Wireless communication device and wireless communication method

Abstract

A wireless communication device according to one aspect of the present invention comprises an acquisition unit, a required delay analysis unit, and a determination unit. The acquisition unit acquires information pertaining to a required delay time of low-delay data. The required delay analysis unit calculates, from the required delay time, a maximum required delay time which is the maximum value of a delay time that is permitted as media access delay of a data link layer. The determination unit determines, on the basis of the maximum required delay time, the payload size of a plurality of radio frames that are related to a data transmission operation for transmitting the plurality of radio frames within a transmission opportunity (TXOP) period.

Description

Wireless communication device and wireless communication method

[0001] The present invention relates to wireless communications.

[0002] The IEEE 802.11 wireless local area network (LAN) standard is widely used. Wireless LANs are required to have high reliability, such as low latency, that can meet traffic requirements.

[0003] IEEE Std 802.11-2020, "9.4.2.28 EDCA Parameter Set element" (pp.1067-1070) and "10.23.2.4 Obtaining an EDCA TXOP" (pp.1740-1742), December 2020. Giovanni Chisci et al., "Preemption techniques to meet low-latency (LL) IEEE 802.11-23 / 1886r3, January 10, 2024.

[0004] An object of the present invention is to provide a technique that enables highly reliable wireless communication.

[0005] A wireless communication device according to one aspect of the present invention includes an acquisition unit, a required delay analysis unit, and a determination unit. The acquisition unit acquires information indicating a required delay time for low-latency data. The required delay analysis unit calculates, from the required delay time, a maximum required delay time, which is the maximum delay time allowed as a media access delay in a data link layer. The determination unit determines a wireless frame payload size for a data transmission operation in which multiple wireless frames are transmitted within a transmission opportunity (TXOP) period, based on the maximum required delay time.

[0006] According to the present invention, it is possible to provide a technique that enables highly reliable wireless communication.

[0007] FIG. 1 is a block diagram showing a wireless system according to a first embodiment. FIG. 2 is a diagram for explaining a wireless communication method according to the first embodiment. FIG. 3 is a diagram for explaining a wireless communication method according to the first embodiment. FIG. 4 is a block diagram showing a hardware configuration of an access point according to the first embodiment. FIG. 5 is a block diagram showing a hardware configuration of a terminal according to the first embodiment. FIG. 6 is a block diagram showing a functional configuration of an access point according to the first embodiment. FIG. 7 is a block diagram showing a functional configuration of a frame processing unit included in an access point according to the first embodiment. FIG. 8 is a block diagram showing a functional configuration of a terminal according to the first embodiment. FIG. 9 is a flowchart showing a method of determining a payload size according to the first embodiment. FIG. 10 is a sequence diagram showing data transmission by preemption according to the first embodiment. FIG. 11 is a block diagram showing a wireless system according to a second embodiment. FIG. 12 is a block diagram showing a functional configuration of an access point according to the second embodiment. FIG. 13 is a block diagram showing a functional configuration of a frame processing unit included in an access point according to the second embodiment. FIG. 14 is a diagram for explaining data transmission by preemption according to the second embodiment. FIG. 15 is a block diagram showing a functional configuration of a terminal according to the second embodiment. Fig. 16 is a block diagram showing a wireless system according to a second embodiment. Fig. 17 is a diagram illustrating data transmission according to a related technique. Fig. 18 is a diagram illustrating preemption according to a related technique. Fig. 19 is a diagram illustrating preemption according to a related technique. Fig. 20 is a diagram illustrating preemption according to a related technique.

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] The embodiments relate to a technology that enables low-latency traffic having strict requirements, such as low latency and low jitter, to be transmitted so as to satisfy the requirements. Low-latency traffic is traffic that should be transmitted with priority. Low-latency traffic is also called latency-sensitive traffic (LST). The traffic is also called data.

[0010] In an IEEE 802.11 wireless local area network (LAN), an access point (AP) performs channel access based on enhanced distributed channel access (EDCA) to acquire a transmission right. When an access point that has acquired a transmission right transmits a PPDU with a long frame length, also known as a long PPDU, the channel is occupied by that access point for that period. As shown in FIG. 17, if low-latency data occurs during the transmission of a long PPDU, the low-latency data is put into a transmission standby state and is transmitted after the long PPDU. This may result in the low-latency data not being able to meet the requirements. PPDU is an abbreviation for physical layer (PHY) protocol data unit. PPDUs are also called physical layer (PHY) frames or radio frames. A PPDU includes a preamble and a payload following the preamble. The preamble stores information used for synchronization, data demodulation, etc. The payload stores a data frame, also known as a MAC protocol data unit (MPDU). A data frame is a MAC (media access control) frame in which data is stored.

[0011] IEEE 802.11bn, currently being developed as a next-generation wireless LAN standard, is considering a data transmission operation called preemption, which transmits multiple radio frames within a transmission opportunity (TXOP) period to enable interrupt transmission of low-latency data. The TXOP period indicates the period during which a wireless station that has acquired the transmission right can transmit continuously. In preemption, an access point divides a long PPDU into multiple small PPDUs and transmits the small PPDUs sequentially at SIFS time intervals within the TXOP period. As shown in Figure 18, if low-latency data occurs during the TXOP period, the access point transmits a PPDU (LST PPDU) containing low-latency data instead of the small PPDU that is scheduled to be transmitted next. In this way, preemption allows the transmission of a PPDU containing low-latency data to be interrupted between small PPDU transmissions. This allows for a reduction in the actual delay that occurs for low-latency data.

[0012] Even during preemption, low-latency data is put into a transmission standby state during the period related to the transmission of the small PPDU. Therefore, as shown in Figure 19, if the frame length of the small PPDU is set long, it may not be possible to meet the requirements for low-latency data. Conversely, as shown in Figure 20, if the frame length of the small PPDU is set short, it is more likely that the requirements for low-latency data will be met, but the total overhead time related to frame transmission will be longer, reducing the time efficiency of frame transmission.

[0013] The embodiment provides a method for setting the frame length of a small PPDU (specifically, the size of the payload of the small PPDU) that enables low-latency data requirements to be met while suppressing a decrease in the time efficiency of frame transmission.

[0014] In the following description, small PPDUs obtained by dividing long PPDUs in preemption may be simply referred to as PPDUs.

[0015] Although this specification describes wireless communication based on the IEEE 802.11 standard as an example, wireless communication standards other than the IEEE 802.11 standard may also be used. The IEEE 802.11 standard has wireless communication functions based on 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 an LLC (logical link control) sublayer and a MAC sublayer.

[0016] 1 is a schematic diagram of a wireless system 40 according to a first embodiment. As shown in FIG. 1, the wireless system 40 includes an access point 10 and a terminal 20.

[0017] The access point 10 is an access point for a wireless LAN. An access point may also be called a base station. The access point 10 is configured to wirelessly communicate with wireless communication devices such as terminals 20. In the example shown in FIG. 1 , the access point 10 is wirelessly connected to one wireless communication device, but the number of wireless communication devices wirelessly connected to the access point 10 may change dynamically. The state in which the access point 10 is wirelessly connected to the wireless communication device indicates that a wireless link is logically established between the access point 10 and the wireless communication device, and data communication is possible between the access point 10 and the wireless communication device using the established wireless link.

[0018] The access point 10 is connected to a communication network 30 that may include the Internet. For example, the access point 10 is connected to a gateway (not shown) such as a router via a LAN cable, and accesses the communication network 30 via the gateway. The access point 10 may also be mounted on the gateway.

[0019] The terminal 20 is configured to wirelessly communicate with a wireless communication device such as the access point 10. For example, the terminal 20 communicates with a computer on the communication network 30 via the access point 10. The terminal 20 is a wireless terminal device having a wireless communication function. Examples of wireless terminal devices include, but are not limited to, a desktop personal computer (PC), a laptop PC, a tablet PC, a smartphone, and a sensor device. The terminal 20 executes a real-time application (RTA) such as a network game application, and communicates with a server 31 that provides services such as a network game via the access point 10.

[0020] The server 31 may generate low-latency data aperiodically (e.g., at unpredictable times) that must arrive at the terminal 20 within a short time. The server 31 signals the required delay time of the low-latency data to the access point 10. The required delay time of the low-latency data is the delay time required for the low-latency data. Specifically, the required delay time of the low-latency data is the maximum delay time (upper limit) allowed for transmission of the low-latency data. The required delay time may include E2E (end-to-end) communication delay and / or queuing delay at layer 3 or higher (network layer or higher). In one example, the required delay time is the maximum delay time allowed for transmission from the network layer of the source (e.g., the server 31) to the network layer of the destination (e.g., the terminal 20). In this case, it is required that the low-latency data arrive from the network layer of the source to the network layer of the destination (e.g., the terminal 20) within the required delay time or less.

[0021] The access point 10 receives requested delay time information indicating the requested delay time of low-latency data from the server 31. The access point 10 calculates a maximum requested delay time from the requested delay time indicated by the received requested delay time information. The maximum requested delay time is the maximum time allowed as a media access delay in Layer 2 (data link layer). Specifically, the maximum requested delay time is the maximum time allowed from the generation of a PPDU including low-latency data to the start or end of transmission of the PPDU.

[0022] The access point 10 calculates the size (length) of the PPDU payload so that the preemption unit length is equal to or less than the calculated maximum required delay time. The preemption unit length is the length of the preemption unit shown in FIG. 2 and indicates the time required for PPDU exchange during preemption. Specifically, the preemption unit length is the sum of the time required to transmit the PPDU payload and the overhead time. In the example shown in FIG. 2, the overhead time may be the sum of the time required to transmit the PPDU preamble, the xIFS waiting time, the time required to receive an acknowledgement (ACK) frame for the PPDU, and the xIFS waiting time. The xIFS represents an IFS such as SIFS (short interframe space) or DIFS (DCF interframe space), and the xIFS waiting time indicates the time interval between successive frames. The ACK frame may be a Block Ack (BA) frame. In an example where there is no Ack transmission, the overhead time may be the sum of the time required to transmit the preamble of the PPDU and the xIFS waiting time.

[0023] Specifically, the access point 10 calculates the overhead time and subtracts the overhead time from the maximum required delay time to calculate the maximum payload size. The maximum payload size is the maximum value of the payload size and is equal to the difference between the maximum required delay time and the overhead time. The access point 10 determines the payload size of the PPDU based on the modulation and coding scheme (MCS) to be used for transmitting the PPDU, within a range equal to or less than the calculated maximum payload size. For example, the access point 10 determines the largest payload size that is available for the MCS to be used for transmitting the PPDU and satisfies the condition that the preemption unit length is equal to or less than the calculated maximum required delay time, as the payload size of the PPDU. Ideally, the payload size is set to a value that makes the preemption unit length equal to the maximum required delay time. Such a value is called an optimal value. However, the optimal value may not be available for the MCS to be used for transmitting the PPDU. In this case, the payload size is set to the closest value to, but less than, the optimum value available for the MCS that is to be used to transmit the PPDU.

[0024] In this way, the access point 10 determines the PPDU payload size so that the preemption unit length is equal to or less than the maximum required delay time. As a result, as shown in FIG. 3, the delay actually occurring for low-latency data is equal to or less than the maximum required delay time. As a result, it becomes possible to meet the requirements for low-latency data. Furthermore, the access point 10 determines the PPDU payload size so that the preemption unit length is equal to or less than the maximum required delay time and the PPDU payload size is as large as possible. This shortens the total overhead time. As a result, it becomes possible to meet the requirements for low-latency data while suppressing a decrease in the time efficiency of frame transmission.

[0025] Fig. 4 shows an example of a hardware configuration of the access point 10. As shown in Fig. 4, the access point 10 includes a central processing unit (CPU) 11 as a processor, a read only memory (ROM) 12, a random access memory (RAM) 13, a wireless communication module 14, and a wired communication module 15.

[0026] The CPU 11 is an integrated circuit capable of executing various programs and controls the overall operation of the access point 10. The ROM 12 is a non-volatile semiconductor memory that stores programs and control data for controlling the access point 10. The RAM 13 is a volatile semiconductor memory that is used as a work area for the CPU 11. At least a portion of the processing described for the access point 10 can be implemented by the CPU 11 executing the programs stored in the ROM 12.

[0027] The wireless communication module 14 is a circuit configured to be able to transmit and receive wireless signals via an antenna, and is used for communication with the terminal 20. The wired communication module 15 is a circuit used for transmitting and receiving data and the like using electrical signals, and is used for communication with the communication network 30.

[0028] It should be noted that the hardware configuration shown in FIG. 4 is an example, and the access point 10 may have a hardware configuration different from that shown in FIG.

[0029] Fig. 5 shows an example of a hardware configuration of the terminal 20. As shown in Fig. 5, the terminal 20 includes a CPU 21 as a processor, a ROM 22, a RAM 23, a wireless communication module 24, a display 25, and a storage 26.

[0030] The CPU 21 is an integrated circuit capable of executing various programs and controls the overall operation of the terminal 20. The ROM 22 is a non-volatile semiconductor memory that stores programs and control data for controlling the terminal 20. The RAM 23 is, for example, a volatile semiconductor memory that is used as a work area for the CPU 21. At least a portion of the processing described for the terminal 20 can be implemented by the CPU 21 executing the programs stored in the ROM 22.

[0031] The wireless communication module 24 is a circuit configured to be able to send and receive wireless signals via an antenna, and is used for communication with the access point 10. The display 25 displays, for example, a graphical user interface (GUI) provided by application software. The storage 26 is a non-volatile storage device, and stores, for example, system software for the terminal 20.

[0032] Note that the hardware configuration shown in Fig. 5 is an example, and the terminal 20 may have a hardware configuration different from that shown in Fig. 5. For example, the display 25 may be omitted from the hardware configuration shown in Fig. 5.

[0033] Next, the functional configurations of the access point 10 and the terminal 20 will be described. Here, processing related to downlink transmission will be described, and processing related to uplink transmission will not be described. Processing related to uplink transmission can be executed in the same manner as processing related to downlink transmission. Downlink transmission refers to transmission from the access point 10 to the terminal 20, and uplink transmission refers to transmission from the terminal 20 to the access point 10. Furthermore, it is assumed that a wireless link between the access point 10 and the terminal 20 has been established, and processing for establishing a wireless link between the access point 10 and the terminal 20 will not be described.

[0034] FIG. 6 schematically illustrates an example of the functional configuration of the access point 10. Components related to the transmission function of the access point 10 are selectively illustrated in FIG. 6 . As illustrated in FIG. 6 , the access point 10 includes an upper layer 110, a data processing unit 120, a frame processing unit 130, a MAC frame generation unit 140, a wireless signal processing unit 150, a request delay analysis unit 160, and a management unit 170. The upper layer 110 may be implemented by a combination of the CPU 11 and a wired communication module 15. The data processing unit 120, the frame processing unit 130, the MAC frame generation unit 140, the wireless signal processing unit 150, the request delay analysis unit 160, and the management unit 170 may be implemented by the wireless communication module 14 or a combination of the CPU 11 and the wireless communication module 14.

[0035] The upper layer 110 receives data addressed to the terminal 20 from the server 31 on the communication network 30, and sends the received data to the data processing unit 120 via an LLC layer (not shown). The data processing unit 120 receives data from the upper layer 110, and sends the received data to the frame processing unit 130.

[0036] The frame processing unit 130 receives data from the data processing unit 120 and buffers the received data. The frame processing unit 130 sends the data to the MAC frame generation unit 140 in response to, for example, the access point 10 acquiring the right to transmit.

[0037] MAC frame generation unit 140 receives data from frame processing unit 130, generates an MPDU (data frame) including the received data, and sends the generated MPDU to radio signal processing unit 150. For example, MAC frame generation unit 140 generates an MPDU by adding a MAC header or the like to the data.

[0038] The radio signal processing unit 150 receives the MPDU from the MAC frame generation unit 140 and performs physical layer processing on the received MPDU. For example, the radio signal processing unit 150 adds a preamble to the MPDU to generate a PPDU, converts the PPDU into a radio signal by performing a predetermined modulation process, and emits the radio signal via an antenna. The modulation process includes, for example, convolutional coding, interleaving, subcarrier modulation, inverse fast Fourier transform (IFFT), orthogonal frequency division multiplexing (OFDM) modulation, and frequency conversion.

[0039] The upper layer 110 receives requested delay time information indicating the requested delay time of low-delay data from the server 31 on the communication network 30 , and sends the received requested delay time information to the requested delay analysis unit 160 .

[0040] The requested delay analysis unit 160 receives requested delay time information from the upper layer 110 and calculates the maximum requested delay time by analyzing the received requested delay time information. The maximum requested delay time is the maximum time allowed as a media access delay in Layer 2. The requested delay analysis unit 160 notifies the management unit 170 of the calculated maximum requested delay time.

[0041] Management section 170 determines the payload size of the PPDU related to preemption based on the maximum requested delay time notified by requested delay analysis section 160, and notifies frame processing section 130 of the determined payload size.

[0042] The combination of the requested delay analysis unit 160 and the management unit 170 functions as a determination unit that determines the payload size of the PPDU related to preemption based on the requested delay time of the low-delay data.

[0043] Furthermore, the management unit 170 manages connections with wireless communication devices such as the terminal 20. For example, the management unit 170 executes a process for establishing a wireless link with the terminal 20.

[0044] 7 shows an example of the functional configuration of the frame processing unit 130. As shown in FIG. 7, the frame processing unit 130 includes a transmission buffer 131, a transmission buffer control unit 132, and an instruction unit 133.

[0045] The transmission buffer 131 buffers data received from the data processing unit 120. The transmission buffer control unit 132 manages the transmission buffer 131. For example, in response to acquisition of the transmission right, the transmission buffer control unit 132 retrieves data from the transmission buffer 131 and provides it to the MAC frame generation unit 140.

[0046] The instruction unit 133 detects low latency data. When the instruction unit 133 detects that low latency data has arrived at the frame processing unit 130, the instruction unit 133 instructs the transmission buffer control unit 132 to immediately transmit the low latency data.

[0047] When transmitting data using preemption, the transmission buffer control unit 132 divides the data in accordance with the payload size notified by the management unit 170 and provides the data to the MAC frame generation unit 140. Specifically, the transmission buffer control unit 132 divides the data so that each piece of data obtained by the division fits into an MPDU having a frame length that matches the payload size notified by the management unit 170. Furthermore, the transmission buffer control unit 132 provides the MAC frame generation unit 140 with information necessary for transmitting data using preemption, including information indicating the payload size.

[0048] Assume that low-latency data addressed to terminal 20 occurs during data transmission using preemption. Specifically, during data transmission using preemption, the low-latency data addressed to terminal 20 is received by upper layer 110 and arrives at frame processing unit 130 via LLC layer and data processing unit 120. In response to the arrival of the low-latency data, instruction unit 133 instructs transmission buffer control unit 132 to immediately transmit the low-latency data. In response to the instruction from instruction unit 133, transmission buffer control unit 132 provides the low-latency data to MAC frame generation unit 140 with priority. For example, transmission buffer control unit 132 provides the low-latency data to MAC frame generation unit 140 before the data scheduled for next transmission. In this way, transmission buffer control unit 132 interrupts the transmission of a PPDU including low-latency data between transmissions of small PPDUs, as shown in FIG. 3 .

[0049] Fig. 8 schematically illustrates an example of the functional configuration of the terminal 20. Components related to the reception function of the terminal 20 are selectively illustrated in Fig. 8. As illustrated in Fig. 8, the terminal 20 includes an upper layer 210, a data processing unit 220, a frame processing unit 230, a MAC frame processing unit 240, and a radio signal processing unit 250. The upper layer 210 may be implemented by the CPU 21. The data processing unit 220, the frame processing unit 230, the MAC frame processing unit 240, and the radio signal processing unit 250 may be implemented by the wireless communication module 24 or a combination of the CPU 21 and the wireless communication module 24.

[0050] The radio signal processing unit 250 receives radio signals via an antenna and performs physical layer processing on the received radio signals. For example, the radio signal processing unit 250 performs predetermined demodulation processing on the radio signals received via the antenna to obtain radio frames. The predetermined demodulation processing includes, for example, frequency conversion, OFDM demodulation, fast Fourier transform (FFT), subcarrier demodulation, deinterleaving, and Viterbi decoding. The radio signal processing unit 250 then extracts MAC frames from the radio frames and sends the extracted MAC frames to the MAC frame processing unit 240.

[0051] The MAC frame processing unit 240 receives a MAC frame from the radio signal processing unit 250 , extracts data from the received MAC frame, and sends the extracted data to the frame processing unit 230 .

[0052] The frame processing unit 230 receives data from the MAC frame processing unit 240 and sends the received data to the upper layer 210 via the data processing unit 220 and the LLC layer (not shown).

[0053] The upper layer 210 receives data from the data processing unit 220. For example, the data is provided to an application running in the upper layer 210.

[0054] When data transmission is performed using preemption, the frame processing unit 230 buffers the received data and combines the data to restore the original data. Upon receiving low-latency data, the frame processing unit 230 immediately sends the data to the data processing unit 220.

[0055] Next, the operation of the wireless system 40 will be described.

[0056] Fig. 9 shows an example of a procedure for determining a payload size of a PPDU related to preemption according to the first embodiment. The method shown in Fig. 9 can be executed by the access point 10 having the configurations shown in Fig. 6 and Fig. 7. Here, it is assumed that the access point 10 is in the situation shown in Fig. 1.

[0057] 9, the upper layer 110 acquires requested delay time information. For example, the upper layer 110 receives the requested delay time information from the server 31 on the communication network 30. For example, the requested delay time information indicates the requested delay time of low-latency data generated by the server 31 and destined for the terminal 20.

[0058] In step S902, the requested delay analysis unit 160 calculates the maximum requested delay time from the requested delay time indicated by the requested delay time information obtained in step S901. The maximum requested delay time indicates the maximum time allowed as a media access delay in Layer 2.

[0059] In step S903, management unit 170 calculates the overhead time related to the transmission of the PPDU. The overhead time related to the transmission of the PPDU is, for example, the sum of the time required to transmit the PPDU preamble, the xIFS waiting time, the time required to receive the Ack, and the xIFS waiting time.

[0060] In step S904, management unit 170 determines the payload size of the PPDU based on the difference between the maximum required delay time obtained in step S902 and the overhead time obtained in step S903. For example, management unit 170 determines the value obtained by subtracting the overhead time from the maximum required delay time as the maximum payload size of the PPDU. Management unit 170 determines the payload size of the PPDU as the payload size of the PPDU, using a payload size value that is usable with the MCS to be used for transmitting the PPDU and is equal to or less than the calculated maximum payload size. For example, management unit 170 determines the payload size of the PPDU as the maximum size value that is usable with the MCS to be used for transmitting the PPDU and is equal to or less than the calculated maximum payload size.

[0061] The payload size of the PPDU determined in this way satisfies the condition that the preemption unit length is equal to or less than the maximum required delay time.

[0062] 10 is a diagram illustrating data transmission using preemption according to the first embodiment. The access point 10 performs channel access based on EDCA, thereby acquiring the right to transmit.

[0063] In step S1001 of Fig. 10 , the access point 10 transmits a first PPDU to the terminal 20. For example, the transmission buffer control unit 132 divides data according to the payload size determined by the process described with reference to Fig. 9 and provides the first of the divided data to the MAC frame generation unit 140. The MAC frame generation unit 140 generates an MPDU by adding a MAC header to the first divided data. The radio signal processing unit 150 generates and transmits a PPDU whose payload includes the MPDU generated by the MAC frame generation unit 140. The terminal 20 receives the first PPDU from the access point 10.

[0064] While the access point 10 is transmitting the first PPDU to the terminal 20, low-delay data addressed to the terminal 20 arrives at the frame processing unit 130 (step S1002).

[0065] In step S1003, in response to the successful reception of the first PPDU, the terminal 20 transmits an Ack to the access point 10. The access point 10 receives the Ack from the terminal 20.

[0066] In step S1004, the access point 10 transmits a second PPDU (LST PPDU) including low latency data to the terminal 20. For example, the transmission buffer control unit 132 provides the low latency data to the MAC frame generation unit 140 before the second fragmented data. The MAC frame generation unit 140 generates an MPDU by adding a MAC header to the low latency data. The radio signal processing unit 150 generates and transmits a PPDU including the MPDU generated by the MAC frame generation unit 140 in its payload. The frame length of the PPDU carrying the low latency data may be different from the frame length of the PPDU carrying the fragmented data. The terminal 20 receives the second PPDU from the access point 10.

[0067] In step S1005, in response to the successful reception of the second PPDU, the terminal 20 transmits an Ack to the access point 10. The access point 10 receives the Ack from the terminal 20.

[0068] In step S1006, access point 10 transmits the third PPDU to terminal 20. For example, transmission buffer control unit 132 provides the second divided data to MAC frame generation unit 140, which then generates an MPDU including the second divided data and provides it to radio signal processing unit 150. Radio signal processing unit 150 then generates and transmits a PPDU including the MPDU in its payload. Terminal 20 receives the third PPDU from access point 10.

[0069] In step S1007, in response to the successful reception of the third PPDU, the terminal 20 transmits an Ack to the access point 10. The access point 10 receives the Ack from the terminal 20.

[0070] Thereafter, the access point 10 similarly transmits PPDUs each containing divided data in its payload to the terminal 20. The access point 10 repeats transmission until all divided data has been transmitted or the TXOP period ends.

[0071] As described above, the access point 10 acquires required delay time information indicating the required delay time of low-latency data, calculates from the required delay time information the maximum required delay time that is the maximum delay time allowed as a media access delay of Layer 2, and determines the payload size of the PPDU so that the preemption unit length is equal to or less than the maximum required delay time. Determining the payload size of the PPDU includes calculating the overhead time for transmitting the PPDU, determining the maximum payload size by subtracting the overhead time from the maximum required delay time, and determining the payload size of the PPDU within a range equal to or less than the maximum payload size.

[0072] According to the above configuration, when low-latency data occurs during data transmission by preemption, it is possible to wirelessly transmit the low-latency data to the terminal 20 so as to satisfy the required delay time of the low-latency data.

[0073] The access point 10 may determine the payload size of the PPDU so that the preemption unit length is equal to or less than the maximum required delay time and the payload size of the PPDU is as large as possible.

[0074] According to the above configuration, it is possible to satisfy the requirements for low-latency data while suppressing a decrease in time efficiency of frame transmission.

[0075] The first embodiment will be described with reference to a situation in which the access point 10 is wirelessly connected to one terminal 20, as shown in Fig. 1. Therefore, the destination of the PPDU (LST PPDU) containing low latency traffic and the destination of the fragmented PPDUs are both the terminal 20. When the access point 10 is wirelessly connected to multiple terminals, the destination of the PPDU (LST PPDU) containing low latency traffic may be different from the destination of the fragmented PPDUs.

[0076] In the above example, the access point 10 acquires one piece of required delay time information. In cases where the access point 10 is wirelessly connected to multiple terminals, the access point 10 may acquire multiple pieces of required delay time information. In such cases, the access point 10 may determine the payload size of the PPDU related to preemption based on the required delay time information with the strictest requirements (specifically, the shortest required delay time).

[0077] Second Embodiment In the second embodiment, a case where an access point communicates with a terminal via multiple transmission paths will be described. The multiple transmission paths include mutually different wireless links. In the second embodiment, configurations and processes that are different from those in the first embodiment will be mainly described, and descriptions of configurations and processes that are the same as or similar to those in the first embodiment will be omitted as appropriate.

[0078] Fig. 11 schematically shows a wireless system 90 according to the second embodiment. As shown in Fig. 11, the wireless system 90 includes an access point 60 and a terminal 70. The access point 60 is wirelessly connected to the terminal 70 in a connection form called a multi-link connection. Specifically, multiple wireless links (two wireless links in this example) are logically established between the access point 60 and the terminal 70. Furthermore, the access point 60 is connected to a communication network 80 that may include the Internet.

[0079] The access point 60 includes an access point multi-link device (APMLD) 61 and affiliated APs 62 and 63. The APMLD is connected to the affiliated APs 62 and 63 by wire. The access point 60 has a hardware configuration similar to that of the access point 10 shown in FIG. 4 .

[0080] The terminal 70 includes a non-APMLD (non-access point multi-link device) 71 and affiliated STAs 72 and 73. The non-APMLD 71 is connected by wire to the affiliated STAs 72 and 73. The terminal 70 has a hardware configuration similar to the hardware configuration of the terminal 20 shown in FIG.

[0081] A wireless link is established between affiliated AP 62 and affiliated STA 72, and frequency channel #1 is used for communication between affiliated AP 62 and affiliated STA 72. A wireless link is established between affiliated AP 63 and affiliated STA 73, and a different frequency channel #2 is used for communication between affiliated AP 63 and affiliated STA 73.

[0082] Fig. 12 shows an example of the functional configuration of the access point 60. Fig. 12 selectively shows components related to the transmission function of the access point 60. In Fig. 12, components similar to those shown in Fig. 6 are denoted by the same reference numerals, and redundant explanations of those components will be omitted where appropriate.

[0083] 12 , the access point 60 includes an upper layer 110 in addition to an APMLD 61 and affiliated APs 62 and 63. The APMLD 61 includes a data processing unit 120, a frame processing unit 130, a request delay analysis unit 160, and a management unit 170. Each of the affiliated APs 62 and 63 includes a MAC frame generation unit 140 and a radio signal processing unit 150.

[0084] The upper layer 110 receives data from a communication network 80, which may include the Internet, and sends the received data to a frame processing unit 130 via an LLC (logical link control) layer (not shown) and a data processing unit 120. The frame processing unit 130 sends the data to one of the affiliated APs 62, 63. The data output destination is specified by the management unit 170.

[0085] In each of affiliated APs 62, 63, MAC frame generation unit 140 receives data from frame processing unit 130, generates an MPDU including the received data, and sends the generated MPDU to wireless signal processing unit 150. Wireless signal processing unit 150 receives the MPDU from MAC frame generation unit 140, generates a PPDU from the received MPDU, converts the PPDU into a wireless signal, and emits the wireless signal via an antenna.

[0086] The upper layer 110 receives requested delay time information indicating the requested delay time of low-latency data from the communication network 80, and sends the received requested delay time information to the requested delay analysis unit 160. The requested delay analysis unit 160 receives the requested delay time information from the upper layer 110, and calculates the maximum requested delay time from the requested delay time indicated by the received requested delay time information. The requested delay analysis unit 160 notifies the management unit 170 of the calculated maximum requested delay time.

[0087] The management unit 170 determines the payload size of the PPDU related to preemption based on the maximum required delay time notified by the requested delay analysis unit 160. The management unit 170 calculates the size of the PPDU payload so that the preemption unit length is equal to or less than the value obtained by multiplying the calculated maximum required delay time by the number of transmission paths. In this example, the number of transmission paths is equal to the number of established wireless links, i.e., 2. The management unit 170 notifies the frame processing unit 130 of the determined payload size.

[0088] For example, the management unit 170 calculates the overhead time and subtracts the overhead time from the maximum required delay time multiplied by the number of transmission paths to calculate the maximum payload size. The management unit 170 determines the payload size of the PPDU based on the MCS to be used for transmitting the PPDU, within a range equal to or less than the calculated maximum payload size. For example, the management unit 170 determines the maximum payload size that is usable with the MCS to be used for transmitting the PPDU and satisfies the condition that the preemption unit length is equal to or less than the maximum required delay time multiplied by the number of transmission paths. Ideally, the payload size is set to a value that makes the preemption unit length equal to the maximum required delay time multiplied by the number of transmission paths. This value is called the optimal value. The optimal value may not be usable with the MCS to be used for transmitting the PPDU. In this case, the payload size is set to a value that is usable with the MCS to be used for transmitting the PPDU, but is smaller than the optimal value and closest to the optimal value.

[0089] The method for determining the payload size of a PPDU according to the second embodiment is the same as that described in the first embodiment with reference to Fig. 9. The difference is that in the first embodiment, the payload size is determined so that the preemption unit length is equal to or less than the maximum required delay time, and in the second embodiment, the payload size is determined so that the preemption unit length is equal to or less than the value obtained by multiplying the maximum required delay time by the number of transmission paths.

[0090] The management unit 170 manages connections with wireless communication devices such as the terminal 70. The management unit 170 determines which of the affiliated APs 62 and 63 to use for data transmission. In one example, wireless links are associated with categories such as a traffic identifier (TID), and data is transmitted using the affiliated AP corresponding to the wireless link associated with the data category. Furthermore, the management unit 170 performs time synchronization of the affiliated APs 62 and 63 during data transmission using preemption. In one example, the management unit 170 maintains a master clock and provides time information generated by the master clock to the affiliated APs 62 and 63. In another example, the management unit 170 obtains time information from the upper layer 110 and provides it to the affiliated APs 62 and 63.

[0091] 13 is a diagram illustrating an example of the functional configuration of the frame processing unit 130. As illustrated in FIG. 13, the frame processing unit 130 includes a transmission buffer 131, a transmission buffer control unit 132, and an instruction unit 133.

[0092] The transmission buffer 131 buffers data received from the data processing unit 120. The transmission buffer control unit 132 manages the transmission buffer 131. For example, the transmission buffer control unit 132 retrieves data from the transmission buffer 131 and sends the data to one of the affiliated APs 62 and 63 in accordance with instructions from the management unit 170.

[0093] The instruction unit 133 detects low latency data. When the instruction unit 133 detects that low latency data has arrived at the frame processing unit 130, the instruction unit 133 instructs the transmission buffer control unit 132 to immediately transmit the low latency data.

[0094] 14 is a schematic diagram illustrating data transmission using preemption according to the second embodiment. When transmitting data using preemption, the transmission buffer control unit 132 divides the data according to the payload size notified by the management unit 170 to generate multiple pieces of divided data, and selectively provides the divided data to the affiliated APs 62 and 63.

[0095] In the example shown in Figure 14, the preemption unit length is twice the maximum required delay time. Immediately after the transmission right is acquired for wireless link #1 using frequency channel #1, the transmission right is acquired for wireless link #2 using frequency channel #2. In this case, the management unit 170 synchronizes the time between wireless links #1 and #2. For example, the management unit 170 sets the timing at which PPDU transmission starts for wireless link #1 as the reference Ref, and starts PPDU transmission for wireless link #2 at a timing that is half the preemption unit length or the maximum required delay time after the reference Ref.

[0096] In the arrangement shown in Figure 14, regardless of the timing at which low-latency data is generated, it is possible to have the low-latency data interrupt any of the wireless links within the maximum required delay time. For example, if low-latency data is generated at the timing shown in Figure 14, wireless link #1 cannot transmit the low-latency data from the generation of the low-latency data until the maximum required delay time has elapsed, but wireless link #2 can. In this case, the low-latency data will be transmitted via wireless link #2.

[0097] Fig. 15 shows an example of a schematic functional configuration of the terminal 70. In Fig. 15, the same components as those shown in Fig. 8 are denoted by the same reference numerals, and redundant explanations thereof will be omitted where appropriate.

[0098] 15, terminal 70 includes upper layers 210 in addition to non-APMLD 71 and affiliated STAs 72 and 73. Non-APMLD 71 includes a data processing unit 220 and a frame processing unit 230. Affiliated STAs 72 and 73 each include a MAC frame processing unit 240 and a radio signal processing unit 250.

[0099] Affiliated STA 72 is used to receive radio signals transmitted from affiliated AP 62 of access point 10, and affiliated STA 73 is used to receive radio signals transmitted from affiliated AP 63 of access point 10.

[0100] In each of the affiliated STAs 72 and 73, the wireless signal processing unit 250 receives a wireless signal, converts the received wireless signal into a wireless frame, and extracts a MAC frame from the wireless frame. The MAC frame processing unit 240 receives the MAC frame from the wireless signal processing unit 250, extracts data from the received MAC frame, and sends the extracted data to the frame processing unit 230.

[0101] Frame processing unit 230 receives data from affiliated STAs 72 and 73 and sends the received data to upper layer 210 via data processing unit 220 and an LLC layer (not shown). Upper layer 210 receives data from data processing unit 220. For example, the data is provided to an application running in upper layer 210.

[0102] When data transmission is performed using preemption, the frame processing unit 230 buffers the received data and combines the data to restore the original data. Upon receiving low-latency data, the frame processing unit 230 immediately sends the data to the data processing unit 220.

[0103] As described above, the access point 60 communicates with the terminal 70 via a transmission path including the wireless link #1 and a transmission path including the wireless link #2. The access point 60 acquires information indicating the required delay time of the low-latency data, calculates the maximum required delay time, which is the maximum delay time allowed as a media access delay in the data link layer, from the required delay time, and determines the payload size of the PPDU so that the preemption unit length is equal to or less than the value obtained by multiplying the maximum required delay time by the number of transmission paths. Synchronization is achieved between the wireless links #1 and #2 so that the transmission timing is shifted by half the preemption unit length.

[0104] According to the above configuration, when low latency data occurs during data transmission by preemption, it is possible to wirelessly transmit the low latency data to the terminal 70 so as to satisfy the required latency time of the low latency data.

[0105] The access point 60 determines the payload size of the PPDU so that the preemption unit length is equal to or less than the maximum required delay time multiplied by the number of transmission paths, and the payload size of the PPDU is as large as possible. This shortens the total overhead time. As a result, it becomes possible to meet the requirements for low-latency data while suppressing a decrease in the time efficiency of frame transmission.

[0106] The technique according to the second embodiment can also be applied to a case in which multiple transmission paths are configured by multiple access points at different geographical locations, as shown in FIG. 16 . The wireless system 91 shown in FIG. 16 includes access points 92, 93, and 94 and a terminal 70. The access point 92 is connected to access points 93 and 94 at different geographical locations via a wired or wireless connection and controls the access points 93 and 94. A wireless link is established between the access point 93 and an affiliated STA 72 of the terminal 70, and frequency channel #1 is used for communication between the access point 93 and the affiliated STA 72. A wireless link is established between the access point 94 and an affiliated STA 73 of the terminal 70, and a different frequency channel #2 is used for communication between the access point 94 and the affiliated STA 73. The connection topology shown in FIG. 16 is sometimes referred to as a multi-AP connection, the access point 92 is sometimes referred to as a sharing access point, and the access points 93 and 94 are sometimes referred to as shared access points. The access point 92 performs processing similar to that performed by the upper layer 110, data processing unit 120, frame processing unit 130, request delay analysis unit 160, and management unit 170 described with reference to Figures 12 and 13, thereby communicating with the terminal 70 via the access points 93 and 94.

[0107] Furthermore, the method according to the first embodiment can also be used in each of the wireless system 90 shown in Fig. 11 and the wireless system 91 shown in Fig. 16. For example, when one of the transmission paths is used for data communication, the method according to the first embodiment may be used.

[0108] 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 components from the disclosed components. For example, if the problem can be solved and the effects can be obtained even if some components are removed from all the components shown in the embodiments, the configuration from which these components are removed can be extracted as an invention.

[0109] DESCRIPTION OF SYMBOLS 10...Access point 11...CPU 12...ROM 13...RAM 14...Wireless communication module 15...Wired communication module 110...Upper layer 120...Data processing unit 130...Frame processing unit 131...Transmission buffer 132...Transmission buffer control unit 133...Instruction unit 140...MAC frame generation unit 150...Wireless signal processing unit 160...Request delay analysis unit 170...Management unit 20...Terminal 21...CPU 22...ROM 23...RAM 24...Wireless communication module 25...Display 26...Storage 210...Upper layer 220...Data processing unit 230...Frame processing unit 240...MAC frame processing unit 250...Wireless signal processing unit 30...Communication network 31...Server 40...Wireless system 60...Access point 61...AP MLD 62, 63...Affiliated AP 70...Terminal 71: Non-AP MLD 72, 73: Affiliated STA 80: Communication network 90, 91: Wireless system 92, 93, 94: Access point

Claims

1. A wireless communication device comprising: an acquisition unit that acquires information indicating a required delay time for low-latency data; a required delay analysis unit that calculates, from the required delay time, a maximum required delay time, which is the maximum delay time allowed as a media access delay in the data link layer; and a determination unit that determines, based on the maximum required delay time, the payload size of wireless frames for a data transmission operation in which multiple wireless frames are transmitted within a TXOP (transmission opportunity) period.

2. The wireless communication device according to claim 1, wherein the determination unit determines the payload size of the wireless frame so that the time required for exchanging the wireless frame is equal to or less than the maximum required delay time.

3. The wireless communication device of claim 2, wherein the determination unit calculates overhead time related to the transmission of the wireless frame, including the time required to transmit the preamble of the wireless frame and a predetermined IFS (interframe space) waiting time, determines a maximum value for the payload size of the wireless frame by subtracting the overhead time from the maximum required delay time, and determines the payload size of the wireless frame within a range not exceeding the maximum value.

4. The wireless communication device according to claim 3, wherein the determination unit determines, as the payload size of the wireless frame, the largest payload size that can be used with the MCS (modulation and coding scheme) to be used for transmitting the wireless frame and that satisfies the condition that the time required for exchanging the wireless frame for the data transmission operation is less than or equal to the maximum required delay time.

5. The wireless communication device according to claim 1, wherein the wireless communication device communicates with other wireless communication devices via multiple transmission paths, and the determination unit determines the payload size of the wireless frame so that the time required to exchange the wireless frame is equal to or less than the maximum required delay time multiplied by the number of the transmission paths.

6. The wireless communication device according to claim 5, wherein the plurality of transmission paths include a first wireless link and a second wireless link, and the first wireless link and the second wireless link are synchronized so that the transmission timing is shifted by half the time required for exchanging the wireless frames between them.

7. The wireless communication device of claim 1, wherein the wireless communication device is an access point.

8. A wireless communication method executed by a wireless communication device, comprising: acquiring information indicating a required delay time for low-latency data; calculating a maximum required delay time, which is the maximum delay time allowed as a media access delay in the data link layer, from the required delay time; and determining a payload size of wireless frames for a data transmission operation that transmits multiple wireless frames within a TXOP (transmission opportunity) period, based on the maximum required delay time.

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