JP5631843B2 - Wireless LAN access control method and wireless LAN system - Google Patents

Description

  The present invention relates to a wireless LAN access control method and a wireless LAN system for performing access control for sharing the same wireless channel of a wireless LAN among a plurality of terminals. In particular, a wireless LAN access control method for minimizing waiting time while avoiding packet collision by a procedure different from CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) that avoids packet collision by carrier sense at random time, and The present invention relates to a wireless LAN system.

  In the Distributed Coordination Function (DCF), which is the basic access procedure of IEEE 802.11 wireless LAN, each terminal checks the use status of the radio channel by carrier sense, and transmits when the radio channel is idle. A CSMA / CA scheme is sometimes used in which collisions are avoided by suspending transmission (Non-Patent Document 1).

FIG. 8 shows an example of conventional wireless LAN access control. In the IEEE 802.11 standard, frame intervals (SIFS, DIFS) are defined as signal transmission intervals.
In FIG. 8, the radio terminals STA1 to STA3 perform carrier sense of the radio channel, and wait for the DIFS time (SIFS <DIFS) triggered by the transition from busy to idle, and are generated from the contention window (CW) range. The carrier sense is continued for the back-off time corresponding to the random number. Here, when the back-off time of STA1 is shorter than STA2 and STA3, STA1 confirms the idle of the radio channel and transmits data until the back-off time elapses. Furthermore, the radio base station AP receives the data and transmits an ACK signal after SIFS time, and the STA1 receives the ACK signal and waits for the DIFS time when the radio channel shifts from busy to idle. Set the backoff time corresponding to the random number generated in.

  On the other hand, STA2 and STA3 are busy with the transmission of STA1 before the back-off time elapses, so the remaining back-off time is carried over, and when the radio channel becomes idle next time, Perform off-time career sense. Thereby, collision of packets transmitted by STA1 to STA3 is avoided.

  Here, when the packets to be transmitted collide with the same back-off time as in STA1 and STA3, the ACK signal is not received within a predetermined time from the end of packet transmission. In this case, STA1 and STA3 determine that the transmission has failed, expand the CW and expand the range of random numbers for determining the backoff time, set the backoff time, and perform retransmission processing. As a result, the CW increases as the number of retransmissions increases, and the variation in the back-off time increases and the collision probability can be reduced.

FIG. 9 shows an example of a conventional wireless LAN access control procedure.
In FIG. 9, when a communication request is generated (S21), the terminal selects a random number from the CW and sets a back-off time according to the random number (S22). When the carrier sense of the radio channel is performed and the transition from busy to idle is waited for the DIFS time, the carrier sense is continued for the backoff time, and the radio channel becomes busy before the backoff time elapses. Waits for the next idle state, and then performs carrier sense of the back-off time carried over (S23, S24). If the radio channel is idle and the back-off time has elapsed, a packet is transmitted (S25), the reception of an ACK signal is awaited (S26), and if an ACK signal is received, the process returns to the initial processing, and the ACK signal Is not received (S27), the process returns to the process of selecting a random number from the CW and setting the back-off time (S22).

IEEE Standard for Local and metropolitan area networks Part 11: Wireless LAN MAC and PHY Specifications, June 2007

  In the conventional technology, although collision avoidance is performed by back-off control, the collision probability increases as the number of wireless terminals increases, and communication efficiency decreases. Further, when a collision occurs, the collision probability is reduced by enlarging the CW. However, there is a problem that the overhead corresponding to the back-off time for waiting due to the expansion of the CW is increased and the communication efficiency is lowered.

  An object of the present invention is to provide a wireless LAN access control method and a wireless LAN system capable of minimizing standby time while avoiding packet collision even when the number of wireless terminals is large.

  According to a first aspect of the present invention, there is provided a wireless LAN access control method in which a plurality of wireless terminals accommodated in a wireless LAN perform packet transmission while avoiding collisions by waiting for different backoff times. A packet is transmitted when the radio channel is idle for the back-off time corresponding to the back-off initial value, and a common back-off period is set with the off-initial value, or the radio channel is not connected during the back-off time. Carry over the remaining backoff time when busy, then the radio channel is idle, then send the packet when the radio channel is idle for the carryover backoff time, and after sending the packet, Carrier for next packet transmission by setting backoff time corresponding to off period The backoff initial value obtained by shifting the backoff initial value set for each wireless terminal is reset by the packet transmission failure, and each wireless terminal returns the backoff value corresponding to the reset backoff initial value. Set the off time and perform carrier sense for the next packet transmission.

  In the wireless LAN access control method of the first invention, when there is no packet to be transmitted when the wireless channel is idle for the backoff time, a backoff time corresponding to the backoff period is set and the next packet is set. Perform carrier sense for transmission.

  In the wireless LAN access control method of the first invention, the backoff initial value and the backoff period are initially set by a radio base station that communicates with a plurality of radio terminals, and the backoff initial value to be reset is a transmission failure. The wireless terminal or the wireless base station sets, and the plurality of wireless terminals set a back-off time corresponding to the back-off initial value after initialization or resetting by the wireless base station, and start carrier sense.

  In the wireless LAN access control method of the first invention, the back-off period common to a plurality of wireless terminals is set to be equal to or greater than the maximum back-off initial value of each wireless terminal.

  A second invention is a wireless LAN system in which a plurality of wireless terminals accommodated in a wireless LAN perform packet transmission while avoiding collisions by waiting for different backoff times. Value and a common backoff period are set and packets are transmitted when the radio channel is idle for the backoff time corresponding to the backoff initial value, or the radio channel is busy during the backoff time. The remaining back-off time is carried over, then the radio channel is idle, then the packet is sent when the radio channel is idle over the carry-back back-off time, and after the packet is sent, the back-off period Set the backoff time corresponding to the carrier sense for the next packet transmission. The backoff initial value obtained by shifting the backoff initial value set for each wireless terminal is reset due to a packet transmission failure, and each wireless terminal receives a backoff time corresponding to the reset backoff initial value. And an access control means for performing carrier sense for the next packet transmission.

  In the wireless LAN system of the second invention, the access control means sets a back-off time corresponding to the back-off period when there is no packet to be transmitted when the wireless channel is idle over the back-off time. In this configuration, carrier sense for the next packet transmission is performed.

  In the wireless LAN system of the second invention, a wireless base station that communicates with a plurality of wireless terminals initializes a back-off initial value and a back-off period, and the back-off initial value to be reset is the wireless terminal that failed to transmit or Set by the radio base station, the plurality of radio terminals set a back-off time corresponding to the back-off initial value after initialization or resetting by the radio base station, and start carrier sense.

  In the wireless LAN system of the second invention, the back-off period common to the plurality of wireless terminals is set to be equal to or greater than the maximum back-off initial value of each wireless terminal.

  A plurality of wireless terminals of the wireless LAN system of the present invention are initialized with different backoff initial values and a common backoff period. Each wireless terminal transmits a packet when the wireless channel is idle over the backoff time corresponding to the backoff initial value by carrier sense, and then sets the backoff time corresponding to the backoff period. As a result, the packets are transmitted in ascending order of the back-off initial value set in each wireless terminal, and thereafter the packet transmission can be repeated without collision every back-off period.

  Furthermore, in a wireless LAN system including a wireless terminal that performs conventional wireless LAN access control (backoff control), when a transmission failure occurs due to a collision with a packet transmitted by the wireless terminal, By shifting and resetting the back-off initial value of the wireless terminal, it is possible to reduce collisions even in retransmission processing and to equalize transmission opportunities of the wireless terminals.

  Here, the wireless terminal according to the present invention sets a back-off time according to the back-off period regardless of transmission success or transmission failure. Is possible. However, since the back-off period is set to be greater than or equal to the maximum value of the back-off initial value of each wireless terminal, shifting the back-off initial value smaller than that and resetting it shortens the time until retransmission. can do. Further, when the transmission failure is due to packet collision, the back-off value of the conventional wireless terminal becomes large, so that the wireless terminal in the present invention can perform retransmission processing with higher priority.

It is a flowchart which shows the Example of the wireless LAN access control procedure of this invention. It is a time chart which shows the wireless LAN access control example 1 of this invention. 6 is a time chart showing a backoff initial setting example 1; 6 is a time chart showing a backoff initial setting example 2; It is a time chart which shows the wireless LAN access control example 2 of this invention. It is a figure which shows the example of a back-off initialization table, and the example of a shift of a back-off initial value. It is a time chart which shows the wireless LAN access control example 3 of this invention. It is a time chart which shows the example of the conventional wireless LAN access control. It is a flowchart which shows the example of the conventional wireless LAN access control procedure.

FIG. 1 shows an embodiment of a wireless LAN access control procedure of the present invention.
The wireless LAN access control procedure of this embodiment is executed by each of a plurality of wireless terminals. Each wireless terminal has a backoff initialization table having a backoff initial value and a backoff period from a wireless base station, for example, at the time of network setup. Initially set. Here, FIG. 6 (1) shows an example of the back-off initialization table when there are M wireless terminals. The backoff initialization table has different backoff initial values for wireless terminal numbers 1 to M, here 2, 4, 6,..., 2M, and a backoff cycle N common to each wireless terminal number. (N ≧ 2M).

  Note that the radio base station may perform back-off initial setting for setting a back-off initial value and a back-off period for a plurality of radio terminals at an arbitrary timing. For example, when a new wireless terminal is connected to the wireless base station, the back-off initialization value and the back-off period assigned to all the wireless terminals may be changed, and the back-off initialization table may be notified all at once. Further, the back-off initial value may be stored in advance in the radio base station, and the radio base station may assign each radio terminal in order from the smallest back-off initial value.

  In FIG. 1, the wireless terminal sets a back-off time according to the back-off initial value at the first communication after the back-off initial setting (S1, S2), and the second and subsequent times after the back-off initial setting. At the time of communication, a back-off time corresponding to the back-off period is set (S3). Subsequently, carrier sense is performed over the set back-off time, and when channel busy is detected, it waits until it enters an idle state, and then carrier sense for the remaining back-off time is performed (S4, S5). When the radio channel is idle and the back-off time has elapsed, if there is transmission data in the transmission queue, the packet is transmitted (S6, S7), and the next transmission process / retransmission process is performed according to the success / failure of the transmission. Return to step S1 to do so. On the other hand, the transmission right is given when the radio channel is idle and the back-off time elapses. However, if there is no transmission data, the transmission right is released, and the carrier sense is set by setting the back-off time according to the back-off period. Restart (S6, S3, S4).

  Accordingly, each wireless terminal transmits a packet at a backoff time different from each other for the first time, and thereafter repeats packet transmission at a common backoff period. Therefore, only the wireless terminal that performs wireless LAN access control of the present invention In principle, packet collision does not occur. Hereinafter, a specific operation example will be described.

(Wireless LAN access control example 1)
FIG. 2 shows a wireless LAN access control example 1 according to the present invention.
Here, in a wireless LAN system composed of the radio base station AP and the radio terminals STA1, STA2, and STA3, the backoff initial values set in the STA1, STA2, and STA3 are 2, 4, and 6, respectively. An example in which the period is 6 is shown. The back-off cycle is set to the maximum value 6 of the back-off initial values 2, 4, and 6 in the present control example 1, but may be a value of 3, 5 or 7 or more, for example. When these values are used, it is possible to realize access control of a wireless terminal that does not cause a collision in principle.

  In addition, when setting the back-off period to be less than the maximum value of the back-off initial value of each STA, care should be taken because a collision may occur between STA 1 to STA 3 in relation to the back-off initial value. . For example, when the back-off initial values set in STA1 to STA3 are set to 2, 4, and 6 that are not continuous, no collision occurs even if the back-off period is set to 3 or 5, but if the back-off period is set to 4, the collision occurs. Will occur. On the other hand, for example, when the back-off initial values set for the four STA1 to STA4 are set to non-continuous 1, 4, 6, and 9, the back-off cycle is set to 6 (same as the back-off initial value 6 of STA3). But no collision occurs. As described above, the back-off period is appropriately selected based on the back-off initial value assigned to each STA. For example, as shown in the back-off initialization table of FIG. If a value equal to or greater than the value is selected, a back-off cycle in which no collision occurs can be set reliably.

  In FIG. 2, after the back-off initial setting by the AP, the STA1 to STA3 perform carrier sense of the radio channel, wait for the DIFS time when the transition from busy to idle occurs, and each backoff according to a specific back-off initial value The carrier sense is continued for the time, and data is transmitted from the wireless terminal whose back-off time has elapsed while the wireless channel is idle. Here, SAT1 with the shortest backoff time transmits data. STA2 and STA3 detected channel busy by starting transmission of STA1 within each backoff time, suspended carrier sense and carried over the current backoff time, and then carried over when the next idle state was entered. Resume carrier sense at backoff time.

  The STA1 that has transmitted the data receives the ACK signal transmitted from the AP, and sets a backoff time corresponding to the backoff period (= 6). STA2 and STA3 are channel busy until the transmission of the ACK signal is completed. STA1 to STA3 perform carrier sense of the radio channel, wait for the DIFS time when the transition from busy to idle occurs, and resume carrier sense at backoff times 6, 2, and 4, respectively. Therefore, the next data to be transmitted is STA2. Similarly, data transmission is performed in the order of STA3, STA1, STA2,.

  As described above, in the wireless LAN system of the present invention, each STA sets the back-off time according to the unique back-off initial value and the common back-off period, thereby avoiding the collision and avoiding the overhead due to the back-off time. Efficient transmission control can be achieved with reduced.

  Note that the AP may also set a backoff initial value and a common backoff period different from those of the STA, and perform transmission control in the same access control procedure as that of the STA. Can be preferentially transmitted.

  In addition, when the AP performs the back-off initialization at an arbitrary timing, the back-off initialization signal is transmitted at a standby time IFS (for example, RIFS, SIFS, PIFS) shorter than the DIFS when the wireless channel shifts from busy to idle. Can be sent.

FIG. 3 shows a backoff initial setting example 1.
In FIG. 3, the AP transmits a back-off initial setting signal including a back-off initial value and a back-off period (back-off initialization table) by multicast with a standby time IFS shorter than DIFS. STA1 to STA3 receive the backoff initial setting signal all at once, wait for only the DIFS time when the wireless channel transitions from busy to idle, and each of the carriers at backoff times 2, 4, and 6 according to the backoff initial value. Continue the sense. In this case, a back-off initial value and a back-off period (back-off initialization table) may be set in a beacon transmitted by the AP and notified to each STA.

FIG. 4 shows a backoff initial setting example 2.
In FIG. 4, the AP individually transmits a backoff initial setting signal including a backoff initial value and a backoff period (backoff initialization table) to each of STA1 to STA3. First, the AP transmits a backoff initialization signal to STA1 with a standby time IFS shorter than DIFS, receives an ACK signal from STA1, transmits a backoff initialization signal to STA2 after SIFS, and receives an ACK signal from STA2. After the SIFS, a backoff initial setting signal is transmitted to the STA3, and an ACK signal is received from the STA3. STA1 to STA3 wait for the DIFS time when the wireless channel transitions from busy to idle, and continue carrier sense at backoff times 2, 4, and 6 according to the backoff initial values.

  In either case of FIG. 3 or FIG. 4, a waiting period exceeding the DIFS time does not occur when the AP transmits a backoff initialization signal to each STA. Therefore, for example, the STA that has received the back-off initial setting signal first does not start the back-off process. That is, all STAs wait for the DIFS time when the radio channel transitions from busy to idle to start backoff processing all at once, so that the collision based on the backoff value assigned by the AP is centralized. No access control can be realized.

(Wireless LAN access control example 2)
FIG. 5 shows a second example of wireless LAN access control according to the present invention.
Here, in addition to STA1, STA2, and STA3 in which the same backoff initial setting as in wireless LAN access control example 1 shown in FIG. 2 is performed, a conventional backoff time is determined in an autonomous and distributed manner without being controlled by an AP. A wireless LAN system including the wireless terminal STA4 will be described.

  In FIG. 5, the initial values of STA1, STA2 and STA3 are set to 2, 4 and 6, but when the STA4 backoff value is set to 2 which is the same as STA1, STA1 and STA4 have the same timing. Will cause a collision. Therefore, the AP does not transmit an ACK signal because it cannot receive normally. The AP that detects this collision waits for the IFS (<DIFS) time and resets the backoff initial value when the data transmission of STA1 and STA4 ends and the wireless channel transitions from busy to idle. Send a setting signal.

  Here, the feature of this control example 2 is that the backoff initial value to be reset is cyclically shifted by one with respect to the terminal number. For example, as shown in FIG. 6 (2), the backoff initial values 2, 4, 6,..., 2M-2, 2M set in the terminal numbers 1, 2, 3,. , 6, 8,..., 2M, 2. Similarly, every time a packet collision occurs, resetting is performed while cyclically shifting the back-off initial value.

  In the example of FIG. 5, STA1 ends data transmission and waits for SIFS time when the wireless channel transitions from busy to idle, and does not receive an ACK signal, so determines a collision (transmission failure). When the data for retransmission is stored, the backoff initial setting signal is received, so that the cyclically shifted backoff initial value is reset. Similarly, STA2 and STA3 receive the backoff initial setting signal and reset the cyclically shifted backoff initial value. At this time, the backoff initial values set in STA1, STA2, and STA3 are cyclically shifted from 2, 4, 6 to 4, 6, 2. Note that the backoff initial value to be reset for each packet collision is not limited to the cyclic shift as long as the transmission opportunity of each wireless terminal can be equalized by a value different from the previous backoff initial value.

  In addition, the back-off initial setting signal for resetting the back-off initial value may be transmitted by the STA1 that detects that the ACK signal is not received due to the collision by the same timing control as the AP.

  On the other hand, STA4 ends the data transmission and waits only for SIFS time when the wireless channel shifts from busy to idle, and does not receive the ACK signal, so determines a collision (transmission failure). Then, in order to expand the CW and redraw the random number, a back-off time corresponding to a statistically large back-off value (here, 9) is set.

  As described above, the STA1 to STA4 are set with the backoff times 4, 6, 2, and 9, respectively, and the transmission of the backoff signal is completed and the carrier sense is resumed after the DIFS time when the wireless channel shifts from busy to idle. . Therefore, the next data to be transmitted is STA3. Similarly, data transmission is performed in the order of STA1, STA2, STA3, STA4,.

  Therefore, in the wireless LAN system including the STA1, STA2, and STA3 that perform the wireless LAN access control of the present invention and the STA4 that performs the conventional wireless LAN access control, the control operation can be executed independently of each other. Even if a collision occurs between them, the probability of re-collision can be reduced by resetting the back-off initial value and appropriately controlling the conventional STA 4 side.

  If the backoff period is set to be equal to or less than the maximum value of the backoff initial value of each STA, STA1, STA2, and STA3 acquire the transmission right in order, and transmission is performed with priority over STA4 that performs conventional wireless LAN access control. can do. For example, if the back-off initial values of STA1, STA2, and STA3 are 1, 2, and 3, and the back-off period is 3, a transmission right is always given to one of STA1 to STA3, and STA4 cannot always transmit due to a collision. It will be. In this case, by setting the back-off period to a value sufficiently larger than the maximum value of the back-off initial value, there is a period in which no transmission right is given to any of STA1 to STA3, during which STA4 is transmitted. It becomes possible. Alternatively, when the back-off initial values set in STA1 to STA3 are set as 2, 4, 6 which are not continuous, the back-off of STA4 is set even if the back-off cycle is set to the maximum back-off initial value 6. When the off time is 1, 3, 5, 7,..., Transmission is possible while avoiding collision. Thus, by appropriately setting the back-off initial value and the back-off period, collisions can be reduced even in a wireless LAN system including a STA that performs conventional wireless LAN access control.

(Wireless LAN access control example 3)
FIG. 7 shows wireless LAN access control example 3 according to the present invention.
Here, in STA1, STA2, and STA3 in which the same back-off initialization is performed as in wireless LAN access control example 1 shown in FIG. 2, there is no data to be transmitted when the back-off time elapses when the wireless channel is idle. Will be described.

  Since the initial backoff values of STA1, STA2, and STA3 are set to 2, 4, and 6, STA1 can transmit data first, and STA2 can transmit data next. However, when there is no data to be transmitted when the transmission right is given to the STA2, the transmission right is released, the back-off time corresponding to the back-off period is set, and the carrier sense is resumed. Since STA1 and STA3 continue carrier sense at their respective back-off times, STA3 next ends the back-off time and transmits data.

  Note that STA1, STA2, and STA3 resume carrier sense by setting a backoff time corresponding to the backoff period in the same manner as after data transmission even when there is no data to be transmitted when the transmission right is given. Therefore, if data to be transmitted is generated before the next transmission right is given, data transmission is possible at that time.

  Further, since the STA that performs the conventional wireless LAN access control can also operate independently, the wireless LAN access control combining the control example 2 shown in FIG. 5 and the control example 3 shown in FIG. 7 can be similarly realized.

  In addition, the wireless terminal that performs wireless LAN access control according to the present invention may be provided with a function of performing conventional wireless LAN access control (CSMA / CA), and may be operated by appropriately switching between the two.

AP wireless base station STA wireless terminal

Claims (8)

In a wireless LAN access control method in which a plurality of wireless terminals accommodated in a wireless LAN perform packet transmission while avoiding collisions by waiting for different backoff times,
The plurality of wireless terminals are:
Different backoff initial values and a common backoff period are set,
A packet is transmitted when the radio channel is idle for a backoff time corresponding to the initial backoff value, or the remaining backoff time is calculated when the radio channel is busy during the backoff time. Carry over, then send the packet when the radio channel is idle, and the radio channel is idle for the carryover backoff time,
After transmitting the packet, set a back-off time corresponding to the back-off period to perform carrier sense for the next packet transmission,
Due to the transmission failure of the packet, a backoff initial value obtained by shifting the backoff initial value set for each wireless terminal is reset, and each wireless terminal receives a backoff time corresponding to the reset backoff initial value. A wireless LAN access control method, wherein carrier sense for the next packet transmission is performed by setting The wireless LAN access control method according to claim 1,
When there is no packet to be transmitted when the radio channel is idle over the back-off time, a back-off time corresponding to the back-off period is set and carrier sense for the next packet transmission is performed. A wireless LAN access control method. The wireless LAN access control method according to claim 1,
The back-off initial value and the back-off period are initially set by a radio base station that communicates with the plurality of radio terminals,
The backoff initial value to be reset is set by the wireless terminal that failed to transmit or the wireless base station,
The wireless LAN access control method, wherein the plurality of wireless terminals start carrier sense by setting a backoff time corresponding to the backoff initial value after the initial setting by the wireless base station or after the reconfiguration . The wireless LAN access control method according to claim 1,
The wireless LAN access control method, wherein a backoff period common to the plurality of wireless terminals is set to be equal to or greater than a maximum value of a backoff initial value of each wireless terminal. In a wireless LAN system in which a plurality of wireless terminals accommodated in a wireless LAN perform packet transmission while avoiding collision by waiting for different backoff times,
The plurality of wireless terminals transmit different packets when a different backoff initial value and a common backoff period are set, and the wireless channel is idle over a backoff time corresponding to the backoff initial value. Or when the radio channel is busy during the backoff time, carry over the remaining backoff time, then the radio channel is idle, and the radio channel is idle for the carryover backoff time Packet is transmitted, and after transmission of the packet, a back-off time corresponding to the back-off period is set to perform carrier sense for the next packet transmission, and is set in each wireless terminal when the packet transmission fails The back-off initial value obtained by shifting the back-off initial value is reset, and each wireless terminal Wireless LAN system to set the back-off time corresponding to the set back-off initial value characterized by comprising an access control means for performing carrier sensing for the next packet transmission. The wireless LAN system according to claim 5, wherein
The access control means sets a back-off time corresponding to the back-off period to transmit a next packet when there is no packet to be transmitted when the radio channel is idle over the back-off time. A wireless LAN system having a configuration for performing carrier sense. The wireless LAN system according to claim 5, wherein
A wireless base station that communicates with the plurality of wireless terminals initially sets the backoff initial value and the backoff period,
The backoff initial value to be reset is set by the wireless terminal that failed to transmit or the wireless base station,
The wireless LAN system, wherein the plurality of wireless terminals set a back-off time corresponding to the back-off initial value after initial setting or re-setting by the wireless base station, and start carrier sense. The wireless LAN system according to claim 5, wherein
A wireless LAN system, wherein a back-off period common to the plurality of wireless terminals is set to be equal to or greater than a maximum back-off initial value of each wireless terminal.

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