Access point and communication method

Abstract

This access point includes a setting unit, a transmission opportunity control part, and a guard interval calculation part. The setting unit sets a service period for preferentially implementing exchange of low-latency traffic. The transmission opportunity control part performs control for terminating the transmission opportunity of an own station before a start time of the service period. The guard interval calculation part calculates a guard interval that is a delay time for delaying the start of the service period on the basis of: the time from the start of synchronization with the other station related to the service period to the start time point of the service period; the accuracy of a first timer for measuring the start time point of the service period in the own station; the accuracy of a second timer for measuring the start time point of the service period in the other station; the first permissible range of the offset in the frequency band used for transmitting radio signals in the own station; and the second permissible range of the offset in the frequency band used for transmitting radio signals in the other station. The transmission opportunity control part determines that the state is in the service period when the guard interval has elapsed after the termination of the transmission opportunity.

Description

Access point and communication method

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

[0002] A wireless LAN (Local Area Network) is known as a system that wirelessly connects an access point (AP) and a terminal. A wireless LAN allows terminals located within the communication range of the AP to access the network via the AP. The AP and terminals may establish a service period for preferentially exchanging low-latency traffic. The function for establishing such a service period is called a restricted TWT (R-TWT) function. In the R-TWT function, an AP exchanging low-latency traffic announces the start time and duration of the service period using a beacon or the like. Other APs that do not exchange low-latency traffic refrain from exchanging traffic during the service period.

[0003] In an overlapping basic service set (OBSS) environment, interference may occur due to a transmission opportunity (TXOP) set by another AP before the start of a service period. Therefore, it has been proposed to share service period setting information among the APs, thereby controlling all APs to terminate their TXOPs at least by the start time of the service period.

[0004] IEEE 802.11-23 / 226r2, July 2023

[0005] The time management until the start of the service period is performed by each AP. However, the accuracy of time measurement by each AP varies. Therefore, the start time of the service period measured by each AP may also vary. For this reason, it is not always possible for all APs to end their TXOP at the same time. If an AP has not yet ended its TXOP at the originally scheduled start time of the service period, interference will occur even during the service period.

[0006] The embodiments provide an access point and a communication method that can suppress interference during a service period.

[0007] An access point according to one embodiment includes a setting unit, a transmission opportunity control unit, and a guard interval calculation unit. The setting unit sets a service period in which low-latency traffic exchange is prioritized. The transmission opportunity control unit controls to end the transmission opportunity of the local station by the start time of the service period. The guard interval calculation unit calculates the guard interval, which is a delay time for delaying the start of the service period, based on the time from the start of synchronization with other stations related to the service period to the start time of the service period, the accuracy of a first timer in the local station that measures the start time of the service period, the accuracy of a second timer in the other station that measures the start time of the service period, a first allowable range of offset in a frequency band used for transmitting wireless signals in the local station, and a second allowable range of offset in a frequency band used for transmitting wireless signals in the other station. The transmission opportunity control unit determines that the service period has begun when the guard interval has elapsed after the end of the transmission opportunity.

[0008] According to the embodiment, an access point and a communication method capable of suppressing interference during a service period are provided.

[0009] FIG. 1 is a block diagram showing an example of the configuration of a communication system according to an 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 an embodiment. FIG. 5 is a diagram showing an example of the format of a beacon frame transmitted before the R-TWT function is performed according to an embodiment. FIG. 6 is a block diagram showing an example of the functional configuration of a terminal according to an embodiment. FIG. 7 is a flowchart showing operations related to the R-TWT function of AP 10-1. FIG. 8 is a flowchart showing operations of AP 10-2. FIG. 9 is a timing chart related to the R-TWT function according to an embodiment. FIG. 10 is a timing chart related to the R-TWT function according to a modified embodiment.

[0010] Hereinafter, an embodiment will be described with reference to the drawings. Fig. 1 is a block diagram showing an example of the configuration of a communication system according to an embodiment. As shown in Fig. 1, the communication system 1 includes access points (APs) 10-1 and 10-2, terminals 20-1 and 20-2, and a network 30.

[0011] The APs 10-1 and 10-2 and the terminals 20-1 and 20-2 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] The APs 10-1 and 10-2 have an R-TWT function for reserving a TXOP for traffic requiring low latency. By utilizing the R-TWT function, the APs 10-1 and 10-2 can set a service period during which the exchange of traffic requiring low latency can be prioritized over the exchange of traffic not requiring low latency. Such a service period is also called an R-TWT SP (service period).

[0013] Furthermore, the terminals 20-1 and 20-2 support the R-TWT function. That is, the terminals 20-1 and 20-2 can exchange traffic requiring low latency during a service period set by the AP 10-1 or the AP 10-2. The terminals 20-1 and 20-2 are, for example, smartphones or personal computers (PCs), and are wireless terminals that comply with the IEEE 802.11 standard.

[0014] Here, AP 10-1 may communicate with a terminal located in coverage area CA-1. Similarly, AP 10-2 may communicate with a terminal located in coverage area CA-2. Coverage areas CA-1 and CA-2 have an overlapping area. In FIG. 1, terminal 20-1 is located in the overlapping area of ​​coverage areas CA-1 and CA-2. Meanwhile, terminal 20-2 is located in an area included only in coverage area CA-2. In this case, AP 10-2 and terminal 20-2 may become sources of interference during communication between terminal 20-1 and AP 10-1. At this time, AP 10-1 may exchange traffic with terminal 20-1 using the R-TWT function. When a service period is set by AP 10-1, AP 10-2 and terminal 20-2 suppress data exchange during the service period. In the embodiment, timing is adjusted to ensure that the TXOP in AP 10-2 ends before the start of the service period in AP 10-1.

[0015] In the following, APs 10-1 and 10-2 have the same configuration. In the following, when there is no particular distinction between APs 10-1 and 10-2, both may be referred to as AP 10. Similarly, in the following, terminals 20-1 and 20-2 have the same configuration. In the following, when there is no particular distinction between terminals 20-1 and 20-2, both may be referred to as terminal 20.

[0016] Next, the hardware configuration of the AP and the terminal in the communication system according to the embodiment will be described.

[0017] 2 is a block diagram showing an example of the hardware configuration of an AP. 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, a wired communication module 15, and an oscillator 16.

[0018] 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. The oscillator 16 functions as a clock that generates time information used by the AP 10. The time information is also called a TSF (time synchronization function) timer.

[0019] 3 is a block diagram showing an example of the hardware configuration of a 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, a storage 26, and an oscillator 27.

[0020] 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 work 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. The oscillator 27 functions as a clock for generating a TSF timer used in the terminal 20.

[0021] Here, the TSF timers of the AP 10 and the terminal 20 in this embodiment conform to the IEEE802.11 standard, and as will be described later, are generated so that their accuracy conforms to the IEEE802.11 standard.

[0022] Next, the functional configuration of the AP and the terminal in the communication system according to the embodiment will be described.

[0023] 4 is a block diagram showing an example of the functional configuration of an AP according to an embodiment. The AP 10 functions as a computer including a timer generation unit 110, a data processing unit 120, a frame processing unit 130, a management unit 140, and a radio signal processing unit 150. The data processing unit 120 is a functional block that executes processing corresponding to the LLC sublayer of layer 2 and layers 3 to 7. The frame processing unit 130 and the management unit 140 are functional blocks that execute processing corresponding to the MAC sublayer of layer 2. The radio signal processing unit 150 is a functional block that executes processing corresponding to layer 1.

[0024] The timer generation unit 110 generates a TSF timer based on the output of the oscillator 16. The TSF timer serves as a reference clock for the operation of each element shown in FIG.

[0025] The data processing unit 120 outputs data input from the network 30 via the LLC layer to the frame processing unit 130. The data processing unit 120 also outputs data input from the frame processing unit 130 to the network 30 via the LLC layer.

[0026] When data is input to frame processing unit 130 from data processing unit 120 or management unit 140, frame processing unit 130 adds a MAC header to the input data to generate a MAC frame. Frame processing unit 130 then outputs the MAC frame to radio signal processing unit 150. Furthermore, when a MAC frame is input from radio signal processing unit 150, frame processing unit 130 extracts data from the MAC frame and outputs the extracted data to data processing unit 120 or management unit 140 depending on the type of MAC frame. Specifically, when the MAC frame is a data frame, frame processing unit 130 inputs the data to data processing unit 120. When the MAC frame is a management frame or a control frame, frame processing unit 130 inputs the data to management unit 140.

[0027] The management unit 140 controls the logical wireless connection between the AP 10 and the terminal 20. For example, the management unit 140 executes wireless connection processing in response to an association request from the terminal 20. Furthermore, when the R-TWT function is implemented, the management unit 140 generates a beacon for announcing a service period R-TWT-SP related to the R-TWT function, and sets a guard interval immediately before the service period R-TWT-SP based on the accuracy of the TSF timer. The management unit 140 includes a synchronization management unit 141, an R-TWT setting unit 142, a guard interval calculation unit 143, and a transmission opportunity control unit 144.

[0028] The synchronization management unit 141 manages time information within its own station. The synchronization management unit 141 transmits information about the TSF timer of its own station to other stations at times when time synchronization with other stations is required, such as when the R-TWT function needs to be implemented. Furthermore, when the synchronization management unit 141 receives TSF timer information from other stations, it updates the TSF timer information it manages itself with the received TSF timer information. Alternatively, the synchronization management unit 141 calculates the difference between the received TSF timer information and the TSF timer it manages itself.

[0029] The information on the TSF timer can be transmitted and received, for example, in a beacon. Fig. 5 is a diagram showing an example of the format of a beacon frame transmitted before the R-TWT function is performed in the embodiment.

[0030] As shown in FIG. 5, an example beacon frame includes, for example, an R-TWT-SP start time and an R-TWT-SP duration as R-TWT management information used in the R-TWT function.

[0031] The R-TWT-SP start time is information indicating the time when the service period R-TWT-SP starts. The R-TWT-SP duration is information indicating the length of the service period R-TWT-SP. In other words, the service period R-TWT-SP is set as the period from the R-TWT-SP start time to the time when the R-TWT-SP duration has elapsed.

[0032] Furthermore, as shown in Fig. 5, the beacon frame in one example includes a timestamp, which is information of the TSF timer at the time of transmission of the beacon frame.

[0033] The R-TWT setting unit 142 manages the service period R-TWT-SP. The R-TWT setting unit 142 sets the R-TWT-SP start time and R-TWT-SP duration at the timing when the R-TWT function needs to be performed, and notifies the R-TWT-SP start time and R-TWT-SP duration to the transmission opportunity control unit 144. In addition, the R-TWT setting unit 142 sets the R-TWT-SP start time and R-TWT-SP duration for its own station based on the R-TWT-SP start time and R-TWT-SP duration received from another station.

[0034] The guard interval calculation unit 143 calculates the guard interval. The guard interval is a delay time for delaying the start of the service period R-TWT-SP. The guard interval is calculated based on the time from the start of synchronization with other stations to the start time of R-TWT-SP, the accuracy of the timer generation unit 110 of the own station, and the accuracy of the timer generation unit 110 of the other station. The guard interval will be explained in detail later.

[0035] The transmission opportunity control unit 144 controls the TXOP related to the transmission of MAC frames. TXOP control can be performed by adjusting the operational parameters CWmin, CWmax, AIFS (arbitration interframe space), and TXOP (transmission opportunity) Limit. CWmin and CWmax respectively indicate the minimum and maximum values ​​of the contention window. The contention window is a parameter used to calculate backoff, which is a transmission waiting time for collision avoidance. AIFS is a fixed transmission waiting time set for each access category of traffic. TXOPLimit indicates the upper limit of TXOP, which is the channel occupation period. In particular, when a service period R-TWT-SP is set, the transmission opportunity control unit 144 controls the TXOP so that it ends by the start time of the R-TWT-SP.

[0036] The radio signal processing unit 150 generates a radio frame by adding a preamble and the like to the MAC frame input from the frame processing unit 130. The radio signal processing unit 150 converts the generated radio frame into a radio signal. The radio signal processing unit 150 then radiates (transmits) the converted radio signal via an antenna. 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 150 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 150 extracts a MAC frame from the converted radio frame. The radio signal processing unit 150 then outputs the extracted MAC frame to the frame processing unit 130.

[0037] 6 is a block diagram showing an example of the functional configuration of a terminal according to an embodiment. The terminal 20 functions as a computer including a timer generation unit 210, a data processing unit 220, a frame processing unit 230, a management unit 240, a radio signal processing unit 250, and an application execution unit 260. The data processing unit 220 is a functional block that executes processing corresponding to the LLC sublayer of layer 2 and layers 3 to 7. The frame processing unit 230 and the management unit 240 are functional blocks that execute processing corresponding to the MAC sublayer of layer 2. The radio signal processing unit 250 is a functional block that executes processing corresponding to layer 1.

[0038] The timer generation unit 210 generates a TSF timer based on the output of the oscillator 27. The TSF timer serves as a reference clock for the operation of each element shown in FIG.

[0039] The data processing unit 220 outputs data input from the application execution unit 260 via the LLC layer to the frame processing unit 230. The data processing unit 220 also outputs data input from the frame processing unit 230 to the application execution unit 260 via the LLC layer.

[0040] When data is input to frame processing unit 230 from data processing unit 220 or management unit 240, frame processing unit 230 adds a MAC header to the input data to generate a MAC frame. Frame processing unit 230 then outputs the MAC frame to radio signal processing unit 250. Furthermore, when a MAC frame is input from radio signal processing unit 250, frame processing unit 230 extracts data from the MAC frame and outputs the extracted data to data processing unit 220 or management unit 240 depending on the type of MAC frame. Specifically, when the MAC frame is a data frame, frame processing unit 230 inputs the data to data processing unit 220. When the MAC frame is a management frame or a control frame, frame processing unit 230 inputs the data to management unit 240.

[0041] The management unit 240 controls the logical wireless connection between the terminal 20 and the AP 10. For example, the management unit 240 generates an association request based on a beacon frame from the AP 10. The management unit 240 also sets a service period R-TWT-SP based on the beacon from the AP 10. The management unit 240 has a synchronization management unit 241, an R-TWT setting unit 242, and a transmission opportunity control unit 243.

[0042] The synchronization management unit 241 manages time information within its own station. The synchronization management unit 241 updates the TSF timer information it manages itself based on the TSF timer information received from the AP 10. Alternatively, the synchronization management unit 241 calculates the difference between the received TSF timer information and the TSF timer it manages itself.

[0043] The R-TWT setting unit 242 manages the service period R-TWT-SP. The R-TWT setting unit 242 sets the R-TWT-SP start time and R-TWT-SP duration for the own station based on the R-TWT-SP start time and R-TWT-SP duration received from the AP 10.

[0044] The transmission opportunity control unit 243 controls TXOP related to the transmission of MAC frames. The TXOP control can be performed based on the operational parameters CWmin, CWmax, AIFS, and TXOPLimit notified by the AP 10.

[0045] The radio signal processing unit 250 generates a radio frame by adding a preamble and the like to the MAC frame input from the frame processing unit 230. The radio signal processing unit 250 converts the generated radio frame into a radio signal. The radio signal processing unit 250 then radiates (transmits) the converted radio signal via an antenna. 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 250 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 250 extracts a MAC frame from the converted radio frame. The radio signal processing unit 250 then outputs the extracted MAC frame to the frame processing unit 230.

[0046] The application execution unit 260 executes an application based on data input from the data processing unit 220. The application execution unit 260 also inputs data to the data processing unit 220. For example, the application execution unit 260 can display application information on the display 25. The application execution unit 260 can also operate based on operations on an input interface.

[0047] Next, the operation of the communication system according to the embodiment will be described. In the following description, it is assumed that wireless connection processing between the AP 10-1 and the terminal 20-1 has been completed and that traffic requiring low latency has occurred between the AP 10-1 and the terminal 20-1. In this case, for example, the synchronization management unit 241 of the terminal 20-1 transmits a bandwidth allocation request for the service period R-TWT-SP to the AP 10-1.

[0048] 7 is a flowchart showing the operation related to the R-TWT function of the AP 10-1. In step S1, the synchronization management unit 141 of the AP 10-1, which has received a bandwidth allocation request for the service period R-TWT-SP, starts synchronization with other stations to implement the R-TWT function. Specifically, the synchronization management unit 141 transmits a synchronization frame, for example, a beacon frame. As shown in FIG. 5, the beacon frame includes a timestamp, an R-TWT-SP start time, and an R-TWT-SP duration. After transmitting the beacon frame, the R-TWT setting unit 142 of the AP 10-1 sets up the R-TWT function with the terminal 20-1. Details of the setup of the R-TWT function will not be described here.

[0049] In step S2, the guard interval calculation unit 143 calculates the guard interval. The method for calculating the guard interval will be described below.

[0050] According to the IEEE 802.11 standard, the accuracy of the TSF timer in a general station (non-DMG STA) that is not a DMG (directional multi-gigabit) station is specified to be within ±100 ppm. On the other hand, the accuracy of the TSF timer in a DMG station (DMG STA) is specified to be within ±20 ppm. In other words, when AP 10-1, AP 10-2, and terminals 20-1 and 20-2 are all non-DMG STAs, the TSF timer value will have a deviation of up to 200 ppm, which is the difference between the earliest and latest counts. Similarly, when AP 10-1, AP 10-2, and terminals 20-1 and 20-2 are all DMG STAs, the TSF timer value will have a deviation of up to 40 ppm, which is the difference between the earliest and latest counts. For example, if AP 10-1 and AP 10-2 both count 0.1 seconds, there will be a maximum difference of 20 microseconds between the counting results.

[0051] On the other hand, the IEEE 802.11 standard specifies that the allowable range of the symbol clock frequency offset of radio signals generated from the same reference oscillator is within ±20 ppm when the transmission frequency band is the 5 GHz or 6 GHz band, and within ±25 ppm when the transmission frequency band is the 2.4 GHz band. In other words, when the transmission frequency band of any of AP 10-1, AP 10-2, and terminals 20-1 and 20-2 is the 5 GHz band, the symbol clock frequency of the radio signal will have a deviation of up to 40 ppm, which is the difference between the lowest and highest frequencies. Similarly, when the transmission frequency band of any of AP 10-1, AP 10-2, and terminals 20-1 and 20-2 is the 2.4 GHz band, the symbol clock frequency of the radio signal will have a deviation of up to 50 ppm, which is the difference between the lowest and highest frequencies.

[0052] Therefore, for example, if AP 10-1, AP 10-2, and terminals 20-1 and 20-2 are all non-DMG STAs and the transmission frequency band of AP 10-1, AP 10-2, and terminals 20-1 and 20-2 is the 5 GHz band, even if AP 10-1 and AP 10-2 are synchronized and manage the R-TWT-SP start time from the same time, a deviation of up to (100 ppm + 100 ppm) + (20 ppm + 20 ppm) = 240 ppm may occur. On the other hand, if AP 10-1, AP 10-2, and terminals 20-1 and 20-2 all comply with the IEEE 802.11 standard, the deviation is at most 240 ppm. Therefore, by delaying the start of the service period R-TWT-SP by an amount equivalent to 240 ppm, interference from AP 10-2 during the service period R-TWT-SP of AP 10-1 due to the TXOP of AP 10-2 not having ended during the service period R-TWT-SP of AP 10-1 can be suppressed. The time for delaying the start of this service period R-TWT-SP is the guard interval. The guard interval g_time is calculated from the following equation (1), where Δt is the time difference between the synchronization start time t1 and the scheduled start time t2 of the service period R-TWT-SP, a [ppm] is the accuracy of the other station's TSF timer, b [ppm] is the accuracy of the station's TSF timer, and c [ppm] is the tolerance for the symbol clock frequency offset. Note that a and b are both 100 or less. Furthermore, c is 20 or less if the transmission frequency band is the 5 GHz band or the 6 GHz band, and is 25 or less if the transmission frequency band is the 2.4 GHz band. g_time=Δt×(a+b+2c) Equation (1)

[0053] Here, simply, a and b are 100 ppm, and c is 25 ppm or 20 ppm. On the other hand, if the accuracy of the TSF timer is reported from another station by a beacon frame, for example, a may be the accuracy value of the reported TSF timer. Furthermore, if the accuracy of the TSF timer is recognized in the own station, b may be the accuracy value of the recognized timer.

[0054] In step S3, the transmission opportunity control unit 144 starts counting the timer e_time1 for measuring the time until the guard interval. Additionally, when the AP 10-1 has obtained the TXOP, the transmission opportunity control unit 144 starts control for ending the TXOP by the R-TWT-SP start time. The service period R-TWT-SP start time here is not a time that takes the guard interval into consideration, but the originally scheduled R-TWT-SP start time t2.

[0055] In step S4, the transmission opportunity control unit 144 determines whether the TXOP has ended. If it is determined in step S4 that the TXOP has ended, the process proceeds to step S5. If it is determined in step S4 that the TXOP has not ended, the transmission opportunity control unit 144 continues control to end the TXOP.

[0056] In step S5, the transmission opportunity control unit 144 notifies other stations of the end of the TXOP. For example, the transmission opportunity control unit 144 notifies other stations of the end of the TXOP by transmitting a CF (contention free)-End frame.

[0057] In step S6, the transmission opportunity control unit 144 determines whether the guard interval has ended. That is, it determines whether the elapsed time of timer e_time1 since the end of TXOP has reached g_time. In step S6, the transmission opportunity control unit 144 waits for processing until it is determined that the guard interval has ended. If it is determined that the guard interval has ended in step S6, the processing proceeds to step S7.

[0058] In step S7, the AP 10-1 performs low latency traffic exchange with the terminal 20-1 during the service period R-TWT-SP.

[0059] In step S8, the R-TWT setting unit 142 determines whether the service period R-TWT-SP has ended. If it is determined in step S8 that the service period R-TWT-SP has ended, the processing in Fig. 7 ends. If it is determined in step S8 that the service period R-TWT-SP has not ended, the AP 10-1 continues exchanging low latency traffic with the terminal 20-1.

[0060] 8 is a flowchart showing the operation of the AP 10-2. In step S21, the synchronization management unit 141 of the AP 10-2 receives a beacon frame as a synchronization frame from the AP 10-1 and starts synchronization with the AP 10-1 by updating the time of its own station based on the timestamp recorded in the beacon frame. In addition, the R-TWT setting unit 142 of the AP 10-2 holds the service period R-TWT-SP specified by the beacon frame as a transmission suppression period.

[0061] In step S22, the guard interval calculation unit 143 calculates the guard interval. The guard interval is calculated as shown in equation (1). Note that in equation (1), the local station is AP 10-2 and the other station is AP 10-1.

[0062] In step S23, the transmission opportunity control unit 144 starts counting the timer e_time2 for measuring the time until the guard interval. Additionally, when the AP 10-2 has obtained the TXOP, the transmission opportunity control unit 144 starts control for ending the TXOP by the R-TWT-SP start time. The R-TWT-SP start time here is not a time that takes the guard interval into consideration, but the R-TWT-SP start time t2 notified by the beacon frame.

[0063] In step S24, the transmission opportunity control unit 144 determines whether the TXOP has ended. If it is determined in step S24 that the TXOP has ended, the process proceeds to step S25. If it is determined in step S24 that the TXOP has not ended, the transmission opportunity control unit 144 continues control to end the TXOP.

[0064] In step S25, the transmission opportunity control unit 144 notifies other stations of the end of the TXOP. For example, the transmission opportunity control unit 144 notifies other stations of the end of the TXOP by transmitting a CF-End frame.

[0065] In step S26, the transmission opportunity control unit 144 determines whether the guard interval has ended. That is, it determines whether the elapsed time of timer e_time2 since the end of TXOP has reached g_time. In step S26, the transmission opportunity control unit 144 waits for processing until it is determined that the guard interval has ended. If it is determined that the guard interval has ended in step S26, the processing proceeds to step S27.

[0066] In step S27, the AP 10-2 suppresses the exchange of traffic with the terminal 20-2 during the service period R-TWT-SP. Here, even during the service period R-TWT-SP, the AP 10-2 may communicate at low power that does not affect the communication between the AP 10-1 and the terminal 20-1.

[0067] In step S28, the R-TWT setting unit 142 determines whether the service period R-TWT-SP has ended. If it is determined in step S28 that the service period R-TWT-SP has ended, the processing in Fig. 8 ends. If it is determined in step S28 that the service period R-TWT-SP has not ended, the AP 10-2 suppresses the exchange of traffic with the terminal 20-2.

[0068] 9 is a timing chart relating to the R-TWT function in this embodiment. t_leader in the upper part of Fig. 9 shows the timing chart for AP 10-1. t_follower in the lower part of Fig. 9 shows the timing chart for AP 10-2.

[0069] 9, the operation of the R-TWT function is initiated by transmitting a synchronization frame sync, such as a beacon frame for synchronizing the R-TWT function, from AP 10-1 to AP 10-2. Here, the synchronization frame sync does not necessarily have to be transmitted from AP 10-1 to AP 10-2. The synchronization frame sync may be transmitted to both AP 10-1 and AP 10-2 from a controller that comprehensively manages both AP 10-1 and AP 10-2, for example. The controller may be wirelessly connected to both AP 10-1 and AP 10-2, or may be wired connected via network 30.

[0070] AP 10-1 calculates the guard interval g_time based on its own scheduled R-TWT-SP start time and timestamp. Similarly, AP 10-2 calculates the guard interval g_time based on the R-TWT-SP start time and timestamp included in the synchronization frame sync. When 100 ppm is used for a and 100 ppm is used for b, the guard intervals calculated by AP 10-1 and AP 10-2 match.

[0071] After calculating the guard interval, both the AP 10-1 and the AP 10-2 start control to terminate the TXOP. The target time for terminating the TXOP is the originally scheduled R-TWT-SP start time.

[0072] After the end of TXOP, a guard interval begins. When AP 10-1, AP 10-2, and terminals 20-1 and 20-2 are all non-DMG STAs and the transmission frequency bands of AP 10-1, AP 10-2, and terminals 20-1 and 20-2 are 5 GHz bands, an error of up to 120 ppm occurs in the count of timer e_time1 measured by AP 10-1 until the end of TXOP. Similarly, an error of up to 120 ppm occurs in the count of timer e_time2 measured by AP 10-2 until the end of TXOP. Ideally, the counts of e_time1 and e_time2 should be the same, but in FIG. 9, the count of e_time1 is slower than the count of e_time2. In this way, the start of both service periods R-TWT-SP is delayed by the amount of the guard interval so that the service period R-TWT-SP does not start even when the difference between the time managed by AP10-1 and the time managed by AP10-2 becomes maximum.

[0073] After the guard interval ends, the service period R-TWT-SP begins. During the service period R-TWT-SP, the AP 10-1 exchanges low-latency traffic with the terminal 20-1. On the other hand, the AP 10-2 suppresses traffic exchange during the service period R-TWT-SP.

[0074] As described above, according to the embodiment, the start of the service period R-TWT-SP is delayed by the guard interval according to the accuracy of the TSF timer of each AP and the tolerance range of the frequency offset. This makes it possible to suppress interference during the service period R-TWT-SP. Furthermore, the guard interval is determined based on the upper limit allowed by the standard. Therefore, the guard interval can be set to the minimum time required. Therefore, communication efficiency is also expected to be improved.

[0075] (Modification) A modification of the embodiment will be described below. In the above-described embodiment, Δt for calculating the guard interval is the difference between the time recorded in the timestamp, i.e., the start time of synchronization and the originally scheduled start time of R-TWT-SP. In contrast, Δt may be the difference between the time recorded in the timestamp and the count time of a timer from the start of synchronization to the end of TXOP. In this case, the guard interval is calculated after the end of TXOP.

[0076] Furthermore, depending on the configuration of the R-TWT function, as shown in FIG. 10, a backoff period may be provided after the start time of the R-TWT-SP, and the service period R-TWT-SP may start after the end of the backoff period. Even in such a case, a guard interval may be provided in the same manner as in the above-described embodiment. Furthermore, by providing a guard interval, if the backoff period is set randomly, its maximum value may be shortened. Conversely, the guard interval may be shortened by the minimum value of the backoff period. Furthermore, if the backoff period is not a random time, the guard interval may be shortened by that time.

[0077] The technology of the embodiment can also be applied to multi-link communication in which an AP and a terminal are connected using a plurality of different channels. In the case of multi-link communication, the service period R-TWT-SP can be set for each link.

[0078] Furthermore, in the embodiment, an example is shown in which there are two APs and two terminals. However, the number of APs and terminals is not limited to two. For example, even if three or more APs may interfere with communication between AP 10-1 and terminal 20-1, the guard interval can be calculated based on equation (1). Note that when three or more APs exist and the accuracy values ​​of the TSF timers of the respective APs are used to calculate the guard interval, the values ​​of a and b used in equation (1) are the accuracy values ​​of the two APs with the worst TSF timer accuracy among the multiple APs.

[0079] The processes in APs 10-1 and 10-2 can also be stored as programs that can be executed by a processor, which is a computer. Alternatively, they can be stored and distributed in a storage medium of an external storage device such as a magnetic disk, optical disk, or semiconductor memory. The processors of APs 10-1 and 10-20 can then load the programs stored in the storage medium of the external storage device and execute various processes by having their operations controlled by the loaded programs.

[0080] 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.

[0081] DESCRIPTION OF SYMBOLS 1...Communication system 10, 10-1, 10-2...Access point (AP) 11...CPU 12...ROM 13...RAM 14...Wireless communication module 15...Wired communication module 16...Oscillator 20, 20-1, 20-2...Terminal 21...CPU 22...ROM 23...RAM 24...Wireless communication module 25...Display 26...Storage 27...Oscillator 30...Network 110...Timer generation unit 120...Data processing unit 130...Frame processing unit 140...Management unit 141...Synchronization management unit 142...R-TWT setting unit 143...Guard interval calculation unit 144...Transmission opportunity control unit 150...Wireless signal processing unit 210...Timer generation unit 220...Data processing unit 230...Frame processing unit 240...Management unit 241...Synchronization management unit 242...R-TWT setting unit 243: Transmission opportunity control unit 250: Radio signal processing unit 260: Application execution unit

Claims

1. A setting unit that sets a service period for preferentially performing low-latency traffic exchange; a transmission opportunity control unit that performs control to end the transmission opportunity of its own station by the start time of the service period; based on the time from the start of synchronization with other stations related to the service period to the start time of the service period, the accuracy of a first timer that measures the start time of the service period at its own station, the accuracy of a second timer that measures the start time of the service period at other stations, a first allowable range of offsets in the frequency band used for transmitting radio signals at its own station, and a second allowable range of offsets in the frequency band used for transmitting radio signals at other stations, a guard interval calculation unit that calculates a guard interval, which is a delay time for delaying the start of the service period; and an access point, wherein the transmission opportunity control unit determines that it is the service period when the guard interval has elapsed after the end of the transmission opportunity.

2. The access point according to claim 1, wherein the guard interval is a value obtained by multiplying the sum of the accuracy of the first timer, the accuracy of the second timer, the first allowable range, and the second allowable range by the time from the start of synchronization with other stations related to the service period to the start time of the service period.

3. The access point according to claim 1, wherein the accuracy of the first timer and the accuracy of the second timer are 100 ppm.

4. The access point according to claim 1, wherein the first allowable range and the second allowable range when the frequency band used for transmitting the radio signal is the 5 GHz band or the 6 GHz band are 20 ppm, and the first allowable range and the second allowable range when the frequency band used for transmitting the radio signal is the 2.4 GHz band are 25 ppm.

5. Setting a service period for preferentially performing low-latency traffic switching, controlling to end the own station's transmission opportunity by the start time of the service period, calculating a guard interval which is a delay time for delaying the start of the service period based on the time from the start of synchronization with other stations related to the service period to the start time of the service period, the accuracy of a first timer for measuring the start time of the service period at the own station, the accuracy of a second timer for measuring the start time of the service period at the other station, a first allowable range of offsets in the frequency band used for wireless signal transmission at the own station, and a second allowable range of offsets in the frequency band used for wireless signal transmission at the other station, and the control of the transmission opportunity includes determining that it is the service period when the guard interval has elapsed after the end of the transmission opportunity. Communication method.

Images