KR20110090746A - Method and device for adjusting transmission power in WLAN - Google Patents

Abstract

Provided are a method and an apparatus for adjusting transmission power in a WLAN. The station receives a setup frame from an access point (AP) that includes an extended channel power information field related to the available channel bandwidth. The station transmits and receives a data frame based on the extended channel power information field. The extended channel power information field includes at least one channel power limit field. The at least one channel power limit field includes a transmission channel bandwidth subfield including information about the channel bandwidth and a maximum transmission power subfield including information about a maximum transmission power used for the channel bandwidth. do.

Description

METHOD AND APPARATUS OF TRANSMISSION POWER CONTROL IN WIRELESS LOCAL AREA NETWORK}

The present invention relates to wireless communication, and more particularly, to a method and apparatus for adjusting frame transmission power of a station in a wireless local area network (WLAN).

Recently, with the development of information and communication technology, various wireless communication technologies have been developed. Among them, WLAN is based on radio frequency technology to provide home, business, or specific service area using portable terminals such as personal digital assistants (PDAs), laptop computers, and portable multimedia players (PMPs). Is a technology that allows users to access high-speed Internet wirelessly.

Communication in a WLAN according to the IEEE 802.11 standard is based on the assumption that the communication is performed in an area called a basic service set (BSS). The boundary is somewhat unclear because the BSS region may vary depending on the propagation characteristics of the wireless medium. These BSSs can be classified into two basic types: Independent BSS (IBSS) and Infrastructure BSS (Infrastructured BSS). The former forms a self-contained network as a distributed system. (BSS) that does not allow access to a distribution system (DS). The latter includes one or more Access Points (APs) and distributed systems, and generally includes all communication processes between stations. The BSS used by the AP.

Stations (STAs) and STAs that want to access a wireless network may use two scanning methods to find an accessible wireless network (BSS or IBSS), that is, a candidate AP.

The first is passive scanning, which uses a beacon frame transmitted from the AP (or STA). That is, an STA wishing to access a wireless network may receive a beacon frame periodically transmitted from an AP managing the corresponding BSS (or IBSS) and find an accessible BSS or IBSS.

The second is Active Scanning. An STA wishing to access a wireless network first transmits a probe request frame. The STA or AP that receives the probe request frame responds with a probe response frame.

There is a frequency band that can coexist with other types of wireless communication systems, one of which is TV White Space (WS). The TV WS is an idle frequency band left by the digitization of analog TV, which may correspond to the 512-698 MHz spectrum allocated for TV broadcasting. If a licensed device that is first authorized to use that frequency domain does not use that frequency domain, an unlicensed device may use that frequency domain instead.

If IEEE 802.11 is applied to the TV WS, there is an advantage that the coverage is significantly extended due to the spectral characteristics of the TV WS. In general, however, as coverage expands, the number of STAs in coverage significantly increases. As the number of STAs increases, a method of flexibly managing users, that is, scalability is a problem. Moreover, the coexistence problem also arises due to the coexistence of various wireless communication systems and various unlicensed devices. If the distributed coordination function (DCF) and enhanced distributed channel access (EDCA) protocols of the IEEE 802.11 are applied to the environment, the problem of scalability may be further exacerbated.

DCF is used in 802.11 and is a channel access mechanism based on carrier sense multiple access / collision avoidance (CSMA / CA). EDCA also corresponds to a competition-based medium access method among channel access models proposed by the Hybrid Coordination Function (HCF) defined by the extension of the general media access control protocol of IEEE 802.11. HCF is a protocol defined in IEEE 802.11e proposed to guarantee quality of service (QoS).

If you want to use the TV WS, the unlicensed equipment must utilize a geo-location database to obtain a channel available in the area. In addition, a scanning procedure is needed to solve the coexistence problem between unlicensed devices using TV WS.

In a WLAN that supports the TV WS band, the STA may use a channel that is not being used by the licensed equipment. However, if it is determined that the licensed equipment uses the adjacent channel adjacent to the channel currently being used, the STA needs to lower the transmission power in order to reduce interference to the licensed equipment. However, lowering the transmission power may cause a hidden node problem or reduce the transmission rate.

There is a need for a more efficient transmission power control method in a WLAN supporting the TV WS band.

The present invention provides a method and apparatus for limiting transmission power for each channel bandwidth in a WLAN supporting a TV WS band.

The present invention provides a scanning method and apparatus for controlling transmission power for each channel bandwidth in a WLAN supporting a TV WS band.

In one aspect, a method of adjusting transmission power in a WLAN is provided. The method includes receiving a setup frame from an access point (AP) including an extended channel power information field related to an available channel bandwidth, and transmitting and receiving a data frame based on the extended channel power information field. . The extended channel power information field includes at least one channel power limit field. The at least one channel power limit field includes a transmission channel bandwidth subfield including information about the channel bandwidth and a maximum transmission power subfield including information about a maximum transmission power used for the channel bandwidth.

The channel bandwidth may be a specific bandwidth of the TV white space frequency band.

The transmitting of the data frame may include transmitting a data frame using a specific transmission power within the range of the maximum transmission power indicated by the maximum transmission power in the channel bandwidth indicated by the channel bandwidth subfield.

 The setup frame may be a beacon frame transmitted periodically from the AP.

The setup frame may be a probe response frame received in response to a probe request frame.

The extended channel power information field may further include a device type field indicating a type of a station allowed to use the channel bandwidth indicated by the transport channel bandwidth field.

In another aspect, a wireless device for adjusting transmission power in a WLAN is provided. The wireless device receives a setup frame from an access point (AP) including an RF unit for transmitting and receiving a frame and an extended channel power information field associated with an available channel bandwidth functionally coupled with the RF unit, and And a processor configured to transmit a data frame based on the extended channel power information field. The extended channel power information field includes at least one channel power limit field. The at least one channel power limit field includes a transmission channel bandwidth subfield including information about the channel bandwidth and a maximum transmission power subfield including information about a maximum transmission power used for the channel bandwidth.

The channel bandwidth may be a specific bandwidth of the TV white space frequency band.

The setup frame may be a beacon frame transmitted periodically from the AP.

The setup frame may be a probe response frame transmitted in response to a probe request frame.

In another aspect, a method of controlling transmission power of an access point (AP) in a WLAN is provided. The method obtains from a database (DB) including information about an empty channel that is not used by a licensed user in a frequency band, and includes a plurality of channel bandwidths available in the empty channel and the plurality of channel bandwidths. Determining a plurality of maximum transmit powers for the plurality of transmit powers, and transmitting a setup frame including an extended channel power information field comprising information about the plurality of channel bandwidths and the plurality of maximum transmit powers.

The maximum transmission power of the channel channel width adjacent to the channel used by the authorized user among the plurality of channel bandwidths may be smaller than the maximum transmission power of the channel channel width not adjacent to the channel used by the authorized user.

The plurality of channel bandwidths may be a specific bandwidth among TV WS bands.

The setup frame may be a beacon frame transmitted periodically by the AP.

The setup frame may be a probe response frame transmitted in response to a probe request frame.

The extended channel power information field may further include a device type field indicating a type of station allowed to use the channel bandwidth indicated by the transport channel bandwidth field.

Stations using TV WS can mitigate interference with licensed equipment using adjacent channels. In addition, it is possible to reduce the occurrence of hidden node problems, and to secure a higher transmission rate.

1 is a diagram illustrating a configuration of a wireless LAN system to which an embodiment of the present invention can be applied.
2 is a flowchart illustrating a method of adjusting a transmission power according to an embodiment of the present invention.
3 is a diagram illustrating an example of channel usage in the TV WS band.
4 is a diagram illustrating an example of allocation of a transport channel according to an embodiment of the present invention.
5 is a flowchart illustrating a transmission power limiting method according to an embodiment of the present invention.
6 is a block diagram illustrating a format of a beacon frame according to an embodiment of the present invention.
7 illustrates a channel power limit field according to another embodiment of the present invention.
8 is a flowchart illustrating a transmission power limiting method according to another embodiment of the present invention.
9 is a block diagram illustrating a format of a probe response frame according to an embodiment of the present invention.
10 is a block diagram illustrating another extended power limit information field according to an embodiment of the present invention.
11 is a block diagram illustrating an example of an extended power limit information field according to an embodiment of the present invention.
12 is a block diagram illustrating a wireless device in which an embodiment of the present invention is implemented.

Hereinafter, a frame transmission method and apparatus related to a wireless LAN system using a TV white space (WS) band will be described as an example to easily describe the present invention. This would be applicable to any wireless communication system that may occur.

1 is a diagram illustrating a configuration of a wireless local area network (WLAN) system to which an embodiment of the present invention can be applied.

Referring to FIG. 1, a WLAN system includes one or more basic service sets (BSSs). The BSS is a set of stations (STAs) that can successfully communicate with each other by synchronizing, and is not a concept indicating a specific area.

The infrastructure BSS (BSS1, BSS2) is one or more non-AP stations (Non-AP STA1, Non-AP STA3, Non-AP STA4), an access point (AP) that provides a distribution service (AP STA1). , AP STA2), and a Distribution System (DS) for connecting a plurality of APs (AP STA1, AP STA2). In the infrastructure BSS, the AP manages non-AP STAs of the BSS.

On the other hand, Independent BSS (IBSS) is a BSS that operates in Ad-Hoc mode. Since IBSS does not include an AP, there is no centralized management entity. That is, in the IBSS, non-AP STAs are managed in a distributed manner. In the IBSS, all STAs may be mobile STAs, and access to the DS is not allowed to form a self-contained network.

A STA is any functional medium that includes a medium access control (MAC) compliant with the IEEE of the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard and a physical layer interface to a wireless medium. It includes both AP and Non-AP Stations.

The non-AP STA is an STA, not an AP, and simply refers to the non-AP STA. The non-AP STA may be a mobile terminal, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), or a mobile subscriber unit (Mobile Subscriber Unit). May also be called other names

An AP is a functional entity that provides access to a DS via a wireless medium for an associated STA to that AP. In an infrastructure BSS including an AP, communication between non-AP STAs is performed via an AP. However, when a direct link is established, direct communication between non-AP STAs is possible. The AP may be called a central controller, a base station (BS), a node-B, a base transceiver system (BTS), or a site controller.

The plurality of infrastructure BSSs may be interconnected through a distribution system (DS). A plurality of BSSs connected through a DS is called an extended service set (ESS). Stations included in an ESS may communicate with each other, and a non-AP station may move from one BSS to another BSS while communicating seamlessly within the same ESS.

DS is a mechanism for one AP to communicate with another AP, which means that an AP transmits a frame for stations that are associated with a BSS it manages, or a frame is sent when one station moves to another BSS. Frames can be delivered with external networks, such as wired networks. This DS does not necessarily need to be a network, and there is no limitation on its form as long as it can provide certain distributed services regulated in IEEE 802.11. For example, the DS may be a wireless network such as a mesh network or a physical structure that connects APs with each other.

The frequency band used in the WLAN system may be shared with other WLAN systems of the same kind or may be used together with other heterogeneous communication systems. If the existing transmission power is used while the frequency band is shared with other communication systems, interference occurs during transmission and / or reception of frames, thereby making it difficult to perform normal communication. Accordingly, the STA needs to transmit the frame by adjusting the transmission power according to the environment of the frequency band. To this end, the AP may transmit information on the available channel and information on the maximum transmit power available when using the channel to the STA based on the environment of the frequency band. Hereinafter, with reference to the drawings will be described in more detail.

2 is a flowchart illustrating a method of adjusting a transmission power according to an embodiment of the present invention.

Referring to FIG. 2, the AP transmits channel information and maximum transmission power information to the STA (S210). The STA determines a transmission channel and a transmission power to use based on the information received from the AP and transmits a data frame to the AP (S220 and S230).

The AP transmits channel information and information on the maximum transmission power to the STA (S210). The channel information indicates a channel usable as a channel used by the STA to transmit a frame in the WLAN system. It can indicate a number assigned to a channel or a frequency band used by the channel. The maximum transmit power information indicates the maximum transmit power that can be used for frame transmission when the STA indicates the channel indicated by the channel information.

The channel information and the maximum transmit power may change continuously according to the frequency band environment. Therefore, the AP may periodically update the corresponding information and transmit the updated information back to the STA. The AP may directly check whether another WLAN system or a heterogeneous communication system is using a frequency band to update channel information and maximum transmission power information. This may be done by sensing a signal transmitted by another wireless device. In addition, a database (DB) in which channel information or maximum transmission power information is periodically updated may be accessed to obtain information about a usage state.

The AP may transmit a setup frame, which is an action frame including channel information and maximum transmission power information, to the STA. In addition, the channel information and the maximum transmission power information may be included in the probe response frame transmitted by the AP to the STA in response to the probe request frame in the active scanning procedure.

The STA needs to receive periodically updated channel information and maximum transmit power information. Accordingly, channel information and maximum transmission power information transmitted by the AP to the STA may be included in a beacon frame transmitted periodically by the AP to the STA in the WLAN system.

Upon receiving the channel information and the maximum transmission power information, the STA selects a specific channel as a transmission channel and transmits a data frame within a numerical range indicated by the maximum transmission power information (S220 and S230).

Meanwhile, the master device among the wireless devices forming the BSS may transmit the channel information to the wireless device subscribed to the BSS based on a database (DB) regarding the channel state and the maximum transmit power allowed for the corresponding channel. In this case, the type of the subscribed wireless device may be one or more. In addition, the master device may be an AP, and the subscribed wireless device may be an AP and / or an STA. Hereinafter, a wireless device receiving channel information will be described using an STA as an example.

Depending on the type of STA, the usable channel and the maximum allowable transmit power value may be different. Therefore, when the AP provides channel information and maximum transmission power information to the STA to be served, the AP may signal the type of the STA to be served by the AP together. The type information of the STA may be included in the beacon frame, the probe response frame, or the setup frame which is a separate action frame together with the channel information and the maximum transmission power information and transmitted to the STA.

The above-described method of adjusting the transmission power may be applied to a WLAN system using a TV white space (WS) band, which is an idle frequency band. Hereinafter, a system using a TV WS band will be described in detail to describe an embodiment of the present invention. However, the scope of the present invention is not limited to this.

TV WS refers to the idle frequency band left by the digitization of analog TV in the United States, for example, the 512 to 698 MHz band. However, this is merely an example, and the TV WS may be referred to as a licensed band that can be preferentially used by a licensed user. An authorized user refers to a user who is authorized to use an authorized band and may also be called other names such as a licensed device, a primary user, an incumbent user, and the like.

A STA that supports the TV WS band and is not an authorized user is called a WS STA. The AP that supports the TV WS band and is not an authorized user is called a WS AP.

The WS AP or the WS STA operating in the TV WS should provide a protection function for the authorized user since the authorized user has priority in using the TV WS band. For example, if an authorized user such as a microphone is already using the channel in a specific channel of the TV WS band, the WS AP or the WS STA cannot use the channel to protect the authorized user. In addition, when the authorized user starts using the currently used transport channel, the use of the corresponding transport channel should be stopped.

Accordingly, the WS AP and the WS STA should be preceded by a procedure for determining whether the channel in the TV WS is available, that is, whether there is an authorized user in the channel. Knowing whether there is an authorized user on the channel is called spectrum sensing. As the spectrum sensing mechanism, energy detection, signal detection, and the like are used. If the received signal strength is greater than or equal to a predetermined value, it may be determined that the authorized user is in use, or if the DTV preamble is detected, it may be determined that the main authorized user is in use. The AP may perform sensing for each channel of the TV WS band, or, if necessary, sense the specific channel to the WS STA and report the result.

If the WS AP can access a database (DB) having information related to the state of the channel of the TV WS band, the WS AP can acquire channel information without performing spectrum sensing.

The AP detects the situation of each channel through the channel information stored in the DB or the spectrum sensing result, and moves to an available channel when the channel used by the authorized user is no longer available. In some cases, when the channel being used is no longer used, it is also possible to pre-set the reserved channel to be used and notify the STA.

On the other hand, when a user authorized to a channel adjacent to a specific channel that can be used by the WS STA is in use, interference may occur when the WS STA uses the channel. Therefore, there is a need for a method for avoiding or minimizing interference, and there is a method of limiting transmission power for a channel to be used by a WS STA.

3 is a diagram illustrating an example of channel usage in the TV WS band.

In general, TV band devices such as WS AP and WS STA in TV WS may use about 30 channels based on a bandwidth of 6 MHz. In order to use these channels, it must be assumed that no authorized user exists for the particular channel to be used.

Let the bandwidths of the channels 32a and 32b used by the authorized user be 6 MHz, respectively. According to the IEEE 802.11a standard, since the STA supports at least one of 5 MHz, 10 MHz, and 20 MHz, the basic channel bandwidth of the WS AP and the WS STA is 5 MHz. Accordingly, the WS AP and the WS STA can support a channel bandwidth of 10 MHz or 20 MHz with 5 MHz as the default bandwidth, depending on how many channels are continuously empty.

Here, the transmission channel refers to a physical radio resource used by a TV band device such as a WS AP and a WS STA to transmit a radio signal such as a frame in a specific frequency band, which is used by an authorized user in the TV WS band and has a specific bandwidth. This is different from the meaning of a channel that is divided by convention. Hereinafter, the WS AP and the WS STA are used for transmitting and receiving a frame, and a channel having a specific bandwidth is called a transmission channel, and the WS channel refers to a channel having a 6 MHz bandwidth divided by protocol so as to have a constant bandwidth in the TV WS band. .

In the TV WS, the center band 31 may be used by the WS STA, the adjacent channels 32a and 32b on both sides thereof are in use by the authorized user, and the center band 31 is called the bandwidth of the transmission channel. lets do it. If the authorized user's signal is detected in the WS channels 32a and 32b adjacent to the transmission channel 31 being used by the WS STA, the transmission power of the transmission channel 31 should be reduced. This is to mitigate interference with authorized users.

For example, although the maximum transmit power of the WS STA is 100 mW, the maximum transmit power may be limited to 40 to 50 mW when the authorized user is using the adjacent WS channels 32a and 32b. Because of this transmit power constraint, using a wide bandwidth transmission channel is not directly related to obtaining a higher throughput. In some cases it may be more efficient to transmit at higher transmission powers instead of using a relatively narrow bandwidth transmission channel.

If three WS channels with 6 MHz bandwidth in the TV WS band are empty, then a band of 18 MHz is available. The WS STA can transmit and receive frames using a transmission channel having a 10 MHz bandwidth in the band. However, the fact that three consecutive WS channels are empty means that an authorized user is using adjacent WS channels located at both sides. Therefore, when transmitting a frame using the transmission channel having the 10MHz bandwidth, the transmission power should be limited to 40 to 50mW in order to protect the authorized user of the adjacent WS channel.

There may be a high gain environment when using low transmit power in a wideband, but there may be a high gain environment when using high transmit power in a narrowband. In addition, when the transmission power is lowered, coverage may be reduced and a hidden node problem may occur.

In the following, embodiments relating to transmission power limitation for protection of an authorized user are proposed. According to an embodiment of the present invention described below, the bandwidth of the transmission channel used by the WS STA and the WS AP is shown as 5MHz, 10MHz, 20MHz, the normal maximum transmission power is shown as 100mW, the limited maximum transmission power is 40mW This is merely an example.

4 is a diagram illustrating an example of allocation of a transport channel according to an embodiment of the present invention.

Referring to FIG. 4, it is assumed that there are seven channels CH1 to CH7 in the TV WS band, the central WS channels CH2 to CH6 are empty channels, and an authorized user uses CH1 and CH7.

Since five channels are empty WS channels, the empty frequency band is 30 MHz. The bandwidth that the WS STA can use based on the center frequency f _c of the empty frequency band is at least one of 5 MHz, 10 MHz, and 20 MHz.

If the WS STA uses a transmission channel having a 5 MHz bandwidth, since there is no adjacent channel used by an authorized user, a maximum transmission power of 100 mW may be used. Similarly, if the WS STA uses a transmission channel of 10 MHz bandwidth, since there is no adjacent channel used by an authorized user, a maximum transmission power of 100 mW may be used.

However, if the WS STA uses a transmission channel having a 20 MHz bandwidth, since there is an adjacent WS channel used by an authorized user, the maximum transmission power may be limited to 40 mW.

5 is a flowchart illustrating a transmission power limiting method according to an embodiment of the present invention. This is a passive scanning procedure of the WS STA 510. The WS STA 510 performs passive scanning to access the infrastructure BSS.

The WS STA 510 performs channel sensing in the TV WS band (S510). The WS STA 510 detects an empty channel not used by the authorized user. Unlicensed users who do not have a priority on the use of the TV WS band, such as the WS STA and / or the WS AP, will periodically check for the presence of an authorized user with priority through channel sensing and, if confirmed, immediately Stop using the channel.

The WS STA 510 receives a beacon frame including extended power constraint information from the WS AP 520 (S520). The beacon frame includes network information of an infrastructure basic service set (BSS) configured by the WS AP 520 and is a management frame that is periodically transmitted. Therefore, even if the WS STA 510 transmits a frame using a specific transmission power to a transmission channel currently being used, upon receiving a beacon frame, the WS STA 510 communicates with the WS AP according to the network information included in the beacon frame based on this. Can be performed.

The beacon frame including extended power limit information may be referred to as a setup frame for setting transmission power for each bandwidth.

The WS STA 510 determines a transmission channel and a transmission power to be used based on the extended power limit information element (S530). The WS STA 510 transmits a data frame to the WS AP 520 (S540).

The beacon frame contains extended power limit information. The extended power limit information indicates a transmission power limit for each channel bandwidth. Accordingly, the WS STA 510 may obtain the information about the WS channels and power limitation information thereof by receiving the beacon frame, and may determine the transmission power of the transmission channel for transmitting the frame based on the information.

6 is a block diagram illustrating a format of a beacon frame according to an embodiment of the present invention.

Referring to FIG. 6, the beacon frame includes a MAC header (Media Access Control header) 50, a frame body 60, and a frame check sequence 70.

The frame body 60 includes a timestamp field 61, a beacon interval field 62, a capability field 63, and an extended power limit information field 600.

The time stamp information field 61 is information provided for time synchronization. The beacon interval field 62 is information indicating a temporal interval at which the beacon frame is transmitted. The capability field 63 is information indicating a communication performance condition required by the WS STA in the BSS managed by the WS AP transmitting the beacon frame.

The extended power limit information field 600 is information indicating a limit of a transmit power used by a WS STA connected to a BSS to transmit a frame. The extended power restriction information field 600 may include an element ID field 610, a length field 620, and one or more channel power constraint fields 631. Here, the number of channel power limit fields may include two, or one or more channel power limit fields.

The element ID field 610 indicates that the corresponding information element is extended power limit information. The length field 620 indicates the length of the extended power limit information field 600.

The channel power limit field 631 includes a transmission channel bandwidth subfield 631a indicating a channel bandwidth and a maximum transmission power subfield 631b indicating a maximum transmission power for the channel bandwidth.

The transport channel bandwidth subfield 631a indicates a channel bandwidth that can be used by the WS STA. The maximum transmit power subfield 631b indicates the maximum allowable transmit power in the channel bandwidth indicated by the transmit channel bandwidth subfield 631a.

In the example of FIG. 4, a transmission channel having a 5 MHz bandwidth has a maximum transmission power of 100 mW, a transmission channel having a 10 MHz bandwidth has a maximum transmission power of 100 mW, and a transmission channel having a 20 MHz bandwidth has a maximum transmission power of 40 mW. You can do that. Accordingly, the extended power limit information element 600 includes three channel power limit fields.

The WS STA 510 may use the extended power limit information to determine the transmit power within a range of the maximum transmit power limit that is allowable in the bandwidth of the transmit channel.

7 illustrates a channel power limit field according to another embodiment of the present invention.

The channel power limit field 731 includes a WS channel number subfield 731a and a maximum transmit power subfield 731b. The channel power limit field 731 designates the maximum transmit power for each channel used by the WA AP.

The WS channel number subfield 731a indicates the WS channel number assigned to the TV WS band. The maximum transmit power subfield 731b indicates the maximum transmit power allowed for the WS channel indicated by the WS channel number subfield 731a.

In the example of FIG. 4, the WS channel number subfield 731a may indicate any one of CH2 through CH6. If the WS channel number subfield 731a indicates any one of CH3 to CH5, the maximum transmission power subfield 731b may indicate 100mW. If the WS channel number subfield 731a indicates either CH2 or CH6, the maximum transmit power subfield 731b may indicate 40mW.

The WS STA 510 can know the maximum transmit power for the available WS channels using the extended power limit information. The WS STA 510 may determine whether to use 40mW of maximum transmission power in a bandwidth of 20MHz or 100mW of maximum transmission power in a bandwidth of 10MHz.

8 is a flowchart illustrating a transmission power limiting method according to another embodiment of the present invention.

The WS STA 810 performs channel sensing (S810). The WS STA 810 transmits a probe request frame to the WS AP 820 to initiate active scanning (S820).

The WS STA 810 receives a probe response frame including extended power limitation information from the WS AP 820 in response to the probe request frame (S830).

The probe response frame including extended power limit information may be referred to as a setup frame for setting transmission power for each bandwidth.

The WS STA 810 determines the bandwidth to be used and the transmission power based on the extended power limitation information (S840). The WS STA 810 transmits a data frame to the WS AP 820 using the determined bandwidth and transmission power (S850).

9 is a block diagram illustrating a format of a probe response frame according to an embodiment of the present invention.

Referring to FIG. 9, the probe response frame includes a MAC header 80, a frame body 90, and an FCS 100.

The frame body 90 includes a timestamp field 91, a beacon interval field 92, a capability field 93, and an extended power limit information field 600. These fields are the same as the timestamp field 61, beacon interval field 62, capability field 63 and extended power limit information field 600 of FIG. Omit.

Meanwhile, the available channel and the allowable maximum power value may differ according to the device type of the WS STA. For example, a WS STA corresponding to a fixed device type cannot use a WS channel adjacent to a WS channel being used by an authorized user. On the other hand, a WS STA corresponding to a personal / portable device type may use the adjacent WS channel under a condition of limiting a maximum transmission power within a specific range, for example, from 100 mW to 40 mW. .

Therefore, when the WS AP provides extended power limitation information to the WS STA to which it wants to service, the WS AP may signal the type of the WS STA to which it serves. The method of signaling the device type together may be performed as in the following embodiments.

10 is a block diagram illustrating another extended power limit information field according to an embodiment of the present invention.

Referring to FIG. 10, the extended power restriction information field 1000 may include an element ID field 1010, a length field 1020, a device type field 1030, and one or more channel power constraints. ) Fields 1040. The element ID field 1010 and the length field 1020 are the same as the fields 610, 620 shown in FIG. 6.

The device type field 1030 indicates the type of WS STA that the WS AP intends to service. If two types of WS STAs exist, a fixed device type and a personal / portable device, the type of the corresponding WS STA may be distinguished by a bit value of the device type field 1030. The device type field 1030 may indicate the type of each WS STA and may indicate a set of WS STA specific type types. The size of the device type field 1010 may vary according to the type of the WS STA.

The channel power limit field 1041 includes a WS channel number subfield 1041a and a maximum transmit power subfield 1041b. Since the channel power limit field 1041 is the same as the channel power limit field 731 according to the above-described embodiment, a detailed description thereof will be omitted.

The extended power limit information field 1000 may be included in the beacon frame, the probe response frame, and transmitted, or may be included in the original setup frame and transmitted.

The WS STA obtains the extended power limit information field 1000 included in the frame, and checks the type field 1010 to know what type of device the information included is for. In addition, the channel power limit field 1021 may be checked to determine the maximum transmit power allowed for the corresponding channel.

11 is a block diagram illustrating an example of an extended power limit information field according to an embodiment of the present invention. Here, assume that WS channel 1 and WS channel 3 are adjacent to the WS channel used by the authorized user and the WS channel is not. In this case, the fixed type WS STA may use only WS channel 2 and the personal / portable type WS STA may use WS channels 1 to 3.

As shown in FIG. 11, the channel power limit field for the WS channel that can be used by each type of WS STA may be included in the extended power limit information field.

Referring to the sub-view (a), when the device type field 1111 indicates a WS STA of a fixed device type, the extended power limit information field 1110 includes a channel power limit field 1112 for WS channel 2. If the device type field 1121 indicates a WS STA of the personal / portable device type, the extended power limit information field 1120 includes channel power limit fields 1122, 1123, 1124 for WS channels 1-3.

Unlike the sub-view (a), as shown in the sub-view (b) of FIG. 11, the channel power limit field for the WS channel commonly used by each type of WS STA is included in one extended power limit information field. The channel power limit field for the WS channel that can be used only by the type of WS STA may be included in different extended power limit information fields.

Referring to FIG. 2B, if the device type field 1131 indicates a WS STA of a fixed device type and a personal / portable device type, the extended power limit information field 1130 is a channel power limit field for WS channel 2. 1132. If the device type field 1141 indicates a WS STA of the personal / portable device type, the extended power limit information field 1140 includes channel power limit fields 1142 and 1143 for WS channels 1 and 3.

12 is a block diagram illustrating a wireless device in which an embodiment of the present invention is implemented. The wireless device 1200 may be part of a WS STA or a WS AP. The wireless device may support TV WS.

The wireless device 1200 may include a processor 1210 and a memory 1220. The processor 1210 and the memory 1220 may be functionally connected.

The memory 1220 stores a frame including extended channel power information. Upon receiving the beacon frame or the probe response frame including the power limit information, the extended channel power information may be stored in the memory 1220.

The processor 1210 implements the functionality of the WS STA or the WS AP in the above embodiments. The processor 1210 senses an empty channel not used by an authorized user in the frequency band. The processor 1210 determines the transport channel bandwidth to use among the available channel bandwidths indicated in the setup frame within the empty channel. The processor 1210 determines the maximum transmit power for the transmit channel bandwidth from the extended channel power information.

The frequency band sensed by the processor 1210 may be a TV white space (WS) band.

The setup frame may be a probe response frame received in response to a beacon frame or a probe request frame periodically received from the AP.

The processor 1210 may include an application-specific integrated circuit (ASIC), another chipset, a logic circuit, and / or a data processing device. The memory 1220 may include a read only memory (ROM), a random access memory (RAM), a flash memory, a memory card, a storage medium, and / or another storage device. When the embodiment is implemented in software, the above-described techniques may be implemented with modules (processes, functions, and so on) that perform the functions described above.

The memory 1220 may be inside or outside the processor 1210 and may be connected to the processor 1210 by various well-known means.

In the above-described embodiment of the present invention, the frequency band and the bandwidth of the channel have been described using the TV WS band as an example. However, the present invention is not limited thereto and may be applied to all frequency bands requiring a mechanism for limiting transmission power according to a communication performance environment. In addition, the specific numerical values of the maximum transmission power before the limit and the maximum transmission power after the limit are exemplary only, and may include all values that may have characteristics in which the transmission power is limited.

In addition, although the types of frames received by the station are limited to beacon frames and probe response frames, this is merely an example, and may be applied to a frame including power limitation information and transmitted to set a network operating environment of the station.

The above-described embodiments include examples of various aspects. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

Claims (16)

In the transmission power control method in a wireless LAN,
Receive a setup frame from an access point (AP) that includes an extended channel power information field related to available channel bandwidth,
Transmitting and receiving a data frame based on the extended channel power information field, wherein the extended channel power information field includes at least one channel power limit field;
The at least one channel power limit field includes a transport channel bandwidth subfield including information about the channel bandwidth; And,
And a maximum transmit power subfield including information about the maximum transmit power used for the channel bandwidth. The method of claim 1, wherein transmitting the data frame,
The channel bandwidth indicated by the channel bandwidth subfield,
A transmission power adjustment method of transmitting a data frame using a specific transmission power within the range of the maximum transmission power indicated by the maximum transmission power. The method of claim 1, wherein the setup frame is a beacon frame transmitted periodically from the AP. The method of claim 1, wherein the setup frame is a probe response frame received in response to a probe request frame. The method of claim 1, wherein the extended channel power information field,
And a device type field indicating the type of station allowed to use the channel bandwidth indicated by the transport channel bandwidth field. The method of claim 1, wherein the channel bandwidth is a specific bandwidth of a TV white space (WS) frequency band. In the wireless device for adjusting the transmission power in the WLAN,
RF unit for transmitting and receiving a frame; And,
Receive a setup frame from an access point (AP) that includes an extended channel power information field associated with the available channel bandwidth functionally coupled to the RF unit, and receives a data frame based on the extended channel power information field. A processor configured to transmit, wherein the extended channel power information field includes at least one channel power limit field,
The at least one channel power limit field includes a transport channel bandwidth subfield including information about the channel bandwidth; And,
And a maximum transmit power subfield containing information about the maximum transmit power used for the channel bandwidth. 8. The wireless device of claim 7, wherein the setup frame is a beacon frame transmitted periodically from the AP. 8. The wireless device of claim 7, wherein the setup frame is a probe response frame sent in response to a probe request frame. The wireless device of claim 7, wherein the channel bandwidth is a specific bandwidth of a TV white space frequency band. In the transmission power control method of the access point (AP) in a WLAN,
Obtained from a database (DB) containing information about empty channels not used by the authorized user in the frequency band,
Determine a plurality of channel bandwidths available in the free channel and a plurality of maximum transmit powers for the plurality of channel bandwidths, and
And transmitting a setup frame including an extended channel power information field including information about the plurality of channel bandwidths and the plurality of maximum transmission powers. 12. The maximum transmit power of the channel channel width according to claim 11, wherein the maximum transmit power of the channel channel width adjacent to the channel used by the authorized user among the plurality of channel bandwidths is not adjacent to the channel used by the authorized user. Smaller transmission power adjustment method. 12. The method of claim 11, wherein the setup frame is a beacon frame transmitted periodically by the AP. 12. The method of claim 11, wherein the setup frame is a probe response frame transmitted in response to a probe request frame. The method of claim 11, wherein the extended channel power information field,
And a device type field indicating a type of station allowed to use the channel bandwidth indicated by the transport channel bandwidth field. 12. The method of claim 11, wherein the plurality of channel bandwidths is a specific one of the TV WS bands.

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