Access point and terminal

Abstract

This access point includes a management unit. In response to a request for transmission of traffic from a terminal, the management unit transmits an inquiry frame for inquiring of a plurality of subordinate terminals whether there is occurrence of low-delay traffic for which a low delay is required. When it is found by a response to the inquiry frame that a low-delay terminal exists in which there is occurrence of low-delay traffic, a resource unit (RU) is preferentially allocated to the low-delay terminal, and a trigger frame including information on the RU allocation is transmitted to at least the low-delay terminal.

Description

Access points and terminals

[0001] The embodiments relate to an access point and a terminal.

[0002] A wireless LAN (Local Area Network) is known as a system for wirelessly connecting an access point (AP) and a terminal (STA). The IEEE 802.11be standard, a wireless LAN standard currently being developed, is studying a method for transmitting low-latency traffic, which requires low latency, with low latency. As one method for transmitting low-latency traffic with low latency, a method is being studied in which a transmission opportunity (TXOP) is granted to a STA that generates low-latency traffic immediately after receiving a request from the STA.

[0003] Daniel Verenzuela et al., “Overlapped Indication to Support Preemption”, IEEE 802.11-23 / 1194r0, July 2023

[0004] Low-delay traffic that requires low latency may occur not only periodically but also aperiodically. Even when aperiodic low-delay traffic occurs, it is required to provide an appropriate TXOP.

[0005] The embodiment provides an access point that can appropriately grant a TXOP even when aperiodic low-latency traffic occurs, and a terminal that can communicate with the access point.

[0006] In one aspect, the access point includes a management unit that, in response to a request for traffic transmission from a terminal, transmits an inquiry frame to a plurality of terminals under its control to inquire whether low-latency traffic requiring low latency is occurring, and if a low-latency terminal is found to be experiencing low-latency traffic in response to the inquiry frame, allocates resource units (RUs) preferentially to the low-latency terminal and transmits a trigger frame including information on the allocation of the RUs to at least the low-latency terminal.

[0007] According to the embodiment, an access point that can appropriately grant a TXOP even when aperiodic low-latency traffic occurs, and a terminal that can communicate with the access point are provided.

[0008] FIG. 1 is a block diagram showing an example of the configuration of a communication system according to each embodiment. FIG. 2 is a block diagram showing an example of the hardware configuration of an AP. FIG. 3 is a block diagram showing an example of the hardware configuration of a terminal. FIG. 4 is a block diagram showing an example of the functional configuration of an AP according to the first embodiment. FIG. 5 is a diagram showing an example of RU allocation in OFDMA transmission using a 20 MHz channel, as an example of RU allocation in OFDMA transmission. FIG. 6 is a conceptual diagram of a trigger frame using an OFDMA frame according to the first embodiment. FIG. 7 is a block diagram showing an example of the functional configuration of a terminal according to the first embodiment. FIG. 8 is a flowchart showing the operation of an AP in UL-OFDMA transmission according to the first embodiment. FIG. 9 is a flowchart showing the operation of each terminal in UL-OFDMA transmission according to the first embodiment. FIG. 10 is a timing chart showing the operation in UL-OFDMA transmission according to the first embodiment. FIG. 11 is a block diagram showing an example of the functional configuration of an AP according to the second embodiment. FIG. 12 is a block diagram showing an example of the functional configuration of a terminal according to the second embodiment. FIG. 13 is a flowchart showing the operation of the AP according to the second embodiment. FIG. 14 is a flowchart showing the operation of a terminal according to the second embodiment. Fig. 15 is a timing chart showing the operation of data transmission in the second embodiment. Fig. 16 is a timing chart showing the operation of data transmission in a modified example of the second embodiment.

[0009] Hereinafter, an embodiment will be described with reference to the drawings.

[0010] First Embodiment First, the first embodiment will be described. Fig. 1 is a block diagram showing an example of the configuration of a communication system according to each embodiment. As shown in Fig. 1, the communication system 1 includes an access point (AP) 10, terminals 20-1, 20-2, ..., 20-N, and a network 30.

[0011] The AP 10 and the terminals 20-1, 20-2, ..., 20-N have wireless communication functions based on, for example, the OSI (Open Systems Interconnection) reference model. In the OSI reference model, wireless communication functions are divided into seven layers (Layer 1: Physical Layer, Layer 2: Data Link Layer, Layer 3: Network Layer, Layer 4: Transport Layer, Layer 5: Session Layer, Layer 6: Presentation Layer, and Layer 7: Application Layer). The data link layer includes a Logical Link Control (LLC) sublayer and a Media Access Control (MAC) sublayer.

[0012] In the first embodiment, the AP 10 and terminals 20-1, 20-2, ..., 20-N support UL-OFDMA transmission. OFDMA is a method that combines orthogonal frequency division multiplexing (OFDM) and frequency division multiple access (FDMA). OFDM is a method of transmitting by dividing a channel bandwidth allocated for wireless communication into multiple subcarriers. In OFDM, subcarrier allocation for multiple STAs is performed in units of RU (resource unit), which is a grouping of subcarriers that make up one channel. By combining this with FDMA, OFDMA can finely change the subcarrier allocation depending on the radio wave conditions of each STA. This enables many-to-one transmission from multiple STAs to the AP, and therefore OFDMA can improve radio wave utilization efficiency compared to OFDM. Furthermore, the AP 10 and the terminals 20-1, 20-2, . . . , 20-N may support a DRU (distributed RU) that configures an RU using discretely allocated subcarriers during UL-OFDMA transmission.

[0013] Terminals 20-1, 20-2, ..., 20-N are N terminals. N is a natural number, typically an integer equal to or greater than 2. Terminals 20-1, 20-2, ..., 20-N can exchange traffic with AP 10. Terminals 20-1, 20-2, ..., 20-N are, for example, smartphones or PCs (personal computers), and are wireless terminals conforming to the IEEE 802.11 standard. In the following, terminals 20-1, 20-2, ..., 20-N have the same configuration. In the following, when there is no particular need to distinguish between terminals 20-1, 20-2, ..., 20-N, they may be referred to as terminals 20.

[0014] Next, the hardware configuration of the AP and the terminal in the communication system according to each embodiment will be described.

[0015] 2 is a block diagram showing an example of the hardware configuration of an AP 10. As shown in FIG. 2, the AP 10 includes, for example, a central processing unit (CPU) 11, a read only memory (ROM) 12, a random access memory (RAM) 13, a wireless communication module 14, and a wired communication module 15.

[0016] The CPU 11 is a processing circuit that controls the overall operation of the AP 10. The ROM 12 is, for example, a non-volatile semiconductor memory. The ROM 12 stores programs and data for controlling the AP 10. The RAM 13 is, for example, a volatile semiconductor memory. The RAM 13 is used as a work area for the CPU 11. The wireless communication module 14 is a circuit used to send and receive data via wireless signals. The wireless communication module 14 is connected to an antenna. The wired communication module 15 is a circuit used to send and receive data via wired signals. The wired communication module 15 is connected to the network 30.

[0017] Although the wired communication module 15 is described as a means for connecting the AP 10 and the network 30, a wireless communication module different from the wireless communication module 14 may alternatively be used, or the wireless communication module 14 may communicate with the network 30 during times when it is not communicating with the terminal 20.

[0018] 3 is a block diagram showing an example of the hardware configuration of the terminal 20. As shown in FIG. 3, the terminal 20 includes, for example, a CPU 21, a ROM 22, a RAM 23, a wireless communication module 24, a display 25, and a storage 26.

[0019] The CPU 21 is a processing circuit that controls the overall operation of the terminal 20. The ROM 22 is, for example, a non-volatile semiconductor memory. The ROM 22 stores programs and data for controlling the terminal 20. The RAM 23 is, for example, a volatile semiconductor memory. The RAM 23 is used as a working area for the CPU 21. The wireless communication module 24 is a circuit used for transmitting and receiving data via wireless signals. The wireless communication module 24 is connected to an antenna. The display 25 is, for example, an LCD (liquid crystal display) or an EL (electro-luminescence) display. The display 25 displays a GUI (graphical user interface) corresponding to application software, etc. The storage 26 is a non-volatile storage device. The storage 26 stores system software, etc. of the terminal 20.

[0020] Next, the functional configuration of the AP and the terminal in the communication system according to the first embodiment will be described.

[0021] 4 is a block diagram showing an example of the functional configuration of an AP according to the first embodiment. The AP 10 functions as a computer including a data processing unit 110, a frame processing unit 120, a management unit 130, and a radio signal processing unit 140. The data processing unit 110 is a functional block that executes processing corresponding to the LLC sublayer of layer 2 and layers 3 to 7. The frame processing unit 120 and the management unit 130 are functional blocks that execute processing corresponding to the MAC sublayer of layer 2. The radio signal processing unit 140 is a functional block that executes processing corresponding to layer 1.

[0022] The data processing unit 110 outputs data input from the network 30 via the LLC layer to the frame processing unit 120. The data processing unit 110 also outputs data input from the frame processing unit 120 to the network 30 via the LLC layer.

[0023] When data is input to frame processing unit 120 from data processing unit 110 or management unit 130, frame processing unit 120 adds a MAC header to the input data to generate a MAC frame. Frame processing unit 120 then outputs the MAC frame to radio signal processing unit 140. When a MAC frame is input from radio signal processing unit 140, frame processing unit 120 extracts data from the MAC frame and outputs the extracted data to data processing unit 110 or management unit 130 depending on the type of MAC frame. Specifically, when the MAC frame is a data frame, frame processing unit 120 inputs the data to data processing unit 110. When the MAC frame is a management frame or a control frame, frame processing unit 120 inputs the data to management unit 130.

[0024] The management unit 130 controls the logical wireless connection between the AP 10 and the terminal 20. For example, the management unit 130 executes wireless connection processing in response to an association request from the terminal 20. The management unit 130 also has a TXOP management unit 131. The TXOP management unit 131 acquires a TXOP in response to a request from the terminal 20 and also provides the acquired TXOP to the terminal 20. The TXOP is provided by transmitting a trigger frame to the terminal 20. The TXOP management unit 131 can allocate TXOPs to multiple terminals 20 simultaneously by using OFDMA frames.

[0025] FIG. 5 is a diagram showing an example of RU allocation in OFDMA transmission using a 20 MHz channel, as an example of RU allocation in OFDMA transmission. Currently, the IEEE 802.11 standard defines a total of four patterns of RU allocation. The pattern in the first row from the top of FIG. 5 is an example in which nine RUs are allocated to a 20 MHz channel. Each of the nine RUs is configured with 26 subcarriers. However, one of the nine RUs is configured with two 13 subcarriers sandwiched between a DC subcarrier, as shown as Middle-26-tone RU. This first row pattern allows simultaneous transmission by nine terminals (STAs). Furthermore, the pattern in the second row from the top of FIG. 5 is an example in which five RUs are allocated to a 20 MHz channel. Of the five RUs, four are each configured with 52 subcarriers. The remaining RU, designated as Middle-26-tone RU, is composed of two 13-tone subcarriers with a DC subcarrier sandwiched between them. This second-stage pattern allows simultaneous transmission by five terminals (STAs). The same applies to the third-stage and fourth-stage patterns.

[0026] In OFDMA transmission, a trigger frame is transmitted to each terminal to synchronize transmission timing from multiple terminals. Fig. 6 is a conceptual diagram of a trigger frame using an OFDMA frame in the first embodiment. In the example of Fig. 6, a trigger frame addressed to each terminal is included in three subcarriers. The trigger frame addressed to each terminal may include, for example, information indicating whether the terminal belongs to a member of OFDMA transmission, information on the number of RUs allocated proportional to the bandwidth requested by each terminal, and information on the maximum frame length according to the allowable delay when low-latency traffic occurs in the terminal.

[0027] In the first embodiment, when the TXOP management unit 131 acquires a transmission right, it transmits a trigger frame to the subordinate terminals 20, thereby granting TXOPs to all the subordinate terminals 20 at once. Prior to this, the TXOP management unit 131 inquires the subordinate terminals 20 as to whether low-latency traffic is occurring. Low-latency traffic is traffic that requires low latency. Hereinafter, low-latency traffic may be referred to as LL traffic, a terminal 20 in which low-latency traffic is occurring may be referred to as an LL terminal, and a terminal 20 in which low-latency traffic is not occurring may be referred to as an NLL terminal. When LL traffic is occurring in the terminal 20, the terminal 20 responds to that effect to the AP 10. At this time, the terminal 20 may transmit information on the required bandwidth required for transmitting LL traffic or information indicating the required bandwidth, and information on the maximum delay that can be tolerated in transmitting LL traffic.

[0028] If there is an LL terminal, the TXOP management unit 131 preferentially allocates RUs to the LL terminal. Furthermore, if the LL terminal transmits information on the required bandwidth and maximum delay, the TXOP management unit 131 allocates RUs to each terminal 20 so as to satisfy the required bandwidth and maximum delay conditions. If necessary, the TXOP management unit 131 may change the RU allocation pattern. If the RU allocation pattern is changed, the number of terminals 20 that can transmit simultaneously may vary. If simultaneous transmission is not possible for all terminals 20 that have requested transmission, the TXOP management unit 131 may not allocate RUs to some NLL terminals. In this case, the TXOP management unit 131 may notify the NLL terminals to which no RUs have been allocated that the transmission of the NLL terminals is not permitted by a response frame in response to the receipt of the inquiry result. The NLL terminals to which no RU is assigned may be determined according to the priority of the traffic to be transmitted, which is determined by, for example, a TID (Traffic Identifier).

[0029] Returning now to the description of FIG. 4 , the radio signal processing unit 140 generates a radio frame by adding a preamble and the like to the MAC frame input from the frame processing unit 120. The radio signal processing unit 140 converts the generated radio frame into a radio signal. The radio signal processing unit 140 then radiates (transmits) the converted radio signal via an antenna. The radio signal processing unit 140 may also assign an OFDMA frame to a subcarrier based on the RU assignment and transmit the assigned subcarrier. The radio signal processing unit 140 may also transmit a trigger frame for UL-OFDMA transmission shown in FIG. 6 . The conversion process from a radio frame to a radio signal includes, for example, convolutional coding, interleaving, subcarrier modulation, inverse fast Fourier transform, OFDM modulation, and frequency conversion. The radio signal processing unit 140 also converts a radio signal received via an antenna into a radio frame. The radio signal processing unit 140 extracts a MAC frame from the converted radio frame. Then, radio signal processing unit 140 outputs the extracted MAC frame to frame processing unit 120. The conversion process from a radio signal to a radio frame includes, for example, frequency conversion processing, OFDM demodulation processing, fast Fourier transform processing, subcarrier demodulation processing, deinterleaving processing, and Viterbi decoding processing.

[0030] 7 is a block diagram showing an example of the functional configuration of a terminal according to the first embodiment. The terminal 20 functions as a computer including a data processing unit 210, a frame processing unit 220, a management unit 230, a radio signal processing unit 240, and an application execution unit 250. The data processing unit 210 and the application execution unit 250 are functional blocks that execute processes corresponding to the LLC sublayer of layer 2 and layers 3 to 7. The frame processing unit 220 and the management unit 230 are functional blocks that execute processes corresponding to the MAC sublayer of layer 2. The radio signal processing unit 240 is a functional block that executes processes corresponding to layer 1.

[0031] The data processing unit 210 outputs data input from the application execution unit 250 via the LLC layer to the frame processing unit 220. The data processing unit 210 also outputs data input from the frame processing unit 220 to the application execution unit 250 via the LLC layer.

[0032] When data is input to frame processing unit 220 from data processing unit 210 or management unit 230, frame processing unit 220 adds a MAC header to the input data to generate a MAC frame. Frame processing unit 220 then outputs the MAC frame to radio signal processing unit 240. When a MAC frame is input from radio signal processing unit 240, frame processing unit 220 extracts data from the MAC frame and outputs the extracted data to data processing unit 210 or management unit 230 depending on the type of MAC frame. Specifically, when the MAC frame is a data frame, frame processing unit 220 inputs the data to data processing unit 210. When the MAC frame is a management frame or a control frame, frame processing unit 220 inputs the data to management unit 230.

[0033] The management unit 230 controls the logical wireless connection between the terminal 20 and the AP 10. For example, the management unit 230 generates an association request based on a beacon frame from the AP 10. The management unit 230 can store information on the RU assigned to each terminal.

[0034] The radio signal processing unit 240 generates a radio frame by adding a preamble and the like to the MAC frame input from the frame processing unit 220. The radio signal processing unit 240 converts the generated radio frame into a radio signal. The radio signal processing unit 240 then radiates (transmits) the converted radio signal via an antenna. The radio signal processing unit 240 may also assign the OFDMA frame to subcarriers based on the RU assignment and transmit the subcarriers. The conversion process from the radio frame to the radio signal includes, for example, convolutional coding, interleaving, subcarrier modulation, inverse fast Fourier transform, OFDM modulation, and frequency conversion. The radio signal processing unit 240 also converts the radio signal received via the antenna into a radio frame. The conversion process from the radio signal to the radio frame includes, for example, frequency conversion, OFDM demodulation, fast Fourier transform, subcarrier demodulation, deinterleaving, and Viterbi decoding. The radio signal processing unit 240 extracts a MAC frame from the converted radio frame. Then, the radio signal processing unit 240 outputs the extracted MAC frame to the frame processing unit 220 .

[0035] The application execution unit 250 executes an application based on data input from the data processing unit 210. The application execution unit 250 also inputs data to the data processing unit 210. For example, the application execution unit 250 can display application information on the display 25. The application execution unit 250 can also operate based on operations on an input interface.

[0036] Next, the operation of UL-OFDMA transmission in the communication system according to the first embodiment will be described. Fig. 8 is a flowchart showing the operation of the AP 10 in UL-OFDMA transmission in the first embodiment. Here, it is assumed that prior to the operation of Fig. 8, the AP 10 has acquired the right to transmit a wireless signal for granting a TXOP to the terminal 20 that made the request, for example, in response to a request from the terminal 20. In other words, it is assumed that the AP 10 has performed a CCA (Clear Channel Assessment) operation and confirmed that the channel used for UL-OFDMA transmission is not in use.

[0037] In step S1, the AP 10 broadcasts an inquiry frame using the wireless signal processing unit 140. The inquiry frame is a frame for inquiring whether LL traffic is occurring. The inquiry frame is received by N terminals 20 under the control of the AP 10. The inquiry frame is, for example, a beacon frame. The inquiry frame may be any frame other than a beacon frame.

[0038] In step S2, the AP 10 receives requests from the subordinate terminals 20 as query results from each of the subordinate terminals 20. The query results may be received only for a certain period of time. When the AP 10 has received query results from all of the subordinate terminals 20 within the certain period of time, or when the certain period has elapsed even if the AP 10 has not received query results from all of the subordinate terminals 20, the process proceeds to step S3.

[0039] In step S3, the AP 10 transmits a response frame including information indicating that the inquiry result has been received to the subordinate terminals 20. The response frame includes information on whether transmission is permitted or not permitted for each terminal 20. The response frame may be transmitted to multiple terminals 20 collectively using OFDMA frames, or may be transmitted to each terminal 20 individually.

[0040] In step S4, the AP 10 generates trigger frames addressed to each terminal 20 using OFDMA frames in response to the inquiry result, and transmits the trigger frames to each terminal 20 using the radio signal processing unit 140. The trigger frame addressed to each terminal may include information indicating whether it belongs to a member of OFDMA transmission, information on the number of RUs allocated proportional to the bandwidth requested by each terminal, and information on the maximum frame length according to the allowable delay when low-latency traffic occurs in the terminal. Here, if there is an LL terminal, the RU is preferentially allocated to that LL terminal, and the maximum frame length is set to be equal to or less than the allowable maximum delay transmitted from that LL terminal.

[0041] In step S5, the AP 10 receives data frames (OFDMA frames) from each terminal 20. If a data frame has been received from each terminal 20, the process proceeds to step S6. Note that if a data frame has not been received within a predetermined period, the process of FIG. 8 may be terminated.

[0042] In step S6, the AP 10 checks whether the data frames received from each terminal 20 have been received correctly, and transmits the check result to each terminal 20 as a block ACK (BACK). The processing in FIG. 8 then ends. Depending on the result of the BACK, a retransmission process or the like may be performed. The retransmission process is omitted in FIG. 8. The AP 10 may also perform various processes in response to the data frames received from each terminal 20. The processing in response to the data frames is also omitted in FIG. 8.

[0043] 9 is a flowchart showing the operation of each terminal 20 in UL-OFDMA transmission in the first embodiment. In step S11, the terminal 20 determines whether traffic to be transmitted to the AP 10 has occurred. If it is determined in step S11 that traffic has occurred, the process proceeds to step S12. If it is determined in step S11 that traffic has not occurred, the process proceeds to step S13.

[0044] In step S12, the terminal 20 uses the wireless signal processing unit 240 to transmit a request to the AP 10 to transmit a wireless signal.

[0045] In step S13, the terminal 20 receives an inquiry frame from the AP 10. Thereafter, the terminal 20 proceeds to step S14. Note that if the terminal 20 is unable to receive an inquiry frame from the AP 10, the processing of FIG. 9 may be terminated.

[0046] In step S14, the terminal 20 determines whether LL traffic is occurring. If it is determined in step S14 that LL traffic is occurring, the process proceeds to step S15. If it is determined in step S14 that LL traffic is not occurring, the process proceeds to step S16.

[0047] In step S15, the terminal 20 transmits a request for transmitting LL traffic, including information on the inquiry result. Then, the process proceeds to step S17. The information on the inquiry result includes information indicating that LL traffic is occurring. The request may include information on the required bandwidth required for transmitting the LL traffic or information indicating the required bandwidth, and information on the maximum delay that can be tolerated in transmitting the LL traffic.

[0048] In step S16, the terminal 20 transmits a request for transmitting non-LL traffic, including information on the inquiry result. Then, the process proceeds to step S17. The information on the inquiry result includes information indicating that no LL traffic is occurring. Note that the terminal 20 that transmitted the request in step S12 does not need to transmit the request again in step S16.

[0049] In step S17, the terminal 20 receives a response frame from the AP 10. If the response frame is not received within a predetermined period, the processing in Fig. 9 may be terminated.

[0050] In step S18, the terminal 20 determines whether or not the transmission of the data frame has been permitted by the AP 10. If the transmission of the data frame has been permitted in step S18, the process proceeds to step S19. If the transmission of the data frame has not been permitted in step S18, the process in Fig. 9 ends. In this case, the terminal 20 may transmit a request to the AP 10 to transmit the data frame again.

[0051] In step S19, the terminal 20 waits until a trigger frame is received. If the trigger frame is not received within a predetermined period or if a frame other than the trigger frame is received, the terminal 20 may proceed to processing the received frame and end the processing in Fig. 9. Furthermore, even if the trigger frame is received, the processing in Fig. 9 also ends if the terminal 20 is not included in the members that perform OFDMA transmission. In step S19, if the trigger frame is received and the terminal 20 is included in the members, the processing proceeds to step S20.

[0052] In step S20, after waiting a predetermined interval from the trigger frame, the terminal 20 transmits a radio signal including a data frame (OFDMA frame) using the radio signal processing unit 240. The predetermined interval is, for example, a Short Inter Frame Space (SIFS).

[0053] In step S21, the terminal 20 receives BACK from the AP 10. In step S21, if the terminal 20 receives BACK from the AP 10, it considers that the data frame it transmitted has been delivered. In step S21, if the terminal 20 cannot confirm receipt of BACK, it considers that the data frame it transmitted has not been delivered. When either of these confirmations is made, the processing in FIG. 9 ends. Here, depending on the result of the BACK, retransmission processing or the like is performed. In FIG. 9, the retransmission processing is omitted.

[0054] 10 is a timing chart showing the operation of UL-OFDMA transmission in the first embodiment. Here, FIG. 10 shows the operation of UL-OFDMA transmission by an AP, one NLL terminal, and one LL terminal. Meanwhile, the number of NLL terminals and the number of LL terminals are not limited to one.

[0055] When traffic occurs that should be transmitted to the AP, the terminal transmits a request for transmitting a data frame to the AP. In Fig. 10, traffic occurs in a certain NLL terminal, and this NLL terminal transmits a request Req to the AP.

[0056] When an AP receives a request from a terminal, it performs a CCA operation to acquire the right to transmit. The AP then transmits an inquiry frame Pol to the terminals under its control. In Figure 10, the AP transmits an inquiry frame Pol to the NLL terminal that sent the request and to the LL terminal.

[0057] Each terminal that receives the inquiry frame Pol transmits a request including information on the inquiry result to the AP. In Fig. 10, the NLL terminal transmits a request Req including information that no LL traffic is occurring to the AP. On the other hand, the LL terminal transmits a request Req including information that LL traffic is occurring to the AP. Here, as described above, the terminal that previously transmitted the request Req may omit transmitting the request Req at this timing. To indicate that the transmission of the request Req can be omitted, the request Req transmitted by the NLL terminal at this timing is indicated by a dashed line in Fig. 10.

[0058] The AP, which receives the request Req containing the inquiry result information, recognizes that LL traffic is occurring. The AP then allocates RUs to the NLL terminal that previously sent the request Req, as well as to the LL terminal that sent a request at this timing. The AP then transmits a response frame Res to each terminal. The response frame contains information on whether each terminal is permitted to transmit data frames. In this example, it is assumed that both the NLL terminal and the LL terminal are permitted to transmit data frames.

[0059] After transmitting the response frame, the AP transmits a trigger frame TF to the terminals under its control. As described above, the trigger frame TF can include information indicating whether the terminal belongs to a member of OFDMA transmission, information on the number of RUs allocated in proportion to the bandwidth requested by each terminal, and information on the maximum frame length according to the allowable delay when low-latency traffic occurs in the terminal.

[0060] A terminal 20 that receives the trigger frame TF and is included as a member of the UL-OFDMA transmission assigns an OFDMA frame to the RU assigned to it, and then transmits a data frame a predetermined frame interval (usually SIFS) from the trigger frame. In Fig. 10, the NLL terminal transmits a data frame DATA, and the LL terminal transmits an LL data frame LL-DATA. Also, although not shown in Fig. 10, the AP that receives the data frame transmits a BACK to each terminal.

[0061] As described above, according to the first embodiment, the AP transmits an inquiry frame to subordinate terminals to check whether LL traffic has occurred prior to transmitting a trigger frame for UL-OFDMA transmission. If the transmission of this inquiry frame identifies terminals experiencing LL traffic, the AP preferentially allocates RUs for transmitting the LL traffic and transmits a trigger frame to each terminal. This allows the LL terminals to immediately transmit data frames even if LL traffic occurs at the same time as another NLL terminal transmits traffic. In this way, in the first embodiment, a TXOP for transmitting LL traffic can be granted to the LL terminals in a short period after non-periodic LL traffic occurs.

[0062] In the first embodiment, the AP can change the allocation of RUs according to information on the required bandwidth and maximum delay from the LL terminal, thereby enabling transmission of LL traffic that satisfies the required delay conditions.

[0063] (Second Embodiment) Next, a second embodiment will be described. Here, in the description of the second embodiment, the description of parts that overlap with the first embodiment will be omitted or simplified as appropriate. The configuration of the communication system in the second embodiment may be the same as that shown in FIG. 1. Furthermore, the hardware configuration of the AP in the second embodiment may be the same as that shown in FIG. 2. Furthermore, the hardware configuration of the terminal in the second embodiment may be the same as that shown in FIG. 3. However, in the second embodiment, the AP and the terminal do not need to support UL-OFDMA transmission.

[0064] 11 is a block diagram showing an example of the functional configuration of an AP according to the second embodiment. The AP 10 functions as a computer including a data processing unit 110, a frame processing unit 120, a management unit 130, and a wireless signal processing unit 140. Here, the data processing unit 110, the frame processing unit 120, and the wireless signal processing unit 140 are the same as those described in the first embodiment. Therefore, a description thereof will be omitted.

[0065] The management unit 130 in the second embodiment controls the logical wireless connection between the AP 10 and the terminal 20. In the second embodiment, the management unit 130 includes an LL terminal detection unit 132. The LL terminal detection unit 132 detects an LL terminal by detecting an LL notification frame transmitted from the LL terminal. In the second embodiment, the LL terminal may transmit an LL notification frame including LL terminal information to the AP even during the TXOP of an NLL terminal. The LL terminal information is information indicating that the LL terminal is experiencing LL traffic. When the LL terminal detection unit 132 detects an LL terminal, it grants the TXOP to the LL terminal even during the TXOP with the NLL terminal. The TXOP is granted by transmitting a trigger frame to the LL terminal. For the LL terminal information, a reference signal such as L-LTF (legacy-long training field) may be used. In this case, the LL terminal detection unit 132 can detect the LL notification frame by detecting a cross-correlation between a known waveform representing the L-LTF in the received radio signal and the LL terminal information. In the second embodiment, the LL notification frame can include a number of pieces of LL terminal information according to the urgency of the LL traffic. The LL terminal detection unit 132 can determine the urgency of the transmission of the LL traffic by detecting the number of repetitions of the LL terminal information through autocorrelation detection with the detected L-LTF.

[0066] 12 is a block diagram showing an example of the functional configuration of a terminal according to the second embodiment. The terminal 20 functions as a computer including a data processing unit 210, a frame processing unit 220, a management unit 230, a radio signal processing unit 240, and an application execution unit 250. Here, the data processing unit 210, the frame processing unit 220, the radio signal processing unit 240, and the application execution unit 250 are the same as those described in the second embodiment. Therefore, a description thereof will be omitted.

[0067] The management unit 130 in the second embodiment controls a logical wireless connection between the AP 10 and the terminal 20. In the second embodiment, the management unit 130 includes an LL terminal information notification unit 231. The LL terminal information notification unit 231 performs control for transmitting an LL notification frame to the AP 10 when LL traffic occurs.

[0068] Next, the operation of the communication system according to the second embodiment will be described. Fig. 13 is a flowchart showing the operation of the AP 10 according to the second embodiment. Here, it is assumed that prior to the operation shown in Fig. 13, the AP 10 has acquired the right to transmit a wireless signal in response to a request from a terminal 20, which is, for example, an NLL terminal, in order to grant a TXOP to the terminal 20 that made the request.

[0069] In step S31, the AP 10 uses the wireless signal processing unit 140 to transmit a trigger frame to the NLL terminal.

[0070] In step S32, the AP 10 receives a data frame from the NLL terminal. If the data frame is received from the NLL terminal, the process proceeds to step S33. If the data frame is not received within a predetermined period, the process may proceed to step S34.

[0071] In step S33, the AP 10 checks whether the data frame received from the NLL terminal has been received correctly, and transmits the check result as BACK to the NLL terminal.

[0072] In step S34, the AP 10 determines whether the TXOP given to the NLL terminal has ended. If it is determined in step S34 that the TXOP given to the NLL terminal has not ended, the process proceeds to step S35. If it is determined in step S34 that the TXOP given to the NLL terminal has ended, the process of FIG. 13 ends.

[0073] In step S35, the AP 10 determines whether an LL notification frame has been detected while receiving a data frame from an NLL terminal. If it is determined in step S35 that an LL notification frame has been detected, the process proceeds to step S36. If it is determined in step S35 that an LL notification frame has not been detected, the process proceeds to step S39.

[0074] In step S36, the AP 10 uses the radio signal processing unit 140 to transmit a trigger frame to the LL terminal.

[0075] In step S37, the AP 10 receives a data frame from the LL terminal. If the data frame is received from the LL terminal, the process proceeds to step S38. If the data frame is not received within a predetermined period, the process may proceed to step S34.

[0076] In step S38, the AP 10 checks whether the data frame received from the LL terminal has been received correctly, and transmits the check result as BACK to the LL terminal, after which the process returns to step S34.

[0077] In step S39, the AP 10 uses the wireless signal processing unit 140 to transmit a trigger frame to the NLL terminal.

[0078] In step S40, the AP 10 receives a data frame from the NLL terminal. If a data frame is received from the NLL terminal, the process proceeds to step S41. If a data frame is not received within a predetermined period, the process may proceed to step S34.

[0079] In step S41, the AP 10 checks whether the data frame received from the NLL terminal has been received correctly, and transmits the check result as BACK to the NLL terminal. After that, the process returns to step S34.

[0080] 14 is a flowchart showing the operation of the terminal 20 in the second embodiment. In step S51, the terminal 20 determines whether LL traffic to be transmitted to the AP 10 has occurred. If it is determined in step S51 that LL traffic has occurred, the process proceeds to step S52. If it is determined in step S51 that LL traffic has not occurred, the process proceeds to step S58.

[0081] In step S52, the terminal 20 sets LL terminal information to be included in the LL notification frame, for example, the number of L-LTF repetitions, depending on the urgency of the LL traffic. Specifically, the higher the urgency, the greater the number of L-LTF repetitions the terminal 20 sets.

[0082] In step S53 , the terminal 20 transmits the LL notification frame to the AP 10 using the wireless signal processing unit 240 .

[0083] In step S54, the terminal 20 determines whether or not it is capable of transmitting LL traffic. In step S54, if the terminal 20 receives a trigger frame from the AP 10 and is included in the members, it is determined that it is capable of transmitting LL traffic. If it is determined in step S54 that it is capable of transmitting LL traffic, the process proceeds to step S55. If it is determined in step S54 that it is not capable of transmitting LL traffic, the process proceeds to step S57.

[0084] In step S55, after waiting a predetermined interval from the trigger frame, the terminal 20 transmits a radio signal including a data frame using the radio signal processing unit 240. The predetermined interval is, for example, SIFS. Note that the data frame may be transmitted using an OFDMA frame.

[0085] In step S56, the terminal 20 receives BACK from the AP 10. After that, the process proceeds to step S59.

[0086] In step S57, if it is determined in step S54 that LL traffic cannot be transmitted, the terminal 20 increases the length of the LL notification frame to increase the possibility of the LL notification frame being detected by the AP 10. Thereafter, the process returns to step S53.

[0087] If it is determined in step S51 that no LL traffic is occurring, the terminal 20 operates as an NLL terminal in step S58. The operation as an NLL terminal is, for example, an operation of waiting for a trigger frame from the AP 10 and transmitting a data frame. If a data frame has been transmitted or if no traffic is occurring, the process proceeds to step S59.

[0088] In step S59, the terminal 20 determines whether the TXOP provided by the AP 10 has ended. If the TXOP provided by the AP 10 has not ended in step S59, the process returns to step S51. If the TXOP provided by the AP 10 has ended in step S59, the process in FIG. 14 ends.

[0089] 15 is a timing chart showing the operation of data transmission in the second embodiment. Here, FIG. 15 shows the operation of data transmission between an AP, one NLL terminal, and one LL terminal. However, the number of NLL terminals and the number of LL terminals are not limited to one.

[0090] When traffic that should be transmitted to the AP occurs, the terminal transmits a request to the AP to transmit a data frame. The AP, upon receiving the request from the terminal, performs a CCA operation to acquire the right to transmit. The AP then transmits a trigger frame to the terminal that transmitted the request, granting the terminal a TXOP. In Figure 15, a trigger frame (TF) is transmitted to an NLL terminal.

[0091] Upon receiving the trigger frame, the NLL terminal transmits a data frame (DATA) to the AP. In FIG. 15 , LL traffic occurs at the LL terminal while the NLL terminal is transmitting the data frame. At this time, the LL terminal transmits an LL notification frame (LL-IF) to the AP. The AP may simultaneously receive the data frame and the LL notification frame. The AP detects the LL notification frame mixed in the data frame by performing cross-correlation processing on the received data frame. The higher the urgency of the LL traffic, the greater the number of repetitions of the LL terminal information is set. This increases the likelihood that the LL notification frame will be detected by AP 10.

[0092] After receiving the data frame, the AP transmits a block ACK (BACK). If the TXOP has not ended and the LL notification frame has not been detected, the AP transmits a trigger frame again to the NLL terminal. On the other hand, if the LL notification frame has been detected, the AP transmits the trigger frame to the LL terminal, not to the NLL terminal. Here, if the LL notification frame is not detected and the trigger frame is not transmitted to the LL terminal, the length of the LL notification frame is adjusted to be longer, and the LL notification frame is transmitted again. This increases the possibility that the LL notification frame will be detected by the AP 10.

[0093] When the LL terminal receives the trigger frame, it transmits a data frame (LL-DATA) including LL traffic. In this way, in the second embodiment, the LL terminal can transmit LL traffic within the TXOP given to the NLL terminal.

[0094] After receiving the data frame, the AP transmits a block ACK (BACK), and the same operation is repeated until the TXOP ends.

[0095] As described above, according to the second embodiment, when an AP receives an LL notification frame from an LL terminal during a TXOP granted to a certain terminal, the AP transmits a trigger frame to the LL terminal that transmitted the LL notification frame, rather than to the terminal that had previously granted the TXOP. This allows the LL terminal to immediately transmit a data frame even if LL traffic occurs at the timing of traffic transmission by another NLL terminal. In this way, in the second embodiment, a TXOP for transmitting LL traffic can be granted to the LL terminal within a short period after non-periodic LL traffic occurs.

[0096] In the second embodiment, the number of repetitions of LL terminal information such as L-LTF is set according to the urgency of LL traffic. Furthermore, in the second embodiment, if a trigger frame cannot be received after transmitting an LL notification frame, the length of the LL notification frame is adjusted. This increases the likelihood that the AP can detect the LL notification frame, and as a result, increases the likelihood that the LL terminal can transmit a data frame.

[0097] (Modification of the Second Embodiment) Next, a modification of the second embodiment will be described. In FIG. 15 , there is one LL terminal. However, there may be two or more LL terminals. In this case, there is a possibility that LL notification frames are transmitted simultaneously from multiple LL terminals. In order for the AP to identify which terminal transmitted the detected LL notification frame, the LL notification frame may include identification information of the terminal that transmitted it. The identification information may be, for example, a MAC address.

[0098] Furthermore, when multiple LL notification frames are detected simultaneously, the AP may determine which LL terminal to give a TXOP to on a priority basis, for example, based on the urgency of LL traffic determined from the LL terminal information. That is, the AP may transmit a trigger frame with the highest priority to an LL terminal where highly urgent LL traffic has occurred. Alternatively, the AP may receive data frames simultaneously from multiple LL terminals using OFDMA transmission.

[0099] Furthermore, Fig. 15 shows an example in which an LL notification frame is transmitted while another terminal is transmitting a data frame. In this case, the AP detects the LL notification frame mixed in with the data frame. In contrast, as shown in Fig. 16, the LL terminal may transmit the LL notification frame during the SIFS between when the other terminal finishes transmitting the data frame and when the AP transmits a BACK. The end of the data frame transmission by the other terminal can be estimated from the frame length recorded in the header of the data frame, etc. Note that when an LL notification frame is transmitted during the SIFS, the LL notification frame can be composed of an L-LTF of up to four symbols.

[0100] (Other Modifications) The above-described processing in the AP 10 and the terminal 20 can be stored as a program that can be executed by a processor, which is a computer. Alternatively, the program can be stored in a storage medium of an external storage device such as a magnetic disk, optical disk, or semiconductor memory and distributed. The processors of the AP 10 and the terminal 20 can then load the program stored in the storage medium of the external storage device and execute various processes by having their operations controlled by the loaded program.

[0101] The present invention is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the invention. Furthermore, the embodiments may be implemented in appropriate combinations, in which case the combined effects can be obtained. Furthermore, the above-described embodiments include various inventions, and various inventions can be extracted by combining selected elements from the disclosed elements. For example, if the problem can be solved and the desired effect can be obtained even if some elements are deleted from all elements shown in the embodiments, the configuration from which these elements are deleted can be extracted as an invention.

[0102] 1...Communication system 10...Access point (AP) 11...CPU 12...ROM 13...RAM 14...Wireless communication module 15...Wired communication module 20, 20-1, 20-2, ..., 20-N...Terminal 21...CPU 22...ROM 23...RAM 24...Wireless communication module 25...Display 26...Storage 30...Network 110...Data processing unit 120...Frame processing unit 130...Management unit 131...TXOP management unit 132...LL terminal detection unit 140...Wireless signal processing unit 210...Data processing unit 220...Frame processing unit 230...Management unit 231...LL terminal information notification unit 240...Wireless signal processing unit 250...Application execution unit

Claims

1. An access point having a management unit that, in response to a request from a terminal to transmit traffic, transmits an inquiry frame to multiple terminals under its control to inquire whether low-latency traffic requiring low latency is occurring; if a low-latency terminal is found to be experiencing low-latency traffic in response to the inquiry frame, allocates resource units (RUs) preferentially to the low-latency terminal; and transmits a trigger frame containing information on the allocation of the RUs to at least the low-latency terminal.

2. The access point described in claim 1, wherein the management unit allocates the RUs according to the requested bandwidth and allowable delay from the low-latency terminal, and transmits the trigger frame including information on the number of RUs allocated proportional to the requested bandwidth and information on the maximum frame length according to the allowable delay.

3. A terminal having a management unit that transmits a request for transmitting low-latency traffic in response to an inquiry frame from an access point as to whether low-latency traffic is occurring, and transmits the low-latency traffic via OFDMA in response to a trigger frame transmitted from the access point in response to the request.

4. The terminal according to claim 3, wherein the management unit transmits to the access point, in response to the inquiry frame, information on the required bandwidth and allowable delay required for transmitting the low-latency traffic, including the information in the request.

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