JP5225345B2 - Radio communication system, master station radio communication device, slave station radio communication device, and communication method - Google Patents

Description

  The present invention relates to a radio communication system, a master station radio communication device, a slave station radio communication device, and a communication method, for example, media access control between a master station and a slave station in a radio communication system.

  As conventional media access control methods, for example, Non-Patent Document 1 discloses DCF (Distributed Coordination Function, autonomous distributed access control) and PCF (Point Coordination Function, access control by centralized control).

  DCF is a media access control method based on CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance), in which a radio station having a data frame in a transmission standby state receives a data frame. The carrier sense is performed before the transmission of the data frame, and the data frame is transmitted after confirming that no other radio station is transmitting. A period based on such a media access control method is called a contention period.

FIG. 1 is a diagram showing a sequence diagram of CSMA / CA. In FIG. 1, wireless communication is performed between an AP 101 (Access Point, a master station) and a STA 102 (Station, a slave station). In FIG. 1, all the slave stations STA102a to STAc wait for a data frame in a transmission standby state until a DIFS (DCF Inter Frame Space) and a back off time elapse. During this waiting period, transmission of a data frame is started in a channel idle state (a state in which transmission from another wireless station has not been detected). Here, the back-off time is expressed by the following equation using a random value in a CW (Contention Window, random number generation range) and a slot time (fixed time).
Backoff time = random value in CW × slot time

  In the (i) transmission procedure of FIG. 1, since the number of back-off slots of the STA 102a is the smallest, the STA 102a transmits a data frame to the AP 101 after carrier sense, and the AP 101 receives the data frame and then receives a SIFS (Short Inter Frame Space, short). ACK (Acknowledgment) is transmitted to the STA 102a after the frame interval), and the STA 102a completes communication. Here, since the STA 102b and the STA 102c are in a channel busy state (a state where a signal is detected) before the back-off slot becomes 0, they wait for transmission and carry over the remaining number of back-off slots next time.

  Next, when (ii) a collision occurs in FIG. 1, the STAs 102b and 102c perform carrier sensing for the number of backoff slots carried over after DIFS, and transmit a data frame when the backoff slot becomes zero. However, in FIG. 1, since the STA 102b and the STA 102c have the same number of back-off slots, they are transmitted at the same time, and radio wave collision occurs, so transmission fails.

  The STAs 102b and 102c that have failed to transmit again determine the number of backoff slots. At this time, the CW is increased exponentially for each retransmission. In the (iii) retransmission procedure in FIG. 1, since the number of backoff slots is determined to be 5 by the STA 102b and 8 by the STA 102c, the STA 102b transmits a data frame to the AP 101, and after receiving the data frame, the AP 101 transmits an ACK to the STA 102b after SIFS. STA 102b completes communication. Thereafter, the STA 102c also performs communication in the same manner.

  On the other hand, PCF is a media access control method in which a master station transmits polls to each slave station in order according to a polling list, and only the slave station that has received the poll addressed to itself transmits a data frame. Radio wave collision can be avoided by centrally managing the transmission timing of the slave stations. Such a period based on the media access control method is called a contention free period.

  FIG. 2 is a diagram showing a sequence diagram of the PCF. In FIG. 2, wireless communication is performed between the AP 201 and the STA 202. In FIG. 2, the AP 201 first transmits a beacon frame and notifies all the STAs 202 that the contention-free period has been shifted. Then, the AP 201 transmits a poll to the STA 202a after waiting for SIFS. On the other hand, the STA 202a transmits a data frame to the AP 201. Thereafter, after waiting for SIFS, the AP 201 transmits ACK to the STA 202a and transmits polling to the STA 202b. On the other hand, the STA 202b transmits a data frame to the AP 201. Thereafter, the AP 201 waits for SIFS, and then transmits ACK to the STA 202b and transmits polling to the STA 202c. On the other hand, the STA 202c transmits a data frame to the AP 201. Then, after waiting for SIFS, the AP 201 transmits an ACK to the STA 202c and transmits an End frame (End) notifying the end of the contention free period.

  Also, in Patent Document 1, when each slave station has a data frame in a transmission standby state, the number of backoff slots derived by random numbers is notified to the master station, and the number of backoff slots received by the master station is in ascending order. A method is disclosed in which only a slave station that transmits polling and receives polling addressed to itself transmits a data frame. According to this method, by reporting the number of backoff slots only when each slave station has a data frame in a transmission standby state, unnecessary polling to a slave station without a data frame is eliminated, and the master station By centrally managing the transmission timing of the data frame of the station, radio wave collision of the data frame can be avoided.

JP 2006-108966 A

IEEE, “Medium Access Control (MAC) Quality of Service Enhancements”, IEEE Std 802.11-2007.

  However, in Non-Patent Document 1, since access control is performed autonomously and distributedly by DCF, when there are many slave stations, radio wave collision is likely to occur and delay time due to retransmission becomes longer than when there are few slave stations. There is. Further, in the PCF, since the master station sequentially transmits polling to all the slave stations in the polling list, a delay time due to waiting for transmission is transmitted by sending useless polling to a slave station having no data frame in a transmission standby state. May become larger.

  Further, in the method of Patent Document 1, since polling is transmitted to each slave station even when there are few slave stations having data in a transmission standby state, the ratio of control signals such as polling to the data frame increases, and transmission is performed. Delay time due to waiting may increase.

  The present invention has been made in view of such a situation, and provides media access control for shortening a delay time in a wireless communication system in which communication is performed between a master station and a slave station.

  In order to solve the above problems, the following processing is executed in the present invention. That is, the slave station radio communication device transmits a polling request to the master station radio communication device and transmits a data frame when polling corresponding to the polling request is received from the master station radio communication device. When the master station radio communication device receives a polling request from one slave station radio communication device, the master station radio communication device registers the slave station radio communication device as a target slave station radio communication device in the polling list, and performs a predetermined number of polls. After transmitting to the target slave station wireless communication device, or after transmitting polling to the target slave station wireless communication device until registration of the target slave station wireless communication device disappears from the polling list, the communication state is shifted to the contention period.

  ADVANTAGE OF THE INVENTION According to this invention, in a radio | wireless communications system which communicates between a master station and a slave station, it becomes possible to shorten delay time.

  Problems, configurations, and effects other than those described above will become apparent from the following embodiments for carrying out the present invention and the accompanying drawings.

It is a figure which shows the sequence of general CSMA / CA. It is a figure which shows the sequence of a general PCF. It is a figure which shows schematic structure of the radio | wireless communications system which concerns on embodiment of this invention. It is a block diagram which shows the internal structure of the radio | wireless communication apparatus which concerns on the 1st Embodiment of this invention. It is a flowchart for demonstrating the processing content of the media access control which concerns on the 1st Embodiment of this invention. It is a sequence diagram which shows the process example when a polling request does not collide in the media access control which concerns on the 1st Embodiment of this invention. It is a sequence diagram which shows the process example when the polling request | requirement of the media access control which concerns on the 1st Embodiment of this invention collides. It is a figure which shows the internal structure of a radio | wireless communication apparatus provided with the polling frequency control part based on the 2nd Embodiment of this invention. It is a figure which shows the internal structure of a radio | wireless communication apparatus provided with the access control switching control part based on the 3rd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be noted that this embodiment is merely an example for realizing the present invention, and does not limit the technical scope of the present invention. In each drawing, the same reference numerals are assigned to common components.

(1) First Embodiment <Configuration of Radio Communication System>
With reference to FIG. 3, the structure of the radio | wireless communications system which concerns on one Embodiment of this invention is demonstrated. FIG. 3 is a diagram illustrating a schematic configuration of a wireless communication system according to an embodiment of the present invention. The wireless communication system includes at least one AP 301 (Access Point, master station), one or more STAs 302 (Station, slave stations), and a backbone network 303 such as a WAN. The AP 301 is connected to a control device or the like (not shown) via the backbone network 303.

  In the wireless communication system of FIG. 3, wireless communication is performed between an AP 301 (Access Point, master station) and an STA 302 (Station, slave station). One master station or two or more slave stations may communicate with one master station. FIG. 3 shows a case where communication is performed between one master station and three slave stations. The AP 301 is connected to the backbone network 303 via an external interface, and the STA 302 is connected to a device 304 that requires data transmission via the external interface. The STA 302 to which data has been transferred from the device 304 that requires data transmission wirelessly transmits the data to the AP 301, and the AP 301 that has received the data transfers the data to the backbone network 303 or the STA 302 according to the destination. The AP 301 to which data has been transferred from the backbone network 303 wirelessly transmits the data to the STA 302 according to the destination, and the STA 302 that has received the data transfers the data to the device 304. Here, a relay station may be used to expand the communication range, and this relay station may have both functions of a master station and a slave station. Further, in FIG. 3, a master station is connected instead of the device 304 connected to the STA 302, and the STA 302 and the master station are combined by wirelessly connecting one or two or more slave stations to the master station. It may function as a relay station. Further, in FIG. 3, a slave station may be connected instead of the backbone 304 connected to the AP 301, and the slave station may be wirelessly connected to the master station so that the AP 301 and the slave station are combined to function as a relay station. .

<Internal configuration of wireless communication device>
Hereinafter, an internal configuration of a wireless communication apparatus according to an embodiment of the present invention will be described. FIG. 4 is a block diagram showing a schematic internal configuration of wireless communication apparatuses (AP and STA) according to an embodiment of the present invention.

  The AP 301 in FIG. 4 includes an external interface 403, a communication control unit 404a, a wireless transmission / reception processing unit 405, and an antenna 406. 4 includes an external interface 403, a communication control unit 404b, a wireless transmission / reception processing unit 405, and an antenna 406. The STA 302 in FIG. 4 (corresponding to any of the STAs 302a to 302c in FIG. Note that the processing in the wireless transmission / reception processing unit 405 and the antenna 406 is performed in the physical layer, and the processing in the communication control units 404a and 404b is performed in the MAC layer.

  The external interface 403 transfers data to the communication control unit 404 when receiving data from the outside, and transfers data to the outside when receiving data from the communication control unit 404.

  The communication control unit 404 generates a frame to be wirelessly transmitted in response to data reception from the external interface 403, data reception from the wireless transmission / reception processing unit 405, or frame reception such as polling, and the wireless transmission / reception processing unit 405 at a predetermined transmission timing. Forward the frame to In addition, when the communication control unit 404 receives a data frame from the wireless transmission / reception processing unit 405, the communication control unit 404 transfers the data to the external interface 403. When the frame is transferred from the communication control unit 404 to the wireless transmission / reception processing unit 405, the wireless transmission / reception processing unit 405 converts the frame into a wireless signal and wirelessly transmits the signal via the antenna 406. When the antenna 406 receives a wireless signal, the wireless signal is converted into a frame by the wireless transmission / reception processing unit 405 and transferred to the communication control unit 404.

  The communication control unit 404a of the AP 301 includes a destination management unit 407, a polling list storage unit 408, a data frame transmission / reception processing unit 409, an ACK transmission / reception processing unit 410, a polling request reception processing unit 411, and an end frame transmission processing unit 412. A polling transmission processing unit 413, a transmission timing control unit 414, and a reception frame analysis unit 415.

  Further, the communication control unit 404b of the STA 302 includes a destination management unit 407, a data frame transmission / reception processing unit 409, an ACK transmission / reception processing unit 410, a polling reception processing unit 416, an end frame reception processing unit 417, and a polling request transmission process. Unit 418, transmission timing control unit 414, and reception frame analysis unit 415.

  In the communication control unit 404a, when data is transferred from the external interface 403, the destination management unit 407 confirms where to send the transferred data by referring to the destination information included in the transfer data. Then, the data frame transmission / reception processing unit 409 generates a data frame. Further, the transmission timing control unit 414 transfers the data frame to the wireless transmission / reception processing unit 405 at a predetermined transmission timing. Since the data frame is retransmitted when transmission fails, the data frame is held in the data frame transmission / reception processing unit 409 until ACK (Acknowledge) is received or retransmitted a predetermined number of times. If an ACK is not received from the slave station after a certain time has elapsed after transmitting the data frame, the data frame is retransmitted.

  In the communication control unit 404a, when an ACK frame is received from the slave station, the data frame transmission / reception processing unit 409 corresponding to the ACK frame deletes the held data frame.

  In the communication control unit 404a, when a frame is transferred from the wireless transmission / reception processing unit 405, the received frame analysis unit 415 checks the presence / absence of an error in the frame and the address. When it is determined that the frame should be received by the local station without error, the received frame analysis unit 415 transfers the frame to the reception processing unit. Here, when an error is detected in the frame, or when it is determined that the frame should not be received by the own station, the received frame is discarded.

  On the other hand, when the communication control unit 404a receives a data frame, the data frame transmission / reception processing unit 409 converts the data frame into a data format to be transferred to the outside and transfers the data frame to the external interface 403. An ACK frame notifying that a data frame has been received is generated. Then, the transmission timing control unit 414 transfers the ACK frame to the wireless transmission / reception processing unit 405 at a predetermined transmission timing. When there is a data frame in a transmission standby state, the transmission timing control unit 414 may add the ACK to the data frame and transfer it.

  When the communication control unit 404 a receives a polling request, the polling request reception processing unit 411 registers the slave station that has transmitted the polling request at the end of the polling list held in the polling list storage unit 408. At this time, the polling request reception processing unit 411 checks whether the slave station that has transmitted the polling request is registered in the polling list held in the polling list storage unit 408. Do not do. This prevents double registration for one piece of data and avoids unnecessary polling.

  When the communication control unit 404a determines that there is a slave station registration in the polling list storage unit 408, the communication control unit 404a generates a polling frame for the slave station registered at the head, and the transmission timing control unit 414 performs a predetermined transmission timing. Then, the polling frame is transferred to the wireless transmission / reception processing unit 405. At this time, the top registration in the polling list storage unit 408 is deleted. Further, when there is a data frame in a transmission standby state or an ACK frame, polling is added to the frame.

  Further, when the communication control unit 404a transmits a predetermined number of polls, or when polling is transmitted to a slave station registered in the polling list until there is no registration in the polling list, the End frame transmission processing unit 412 generates an End frame. Then, the transmission timing control unit 414 transfers the End frame to the wireless transmission / reception processing unit 405 at a predetermined transmission timing. Further, when an ACK frame in a transmission standby state is included, End is added to the ACK frame.

  In the communication control unit 404b of the slave station STA 302, when data is transferred from the external interface 403, the destination management unit 407 confirms where the transferred data is transmitted. The data frame transmission / reception processing unit 409 generates a data frame, the polling request transmission processing unit 418 generates a polling request frame, and the transmission timing control unit 414 transmits the polling request frame to the wireless transmission / reception processing unit 405 at a predetermined transmission timing. Forward to. The polling request frame is held in the polling request transmission processing unit 418 until polling is received or until a predetermined number of times are retransmitted so that it can be retransmitted when transmission fails. If the polling cannot be received after a predetermined time has elapsed after transmitting the polling request frame, the transmission timing control unit 414 retransmits the polling request frame.

  In addition, in the communication control unit 404b, when the frame is transferred from the wireless transmission / reception processing unit 405, the reception frame analysis unit 415 confirms the presence / absence of the frame error and the address, and the frame to be received by the local station without any error in the frame. When it is determined that the frame is received, it is transferred to the reception processing unit for each frame. Here, when an error is detected in the frame, or when it is determined that the frame should not be received by the own station, the received frame analysis unit 415 discards the received frame.

  When the communication control unit 404b receives a polling frame addressed to itself, the polling reception processing unit 416 instructs the transmission timing control unit 414 to perform control for the contention-free period, and the data frame transmission / reception processing unit 409. Check if has a generated data frame. When the data frame transmission / reception processing unit 409 has a generated data frame, the transmission timing control unit 414 transfers the data frame to the wireless transmission / reception processing unit 405 at a predetermined transmission timing. Further, the polling request frame held by the polling request transmission processing unit 418 corresponding to the polling frame is deleted. Further, when a polling request frame in a transmission standby state is included, data is added to the polling request frame. Since the data frame is retransmitted when transmission fails, the data frame transmission / reception processing unit 409 holds the ACK until the data frame is received or retransmitted a predetermined number of times. The transmission timing control unit 414 retransmits the data frame when ACK is not received even after a certain time has elapsed after transmitting the data frame. At the time of retransmission, the transmission timing control unit 414 again generates and transmits a polling request, receives the polling, and then retransmits it. When the communication control unit 404b receives an ACK frame, the communication control unit 404b deletes the data frame held by the data frame transmission / reception processing unit 409 corresponding to the ACK frame.

  When the communication control unit 404b receives a polling frame addressed to another station, the polling reception processing unit 416 instructs the transmission timing control unit 414 to perform control for the contention-free period, and discards the polling frame. .

  When the communication control unit 404b receives the data frame, the data frame transmission / reception processing unit 409 converts the data frame into a data format to be transferred to the outside and transfers the data frame to the external interface 403. At the same time, the ACK transmission / reception processing unit 410 generates an ACK frame notifying that the data frame has been received. Then, the transmission timing control unit 414 transfers the ACK frame to the wireless transmission / reception processing unit 405 at a predetermined transmission timing. Further, when there is a polling request frame or data frame in a transmission standby state, ACK is added to the frame.

  When the communication control unit 404b receives the End frame, the End frame reception processing unit 417 instructs the transmission timing control unit 414 to end the contention-free period and switch to control for the contention period.

<Outline of media access control processing>
Next, an outline of the media access control process according to the first embodiment of the present invention will be described. FIG. 5 is a flowchart for explaining the outline of the media access control process.

  First, the slave station STA 302 transmits a polling request to the master station AP 301 (S501).

  When polling requests from a plurality of slave stations collide (in the case of Yes in S502), retransmission processing of the polling request is performed. Each slave station STA 302 determines that the polling request has collided because it cannot receive polling even after a certain period of time has elapsed, resets the CW (Contention Window), and performs DIFS (DCF Inter Frame) according to CSMA / CA. Detects transmission from other radio stations by performing carrier sense (detecting radio waves of a certain level or more from other slave stations) between the Space and the frame interval for distributed control) and the back off time. If not, the polling request is transmitted again to the master station AP 301 (S503).

  When it is determined that polling requests from a plurality of slave stations STA have not collided (No in S502), the polling transmission processing unit 413 of the master station AP301 transmits polling to the target slave station STA ( S504).

  When the polling reception processing unit 416 of the target child station STA receives polling from the parent station AP 301, the data frame transmission / reception processing unit 409 of the child station STA generates a data frame including data to be transmitted, and the transmission timing control unit 414. The wireless transmission / reception processing unit 405 transmits the data frame to the master station AP 301 (S505). If there is more data to be transmitted, a polling request is also transmitted.

  In the data frame transmission / reception processing unit 409 of the master station AP 301 that has received the data frame, the target slave station STA is registered in the polling list held in the polling list storage unit 408, and the number of polling transmissions is less than the specified number. It is determined whether or not (S506).

  When the target slave station STA is registered in the polling list and the number of polling transmissions is equal to or less than the predetermined number (Yes in S506), the polling transmission processing unit 413 of the master station AP sets the target slave station STA to the target slave station STA. Polling is transmitted to the server (S507). When a data frame is received from the target slave station STA, the ACK transmission / reception processing unit 410 transmits ACK to the slave station.

Subsequently, as in S505, when the polling reception processing unit 416 of the target child station STA receives polling from the parent station AP 301, the data frame transmission / reception processing unit 409 of the child station STA generates a data frame including data to be transmitted. Then, the transmission timing control unit 414 and the wireless transmission / reception processing unit 405 transmit the data frame to the master station AP 301 (S505). If there is more data to be transmitted, a polling request is also transmitted.
Then, the process returns to S506.

  On the other hand, if the target slave station STA is not registered in the polling list or if the number of polling transmissions is greater than the specified number (No in S506), the end frame transmission processing unit 412 of the parent station AP301 End is transmitted to the slave station STA (S509). When a data frame is received from the target child station STA, the ACK transmission / reception processing unit 410 also transmits ACK to the child station. Then, the process proceeds to S501.

<Example sequence of media access control>
Hereinafter, a sequence example of the media access control will be described separately when the polling request does not collide (FIG. 6) and when it collides (FIG. 7).

(I) When there is no polling request collision FIG. 6 is a sequence diagram of media access control (when there is no polling request collision) according to the first embodiment of the present invention.

(Sequence 601)
When the STA 302a has a data frame in a transmission standby state, the STA 302a transmits a polling request (Poll-req.) To the AP 301 in order to obtain a transmission right. At this time, according to CSMA / CA, carrier sense (detecting radio waves of a certain level or more from other slave stations between DIFS (DCF Inter Frame Space) and back off time). When a transmission from another wireless station is not detected, a polling request is transmitted.

  Upon receiving the polling request, the AP 301 adds the polling request transmitting station STA 302a to the polling list, and recognizes that it has shifted to the contention-free period. For example, when the STA 302b receives a polling request from the STA 302a to the AP 301, the STA 302b recognizes that the contention-free period has been entered. All STAs 302 during the contention-free period do not transmit frames until they receive a polling frame, data frame, or end frame addressed to their own station. If a frame cannot be received even after a certain period of time has elapsed in the contention-free period, it may be recognized that the contention period has started.

(Sequence 602)
The AP 301 transmits polling to the STA 302a registered at the head of the polling list after SIFS (Short Inter Frame Space) after receiving the polling request, and deletes the top registration of the polling list. All STAs 302 recognize that the contention-free period has been entered when receiving polling from the AP 301.

(Sequence 603)
The STA 302 a that has received the polling addressed to itself transmits a data frame to the AP 301. At this time, if there is a data frame waiting for transmission, a polling request is added to the data frame and transmitted. The AP 301 that has received the data frame generates an ACK frame to the transmitting slave station STA 302a of the data frame. Upon receiving the polling request, the AP 301 adds the polling request transmitting station STA 302a to the polling list.

(Sequence 604)
The AP 301 transmits an ACK frame to the data frame transmitting station STA 302a after SIFS from the reception of the data frame. At this time, polling to the STA 302a registered at the top of the polling list is added to the ACK frame, and the top registration of the polling list is deleted. When receiving the ACK addressed to the local station, the STA 302a deletes the data frame corresponding to the ACK.

(Sequence 605)
The STA 302 a that has received the polling transmits a data frame to the AP 301. At this time, if there is a data frame in a transmission standby state, a polling request may be added to the data frame and transmitted. The AP 301 that has received the data frame generates an ACK frame to the data station transmitting station STA 302a. Upon receiving the polling request, the AP 301 adds the polling request transmitting station STA 302a to the polling list.

(Sequence 606)
The AP 301 transmits an ACK frame to the data frame transmitting station STA 302a after SIFS from the reception of the data frame. At this time, if the specified number of polls have been transmitted, or if there is no registration in the polling list, End is added to the ACK frame and transmitted. The specified number of polling transmissions can be set to an integer value of 1 or more. FIG. 6 shows a case where the prescribed number of polling transmissions is two.

  After transmitting the End frame, the AP 301 shifts to a contention-free period as a polling request reception period. The AP 301 sets the polling request reception period as a period until the polling request is received from the STA 302, the maximum time required for the STA 302 to transmit the polling request, or a period until one of them is satisfied. Either of these may be used. When all the STAs 302 receive an End from the AP 301, they recognize that the contention period has been started. The STA 302a that has received the ACK addressed to itself deletes the data frame corresponding to the ACK.

(Sequence 607)
If the STA 302b has a data frame waiting for transmission, the STA 302b transmits a polling request to the AP 301 during the contention period in order to obtain a transmission right. At this time, according to CSMA / CA, carrier sense is performed between the DIFS and the backoff time, and a polling request is transmitted when transmission from another wireless station is not detected. Upon receiving the polling request, the AP 301 adds the polling request transmitting station STA 302b to the polling list and recognizes that it has shifted to the contention-free period. When the STA 302a receives a polling request from the STA 302b to the AP 301, the STA 302a recognizes that it has shifted to the contention-free period.

(Sequence 608)
The AP 301 transmits polling to the STA 302a registered at the top of the polling list after SIFS from reception of the polling request, and deletes the top registration of the polling list. All STAs 302 recognize that the contention-free period has been entered when receiving polling from the AP 301.

(Sequence 609)
The STA 302 a that has received the polling addressed to itself transmits a data frame to the AP 301. At this time, if there is a data frame in a transmission standby state, a polling request may be added to the data frame and transmitted. The AP 301 that has received the data frame generates an ACK frame to the transmitting slave station STA 302a of the data frame. Upon receiving the polling request, the AP 301 adds the polling request transmitting slave station STA 302a to the polling list.

(Sequence 610)
The AP 301 transmits an ACK frame to the data frame transmitting station STA 302a after SIFS from the reception of the data frame. At this time, polling to the STA 302b registered at the top of the polling list is added to the ACK frame, and the top registration of the polling list is deleted. The STA 302a that has received the ACK addressed to itself deletes the data frame corresponding to the ACK.

(Sequence 611)
The STA 302b that has received the polling transmits a data frame to the AP 301. At this time, if there is a data frame in a transmission standby state, a polling request may be added to the data frame and transmitted. The AP 301 that has received the data frame generates an ACK frame to the data station transmitting station STA 302b. Upon receiving the polling request, the AP 301 adds the polling request transmitting station STA 302b to the polling list.

(Sequence 612)
The AP 301 transmits an ACK frame to the data frame transmitting station STA 302b after SIFS from the reception of the data frame. At this time, if the specified number of polls have been transmitted, or if there is no registration in the polling list, End is added to the ACK frame and transmitted. After transmitting the End frame, the AP 301 shifts to a contention-free period as a polling request reception period. When all the STAs 302 receive an End from the AP 301, they recognize that the contention period has been started. The STA 302a that has received the ACK addressed to itself deletes the data frame corresponding to the ACK.

  As described above, when a slave station has a data frame in a transmission standby state, it transmits a polling request to the master station during the contention period, receives a poll from the master station, and acquires a transmission right. By transmitting the data frame, radio wave collision of the data frame can be avoided.

  On the other hand, when receiving the polling request from the slave station, the master station registers the polling request transmitting station in the polling list and transmits the specified number of polls, or keeps the top of the polling list until there is no registration in the polling list. Send polling to registered slave stations. By doing this, even when there are few slave stations having data in the transmission standby state, the transmission rate of control signals such as polling can be suppressed with respect to the data frame, and the data frame in the transmission standby state It is possible to prevent polling of a slave station that does not have a delay, and to suppress a delay time due to waiting for transmission.

  Further, the master station transmits polling until a specified number of polls have been transmitted or until there is no registration in the polling list, and then transmits an End frame, and shifts to a contention-free period as a polling request reception period. In this way, a plurality of slave stations having data frames in a transmission standby state can participate in communication.

  In addition, when transmitting a data frame or an ACK frame, the slave station adds a polling request to the data frame or the ACK frame if it has a data frame waiting for transmission. By doing in this way, the transmission rate of control signals, such as a polling request, can be suppressed, and the delay time due to waiting for transmission can be suppressed.

(Ii) When polling requests collide FIG. 7 is a sequence diagram of media access control (when polling requests collide) according to the first embodiment of the present invention.

(Sequence 701)
When the STA 302a and the STA 302b have a data frame in a transmission standby state, the STA 302a and the STA 302b transmit a polling request to the AP 301 in order to obtain a transmission right. At this time, according to CSMA / CA, carrier sense is performed between the DIFS and the backoff time, and a polling request is transmitted when transmission from another wireless station is not detected. FIG. 7 shows a case where the STA 302a and the STA 302b accidentally transmit polling requests at the same time. When the STA 302a and the STA 302b transmit polling requests at the same time, radio wave collision occurs and transmission fails.

(Sequence 702)
The STA 302a and the STA 302b that failed to transmit the polling request again sense the carrier during the DIFS and the back-off time in accordance with CSMA / CA, and transmit a polling request when transmission from another wireless station is not detected. Here, the CW (Contention Window, random number generation range) may be increased exponentially for each retransmission.

  FIG. 7 shows a case where the STA 302a has a smaller number of backoff slots than the STA 302b and transmits a polling request. Upon receiving the polling request, the AP 301 adds the polling request transmitting station STA 302a to the polling list, and recognizes that it has shifted to the contention-free period. When the STA 302b receives a polling request from the STA 302a to the AP 301, the STA 302b recognizes that it has shifted to the contention-free period. All STAs 302 during the contention-free period do not transmit frames until they receive a polling frame, data frame, or end frame addressed to their own station. If a frame cannot be received even after a certain time has elapsed in the contention-free period, it may be recognized that the contention period has started.

(Sequence 703)
The AP 301 transmits polling to the STA 302a registered at the top of the polling list after SIFS from reception of the polling request, and deletes the top registration of the polling list. All STAs 302 recognize that the contention-free period has been entered when receiving polling from the AP 301.

(Sequence 704)
The STA 302 a that has received the polling addressed to itself transmits a data frame to the AP 301. The AP 301 that has received the data frame generates an ACK frame to the data station transmitting station STA 302a. Although a sequence for transmitting a data frame only once is shown here, when there are more data frames to be transmitted, the STA 302a transmits a specified number of data frames as in the case of FIG. It can be carried out. That is, even when polling requests collide, the processing when entering the contention-free period is the same as in FIG.

(Sequence 705)
The AP 301 transmits an ACK frame to the data frame transmitting station STA 302a after SIFS from the reception of the data frame. At this time, if there is no registration in the polling list, End is added to the ACK frame and transmitted. After transmitting the End frame, the AP 301 shifts to a contention-free period as a polling request reception period. The AP 301 may set the polling request reception period as a period until receiving the polling request from the STA 302.

  When all the STAs 302 receive an End from the AP 301, they recognize that the contention period has been started. The STA 302a that has received the ACK addressed to itself deletes the data frame corresponding to the ACK.

(Sequence 706)
If the STA 302b has a data frame waiting for transmission, the STA 302b transmits a polling request to the AP 301 during the contention period in order to obtain a transmission right. At this time, according to CSMA / CA, carrier sense is performed between the DIFS and the backoff time, and a polling request is transmitted when transmission from another wireless station is not detected.

  Upon receiving the polling request, the AP 301 adds the polling request transmitting station STA 302b to the polling list and recognizes that it has shifted to the contention-free period.

  When the STA 302a receives a polling request from the STA 302b to the AP 301, the STA 302a recognizes that it has shifted to the contention-free period.

(Sequence 707)
The AP 301 transmits polling to the STA 302b registered at the top of the polling list after SIFS from reception of the polling request, and deletes the top registration of the polling list. All STAs 302 recognize that the contention-free period has been entered when receiving polling from the AP 301.

(Sequence 708)
The STA 302b that has received the polling addressed to itself transmits a data frame to the AP 301. The AP 301 that has received the data frame generates an ACK frame to the data station transmitting station STA 302b.

(Sequence 709)
The AP 301 transmits an ACK frame to the data frame transmitting station STA 302b after SIFS from the reception of the data frame. At this time, if there is no registration in the polling list, the AP 301 adds End to the ACK frame and transmits it.

  After transmitting the End frame, the AP 301 shifts to a contention-free period as a polling request reception period. The AP 301 may set the polling request reception period as a period until receiving the polling request from the STA 302.

  When all the STAs 302 receive an End from the AP 301, they recognize that the contention period has been started. The STA 302b that has received the ACK addressed to itself deletes the data frame corresponding to the ACK.

  As described above, if the slave station fails to receive the polling after transmitting the polling request, the slave station resends the polling request, so that even if the polling request is not received by the parent station due to radio wave collision or the like, The transmission right can be acquired. Further, the slave station can reduce the radio wave collision probability at the time of resending the polling request by increasing the CW (Contention Window, random number generation range) at the time of resending the polling request.

(2) Second Embodiment A configuration of a wireless communication apparatus according to a second embodiment of the present invention will be described with reference to FIG. FIG. 8 is a configuration diagram of a wireless communication apparatus having a polling frequency control unit according to the second embodiment of the present invention.

  A master station AP 801 in FIG. 8 includes a polling frequency control unit 803 in the communication control unit 802 in addition to the configuration of the master station AP 301 in FIG. The processing contents of the other components are the same as in FIG. Therefore, in the following, the processing contents of the polling number control unit 803 will be mainly described.

  The polling frequency control unit 803 controls the polling frequency according to the communication state. For example, when the number of slave stations connected to the AP 801 is small, the number of polls is increased, and when the number of slave stations connected to the AP 801 is large, the number of polls is decreased. Here, the number of slave stations connected to the AP 801 may be the number of slave stations registered in the destination management unit 407.

  Further, for example, when the registration ratio of the polling list with respect to the number of slave stations connected to the AP 801 is higher than a predetermined value, the number of polling is increased, and the registration ratio of the polling list with respect to the number of slave stations connected to the AP 801 is equal to or less than the predetermined value. In this case, the number of polling may be reduced. Here, the number of slave stations connected to the AP 801 may be the number of slave stations registered in the destination management unit 407, and the registration number of the polling list may be the number of slave stations registered in the polling list management unit.

  Further, for example, when the usage rate of the communication frequency used by the AP 801 is lower than a predetermined value, the number of polling is increased, and when the usage rate of the communication frequency used by the AP 801 is equal to or higher than the predetermined value, the polling frequency is decreased. You may do it. Here, the usage rate of the communication frequency used by the AP 801 may be derived from the time during which the AP 801 is transmitting and the time during which it is received.

  Further, for example, the polling request may be increased when the collision probability of the polling request transmitted by the STA 302 is lower than a predetermined value, and may be decreased when the collision probability of the polling request is equal to or higher than the predetermined value. . The collision probability of the polling request transmitted by the STA 302 may be controlled by using the retransmission ratio of the polling request in the STA 302 and transmitting the retransmission ratio to the AP 801.

  According to the embodiment described above, it is possible to suppress the transmission rate of control signals such as polling for data frames by controlling the number of polling according to the communication state, and further suppress the delay time due to transmission waiting. be able to.

(3) Third Embodiment With reference to FIG. 9, an internal configuration of a wireless communication apparatus according to a third embodiment of the present invention will be described. FIG. 9 is a diagram illustrating an internal configuration of a wireless communication apparatus having an access control switching control unit according to the third embodiment of the present invention.

  9 includes an access control switching control unit 903 in the communication control unit 902 in addition to the configuration of the STA 302 in FIG. With the addition of the configuration, the processing contents of the data frame transmission / reception processing unit 409 and the polling request transmission processing unit 418 are different. The processing contents of the other components are the same as in FIG. Therefore, in the following, the processing contents of the access control switching control unit 903, the data frame transmission / reception processing unit 409, and the polling request transmission processing unit 418 will be mainly described.

  The access control switching control unit 903 performs an operation of switching the media access control method according to the communication state. For example, when the number of slave stations connected to the AP 301 is larger than a predetermined number, the media access control method (improved access control method) according to FIGS. 4 to 8 is used, and the number of slave stations connected to the AP 301 is equal to or less than the predetermined number. In some cases, CSMA / CA is used. Here, in the method of grasping the number of slave stations connected to the AP 301 in the STA 901, the AP 301 notifies the number of slave stations connected to the AP 301 by a beacon or the like, and the STA 901 connects to the AP 301 by receiving the notification of the number of slave stations. The number of slave stations may be grasped, or polling or ACK transmitted by the AP 301 may be collected, and the number of transmission destinations may be grasped as the number of slave stations connected to the AP 301.

  For example, when a hidden terminal exists between two or more slave stations STA connected to one master station AP, the media access control method (improved access control method) according to FIGS. CSMA / CA is used when there is no terminal. Here, a hidden terminal is a radio station that is outside the reach of radio waves, for example, when a radio wave shielding wall is provided between slave stations, and is unable to detect each other's radio waves. Become.

  A method for recognizing the presence or absence of a hidden terminal in the STA 901 collects polling and ACK transmitted by the AP 301 and grasps the number of polling and ACK transmission destinations as the number of slave stations connected to the AP 301. And collect the number of transmission sources as the number of slave stations in the range where radio waves reach, or recognize that there is a hidden terminal if the number of slave stations in the range where radio waves reach is smaller than the number of slave stations connected to the AP 301 You may do it. For example, when the usage rate of the communication frequency used by the AP 301 is higher than a predetermined value, the media access control method (improved access control method) according to FIGS. 4 to 8 is used to use the communication frequency used by the AP 301. When the rate is equal to or less than the predetermined value, CSMA / CA is used. Here, the usage rate of the communication frequency used by the AP 301 is derived from the transmission time and the reception time of the AP 301, the AP 301 notifies the usage rate of the derived communication frequency, and the STA 901 notifies the notification. You may grasp | ascertain the utilization rate of the communication frequency which AP301 uses by receiving.

  In the third embodiment, when the media access control method according to FIGS. 4 to 7 is selected by the access control switching control unit 903, the data frame transmission / reception processing unit 409 of the STA 901 has transferred data from the external interface 403. At this time, the destination management unit 407 confirms where the transferred data is to be transmitted, and generates a data frame. At this time, the polling request transmission processing unit 418 generates a polling request frame, and the transmission timing control unit 414 transfers the polling request frame to the wireless transmission / reception processing unit 405 at a predetermined transmission timing.

  When CSMA / CA is selected by the access control switching control unit 903, when the data is transferred from the external interface 403, the destination management unit 407 confirms where to transmit the transferred data, and the data The frame transmission / reception processing unit 409 generates a data frame. Then, the transmission timing control unit 414 transfers the data frame to the wireless transmission / reception processing unit 405 at a predetermined transmission timing. Since the data frame is retransmitted when transmission fails, the data frame transmission / reception processing unit 409 holds the ACK until the data frame is received or retransmitted a predetermined number of times. If an ACK is not received after a certain time has elapsed after transmitting the data frame, the data frame is retransmitted.

  According to the third embodiment described above, by switching the media access control method, it is possible to suppress the transmission rate of control signals such as polling for data frames while suppressing the probability of occurrence of radio wave collision. The delay time due to waiting can be further suppressed.

  In addition, in a wireless communication system that communicates between a master station and a slave station, there is an effect of shortening the delay time, and it is particularly effective when applied to a wireless communication system that is required to transmit data within a predetermined time. Industrial value is great.

(4) Summary The present invention can be widely applied to a wireless communication system that is required to transmit data within a predetermined time.

  In the present invention, when receiving a polling request from one slave station, the master station registers the slave station in the polling list as a slave station to be processed, and transmits a specified number of polls to the target slave station. Alternatively, after transmitting polling to the target slave station until the registration of the target slave station disappears from the polling list, the communication state is shifted to the contention period (improved access control). By doing so, it is possible to prevent infinite communication between the slave station with which communication was first established and the master station, and to guarantee the transmission of another slave station. Can be shortened. Also, the master station does not need to perform useless polling transmission to all the slave stations, and communication resources can be used efficiently.

  The master station receives a polling request from one or more slave stations different from the target slave station during the contention period, and when there is a polling request from the target slave station, the target slave station and the target slave station Polling transmissions to slave stations different from those are executed in order. When there are polling requests from two slave stations, polling transmission is executed alternately. In this way, monopolization of the communication channel by one slave station can be prevented, and equal communication to each slave station can be guaranteed.

  When a plurality of polling requests from a plurality of slave stations collide, a polling request retransmission process is performed. On the other hand, the master station registers the slave station that has resent the polling request as a target slave station in the polling list. In this way, even when polling requests collide, it can be processed efficiently. In addition, since the slave station that has acquired the transmission right first is guaranteed preferential communication for a specified number of times, and after that, communication is processed in order with other slave stations, so the situation of monopolizing the communication channel by one slave station Thus, communication to each slave station can be executed equally and the delay time can be shortened.

  The slave station adds the next polling request to the data to be transmitted and transmits it to the master station. The master station processes data transmitted from the target slave station and executes polling transmission in response to the next polling request. By doing so, the transmission rate of control signals such as polling can be suppressed for the data frame, and the delay time due to transmission waiting can be suppressed.

  The master station adaptively controls the number of polling transmissions based on the number of slave stations and / or the registration ratio of the slave stations in the polling list or the usage rate of the communication frequency used by the master station. By doing so, it is possible to suppress the transmission rate of control signals such as polling for data frames according to the communication environment, and it is possible to suppress the delay time due to transmission waiting.

  In addition, it is determined whether or not there are hidden terminals that cannot detect the presence of each other in a plurality of slave stations, and the improved access control and the access control by CSMA / CA are switched and executed based on the presence or absence of the hidden terminal. . By doing so, communication between the master station and the slave station can be efficiently executed even in a communication environment where a hidden terminal exists.

  Furthermore, the master station may be executed while switching between improved access control and access control by CSMA / CA based on the number of slave stations and the usage rate of the communication frequency used by the master station.

  Note that the present invention is not limited to the embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  In addition, each configuration, function, processing unit, processing unit, and the like described in the embodiments may be realized in hardware by designing a part or all of them with, for example, an integrated circuit. Further, each of the above-described configurations, functions, etc. may be realized by software by the processor interpreting and executing a program that realizes each function. Information such as programs, tables, and files for realizing each function is stored in a recording or storage device such as a memory, hard disk, or SSD (Solid State Drive), or in a recording or storage medium such as an IC card, SD card, or DVD. be able to.

  Furthermore, in the above-described embodiment, control lines and information lines are those that are considered necessary for explanation, and not all control lines and information lines on the product are necessarily shown. All the components may be connected to each other.

101, 201, 301, 801: Master station 102, 202, 302, 901: Slave station 303: Backbone network 304: Device that requires data transmission 403: External interface 404, 802, 902: Communication control unit 405: Wireless Transmission / reception processing unit 406: Antenna 407: Destination management unit 408: Polling list storage unit 409: Data frame transmission / reception processing unit 410: ACK transmission / reception processing unit 411: Polling request reception processing unit 412: End frame transmission processing unit 413: Polling transmission processing unit 414: Transmission timing control unit 415: Received frame analysis unit 416: Polling reception processing unit 417: End frame reception processing unit 418: Polling request transmission processing unit 803: Polling count control unit 903: Access control switching unit

Claims (13)

A wireless communication system including at least one master station wireless communication device and a plurality of slave station wireless communication devices,
Each of the plurality of slave station radio communication devices has a slave station communication control unit and a slave station radio transmission / reception processing unit that executes processing necessary for data transmission / reception,
The slave station communication control unit transmits a polling request to the master station radio communication device via the slave station radio transmission / reception processing unit, and when polling corresponding to the polling request is received from the master station radio communication device Sending a data frame to the master station radio communication device via the slave station radio transmission / reception processing unit,
The master station radio communication device has a master station communication control unit that controls communication using a polling list, and a master station radio transmission / reception processing unit,
The master station communication control unit (i), when receiving the polling request from one slave station radio communication device, registers the slave station radio communication device in the polling list as a target slave station radio communication device, ii) After transmitting the specified number of polls to the target slave station wireless communication device or until the registration of the target slave station wireless communication device disappears from the polling list, the polling is transmitted to the target slave station wireless communication device Thereafter, improved access control is executed to shift the communication state to the contention period. The wireless communication system of claim 1.
The master station communication control unit receives a polling request from one or more slave station radio communication apparatuses different from the target slave station radio communication apparatus during the contention period, and from the target slave station radio communication apparatus When there is a polling request, a wireless communication system that sequentially executes polling transmission to the target slave station wireless communication device and the one or more slave station wireless communication devices. The wireless communication system of claim 1.
When a plurality of polling requests from the plurality of slave station wireless communication devices collide,
The slave station communication control unit of the slave station radio communication device retransmits a polling request to the master station radio communication device via the slave station radio transmission / reception processing unit,
The master station communication controller is
A radio communication system, wherein a slave station radio communication device that has retransmitted the polling request is registered in the polling list as a target slave station radio communication device. The wireless communication system of claim 1.
The slave station communication control unit adds a new polling request to data to be transmitted, and transmits the data to the master station radio communication device via the slave station radio transmission / reception processing unit,
The wireless communication system, wherein the master station communication control unit processes data transmitted from the target slave station wireless communication device and executes polling transmission in response to the new polling request. The wireless communication system of claim 1.
The radio communication system, wherein the master station communication control unit adaptively controls the number of polling transmissions based on the number of the slave station radio communication devices communicating with the master station radio communication device. The wireless communication system of claim 1.
The master station communication control unit adapts the number of times of polling transmission based on the number of slave station radio communication devices communicating with the master station radio communication device and the registration ratio of the slave station radio communication devices in the polling list. Wireless communication system characterized by controlling the operation of the wireless communication system. The wireless communication system of claim 1.
The radio communication system, wherein the master station communication control unit adaptively controls the number of times of poll transmission based on a use rate of a communication frequency used by the master station radio communication apparatus. The wireless communication system of claim 1.
The master station communication controller is
In the plurality of slave station wireless communication devices, determine whether there is a hidden terminal that can not detect the presence of each other,
If the hidden terminal exists, perform the improved access control;
When there is no hidden terminal, access control by CSMA / CA is executed. The wireless communication system of claim 1.
The master station communication control unit performs switching between the improved access control and the access control by CSMA / CA based on the number of slave station radio communication devices communicating with the master station radio communication device. Wireless communication system. The wireless communication system of claim 1.
The base station communication control unit performs wireless communication while switching between the improved access control and the access control by CSMA / CA based on a usage rate of a communication frequency used by the base station radio communication device. system. A master station radio communication device that communicates with a plurality of slave station radio communication devices,
A master station communication control unit for controlling communication using a polling list;
A master station wireless transmission / reception processing unit that performs processing necessary for data transmission / reception,
The master station communication controller is
When a polling request is received from one slave station wireless communication device, the slave station wireless communication device is registered in the polling list as a target slave station wireless communication device,
After transmitting a specified number of polls to the target slave station wireless communication device, or after transmitting the polling to the target slave station wireless communication device until registration of the target slave station wireless communication device disappears from the polling list, A master station radio communication apparatus, wherein a communication state is shifted to a contention period. A slave station radio communication device that communicates with at least one master station radio communication device,
Slave station communication control unit,
A slave station wireless transmission / reception processing unit that performs processing necessary for data transmission / reception,
The slave station communication control unit transmits a polling request to the master station radio communication device via the slave station radio transmission / reception processing unit, and performs polling corresponding to the polling request via the slave station radio transmission / reception processing unit. A data frame when received from the master station wireless communication device,
When transmitting the data frame via the slave station wireless transmission / reception processing unit, the slave station communication control unit adds a polling request for transmission of the next data frame to the data frame, thereby transmitting the master station wireless communication A slave station radio communication apparatus, characterized by transmitting to a device. A communication method in a wireless communication system including at least one master station wireless communication device and a plurality of slave station wireless communication devices,
Each of the plurality of slave station radio communication devices has a slave station communication control unit and a slave station radio transmission / reception processing unit that executes processing necessary for data transmission / reception,
The master station radio communication device has a master station communication control unit that controls communication using a polling list, and a master station radio transmission / reception processing unit,
When the slave station communication control unit transmits a polling request to the master station radio communication device via the slave station radio transmission / reception processing unit and receives polling corresponding to the polling request from the master station radio communication device Sending a data frame to the master station radio communication device via the slave station radio transmission / reception processing unit,
The master station communication control unit
When the polling request is received from one slave station wireless communication device, the slave station wireless communication device is registered in the polling list as a target slave station wireless communication device,
After transmitting a specified number of polls to the target slave station wireless communication device, or after transmitting the polling to the target slave station wireless communication device until registration of the target slave station wireless communication device disappears from the polling list, A communication method, wherein a communication state is shifted to a contention period.

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