JP7476966B2 - Base station and communication method - Google Patents

Description

The embodiments relate to a base station and a communication method.

Wireless LAN base stations and terminals access channels and transmit radio signals using CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). In CSMA/CA, the base station and terminal wait for a time specified by the access parameters, and then use carrier sense to confirm that the channel is not being used by other terminals, etc. before transmitting radio signals.

EDCA (Enhanced Distribution Channel Access) is defined as one of the priority control methods for wireless LANs. In EDCA, traffic from higher layers is classified into one of four access categories (AC): AC_VO (Voice), AC_VI (Video), AC_BE (Best effort), and AC_BK (Background). In EDCA, CSMA/CA is performed for each access category. In EDCA, access parameters are assigned so that the transmission of wireless signals is given a relative priority in the order of AC_VO, AC_VI, AC_BE, and AC_BK.

IEEE Std 802.11-2016,"10.22.2 HCF contention based channel access (EDCA)", 7 December 2016

EDCA allows for relative prioritization between traffic streams. Here, for example, RTAs (Real-Time Applications) such as network games and industrial robot control may have absolute delay requirements for each application. Relative prioritization between traffic streams alone may not necessarily satisfy the requirements.

The embodiments provide a base station and a communication method that can utilize applications (RTA) that have absolute requirements regarding delay.

A base station according to one aspect includes a wireless signal processing unit, a management unit, and a control unit. The wireless signal processing unit receives information on a measurement result of a delay when transmitting a wireless signal from a terminal. The management unit analyzes whether the cause of the delay is due to a contention in the transmission of the wireless signal or due to a retransmission of the wireless signal based on the information on the measurement result. The control unit changes the manner of control of an access parameter or an access method related to the transmission, or both the access parameter and the access method, depending on whether the cause of the delay is due to a contention in the transmission of the wireless signal or due to a retransmission of the wireless signal .

According to an embodiment, a base station and a communication method can be provided that can utilize applications (RTA) that have absolute requirements regarding delay.

FIG. 1 is a diagram illustrating an example of a configuration of a communication system according to an embodiment. FIG. 2 is a diagram illustrating a hardware configuration of an example of a base station. FIG. 3 is a diagram illustrating a hardware configuration of an example of a terminal. FIG. 4 is a diagram showing processing of a MAC (Media Access Control) layer during communication between a base station and a terminal. FIG. 5 is a functional block diagram of the base station. FIG. 6 is a functional block diagram of the terminal. FIG. 7 is a diagram showing the format of a field for storing a measurement report. FIG. 8 is a diagram for explaining the delay measured by the measurement unit in the embodiment. FIG. 9 is a diagram showing the frame format of a data frame including a measurement report. FIG. 10 is a flowchart illustrating an example of a transmission process of a terminal. FIG. 11 is a flowchart showing the reception process of the base station. FIG. 12 is a conceptual diagram for explaining an example of adjusting access parameters only within one's own BSS. FIG. 13 illustrates an example of adjusting access parameters to reduce delay while taking into account interference from other BSSs. FIG. 14 is a diagram for explaining the delay measured by the measurement unit in the third modification.

The following describes an embodiment with reference to the drawings. FIG. 1 is a diagram showing an example of a configuration of a communication system according to an embodiment. The communication system 1 has a base station 10 and a terminal 20. The base station 10 communicates with terminals within a predetermined service area via wireless LAN. Although not shown in FIG. 1, communication may also take place between the terminals 20.

Figure 2 is a diagram showing an example of the hardware configuration of a base station 10. The base station 10 is an access point (AP) for the terminal 20. The base station 10 is not limited to being fixed, and may be mounted on a mobile object.

The base station 10 has a processor 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, a wireless module 14, and a routing module 15.

The processor 11 is a processing device that controls the entire base station 10. The processor 11 is, for example, a CPU (Central Processing Unit). The processor 11 is not limited to a CPU. An ASIC (Application Specific IC) or the like may be used instead of a CPU. The number of processors 11 may be two or more.

ROM 12 is a read-only storage device. ROM 12 stores firmware and various programs necessary for the operation of base station 10.

RAM 13 is a memory device that can be written to at will. RAM 13 is used as a working area for processor 11 and temporarily stores firmware and the like stored in ROM 12.

The wireless module 14 is a module configured to perform processing required for wireless LAN communication. The wireless module 14, for example, configures a MAC frame from data transferred from the processor 11, converts the configured MAC frame into a wireless signal, and transmits it to the terminal 20. The wireless module 14 also receives a wireless signal from the terminal 20, extracts data from the received wireless signal, and transfers it to the processor 11, for example.

The routing module 15 is provided so that the base station 10 can communicate with, for example, a server (not shown) via a network. The base station 10 does not necessarily have to have the routing module 15. The base station 10 may be configured to access a router provided outside the base station 10 by wireless communication or wired communication, and connect to the network via this router.

Figure 3 is a diagram showing an example of the hardware configuration of terminal 20. Terminal 20 is a terminal device (station) such as a smartphone. Terminal 20 may be a mobile terminal, a terminal mounted on a moving object, or a fixed terminal.

The terminal 20 has a processor 21, a ROM 22, a RAM 23, a wireless module 24, a display 25 and storage 26.

The processor 21 is a processing device that controls the entire terminal 20. The processor 21 is, for example, a CPU. The processor 21 is not limited to a CPU. An ASIC or the like may be used instead of a CPU. The processor 21 may be two or more processors rather than one.

ROM 22 is a read-only storage device. ROM 22 stores firmware and various programs necessary for the operation of terminal 20.

RAM 23 is a storage device that can be written to at will. RAM 23 is used as a working area for processor 21, and temporarily stores firmware and the like stored in ROM 22.

The wireless module 24 is a module configured to perform processing necessary for wireless LAN communication. The wireless module 24 configures a MAC frame for wireless communication from data transferred from the processor 21, for example, and converts the configured MAC frame into a wireless signal to transmit to the base station 10. The wireless module 24 also receives a wireless signal from the base station 10, extracts data from the received wireless signal, and transfers it to the processor 21, for example.

The display 25 is a display device that displays various screens. The display 25 may be a liquid crystal display, an organic electroluminescence display, or the like. The display 25 may also be equipped with a touch panel.

Storage 26 is a storage device such as a hard disk. Storage 26 stores, for example, various applications executed by processor 21.

Figure 4 is a diagram showing the processing of the MAC (Media Access Control) layer during communication between the base station 10 and the terminal 20. Figure 4 shows both the transmitting side processing and the receiving side processing. When one of the wireless modules of the base station 10 and the terminal 20 performs the transmitting side processing, the other wireless module performs the receiving side processing. In the following examples, the transmitting side and receiving side wireless modules will be described without distinction.

First, the processing on the transmitting side will be described. In step S10, the wireless module performs A-MSDU aggregation. Specifically, the wireless module combines multiple data input from higher layers such as the application layer to generate an A-MSDU (Aggregate-MAC service data unit).

In step S11, the wireless module assigns a sequence number (SN) to the A-MSDU. The sequence number is a unique number for identifying the A-MSDU.

In step S12, the wireless module fragments (divides) the A-MSDU into multiple MPDUs (MAC protocol data units).

In step S13, the wireless module encrypts each MPDU and generates an encrypted MPDU.

In step S14, the wireless module adds a MAC header and an error detection code (FCS) to each encrypted MPDU. The error detection code is, for example, a CRC (Cyclic Redundancy Check) code.

In step S15, the wireless module performs A-MPDU aggregation. Specifically, the wireless module combines multiple MPDUs to generate an A-MPDU (Aggregate-MAC protocol data unit) as a MAC frame.

After step S15, the wireless module performs physical layer processing on the MAC frame. That is, the wireless module performs modulation processing on the MAC frame to generate a wireless signal, and transmits the wireless signal to the base station 10.

Next, the process on the receiving side will be described. When a wireless signal is received, the wireless module performs physical layer processing to restore a MAC frame from the wireless signal. The wireless module then performs the MAC layer processing shown in FIG. 4.

In step S20, the wireless module performs A-MPDU deaggregation. Specifically, the wireless module divides the A-MPDU into MPDU units.

In step S21, the wireless module performs error detection. For example, the wireless module uses CRC to determine whether reception of the wireless signal has been successful. If reception of the wireless signal has failed, the wireless module may request retransmission. At this time, the wireless module may request retransmission in MPDU units. On the other hand, if reception of the wireless signal has been successful, the wireless module performs the following process.

In step S22, the wireless module performs address detection. At this time, the wireless module determines whether or not the transmitted MPDU is addressed to itself based on the address recorded in the MAC header of each MPDU. If the MPDU is not addressed to itself, the wireless module does not perform the next process. If the MPDU is addressed to itself, the wireless module performs the next process.

In step S23, the wireless module decrypts the encrypted MPDU.

In step S24, the wireless module defragments the MPDU. In other words, the wireless module reconstructs the A-MSDU from multiple MPDUs.

In step S25, the wireless module performs A-MSDU deaggregation. Specifically, the wireless module restores the A-MSDU to data in MSDU units.

After step S25, the wireless module outputs the data to a layer above the MAC layer, such as an application layer.

Figure 5 is a functional block diagram of the base station 10. The base station 10 has a data processing unit 101, a radio signal processing unit 102, a management unit 103, and a control unit 104. The data processing unit 101, the radio signal processing unit 102, the management unit 103, and the control unit 104 are realized, for example, by the processor 11 and the radio module 14.

The data processing unit 101 constructs a MAC frame from data transferred from, for example, a server on the network. The data processing unit 101 also restores data from the MAC frame transferred from the wireless signal processing unit 102. This data includes a measurement report sent from the terminal 20.

The wireless signal processing unit 102 performs processing for transmitting or receiving wireless signals. For example, the wireless signal processing unit 102 converts a MAC frame constructed by the data processing unit 101 into a wireless signal and transmits the wireless signal to the terminal 20. The wireless signal processing unit 102 also receives a wireless signal from the terminal 20, extracts the MAC frame from the received wireless signal, and transfers it to the data processing unit 101.

Here, the wireless signal processing unit 102 may be configured to transmit wireless signals, for example, by EDCA. In this case, the wireless signal processing unit 102 has transmission queues AC_VO, AC_VI, AC_BE, and AC_BK for each access category (AC). The transmission queue AC_VO is a queue for holding MAC frames categorized as VO (Voice). The transmission queue AC_VI is a queue for holding MAC frames categorized as VI (Video). The transmission queue AC_BE is a queue for holding MAC frames categorized as BE (Best effort). The transmission queue AC_BK is a queue for holding MAC frames categorized as BK (Background). Furthermore, the wireless signal processing unit 102 may have a transmission queue AC_LL for holding MAC frames categorized as access category LL (Low latency). The access category AC_LL is an access category for RTAs that have absolute latency requirements, such as network games, industrial robot control applications, etc. The transmission queue AC_LL may have multiple transmission queues, each of which corresponds to a limit of tolerable latency.

The wireless signal processing unit 102 maps the MAC frame transferred from the data processing unit 101 to one of four or five access categories according to the category of the data recorded in the MAC frame. According to the result of this mapping, the wireless signal processing unit 102 inputs the MAC frame to the corresponding transmission queue.

The wireless signal processing unit 102 waits for transmission for a time specified by the access parameters set for each access category, while confirming by carrier sense for each access category that there are no wireless signals being transmitted by other terminals, etc. If the channel becomes busy while waiting for transmission, it waits for the specified time to count. A busy channel means that the channel is being used for other transmissions. If the channel is idle while waiting for transmission, the wireless signal processing unit 102 takes out a MAC frame from the corresponding transmission queue, converts this MAC frame into a wireless signal, and transmits it. An idle channel means that the channel is not being used for other transmissions.

Here, the access parameters may be assigned in the order of LL, VO, VI, BE, and BK so that the transmission of the wireless signal is prioritized. The access parameters may include CW _min , CW _max , AIFS, and TXOP _Limit . CW _min and CW _max are the maximum and minimum values of the contention window (CW), which is a transmission waiting time for contention avoidance, respectively. The shorter the CW _min and CW _max are, the more likely the transmission queue is to obtain a transmission opportunity. AIFS (Arbitration Inter Frame Space) is a fixed transmission waiting time set for each access category of the wireless signal. The smaller the AIFS is, the higher the priority of the transmission queue is. TXOP _Limit is the upper limit of the transmission opportunity (TXOP), which is the occupancy time of the channel. The larger the value of TXOP _Limit is, the more wireless signals can be transmitted at one transmission opportunity.

The management unit 103 manages the measurement reports sent from the terminal 20. For example, the management unit 103 stores the measurement reports and analyzes the measurement reports at the necessary timing. The measurement reports are reports that include information regarding delays in the transmission of wireless signals at the terminal 20. As will be explained in detail later, delays in the transmission of wireless signals occur according to a number of delay factors. The measurement reports include information on the measurement results of delays for each delay factor.

The control unit 104 performs the necessary control for transmitting the wireless signal according to the cause of the delay analyzed by the management unit 103. This control includes adjusting the access parameters in the wireless signal processing unit 102. The operation of the control unit 104 will be described in detail later.

Figure 6 is a functional block diagram of the terminal 20. The terminal 20 has a data processing unit 201, a wireless signal processing unit 202, and a measurement unit 203. The data processing unit 201, the wireless signal processing unit 202, and the measurement unit 203 are realized, for example, by the processor 21 and the wireless module 24.

The data processing unit 201 constructs a MAC frame from data input from, for example, a higher-level application. The data processing unit 201 also restores data from the MAC frame transferred from the wireless signal processing unit 202. This data is used, for example, by the higher-level application. Furthermore, the data processing unit 201 generates a MAC frame including a measurement report that stores the results of measurements made by the measurement unit 203.

The wireless signal processing unit 202 performs processing for transmitting or receiving wireless signals. For example, the wireless signal processing unit 202 converts a MAC frame configured by the data processing unit 201 into a wireless signal and transmits the wireless signal to, for example, the base station 10. The wireless signal processing unit 202 also receives a wireless signal from the base station 10, extracts a MAC frame from the received wireless signal, and transfers it to the data processing unit 201. Here, the wireless signal processing unit 202 may be configured to transmit a wireless signal, for example, by EDCA, in the same way as the base station 10.

The measurement unit 203 measures the delay of the transmission of the wireless signal in the terminal 20 for each factor. Then, the measurement unit 203 creates a measurement report including information on the delay based on the measurement result. FIG. 7 is a diagram showing the format of a field that stores a measurement report. The field in which the measurement report is stored includes a plurality of fields in which data of the measurement result for each access category is stored. The field in which the measurement report is stored may include only one field in which data of the measurement result of, for example, AC_LL is stored. In addition, the field in which the measurement report is stored may store the measurement result of the delay for each traffic type (TID) instead of for each access category. The TID is assigned for each application (session) handled by the terminal 20. The mapping to the access category described above may be performed based on the TID. By storing the measurement result for each TID, the delay distinguished for each application can be measured.

8 is a diagram for explaining delays measured by the measurement unit 203 in the embodiment. The delays measured in the embodiment include 1) queuing time T _Q , 2) contention waiting time T _W , 3) contention time T _C , 4) retransmission time T _R , and 5) transmission time T _TX . The queuing time T _Q , contention waiting time T _W , contention time T _C , retransmission time T _R , and transmission time T _TX may be measured by a clock (not shown) provided in the terminal 20.

The queuing time _TQ is the time from when a MAC frame is input to the tail of a transmission queue until it reaches the head of the transmission queue. A long queuing time _TQ means, for example, that a delay is occurring due to many MAC frames being stored in the transmission queue.

The contention waiting time T _W is a waiting time determined by the AIFS for collision avoidance control having a function of controlling wireless transmission with priority among access categories. If the channel becomes busy during the contention waiting time T _W , the channel waits for the AIFS again after it becomes idle. A long contention waiting time T _W means that a delay is occurring due to the existence of another access category (which may be from another BSS) that is being preferentially transmitted.

The contention time _Tc is a waiting time for avoiding collisions in the transmission of wireless signals between a plurality of access categories or between terminals. The contention time _Tc is a back-off time that is randomly determined within a range in which the minimum value is _{CWmin and} the maximum value is CW, which is a value equal to or less than _CWmax . After the counting of the contention time _Tc is completed, the wireless signal is transmitted. When the channel becomes busy before the counting of the contention time _Tc is completed, the remaining contention time _Tc is counted after the channel becomes idle thereafter. In other words, the counting of the contention time _Tc is carried over. Therefore, a long measured contention time _Tc means that a delay occurs due to the contention of the transmission of wireless signals between a plurality of access categories or a delay occurs due to the contention of the transmission of wireless signals between a plurality of terminals.

The retransmission time _TR is an additional time when a wireless signal needs to be retransmitted. In other words, the retransmission time _TR is the time from when wireless transmission is performed and it is determined that retransmission is necessary to when retransmission is actually performed. Here, the retransmission time _TR includes an additional contention waiting time _TW at the time of retransmission and a contention time _Tc ' determined by a new CW. Therefore, a long retransmission time _TR means that a delay occurs due to a collision or a transmission error.

The transmission time _TTX is the time from when a radio signal is transmitted until an acknowledgement (ACK) is received from the base station 10. In Fig. 8, the transmission time _TTX is shown as the time from the end of the retransmission time _TR until the ACK is received. If there is no retransmission, the transmission time _TTX is the time from the end of the contention time Tc until the ACK is received.

When transmitting the measurement report to the base station 10, the measurement report may be included in a data frame and transmitted. FIG. 9 is a diagram showing the frame format of a data frame including a measurement report. For example, the measurement report is stored in a new field for storing the measurement report, which is added to a data frame, which is a MAC frame including the data to be transmitted. When transmitting data with delay requirements, the terminal 20 attaches a measurement report based on the delay measurement results to the data frame. This allows the delay situation to be notified to the base station 10 in relatively real time.

Next, we will explain the operation of the communication system 1. In the following explanation, it is assumed that the terminal 20 transmits a radio signal and the base station 10 receives the radio signal.

Figure 10 is a flowchart showing an example of a transmission process of the terminal 20. In step S31, the data processing unit 201 determines whether data to be transmitted has been input from a higher layer such as an application layer. If it is determined in step S31 that no data has been input, the process of Figure 10 ends. If it is determined in step S31 that data has been input, the process proceeds to step S32.

In step S32, the data processing unit 201 performs the MAC layer processing shown in FIG. 4 on the input data to generate a MAC frame. When the measurement report is included in the data frame and transmitted, the data processing unit 201 includes the measurement report created by the measurement unit 203 when generating the MAC frame. As will be described later, the measurement report may be transmitted to the base station 10 using a management frame, or may be transmitted to the base station 10 using an Action frame. After generating the MAC frame, the data processing unit 201 outputs the MAC frame to the wireless signal processing unit 202. The wireless signal processing unit 202 outputs the time when the MAC frame was input to the tail of the transmission queue to the measurement unit 203.

In step S33, the wireless signal processing unit 202 transmits a wireless signal. At this time, the wireless signal processing unit 202 performs carrier sense to determine the channel state, and waits for transmission during a waiting time specified by the access parameters for each access category. If the channel is not being used by other terminals, the wireless signal processing unit 202 converts the MAC frame into a wireless signal and transmits the wireless signal. The wireless signal processing unit 202 also outputs to the measurement unit 203 the time when the MAC frame reaches the head of the transmission queue, the end time of the waiting time determined by the AIFS, the end time of the backoff time, and the time when the wireless signal was transmitted.

In step S34, the radio signal processing unit 202 determines whether or not to retransmit. For example, when a retransmission request is made from the base station 10, it is determined that retransmission is to be made. Alternatively, it may be determined that retransmission is to be made when no ACK is sent from the base station 10 for a certain period of time. Also, when a block ACK is sent from the base station 10, it is determined that retransmission is to be made if the block ACK contains information about the MPDU that was not successfully received. When it is determined in step S34 that retransmission is to be made, processing proceeds to step S35. When it is determined in step S34 that retransmission is not to be made, processing proceeds to step S36.

In step S35, the wireless signal processing unit 202 performs retransmission. The wireless signal processing unit 202 also outputs to the measurement unit 203 the time at which the wireless signal was retransmitted.

In step S36, the radio signal processing unit 202 outputs the time when transmission is completed (e.g., when the ACK in Figure 8 is received) to the measurement unit 203.

In step S37, the measurement unit 203 creates a measurement report. The queuing time is calculated from the time difference between the time when the MAC frame reaches the head of the transmission queue and the time when it is input to the tail of the transmission queue. The contention waiting time is calculated from the time difference between the end time of the waiting time determined by the AIFS and the time when the MAC frame reaches the head of the transmission queue. The contention time is calculated from the time difference between the end time of the backoff time and the end time of the waiting time determined by the AIFS. The retransmission time is calculated from the time difference between the time when the retransmission is performed and the time when the first wireless signal is transmitted. The transmission time is calculated from the time difference between the time when the ACK is received and the time when the first wireless signal is transmitted or the time when the retransmission is performed. After calculating the time information related to these delays, the measurement unit 203 creates a measurement report by associating the measurement result with the access category and sequence number.

In step S38, the data processing unit 201 stores the measurement report, for example, in the storage 24. The process of FIG. 10 then ends. Here, the stored measurement report is transmitted, for example, by being included in a MAC frame the next time data of the same access category is transmitted.

Figure 11 is a flowchart showing the reception process of the base station 10 including the communication method according to the embodiment. In step S51, the wireless signal processing unit 102 determines whether or not a wireless signal has been received. When it is determined in step S51 that a wireless signal has not been received, the process of Figure 11 ends. When it is determined in step S51 that a wireless signal has been received, the process proceeds to step S52.

In step S52, the wireless signal processing unit 102 performs reception processing of the wireless signal. That is, the wireless signal processing unit 102 performs demodulation processing and the like on the wireless signal to extract the MAC frame. The wireless signal processing unit 102 outputs the MAC frame to the data processing unit 101. The data processing unit 101 performs MAC layer processing on the MAC frame to restore the data.

In step S53, the data processing unit 101 determines whether reception has been successful. Whether reception has been successful can be determined, for example, by CRC. When it is determined in step S53 that reception has been successful, the process proceeds to step S54. When it is determined in step S53 that reception has not been successful, the process proceeds to step S55.

In step S54, the wireless signal processing unit 102 transmits an ACK. The ACK may be sent using a block ACK. The block ACK is an ACK that includes information on the success or failure of reception for each MPDU. Then, the process proceeds to step S56.

In step S55, the wireless signal processing unit 102 requests retransmission. The retransmission may be requested using a block ACK. Then, the process returns to step S51.

In step S56, the data processing unit 101 outputs the data to a higher layer such as an application layer.

In step S57, the data processing unit 101 determines whether or not there is a measurement report. For example, when a measurement report is included in the MAC frame, it is determined that there is a measurement report. In addition, it may be determined that there is a measurement report when the measurement report is sent from the terminal 20 using a management frame. Furthermore, it may be determined that there is a measurement report when the base station 10 requests a measurement report using an Action frame and the measurement report is sent in response to this request. If it is determined in step S57 that there is a measurement report, the process proceeds to step S58. If it is determined in step S57 that there is no measurement report, the process of FIG. 11 ends.

In step S58, the management unit 103 determines whether or not there is a delay based on the delay measurement result included in the measurement report. For example, the management unit 103 determines whether or not the delay of the access category AC_LL is shorter than a threshold. This threshold may be, for example, a fixed value. This threshold may also be set according to the result of negotiation with the terminal 20. For example, when transmitting and receiving RTA traffic, the base station 10 inquires of the terminal 20 about the delay requirements in transmitting and receiving RTA traffic. Then, the base station 10 sets the threshold according to this inquiry. If it is determined in step S58 that there is a delay, the process proceeds to step S59. If it is determined in step S58 that there is no delay, the process of FIG. 11 ends.

In step S59, the management unit 103 analyzes the cause of the delay based on the delay information stored in the measurement report. In the embodiment, the causes of the delay are broadly classified into those due to contention and those due to retransmission. The delay due to contention is a delay when the contention time is long, and means that a delay occurs due to contention for the transmission of wireless signals between multiple access categories or terminals, for example. The delay due to retransmission is a delay when the retransmission time is long, and means that a delay occurs because many retransmissions occur. The management unit 103 compares the difference between the allowable delay time and the actual delay time assigned to each of the contention time and the retransmission time, and identifies the time with the larger difference as the cause of the delay. Note that if both the contention time and the actual retransmission time exceed the allowable time, both may be identified as causes of delay, and the time with the larger difference may be identified as the main cause of delay.

In step S60, the control unit 104 adjusts the access parameters. The adjustment of the access parameters will be described later. After adjusting the access parameters, the control unit 104 notifies the wireless signal processing unit 102 of the adjusted access parameters. Then, the process proceeds to step S61.

In step S61, the wireless signal processing unit 102 notifies the terminal 20 of the adjusted access parameters. For example, the wireless signal processing unit 102 includes the adjusted access parameters in a beacon and broadcasts them. Alternatively, the adjusted access parameters may be individually notified using an action frame or the like. Then, the processing in FIG. 11 ends. Upon receiving this notification, the terminal 20 also uses the adjusted access parameters to carry out subsequent communications.

Next, the adjustment of access parameters will be described. FIG. 12 is a conceptual diagram for explaining an example of the adjustment of access parameters. FIG. 12 shows an example in which the access parameters are adjusted between terminals 20 in its own BSS without taking into account interference from other BSSs (Basic Service Sets).

In the example of FIG. 12, the access parameters are adjusted based on defaults. The defaults are the initial values of the access parameters. The defaults are predetermined, for example, for each access category.

The horizontal axis of FIG. 12 shows an example of the adjustment of access parameters to deal with delays due to contention. The adjustment of the access parameters to deal with delays due to contention is performed, for example, sequentially toward the right each time it is determined that there is a delay. The adjustment of each access parameter may be performed in combination, or may be performed by switching between them one by one. The order in which the adjustment of the access parameters is performed may also be changed.

"LL CW _min small" in Fig. 12 means that the CW _min of the access category AC_LL is made smaller than the default. The amount of reduction in CW _min may be a fixed value, or may be determined according to the magnitude of delay, i.e., the time difference between the tolerable time and the actual contention time. By reducing the CW _min of the access category AC_LL, the probability that the transmission queue of the access category AC_LL can obtain a transmission opportunity is relatively increased. As a result, it is expected that delays due to contention will be reduced.

"Other TXOP _Limit Small" in FIG. 12 means that the TXOP _Limit of the access categories other than the access category AC_LL, i.e., the access categories AC_VO, AC_VI, AC_BE, and AC_BK that do not have an absolute delay requirement, is made smaller than the default. The amount of reduction in the TXOP _Limit may be a fixed value, or may be determined according to the magnitude of the delay, i.e., the time difference between the allowable time and the actual contention time. By reducing the TXOP _Limit of the other access categories, the time that the channel is occupied in one transmission opportunity for the other access categories is shortened. As a result, the waiting time for the transmission queue of the access category AC_LL to obtain a transmission opportunity is shortened. As a result, it is expected that the delay due to contention will be reduced.

12 means that the TXOP _limit of the other access category is set to 0. By setting the TXOP _limit of the other access category to 0, the probability that the transmission queue of the access category AC_LL can obtain a transmission opportunity is relatively increased. As a result, it is expected that delays due to contention will be reduced.

The vertical axis in FIG. 12 shows an example of the adjustment of access parameters to accommodate delays due to retransmission. The adjustment of the access parameters to accommodate delays due to retransmission is performed, for example, sequentially in the upward direction each time it is determined that there is a delay. The adjustment of each access parameter may be performed in combination, or may be performed by switching between them one by one. The order in which the adjustment of the access parameters is performed may also be changed.

"LL CW _min large" in Fig. 12 means that the CW _min of the access category AC_LL is made larger than the default. The increase in CW _min may be a fixed value, or may be determined according to the magnitude of the delay, i.e., the time difference between the tolerable time and the actual retransmission time. By making the CW _min of the access category AC_LL larger, the probability of wireless signal collision for the access category AC_LL is reduced. As a result, it is expected that the delay due to retransmission will be reduced.

"Other CW _min large" in Fig. 12 means that the CW _min of the other access categories is made larger than the default. The increase in CW _min may be a fixed value, or may be determined according to the magnitude of delay, i.e., the time difference between the tolerable time and the actual retransmission time. By making the CW _min of the other access categories larger, the collision probability between the access category AC_LL and the other access categories is reduced. As a result, it is expected that the delay due to retransmission will be reduced.

"LL CW _max large" in Fig. 12 means that the CW _max of the access category AC_LL is made larger than the default. The increase in CW _max may be a fixed value, or may be determined according to the magnitude of the delay, i.e., the time difference between the tolerable time and the actual retransmission time. By making the CW _max of the access category AC_LL larger, the probability of collision of wireless signals for the access category AC_LL is reduced. As a result, it is expected that the delay due to retransmission will be reduced.

"LL MCS small" in Figure 12 means that an available MCS (Modulation and Coding Scheme) for access category AC_LL that has high transmission quality is used. MCS is an index value that represents a set of the modulation scheme and error correction coding rate used when generating a wireless signal in the wireless signal processing unit. When a small error correction coding rate is selected as the MCS for access category AC_LL, the probability of successful transmission of the wireless signal is increased. As a result, it is expected that delays due to retransmission will be reduced.

"LL MCS designation" in Figure 12 means that the index value of the available MCS for access category AC_LL is designated to a predetermined value, for example, the minimum value. By designating the index value of the MCS for access category AC_LL to, for example, the minimum value, the probability of successful retransmission of a wireless signal for access category AC_LL is increased. As a result, it is expected that delays due to retransmission will be reduced.

The "LL AIFS small", "Other, AIFS large", "Other CW _max large", and "LL centralized control" in FIG. 12 are effective measures for both delay due to contention and delay due to retransmission. These measures are implemented when both delay due to contention and delay due to retransmission are determined to be the cause of delay. "LL AIFS small", "Other, AIFS large", "Other CW _max large", and "LL centralized control" are implemented, for example, in this order. Each measure may be implemented in combination, or may be implemented by switching one by one. The implementation order of the measures may be changed. Furthermore, after implementing these measures, the above-mentioned adjustment of access parameters for delay due to contention or the above-mentioned adjustment of access parameters for delay due to retransmission may be performed according to the main cause of delay. Furthermore, these measures may be implemented when delay due to contention is not eliminated even if the above-mentioned adjustment of access parameters for delay due to contention is implemented, or when delay due to retransmission is not eliminated even if the above-mentioned adjustment of access parameters for delay due to retransmission is implemented.

"LL AIFS small" means that the AIFS of the access category AC_LL is made smaller than the default. The amount of reduction in AIFS may be a fixed value, or may be determined according to the magnitude of the delay, i.e., the time difference between the tolerable time and the actual retransmission time. By making the AIFS of the access category AC_LL smaller, the probability that a wireless signal for the access category AC_LL is preferentially transmitted increases. As a result, it is expected that delays due to contention will be reduced for the access category AC_LL. In addition, since wireless signals of the access category AC_LL are more often preferentially transmitted over wireless signals of other access categories, collisions will also be reduced, and it is expected that delays due to retransmission will be reduced for the access category AC_LL.

"Other AIFS Large" means that the AIFS for other access categories is made larger than the default. The increase in AIFS may be a fixed value, or may be determined according to the magnitude of delay, i.e., the time difference between the tolerable time and the actual retransmission time. By making the AIFS for other access categories larger, the probability that the transmission queue of access category AC_LL can obtain a transmission opportunity is relatively increased, so that delays due to contention for access category AC_LL are expected to decrease. In addition, wireless signals of access category AC_LL are more often given priority in transmission over wireless signals of other access categories, so collisions are reduced, and delays due to retransmission for access category AC_LL are expected to decrease.

"Other CW _max large" means that the CW _max of the other access categories is made larger than the default. The increase in CW _max may be a fixed value, or may be determined according to the magnitude of delay, i.e., the time difference between the allowable time and the actual retransmission time. By increasing the CW _max of the other access categories, collisions between the radio signals of the other access categories and the radio signals of AC_LL are reduced. As a result, it is expected that the delay due to the retransmission of the radio signals of AC_LL is reduced. In addition, by increasing the CW _max of the other access categories, the probability that the transmission queue of the access category AC_LL can obtain a transmission opportunity is relatively increased. As a result, it is expected that the delay due to contention is reduced for the access category AC_LL.

"LL centralized control" means implementing centralized control to actively secure transmission opportunities for the access category AC_LL. Additional transmission opportunities for the access category AC_LL can be provided using various centralized controls such as HCCA (HCF Control Channel Access), TWT (Target Wake Time), and CFP (Contention Free Period).

As described above, according to the embodiment, the base station 10 collects information on delays in the transmission of radio signals from the terminals 20, analyzes the causes of the delays from the delay information, and adjusts the access parameters according to the analyzed causes of the delays. By repeating this process until the required delay conditions are met, the base station 10 can handle RTA traffic with absolute delay requirements.

[Modification 1]
In the following, a modified example of the embodiment will be described. In the above-described embodiment, the causes of delay are roughly divided into those due to contention and those due to retransmission. However, the causes of delay may be analyzed in more detail.

For example, when the cause of the delay is queuing time or contention waiting time, the delay may be eliminated by increasing the number of transmission opportunities for LL compared to other access categories. Therefore, the control unit 104 can adjust the access parameters, such as decreasing the TXOP _Limit for access categories other than LL, decreasing the AIFS for LL, or increasing the AIFS for access categories other than LL.

Also, for example, when the cause of the delay is contention time, the delay may be eliminated by setting the backoff time of LL to be shorter than that of other access categories. Therefore, the control unit 104 can adjust the access parameters, such as decreasing the CW _max of LL and increasing the CW _max of access categories other than LL.

Also, for example, if the cause of the delay is the retransmission time, the delay may be eliminated by increasing the probability of successful retransmission. Therefore, the control unit 104 can adjust the access parameters, such as increasing the CW _max for LL and other access categories. The control unit 104 can also adjust the index value of the available MCS to be smaller.

Also, for example, if the cause of the delay is transmission time, the control unit 104 can adjust the available MCS to be larger.

[Modification 2]
In the embodiment, an example is shown in which access parameters are adjusted between the terminal 20 in the BSS of the base station 10. Here, depending on the location of the terminal 20, delay may increase due to the influence of interference sources such as other BSSs. By including such information related to interference in a measurement report and sending it to the base station 10, the base station 10 can adjust the access parameters taking the interference into consideration.

For example, the terminal 20 identifies base stations of different BSSs by BSS Color and measures the channel occupancy time for each BSS. Here, the BSS Color represents the "color" of the BSS and is set differently for each adjacent BSS. The channel occupancy time is, for example, the total time of the queuing time, contention waiting time, contention time, retransmission time, and transmission time described above. The terminal 20 then stores information on the channel occupancy time for each BSS together with the BSS Color in a measurement report to the base station 10. The base station 10 obtains the channel occupancy time of other BSSs from the BSS Color stored in the measurement report as information on interference from other BSSs. When the channel occupancy time of other BSSs exceeds a predetermined threshold, the base station 10 adjusts the access parameters to reduce delays caused by interference from other BSSs.

Figure 13 shows an example of adjusting access parameters to reduce delay while taking into account interference from other BSSs. In addition to Figure 12, Figure 13 also includes "change of link or channel." Therefore, the same processes as Figure 12 will not be described.

"Changing the link or channel" means making the link used for multi-link communication between the base station 10 and the terminal 20 different from the link used for multi-link communication between another base station and the terminal 20, or making the channel used for communication between the base station 10 and the terminal 20 different from the channel used for communication between another base station and the terminal 20.

Multi-link communication is communication between the base station 10 and the terminal 20 using multiple different links. The multiple links may differ in terms of frequency bands or channels. When different links are used, the base station 10 may maintain the link used for its own communication and negotiate with the other station to make the link used for the other station's communication different from that of the base station, or may maintain the link used for the other station's communication and negotiate with the other station to make the link used for the base station's communication different from that of the other station.

The same applies when the channels are to be different; base station 10 may maintain the channel used for its own communications while negotiating with other stations to make the channel used for the other stations' communications different from that of its own station, or may maintain the channel used for the other stations' communications while negotiating with other stations to make the channel used for the other stations' communications different from that of its own station.

Here, the "Other TXOP _Limit Small", "Other No TXOP Continuous", "Other CW _min Large", "Other AIFS Large", "Other CW _max Large", and "LL Centralized Control" shown in the dashed line frame in Fig. 13 have a relatively low effect of reducing delay when the delay due to interference is large. Therefore, the processing of "Other TXOP _Limit Small", "Other No TXOP Continuous", "Other CW _min Large", "Other AIFS Large", "Other CW _max Large", and "LL Centralized Control" may be omitted.

In the second variant described above, the access parameters are adjusted taking into account the degree of interference from other BSSs. This is expected to lead to further optimization of the access parameters.

[Modification 3]
In the embodiment, the measurement report is added to the data that should be originally transmitted and transmitted. In contrast, the measurement report can also be transmitted to the base station 10 using an Action frame. For example, the base station 10 transmits to the terminal 20 an Action frame to which a new field including a status notification request for requesting the measurement report has been added. In response to this, the terminal 20 transmits the measurement report. When returning the measurement report, the terminal 20 can use an Action frame to which a new field for storing the measurement report has been added.

The measurement report can also be transmitted to the base station 10 using a management frame. In this case, the terminal 20 periodically transmits to the base station 10 a management frame to which a new field for storing the measurement report has been added.

In the case of examples where these Action frames are used or where management frames are used, if the MAC frame to be transmitted in terminal 20 is not stored in the transmission queue, a MAC frame for delay measurement may be input to the top of the transmission queue. This MAC frame for delay measurement may be transmitted using access parameters based on conditions specified by the base station. For example, if the base station wishes to measure the delay for a specific TID, it may transmit a MAC frame for delay measurement using parameters of the access category corresponding to that TID. Here, FIG. 14 shows an example where an Action frame is used, but the same applies when a management frame is used.

[Other Modifications]
In the above-described embodiment and its modified example, the delay is measured in the terminal 20, and the measurement result is transmitted from the terminal 20 to the base station 10. Alternatively, the delay may be measured in the base station 10. In this case, the base station 10 can adjust the access parameters based on the delay measured by itself.

In addition, each process according to the above-described embodiment can be stored as a program that can be executed by a processor, which is a computer. Alternatively, the program can be stored in a storage medium of an external storage device, such as a magnetic disk, optical disk, or semiconductor memory, and distributed. The processor can then read the program stored in the storage medium of the external storage device, and have its operation controlled by the read program, thereby executing the above-described process.

Note that the present invention is not limited to the above-described embodiments, and can be modified in various ways in the implementation stage without departing from the gist of the invention. The embodiments may also be implemented in appropriate combination, in which case the combined effects can be obtained. Furthermore, the above-described embodiments include various inventions, and various inventions can be extracted by combinations selected from the multiple constituent elements disclosed. For example, if the problem can be solved and an effect can be obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiments, the configuration from which these constituent elements are deleted can be extracted as an invention.

1... communication system 10... base station 11... processor 12... ROM
13...RAM
14: wireless module 15: routing module 20: terminal 21: processor 22: ROM
23...RAM
24: Wireless module 25: Display 26: Storage 101: Data processing unit 102: Wireless signal processing unit 103: Management unit 104: Control unit 201: Data processing unit 202: Wireless signal processing unit 203: Measurement unit

Claims (10)

a wireless signal processing unit that receives information on a measurement result of a delay when transmitting a wireless signal from a terminal;
a management unit that analyzes whether the cause of the delay is a contention in the transmission of a wireless signal or a retransmission of a wireless signal based on information of the measurement result;
a control unit that changes a control method of an access parameter or an access method related to the transmission, or a control method of both the access parameter and the access method, depending on whether the cause of the delay is due to a contention in the transmission of a wireless signal or due to a retransmission of a wireless signal;
A base station comprising: The base station according to claim 1, wherein the control unit controls the access parameters so that when the cause of the delay is a contention in the transmission of the wireless signals, a wireless signal including data with a delay requirement is transmitted with higher priority than a wireless signal including data without the delay requirement. The base station according to claim 2, wherein the control unit performs at least one of the following: reducing the minimum value of a contention window related to the transmission of a wireless signal including data with the delay requirement, reducing the upper limit of a channel occupancy time in a transmission opportunity related to the transmission of a wireless signal including data without the delay requirement, or setting the number of transmissions in a transmission opportunity related to the transmission of a wireless signal including data without the delay requirement to one. The base station according to claim 1, wherein the control unit controls the access parameters to increase the probability of successful transmission of a wireless signal including data with a delay requirement when the cause of the delay is retransmission of the wireless signal. The base station according to claim 4, wherein the control unit performs at least one of the following: increasing the minimum value of a contention window related to the transmission of a wireless signal including data with the delay requirement, increasing the minimum value of a contention window related to the transmission of a wireless signal including data without the delay requirement, increasing the maximum value of a contention window related to the transmission of a wireless signal including data with the delay requirement, changing an index value of a modulation method and coding rate related to the transmission of a wireless signal including data with the delay requirement to an index value with higher transmission quality, or specifying an index value of a modulation method and coding rate related to the transmission of a wireless signal including data with the delay requirement to a predetermined value. The base station according to any one of claims 2 to 5, wherein the control unit further performs at least one of the following: decreasing an AIFS value related to the transmission of a radio signal including data with the delay requirement, increasing an AIFS value related to the transmission of a radio signal including data without the delay requirement, and increasing a maximum value of a contention window related to the transmission of a radio signal including data without the delay requirement. The base station according to any one of claims 2 to 6, wherein the control unit further performs centralized control of radio signals including data having the delay requirement. The wireless signal processing unit receives, from the terminal, information on interference to the terminal caused by communication between another base station and the terminal;
The base station according to claim 2 , wherein the management unit analyzes a cause of the delay further based on the information on the interference. The base station according to claim 8, wherein the control unit makes the link used for communication with the terminal different from the link used for communication between the other base station and the terminal, or makes the channel used for communication with the terminal different from the channel used for communication between the other base station and the terminal. The base station receives information on a measurement result of a delay when transmitting a radio signal from the terminal;
The base station analyzes whether the cause of the delay is due to a contention in transmission of a wireless signal or due to a retransmission of a wireless signal based on information of the measurement result;
The base station changes a control method of an access parameter or an access method related to the transmission, or both of the access parameter and the access method, depending on whether the cause of the delay is due to a contention in the transmission of a wireless signal or due to a retransmission of a wireless signal;
A communication method comprising:

Images