WO2014065488A1

WO2014065488A1 - Method for transceiving information of traffic indication map

Info

Publication number: WO2014065488A1
Application number: PCT/KR2013/006106
Authority: WO
Inventors: Wei Ping Sun; Yang Seok Jeong; Weon Yong Joo; Sung Hyun Choi; Jung Su Lee; Mun Hwan Choi; Hyun Pyo Kim
Original assignee: KT Corp; SNU R&DB Foundation
Current assignee: KT Corp; SNU R&DB Foundation
Priority date: 2012-10-22
Filing date: 2013-07-09
Publication date: 2014-05-01
Anticipated expiration: 2015-04-22

Abstract

The method includes generating a delivery traffic indication map (DTIM) beacon including a segmentation information element, and dividing the TIM information of the TIM transmission target page into the segments with variable sizes using the DTIM beacon and beacons within a DTIM interval corresponding to the DTIM beacon, and transmitting the divided segments. Accordingly, downlink traffic stored in a buffer of an AP can be appropriately distributed in a predetermined range, and therefore power consumption required for terminals operated in a PS mode to receive downlink frames stored in the buffer of the AP can be reduced. In addition, only a single beacon frame can be transmitted together with a single TIM segment, and therefore a size of the beacon frame can be appropriately adjusted.

Description

METHOD FOR TRANSCEIVING INFORMATION OF TRAFFIC INDICATION MAP

The present invention relates to wireless communication, and more particularly, to a method of transceiving traffic indication map (TIM) information that can reduce power consumption of a terminal and adjust a length of a beacon frame.

With the development of information communication technologies, a variety of wireless communication technologies have been developed. Among these technologies, wireless LAN technology (or Wi-Fi, HIPERLAN, or system such as IEEE 802.11, hereinafter referred to as “wireless LAN”) is a technology that wirelessly connects a portable terminal such as personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), or the like, to the Internet in homes, businesses or other specific service providing areas, based on wireless transmission technologies.

Wireless LAN technology is developed according to the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards.

IEEE 802.11a provides a transmission speed of 54 Mbps using unlicensed bands at 5 GHz. IEEE 802.11b provides a transmission speed of 11 Mbps by applying a direct sequence spread spectrum (DSSS) method at 2.4 GHz. IEEE 802.11g provides a transmission speed of 54 Mbps by applying orthogonal frequency division multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmission speed of 300 Mbps with four spatial streams by applying multiple input multiple output-OFDM (MIMO-OFDM). IEEE 802.11n supports channel bandwidth up to 40 MHz, and in this case, provides a transmission speed of 600 Mbps.

Meanwhile, wireless LAN terminals consume a large amount of power when transceiving data. Also, even in an idle listening state for transceiving data, the terminal may consume a significantly large amount of power.

In order to save power in these wireless terminals, it is advantageous for power to be consumed only when the wireless terminals transmit and receive data.

For this, in the IEEE 802.11 wireless LAN standards, two power states of a terminal are defined. One is called awake state, in which the terminal is awake and capable of transceiving data, and the other one is called doze state, in which the wireless device turns off radio components that the power consumption is minimized.

As two power management methods in accordance with a conversion method of the awake state and the doze state, an active mode that is always operated in the awake state, and a power saving mode (hereinafter, referred to as “PS mode”) in which the awake state and the doze state are periodically repeated may be used.

In addition, a terminal that is set as the PS mode may be periodically awake, and check a beacon frame transmitted from an access point to determine whether a frame to be transmitted to the terminal is stored by the access point.

Here, a traffic indication map (hereinafter, referred to as “TIM”) information element (hereinafter, referred to as “IE”) including a list for a destination terminal of a frame to be transmitted is included in the beacon frame, and a terminal that is specified in the list transmits a power-saving poll (hereinafter, referred to as “PS Poll”) message to the access point to request transmission of the frame to the terminal. A terminal that is not specified in the list may return to the doze state again. This operation is made possible only when the terminal is aware of a transmission cycle of the beacon frame transmitted by the access point, and therefore terminals should accomplish time synchronization with the access point.

Beacon interval that is a cycle in which the beacon frame is transmitted may be contained in the beacon frame, and the terminals that receive the beacon interval may estimate a target beacon transmission time (TBTT), which is a time when the beacon frame is transmitted.

The access point may allocate association ID (hereinafter, referred to as “AID”) for each terminal so as to support the above-described PS mode, and terminals may determine presence or absence of a frame to be transmitted to the terminal among frames stored in a buffer of the access point, using a partial virtual bitmap of TIM IE included in the beacon frame.

An AID allocation range in an existing wireless LAN may be 1 to 2007. This is because the AID range that can be represented with the 2008 bits of the partial virtual bitmap is 0 to 2007, and AID 0 is used for representing a group address frame, and therefore AID values that can be allocated to the terminal are 1 to 2007.

That is, a total number of the terminals that can be supported by a single access point is 2007. However, when considering the increasing number of wireless LAN terminals and a more diversified wireless LAN environment, a method that can support connection of a larger number of terminals compared to an existing method is required.

As a representative example, IEEE 802.11ah may be given.

The IEEE 802.11ah standard, which is currently under development, may refer to a wireless LAN that uses a frequency band of 1 GHz or less, and the main application field is a smart grid using Wi-Fi, a sensor network, and the like. In the standardization that is currently being conducted, to enable communication between sensor terminals, new wireless LAN-based technologies are actively being discussed.

Among these, one thing that is cited as a major issue is that a much larger number of terminals should be supported in the smart grid or the sensor network when compared to an existing wireless LAN, and therefore it is necessary to support a function in which several thousands of terminals are connected to a single AP.

However, when several thousands of terminals operated in the PS mode are displayed using a single TIM IE, a length of the beacon frame may be increased beyond tolerance due to the enormous size of the partial virtual bitmap.

In addition, since the number of frames that can be transmitted in a single beacon interval is limited, it is not necessary for the frames to be transmitted together with information about whether a frame is stored in a buffer of an AP of all terminals for each beacon frame.

In addition, when the frame together with frame information stored in the buffer of the AP of all terminals are transmitted to a single TIM IE, due to limited wireless resources, only some terminals may receive the frame stored in the buffer of the AP while the remaining terminals remain awake to receive the frame stored in the buffer of the AP during the beacon interval, which inevitably leads to energy loss.

The present invention is directed to providing a method of transmitting traffic indication map (TIM) information of an access point, which can reduce power consumption required for receiving a frame by a terminal and can adjust a length of a beacon frame.

The present invention is also directed to providing a method of receiving TIM information of a terminal, which can reduce power consumption required for receiving a frame by the terminal and can adjust the length of the beacon frame.

One aspect of the present invention provides a method of transmitting traffic indication map (TIM) information of an access point, in which a TIM transmission target page is divided into segments having variable sizes in a hierarchical TIM structure including a page, a block, and a sub-block, and TIM information of the TIM transmission target page is transmitted, the method including: (a) generating a delivery traffic indication map (DTIM) beacon including a segmentation information element; and (b) dividing the TIM information of the TIM transmission target page into the segments with variable sizes using the DTIM beacon and beacons within a DTIM interval corresponding to the DTIM beacon, and transmitting the divided segments.

In the (a) generating, the segmentation information element may include a page index designating the TIM transmission target page; page segment counts of the segments into which the TIM transmission target page is divided; a page offset designating a first block of the TIM transmission target page included in a first segment among the segments; and a page bitmap providing information about presence and absence of buffered data and information about segment division to blocks included in the segments.

In the (b) dividing, the access point may divide the TIM information of the TIM transmission target page into the segments based on the number of blocks containing the buffered data included in the bitmap, and transmit the divided segments.

At least two of the segments may be divided so that the number of blocks containing the buffered data included in the bitmap corresponding to each of the segments in the bitmap is uniform.

In the (a) generating, the segmentation information element may include a page index designating the TIM transmission target page; a page offset designating a first block of the TIM transmission target page included in a first segment among the segments; and a page bitmap providing information about presence and absence of buffered data and information about segment division to blocks included in the segments.

In the (b) dividing, the bitmap may include block traffic indication elements including predetermined bits which indicate the segment division with respect to a corresponding block and the presence and absence of the buffered data, and the access point may divide the TIM information of the TIM transmission target page into segments using the block traffic indication elements and transmit the divided segments.

The block traffic indication elements may have any one of a first value indicating absence of the buffered data with respect to the corresponding block; a second value indicating presence of the buffered data with respect to the corresponding block and indicating the corresponding block as a block in which a new segment starts; and a third value indicating presence of the buffered data with respect to the corresponding block and designating the corresponding block as a block included in a previous segment.

In the (b) dividing, the bitmap may include a first bitmap indicating presence and absence of the buffered data with respect to a block to which each bit corresponds, and a second bitmap providing segment division information having the same length as the first bitmap by bit transition, and the access point may divide the TIM information of the TIM transmission target page into the segments using the second bitmap and transmit the divided segments.

Another aspect of the present invention provides a method of receiving TIM information of a terminal, in which TIM information of a TIM reception target page is received as divided segments with variable sizes in a hierarchical TIM structure including a page, a block and a sub-block, the method including: (a) receiving a DTIM beacon including a segmentation information element; and (b) receiving the TIM information of the TIM reception target page as the divided segments with the variable sizes using the DTIM beacon and beacons within a DTIM interval corresponding to the DTIM beacon.

In the (a) receiving, the segmentation information element may include a page index designating the TIM reception target page; page segment counts of the segments into which the TIM reception target page is divided; a page offset designating a first block of the TIM reception target page included in a first segment among the segments; and a page bitmap providing information about presence and absence of buffered data and information about segment division to blocks included in the segments.

In the (b) receiving, the terminal may divide the TIM information of the TIM reception target page into the segments based on the number of blocks containing the buffered data included in the bitmap, and receive the divided segments.

At least two among the segments may be divided so that the number of the blocks containing the buffered data included in the bitmap corresponding to each of the segments is uniform.

In the (a) receiving, the segmentation information element may include a page index designating the TIM reception target page; a page offset designating a first block of the TIM reception target page included in a first segment among the segments; and a page bitmap providing information about presence and absence of buffered data and information about segment division to blocks included in the segments.

In the (b) receiving, the bitmap may include block traffic indication elements including predetermined bits which indicate the segment division with respect to a corresponding block and the presence and absence of the buffered data, and the terminal may divide the TIM information of the TIM reception target page into segments using the block traffic indication elements and receive the divided segments.

In the (b) receiving, the bitmap may include a first bitmap indicating presence and absence of the buffered data with respect to a block to which each bit corresponds, and a second bitmap providing segment division information having the same length as the first bitmap by bit transition, and the access point may divide the TIM information of the TIM reception target page into the segments using the second bitmap and receive the divided segments.

According to the above-described method of transceiving traffic indication map (TIM) information according to an embodiment of the present invention, a delivery traffic indication map (DTIM) beacon including segmentation information is generated, and the generated DTIM and TIM information corresponding to the DTIM beacon are divided into segments having a variable size to be transmitted.

Accordingly, downlink traffic stored in a buffer of an access point is appropriately distributed in a predetermined range, so that power consumption required for receiving a downlink frame stored in the buffer of the access point by terminals operated in a PS mode can be reduced. In addition, only a single beacon frame is transmitted together with a single TIM segment, thereby appropriately adjusting a length of the beacon frame.

FIG. 1 shows a traffic indication map (TIM) information element (IE) format;

FIG. 2 shows a PS mode operation defined in an 802.11 wireless LAN standard;

FIG. 3 shows power loss of a terminal that can occur whenone or more frames stored in the buffer of the AP fails to be transmitted during a single beacon interval;

FIG. 4 shows a PS mode operation to which a TIM segmentation method according to an embodiment of the present invention is applied;

FIG. 5 shows a hierarchical association ID (AID) structure;

FIG. 6 shows a TIM segmentation method considering a hierarchical AID structure;

FIG. 7 shows a fixed length segmentation count IE format that can be used in a fixed length TIM segmentation method;

FIG. 8 is a conceptual diagram showing utilization of fixed length segmentation;

FIG. 9 shows an equal number of value-1 (ENV) segmentation count IE format that can be used in an ENV segmentation method according to an embodiment of the present invention;

FIG. 10 is a conceptual diagram showing a difference between fixed length segmentation and ENV segmentation according to an embodiment of the present invention;

FIG. 11 is a conceptual diagram showing an example of utilizing ENV segmentation according to an embodiment of the present invention;

FIG. 12 is a conceptual diagram showing a block TI-based segmentation count IE format according to an embodiment of the present invention;

FIG. 13 is a conceptual diagram showing a page bitmap of a block TI-based segmentation count IE according to an embodiment of the present invention;

FIG. 14 is a conceptual diagram showing a toggle-based segmentation count IE format according to an embodiment of the present invention;

FIG. 15 is a conceptual diagram showing a page bitmap of a toggle-based segment count IE according to an embodiment of the present invention;

FIG. 16 is a conceptual diagram showing a state of segmentation in a dynamic segmentation method according to an embodiment of the present invention;

FIG. 17 is a flowchart showing a method of transmitting TIM information of an access point according to an embodiment of the present invention; and

FIG. 18 is a flowchart showing a method of receiving TIM information of a terminal according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail. However, the present invention is not limited to the exemplary embodiments disclosed below, but can be implemented in various forms. The following exemplary embodiments are described in order to enable those of ordinary skill in the art to embody and practice the invention.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used here, the term “and/or” includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined here.

Hereinafter, preferred embodiments of the present invention will be described in detail with the accompanying drawings. In the following description, the same reference numerals denote the same elements to facilitate the overall understanding, and repeated description thereof will be omitted.

In the specification, station (STA) denotes an arbitrary functional medium including a medium access control (MAC) layer defined by the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard and a physical layer interface with respect to a wireless medium. STAs may be divided into STAs that are access points (APs) and STAs that are not APs. An STA that is an AP may be simply referred to as an AP, and an STA that is not an AP may be simply referred to as a terminal. The terminal may include a processor and a transceiver, and may further include a user interface, a display device, and the like. The processor denotes a unit that is designed to generate a frame to be transmitted through a wireless network or process a frame received through the wireless network, and performs a variety of functions for controlling the station (STA). The transceiver may be functionally connected with the processor, and denotes a unit that is designed to transmit and receive a frame through the wireless network for the STA.

The AP may refer to a centralized controller, a base station (BS), a Node-B, an eNode-B, a base transceiver system, a site controller, or the like, and may include some or all functions thereof.

The terminal may refer to a wireless transmit/receive unit (WTRU), user equipment (UE), a user terminal (UT), an access terminal (AT), a mobile station (MS), a mobile terminal, a subscriber unit, a subscriber station (SS), a wireless device, a mobile subscriber unit, or the like, and may include some or all functions thereof.

Here, the terminal may be a desktop computer enabling communication, a laptop computer, a tablet PC, a wireless phone, a mobile phone, a smart phone, an e-book reader, a portable multimedia player (PMP), a portable game console, a navigation device, a digital camera, a digital multimedia broadcasting (DMB) player, a digital audio recorder, a digital audio player, a digital picture recorder, a digital picture player, a digital video recorder, a digital video player, or the like.

FIG. 1 shows a traffic indication map (TIM) information element (IE) format.

Referring to FIG. 1, TIM IE may include a delivery traffic indication map (DTIM) count required in a PS mode, a DTIM period, a bitmap control, and a partial virtual bitmap.

First, the DTIM count is used to indicate number of remaining beacon frames until next DTIM beacon transmission, and is a value that is circulated while being decreased from DTIM Period-1 to 0 every time a beacon frame is transmitted. When the DTIM count value is 0, a current TIM IE is a DTIM indicating that a group-addressed frame is to be transmitted soon. The DTIM Period is the number of beacon intervals within two consecutive DTIMs. When the DTIM Period value is 3, a broadcast/multicast frame may be transmitted for each of three beacon intervals. A first bit of the bitmap control is a bit corresponding to associated ID (hereinafter, referred to as “AID”) 0, and AID 0 may be used for indicating whether a group-addressed frame is stored in AP. The remaining 7 bits may be used for offset with respect to a partial virtual bitmap of a next region.

In addition, a traffic-indication virtual bitmap may have a length of 2008 bits, and each bit may indicate presence/absence of AP’s buffered traffic destined to a certain terminal . That is, a case in which a frame to be transmitted to a terminal is stored in the buffer of the AP can be displayed as 1, and other cases can be displayed as 0.

Alternatively, the case in which the frame to be transmitted to the terminal is stored in the buffer of the AP can be displayed as 0, and other cases can be displayed as 1. In this specification, for convenience, the case in which the frame to be transmitted to the terminal is stored in the buffer of the AP is displayed as 1.

'Partial' means that although the number of required octets to support 2008 AIDs is 251 octets (2008 bits), we can omit leading part of several consecutive 0 bits by using 7-bit bitmap control.

FIG. 2 shows a PS mode operation defined in an 802.11 wireless LAN standard.

Referring to FIG. 2, in a state in which a DTIM interval value is 3, four terminals maintain doze state in order to reduce power consumption, and then switch into an awake state in accordance with a target beacon transmission time (TBTT) to which a beacon frame is transmitted.

The terminals that have received the beacon frame may determine presence or absence of frames that should be received by the terminals among frames stored in a buffer of an AP through a partial virtual bitmap included in a TIM IE.

A terminal having AID1 transmits a PS Poll to the AP based on bitmap information included in the first beacon so as to receive the frame stored in the buffer of the AP. Next, the AP that has received the PS Poll may transmit the frame stored in the buffer to the terminal having the AID1.

When reception of the frame stored in the buffer is completed, the terminal having the AID1 may return to the doze state. On the other hand, the remaining terminals may remain awake to receive the beacon frame, determine whether a bit corresponding to the remaining terminals is set as 0 in the partial virtual bitmap, and then return to the doze state.

In the same manner, in the following TBTT, terminals may be awake for a required time period while repeatedly switching between the doze state and the awake state, and then return to the doze state to reduce power consumption when required transmission and reception of data is completed.

The above-described PS mode operation method may be an effective way to reduce power consumption by reducing a time during which terminals are unnecessarily awake compared to an active mode operation method in which terminals continuously remain awake to transmit and receive data.

However, when the number of frames stored in the buffer of the AP is much larger than the number of frames that can be transmitted during a single beacon interval, only some terminals successful in a channel contending during a corresponding beacon interval may request transmission of frames, and the remaining terminals that fail to acquire the channel remain awake for an unnecessarily long time period, and therefore the above-described power loss problem may still exist.

Accordingly, hereinafter, terminal power loss that can occur when all of the frames stored in the buffer of the AP fail to be transmitted will be described with reference to FIG. 3.

FIG. 3 shows power loss of a terminal that can occur when a frame stored in the buffer of the AP fails to be transmitted during a single beacon interval.

Referring to FIG. 3, terminals may determine presence or absence of frames that should be received by the terminals through a bitmap included in a first beacon.

The terminals in which a bit of a partial virtual bitmap included in the beacon is set as 1 may transmit a PS Poll to the AP so as to request transmission of frames. However, when the number of the terminals is increased, there may be a case in which the frame stored in the buffer of the AP fails to be transmitted to all of the terminals until the following beacon is transmitted.

A terminal having AID N-1 and a terminal having AID N may attempt to transmit the PS Poll so as to receive their own frames stored in the buffer of the AP, through the bitmap included in the first beacon.

However, when the terminals fail in channel contending several times, the terminals may transmit the PS Poll in the next beacon interval, and receive their own frames.

An area displayed as a dotted border may indicate power loss that occurs by maintaining, by two terminals, an idle listening state for channel contending, which is different from the doze state, during a single beacon interval. When the two terminals have been aware of the fact that they can receive their own frames in a second beacon interval in advance, they may operate in the doze state in the first beacon interval to reduce power loss.

In the present invention, power loss occurred in FIG. 3 can be reduced by dividing a TIM into several segments, considering the amount of wireless resources that can be used to deliver the buffered traffic and the distribution of traffic stored in the buffer of the AP., and terminals corresponding to a single segment are allowed to be included in a single TIM IE.

As a result, a TIM segmentation method is proposed so that power consumption required for terminals operated in a PS mode to receive a downlink frame stored in the buffer of the AP is reduced by appropriately distributing downlink traffic stored in the buffer of the AP in a predetermined range.

In addition, the terminals may receive in advance, from the AP, information about the TBTT to which the TIM IE corresponding to the segment in which the terminals are involved is transmitted.

When aware of the information about the TBTT, the terminals may skip the beacon frame including the segment in which the terminals are not involved and therefore power consumption may be further reduced compared to an operation method in which the terminals are awake for each TBTT.

In addition, in the TIM segmentation method proposed in the present invention, a partial virtual bitmap constituted of terminals corresponding to a single segment may be included in a single TIM IE, and therefore a length of the beacon frame can be appropriately adjusted compared to an existing method.

FIG. 4 shows a PS mode operation to which a TIM segmentation method according to an embodiment of the present invention is applied.

Referring to FIG. 4, a TIM IE included in a first beacon frame includes a partial virtual bitmap that can cover AID 1 to AID M. Accordingly, the following beacon frame to be transmitted may include a partial virtual bitmap that can cover AID M+1 to AID N.

That is, terminals included in the first segment may correspond to AID 1 to AID M, and terminals included in the second segment may correspond to AID M+1 to AID N.

Since the terminals may receive in advance, from the AP, information about a TBTT to which a segment corresponding to the terminals is transmitted, the terminals may be awake only in the TBTT corresponding to the terminals.

Unlike the existing PS mode operation example shown in FIG. 3, the terminals included in the first segment are continuously operated in a doze state, not awake, in a second TBTT, and therefore power consumption can be reduced compared to the existing method.

In addition, since terminals included in a second segment are operated in the doze state during the first beacon interval, power loss that can occur in the above-described unnecessary idle listening state may be effectively reduced.

Therefore, a new hierarchical AID structure for supporting connection of a large number of terminals has been proposed in IEEE 802.11ah, and will be described with reference to FIG. 5.

FIG. 5 shows a hierarchical association ID (AID) structure.

Referring to FIG. 5, eight terminals are included in a single sub-block, and eight sub-blocks may form a single block. That is, a single block may form a group including 64 terminals. Further, a single page including 32 blocks may include 2048 terminals in total, and the number of the pages is four. Accordingly, the hierarchical AID structure of FIG. 5 may include 8192 terminals in total.

Hereinafter, the TIM segmentation method considering the AID structure will be described with reference to FIG. 6.

FIG. 6 shows a TIM segmentation method considering a hierarchical AID structure.

Referring to FIG. 6, an example of page segmentation that can be thought as one example of the TIM segmentation will be described. That is, since the example uses the page as a unit of segmentation, the TIM segmentation shown in the present example may be referred to as page segmentation.

An AP may divide a single page into four segments and transmit the four segments together with a beacon frame for each segment. In addition, terminals may be awake in accordance with the beacon frame including a segment in which the terminals are involved in order to reduce power consumption.

A DTIM period is 4, and the number of segments of the divided page is also 4. That is, the beacon including the DTIM may be transmitted for each of four beacon intervals, and a single page may be divided into four segments and the divided segments may be transmitted together with each of four beacon frames that are transmitted during a single DTIM interval.

In order to enable a segment count IE that is newly defined in the present invention to be included in a DTIM beacon which can be received by all terminals, a single page may be segmented in accordance with a DTIM beacon interval.

The segment count IE is a newly defined IE that can be used when the AP transmits TIM segmentation information to a terminal.

Here, the IE may represent an AID range covered by each segment and presence and absence of traffic that is stored in a buffer of the AP for each block in a TIM segmentation process.

That is, terminals may be aware of a time when the segment in which the terminals are involved is to be transmitted, that is, information about a TBTT to which the beacon frame including a corresponding segment is transmitted, and presence and absence of downlink traffic with respect to the block in which the terminals are involved. Accordingly, when there is downlink traffic with respect to the block in which the terminals are involved among the frames stored in the buffer of the AP, the terminals may be awake in accordance with a corresponding beacon frame, and therefore power loss that can occur when the terminals are unnecessarily awake can be reduced.

FIG. 7 shows a fixed length segmentation count IE format that can be used in a fixed length TIM segmentation method.

Referring to FIG. 7, a fixed length segment count IE may include a large number of pieces of information such as a page index, format indication bits, a page segment count, page offset, a page bitmap, and the like, other than a length field in which an element ID and a length of IE used for referring to a segment count IE are represented in bytes, and may additionally include 2 reserved bits in order to set the entire length in bytes.

Here, the page index may be used to represent a page to which segmentation information included in a current segment count IE corresponds.

In addition, the format indication bits may be used to indicate the segment count IEs having a variety of different formats according to an embodiment of the present invention. When the format indication bits are set as (0, 0), the current count IE may be considered as a fixed length segment count IE.

The page segment count value may be used to represent the number of segments into which a single page is divided.

The page offset may be used as an offset value when displaying a page bitmap of a next region, and may be an index of a block that is displayed by a first bit of the page bitmap.

The page bitmap may be used to represent presence and absence of the frame stored in the buffer of the AP for each block. That is, a case in which a destination terminal of the frame stored in the buffer of the AP is among 64 terminals included in a single block is set as 1, and otherwise is set as 0.

When the number of blocks included in the single page is 32, the page bitmap may be increased up to 4 octets in order to represent TIM information of 32 blocks as a maximum. On the other hand, when bits set as 0 exist at the beginning part of the bitmap, the bit set as 0 may be skipped, and therefore an actual length of the page bitmap may be much shorter than 4 octets. Here, the page offset may have an index value of a block that is an actual starting point of the page bitmap based on the skipped bit.

The fixed length segment count IE may be used in a fixed length TIM segmentation method, which is the most basic segmentation method. The fixed length TIM segmentation method may be a method of dividing a single page into segments having the same length.

Here, the length may refer to the number of blocks. That is, the page segments transmitted during a single DTIM interval are divided so as to have the same number of blocks.

On the other hand, the page segment count value may differ between several DTIM intervals, and therefore the number of blocks of a single page segment may differ. In this manner, the length of the page segment generated in the above-described segmentation method may be represented as the following Equation1.

[Equation 1]

Length of page segment = (Number of blocks in one page / page segment count)

Here, a starting point and an end point of the page segment are represented as the following

Equations

2 and 3, respectively.

[Equation 2]

Segment start = page offset + ((length of page segment) × (page segment number -1)) + 1

[Equation 3]

Segment end = page offset + length of page segment × TIM segment number

However, although the number of the blocks of all of the page segments is the same, the traffic stored in the buffer of the AP corresponding to each segment may be not uniform.

The reason may be roughly interpreted in two aspects.

One is because the number of blocks is the same but the number of blocks including a destination terminal of the frame stored in the buffer of the actual AP may differ. That is, the number of bits that are set as 1 in the page bitmap may differ.

The other is because presence and absence of traffic is displayed in a block unit and therefore there may be a difference in sizes of traffic stored in the buffer of the actual AP even between the blocks set as 1. When the traffic stored in the buffer of the AP is not appropriately distributed, there may be a high possibility that the power loss problem described in FIG. 3 will be still not be solved even though TIM segmentation is performed.

FIG. 8 is a conceptual diagram showing utilization of fixed length segmentation.

Referring to FIG. 8, a length of the page bitmap is 3 octets, and a page segment count value is 4. Terminals involved in each TIM segment may be awake in a corresponding TBTT in order to receive a beacon frame to which a TIM IE including a segment of the terminals is transmitted.

In addition, since one bit may represent TIM information corresponding to a single block, an actual size of downlink traffic may differ for each block.

In addition, when the page is divided by the same number of blocks, the traffic stored in the buffer of the actual AP may not be uniformly distributed.

As shown in FIG. 8, only some among frames stored in the buffer of the AP corresponding to a first segment may be transmitted within a corresponding beacon interval, and the remaining frames may be delayed and transmitted within a second beacon interval. In this case, unnecessary terminal power loss that can occur when the TIM segmentation is not performed may still occur.

In the same manner, when a special area for uplink transmission is allocated in advance at a third beacon interval, some terminals involved in a segment 3 have to be awake until they receive their own frames, and therefore unnecessary power loss may occur.

Based on this, in the present invention, a TIM segmentation method in which a length of a TIM segment may vary in consideration of traffic distribution is proposed. The variable TIM segmentation may effectively distribute traffic and reduce power consumption of the terminal.

In describing the variable TIM segmentation method of the present invention, an equal number of value-1, (hereinafter, referred to as “ENV”) Segmentation method and a dynamic segmentation method will be described.

FIG. 9 shows an ENV segmentation count IE format that can be used in an ENV segmentation method according to an embodiment of the present invention, and FIG. 10 is a conceptual diagram showing a difference between fixed length segmentation and ENV segmentation according to an embodiment of the present invention.

First, referring to FIG. 9, compared to the fixed length segment count IE of FIG. 7, there is no big difference except for the format indication bits set as (0, 1).

The page index may be used to represent which page information of the segment count IE corresponds to.

The page segment count may refer to the number of segments included in a single page.

The page offset may indicate an index of a block corresponding to a first bit of the page bitmap. In addition, the page bitmap may be used to represent presence and absence of traffic stored in the buffer of the AP in the block unit as described above.

However, in the ENV segmentation method, segmentation may be performed based on the number of 1s included in the page bitmap, unlike the fixed length segmentation method. That is, the number of 1s included in each TIM segment may be made the same by appropriately dividing the page bitmap. Therefore, when an amount of traffic stored in the buffer of the AP for each block is the same, an effect of uniformly distributing the traffic may be obtained.

Referring to FIG. 10, a difference between the fixed length segmentation and the ENV segmentation is shown, and it can be found that the ENV segmentation distributes the traffic through the page bitmap compared to the fixed length segmentation.

FIG. 11 is a conceptual diagram showing an example of utilizing ENV segmentation according to an embodiment of the present invention.

Referring to FIG. 11, each segment is segmented so as to include the same number of 1s existing in the page bitmap. That is, unlike FIG. 9, some blocks allocated to a first segment may be moved to a second segment, and corresponding terminals may be awake in accordance with a TBTT to which a second beacon different from a first beacon is transmitted.

Accordingly, power loss that can occur while waiting for an unnecessarily long time period can be reduced to some extent. However, an amount of wireless resources allowed for transmitting a frame stored in the buffer of the AP for each beacon interval may differ, and an amount of traffic stored in the buffer of the AP for each block may differ, and therefore the ENV segmentation may not be still an appropriate TIM segmentation method considering wireless resources.

In order for the AP to perform a free TIM segmentation method considering the wireless resources, a segment count IE capable of freely defining the number of blocks included in a single segment may be required.

Therefore, in an embodiment of the present invention, a segment count IE that can be used in the above-described dynamic segmentation method is proposed. Hereinafter, as a specific example, a block TI-based segment count IE and a toggle-based segment count IE may exist, but any segment count IE may be used as long as the segment count IE has a format for supporting a TIM segmentation method capable of freely adjusting the number of blocks included in a single segment.

FIG. 12 is a conceptual diagram showing a block TI-based segmentation count IE format according to an embodiment of the present invention, and FIG. 13 is a conceptual diagram showing a page bitmap of a block TI-based segmentation count IE according to an embodiment of the present invention.

First, referring to FIG. 12, format indication bits are set as (1, 0), and a corresponding segment count IE may be referred to as a block TI-based segment count IE.

TIM information corresponding to a single block in the page bitmap may be displayed as a block TI having 2 bits, and the meaning corresponding to the set value may be shown in the following Table 1.

[Table 1]

In Table 1, the meaning of a block TI value included in a page bitmap region in the block TI-based segment count IE is shown.

When the block TI value is set as (0, 0), it may mean that a corresponding block does not have traffic stored in the buffer of the AP.

In addition, when the block TI value is set as (0, 1), it may mean that a corresponding block has traffic to be transmitted from the AP and at the same time is a starting point of a new TIM segment. In addition, when the block TI value is set as (1, 0), it may mean that a corresponding block has traffic to be transmitted from the AP and is included in the same segment as the previous block.

The block TI value of (1, 1) may be used in a part which is required in the future.

Referring to FIG. 13, the number of the block TIs which are set as (0, 1) among the page bitmap is four, and therefore a corresponding page may be divided into four TIM segments.

The remaining block TIs may have (0, 0) or (1, 0), and the corresponding meaning may be the same as defined in Table 1.

Accordingly, when wishing to make a new page segment, the AP may set the block TI value as (0, 1), and set the block TI value as (0, 0) or (1, 0) to continue the same segment. That is, the AP may appropriately perform TIM segmentation considering wireless resources as desired.

FIG. 14 is a conceptual diagram showing a toggle-based segmentation count IE format according to an embodiment of the present invention, and FIG. 15 is a conceptual diagram showing a page bitmap of a toggle-based segment count IE according to an embodiment of the present invention.

Referring to FIG. 14, it may mean that a corresponding segment count IE follows a toggle-based segment count IE format by setting format indication bits as (1, 1).

The page bitmap may have the same format as the page bitmap that is defined in the fixed length segment count IE described in FIG. 7. That is, in the page bitmap, a case in which there is traffic to be transmitted from the AP by a corresponding block may be set as 1, and other cases may be set as 0.

The segmentation bitmap that is a next region may have the same length as the page bitmap and include information about a starting point and an end point of a segment.

In FIG. 14, an example in which a new segment can start in a place where bit transition is performed is shown. When the new segment starts as 0, a block corresponding to a bit that is initially set as 1 after 0 may be a starting point of the next segment. Accordingly, a block having the same value as an immediately preceding block can be seen as a continuation of the same segment.

Referring to FIG. 15, examples of a page bitmap and a segmentation bitmap in a toggle-based count IE are shown.

Bits of the page bitmap may be used to represent presence and absence of traffic, and bits of the segmentation bitmap may be used to represent a starting point and an end point of each segment. In FIG. 15, a case of division into four segments is shown.

FIG. 16 is a conceptual diagram showing a state of segmentation in a dynamic segmentation method according to an embodiment of the present invention.

Referring to FIG. 16, an AP may apply an appropriate TIM segmentation method considering wireless resources using a segment count IE that can support the dynamic segmentation method described above.

Each TIM segment is appropriately segmented considering available wireless resources in a corresponding beacon interval.

Unlike the fixed length segmentation and the ENV segmentation which have been described in FIGS. 8 and 11, in the dynamic segmentation, terminals are awake to receive a beacon frame including a segment in which the terminals are involved, and then may receive, from an AP, a frame stored in a buffer of the AP before a TBTT to which the following beacon frame is transmitted.

FIG. 17 is a flowchart showing a method of transmitting TIM information of an AP according to an embodiment of the present invention.

Referring to FIG. 17, in step S1710, the AP may generate a DTIM beacon including a segmentation information element.

Here, the segmentation information element may include a page index designating a TIM transmission target page, a page segment count of segments obtained by dividing the TIM transmission target page, page offset designating a first block of the TIM transmission target page included in a first segment among the segments, and a bitmap providing information about presence and absence of buffered data with respect to blocks included in the segments and information about segment division.

Next, in step S1720, the AP may divide TIM information of the TIM transmission target page into segments having variable sizes, using a DTIM beacon and beacons within a DTIM interval corresponding to the DTIM beacon.

Specifically, in step S1721, the AP may divide TIM information of the TIM transmission target page into segments based on the number of blocks containing the buffered data included in the bitmap, and transmit the divided segments.

Here, at least two of the segments may be divided so that the number of blocks in which the buffered data included in a bitmap part corresponding to each segment is uniform in the bitmap.

Alternatively, in step S1723, when the bitmap includes segment division with respect to a corresponding block and block traffic indication elements including predetermined bits indicating presence and absence of the buffered data, the AP may divide the TIM information of the TIM transmission target page into segments using the block traffic indication elements, and transmit the divided segments.

Here, the block traffic indication elements may have one of a first value indicating absence of the buffered data with respect to the corresponding block, a second value indicating presence of the buffered data with respect to the corresponding block and indicating that the corresponding block is a block in which a new segment starts, and a third value designating presence of the buffered data with respect to the corresponding block and indicating that the corresponding block is a block included in a previous segment.

Alternatively, in step S1725, when the bitmap includes a first bitmap indicating presence and absence of the buffered data with respect to a block to which each bit corresponds, and a second bitmap having the same length as the first bitmap and providing segment division information by bit transition, the AP may divide the TIM information of the TIM transmission target page into segments using the second bitmap, and transmit the divided segments.

Therefore, according to the TIM information transmission method according to an embodiment of the present invention, downlink traffic stored in the buffer of the AP is appropriately distributed within a predetermined range, and therefore power consumption required for receiving, by the terminals, downlink frames stored in the buffer of the AP can be reduced, and a length of the beacon frame can be appropriately adjusted.

Referring to FIG. 18, in step S1810, a terminal may receive a DTIM beacon including a segmentation information element from an AP.

Here, the segmentation information element may include a page index designating a TIM reception target page, a page segment count of segments into which the TIM reception target page is divided, a page offset designating a first block of the TIM reception target page included in a first segment among the segments, and a bitmap providing information about presence and absence of buffered data with respect to blocks included in the segments and information about segment division.

In step S1820, the terminal may receive the TIM information of the TIM reception target page as divided segments having variable sizes using the DTIM beacon received through step S1810 and beacons within a DTIM interval corresponding to the DTIM beacon.

Specifically, in step S1821, the terminal may acquires the information about TIM segment division, and receives the divided segments based on the acquired division information.

Also, the terminal may divide the TIM information of the TIM reception target page into segments based on the number of blocks containing buffered data included in the bitmap, and receive the divided segments.

Here, at least two of the segments may be divided so that the number of the blocks in which the buffered data included in a bitmap part corresponding to each segment is uniform in the bitmap.

Alternatively, in step S1823, when the bitmap includes segment division with respect to a corresponding block, and block traffic indication elements including predetermined bits indicating presence and absence of the buffered data, the terminal may divide the TIM information of the TIM reception target page into segments using the block traffic indication elements and receive the divided segments.

Here, the block traffic indication elements may have any one of a first value indicating absence of the buffered data with respect to the corresponding block, a second value indicating presence of the buffered data with respect to the corresponding block and indicating that the corresponding block is a block in which a new segment starts, and a third value designating that the corresponding block is a block included in a previous segment.

Alternatively, in step S1825, when the bitmap includes a first bitmap designating presence and absence of the buffered data with respect to the corresponding block, and a second bitmap of having the same length as the first bitmap and providing segment division information by bit transition, the terminal may divide the TIM information of the TIM reception target page into segments using the second bitmap and receive the divided segments.

According to the TIM information transmission method according to an embodiment of the present invention, the downlink traffic stored in the buffer of the AP can be appropriately distributed in a predetermined range. Therefore, power consumption required for terminals operated in a PS mode to receive the downlink frames stored in the buffer of the AP can be reduced.

In this specification, to be concise, exemplary embodiments of the present invention have been classified into the first, second and third exemplary embodiments. However, steps or functions of any exemplary embodiment may be combined with those of another exemplary embodiment to implement still another exemplary embodiment of the present invention.

While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

A method of transmitting traffic indication map (TIM) information of an access point, in which a TIM transmission target page is divided into segments having variable sizes in a hierarchical TIM structure including a page, a block, and a sub-block, and TIM information of the TIM transmission target page is transmitted, the method comprising:

(a) generating a delivery traffic indication map (DTIM) beacon including a segmentation information element; and

(b) dividing the TIM information of the TIM transmission target page into the segments with variable sizes using the DTIM beacon and beacons within a DTIM interval corresponding to the DTIM beacon, and transmitting the divided segments.
The method of claim 1, wherein, in the (a) generating, the segmentation information element comprises:

a page index designating the TIM transmission target page;

page segment counts of the segments into which the TIM transmission target page is divided;

a page offset designating a first block of the TIM transmission target page included in a first segment among the segments; and

a page bitmap providing information about presence and absence of buffered data and information about segment division to blocks included in the segments.
The method of claim 2, wherein, in the (b) dividing, the access point divides the TIM information of the TIM transmission target page into the segments based on the number of blocks containing the buffered data included in the bitmap, and transmits the divided segments.
The method of claim 3, wherein at least two of the segments are divided so that the number of blocks containing the buffered data included in the bitmap corresponding to each of the segments in the bitmap is uniform.
The method of claim 1, wherein, in the (a) generating, the segmentation information element comprises:

a page index designating the TIM transmission target page;

a page offset designating a first block of the TIM transmission target page included in a first segment among the segments; and

a page bitmap providing information about presence and absence of buffered data and information about segment division to blocks included in the segments.
The method of claim 5, wherein, in the (b) dividing,

the bitmap comprises block traffic indication elements including predetermined bits which indicate the segment division with respect to a corresponding block and the presence and absence of the buffered data, and

the access point may divide the TIM information of the TIM transmission target page into segments using the block traffic indication elements and transmit the divided segments.
The method of claim 6, wherein the block traffic indication elements have any one of a first value indicating absence of the buffered data with respect to the corresponding block;

a second value indicating presence of the buffered data with respect to the corresponding block and indicating the corresponding block as a block in which a new segment starts; and

a third value indicating presence of the buffered data with respect to the corresponding block and designating the corresponding block as a block included in a previous segment.
The method of claim 5, wherein, in the (b) dividing,

the bitmap includes a first bitmap indicating presence and absence of the buffered data with respect to a block to which each bit corresponds, and a second bitmap providing segment division information having the same length as the first bitmap by bit transition, and

the access point divides the TIM information of the TIM transmission target page into the segments using the second bitmap and transmits the divided segments.
A method of receiving TIM information of a terminal, in which TIM information of a TIM reception target page is received as divided segments with variable sizes in a hierarchical TIM structure including a page, a block and a sub-block, the method comprising:

(a) receiving a DTIM beacon including a segmentation information element; and

(b) receiving the TIM information of the TIM reception target page as the divided segments with the variable sizes using the DTIM beacon and beacons within a DTIM interval corresponding to the DTIM beacon.
The method of claim 9, wherein, in the (a) receiving, the segmentation information element comprises:

a page index designating the TIM reception target page;

page segment counts of the segments into which the TIM reception target page is divided;

a page offset designating a first block of the TIM reception target page included in a first segment among the segments; and

a page bitmap providing information about presence and absence of buffered data and information about segment division to blocks included in the segments.
The method of claim 10, wherein, in the (b) receiving, the terminal acquires the information about TIM segment division, and receives the divided segments based on the acquired division information.
The method of claim 11, wherein at least two among the segments are divided so that the number of the blocks containing the buffered data included in the bitmap corresponding to each of the segments is uniform.
The method of claim 9, wherein, in the (a) receiving, the segmentation information element comprises:

a page index designating the TIM reception target page;

a page offset designating a first block of the TIM reception target page included in a first segment among the segments; and

a page bitmap providing information about presence and absence of buffered data and information about segment division to blocks included in the segments.
The method of claim 13, wherein, in the (b) receiving,

the bitmap comprises block traffic indication elements including predetermined bits which indicate the segment division with respect to a corresponding block and the presence and absence of the buffered data, and

the terminal divides the TIM information of the TIM reception target page into segments using the block traffic indication elements and receives the divided segments.
The method of claim 14, wherein the block traffic indication elements have any one of a first value indicating absence of the buffered data with respect to the corresponding block;

a second value indicating presence of the buffered data with respect to the corresponding block and indicating the corresponding block as a block in which a new segment starts; and

a third value indicating presence of the buffered data with respect to the corresponding block and designating the corresponding block as a block included in a previous segment.
The method of claim 13, wherein, in the (b) receiving,

the bitmap comprises a first bitmap indicating presence and absence of the buffered data with respect to a block to which each bit corresponds, and a second bitmap providing segment division information having the same length as the first bitmap by bit transition, and

the access point divides the TIM information of the TIM reception target page into the segments using the second bitmap and receives the divided segments.