WO2013131399A1 - Data transmission method and access point - Google Patents

Abstract

The embodiments of the present invention relate to a data transmission method and an access point. The data transmission method comprises: identifying target bits in a traffic indication map (TIM); inversing all or partial target bits; compressing the TIM and obtaining compressed TIM; sending the compressed TIM to a station. According to the embodiments of the present invention, by utilizing unoccupied or delay bits to assist the bit compression of the TIM, redundant bits in the TIM are further decreased, compression effect is improved, and thus sending efficiency of the TIM is increased, overhead of the access point is reduced, and performance of a network system is enhanced.

Description

 Data transmission method and access point

 Embodiments of the present invention relate to the field of wireless communications, and more particularly, to a data transmission method, an access point. Background technique

 In a WiFi network, the access point periodically broadcasts beacon frames. The beacon frame may include a Traffic Indication Map (TIM) portion, and the initial TIM is in the form of a bitmap, where each bit represents a station, if the beacon period If the access point has downlink data to send to the station, the corresponding bit of the station is set to 1, otherwise it is set to 0. After receiving the beacon frame, the station will detect whether the bit corresponding to itself is 1 or 0. If it is 1, it can send the energy-saving polling frame to request downlink data from the access point. If it is 0, it can enter the sleep state until Wake up by the next beacon.

 Currently, an access point can support up to 6000 sites. The access point needs to write the downlink data indication of each site in the TIM part of the beacon, which brings huge overhead to the access point. Summary of the invention

 The embodiment of the invention provides a data transmission method, which can reduce redundant bits in the bitmap of the TIM and improve the compression effect.

 In one aspect, a data transmission method is provided,

 The method includes:

 Identifying the target bit in the transmission indication mapping TIM;

 Invert all or part of the target bit;

 Perform TIM compression on the TIM to obtain a compressed TIM;

 Send the compressed TIM to the site.

 In another aspect, an access point is provided, and the access point includes:

 An identifying unit, configured to identify a target bit in the transmission indication mapping TIM;

 a processing unit, configured to invert all or part of the target bit;

 a compression unit, configured to perform TIM compression on the TIM to obtain a compressed TIM;

a sending unit, configured to send the compressed TIM to the station. According to the embodiment of the present invention, by using the target bit, it can also be called the text auxiliary bit, and the bit compression of the auxiliary TIM further reduces the redundant bits in the TIM, thereby improving the compression effect, thereby improving the transmission efficiency of the TIM and reducing the transmission efficiency. The overhead of the access point improves the performance of the network system. DRAWINGS

 In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings to be used in the embodiments or the description of the prior art will be briefly described below. Obviously, the drawings in the following description are only the present invention. For some embodiments, other drawings may be obtained from those of ordinary skill in the art without departing from the drawings.

 1 is a schematic flow chart of a data transmission method according to an embodiment of the present invention;

 2 is a schematic diagram of a bitmap hierarchical compression method of a TIM adopted by a data transmission method according to an embodiment of the present invention;

 3 is a schematic diagram of a bitmap hierarchical compression method of a TIM adopted by a data transmission method according to an embodiment of the present invention;

 4A is a schematic diagram of a bitmap hierarchical compression method for a TIM according to an embodiment of the present invention; FIG. 4B is a schematic diagram of a data transmission method applied to a hierarchical compression method according to an embodiment of the present invention;

 FIG. 5 is a schematic structural diagram of an access point according to an embodiment of the present invention. detailed description

 The technical solutions in the embodiments of the present invention will be clearly and completely described in the following with reference to the accompanying drawings in the embodiments. The method and the method for implementing the method of the embodiments of the present invention are applied to a wireless local area network system.

 1 is a schematic flow diagram of a data transmission method 100 in accordance with an embodiment of the present invention. As shown in Figure 1, method 100 includes:

 110: Identify a transmission indication mapping target bit in the TIM;

 120: Invert all or part of the target bit;

 130: Perform TIM compression on the TIM to obtain a compressed TIM;

 140: Send the compressed TIM to the site.

In order to compress the number of bits of the TIM transmitted in the beacon frame, this can be done with some auxiliary bits. The auxiliary bits here are called target bits. According to an embodiment of the present invention, Two types of target bits are defined: one is an idle bit, wherein the idle bit is a bit corresponding to an association identifier (AID) of a station that does not have downlink data to be transmitted in the current beacon period, and The bit corresponding to the AID that has not been allocated. Since no downlink data needs to be transmitted, the bits corresponding to the AIDs of these sites are generally set to zero. By inverting some or all of these idle bits, that is, by setting 1, the number of bits in the TIM can be compressed by means of a preset TIM compression. For example, the idle bit herein refers to a bit that satisfies one of the following conditions: AID is not allocated for the station; the site corresponding to the AID is in a dormant state; the site corresponding to the AID is not scheduled to be received in the current beacon period for downlink data reception; The site corresponding to the AID has notified the access point AP that the site does not require a TIM indication.

 The other is a delay bit, wherein the delay bit is a bit corresponding to the AID of the station currently transmitting downlink data but being scheduled to transmit after the current beacon period. In general, the bit corresponding to the AID of the station that currently has downlink data to send will be set to 1. In accordance with an embodiment of the invention, these delay bits are set to zero by negation. The number of bits in the TIM can then be compressed by means of a preset compression method. The examples are merely illustrative and are not intended to limit the scope of the embodiments of the invention.

 For example, in the TIM compression of the TIM, the compressed TIM process can be used in a hierarchical compression mode.

 For example, a hierarchical compression method is used in the embodiment of the present invention to compress a TIM portion in a beacon frame. This will be explained with reference to Fig. 2 below. The bitmap of the TIM part is divided into three levels according to the preset capacity: Page (Page), Block (Block), Sub-Block (Sub-Block). The bitmap corresponding to all sites is divided into several Pages, for example, 4 Pages, each Page includes several Blocks, for example, 32 Blocks, and each Block includes several Sub-blocks, for example, 8 Sub-blocks, and each Sub-block. It includes several bits, for example 8 bits, each of which indicates a station. In this way, the association identifier (Association Identity, AID) of each site can be indexed by the Page identifier, the Block identifier and the Sub-Block identifier, and the bit identifier of the AID in the corresponding Sub-block. Hereinafter, in order to describe the bill, the station having the downlink data is represented by 1 in the Sub-block, and the reference 1 in the Sub-block indicates that the station corresponding to the 1 bit has downlink data.

 In this case, the TIM part of the beacon frame contains the Page field and the Block offset field.

( Block offset ), block control ( Block Ctrl ) field, Block bitmap ( Block bitmap ) Field and Sub-block bitmap field. The Page field indicates the page where the site with the downlink data is located in the bitmap, the Block offset field indicates the offset of the block in which the site is located, and the Block Ctrl field indicates the mode used for the beacon transmission (below) Specifically, the Block bitmap field indicates the mapping position of the Sub-block in which the downlink data station is located in the Block to which it belongs, and the Sub-block bitmaps field indicates which bit is 1. For example, in a specific application, the Page field is 2 bits, the Block offset field is 5 bits, the Block Ctrl field is 3 bits, the Block bitmap field is 1 byte, and the Sub-block bitmaps field is variable in capacity. The following description will be made with reference to the specific example shown in FIG. 2.

 In Figure 3, the Block Ctrl field indicates that the beacon transmission is used in normal mode (Normal), and a bit in the Block bitmap field is 0, indicating that all stations in the corresponding Sub-block have no downlink data. Receive, if 1 is selected, it means that at least one station in the corresponding Sub-block has downlink data to be sent. When the block bitmap field contains n 1s, the TIM part will be accompanied by n Sub-blocks. Each bit in each Sub-block indicates the downlink data of a corresponding station, and the value 0 indicates no downlink data. A value of 1 indicates that there is downlink data.

 In the above method, when more than half of the Sub-blocks in a block are "Γ", the Block Ctrl can adopt the normal mode plus the inverse mode ("Normal + Inv"). As shown in Figure 3, the first pass Inverse operation (inverse) swaps "Γ and "0" in the block so that most of the Sub-blocks are all "0", and then use Block bitmap to indicate the case of Sub-block after the reverse, Block bitmap A value of 0 in the bit indicates that all of the inverted Sub-blocks are 0, and a value of 1 indicates that at least one of the inverted Sub-blocks is at least one. After the block bitmap field is placed, the reverse of the Sub-block indicated by 1 in the Block bitmap is placed.

 Referring to FIG. 4A, the 2-6th and 8th Sub-blocks in a block are all 1s, and after the block is inverted, only the 1st and 7th Sub-blocks have a bit of 1 . Therefore, the Block Ctrl of the TIM part is set to Normal+Inv, the Block bitmap is set to 1000 0010, and the subsequent Sub-block bitmap is 1101 0110, 1110 0000, which corresponds to the 1st and 7th Sub-blocks. After the station receives the beacon frame containing the TIM and performs the reverse operation, it can determine whether the downlink data needs to be received at the station.

 The method of the embodiment of the present invention may be specifically implemented in the following application scenarios:

Determining, by the first sub-block, the sub-block corresponding to the AID of the station that has the downlink data to be sent in the current beacon period, and the block to which the first sub-block belongs is the first block; Identifying idle bits in the first block, setting all or part of the idle bits to 1;

 Compress the first block in "Normal + Inv" mode;

 Determining that the sub-block containing the non-zero bit after the first block is inverted is the second sub-block;

 In the beacon frame, the second sub-block in the TIM is sent to the station.

 It should be noted that the terms "first block", "first sub-block" and "second sub-block" are merely used for the convenience of description, and do not represent any order or limitation.

 According to the above, the idle bit referred to herein corresponds to the idle AID, which refers to the AID that has not been assigned to any site; or although the AID has been assigned to a certain site, the site is in need of power saving. The current beacon transmission moment is in a dormant state; or although the AID has been assigned to a certain station, the station is not scheduled to receive downlink data reception within the current beacon period due to grouping or the like. For example, an access point schedules stations belonging to different groups to communicate within different beacon periods.

 According to an embodiment of the present invention, there is a site in the current beacon period where downlink data needs to be transmitted.

The sub-block corresponding to the AID is the first sub-block, and the block to which the first sub-block belongs is the first block. Referring to FIG. 4B, the idle bit corresponding to the idle AID is set to 1, and the number of Sub-blocks in which all bit values in the first block are taken 1 can be increased, and then the Sub-blocks are inverted and become bit values. The sub-block of 0 is not required to be transmitted in the TIM, and only the Sub-block containing the non-zero bit in the first block after the negation is required, which is referred to as the second Sub-block in the embodiment of the present invention. For example, the bit in the 4th Sub-block in the first block shown in FIG. 4B takes a value of 0 as an idle bit. By inverting the idle bit, the bits in the 4th Sub-block can be all 1. In this way, after the first block is negated, the 4th Sub-block that needs to be sent will not be sent because the value is all 0 after the negation. In the case of a large number of idle AIDs, this method can greatly reduce the number of Sub-blocks sent in the TIM. In this case, the TIM portion of the beacon frame includes a Block Ctrl field for instructing the station to negate the first block. After receiving the beacon frame, the station first determines according to the Block bitmap of the TIM part. If the corresponding bit of the sub-block corresponding to the AID of the station in the Block bitmap is 0, it indicates that the station has downlink data to receive. . If the corresponding bit of the Sub-block corresponding to the AID of the site is 1 in the block bitmap, after the Sub-block is inverted, it is determined whether the bit corresponding to the AID of the station is 1, and the value is 1 The site has downlink data to receive.

According to an alternative of the embodiment of the present invention, the access point may also achieve the effect of compressing the TIM by delaying the transmission of the downlink data of a part of the site. The delay mentioned here is delayed. The bit corresponding to the AID of the site of the data is the delay bit. For example, when most of the stations with downlink data are concentrated but a few downlink data stations are in relatively scattered bits, the access point may choose to delay the transmission of downlink data of the partially dispersed station, that is, the TIM of the current beacon frame. In the section, these delay bits are set to "0" by "Γ" to achieve the purpose of compressing the TIM.

 The method of the embodiment of the present invention may be specifically implemented in the following application scenarios:

 Determining delay bits in the first sub-block, the delay bits now taking a value of 1;

 Inverting all or part of the delay bits in the first sub-block, that is, all or part of the delay bits in the first sub-block are set to 0;

 Determining that the first sub-block containing non-zero bits is a second sub-block;

 In the beacon frame, the second sub-block in the TIM is sent to the station.

 For example, in the first sub-block, all delay bits in the first sub-block whose number of delay bits is less than or equal to the first threshold are inverted.

 For example, in the block to which the first sub-block belongs, all delay bits in the block whose number of delay bits is less than or equal to the second threshold are inverted.

 For example, in the page to which the first sub-block belongs, all delay bits in the page whose number of delay bits is less than or equal to the third threshold are inverted.

 In a specific application, if only one or less bits of a Sub-block have a value of 1, the bit can be set to 0 to delay the transmission of downlink data of the station corresponding to the one bit. The first threshold is 1. Those skilled in the art can set different first thresholds according to specific needs to achieve the desired purpose of compressing the TIM.

 Further, the access point may set the number of bits in the Block to which the first Sub-block belongs to 1 to be less than or equal to a preset second threshold, and all the bit positions in the block are 0, and then Determining that the first Sub-block containing non-zero bits is the second sub-block. That is to say, for example, referring to the above example, in the case where each Sub-block includes 8 bits and each block includes 8 Sub-blocks, if only one of the blocks is less than or equal to 4 bits, the value is 1 Then, all the bits of the block can be set to 0 to delay the transmission of downlink data belonging to all stations of the block. At this time, the preset second threshold is 4. A person skilled in the art can set different second thresholds according to specific needs to achieve the desired purpose of compressing the TIM.

In addition, the access point sets the number of bits in the Page to which the first Sub-block belongs to 1 to be less than or equal to a preset third threshold, and all the bit positions in the Page are 0, and then determines to include non- The first Sub-block of 0 bits is the second Sub-block. For example, refer to For example, if each Sub-block includes 8 bits, and each Page includes 32 blocks, and each block includes 8 Sub-blocks, if there is only 32 bits in a Page, the value is 1 or less. , the entire page bit can be set to 0 to delay the transmission of downlink data belonging to all stations of the Page. At this time, the preset second threshold is 32. A person skilled in the art can set different third thresholds according to specific needs to achieve the desired purpose of compressing the TIM.

 According to the embodiment of the present invention, the bit compression of the TIM is further reduced by using the idle bit or the delay bit to further reduce the redundancy bit in the TIM, thereby improving the compression effect, thereby improving the transmission efficiency of the TIM and reducing the overhead of the access point. Improve the performance of the network system.

 An access point for implementing the method of an embodiment of the present invention is also proposed in accordance with an embodiment of the present invention. FIG. 5 is a schematic block diagram of an access point 500 in accordance with an embodiment of the present invention. The access point 500 includes: an identifying unit 510, configured to identify a target bit in the transmission indication mapping TIM;

 The processing unit 520 is configured to invert all or part of the target bit;

 a compression unit 530, configured to perform TIM compression on the TIM to obtain a compressed TIM;

 The sending unit 540 is configured to send the compressed TIM to the station;

 According to an embodiment of the present invention, the target bit is an idle bit, where the idle bit is a bit corresponding to an association identifier AID of a station that has no downlink data to be transmitted in a current beacon period, and an AID corresponding to the AID that has not been allocated. Bit.

 According to an embodiment of the invention, the idle bit comprises a bit corresponding to an AID of a station that satisfies one of the following conditions:

 The AID is not allocated for the site;

 The site corresponding to the AID is in a dormant state;

 The station corresponding to the AID is not scheduled to receive downlink data in the current beacon period; the station corresponding to the AID has notified the AP that it does not need the TIM indication.

 According to an embodiment of the present invention, the target bit is a delay bit, wherein the delay bit is a bit corresponding to an AID of a station that is currently transmitting downlink data but is scheduled to be transmitted after the current beacon period.

 According to the embodiment of the present invention, the compression unit 530 performs TIM compression on the TIM to obtain a compressed TIM process, and uses a hierarchical compression method.

According to the embodiment of the present invention, the compression unit 530 performs TIM compression on the TIM to obtain a compressed TIM process, and adopts a hierarchical compression mode, wherein all bits in the TIM are large in capacity. The sub-block corresponding to the AID of the station that has downlink data to be sent in the current beacon period is the first sub-block, and the block to which the first sub-block belongs is the first. Blocking unit 510 is configured to identify idle bits in the first block;

 The processing unit 520 is configured to invert all or part of the idle bits in the first block;

 The compressing unit 530 is configured to determine that the sub-block that includes the non-zero bit after the first block is inverted is the second sub-block;

 The sending unit 540 is configured to send the second sub-block in the TIM to the station. According to the embodiment of the present invention, the compression unit 530 performs TIM compression on the TIM to obtain a compressed TIM process, and adopts a hierarchical compression mode, wherein all bits in the TIM are divided into three levels according to the capacity: a page, a block, and a sub-block, where The sub-block corresponding to the AID of the station that needs to send the downlink data in the current beacon period is the first sub-block,

 The identifying unit 510 is configured to determine a delay bit in the first sub-block;

 The processing unit 520 is configured to invert all or part of the delay bits in the first sub-block;

 The compressing unit 530 is configured to determine that the first sub-block that includes non-zero bits is a second sub-block; and the sending unit 540 is configured to send the second sub-block in the TIM to the station. According to an embodiment of the present invention, in the first sub-block, the processing unit 520 is configured to invert all delay bits in the first sub-block with the number of delay bits being less than or equal to a first threshold; In an embodiment of the invention, in the block to which the first sub-block belongs, the processing unit 520 is configured to invert all delay bits in the block whose number of delay bits is less than or equal to a second threshold.

 According to an embodiment of the present invention, in the page to which the first sub-block belongs, the processing unit 520 is configured to invert all delay bits in the page whose number of delay bits is less than or equal to a third threshold.

 Those of ordinary skill in the art will appreciate that the elements and algorithm steps of the various examples described in connection with the embodiments disclosed herein can be implemented in a combination of electronic hardware or computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specifics of the technical solutions to achieve the described functions, but such implementations are not considered to be beyond the scope of the present invention.

It will be apparent to those skilled in the art that for the convenience and cleanness of the description, the specific working processes of the systems, devices and units described above may be referred to the corresponding embodiments in the foregoing method embodiments. The process is not repeated here.

 In the several embodiments provided herein, it should be understood that the disclosed systems, devices, and methods may be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the unit is only a logical function division. In actual implementation, there may be another division manner, for example, multiple units or components may be combined or Can be integrated into another system, or some features can be ignored, or not executed. In addition, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interface, device or unit, and may be electrical, mechanical or otherwise. The components displayed for the unit may or may not be physical units, ie may be located in one place, or may be distributed over multiple network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solution of the embodiment.

 In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

 The functions, if implemented in the form of software functional units and sold or used as separate products, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention, which is essential to the prior art or part of the technical solution, may be embodied in the form of a software product stored in a storage medium, including A plurality of instructions are used to make a computer device (which may be a personal computer, a server, and the storage medium includes: a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM, a random access memory). Memory ), a variety of media such as a disk or a disc that can store program code.

 The above is only the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think of changes or substitutions within the technical scope of the present invention. It should be covered by the scope of the present invention. Therefore, the scope of the invention should be determined by the scope of the claims.

Claims

Rights request  A data transmission method, the method comprising:  Identifying the target bit in the transmission indication mapping TIM;  Invert all or part of the target bit;  Perform TIM compression on the TIM to obtain a compressed TIM;  Sending the compressed TIM to the site.  2. The method according to claim 1, wherein the target bit is an idle bit, wherein the idle bit is a bit corresponding to an association identifier AID of a station that does not have downlink data to be transmitted in a current beacon period. And the bit corresponding to the AID that has not been allocated.  3. The method according to claim 2, wherein the idle bit comprises a bit corresponding to an AID of a station that satisfies one of the following conditions:  The AID is not allocated for the site;  The site corresponding to the AID is in a dormant state;  The site corresponding to the AID is not scheduled to receive downlink data in the current beacon period; the site corresponding to the AID has notified the access point AP that the site does not need the TIM indication.  4. The method according to claim 1, wherein the target bit is a delay bit, wherein the delay bit is a station that currently has downlink data to transmit but is scheduled to transmit after the current beacon period. The bit corresponding to the AID.  The method according to claim 1, wherein the TIM compression is performed on the TIM to obtain a compressed TIM process, and the hierarchical compression mode is adopted.  6. The method of claim 2, wherein  The TIM compression is performed on the TIM, and the compressed TIM process is performed by using a hierarchical compression method, wherein all bits in the TIM are divided into three levels according to the capacity: a page, a block, and a sub-block, wherein the current beacon period has a downlink. The sub-block corresponding to the AID of the site to which the data needs to be sent is the first sub-block, and the block to which the first sub-block belongs is the first block;  The identifying the transmission indication mapping target bits in the TIM, including:  Identifying idle bits in the first block;  The inverting all or part of the target bit includes:  Inverting all or part of the idle bits in the first block; Performing TIM compression on the TIM to obtain the compressed TIM includes: Determining, after the first block is inverted, the sub-block that includes the non-zero bit is the second sub-block; the sending the compressed TIM to the station includes:  Sending the second sub-block in the TIM to the station.  7. The method of claim 4, wherein  The TIM compression is performed on the TIM, and the compressed TIM process is performed by using a hierarchical compression method, wherein all bits in the TIM are divided into three levels according to the capacity: a page, a block, and a sub-block, wherein the current beacon period has a downlink. The sub-block corresponding to the AID of the site to which the data needs to be sent is the first sub-block.  The identifying the transmission indication mapping target bits in the TIM, including:  Determining a delay bit in the first sub-block;  The inverting all or part of the target bit includes:  Inverting all or part of the delay bits in the first sub-block;  The TIM is compressed by the TIM to obtain a compressed TIM, including:  Determining that the first sub-block containing non-zero bits is a second sub-block;  The sending the compressed TIM to the station includes:  Sending the second sub-block in the TIM to the station.  8. The method of claim 7 wherein:  The inverting all or part of the delay bits in the first sub-block includes: in the first sub-block, the first sub-block in which the number of delay bits is less than or equal to a first threshold All delay bits are inverted;  9. The method of claim 7 wherein:  The inverting the delay bit of all or part of the first sub-block includes: in the block to which the first sub-block belongs, the number of the delay bits is less than or equal to a second threshold All delay bits are negated.  10. The method of claim 7 wherein:  The inverting the delay bit of all or part of the first sub-block includes: in the page to which the first sub-block belongs, the number of the delay bits is less than or equal to a third threshold in the page All delay bits are negated.  An access point, where the access point includes:  An identifying unit, configured to identify a target bit in the transmission indication mapping TIM; a processing unit, configured to invert all or part of the target bit; a compression unit, configured to perform TIM compression on the TIM to obtain a compressed TIM;  And a sending unit, configured to send the compressed TIM to the station.  12. The access point according to claim 11, wherein the target bit is an idle bit, wherein the idle bit is a station that does not have downlink data to be transmitted within a current beacon period. 13. The access point of claim 12, wherein the idle bit comprises a bit corresponding to an AID of a station that satisfies one of the following conditions:  The AID is not allocated for the site;  The site corresponding to the AID is in a dormant state;  The station corresponding to the AID is not scheduled to receive downlink data in the current beacon period; the station corresponding to the AID notifies the access point AP that the station does not need the TIM indication.  The access point according to claim 11, wherein the target bit is a delay bit, wherein the delay bit is that there is currently downlink data to be transmitted, but is scheduled to be sent after the current beacon period. The bit corresponding to the AID of the site.  The access point according to claim 11, wherein the compression unit performs a TIM compression on the TIM to obtain a compressed TIM process, and uses a hierarchical compression method.  16. The access point of claim 12, wherein  The compression unit performs TIM compression on the TIM to obtain a compressed TIM process, and adopts a hierarchical compression mode, wherein all bits in the TIM are divided into three levels according to the capacity: pages, blocks, sub-blocks, where the current beacon period The sub-block corresponding to the AID of the site in which the downlink data needs to be sent is the first sub-block, and the block to which the first sub-block belongs is the first block;  The identifying unit is configured to identify idle bits in the first block;  The processing unit is configured to invert all or part of the idle bits in the first block; the compression unit is configured to determine that the first block is inverted and the sub-block containing non-zero bits is the second sub-block Piece;  The sending unit is configured to send the second sub-block in the TIM to the station.  17. The access point of claim 14 wherein: The compression unit performs TIM compression on the TIM to obtain a compressed TIM process, and adopts a hierarchical compression mode, wherein all bits in the TIM are divided into three levels according to the capacity: pages, blocks, sub-blocks, where the current beacon period The sub-block corresponding to the AID of the site in which the downlink data needs to be sent is the first sub-block, The identifying unit is configured to determine a delay bit in the first sub-block;  The processing unit is configured to invert all or part of delay bits in the first sub-block; the compression unit is configured to determine that the first sub-block that includes non-zero bits is a second sub-block; The sending unit is configured to send the second sub-block in the TIM to the station.  18. The access point of claim 17 wherein:  In the first sub-block, the processing unit is configured to invert all delay bits in the first sub-block whose number of delay bits is less than or equal to a first threshold;  19. The access point of claim 17 wherein:  In the block to which the first sub-block belongs, the processing unit is configured to invert all delay bits in the block whose number of delay bits is less than or equal to the second threshold.  20. The access point of claim 17 wherein:  In the face to which the first sub-block belongs, the processing unit is configured to invert all delay bits in the page whose number of delay bits is less than or equal to a third threshold.