scanning in step 506.

The stations facilitate the radar detection function

[0072] In one embodiment, the access point can further reduce the start time by means of the help of one or more associated stations that are capable of performing the radar detection function. Figures 6A and 6B illustrate an exemplary start operation in which the stations can assist the access point in the radar detection function. In one embodiment, the access point may use steps 101-103, as described in reference to Figure 1, to fill in the list of channels without radar.

[0073] Next, in step 601, the access point can perform a 60 second radar scan on a randomly selected channel in the list of channels without radar. This scan can continue until the access point finds a first channel without radar. Any scanned channel including radar can be deleted from the list of channels without radar. In step 602, the access point can choose the first channel without radar as the current channel, remove this channel from the list of channels without radar and start sending beacons on that channel in step 603. Note that because Support channels are not yet selected, the start time can be significantly reduced compared to the process described in reference to Figure 1.

[0074] Next, in step 604, the access point may allow the stations to authenticate and associate. If at least one new station has been associated with the access point, as determined in step 605, then, before sending or receiving data frames, the access point can immediately send a Basic Measurement Request tranche to an associated station in step 606. In one embodiment, the access point can send the frame to the station that the association first requested. This signal asks the station to scan a candidate channel in the list of channels without radar in search of a radar. The access point may request that the scan be limited to a short duration (eg, 2-5 s). In one embodiment, the access point can identify a channel for the station to scan. For example, the channel identification process may include steps substantially similar to steps 312-319 (ie, instead of configuring the support channel to the current channel, the candidate channel would be scanned for radar search).

[0075] However, the station may or may not be willing to accept and make the measurement request in the designated channel, as determined in step 607. If the station responds that it will not measure the radar (p (eg, refuses, is incapable, or does not respond to the request at all), then the access point can determine if there is another station just associated in step 605. If so, then the process continues with step 606 If there is no other newly associated station to measure, then the access point will indicate any

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associated station or stations that the communication will be delayed for a predetermined period of time while the access point itself switches to the alternative channel and performs a short scan of the radar in step 609.

[0076] To minimize the latency and interruption of data processing during normal operation in step 609, in particular when many stations may require access to the network, the duration of scanning of the access point may be short enough for ensure the continuity of the network operation, for example 100 to 200 ms. In one embodiment, stations can be informed that they stop transmitting during this period (plus a short buffer time period for the access point to change and return to the current operating channel) using a coordination function. of points (PCF) of the access point in combination with an appropriate perforation value without containment, which results in a long NAV value at the station. Note that the PCF, provided by the IEEE 802.11 standard, allows an access point to control the timing of transmissions from its associated stations. Specifically, using the PCF, the broadcasting access point will poll at each station and the station can only respond after being polled. The NAV value indicates the minimum time a station must wait until it attempts to communicate with the access point again. After scanning, the access point can return to the current operating channel, reset the NAV and PCF and continue listening to the radar on the current channel. After approximately the same time period used for scanning, for example 100 to 200 ms, the access point can repeat its scanning on that support channel. Assuming a scan / standby time of 200 ms, the access point would repeat the process 300 times to meet a regulatory requirement as an example of a 60-second scan for a support channel.

[0077] If the candidate support channel does not have radar, then the access point can set the update time for that support channel. On the other hand, if the candidate support channel has radar, then the access point can delete that channel from the list of channels without radar. Note that if the access point detects radar on the current channel before support channels have been identified in the list of non-radar channels of the candidate support channels, then the access point typically restarts (i.e. , go back to step 101, in figure 1 or figure 6A).

[0078] In step 610, the access point can determine whether another candidate support channel from the list of channels without radar should be scanned (ie, if the number of support channels without radar is less than a predetermined number, such as 2). If not, then normal WLAN operation can begin in step 612. If so, then the access point can return to the current channel, send beacons and listen to any additional stations requesting association in step 611. The procedure then returns to the Step 605

[0079] It should be noted that this process could be followed even if no station tries to associate after the start. In that case, after determining that there are no associated channels available in step 605, the access point could go directly to step 609 to alternatively perform short radar checks on a different channel and send beacons on the current operating channel until a full scan has been performed.

[0080] With reference again to step 607, if the newly associated station responds that it will perform radar measurement, then that the station proceeds to perform radar measurement in step 613. Note that if the station detects radar, the access point can delete that channel from the list of channels without radar and another unsupported candidate support channel from that list can be used in the next scan. In step 614, the access point can determine if another support channel is needed. If not, then normal operation can begin in step 612. If so, then the access point can determine if another newly associated station is available in step 605. The steps described in reference to Figure 6B can be repeated until A complete scan has been produced for each support channel.

[0081] Assuming that multiple associated stations are available and can perform radar measurement, scanning of the desired number of support channels in the list of channels without radar can be done quickly. For example, the access point may request an associated station to scan a channel and also request another station to scan another channel. Therefore, assuming that a full scan takes 60 s, if two stations capable of making measurements are associated with the access point immediately after the start of the operation of the access point in the initial channel, then the two channels can be found of desired support and added to the list of channels without radar in 60-120 seconds. Note that if two substantially parallel scans are performed and only one additional support channel is needed, then the first channel without radar will be designated as the support channel (in which the access point could immediately stop the second scan channel) .

[0082] Advantageously, by requesting the stations to perform the radar scans, the start of the WLAN network can start a faster number of minutes compared to the scanning access point itself 3 or more channels during startup. Note that a station is allowed to associate after it is found that only one channel is without radar, thus ensuring that communication between the access point and that station can begin immediately after completing its scan period, if applicable. Also,

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Because an associated station is not allowed to begin transmitting or receiving data until the station indicates that it will not measure, it has performed a full scan of a channel in the list of channels without radar or the desired number of channels is provided support, the associated station will not start any application that can be interrupted.

[0083] In an embodiment of step 613, the access point may repeatedly request a station to perform short scans (eg, 2-5 s) in a support channel (using the basic measurement request) until These cumulatively short scans meet the regulatory requirements for radar scanning (e.g., 60 seconds on each support channel). Therefore, during normal operation and assuming that the predetermined number of desired support channels has not been scanned, the access point may continue to request that each newly associated station perform a short scan on one of the candidate channels not yet scanned. in the list of channels without radar. It is important to note that through the help of any newly associated station to perform the radar scanning function, the start delay for any new station is limited to the required cumulative scanning time (e.g., 60 s). In one embodiment, the access point will not make this request if the station is re-associating with the access point, thus avoiding interrupting the reception of data that may be queued or otherwise interrupting any latency-sensitive application that It is currently running in the station.

Other embodiments

[0084] Although the illustrative embodiments have been described in detail in this document with reference to the attached figures, it should be understood that the invention is not limited to those precise embodiments. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. As such, many modifications and variations will be apparent to those skilled in this technique.

[0085] For example, the scan times associated with the access point and stations are illustrative only and not limiting. Other embodiments of the invention may include different scan times, that is, longer or shorter, depending on the device, system and / or political considerations. Specifically, although DFS has been described in detail in reference to European regulations, other countries may soon enact DFS rules. For example, some organizations, such as the International Telecommunication Union (which currently includes 144 member countries worldwide) are working on a global allocation to harmonize the 5 GHz spectrum. As part of that harmonization, many regional domains throughout The world can adopt rules that make DFS a requirement, although not all regional domains can specify the same implementation details.

[0086] In one embodiment of the invention, instead of simply facilitating radar scanning of a channel (see Figure 6B), station devices could be periodically requested to scan in search of radar in multiple channels. . For example, an access point could implement certain different defined scanning sequences and sequences. During these defined scanning periods, a number of capable stations could search for radar on multiple channels in parallel, thus significantly improving the performance of the access point

[0087] In another embodiment of the invention, instead of providing an update time for all support channels, each support channel may have its own update time.

[0088] In another embodiment shown in Figure 7, a startup process 700 may take into account if a regulatory domain exempts WLAN devices from detecting radars in the 5150-5250 MHz sub-band. If they are exempt, WLAN devices can use a quick start procedure that still meets the mandatory propagation requirements. In one embodiment, process 700, after being called by a main routine, can perform steps 101-103 (described in reference to Figure 1).

[0089] In step 701, a channel can be randomly selected from the list of channels without radar. Note that this random selection is necessary to maintain compliance with the propagation rules (that is, to prevent WLAN devices from choosing channels at 5150-5250 MHz for startup each time). If the selected channel is in the 5150-5250 MHz sub-band and the regulatory domain exempts scanning of channels in this sub-band, then a quick start routine can be performed in step 703. In this quick start routine , the procedure 700 can advantageously derive all start-up radar scanning (which normally lasts 60 seconds or more). Importantly, this derivation is acceptable because a regulatory domain that exempts scanning in the 5150-5250 MHz subband does not allow radar in this subband. Therefore, if the selected channel is in the 5150-5250 MHz sub-band, then the selected channel has a sufficiently high probability of not having radar and that the selected channel can be designated as the current operating channel.

[0090] In one embodiment, a support channel can also be randomly selected from the 5150-5250 MHz subband in step 703. Advantageously, because the support channel also resides in the 5150 subband -5250 MHz, you can also eliminate the need for radar scanning (which

normally it takes 60 seconds or more) to select the support channel. Note that the selection of the support channel of the 5150-5250 MHz sub-band (instead of a random selection among all available channels) does not contradict the propagation rules because the use of this support channel is not likely It happens in practice.

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[0091] In other words, assuming normal operation, the support channel will not be accessed because the radar would typically not be detected in the current channel. In this way, the selection of the support channel can be done in step 703 to take into account the rare event that the radar, although prohibited in this subband, is detected in the current channel. After selecting the support channel, normal operation in the

10 current channel can start in step 107.

[0092] If the current channel is not in the 5150-5250 MHz subband or if the regulatory domain does not exempt scanning in this subband, then a start radar scan can be performed on each channel in the list of channels without radar in step 704. Note that if the regulatory domain exempts scanning, you can

15 skip any scanning of channels in the list of channels without radar in the 5150-5250 MHz subband. Steps 105-108 can then be performed as described with reference to Figure 1. Accordingly, it is intended that the range of the invention is defined by the following claims and their equivalents.

Claims (1)

5 10 fifteen twenty 25 30 35 40 A method for filling in a list of support channels for a WAN wireless local area network device operable in a spectrum, the procedure comprising: perform a search for allowed channels within the allowed subbands (101) to create a list of candidate channels; weighting the candidate channels based on the actual and potential use of subbands allowed in the spectrum giving preference first (201, 202, 203) to channels towards the lower end of the spectrum and second (204-214) to channels that currently do not have no transmission of other basic service sets, BSS; Y Select channels from the allowed subbands according to the weighting to achieve the mandatory channel propagation requirements. The method according to claim 1, wherein the selection further comprises preferably selecting: channels of at least one of each of the different subbands (205, 209) on channels that currently have no transmission from other BSS (205, 206, 207) where they are less than all allowed subbands (206) . The method according to claim 1, wherein the preference for channels that currently do not have transmission from other Basic Service Sets, BSS, also encompasses channels that have a current WLAN transmission level below an acceptable level. A WLAN device comprising means for filling a list of support channels for a WLAN wireless local area network device operable in a spectrum and also comprising means for: perform a search for allowed channels within the allowed subbands (101) to create a list of candidate channels; weighting the candidate channels based on the actual and potential use of subbands allowed in the spectrum giving preference first (201, 202, 203) to channels towards the lower end of the spectrum and second (204-214) to channels that currently do not have no transmission of other basic service sets, BSS; Y Select channels from the allowed subbands according to the weighting to achieve the mandatory channel propagation requirements.