JP7613468B2 - Communication method and terminal - Google Patents

Description

The embodiments relate to a communication method and a terminal.

In wireless communication that uses frequency bands that do not require a radio station license (unlicensed bands), various standards have been established to efficiently utilize frequency resources in base stations and terminals.

For example, a base station and a terminal access a channel using CSMA/CA (Carrier sense multiple access with collision avoidance) and transmit a radio signal. In CSMA/CA, the base station and the terminal wait for the time set by the access parameters, and then use a carrier sense operation to confirm that the channel is not being used by another terminal, etc., before transmitting a radio signal.

In addition, the terminal is specified with a transmission pause time, which is a lower limit that must be met by the transmission interval between transmitting a radio signal and transmitting the next radio signal, depending on the frequency band and frame size of the radio signal.

In order to comply with the transmission pause time regulations, a method is known in which the time during which the carrier sense operation is performed (carrier sense time) includes the transmission pause time. For example, by setting the access parameters so that the carrier sense time is always longer than the transmission pause time, a terminal can be realized that complies with the restrictions on the transmission interval.

ARIB STD-T108 1.3 edition, "Standard for 920MHz band radio equipment for telemetry, telecontrol and data transmission", April 12, 2019 IEEE Std 802.11ah TM-2016 (IEEE Standard for Information technology - Telecommunications and information exchange between systems Local and metropolitan area networks - Specific requirements, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, Amendment 2 : Sub 1 GHz License Exempt Operation, IEEE Computer Society, 7 December 2016

However, the access parameters used for carrier sense operation are set individually according to the priority of the transmission data, but are not dynamically set according to the transmission pause time. As a result, even in situations where the transmission pause time does not need to be taken into consideration, carrier sense operation is performed for a period longer than the transmission pause time, resulting in inefficient use of frequency resources.

The present invention has been made in light of the above circumstances, and its purpose is to provide a wireless communication environment that can efficiently use frequency resources while complying with standards.

A communication method according to one aspect includes determining a constraint imposed on a transmission start time of an untransmitted first radio frame, and setting an arbitration inter frame space number (AIFSN) as a parameter used for a carrier sense operation of the first radio frame in accordance with the determined constraint.

According to an embodiment, a wireless communication environment can be provided that can efficiently use frequency resources while complying with standards.

FIG. 1 is a block diagram showing the configuration of a communication system according to the first embodiment. FIG. 2 is a block diagram showing the hardware configuration of a terminal according to the first embodiment. FIG. 3 is a block diagram showing the functional configuration of the terminal according to the first embodiment. FIG. 4 is a timing chart showing the relationship between the access parameters and the transmission interval in the terminal according to the first embodiment. FIG. 5 is a flowchart showing a wireless signal transmission operation in the terminal according to the first embodiment. FIG. 6 is a flowchart showing a first example of a constraint determination operation in the terminal according to the first embodiment. FIG. 7 is a flowchart showing a second example of the constraint determination operation in the terminal according to the first embodiment. FIG. 8 is a flowchart showing a third example of a constraint determination operation in the terminal according to the first embodiment. FIG. 9 is a timing chart showing the relationship between the access parameters and the transmission interval in the terminal according to the second embodiment. FIG. 10 is a flowchart showing a wireless signal transmission operation in the terminal according to the second embodiment. FIG. 11 is a flowchart showing a first example of a waiting time calculation operation in a terminal according to the second embodiment. FIG. 12 is a flowchart showing a second example of the waiting time calculation operation in the terminal according to the second embodiment. FIG. 13 is a flowchart showing a third example of the waiting time calculation operation in the terminal according to the second embodiment. FIG. 14 is a flowchart showing a wireless signal transmission operation in a terminal according to the third embodiment. FIG. 15 is a flowchart showing a constraint avoidance operation in a terminal according to the third embodiment.

Below, the embodiments are described with reference to the drawings. In the following description, components having the same function and configuration are given a common reference symbol. Furthermore, when distinguishing between multiple components having a common reference symbol, they are distinguished by an additional reference symbol (for example, a hyphen and a number such as "-1") following the common reference symbol.

1. First Embodiment A terminal according to a first embodiment will be described.

1.1 Configuration 1.1.1 Wireless Communication System FIG. 1 is a block diagram showing an example of the configuration of a wireless communication system including a terminal according to the first embodiment.

As shown in Figure 1, the wireless communication system 1 includes a base station 10 and multiple terminals 20-1, 20-2, and 20-3. Hereinafter, when there is no particular distinction between the multiple terminals 20-1 to 20-3, they may be referred to as "terminals 20."

The base station 10 has a predetermined service area (not shown) and can communicate with terminals 20 within the service area. The base station 10 connects between the terminals 20 within the service area it is responsible for and a network NW (not shown), and functions as an access point for the terminals 20 within the service area it is responsible for to access the network NW.

The terminal 20 is a wireless terminal that can operate with low power, such as an IoT (Internet of Things) device. The terminal 20 is configured to be able to transmit and receive data to and from the network NW via the base station 10.

1.1.2 Terminal Figures 2 and 3 are block diagrams showing an example of the hardware configuration and functional configuration of a terminal according to the embodiment. Note that the multiple terminals 20-1 to 20-3 in Figure 1 may have the same configuration. Figures 2 and 3 show an example of the configuration of any one terminal 20 among the multiple terminals 20-1 to 20-3.

First, using Figure 2, we will explain the hardware configuration of terminal 20.

As shown in FIG. 2, the terminal 20 includes a processor 21, a ROM (Read only memory) 22, a RAM (Random access memory) 23, a wireless module 24, a display 25, and a sensor 26.

The processor 21 is a circuit capable of executing various programs, and is an operating device that controls the entire terminal 20. The processor 21 is, for example, a CPU (Central Processing Unit), but is not limited to this, and an ASIC (Application Specific Integrated Circuit) or the like may be used instead of the CPU. The ROM 22 is, for example, a non-volatile semiconductor memory, and stores firmware and various programs required for the operation of the terminal 20. The RAM 23 is, for example, a volatile semiconductor memory, and is used as a working area for the processor 21, or a storage area for data measured by the sensor 26.

The wireless module 24 is a circuit used to transmit and receive data by wireless signals, and is connected to an antenna. The display 25 displays, for example, a GUI (Graphical User Interface) corresponding to application software. The display 25 may also function as an input interface for the terminal 20. The sensor 26 is a device with a data measurement function that is attached to the terminal 20, and measures specified data according to instructions from the processor 21.

Next, using Figure 3, the functional configuration of terminal 20 will be explained.

As shown in FIG. 3, the terminal 20 functions as a computer including a radio signal processing unit 210, a data processing unit 220, and an application execution unit 230. The radio signal processing unit 210 and the data processing unit 220 are functional blocks for performing data communication based on the OSI (Open Systems Interconnection) reference model. In the OSI reference model, 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, layer 7: application layer). The data link layer includes an LLC (Logical link control) layer and a MAC (Media access control) layer. In this specification, layers 3 to 7 are referred to as "upper layers" based on the data link layer of layer 2.

The application execution unit 230 executes an application capable of using data input from the data processing unit 220. For example, the application execution unit 230 can display information about the application on the display 25. The application execution unit 230 can also operate based on the operation of an input interface.

The data processing unit 220 performs operations corresponding to the LLC layer and higher layers on the input data. For example, the data processing unit 220 outputs data input from the application execution unit 230 to the wireless signal processing unit 210. The data processing unit 220 also outputs data input from the wireless signal processing unit 210 to the application execution unit 230.

The wireless signal processing unit 210 performs MAC layer and physical layer operations on the input data, and transmits and receives data between the terminal 20 and the base station 10 using wireless communication. The wireless signal processing unit 210 includes a receiving unit 211, a demodulating unit 212, a received frame transferring unit 213, a transmitted frame waiting unit 214, a modulating unit 215, a transmitting unit 216, a communication control unit 217, a constraint determining unit 218, and a parameter setting unit 219.

When the wireless signal received via the antenna is data to be demodulated, the receiving unit 211 outputs the wireless signal to the demodulation unit 212. The receiving unit 211 also measures the received power of the wireless signal and outputs the measurement result of the received power to the communication control unit 217.

The demodulation unit 212 demodulates the wireless signal input from the receiving unit 211, converts it into a wireless frame (e.g., a MAC frame), and outputs the wireless frame to the received frame transfer unit 213. The demodulation unit 212 also outputs frame information of the demodulated wireless frame to the communication control unit 217. The frame information includes, for example, the frame type of the wireless frame, the frame size, the transmission rate, the frame format, the frequency band, whether a response is required, and the number of retransmissions.

The received frame transfer unit 213 transfers to the data processing unit 220 data within the wireless frame input from the demodulation unit 212 that is determined by the communication control unit 217 to require transfer to the data processing unit 220.

The transmission frame waiting unit 214 generates a wireless frame based on data input from the data processing unit 220, and stores the wireless frame until a transmission operation is started. For example, the transmission frame waiting unit 214 assigns the wireless frame to one of a plurality of transmission queues according to the category recorded in the wireless frame. Specifically, the transmission frame waiting unit 214 may have a plurality of 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 wireless frames categorized as VO (Voice). The transmission queue AC_VI is a queue for holding wireless frames categorized as VI (Video). The transmission queue AC_BE is a queue for holding wireless frames categorized as BE (Best effort). The transmission queue AC_BK is a queue for holding wireless frames categorized as BK (Background). This allows the wireless frames to be classified according to the transmission priority. When a wireless frame is stored in each transmission queue, the transmission frame waiting section 214 notifies the communication control section 217 that there is a wireless frame to be transmitted.

Based on instructions from the communication control unit 217, the modulation unit 215 modulates the wireless frames that have been determined to be transmitted from among the wireless frames stored in the transmission queue of the transmission frame waiting unit 214, to generate a wireless signal. The modulation unit 215 outputs the generated wireless signal to the transmission unit 216.

The transmitting unit 216 transmits the radio signal input from the modulation unit 215 to the base station 10 via the antenna.

The communication control unit 217 controls the transmission and reception of radio signals in the radio signal processing unit 210. For example, the communication control unit 217 determines whether or not to transfer the radio frame to the data processing unit 220 based on frame information of the received signal input from the demodulation unit 212.

For example, when the communication control unit 217 receives a notification from the transmission frame waiting unit 214 that there is a radio frame to be transmitted, it sets frame information of the radio frame, notifies the constraint determination unit 218, and executes a carrier sense operation. In the carrier sense operation, the communication control unit 217 monitors the measurement result of the received power input from the receiving unit 211 over a carrier sense time Tc. The length of the carrier sense time Tc is determined based on the access parameters set by the parameter setting unit 219. The access parameters include, for example, AIFSN (Arbitration inter frame space number).

When the received power in a channel (frequency band) available to the station is below the threshold value for the carrier sense time Tc, the communication control unit 217 determines that no other terminals are transmitting wireless signals on that channel, and considers the station to have acquired the transmission right for that channel. Upon acquiring the transmission right, the communication control unit 217 takes out a wireless frame from the transmission queue, and instructs the modulation unit 215 to modulate the wireless frame into a wireless signal using the channel for which the transmission right has been acquired.

In addition, since the channel to be used for the wireless frame is not determined until the carrier sense operation is completed, when notifying the constraint determination unit 218 of frame information, the communication control unit 217 may notify candidate channels for performing the carrier sense operation as frequency bands.

When the constraint determination unit 218 receives frame information of the next radio frame scheduled to be transmitted from the communication control unit 217, it determines the constraints imposed on the transmission interval Ti based on the frame information. The transmission interval Ti is the time from the transmission completion time of the immediately preceding transmitted radio frame to the transmission start time of the next radio frame to be transmitted. As a constraint determination operation, the constraint determination unit 218 determines whether the transmission interval Ti is constrained by the transmission pause time Ts, and if it is determined that the transmission interval Ti is constrained, specifically calculates the value of the transmission pause time Ts to be observed. Note that the constraint includes, for example, that the transmission interval Ti is equal to or greater than the transmission pause time Ts (Ti ≧ Ts). In other words, the transmission pause time Ts can be defined as the lower limit value of the transmission interval Ti.

Prior to determining the constraint, the constraint determination unit 218 may further acquire additional information other than the frame information as a parameter for calculating the value of the transmission pause time Ts. The additional information includes, for example, restriction information set for the service area in which the terminal 20 is located, and information on the elapsed time from the completion time of transmission of the wireless signal most recently transmitted by the terminal 20. The constraint determination unit 218 notifies the parameter setting unit 219 of the transmission pause time Ts calculated as the determination result of the constraint.

The parameter setting unit 219 sets the access parameter AIFSN for determining the length of the carrier sense time Tc based on the transmission pause time Ts input from the constraint determination unit 218.

With the above configuration, the communication control unit 217 can perform carrier sense operation using the access parameter AIFSN, which is set to a different value depending on the transmission status of the wireless frame. Therefore, the communication control unit 217 can dynamically change the length of the carrier sense time Tc so that the transmission interval Ti satisfies the constraint of the transmission pause time Ts.

1.1.3 Relationship Between Access Parameter and Transmission Interval Next, the relationship between the access parameter AIFSN used in the carrier sense operation in the terminal according to the first embodiment and the transmission interval Ti will be described.

The carrier sense time Tc is determined by the sum of a part of the arbitration inter frame space AIFS (Arbitration inter frame space) and the random backoff Tr. The arbitration inter frame space AIFS is determined by the sum of the short inter frame space SIFS (Short inter frame space) and the product of the access parameter AIFSN and the slot time aSlotTime. Of these, the short inter frame space SIFS is a time provided for processing delays and transmission/reception switching processing, and is not included in the carrier sense time Tc. The access parameter AIFSN can be set to, for example, any integer value, and the slot time aSlotTime is a unit time for increasing or decreasing the carrier sense time Tc. The random backoff is determined by the product of a random number (rand) and the slot time aSlotTime. To summarize the above, the carrier sense time Tc is expressed as the following formula (1).

Tc = AIFSN*aSlotTime + rand*aSlotTime …(1)
For the access parameter AIFSN used in calculating the carrier sense time Tc, a default value AIFSN1 is preset for each access category. For example, the default value AIFSN1 set for an access category with high priority is lower than that set for an access category with low priority. This is set to be smaller than the prescribed value AIFSN1 set for the category. As a result, the carrier sense time Tc can be set shorter for a wireless frame that belongs to an access category with a higher priority, and the wireless frame can acquire the transmission right more easily. Therefore, the higher the priority of a wireless frame that belongs to an access category, the shorter the latency until data transmission can be.

In this embodiment, when a carrier sense operation is performed taking into account the transmission pause time Ts, the access parameter AIFSN may be set to a reset value AIFSN2 larger than the specified value AIFSN1 instead of the specified value AIFSN1 for each access category described above. This allows the carrier sense time Tc to be lengthened when it is necessary to take the transmission pause time Ts into account, and the carrier sense time Tc to be shortened when it is not necessary to take the transmission pause time Ts into account.

Figure 4 is a timing chart showing the relationship between the access parameters and the transmission interval in the terminal according to the first embodiment. Figure 4(A) shows the transmission interval Ti1 and the carrier sense time Tc1 when the transmission pause time Ts is not taken into account, and Figure 4(B) shows the transmission interval Ti2 and the carrier sense time Tc2 when the transmission pause time Ts is taken into account.

When the transmission pause time Ts does not need to be taken into consideration, the first data transmission is completed at time t10, as shown in FIG. 4(A). Then, during the period Tc1 from time t20 to time t30, a carrier sense operation based on the specified value AIFSN1 is performed. After that, at time t40, the second data transmission is started.

On the other hand, when it is necessary to take the transmission pause time Ts into consideration, as shown in FIG. 4(B), the first data transmission is completed at time t10. Then, during the period Tc2 from time t20 to time t30', a carrier sense operation based on the reset value AIFSN2 is performed. After that, at time t40', the second data transmission is started.

When the transmission pause time Ts needs to be taken into consideration, if the carrier sense operation is performed based on the specified value AIFSN1, the transmission pause time Ti1 may become shorter than the transmission pause time Ts, which is undesirable. For this reason, when the transmission pause time Ts needs to be taken into consideration, a reset value AIFSN2 larger than the specified value AIFSN1 is set. This allows the carrier sense time Tc2 (= t30'-t20) to be longer than the carrier sense time Tc1 (= t30-t20), and therefore the transmission interval Ti2 (= t40'-t10) to be longer than the transmission interval Ti1 (= t40-t10). Then, by appropriately setting the reset value AIFSN2, the transmission interval Ti2 can be made longer than the transmission pause time Ts.

In the example of FIG. 4, the carrier sense time Tc2 is longer than the transmission pause time Ts, but this is not limited to the above. For example, if the transmission interval Ti2 is longer than the transmission pause time Ts, the carrier sense time Tc2 may be shorter than the transmission pause time Ts.

1.2 Operation Next, a wireless signal transmission operation in the terminal according to the first embodiment will be described.

1.2.1 Transmission Operation Fig. 5 is a flowchart showing an overview of a wireless signal transmission operation in the terminal according to the first embodiment. Fig. 5 shows an overview of an operation from when a wireless frame is stored in a transmission queue in the transmission frame waiting unit 214 to when the wireless frame is transmitted as a wireless signal.

5, in step ST10, when the communication control unit 217 receives a notification from the transmission frame waiting unit 214 that a wireless frame has been stored in the transmission queue, the communication control unit 217 sets frame information related to the wireless frame. The communication control unit 217 outputs the frame information to the constraint determination unit 218.

In step ST20, when the constraint determination unit 218 receives frame information from the communication control unit 217, it determines whether or not the transmission interval Ti is subject to constraints based on the frame information. As described above, the frame information includes, for example, the frame type of the wireless frame, the frame size, the transmission rate, the frame format, the channel candidates, the need for a response, and the number of retransmissions. The constraint determination unit 218 appropriately analyzes these various information included in the frame information and determines whether or not the transmission interval Ti until the wireless frame corresponding to the frame information is transmitted is subject to constraints by the transmission pause time Ts. If the result of the determination is that the transmission interval Ti is subject to constraints by the transmission pause time Ts (step ST20; yes), the process proceeds to step ST30, and if it is not subject to constraints by the transmission pause time Ts (step ST20; no), the constraint determination unit 218 notifies the parameter setting unit 219 that consideration of the transmission pause time Ts is not required, and the process proceeds to step ST50.

In step ST30, the constraint determination unit 218 calculates a specific value of the transmission pause time Ts that restricts the transmission interval Ti based on the frame information. The constraint determination unit 218 notifies the parameter setting unit 219 of the calculated transmission pause time Ts, and the process proceeds to step ST40. In other words, steps ST20 and ST30 correspond to the constraint determination operation described above.

In step ST40, the parameter setting unit 219 sets the access parameter reset value AIFSN2 taking into account the constraint of the transmission pause time Ts, as illustrated in FIG. 4 (B).

In step ST50, the parameter setting unit 219 sets a default value AIFSN1 of the access parameter that does not take into account the constraint of the transmission pause time Ts, as illustrated in FIG. 4 (A).

In step ST60, the communication control unit 217 performs a carrier sense operation using the access parameter AIFSN (reset value AIFSN2 or default value AIFSN1) set by the parameter setting unit 219.

In step ST70, the communication control unit 217 determines whether or not the transmission right for the channel used to transmit the wireless frame has been acquired as a result of the carrier sense operation. If the transmission right has been acquired (step ST70; yes), the process proceeds to step ST80. On the other hand, if the transmission right has not been acquired (step ST70; no), the process returns to step ST60, and the carrier sense operation is continued until the transmission right is acquired.

In step ST80, the modulation unit 215 modulates the radio frame in the transmission queue based on the channel for which the transmission right has been acquired to generate a radio signal, and the transmission unit 216 transmits the radio signal to the outside.

This completes the wireless signal transmission operation.

1.2.2 Constraint Determination Operation Next, several aspects of the constraint determination operation performed by the constraint determination unit 218 will be described in detail.

(First Example: Determination Based on Frequency Band)
The transmission pause time Ts may be defined in association with a frequency band used for transmitting a wireless signal. In addition, the transmission pause time Ts defined in association with the frequency band may be defined to have a different value for each service area in which the terminal 20 is located.

Figure 6 is a flowchart showing a first example of a constraint determination operation in a terminal related to the first embodiment, and corresponds to steps ST20 and ST30 in Figure 5.

As shown in FIG. 6, in step ST111, the restriction determination unit 218 receives frame information from the communication control unit 217 and further acquires restriction information related to the transmission interval Ti in the service area in which the terminal 20 is located. The restriction information includes, for example, information relating, on a service area basis, the relationship between a frequency band and a transmission pause time Ts that should be considered when using that frequency. Note that the restriction information may be acquired by a wireless signal received separately from outside the terminal 20, or may be stored in advance in the ROM 22.

In step ST112, the constraint determination unit 218 determines whether or not the transmission interval Ti is constrained by the restriction information acquired in step ST111 in the frequency band in the frame information. If the transmission interval Ti is constrained by the restriction information (step ST112; yes), the process proceeds to step ST113, and if the transmission interval Ti is not constrained by the restriction information (step ST112; no), the process omits step ST113.

In step ST113, the constraint determination unit 218 calculates the transmission pause time Ts that should be taken into account by the transmission interval Ti in the frequency band within the frame information based on the restriction information.

This completes the frequency band-based constraint determination operation in the constraint determination unit 218.

(Second Example: Determination Based on Frame Time Length)
Furthermore, the transmission pause time Ts may be defined in association with the frame time length of a wireless frame. If the frame size, transmission rate, and frame format are determined, the frame time length can be calculated based on this frame information.

Figure 7 is a flowchart showing a second example of constraint determination operation in a terminal related to the first embodiment, and corresponds to steps ST20 and ST30 in Figure 5.

As shown in FIG. 7, in step ST121, when the constraint determination unit 218 receives frame information from the communication control unit 217, it calculates the frame time length based on the frame size, transmission rate, and frame format in the frame information.

In step ST122, the constraint determination unit 218 determines whether or not the transmission interval Ti is constrained by the frame time length calculated in step ST121. If the transmission interval Ti is constrained by the frame time length (step ST122; yes), the process proceeds to step ST123, and if the transmission interval Ti is not constrained by the frame time length (step ST122; no), the process omits step ST123.

In step ST123, the constraint determination unit 218 calculates the transmission pause time Ts that should be taken into account in the transmission interval Ti based on the frame time length.

This completes the constraint determination operation based on frame time length in the constraint determination unit 218.

(Third Example: Determination Based on Frame Type)
As described above, the transmission pause time Ts may be specified in association with the frame time length of a wireless frame. Therefore, in the case of a frame type (e.g., a beacon frame, etc.) in which the frame size, transmission rate, and frame format that specify the frame time length are predetermined, the frame time length calculated in advance may be used in the constraint determination operation. In other words, the constraint determination unit 218 may be able to determine whether or not it is necessary to take the transmission pause time Ts into consideration based on the frame type.

Figure 8 is a flowchart showing a third example of constraint determination operation in a terminal related to the first embodiment, and corresponds to steps ST20 and ST30 in Figure 5.

As shown in FIG. 8, in step ST131, when the constraint determination unit 218 receives frame information from the communication control unit 217, it determines whether or not the frame time length is determined by the frame type in the frame information. In making this determination, the constraint determination unit 218 may store a frame type with a fixed frame time length in association with the frame time length for that frame type, and determine whether or not the frame type in the frame information corresponds to the stored frame type. If the frame time length is determined by the frame type (step ST131; yes), the process proceeds to step ST132. On the other hand, if the frame time length is not determined by the frame type (step ST131; no), the operation proceeds to the constraint determination operation based on the frame time length shown in FIG. 7 (i.e., steps ST121 to ST123).

In step ST132, the constraint determination unit 218 determines whether the transmission interval Ti is constrained by the frame time length determined in step ST131 to be determined by the frame type. If the transmission interval Ti is constrained by the frame time length (step ST132; yes), the process proceeds to step ST133, and if the transmission interval Ti is not constrained by the frame time length (step ST132; no), the process omits step ST133.

In step ST133, the constraint determination unit 218 calculates the transmission pause time Ts that should be taken into account in the transmission interval Ti based on the frame type (and the corresponding frame time length).

This completes the constraint determination operation based on frame type in the constraint determination unit 218.

1.3 Effects of the Present Embodiment According to the first embodiment, the constraint determination unit 218 determines whether the transmission interval Ti is restricted by the transmission pause time Ts, and calculates the transmission pause time Ts if the transmission interval Ti is restricted. If the transmission interval Ti is not restricted, the parameter setting unit 219 sets the access parameter AIFSN to a specified value AIFSN1 that does not take into account the transmission pause time Ts. On the other hand, if the transmission interval Ti is restricted, the parameter setting unit 219 sets the access parameter AIFSN to a reset value AIFSN2 according to the transmission pause time Ts. This makes it possible to set different access parameters AIFSN depending on whether the transmission pause time Ts is restricted. Therefore, if the transmission interval Ti is restricted, the latency of the transmission operation can be shortened by shortening the carrier sense time Tc, and if the transmission interval Ti is not restricted, the carrier sense time Tc can be lengthened to perform the transmission operation while satisfying the restriction of the transmission interval Ti. Therefore, it is possible to provide a wireless communication environment that can efficiently use frequency resources while complying with the standard.

In addition, in the constraint determination operation, the constraint determination unit 218 determines whether or not to take into account the transmission pause time Ts, which is a constraint on the transmission interval Ti, and if so, what the specific value should be, based on at least one of the frequency band, frame time length, and frame type set in the wireless frame to be transmitted. This makes it possible to appropriately calculate the transmission pause time Ts to be observed while minimizing the number of items to be monitored.

2. Second embodiment Next, a terminal according to the second embodiment will be described. In the first embodiment, a case was described in which the constraints imposed on the transmission interval Ti were determined based on parameters (frequency band, frame time length, frame type) that determine the length of the transmission pause time Ts. The second embodiment differs from the first embodiment in that the constraints that the transmission interval Ti is substantially imposed on are determined by further considering a waiting time that occurs in the transmission interval Ti. In the following, a description of the configuration and operation equivalent to those of the first embodiment will be omitted, and a description will be mainly given of the configuration and operation different from those of the first embodiment.

2.1 Relationship between Access Parameter and Transmission Interval Fig. 9 is a timing chart showing the relationship between the access parameter and the transmission interval in the terminal according to the second embodiment. Fig. 9 shows a case where a known waiting time Tw exists before a carrier sense operation is performed.

As shown in FIG. 9, at time t10, the first data transmission is completed. Then, during time Tw from time t20 to time t25, some known operation is executed. Examples of known operations include a receiving operation of a response frame to the first data transmission, and a transmission operation by another terminal 20 that has acquired the transmission right. Then, during time Tc2' from time t25 to time t30', a carrier sense operation based on the reset value AIFSN2' is executed. Then, at time t40', the second data transmission is started.

If a waiting time Tw occurs due to a known operation before the carrier sense operation, the transmission interval Ti necessarily includes the waiting time Tw. Therefore, the actual constraint on the transmission interval Ti to be considered when setting the access parameter AIFSN is the difference between the transmission pause time Ts and the waiting time Tw (Ts-Tw). Therefore, the reset value AIFSN2' when the waiting time Tw is known can be set to a value smaller than the reset value AIFSN2 that does not consider the waiting time Tw. Also, when the waiting time Tw is equal to or greater than the transmission pause time Ts, the reset value AIFSN2' can be equal to the specified value AIFSN1 (AIFSN1≦AIFSN2'<AIFSN2).

2.2 Transmission Operation Fig. 10 is a flowchart showing an overview of a wireless signal transmission operation in a terminal according to the second embodiment, and corresponds to Fig. 5 in the first embodiment. In Fig. 10, a new step ST35 is provided between step ST30 and step ST40 shown in Fig. 5.

As shown in Figure 10, the operations from step ST10 to step ST30 are the same as those in Figure 5, so the explanation will be omitted.

After the transmission pause time Ts is calculated in step ST30, in step ST35, the constraint determination unit 218 calculates the waiting time Tw of the terminal 20 from the transmission completion time of the previous radio frame to the carrier sense operation. The constraint determination unit 218 outputs the calculated waiting time Tw to the parameter setting unit 219.

In step ST40, the parameter setting unit 219 sets a reconfiguration value AIFSN2' taking into account constraints based on the waiting time Tw in addition to the transmission pause time Ts, for example as illustrated in FIG. 9.

The operations from step ST50 to step ST80 are the same as those in Figure 5, so the explanation will be omitted.

This completes the wireless signal transmission operation.

2.3 Waiting Time Calculation Operation Next, several aspects of the waiting time calculation operation by the constraint determination unit 218 will be described in detail.

(Example 1: Calculating waiting time based on whether a response is required)
Depending on the frame type, a wireless frame may require a response frame from the base station 10 that has received the wireless frame. For example, if the frame information of the wireless frame transmitted immediately before includes information indicating whether or not a response to the wireless frame is requested (whether or not a response is required), or if the frame information of the wireless frame to be transmitted next includes information requesting a response every time, the constraint determination unit 218 acquires the information and uses it to calculate the waiting time Tw.

Figure 11 is a flowchart showing a first example of a waiting time calculation operation in a terminal according to the second embodiment, and corresponds to step ST35 in Figure 10. Steps ST211 to ST213 shown in Figure 11 correspond to step ST35 in Figure 10.

As shown in FIG. 11, in step ST211, the constraint determination unit 218 further acquires frame information of the wireless frame most recently transmitted from the communication control unit 217.

In step ST212, the constraint determination unit 218 determines whether the frame information acquired in step ST211 includes information requesting a response frame, or whether the frame information of the next wireless frame to be transmitted includes information requesting a response frame every time. If the wireless frame transmitted immediately before requests a response frame, or if the wireless frame transmitted next requests a response frame every time (step ST212; yes), the process proceeds to step ST213; if a response frame is not requested (step ST212; no), the process omits step ST213.

In step ST213, the constraint determination unit 218 calculates the waiting time Tw based on the frame time length of the response frame. If the terminal 20 has already received the response frame, the constraint determination unit 218 can use the actual value of the frame time length to calculate the waiting time Tw. If the terminal 20 has not yet received the response frame, the constraint determination unit 218 can use the predicted value of the frame time length to calculate the waiting time Tw.

This completes the waiting time calculation operation in the constraint determination unit 218 based on whether or not a response is required. In the above-mentioned step ST212, the constraint determination unit 218 may make a determination based only on the radio frame transmitted immediately before, or based only on the radio frame to be transmitted next. When making a determination based only on the radio frame to be transmitted next, the constraint determination unit 218 may omit the processing of step ST211.

(Second Example: Calculating Wait Time Based on Number of Retransmissions)
Furthermore, even if the next wireless frame to be transmitted is a frame type that requires a response frame, if the number of retransmissions of the wireless frame is equal to or less than a threshold (e.g., 0), the terminal 20 must determine the constraint without considering the frame time length of the response frame. On the other hand, if the number of retransmissions is greater than the threshold (e.g., 1 or more), the response frame can be considered as the waiting time Tw. In this way, the waiting time Tw may be calculated based on the number of retransmissions included in the frame information of the next wireless frame to be transmitted.

Figure 12 is a flowchart showing a second example of the waiting time calculation operation in a terminal according to the second embodiment, and corresponds to step ST35 in Figure 10. Figure 12 shows the case where the threshold value for the number of retransmissions is 0.

12, in step ST221, the constraint determination unit 218 determines whether or not information requesting a response frame is included in the frame information of the wireless frame to be transmitted next. If the wireless frame transmitted next requests a response frame (step ST221; yes), the process proceeds to step ST222. If the wireless frame does not request a response frame (step ST221; no), the process omits steps ST222 and ST223.

In step ST222, the constraint determination unit 218 determines whether the number of retransmissions in the frame information of the next radio frame to be transmitted is 0. If the number of retransmissions is 1 or more (i.e., the next radio frame to be transmitted is a retransmitted frame) (step ST222; yes), the process proceeds to step ST223, and if the number of retransmissions is 0 (step ST222; no), the process omits step ST223.

In step ST223, the constraint determination unit 218 calculates the waiting time Tw based on the frame time length of the response frame.

This completes the waiting time calculation operation in the constraint determination unit 218 based on whether a response is required and the number of retransmissions.

(Third Example: Calculation of waiting time based on elapsed time from transmission completion time)
The waiting time Tw is not limited to the time required to receive the response frame described in the first and second examples, but may be defined as the period from the completion time of the transmission of the immediately preceding wireless frame to the start time of the carrier sense operation. In this case, the waiting time Tw may be calculated by monitoring the elapsed time from the completion time of the transmission of the immediately preceding wireless frame.

Figure 13 is a flowchart showing a third example of waiting time calculation operation in a terminal according to the second embodiment, which corresponds to step ST35 in Figure 10.

13, in step ST231, the constraint determination unit 218 acquires the transmission completion time of the immediately preceding transmitted wireless frame. The constraint determination unit 218 may calculate the transmission completion time based on the transmission start time of the immediately preceding transmitted wireless frame and the frame time length of the wireless frame.

In step ST232, the constraint determination unit 218 calculates the waiting time Tw as the elapsed time from the transmission completion time obtained in step ST231.

This completes the waiting time calculation operation based on the elapsed time from the transmission completion time in the constraint determination unit 218.

2.4 Effects of the Present Embodiment According to the second embodiment, the constraint determination unit 218 determines the constraints imposed on the transmission interval Ti based on the waiting time Tw of the terminal 20 until the carrier sense operation is performed in addition to the transmission pause time Ts. This makes it possible to reduce the substantial constraint that must be absorbed by the carrier sense time Tc of the transmission pause time Ts that the transmission interval Ti must comply with by the waiting time Tw. For this reason, it is possible to set the carrier sense time Tc shorter than when the waiting time Tw is not taken into consideration. This allows the frequency resources to be used efficiently.

Specifically, the constraint determination unit 218 calculates the waiting time Tw based on whether the wireless frame transmitted immediately before requests a response frame or whether the wireless frame to be transmitted next requests a response frame every time. This reduces the effective constraint on the transmission interval Ti by the time required to receive the response frame.

In addition, when the next wireless frame to be transmitted requests a response frame, the constraint determination unit 218 calculates the waiting time Tw based on the number of retransmissions of the next wireless frame. This makes it possible to calculate an appropriate waiting time Tw, even when the next wireless frame to be transmitted requests a response frame, while taking into consideration the case where the next wireless frame is transmitted without waiting for the response frame to be received.

In addition, the constraint determination unit 218 calculates the waiting time Tw based on the elapsed time from the completion time of the immediately preceding wireless frame. This allows the calculation of an appropriate waiting time Tw according to the situation, not only when it is required to receive a response frame as described above, but also when the terminal 20 waits for an operation until the start of a carrier sense operation.

3. Third embodiment In the first and second embodiments, a case has been described in which frame information of a wireless frame is set, and then a constraint on the transmission interval Ti is determined when the frame information is applied. The third embodiment differs from the first and second embodiments in that, when a wireless frame satisfies a condition, frame information is set in advance so that the transmission interval Ti is not constrained. In the following, a description of the same configuration and operation as the first embodiment will be omitted, and a description will be mainly given of the configuration and operation that are different from the first embodiment.

3.1 Transmission Operation Fig. 14 is a flowchart showing an overview of a wireless signal transmission operation in a terminal according to the third embodiment, and corresponds to Fig. 5 in the first embodiment. In Fig. 14, step ST5 is provided before step ST10 shown in Fig. 5, and step ST15 is further provided between step ST5 and step ST50.

As shown in FIG. 14, in step ST5, the communication control unit 217 determines whether the priority of the wireless frame is low or not. When making this determination, the communication control unit 217 may, for example, refer to the access category of the wireless frame. In this case, the access category is pre-classified into a group determined to have low priority and a group determined to have high priority. If the result of the determination is that the priority is low (step ST5; yes), the process proceeds to step ST10, and if the priority is determined to be high (step ST5; no), the process proceeds to step ST15.

In step ST15, the communication control unit 217 sets the frame information so that the transmission interval Ti is not restricted, and the process proceeds to step ST50. On the other hand, in step ST10, the communication control unit 217 sets the frame information regardless of whether the transmission interval Ti is restricted or not. Hereinafter, for convenience of explanation, the operation in step ST15 is also referred to as a restriction avoidance operation.

The operations from step ST20 to step ST80 are the same as those in Figure 5, so the explanation will be omitted.

By operating as described above, the communication control unit 217 can select, depending on the priority of the wireless signal, whether to set frame information so that the transmission interval Ti is not restricted, or to set frame information without considering whether the transmission interval Ti is restricted or not.

3.2 Restriction Avoidance Operation Next, an example of the constraint avoidance operation performed by the communication control unit 217 will be described.

Figure 15 is a flowchart showing an example of constraint avoidance operation in a terminal in the third embodiment, and corresponds to step ST15 in Figure 14.

As shown in Fig. 15, in step ST311, the communication control unit 217 selects a frame time length in which the transmission interval Ti is not restricted. The communication control unit 217 grasps in advance a range of frame time lengths in which the transmission interval Ti is not restricted, and selects, for example, the maximum frame time length within that range.

In step ST312, the communication control unit 217 sets the transmission rate and frame size, which are parameters of the frame time length, so that it becomes the frame time length selected in step ST311.

As a result, the communication control unit 217 can set frame information that realizes a frame time length that is not restricted by the transmission interval Ti.

3.3 Effects of this embodiment According to the third embodiment, when the condition that the next wireless frame to be transmitted has a high priority is satisfied, the communication control unit 217 sets a frame time length that is not restricted by the transmission interval Ti. As a result, when the priority of the wireless frame is high, the access parameter AIFSN used in the carrier sense operation is always set to the specified value AIFSN1. Therefore, the time required for the carrier sense operation can be set to the shortest possible value, and even in the case of contention with other terminals 20, the possibility of acquiring the transmission right can be increased. Therefore, an increase in the delay time until the transmission of a wireless frame with a high priority can be suppressed.

4. Others Various modifications can be applied to the first to third embodiments described above.

For example, each of the operations according to the first to third embodiments described above can be stored as a program that can be executed by a processor, which is a computer. Alternatively, the operations 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 load the program stored in the storage medium of the external storage device, and execute the operations described above by having its operations controlled by the loaded program.

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 wireless communication system 10 base station 20-1, 20-2, 20-3 terminal 21 processor 22 ROM
23...RAM
24 wireless module 25 display 26 sensor 210 wireless signal processing unit 211 receiving unit 212 demodulation unit 213 received frame transfer unit 214 transmission frame waiting unit 215 modulation unit 216 transmission unit 217 communication control unit 218 constraint determination unit 219 parameter setting unit 220 data processing unit 230 application execution unit

Claims (8)

determining a constraint on a transmission start time of an untransmitted first radio frame;
setting an arbitration inter frame space number (AIFSN) as a parameter used in a carrier sense operation of the first radio frame according to the determined constraint;
Equipped with
the determining step includes determining, as the constraint, whether or not there is a transmission pause time from a transmission of a second radio frame that is transmitted immediately before the first radio frame;
The setting includes setting a first AIFSN when the transmission pause time does not exist, and setting a second AIFSN larger than the first AIFSN when the transmission pause time exists.
The communication method of the device. the determining step includes determining the constraint based on at least one of a frequency band, a frame time length, and a frame type of the first radio frame.
The communication method according to claim 1. the determining includes determining the restriction based on whether or not a response frame to the first radio frame or a second radio frame transmitted immediately before the first radio frame is received.
The communication method according to claim 1 or 2. The determining step includes determining the constraint based on a number of retransmissions of the first radio frame.
The communication method according to claim 1 or 2. the determining includes determining the restriction based on an elapsed time from a transmission completion time of a second radio frame that is transmitted immediately before the first radio frame.
A communication method according to any one of claims 1 to 4. and setting a frame time length, in which a transmission interval is not subject to the constraint, for the first radio frame when the priority of the first radio frame satisfies a condition.
A communication method according to any one of claims 1 to 5. the constraint specifies a minimum value of a transmission interval from a transmission completion time of a second radio frame transmitted immediately before the first radio frame to a transmission start time of the first radio frame.
The communication method according to claim 1. a determination unit that determines a restriction imposed on a transmission start time of an untransmitted first wireless frame;
a setting unit that sets an arbitration inter frame space number (AIFSN) as a parameter used in a carrier sense operation of the first radio frame in accordance with the determined constraint;
a transmitter that transmits a radio signal based on the first radio frame in accordance with a transmission right acquired by the carrier sense operation;
Equipped with
the determining step includes determining, as the constraint, whether or not there is a transmission pause time from a transmission of a second radio frame that is transmitted immediately before the first radio frame;
The setting includes setting a first AIFSN when the transmission pause time does not exist, and setting a second AIFSN larger than the first AIFSN when the transmission pause time exists.
Terminal.

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