JP7486174B2 - Congestion controller, congestion control method and receiving method - Google Patents

Description

The present invention relates to a congestion controller and a congestion control method.

For example, Patent Document 1 describes a method for forming a network that can share frequency resources equally and efficiently.

JP2020-005162Publication

However, conventional methods such as those described in Patent Document 1 have the problem that congestion due to multiple terminals can occur in the wireless channel.

One aspect of the embodiment of the present invention aims to provide a congestion controller and congestion control method that allows multiple terminals to communicate on the same wireless channel and that can suppress the occurrence of congestion caused by multiple terminals.

A congestion controller provided in a terminal that exchanges signals with other terminals via frames, the congestion controller includes a channel access right acquisition confirmation unit that confirms whether the terminal has acquired a channel access right, which is rights information required when transmitting a signal, and measures a transmission waiting time, which is the time from the start of the frame being processed until the channel access right is acquired, and an attenuation value calculation unit that calculates an attenuation value to be used in the next frame using the transmission waiting time, and generates congestion control that controls congestion by attenuating the signal received by the terminal for each frame using the attenuation value.

A congestion control method using a congestion controller provided in a terminal that exchanges signals with other terminals via frames is provided, which includes a first step of checking whether the terminal has acquired a channel access right, which is rights information required for transmitting a signal, and measuring a transmission latency time, which is the time from the start of the frame being processed until the channel access right is acquired, and a second step of calculating an attenuation value to be used in the next frame using the transmission latency time, and controls congestion by attenuating the signal received by the terminal for each frame using the attenuation value.

According to one aspect of the embodiment of the present invention, it is possible to realize a congestion controller that allows multiple terminals to communicate on the same wireless channel and can suppress the occurrence of congestion caused by multiple terminals.

FIG. 1 is a block diagram showing a configuration of a communication system including a congestion controller provided in a terminal according to this embodiment. FIG. 2 is a conceptual diagram of the time from the start of a frame until a terminal acquires channel access right and transmits a data packet. FIG. 3 is a flowchart showing a procedure of the congestion control process. FIG. 4 is a flowchart showing a procedure of the attenuation value calculation process when no congestion control is performed in the previous frame. FIG. 5 is a diagram for explaining the attenuation value calculation process when no congestion control is performed in the previous frame. FIG. 6 is a flowchart showing a procedure of the attenuation value calculation process when congestion control is performed in the previous frame. FIG. 7 is a flowchart showing the procedure of the attenuation value calculation process when the channel access right is not acquired.

The following describes in detail one embodiment of the present invention with reference to the drawings. For example, one embodiment of the present invention may use the Peer Aware Communication (PAC) specification as described in the international standard IEEE 802.15.8-2017.

Fig. 1 is a block diagram showing the configuration of a communication system including a congestion controller 4 provided in a terminal 1 according to this embodiment. In the communication system shown in Fig. 1, a terminal 1 (which may be referred to as the own terminal hereinafter) mounted on a mobile object such as a drone or a ship and one or more terminals 15 (which may be referred to as other terminals hereinafter) mounted on one or more mobile objects communicate by broadcast.

Specifically, terminal 1 includes a receiver 2 that receives signals transmitted from a transmitter 3 included in one or more terminals 15, and a congestion controller 4 that controls congestion by attenuating the signal received by receiver 2 for each frame.

The maximum receivable distance d _max is the maximum distance at which a signal broadcast by a nearby terminal 15 can be received, and is determined by the hardware performance of the receiver 2 included in the terminal 1. Note that in this application, reception refers to the process of performing carrier sensing.

The threshold distance d _th is the minimum distance at which a signal broadcast by a surrounding terminal 15 should be received, and is a setting index determined by the specifications of the software of the receiver 2 included in the terminal 1. For example, the software of the receiver 2 included in the terminal 1 prevents collisions between moving objects such as drones and ships by mutual position notification with other receivers 2. The reception distance d _R is the actually measured distance, which is equal to or greater than the threshold distance d _th and equal to or less than the maximum receivable distance d _max .

The congestion controller 4 includes a channel access right acquisition confirmation unit 5 that confirms whether the receiver 2 included in the terminal 1 has acquired a channel access right (hereinafter, this may be called a transmission right) by performing CSMA (Carrier Sense Multiple Access), and an attenuation value calculation unit 6 that calculates an attenuation value ATT, which will be described later. For example, the channel access right acquisition confirmation unit 5 and the attenuation value calculation unit 6 are integrated circuits.

The terminal 1 controls the receiving sensitivity by changing the receiving distance _dR according to the attenuation value ATT. When congestion occurs, the closer the terminal 1 is to the terminal 1, the higher the priority of the terminal 15 as a target for broadcast communication. Note that the closer a mobile unit is to the mobile unit being measured, the higher the risk of collision, and therefore the position information of the nearby mobile unit is important, so the priority of broadcast communication is higher.

Here, the channel access right refers to the right (hereinafter, this may be referred to as right information) required when the terminal 1 transmits a signal such as a data packet via the transmitter 3 equipped in the terminal 1, and the channel access right acquisition confirmation unit 5 measures the transmission waiting time t described below, and the attenuation value calculation unit 6 acquires the measured transmission waiting time t.

The attenuation value ATT (hereinafter, this may be referred to as ATT[n+1]) calculated in the nth frame is the value used in the next frame, the n+1th frame. In this embodiment, when receiving a signal broadcast by terminal 15 present around terminal 1 in the next frame, the congestion controller 4 controls congestion by attenuating the received signal using the attenuation value ATT calculated by the attenuation value calculator 6.

Next, using Figure 2, we will explain the transmission waiting time t from the start of the frame being processed until terminal 1 acquires channel access rights and transmits a data packet via transmitter 3. Figure 2 is a conceptual diagram of the transmission waiting time t from the start of the frame until terminal 1 acquires channel access rights and transmits a data packet.

A frame is a time unit in the data link layer protocol, and is repeated at a period T as shown in Fig. 2. A data packet is actual data, and the time required for transmission is designated as transmission time _ts as shown in Fig. 2.

Terminal 1 and one or more other terminals 15 transmit the information they each have as a broadcast signal for each frame, and all terminals other than the transmitting terminal 1 or one or more other terminals 15 must receive the transmitted information.

The contention window value CW indicates the time per contention window, which is a mechanism for avoiding collisions between data packets. The backoff slot value bkoffslt is the value of the minimum time step that the processor in the terminal advances through, and is also used to measure the transmission waiting time t. When the backoff counter value, which is counted using the backoff slot value bkoffslt, reaches 0, terminal 1 acquires the channel access right.

…（１）

…（２） The discrete time k _CW in the nth frame (hereinafter, this may be referred to as k _CW [n]) is an index showing the occurrence state of congestion, and is a time-dependent value represented by 0 and positive integers, and can be expressed by the following formula (1). In addition, since the maximum value of the transmission waiting time t is the period T, the maximum discrete time k _{CW_max} , which is the maximum value of the discrete time k _CW , can be expressed by the following formula (2). int() indicates the integer number in the parentheses.

…(1)

…(2)

The smaller the discrete time k _CW is, the lower the occurrence rate of congestion. When the discrete time k _CW is sufficiently small, such as 0, the receiver 2 of the terminal 1 sets the attenuation value ATT to 0 and can receive a signal broadcast by the terminal 15 present around the terminal 1 without attenuating the signal by the attenuation value ATT in the next frame.

When the discrete time k _CW is equal to or greater than the upper discrete time B described below, the data packet cannot be transmitted within the frame at that time, and therefore the transmitter 3 of the terminal 1 cannot transmit a signal by broadcast in the frame at that time.

The congestion controller 4 according to this embodiment determines the attenuation value ATT using the transmission waiting time t, which is the time required to acquire channel access rights. When receiving a broadcast signal, the congestion controller 4 according to this embodiment controls congestion by attenuating the received signal for each frame according to the attenuation value ATT.

Next, the congestion control process performed by the congestion controller 4 will be described with reference to FIG. 3. FIG. 3 is a flowchart showing the procedure of the congestion control process. As shown in FIG. 3, the attenuation value ATT is calculated in different ways depending on whether or not the channel access right was obtained and whether or not congestion control occurred in the previous frame (hereinafter, this may be referred to as the n-1th frame).

First, the channel access right confirmation unit 5 determines whether the frame being processed has not ended by measuring the time from the start of the frame (S1). If the determination in step S1 is positive (S1: YES) and it is determined that the frame being processed has not ended, the channel access right confirmation unit 5 checks with the receiver 2 to determine whether the channel access right has been acquired (S2).

If the determination in step S1 is negative (S1: NO) and it is determined that the channel access right has not been acquired, the attenuation value calculation unit 6 performs the attenuation value calculation process when the channel access right has not been acquired (S40), which is shown in FIG. 7 described below.

If the determination in step S2 is negative (S2: NO) and it is determined that channel access rights have not been acquired, the channel access right acquisition confirmation unit 5 performs the process of step S1 again.

If the determination in step S2 is positive (S2: YES) and it is determined that channel access rights have been acquired, the channel access right acquisition confirmation unit 5 checks the congestion control record of the previous frame stored in the channel access right acquisition confirmation unit 5 to determine whether congestion control occurred in the previous frame (S3).

If the determination in step S3 is negative (S3: NO), and it is determined that congestion did not occur in the previous frame, the attenuation value calculation unit 6 performs the attenuation value calculation process when no congestion control was performed in the previous frame shown in FIG. 4 (S10), which will be described later.

If the determination in step S3 is positive (S3: YES), and it is determined that congestion occurred in the previous frame, the attenuation value calculation unit 6 performs processing with previous frame congestion control shown in FIG. 6 (S20), which will be described later.

Next, with reference to FIG. 4, the attenuation value calculation process _S10 when no congestion control occurred in the previous frame, which is performed by the attenuation value calculation unit 6, will be described in the case where the terminal 1 acquires a channel access right at the discrete time k CW of the frame being processed and congestion control did not occur in the previous frame (hereinafter, the attenuation value ATT[n] calculated in the previous frame may be regarded as 0).

4 is a flowchart showing the procedure of the attenuation value calculation process S10 when no congestion control is performed in the previous frame. In the attenuation value calculation process S10 when no congestion control is performed in the previous frame, the attenuation value calculation unit 6 calculates the attenuation value ATT based on the discrete time k _CW .

First, the damping value calculation unit 6 determines the range of the value of the discrete time k _CW (S11). If it is determined that the discrete time k _CW is smaller than the lower limit discrete time A, the damping value calculation unit 6 sets the damping value to 0 (S12).

…（３） The lower limit discrete time A can be expressed by the following formula (3): The coefficient a is a coefficient for determining the position at which the attenuation value ATT begins to be taken into consideration in one frame, and is set to a value, for example, greater than 1 and less than 2, taking into consideration a usage scenario that assumes a specific situation when the terminal 1 is used.

…(3)

When it is determined that the discrete time k _CW is the lower limit discrete time A, the attenuation value calculation unit 6 sets the lower limit attenuation value A _S to the attenuation value ATT (S13). The lower limit attenuation value A _S is a predetermined value that is set in advance in consideration of the usage scenario.

…（４） If it is determined that the discrete time _kCW is greater than the lower limit discrete time A and less than the upper limit discrete time B, the attenuation value calculation unit 6 sets the attenuation value ATT to a value calculated using a first function f( _kCW ) as shown in Fig. 5 (S14). The upper limit discrete time B can be expressed by the following formula (4).

…(4)

When it is determined that the discrete time k _CW is equal to or greater than the upper discrete time B, the attenuation value calculation unit 6 sets the upper limit attenuation value A _E to the attenuation value ATT (S15). The upper limit attenuation value A _E is a predetermined value that is set in advance in consideration of the usage scenario.

The lower limit attenuation value A _S , the upper limit attenuation value A _E , the lower limit discrete time A and the upper limit discrete time B respectively indicate the lower limit value that the attenuation value ATT can take, the upper limit value that the attenuation value ATT can take, the lower limit value that the discrete time k _CW can take, and the upper limit value that the discrete time k _CW can take in the first function f( _k CW ).

The lower limit attenuation value A _S is, for example, 1 dB or more, and the upper limit attenuation value A _E is, for example, 3 to 20 dB, which is a sufficiently large value, for example, 2 to 100 times larger than the lower limit attenuation value A _S. The upper limit attenuation value A _E is the value of the attenuation value ATT when the back-off counter value becomes 0 but the remaining time of the frame being processed is shorter than the transmission time t _s .

Next, the relationship between the attenuation value ATT and the discrete time k _CW in the attenuation value calculation process S10 when no congestion control is performed in the previous frame will be described with reference to Fig. 5. Fig. 5 is a diagram for explaining the attenuation value calculation process S10 when no congestion control is performed in the previous frame.

As shown in Fig. 5, the attenuation value ATT is expressed in dB, for example, and the discrete time _kCW is expressed by an integer value in milliseconds or microseconds, for example. Graph 21 shows the cases of steps S12 and S13 in Fig. 4, graphs 22 and 23 show the case of step S14, and graph 24 shows the case of step S15.

The first function f(k _CW ) can be expressed, for example, as a linear function as shown in graph 22 (which may hereinafter be referred to as option A) or as an exponential function as shown in graph 23 (which may hereinafter be referred to as option B).

…（５） Option A can be expressed by equation (5) below: As mentioned before, the attenuation value ATT is relative to the next frame and the discrete time k _CW is relative to the frame being processed.

…(5)

…（６） Option B can be expressed by equation (6) below: As mentioned before, the attenuation value ATT is relative to the next frame and the discrete time k _CW is relative to the frame being processed.

…(6)

Next, with reference to FIG. 6, an explanation will be given of the attenuation value calculation process S20 when the terminal 1 acquires a channel access right in the discrete time k _CW of the frame being processed and congestion control occurs in the previous frame (hereinafter, the attenuation value ATT[n] calculated in the previous frame may not be 0).

In the attenuation value calculation process S20 when congestion control is present in the previous frame, the discrete time k _CW is, for example, equal to or greater than the lower limit discrete time A and equal to or less than the upper limit discrete time B. Also, in the attenuation value calculation process S20 when congestion control is present in the previous frame, the attenuation value ATT[n] (hereinafter, this may be referred to as the previous attenuation value ATT _pre ) calculated in the previous frame is, for example, equal to or greater than the lower limit attenuation value A _S and equal to or less than the upper limit attenuation value A _E.

6 is a flowchart showing the procedure of the attenuation value calculation process S20 when congestion control is present in the previous frame. In the attenuation value calculation process S20 when congestion control is present in the previous frame, the attenuation value calculation unit 6 calculates the attenuation value ATT based on the change in the discrete time k _CW .

First, the attenuation value calculation unit 6 judges whether or not the terminal 1 can transmit a signal (S21). Specifically, it judges whether or not the discrete time k _CW is smaller than the upper discrete time B. If the judgment in step S21 is positive (S21: YES), and it is judged that the terminal 1 can transmit a signal, the attenuation value calculation unit 6 calculates a first provisional attenuation value ATT _pg using a second function g(k _CW ) (S22).

…（７）

…（８） The second function g(k _CW ) corresponds to the function used in the first function f(k _CW ). When the function used in the first function f(k _CW ) is a linear function, the second function g(k _CW ) can be expressed by the following formula (7), and when the function used in the first function f(k _CW ) is an exponential function, the second function g(k _CW ) can be expressed by the following formula (8). Note that formulas (7) and (8) use the discrete time k _CWpre in the previous frame (hereinafter, this may be referred to as k _CW [n-1]).

…(7)

…(8)

…（９） If the determination in step S21 is negative (S21: NO), and it is determined that the terminal 1 cannot transmit a signal, the attenuation value calculation unit 6 calculates a first provisional attenuation value ATT _pg in consideration of a step change value Δ1, which is a predetermined value set in advance, as shown in formula (9) (S23), and proceeds to step S26 described below. The step change value Δ1 is, for example, about 1 to 3 dB, and is used when the attenuation value ATT is increased little by little.

…(9)

In step S22, after calculating the first provisional attenuation value ATT _pg using the second function g(k _CW ), the attenuation value calculation unit 6 determines whether the amount of change ΔATT in the attenuation value is equal to or larger than the chattering prevention value Δ2 (S24).

…（１０） The amount of change in the attenuation value ΔATT can be expressed by the following formula (10), and the chattering prevention value Δ2 is a predetermined value that is set in advance. The chattering prevention value Δ2 is a value for preventing chattering, such as the attenuation value ATT fluctuating between certain values over time, and is, for example, 1 to 3 dB.

…(10)

If the judgment in step S24 is negative (S24: NO) and it is determined that chattering is occurring, the attenuation value calculation unit 6 sets the attenuation value ATT to the previous attenuation value ATT _pre (S30) and terminates the attenuation value calculation process S20 when congestion control is present in the previous frame.

If the determination in step S24 is positive (S24: NO), that is, if it is determined that chattering is not occurring, the damping value calculation unit 6 determines whether the first provisional damping value _{ATT_pg} is smaller than the lower limit damping value _AS (S25).

If the determination in step S25 is positive (S25: YES), the attenuation value calculation unit 6 sets the attenuation value ATT to 0 (S28) and ends the attenuation value calculation process S20 when congestion control is present in the previous frame. If the determination in step S25 is negative (S25: NO), the attenuation value calculation unit 6 proceeds to step S26.

When the process of step S23 is completed or the determination in step S25 is negative, the attenuation value calculation unit 6 determines whether the first provisional attenuation value _{ATT_pg} is greater than the attenuation value _Ath at the threshold distance (S26). The attenuation value _Ath at the threshold distance is set to the attenuation value ATT previously measured at the threshold distance _dth .

If the determination in step S26 is negative (S26: NO), the attenuation value calculation unit 6 sets the attenuation value ATT to the first provisional attenuation value _{ATT_pg,} and ends the attenuation value calculation process S20 when congestion control is performed in the previous frame.

If the determination in step S26 is positive (S26: YES), the attenuation value calculation unit 6 sets the attenuation value ATT to the threshold distance attenuation value _Ath , and ends the attenuation value calculation process S20 with congestion control in the previous frame.

7, a description will be given of a channel access right non-acquired attenuation value calculation process S40 performed by the attenuation value calculation unit 6 when the terminal 1 does not acquire a channel access right in the frame being processed. In the channel access right non-acquired attenuation value calculation process S40, the discrete time k _CW becomes greater than the maximum discrete time k _{CW_max} .

7 is a flowchart showing the procedure of the attenuation value calculation process S40 when the channel access right is not acquired. The attenuation value calculation unit 6 calculates the attenuation value based on the nearest terminal distance _{d_nst} , which is the distance to the other terminal 15 that is nearest to the terminal.

First, the attenuation value calculation unit 6 determines the range of the nearest terminal distance _{d_nst} (S41). If the nearest terminal distance _{d_nst} is equal to or greater than the threshold distance _{d_th} , the attenuation value calculation unit 6 sets the nearest terminal distance and the threshold distance reflected attenuation value _{A_ε} to the second provisional attenuation value _{ATT_R} (S42).

…（１１） The nearest terminal distance and the attenuation value A _ε reflecting the threshold distance can be expressed by the following formula (11).

…(11)

If the nearest terminal distance _{d_nst} is equal to or greater than half the threshold distance _{d_th} and smaller than the threshold distance _{d_th} , the attenuation value calculation unit 6 sets the nearest terminal distance reflected attenuation value _{A_δ} to the second provisional attenuation value _{ATT_R} (S43).

…（１２） The nearest terminal distance reflection attenuation value A _δ can be expressed by the following formula (12).

…(12)

If the nearest terminal distance _{d_nst} is smaller than half the threshold distance _{d_th} , the attenuation value calculation unit 6 sets the second provisional attenuation value _{ATT_R} to the threshold distance attenuation value _Ath (S44).

Next, the attenuation value calculation unit 6 judges whether the second provisional attenuation value ATT _R is smaller than the sum of the upper limit attenuation value A _E and the step change value Δ1 (S45). If the judgment in step S45 is negative (S45: NO), the attenuation value calculation unit 6 sets the attenuation value ATT to the second provisional attenuation value ATT _R and ends the attenuation value calculation process S40 when the channel access right is not acquired.

If the determination in step S45 is positive (S45: YES), the attenuation value calculation unit 6 sets the attenuation value ATT to the sum of the upper limit attenuation value _AE and the step change value Δ1, and ends the attenuation value calculation process S40 when the channel access right is not acquired.

As described above, the congestion controller 4 according to this embodiment controls congestion using the time required for the terminal 1 to acquire channel access rights. Since congestion control is possible by measuring the elapsed time from the start of the frame being processed in the terminal 1 (for example, the discrete time K _CW ), adaptive control based on control results such as whether or not congestion control occurred in past frames becomes possible, enabling control that is more in line with what is actually happening.

The congestion controller 4 according to this embodiment is effective in a communication network made up of moving objects such as drones, cars, ships, and robots, in which each moving object transmits its own position information as a broadcast signal.

Other moving objects use the location information sent by a moving object to control themselves so as not to collide with the moving object, ensuring safety during movement. By making it less likely for congestion to occur, the possibility of location information not being notified can be reduced, and the possibility of moving objects colliding with each other can be reduced.

In the above embodiment, the channel access right acquisition confirmation unit 5 and the attenuation value calculation unit 6 are described as integrated circuits, but this embodiment is not limited to this. The channel access right acquisition confirmation unit 5 and the attenuation value calculation unit 6 may be implemented by a program stored in, for example, a smartphone.

1, 15... terminal, 2... receiver, 3... transmitter, 4... congestion controller, 5... channel access right acquisition confirmation unit, 6... attenuation value calculation unit.

Claims (6)

A congestion controller provided in a terminal that exchanges signals with other terminals via frames,
a channel access right acquisition confirmation unit that confirms whether the terminal has acquired a channel access right, which is rights information required when the terminal transmits the signal, and measures a transmission waiting time that is a time from the start of a frame being processed to the acquisition of the channel access right;
an attenuation value calculation unit that calculates an attenuation value to be used in a next frame by using the transmission waiting time,
A congestion controller that generates congestion control to control congestion by attenuating the signal transmitted from the other terminal and received by the terminal for each frame using the attenuation value. The attenuation value is calculated in different ways depending on whether the terminal has acquired the channel access right and whether the congestion control has occurred in the previous frame.
The congestion controller of claim 1 . When the terminal acquires a channel access right in the frame being processed and congestion control does not occur in the previous frame, the attenuation value calculation unit calculates the attenuation value based on a discrete time, which is an index indicating the occurrence state of the congestion and is a time-dependent value indicated by 0 and a positive integer.
The congestion controller of claim 1 . When the terminal acquires a channel access right in the frame being processed and congestion control occurs in the previous frame, the attenuation value calculation unit calculates the attenuation value based on a change in a discrete time, which is an index indicating the occurrence state of the congestion and is a time-dependent value indicated by 0 and a positive integer.
The congestion controller of claim 1 . When the terminal does not acquire a channel access right in the frame being processed, the attenuation value calculation unit calculates the attenuation value based on a nearest terminal distance, which is a distance of the other terminal that is nearest to the terminal.
The congestion controller of claim 1 . A congestion control method by a congestion controller provided in a terminal that exchanges signals with other terminals via frames, comprising:
a first step of checking whether the terminal has acquired a channel access right, which is rights information required when the terminal transmits the signal, and measuring a transmission waiting time, which is a time from the start of a frame being processed to the acquisition of the channel access right;
a second step of calculating an attenuation value to be used in a next frame using the transmission latency time;
A congestion control method for controlling congestion by attenuating the signal received by the terminal and transmitted from the other terminal for each frame using the attenuation value.

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