JP4728036B2 - Wireless communication system - Google Patents

Description

  The present invention relates to an access control technique between an access point and a wireless terminal.

  There is a DCF (Distributed Coordination Function) as a wireless LAN access control control technique (Non-patent Document 1). Hereinafter, typical DCF will be briefly described.

1. DCF (access procedure when RTS (Request to Send) / CTS (Clear to Send) is not used)
The DCF employs CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) technology in which each of an access point and a wireless terminal confirms a non-use state of a wireless channel and transmits data. When DCF is employed without RTS / CTS, there is a so-called hidden terminal problem.

  FIG. 19 is a diagram for explaining an access control method in DCF when RTS / CTS is not used. Here, it is assumed that the access point AP can detect (carrier sense) the signals of the wireless terminal A and the wireless terminal B, but the wireless terminal A and the wireless terminal B cannot detect each other's signal.

1-1. Access point AP
First, it is assumed that the access point AP transmits data “DataP1” addressed to the wireless terminal A (T901). The access point AP receives an ACK signal from the wireless terminal A, and then waits for a period in which a random number P generated by itself is added during a DIFS (Distributed Inter-Frame Space) period, during which other devices It is confirmed whether or not a signal has been transmitted (T902). Since the access point AP detects the signal of the wireless terminal A during this DIFS + random number P period, it does not transmit data. Next, after the end of the received signal, the access point AP waits for the DIFS + random number P period to elapse, and confirms whether another device has transmitted a signal during that time (T903). Since the access point AP starts receiving data “DataA1” from the wireless terminal A during the DIFS + random number P period, the access point AP does not transmit data.

1-2. Wireless terminal A
When the reception of the data “DataP1” transmitted from the access point AP is completed, the wireless terminal A transmits an ACK signal to the access point AP after waiting for a SIFS (Short Inter-Frame Space) period to elapse (T911). ). Next, after transmitting the ACK signal, the wireless terminal A waits for a period in which the random number A generated by itself (provided that the random number A <random number P) is added to the DIFS period, during which other devices It is confirmed whether or not a signal has been transmitted (T912). Since the wireless terminal A has not detected a signal from another device during this DIFS + random number A period, it transmits data “DataA1” addressed to the access point AP (T913). Next, after transmitting “DataA1”, the wireless terminal A waits for the DIFS + random number A period to elapse, and confirms whether another device has transmitted a signal during that time (T914). Since the wireless terminal A cannot detect the signal of the wireless terminal B, the wireless terminal A does not detect signals of other devices during this DIFS + random number A period. Therefore, data “Data A2” addressed to the access point AP is transmitted (T915).

1-3. Wireless terminal B
When the transmission of the data “DataP1” of the access point AP is completed, the wireless terminal B waits for the SIFS period to elapse and waits for an ACK signal to be transmitted from another device (T921). An ACK signal is transmitted from the wireless terminal A, but the wireless terminal B cannot recognize it. The wireless terminal B assumes that an ACK signal has been transmitted from another device, and after the ACK signal end estimated time has elapsed (after the SIFS period + ACK signal period has elapsed since the end of “DataP1”), Is waited for the elapse of a period in which the random number B generated by the user (provided that the random number B <the random number P) is added, and confirms whether another device has transmitted a signal during that period (T922). Data “Data A1” is transmitted from the wireless terminal A, but the wireless terminal B cannot recognize it. Therefore, the wireless terminal B transmits data “DataB1” addressed to the access point AP (T923). Next, after transmitting “DataB1”, the wireless terminal B waits for the DIFS + random number B period to elapse, and confirms whether another device has transmitted a signal during that period (T924). Data “Data A2” is transmitted from the wireless terminal A, but the wireless terminal B cannot recognize it. Therefore, the wireless terminal B transmits data “DataB2” addressed to the access point AP (T925).

  As a result, since the wireless terminals A and B transmit data simultaneously using the same wireless carrier, interference occurs at the access point AP. For this reason, there is a possibility that the access point AP cannot receive data normally.

2. DCF (access procedure when using RTS / CTS)
Next, a DCF access procedure using RTS / CTS will be described. In RTS / CTS, a wireless terminal that is going to transmit data transmits an RTS signal to an access point. The access point transmits a CTS signal only to a wireless terminal that permits data transmission among wireless terminals that have transmitted the RTS signal. Only the wireless terminal that has received the CTS signal transmits data to the access point.

  FIG. 20 is a diagram for explaining an access control method using DCF when RTS / CTS is used. Here, it is assumed that the access point AP can detect the signals of the wireless terminals A and B, but the wireless terminals A and B cannot detect each other's signals.

2-1. Access point AP
First, it is assumed that the access point AP transmits data “DataP1” addressed to the wireless terminal A (T931). The access point AP receives the ACK signal from the wireless terminal A, and then waits for another device to transmit the RTS signal during the period in which the random number P generated by itself is added to the DIFS period (T932). The access point AP receives the RTS signal from each of the wireless terminals A and B during the DIFS + random number P period. In this case, after the reception of the previous RTS signal, after the SIFS period has elapsed, the CTS signal is transmitted to the wireless terminal A that has transmitted the previous RTS signal (T933). Thereafter, the access point AP receives the data “DataA1” from the wireless terminal A, and after the reception ends, waits for the SIFS period to elapse and transmits an ACK signal to the wireless terminal A (ST934).

2-2. Wireless terminal A
When the reception of the data “DataP1” transmitted from the access point AP is completed, the wireless terminal A transmits an ACK signal to the access point AP after the SIFS period elapses (T941). Next, after transmitting the ACK signal, the wireless terminal A waits for a period in which a random number A generated by itself (provided that the random number A <random number P) is added to the DIFS period, during which other devices It is confirmed whether or not a signal has been transmitted (T942). The wireless terminal A transmits an RTS signal to the access point AP because it has not detected a signal from another device during this DIFS + random number A period (T943). Then, the wireless terminal A waits for the SIFS period to elapse. If the CTS signal addressed to itself is received by that time, the access point AP is received after the SIFS period elapses after the reception of the CTS signal. Data “Data A1” is transmitted to the access point AP (T944), and an ACK signal is received from the access point AP.

2-3. Wireless terminal B
When the transmission of the data “DataP1” of the access point AP is completed, the wireless terminal B waits for the SIFS period to elapse and waits for an ACK signal to be transmitted from another device (T951). An ACK signal is transmitted from the wireless terminal A, but the wireless terminal B cannot recognize it. The wireless terminal B assumes that an ACK signal has been transmitted from another device, and after the ACK signal end estimated time has elapsed (after the SIFS period + ACK signal period has elapsed since the end of “DataP1”), Waits for the period of addition of the random number B generated by (where random number B <random number P) to be added, and confirms whether another device has transmitted a signal during that time (T952). An RTS signal is transmitted from the wireless terminal A, but the wireless terminal B cannot recognize it. The wireless terminal B transmits an RTS signal to the access point AP (T953). Then, the wireless terminal B waits for the SIFS period to elapse, and waits for the duration time to elapse since a CTS signal addressed to a wireless terminal other than its own wireless terminal has been transmitted from the access point AP. T954). After that, it waits for the DIFS period + random number B period to elapse, and confirms whether another device has transmitted a signal during that period (T955). The wireless terminal B transmits an RTS signal to the access point AP because it has not detected a signal from another device during this DIFS + random number B period (T956).

  As described above, in RTS / CTS, only the wireless terminal that has received the CTS signal transmits data to the access point AP, so that no interference occurs in the access point AP.

"Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications", ANSI / IEEE Std 802.11, 1999 Edition

  As described above, RTS / CTS has an advantage that interference at the access point can be prevented. However, in RTS / CTS, an RTS signal and a CTS signal are exchanged between a wireless terminal and an access point prior to data transmission, so that the overhead is large.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a wireless communication access control technique with low overhead.

  In the second aspect of the present invention, the access point transmits a multicast CTS (Clear to Send) that defines the data transmission timing of each of the plurality of wireless terminals, and each of the plurality of wireless terminals receives the multicast CTS. In this case, the communication frame addressed to the access point is transmitted according to the transmission timing of the own wireless terminal defined by the multicast CTS.

For example, an aspect of the present invention is a wireless communication system having a plurality of wireless terminals and an access point,
The access point is
First transmission means for transmitting data to the plurality of wireless terminals;
First receiving means for receiving data from the plurality of wireless terminals,
The wireless terminal is
Second transmitting means for transmitting data to the access point;
Second receiving means for receiving data from the access point;
The first receiving means includes
For each predetermined time, a multicast CTS (Clear to Send) that defines the data transmission timing of each of the plurality of wireless terminals is transmitted to the first transmission means, and a communication frame is received from each of the plurality of wireless terminals,
The second transmission means includes
When the second receiving means receives the multicast CTS, it transmits a communication frame addressed to the access point according to the transmission timing of the own wireless terminal defined by the multicast CTS,
The duration period included in the multicast CTS is:
This is a period obtained by multiplying the number of wireless terminals that can be simultaneously connected to the access point by a predetermined period as a period for transmitting data by each wireless terminal.

  According to the present invention, the access point can transmit data addressed to each of a plurality of wireless terminals in one multicast communication frame. Therefore, compared with the case where data addressed to each of a plurality of wireless terminals is transmitted in separate communication frames, the overhead due to the preamble of the frame can be reduced. According to the present invention, the access point can receive a communication frame from each of a plurality of wireless terminals using one multicast CTS. Therefore, the overhead can be reduced as compared with the case where the RTS signal and the CTS signal are exchanged with each of the plurality of wireless terminals prior to the reception of the communication frame.

  Embodiments of the present invention will be described below.

<< first embodiment >>
FIG. 1 is a schematic diagram of a wireless LAN system to which the first embodiment of the present invention is applied.

  As shown in the figure, the wireless LAN system of this embodiment includes an access point (AP) 1, a wireless terminal 2 that performs wireless communication with AP 1, and a router 3 that connects AP 1 to a network 4 such as the Internet. Have.

  The AP 1 transmits a multicast communication frame in which data addressed to each wireless terminal 2 existing in the jurisdiction area of the own AP is multiplexed. Also, a CTS signal destined for the wireless terminal 2 that is permitted to transmit data is transmitted, and a unicast communication frame storing the data of the wireless terminal 2 is received from the wireless terminal 2 that is the destination of the CTS signal. Further, the AP 1 receives the registration request signal transmitted from the wireless terminal 2, manages the transmission source of the signal as the wireless terminal 2 existing in the jurisdiction area of the own AP, and cancels the registration transmitted from the wireless terminal 2. The request signal is received, and the transmission source of the signal is removed from the management target.

  On the other hand, the wireless terminal 2 receives the multicast communication frame transmitted by the AP 1 and extracts data addressed to the wireless terminal 2 from the frame. Further, when a CTS signal addressed to the own wireless terminal 2 is received from AP1, a unicast communication frame storing data is transmitted to AP1. Further, the wireless terminal 2 transmits a registration request signal to the connection destination AP1. Also, a registration cancellation request is transmitted to the AP 1 that cancels the connection.

  FIG. 2A is a diagram schematically illustrating a unicast communication frame transmitted from the wireless terminal 2 to the AP 1. As illustrated, the communication frame transmitted from the wireless terminal 2 to the AP 1 includes a preamble 501, a header 502, a payload 503, and a parity 504. The preamble 501 is a training signal for demodulating the radio modulation signal on the receiving side. The header 502 includes a control signal indicating the type and function of the frame, a duration period indicating a time during which wireless signals are prohibited from being transmitted to other devices, and a source address. Parity 504 is a signal for detecting a transmission error in header 502 and payload 503. The payload 503 has a unicast address 5031 of the communication partner of the wireless terminal 2 that has transmitted the communication frame, a data length 5032 of transmission data to be transmitted to the communication partner, and transmission data 5033.

FIG. 2B is a diagram schematically showing a multicast communication frame transmitted from the AP 1 to the wireless terminal 2. Here, the same reference numerals are assigned to the same unicast communication frames as shown in FIG. The multicast communication frame transmitted from the AP 1 to the wireless terminal 2 is different in the configuration of the payload 513 from the payload 503 of the unicast communication frame transmitted from the wireless terminal 2 to the AP 1. As shown in the figure, the payload 513 includes a multicast address 5131 indicating that all wireless terminals 2 connected to the AP 1 are destined, and data units 5132 _{1 to} 5132 _n provided for each wireless terminal 2 connected to the AP _1. Have. Each of the data units 5132 _{1 to} 5132 _n has a unicast address of the wireless terminal 2, a data length 5133 of transmission data to be transmitted to the wireless terminal 2, and the transmission data 5134.

  FIG. 2C is a diagram schematically showing a CTS signal frame transmitted from the AP 1 to the wireless terminal 2. As shown in the figure, a CTS signal frame includes a CTS frame control 521 indicating that the frame is CTS control, a duration period 522 indicating a signal transmission waiting time, a destination address (a wireless terminal 2 that permits signal transmission). ), A CTS frame control 521, a duration 522, and a parity 524 for detecting transmission errors in the destination address 523. The CTS frame control 521 and the duration period 522 correspond to the header of the CTS signal frame.

  FIG. 2D is a diagram schematically showing a frame of a registration request signal and a registration cancellation request signal transmitted from the wireless terminal 2 to the AP 1. As shown in the figure, the registration request signal and deregistration request signal frames include a request type 531 indicating that the frame is a registration request or deregistration request, and an address 532 of the wireless terminal 2 to be registered or deregistered. And a parity 533 for detecting a transmission error of the request type 531 and the destination address 532. The request type 531 corresponds to the header of the registration request signal frame and the registration cancellation request signal frame.

  FIG. 3 is a schematic diagram of AP1. As illustrated, the AP 1 includes a wireless reception unit 11, a wireless transmission unit 12, a communication control unit 13, a wired IF (Interface) unit 14, and an antenna 15.

  The wireless reception unit 11 receives data from the wireless terminal 2 via the antenna 15 and outputs the data to the wired IF unit 14. As illustrated, the wireless reception unit 11 includes an AFE (Analog Front End) unit 111, an AD (Analog Digital) conversion unit 112, a frame detection unit 113, and a reception buffer 114.

  The AFE unit 111 receives a radio wave transmitted from the wireless terminal 2 via the antenna 15 and converts it into an analog signal. The AD conversion unit 112 converts the analog signal received by the AFE unit 111 into a digital signal and outputs the digital signal to the frame detection unit 113.

  The frame detection unit 113 detects a signal frame from the digital signal output from the AD conversion unit 112. If the detected signal frame is the unicast communication frame shown in FIG. 2A, the payload 503 is extracted from the detected unicast communication frame and output to the reception buffer 114. On the other hand, when the extracted signal frame is the registration request signal frame or the registration cancellation request signal frame shown in FIG. 2D, the signal frame is output to the communication control unit 13.

  The reception buffer 114 buffers the payload 503 received from the frame detection unit 113, and then outputs the payload 503 to the wired IF unit 14 as reception data including a header and data including an address and a data length.

  The wireless transmission unit 12 includes a transmission buffer 121, a multicast communication frame generation unit 122, a DA conversion unit 123, and an AFE unit 124.

  The transmission buffer 121 receives transmission data including a header and data including an address and a data length from the wired IF unit 14 and buffers the transmission data.

  The multicast communication frame generation unit 122 reads data addressed to each wireless terminal 2 existing in the jurisdiction area of the own AP 1 and stored in the transmission buffer 121 in accordance with an instruction from the communication control unit 13, and transmits the transmission data and the multicast data. A multicast communication frame as shown in FIG. 2B, in which the address is stored in the payload, is generated and output to the DA converter 123.

  The DA conversion unit 123 converts the multicast communication frame output from the multicast communication frame generation unit 122 and the CTS signal frame output from the communication control unit 13 into analog signals. The AFE unit 124 converts the analog signal output from the DA conversion unit 123 into a radio wave and transmits it from the antenna 15.

  The communication control unit 13 includes a terminal management unit 131, a communication instruction unit 132, and a CTS generation unit 133.

  The terminal management unit 131 includes a terminal management table (not shown) for managing the wireless terminals 2 existing in the jurisdiction area of the own AP 1. When the terminal management unit 131 receives a registration request signal from the wireless reception unit 11, the terminal management unit 131 adds the address of the wireless terminal 2 included in the registration request signal to the terminal management table. Further, when a registration cancellation request signal is received from the wireless reception unit 11, the address of the wireless terminal 2 included in the registration cancellation request signal is deleted from the terminal management table.

  FIG. 4 is a flowchart for explaining the operation of the terminal management unit 131.

  When receiving the registration request signal frame from the communication frame detection unit 113 (YES in S101), the terminal management unit 131 analyzes the registration request signal frame and analyzes the address of the transmission source wireless terminal 2. Then, the address is added to the terminal management table (S102).

  Then, the terminal management unit 131 identifies the timer with the smallest measured value among the timers TM and TU that are measuring. Then, it is checked whether or not the measured value of the timer has passed the predetermined time t1 (S103). Here, the timer TM is for detecting the transmission timing of the multicast communication frame, and the timer TUx is for detecting the transmission timing of the CTS signal frame addressed to the wireless terminal having the address x. The predetermined time t1 is set to a time longer than at least the duration time. If it has elapsed (YES in S103), the timer TUx associated with the address x of the wireless terminal 2 that is the transmission source of the registration request signal frame is set, and measurement of the timer TUx is started (S104). If it has not elapsed (NO in S103), it waits for it to elapse. Then, a timer TUx associated with the address x of the wireless terminal 2 that is the transmission source of the registration request signal frame is set, and measurement of the timer TUx is started (S104).

  Next, the terminal management unit 131 checks whether or not the timer TM is stopped (S105). If the timer TM is stopped (YES in S105), the measured value is the smallest among the timer TUs that are measuring. Specify the timer. Then, it is checked whether or not the measured value of the timer has passed the predetermined time t1 (S106). If it has elapsed (YES in S106), the timer TM starts to be measured (S107). If it has not elapsed (NO in S106), it waits for it to elapse. Then, the timer TM starts to be measured (S107).

  In addition, when receiving the deregistration request signal frame from the communication frame detection unit 113 (YES in S111), the terminal management unit 131 analyzes the deregistration request signal frame and analyzes the address x of the transmission source wireless terminal 2. To do. Then, the address x is deleted from the terminal management table (S112). Further, the measurement of the timer TUx provided in association with the wireless terminal 2 having the address x is stopped (S113). Then, the terminal management unit 131 checks whether all timers TU provided for each address of the wireless terminal 2 registered in the terminal management table are stopped (S114). If all are stopped (YES in S114), the measurement of the timer TM is stopped (S115).

  Returning to FIG. 3, the description will be continued. The communication instruction unit 132 periodically (for example, every 20 ms when the transmission data is a voice) of a multicast communication frame whose destination is each wireless terminal 2 whose address is registered in the terminal management table of the terminal management unit 131. Creation is instructed to the wireless transmission unit 12. In addition, the communication instruction unit 132 periodically (for example, every 20 ms when the transmission data is voice) for each wireless terminal 2 whose address is registered in the terminal management table of the terminal management unit 131. Instructs the CTS generation unit 133 to create a frame. Note that the CTS signal frame creation instruction is such that a unicast communication frame transmitted from the wireless terminal 2 in response to the CTS signal frame is transmitted as a unicast communication frame transmitted from another wireless terminal 2 and a multicast communication frame transmitted from the AP1. This is done at a timing where there is no interference.

  FIG. 5 is a flowchart for explaining the operation of the communication instruction unit 132.

  When the communication instruction unit 132 detects a timer that has passed the predetermined time t2 from the timers TM and TU being measured set by the terminal management unit 131 (YES in S201), the timer is registered in the terminal management table. If it is the timer TUx associated with the address x of any one of the wireless terminals 2, the process proceeds to S203, and if it is the timer TM, the process proceeds to S205 (S202). Here, the predetermined time t2 is determined by the communication quality. For example, when the communication target data is audio data, the time is 20 ms.

  In S203, the communication instruction unit 132 notifies the CTS generation unit 133 of a CTS generation instruction with the address x associated with the timer TUx that has passed the predetermined time t2. In response to this, the CTS generator 133 generates a CTS signal frame as shown in FIG. The CTS signal frame is converted into an analog signal by the DA conversion unit 122 and then wirelessly transmitted from the AFE unit 121. Next, the communication instruction unit 132 resets the measured value of the timer TUx that has passed the predetermined time t2 to 0 (S204). Thereafter, the process returns to S201.

  In step S205, the communication instruction unit 132 instructs the multicast communication frame generation unit 123 to generate a multicast communication frame with the address of each wireless terminal 2 registered in the terminal management table. In response to this, the multicast communication frame generation unit 123 stores transmission data for each address added to the multicast communication frame generation instruction from the transmission buffer 124 (a plurality of transmission data for one address is stored in the transmission buffer 124. In this case, the earliest transmission data) is read from the transmission buffer 124. Then, a multicast communication frame as shown in FIG. 2A storing these transmission data is generated. The multicast communication frame is converted into an analog signal by the DA conversion unit 122 and then wirelessly transmitted from the AFE unit 121. Next, the communication instruction unit 132 resets the measured value of the timer TM that has passed the predetermined time t2 to 0 (S204). Thereafter, the process returns to S201.

  Returning to FIG. 3, the description will be continued. In accordance with the CTS signal frame creation instruction received from the communication instruction unit 132, the CTS generation unit 133 has a CTS signal frame as illustrated in FIG. Is output to the wireless transmission unit 12.

  The wired IF unit 14 outputs the data received from the wireless reception unit 11 to the router 3. In addition, the data addressed to each wireless terminal 2 existing in the jurisdiction area of the own AP 1 received from the router 3 is output to the wireless transmission unit 12.

  FIG. 6 is a schematic diagram of the wireless terminal 2. As illustrated, the wireless terminal 2 includes a wireless reception unit 21, a wireless transmission unit 22, a communication control unit 23, an application processing unit 24, and an antenna 25.

  The wireless reception unit 21 receives data from the AP 1 via the antenna 25 and outputs the data to the application processing unit 24. As illustrated, the wireless reception unit 21 includes an AFE unit 211, an AD conversion unit 212, a frame detection unit 213, and a reception buffer 214.

  The AFE unit 211 receives a radio wave transmitted from the AP 1 via the antenna 25 and converts it into an analog signal. The AD conversion unit 212 converts the analog signal received by the AFE unit 211 into a digital signal and outputs the digital signal to the frame detection unit 213.

  The frame detection unit 213 detects a signal frame from the digital signal output from the AD conversion unit 212. If the detected signal frame is the multicast communication frame shown in FIG. 2B, the data unit 5132 having the address of the own wireless terminal 2 is extracted from the payload 513 of the communication frame and output to the reception buffer 214. On the other hand, when the extracted signal frame is the CTS signal frame shown in FIG. 2C, the signal frame is output to the communication control unit 23.

  The reception buffer 214 buffers the data unit 5132 received from the frame detection unit 213, and then outputs the data unit 5132 to the application processing unit 24 as reception data including a header and data including an address and a data length. .

  The wireless transmission unit 22 includes a transmission buffer 221, a unicast communication frame generation unit 222, a DA conversion unit 223, and an AFE unit 224.

  The transmission buffer 221 receives transmission data composed of a header and data including an address and a data length from the application processing unit 24 and buffers it.

  The unicast communication frame generation unit 222 reads the transmission data stored in the transmission buffer 221 in accordance with an instruction from the communication control unit 23, and stores the transmission data in the payload as shown in FIG. A cast communication frame is generated and output to the DA converter 223.

  The DA conversion unit 223 converts the unicast communication frame output from the unicast communication frame generation unit 222 and the registration request signal frame and registration cancellation request signal frame output from the communication control unit 23 into analog signals. The AFE unit 224 converts the analog signal output from the DA converter 223 into a radio wave and transmits it from the antenna 25.

  The communication control unit 23 includes an AP selection unit 231, a communication timing management unit 232, and a registration / release request generation unit 233.

  The AP selection unit 231 selects a connection destination AP 1 based on the received radio wave intensity of each AP 1 detected by the AFE unit 211 (assuming that each AP 1 uses a different carrier frequency). The AFE units 211 and 214 are set to connect to the selected AP1. As a result, the AFE 211 demodulates the received radio wave at the carrier frequency of AP1 set by the AP selection unit 231 and receives the signal transmitted from the AP1. The AFE 224 modulates the analog signal output from the DA converter 223 with the carrier frequency of AP1 set by the AP selector 231 and transmits radio waves from the antenna 25 to the connected AP1.

  The communication timing management unit 232 instructs the wireless transmission unit 22 to create a unicast communication frame whose destination is AP1. In addition, the communication timing instruction unit 232 instructs the registration / cancellation request generation unit 233 to create a registration request signal frame and a registration cancellation request signal frame. Note that the instruction to create the registration request signal frame and the registration cancellation request signal frame is performed at a timing that does not interfere with signals transmitted from the AP 1 and other wireless terminals 2.

  FIG. 7 is a diagram for explaining the operation of the communication timing management unit 232.

  When the communication timing management unit 232 receives the CTS signal frame from the frame detection unit 213 (S301), the communication timing management unit 232 analyzes the CTS signal frame and checks whether or not the destination address is the own wireless terminal 2 (S302). In the case of the own wireless terminal 2 (YES in S302), the unicast communication frame generation unit 222 is instructed to generate a unicast communication frame (S303). In response to this, the unicast communication frame generation unit 222 reads transmission data from the transmission buffer 124 after the SIFS period elapses. Then, a unicast communication frame as shown in FIG. 2A storing the transmission data is generated. The unicast communication frame is converted into an analog signal by the DA conversion unit 223 and then wirelessly transmitted from the AFE unit 224. Thereafter, the communication timing management unit 232 waits for the duration period specified in the CTS signal frame to elapse (S304), and then returns to S301.

  When the communication timing management unit 232 receives an instruction to start communication from the application processing unit 24 (S311), the communication timing management unit 232 generates a random number, and the wireless reception unit 21 (AFE unit 211) connects during a period corresponding to the random number. It is determined whether the carrier of the previous AP1 has been detected (S312). If the carrier has not been detected (NO in S312), the registration / release request generation unit 233 is instructed to generate a registration request (S313). ). In response to this, the registration / cancellation request generation unit 233 generates a registration request signal frame as shown in FIG. The registration request signal frame is converted into an analog signal by the DA conversion unit 223 and then wirelessly transmitted from the AFE unit 224. Thereafter, the process returns to S301.

  When the communication timing management unit 232 receives an instruction to end communication from the application processing unit 24 (S321), the communication timing management unit 232 generates a random number, and the wireless reception unit 21 (AFE unit 211) connects during a period according to the random number. It is determined whether the carrier of the previous AP1 has been detected (S322). If the carrier has not been detected (NO in S322), the registration / release request generation unit 233 is instructed to generate a registration cancellation request ( S323). In response to this, the registration / cancellation request generation unit 233 generates a registration cancellation request signal frame as shown in FIG. The deregistration request signal frame is converted into an analog signal by the DA conversion unit 223 and then wirelessly transmitted from the AFE unit 224. Thereafter, the process returns to S301.

  Returning to FIG. 3, the description will be continued. As described above, the registration / cancellation request generation unit 233 has the AP1 as the destination in accordance with the registration request communication frame or registration cancellation request communication frame generation instruction received from the communication timing instruction unit 232, as shown in FIG. Such a registration request communication frame or a registration cancellation request communication frame is generated and output to the wireless transmission unit 22.

  The application processing unit 24 generates transmission data for the communication partner and outputs the transmission data to the wireless transmission unit 12, and receives reception data from the communication partner from the wireless reception unit 21. The application processing unit 24 outputs a communication start instruction to the communication control unit 23 prior to the start of data transmission / reception with the communication partner. When the data transmission / reception with the communication partner is to be ended, an instruction to end the communication is output to the communication control unit 23. The application processing unit 24 is realized by, for example, a program that performs VoIP processing.

  The AP 1 described above includes, for example, a CPU 51, a program memory 52 in which a program is stored, a data memory 53 in which data is stored, and a wired IF 54 that performs communication via a wired LAN, for example, as shown in FIG. In a computer system having a wireless IF 55 that communicates with the wireless terminal 2 via a wireless LAN and an internal bus 57 that interconnects these components 51 to 55, the CPU 51 stores a program stored in the program memory 52. It is realized by executing. In this case, a data memory 53 is used for the terminal management table held by the terminal management unit 131, a wired IF 54 is used for the wired IF unit 14, and a wireless IF 55 is used for the wireless reception unit 11 and the wireless transmission unit 12.

  The wireless terminal 2 is a computer system in which an input / output device such as a keyboard, a mouse, a microphone, a display, and a speaker is provided instead of the wired IF 54 in FIG. It is realized by executing. In this case, the wireless IF 55 is used for the wireless receiver 21 and the wireless transmitter 22.

  Next, the operation of the wireless LAN system having the above configuration will be described.

  FIG. 9 is a diagram for explaining data exchange in the wireless LAN system to which the first embodiment of the present invention is applied. Here, a case where two wireless terminals 2 (terminal A and terminal B) are connected to AP1 will be described as an example.

  In AP1, when the communication instruction unit 132 detects that the timer TM for measuring the transmission timing of the multicast communication frame has passed a predetermined time t2 (a time determined by communication quality, for example, 20 ms when the communication target data is voice data), Then, a multicast communication frame generation instruction is output to the multicast communication frame generation unit 122. In response to this, the multicast communication frame generation unit 122 generates a multicast communication frame including the data unit 5132 addressed to the terminal A, and transmits it from the antenna 15 via the DA conversion unit 123 and the AFE unit 124 (T101). Terminal A receives this multicast communication frame and extracts data unit 5132 addressed to its own terminal A from payload 513 of the communication frame.

  In AP1, communication instruction unit 132 outputs a CTS signal frame generation instruction to CTS generation unit 133 upon detecting that timer TUa for measuring the transmission timing of the CTS signal frame addressed to terminal A has passed a predetermined time t2. To do. In response to this, the CTS generation unit 133 generates a CTS signal frame addressed to the terminal A, and transmits the CTS signal frame from the antenna 15 via the DA conversion unit 123 and the AFE unit 124 (T102).

  In the terminal A connected to the AP 1, the communication timing management unit 232 outputs a unicast communication frame generation instruction to the unicast communication frame generation unit 222 when receiving the CTS signal frame addressed to the terminal A from the wireless reception unit 21. To do. In response, the unicast communication frame generation unit 222 generates a unicast communication frame including transmission data, and transmits the unicast communication frame from the antenna 25 via the DA conversion unit 223 and the AFE unit 224 (T201). AP1 receives this unicast communication frame and extracts received data from the payload 503 of the communication frame.

  In the terminal B not connected to the AP 1, when the communication timing management unit 232 instructed to start communication from the application processing unit 24 receives a CTS signal frame addressed to another terminal from the wireless reception unit 21, the communication timing management unit 232 is defined by the CTS signal frame. Waiting for the current duration period t1 to elapse, and after confirming that AP1 and other terminals are not outputting signals, instruct the registration / cancellation request generation unit 233 to generate a registration request signal frame To do. In response, the registration / cancellation request generation unit 233 generates a registration request signal frame and transmits it from the antenna 25 via the DA conversion unit 223 and the AFE unit 224 (T301). AP1 receives this registration request signal frame, adds terminal B to the terminal management table, sets a timer TUb associated with terminal B, and starts measuring this timer TUb (T103).

  In the terminal A connected to the AP 1, when the communication timing management unit 232 is instructed to end communication from the application processing unit 24, the communication timing management unit 232 passes the duration period t 1 defined by the CTS signal frame received from the wireless reception unit 21. And confirming that the AP1 and other terminals are not outputting signals, the registration / cancellation request generation unit 233 is instructed to generate a registration cancellation request signal frame. In response to this, the registration / release cancellation request generation unit 233 generates a registration cancellation request signal frame and transmits it from the antenna 25 via the DA conversion unit 223 and the AFE unit 224 (T202). AP1 receives this deregistration request signal frame, deletes terminal A from the terminal management table, and ends the measurement of timer TUa associated with terminal A (T104).

  In AP1, communication instruction unit 132 outputs a multicast communication frame generation instruction to multicast communication frame generation unit 122 when it detects that timer TM for measuring the multicast communication frame transmission timing has passed a predetermined time t2. In response, the multicast communication frame generation unit 122 generates a multicast communication frame including the data unit 5132 addressed to the terminal B, and transmits the multicast communication frame from the antenna 15 via the DA conversion unit 123 and the AFE unit 124 (T105). Terminal B receives this multicast communication frame and extracts data unit 5132 addressed to its own terminal B from payload 513 of the communication frame.

  In AP1, communication instruction section 132 outputs a CTS signal frame generation instruction to CTS generation section 133 when it detects that timer TUb for measuring the CTS signal frame transmission timing addressed to terminal B has passed a predetermined time t2. To do. In response to this, the CTS generator 133 generates a CTS signal frame addressed to the terminal B, and transmits it from the antenna 15 via the DA converter 123 and the AFE unit 124 (T106).

  In the terminal B connected to the AP 1, the communication timing management unit 232 outputs a unicast communication frame generation instruction to the unicast communication frame generation unit 222 when receiving the CTS signal frame addressed to the terminal B from the wireless reception unit 21. To do. In response, the unicast communication frame generation unit 222 generates a unicast communication frame including transmission data, and transmits the unicast communication frame from the antenna 25 via the DA conversion unit 223 and the AFE unit 224 (T302). AP1 receives this unicast communication frame and extracts received data from the payload 503 of the communication frame.

  The first embodiment of the present invention has been described above.

  According to this embodiment, the AP 1 can collectively transmit data addressed to each of the plurality of wireless terminals 2 in one multicast communication frame. Therefore, compared to the case where data addressed to each of the plurality of wireless terminals A is transmitted in separate unicast communication frames, the overhead due to the frame preamble or the like can be reduced.

<< Second Embodiment >>
The wireless LAN system of this embodiment is configured to receive a communication frame from each of the plurality of wireless terminals 2 using one multicast CTS in the wireless LAN system of the first embodiment. The schematic configuration of the wireless LAN system of this embodiment is basically the same as that of the wireless LAN system of the first embodiment shown in FIG. However, the operations of AP1 and wireless terminal 2 are partially different.

  AP1 of this embodiment is basically the same as that of the first embodiment except that the processing in the communication control unit 13 is different. In order to distinguish from the first embodiment, the terminal management unit 131, the communication instruction unit 132, and the CTS generation unit 133 constituting the communication control unit 13 are referred to as the terminal management unit 131A, the communication instruction unit 132A, and the CTS generation in this embodiment. It will be referred to as a section 133A.

  The terminal management unit 131A includes a terminal management table (not shown) for managing the wireless terminals 2 existing in the jurisdiction area of the own AP1. When the terminal management unit 131A receives a registration request signal from the wireless reception unit 11, the terminal management unit 131A adds the address of the wireless terminal 2 included in the registration request signal to the terminal management table. Further, when a registration cancellation request signal is received from the wireless reception unit 11, the address of the wireless terminal 2 included in the registration cancellation request signal is deleted from the terminal management table.

  FIG. 10 is a flowchart for explaining the operation of the terminal management unit 131A.

  Upon receiving the registration request signal frame from the communication frame detection unit 113 (YES in S121), the terminal management unit 131A analyzes the registration request signal frame and analyzes the address of the transmission source wireless terminal 2. Then, the address is added to the terminal management table (S122). Then, the terminal manager 131A checks whether or not the timers TM and TU are being measured (S123). Here, the timer TM is for detecting the transmission timing of the multicast communication frame, and the timer TU is for detecting the transmission timing of the multicast CTS signal frame. If the timers TM and TU are not being measured (NO in S123), the terminal management unit 131A resets the timer TU and starts measurement (S124). Then, after a predetermined time t3 has elapsed (S125), the timer TM is reset and measurement is started (S126). The predetermined time t3 is set to a time longer than at least the duration time.

  Further, when receiving the deregistration request signal frame from the communication frame detecting unit 113 (YES in S131), the terminal managing unit 131A analyzes the deregistration request signal frame and analyzes the address x of the transmission source wireless terminal 2. To do. Then, the address x is deleted from the terminal management table (S312). Then, the terminal management unit 131A checks whether there is a wireless terminal 2 registered in the terminal management table (S133). If there is no wireless terminal 2 registered in the terminal management table, the timers TU and TM are stopped (S134).

  The communication instruction unit 132A periodically (for example, every 20 ms when the transmission data is a voice) of a multicast communication frame whose destination is each wireless terminal 2 whose address is registered in the terminal management table of the terminal management unit 131A. The creation is instructed to the wireless transmission unit 12. Also, the communication instruction unit 132A periodically (for example, every 20 ms when the received data is voice) multicast CTS signal frames for all the wireless terminals 2 whose addresses are registered in the terminal management table of the terminal management unit 131A. Is generated to the CTS generator 133A.

  Note that the multicast CTS signal frame used in the present embodiment is basically the same as the CTS signal frame shown in FIG. However, the duration period 522 is a period obtained by multiplying the duration period per wireless terminal by the maximum number of simultaneous connections of the wireless terminal 2 to the AP 1. The destination address 523 describes the transmission order of unicast communication frames of all the wireless terminals 2 whose addresses are registered in the terminal management table of the terminal management unit 131A.

  FIG. 11 is a diagram schematically showing the destination address of the multicast CTS signal frame. According to IEEE 802.11, when the CTS signal frame is unicast, the destination address describes the MAC address (48 bits) of the destination wireless terminal 2. When the CTS signal frame is multicast, a bit string (48 bits) composed of the upper 25 bits of the fixed value and the lower 23 bits of the multicast IP address is described. The multicast IP address has a fixed value “1110” indicating that the upper 4 bits are multicast, and the lower 28 bits can be freely set (except for some reserved values such as all “0”). The multicast CTS signal frame of the present embodiment adopts the destination address configuration shown in FIG. 11, for example, so that it can be distinguished from the multicast CTS signal frame assumed by the above-mentioned IEEE 802.11.

  That is, the upper 25 bits are set to a fixed value similar to the destination address of the multicast CTS signal frame defined by IEEE 802.11 (1101). The 26th bit is fixed to “0” (1102). The remaining 27th to 48th bits are assigned to the wireless terminal 2 (1103). When the bit value is “0”, the CTS issuance “None” to the wireless terminal 2 assigned to the bit is set, and when the bit value is “1”, the CTS issuance “ “Yes”. Note that the wireless terminal 2 assigned to each bit of the 27th to 48th bits is specified in advance by registering an address management table indicating the correspondence between the bit position and the address of the wireless terminal 2 in the communication instruction unit 132A of AP1. In addition, the address management table may be used. Alternatively, the registration request or registration cancellation request transmitted by the wireless terminal 2 includes the bit position assigned to the own wireless terminal 2 or the assigned bit position, and the registration request or registration cancellation request received from the wireless reception unit 11 by the communication instruction unit 132A. The correspondence between the bit position and the address of the wireless terminal 2 may be added to or deleted from the address management table based on the transmission source address and the bit position included in the registration request or deregistration request. Good.

  FIG. 12 is a flowchart for explaining the operation of the communication instruction unit 132A.

  If the communication instruction unit 132A detects that any of the timers TM and TU being measured set by the terminal management unit 131 has passed the predetermined time t4 (YES in S211), the communication instruction unit 132A determines that the timer is a timer TU. On the other hand, if it is the timer TM, the process proceeds to S215 (S212). Here, the predetermined time t4 is determined by the communication quality. For example, when the communication target data is voice data, 20 ms × (the maximum number of simultaneous connections of the wireless terminal 2 to AP1).

  In S213, for each address registered in the terminal management table, the communication instruction unit 132A uses, for example, the above-described address management table to set the destination address (48 bits) assigned to the wireless terminal 2 having the address. Specify the bit position. Then, the CTS generator 133A is notified of each bit position of the specified destination address, and an instruction to generate a multicast CTS signal frame is given. In response to this, the CTS generation unit 133A generates a multicast CTS signal frame in which the bit at each bit position of the destination address notified from the communication instruction unit 132A is set to a bit value indicating CTS issuance “present” (FIG. 2 (C), see FIG. 11). The CTS signal frame is converted into an analog signal by the DA conversion unit 122 and then wirelessly transmitted from the AFE unit 121. Next, the communication instruction unit 132A resets the measured value of the timer TU to 0 (S214). Thereafter, the process returns to S211.

  In S215, the communication instruction unit 132A instructs the multicast communication frame generation unit 123 to generate a multicast communication frame with the address of each wireless terminal 2 registered in the terminal management table. In response to this, the multicast communication frame generation unit 123 stores transmission data for each address added to the multicast communication frame generation instruction from the transmission buffer 124 (a plurality of transmission data for one address is stored in the transmission buffer 124. In this case, the earliest transmission data) is read from the transmission buffer 124. Then, a multicast communication frame as shown in FIG. 2A storing these transmission data is generated. The multicast communication frame is converted into an analog signal by the DA conversion unit 122 and then wirelessly transmitted from the AFE unit 121. Next, the communication instruction unit 132 resets the measured value of the timer TM to 0 (S216). Thereafter, the process returns to S211.

  The CTS generation unit 133A, in accordance with the multicast CTS signal frame creation instruction received from the communication instruction unit 132A, the multicast CTS signal frame in which each bit position specified by the instruction is set to a bit value indicating “present” CTS issuance Is output to the wireless transmission unit 12.

  The wireless terminal 2 of this embodiment is basically the same as that of the first embodiment except that the processing in the communication control unit 23 is different. For distinction from the first embodiment, the communication timing management unit 232, the registration / cancellation request generation unit 233, and the AP selection unit 231 constituting the communication control unit 23 are referred to as a communication timing management unit 232A, a registration / These will be referred to as a release request generation unit 233A and an AP selection unit 231A.

  The AP selection unit 231A performs the same process as the AP selection unit 231 of the first embodiment. That is, a connection destination AP1 is selected based on the received radio wave intensity of each AP1 detected by the AFE unit 211 (each AP1 uses a different carrier frequency), and the selected AP1 is connected. AFE units 211 and 214 are set.

  The communication timing management unit 232A analyzes the multicast CTS signal frame, determines the communication timing of the unicast communication frame destined for AP1, and instructs the radio transmission unit 22 to create the unicast communication frame at the communication timing. . Further, the communication timing management unit 232A notifies the registration / release request generation unit 233A of the bit position of the bit to be allocated to the own wireless terminal 2 in the bit string constituting the destination address of the multicast CTS signal frame. Instructs creation of a frame and a deregistration request signal frame.

  FIG. 13 is a diagram for explaining the operation of the communication timing management unit 232A.

  When the communication timing management unit 232A receives the multicast CTS signal frame from the frame detection unit 213 (S351), the communication timing management unit 232A analyzes the multicast CTS signal frame and determines the bit assigned to the own wireless terminal 2 in the bit string constituting the destination address. It is checked whether or not the bit value is CTS issue “present” (S352). If the CTS issuance is “Yes” (YES in S352), it waits for the elapse of a period (corresponding period) corresponding to the bit position of the bit allocated to the own wireless terminal 2 in the bit string constituting the destination address ( Then, the unicast communication frame generation unit 222 is instructed to generate a unicast communication frame (S354). Here, the period corresponding to the bit position is a period obtained by multiplying the order of the wireless terminals 2 determined by the bit position by the duration period for each wireless terminal. As described above, in this embodiment, the first wireless terminal 2 is assigned to the 27th bit of 48 bits constituting the destination address of the multicast CTS signal frame, the second wireless terminal 2 is assigned to the 28th bit, and The 48th bit is assigned to the 22nd wireless terminal 2. When the unicast communication frame generation unit 222 receives a unicast communication frame generation instruction from the communication timing management unit 232A, the unicast communication frame generation unit 222 reads transmission data from the transmission buffer 124 after the SIFS period elapses. Then, a unicast communication frame as shown in FIG. 2A storing the transmission data is generated. The unicast communication frame is converted into an analog signal by the DA conversion unit 223 and then wirelessly transmitted from the AFE unit 224. Thereafter, the communication timing management unit 232 waits for a period (remaining period) obtained by subtracting a period corresponding to the bit position from the duration period 522 specified in the multicast CTS signal frame (S355), Then, the process returns to S351.

  In addition, when the communication timing management unit 232A receives an instruction to start communication from the application processing unit 24 (S361), the communication timing management unit 232A generates a random number, and the wireless reception unit 21 (AFE unit 211) connects during a period according to the random number. It is determined whether the carrier of the previous AP1 has been detected (S362). If the carrier has not been detected (NO in S362), the registration / release request generation unit 233 is instructed to generate a registration request (S363). ). In response to this, the registration / cancellation request generation unit 233 generates a registration request signal frame as shown in FIG. However, the request type 531 or the address 532 of the registration request signal frame includes the bit position of the bit assigned to the own radio terminal 2 in the bit string constituting the destination address of the multicast CTS signal frame. This bit position may be determined so as not to overlap with the other wireless terminal 2 and set in the registration / cancellation request generation unit 233 in advance, or the communication timing management unit 232A may transmit the multicast CTS signal frame. Analyze and check the bit position where the bit value in the bit string constituting the destination address is set to “None” issued by CTS, and register / cancel the bit position as the bit position of the bit assigned to the own wireless terminal 2 The request generation unit 233 may be notified. The registration request signal frame is converted into an analog signal by the DA conversion unit 223 and then wirelessly transmitted from the AFE unit 224. Thereafter, the process returns to S351.

  When the communication timing management unit 232A receives an instruction to end communication from the application processing unit 24 (S371), the communication timing management unit 232A generates a random number, and the wireless reception unit 21 (AFE unit 211) connects during the period corresponding to the random number. It is determined whether or not the carrier of the previous AP1 has been detected (S372). If the carrier has not been detected (NO in S372), the registration / release request generation unit 233 is instructed to generate a registration release request ( S373). In response to this, the registration / cancellation request generation unit 233 generates a registration cancellation request signal frame as shown in FIG. However, the request type 531 or the address 532 of the registration request signal frame includes the bit position of the bit assigned to the own wireless terminal 2 in the bit string constituting the destination address of the multicast CTS signal frame. The deregistration request signal frame is converted into an analog signal by the DA conversion unit 223 and then wirelessly transmitted from the AFE unit 224. Thereafter, the process returns to S351.

  Next, the operation of the wireless LAN system having the above configuration will be described.

  FIG. 14 is a diagram for explaining data exchange in a wireless LAN system to which the second embodiment of the present invention is applied. Here, a case where two wireless terminals 2 (terminal A and terminal B) are connected to AP1 will be described as an example.

  In AP1, communication instruction unit 132A detects that timer TM that measures the multicast communication frame transmission timing has passed a predetermined time t4 (a time determined by communication quality, for example, 20 ms when the communication target data is voice data). Then, a multicast communication frame generation instruction is output to the multicast communication frame generation unit 122. In response, the multicast communication frame generation unit 122 generates a multicast communication frame including the data unit 5132 addressed to each of the terminals A and B, and transmits it from the antenna 15 via the DA conversion unit 123 and the AFE unit 124 ( T111, T113). Terminal A receives this multicast communication frame and extracts data unit 5132 addressed to its own terminal A from payload 513 of the communication frame. Similarly, the terminal B receives this multicast communication frame and extracts the data unit 5132 addressed to its own terminal B from the payload 513 of the communication frame.

  In AP1, communication instruction section 132A outputs a CTS signal frame generation instruction to CTS generation section 133A when it detects that timer TU for measuring the multicast CTS signal frame transmission timing has passed a predetermined time t4. In response to this, the CTS generator 133A sets the bit value of each bit assigned to the terminals A and B in the bit string constituting the destination address of the multicast CTS signal frame to the CTS issue “present”. A signal frame is generated and transmitted from the antenna 15 via the DA conversion unit 123 and the AFE unit 124 (T112, T114).

  In the terminal A connected to the AP 1, when the communication timing management unit 232 A receives the multicast CTS signal frame from the radio reception unit 21, the communication timing management unit 232 A analyzes the multicast CTS signal frame and configures the destination address of the multicast CTS signal frame It is confirmed that the bit value of the bit assigned to the own terminal A in the bit string is CTS issue “present”. Then, a unicast communication frame generation instruction is output to the unicast communication frame generation unit 222 at a transmission timing determined according to the bit position of the bit allocated to the own terminal A. In response, the unicast communication frame generation unit 222 generates a unicast communication frame including transmission data, and transmits the unicast communication frame from the antenna 25 via the DA conversion unit 223 and the AFE unit 224 (T211 and T212). AP1 receives this unicast communication frame and extracts received data from the payload 503 of the communication frame.

  Similarly, in the terminal B connected to the AP1, when the communication timing management unit 232A receives the multicast CTS signal frame from the radio reception unit 21, the communication timing management unit 232A analyzes the multicast CTS signal frame and transmits the destination address of the multicast CTS signal frame. It is confirmed that the bit value of the bit assigned to own terminal B in the bit string constituting the CTS is “present”. Then, a unicast communication frame generation instruction is output to the unicast communication frame generation unit 222 at a transmission timing determined according to the bit position of the bit allocated to the terminal B. In response, the unicast communication frame generation unit 222 generates a unicast communication frame including transmission data, and transmits the unicast communication frame from the antenna 25 via the DA conversion unit 223 and the AFE unit 224 (T311 and T312). AP1 receives this unicast communication frame and extracts received data from the payload 503 of the communication frame.

  The second embodiment of the present invention has been described above.

  This embodiment also has the same effect as the first embodiment. Further, according to the present embodiment, the AP 1 can receive a unicast communication frame from each of the plurality of wireless terminals 2 using one multicast CTS signal frame. Therefore, the overhead can be further reduced as compared with the case where the RTS signal and the CTS signal are exchanged with each of the plurality of wireless terminals 2 prior to the reception of the unicast communication frame.

<< Third Embodiment >>
The wireless LAN system of this embodiment uses the order and data length of the data units addressed to each wireless terminal 2 included in the payload of the multicast communication frame instead of the multicast CTS in the wireless LAN system of the third embodiment. Thus, communication frames can be received from each of the plurality of wireless terminals 2. The schematic configuration of the wireless LAN system of this embodiment is basically the same as that of the wireless LAN system of the first embodiment shown in FIG. However, the operations of AP1 and wireless terminal 2 are partially different.

  AP1 of this embodiment is basically the same as that of the first embodiment except that the processing in the communication control unit 13 is different. In order to distinguish from the first embodiment, the terminal management unit 131, the communication instruction unit 132, and the CTS generation unit 133 that constitute the communication control unit 13 are referred to as the terminal management unit 131B, the communication instruction unit 132B, and the CTS generation in this embodiment. It will be referred to as a section 133B.

  The terminal management unit 131B includes a terminal management table (not shown) for managing the wireless terminals 2 existing in the jurisdiction area of the own AP1. When the terminal management unit 131A receives a registration request signal from the wireless reception unit 11, the terminal management unit 131A adds the address of the wireless terminal 2 included in the registration request signal to the terminal management table. Further, when a registration cancellation request signal is received from the wireless reception unit 11, the address of the wireless terminal 2 included in the registration cancellation request signal is deleted from the terminal management table.

  FIG. 15 is a flowchart for explaining the operation of the terminal management unit 131B.

  When receiving the registration request signal frame from the communication frame detection unit 113 (YES in S141), the terminal management unit 131B analyzes the registration request signal frame and analyzes the address of the transmission source wireless terminal 2. Then, the address is added to the terminal management table (S142). Then, the terminal management unit 131B checks whether or not the timer TM is measuring (S143). Here, the timer TM is for detecting the transmission timing of the multicast communication frame. If the timer TM is not being measured (NO in S143), the terminal management unit 131B resets the timer TM and starts measurement (S144).

  In addition, when receiving the deregistration request signal frame from the communication frame detecting unit 113 (YES in S151), the terminal managing unit 131B analyzes the deregistration request signal frame and analyzes the address x of the transmission source wireless terminal 2. To do. Then, the address x is deleted from the terminal management table (S152). Then, the terminal management unit 131B checks whether there is a wireless terminal 2 registered in the terminal management table (S153). If there is no wireless terminal 2 registered in the terminal management table, the timer TM measurement is stopped (S154).

  The communication instructing unit 132B periodically (for example, every 20 ms when the transmission data is voice) of a multicast communication frame whose destination is each wireless terminal 2 whose address is registered in the terminal management table of the terminal management unit 131B. The creation is instructed to the wireless transmission unit 12.

  FIG. 16 is a flowchart for explaining the operation of the communication instruction unit 132B.

  When the communication instruction unit 132B detects that the timer TM being measured set by the terminal management unit 131 has passed the predetermined time t5 (YES in S221), the process proceeds to S222. Here, the predetermined time t5 is determined by the communication quality. For example, when the communication target data is voice data, 20 ms × (the maximum number of simultaneous connections of the wireless terminal 2 to AP1).

  In S222, the communication instruction unit 132B instructs the multicast communication frame generation unit 123 to generate a multicast communication frame with the address of each wireless terminal 2 registered in the terminal management table. In response to this, the multicast communication frame generation unit 123 stores transmission data for each address added to the multicast communication frame generation instruction from the transmission buffer 124 (a plurality of transmission data for one address is stored in the transmission buffer 124. In this case, the earliest transmission data) is read from the transmission buffer 124. Then, a multicast communication frame as shown in FIG. 2A storing these transmission data is generated. The multicast communication frame is converted into an analog signal by the DA conversion unit 122 and then wirelessly transmitted from the AFE unit 121. Next, the communication instruction unit 132 resets the measured value of the timer TM to 0 (S223). Thereafter, the process returns to S221.

  The wireless terminal 2 of the present embodiment is basically the same as that of the first embodiment except that the processing in the frame detection unit 213 and the communication timing management unit 232 is different. In order to distinguish from the first embodiment, the frame detection unit 213 and the communication timing management unit 232 are referred to as a frame detection unit 213B and a communication timing management unit 232B in this embodiment.

  The frame detection unit 213B detects a signal frame from the digital signal output from the AD conversion unit 212. If the detected signal frame is the multicast communication frame shown in FIG. 2B, the data unit 5132 having the address of the own wireless terminal 2 is extracted from the payload 513 of the communication frame and output to the reception buffer 214. Further, the frame detection unit 213B generates a list in which the destination addresses of the data units 5132 stored in the payload 513 of the communication frame are described in the order of arrangement of the data units 5132 in the payload 513, and communicates the list. The timing management unit 232B is notified.

  The communication timing management unit 232A determines the communication timing of the unicast communication frame destined for AP1 using the list notified from the frame detection unit 213B, and creates a unicast communication frame at the communication timing as a wireless transmission unit 22 is instructed. Further, the communication timing instruction unit 232B instructs the registration / cancellation request generation unit 233 to create a registration request signal frame and a registration cancellation request signal frame. Note that the instruction to create the registration request signal frame and the registration cancellation request signal frame is performed at a timing that does not interfere with signals transmitted from the AP 1 and other wireless terminals 2.

  FIG. 17 is a diagram for explaining the operation of the communication timing management unit 232B.

  When the communication timing management unit 232B receives the list from the frame detection unit 213 (S381), the communication timing management unit 232B calculates the waiting period according to the order of the address of the own wireless terminal 2 in the list (S382). Here, the waiting period is a period obtained by multiplying the description order in the list of the address of the own wireless terminal 2 by the duration period for each wireless terminal. Next, the communication timing management unit 232A waits for the waiting period to elapse (S383), and then instructs the unicast communication frame generation unit 222 to generate a unicast communication frame (S384). In response to this, when receiving a unicast communication frame generation instruction from the communication timing management unit 232B, the unicast communication frame generation unit 222 reads transmission data from the transmission buffer 124 after the SIFS period elapses. Then, a unicast communication frame as shown in FIG. 2A storing the transmission data is generated. The unicast communication frame is converted into an analog signal by the DA conversion unit 223 and then wirelessly transmitted from the AFE unit 224. Thereafter, the communication timing management unit 232 subtracts the waiting period from the period obtained by multiplying the number of addresses listed in the list by the duration period for each wireless terminal (remaining period). ) (S385), and then returns to S381.

  In addition, when the communication timing management unit 232B receives an instruction to start communication from the application processing unit 24 (S391), the communication timing management unit 232B generates a random number, and the wireless reception unit 21 (AFE unit 211) connects during a period corresponding to the random number. It is determined whether the carrier of the previous AP1 has been detected (S392). If the carrier has not been detected (NO in S392), the registration / release request generation unit 233 is instructed to generate a registration request (S393). ). In response to this, the registration / cancellation request generation unit 233 generates a registration request signal frame as shown in FIG. The registration request signal frame is converted into an analog signal by the DA conversion unit 223 and then wirelessly transmitted from the AFE unit 224. Thereafter, the process returns to S381.

  When the communication timing management unit 232B receives an instruction to end communication from the application processing unit 24 (S401), the communication timing management unit 232B generates a random number, and the wireless reception unit 21 (AFE unit 211) connects during a period according to the random number. It is determined whether the carrier of the previous AP1 has been detected (S402). If the carrier has not been detected (NO in S402), the registration / cancellation request generation unit 233 is instructed to generate a registration cancellation request ( S403). In response to this, the registration / cancellation request generation unit 233 generates a registration cancellation request signal frame as shown in FIG. The deregistration request signal frame is converted into an analog signal by the DA conversion unit 223 and then wirelessly transmitted from the AFE unit 224. Thereafter, the process returns to S381.

  Next, the operation of the wireless LAN system having the above configuration will be described.

  FIG. 18 is a diagram for explaining data exchange in a wireless LAN system to which the third embodiment of the present invention is applied. Here, a case where two wireless terminals 2 (terminal A and terminal B) are connected to AP1 will be described as an example.

  In AP1, when the communication instruction unit 132B detects that the timer TM for measuring the transmission timing of the multicast communication frame has passed a predetermined time t5 (a time determined by communication quality, for example, 20 ms when the communication target data is voice data), Then, a multicast communication frame generation instruction is output to the multicast communication frame generation unit 122. In response, the multicast communication frame generation unit 122 generates a multicast communication frame including the data unit 5132 addressed to each of the terminals A and B, and transmits it from the antenna 15 via the DA conversion unit 123 and the AFE unit 124 ( T121, T122). Terminal A receives this multicast communication frame and extracts data unit 5132 addressed to its own terminal A from payload 513 of the communication frame. Similarly, the terminal B receives this multicast communication frame and extracts the data unit 5132 addressed to its own terminal B from the payload 513 of the communication frame.

  In the terminal A that is connected to the AP 1, the communication timing management unit 232 B receives the destination address of each data unit 5132 stored in the payload 513 of the multicast communication frame from the wireless reception unit 21 and sets the destination address of each data unit 513 in the payload 513. When the list described in the arrangement order is received, a unicast communication frame generation instruction is output to the unicast communication frame generation unit 222 at a transmission timing determined according to the description order of the address of the own terminal A in the list. In response to this, the unicast communication frame generation unit 222 generates a unicast communication frame including transmission data, and transmits it from the antenna 25 via the DA conversion unit 223 and the AFE unit 224 (T221, T222). AP1 receives this unicast communication frame and extracts received data from the payload 503 of the communication frame.

  Similarly, in the terminal B connected to AP1, the communication timing management unit 232B sends the destination address of each data unit 5132 stored in the payload 513 of the multicast communication frame from the wireless reception unit 21 to each data in the payload 513. When a list described in the arrangement order of the units 513 is received, a unicast communication frame generation instruction is output to the unicast communication frame generation unit 222 at a transmission timing determined according to the description order of the address of the terminal B in the list. In response to this, the unicast communication frame generation unit 222 generates a unicast communication frame including transmission data, and transmits the unicast communication frame from the antenna 25 via the DA conversion unit 223 and the AFE unit 224 (T321, T322). AP1 receives this unicast communication frame and extracts received data from the payload 503 of the communication frame.

  The third embodiment of the present invention has been described above.

  This embodiment also has the same effect as the second embodiment. Further, according to the present embodiment, the AP 1 can receive a unicast communication frame from each of the plurality of wireless terminals 2 without using a CTS signal frame. Therefore, the overhead can be further reduced as compared with the case where the RTS signal and the CTS signal are exchanged with each of the plurality of wireless terminals 2 prior to the reception of the unicast communication frame.

  In addition, this invention is not limited to said embodiment, Many deformation | transformation are possible within the range of the summary.

  For example, in the above embodiment, the ACK signal transmission after receiving the communication frame (multicast communication frame, unicast communication frame) is omitted in each of the AP1 and the wireless terminal 2, but the present invention is not limited to this. Each of AP1 and wireless terminal 2 may transmit an ACK signal after receiving a communication frame (multicast communication frame, unicast communication frame).

  Moreover, each structure of AP1 mentioned above and the radio | wireless terminal 2 is not restricted to what is implement | achieved by the general computer as shown in FIG. It may be executed in hardware by an integrated logic IC such as ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array), or may be executed in software by a computer such as DSP (Digital Signal Processor). It may be a thing.

FIG. 1 is a schematic diagram of a wireless LAN system to which the first embodiment of the present invention is applied. 2A is a diagram schematically showing a unicast communication frame transmitted from the wireless terminal 2 to the AP 1, and FIG. 2B is a schematic diagram showing a multicast communication frame transmitted from the AP 1 to the wireless terminal 2. 2 (C) is a diagram schematically showing a frame of a CTS signal transmitted from AP1 to the wireless terminal 2, and FIG. 2 (D) is a diagram from the wireless terminal 2 to AP1. It is the figure which represented typically the frame of the registration request signal and registration cancellation request signal which are transmitted. FIG. 3 is a schematic diagram of AP1. FIG. 4 is a flowchart for explaining the operation of the terminal management unit 131. FIG. 5 is a flowchart for explaining the operation of the communication instruction unit 132. FIG. 6 is a schematic diagram of the wireless terminal 2. FIG. 7 is a diagram for explaining the operation of the communication timing management unit 232. FIG. 8 is a diagram for explaining a hardware configuration example of the AP 1 and the wireless terminal 2. FIG. 9 is a diagram for explaining data exchange in the wireless LAN system to which the first embodiment of the present invention is applied. FIG. 10 is a flowchart for explaining the operation of the terminal management unit 131A. FIG. 11 is a diagram schematically showing the destination address of the multicast CTS signal frame. FIG. 12 is a flowchart for explaining the operation of the communication instruction unit 132A. FIG. 13 is a diagram for explaining the operation of the communication timing management unit 232A. FIG. 14 is a diagram for explaining data exchange in a wireless LAN system to which the second embodiment of the present invention is applied. FIG. 15 is a flowchart for explaining the operation of the terminal management unit 131B. FIG. 16 is a flowchart for explaining the operation of the communication instruction unit 132B. FIG. 17 is a diagram for explaining the operation of the communication timing management unit 232B. FIG. 18 is a diagram for explaining data exchange in a wireless LAN system to which the third embodiment of the present invention is applied. FIG. 19 is a diagram for explaining an access control method in DCF when RTS / CTS is not used. FIG. 20 is a diagram for explaining an access control method using DCF when RTS / CTS is used.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... AP, 2 ... Wireless terminal, 3 ... Router, 4 ... Network, 11 ... Wireless reception part, 12 ... Wireless transmission part, 13 ... Communication control part, 14 ... Wired IF part, 15 ... Antenna, 21 ... Wireless reception part , 22 ... wireless transmission unit, 23 ... communication control unit, 24 ... application processing unit

Claims (7)

A wireless communication system having a plurality of wireless terminals and an access point,
The access point is
First transmission means for transmitting data to the plurality of wireless terminals;
First receiving means for receiving data from the plurality of wireless terminals,
The wireless terminal is
Second transmitting means for transmitting data to the access point;
Second receiving means for receiving data from the access point;
The first receiving means includes
For each predetermined time, a multicast CTS (Clear to Send) that defines the data transmission timing of each of the plurality of wireless terminals is transmitted to the first transmission means, and a communication frame is received from each of the plurality of wireless terminals,
The second transmission means includes
When the second receiving means receives the multicast CTS, it transmits a communication frame addressed to the access point according to the transmission timing of the own wireless terminal defined by the multicast CTS,
The duration period included in the multicast CTS is:
A wireless communication system, characterized in that it is a period obtained by multiplying the number of wireless terminals that can be simultaneously connected to the access point by a predetermined period as a period for transmitting data per wireless terminal. The wireless communication system according to claim 1,
The access point is
An address management table in which the bit position in the lower 22 bits of the destination address of the multicast CTS is associated with each address of the wireless terminal belonging to the own access point;
The first transmission means includes
When transmitting the multicast CTS, referring to the address management table, the bit at the position corresponding to the subordinate radio terminal in the lower 22 bits of the destination address of the multicast CTS is set to a predetermined value. Set it up, send it,
The second transmission means includes
In the lower 22 bits of the destination address of the multicast CTS received by the second receiving means, when the bit of the position assigned to the own wireless terminal is set to a predetermined value, the bit position A wireless communication system, wherein a communication frame addressed to the access point is transmitted after a period obtained by multiplying a predetermined period in the order determined by The wireless communication system according to claim 2,
The access point is
When the first receiving means receives from the wireless terminal a registration request including information indicating the position of the bit to be allocated to the wireless terminal in the lower 22 bits of the destination address of the multicast CTS, In correspondence with the address of the wireless terminal, further comprising a registration means for registering information indicating the bit position specified in the registration request in the address management table,
The second receiving means includes
Referring to the lower 22 bits of the destination address of the multicast CTS transmitted from the access point, detecting the position of the bit for which a predetermined value is not set as the position of the bit to be allocated to the own wireless terminal;
The second transmission means includes
When transmitting a registration request, a wireless communication system characterized in that a position of a bit to be allocated to its own wireless terminal detected by the second receiving means is included in the registration request and transmitted to the access point . The wireless communication system according to any one of claims 1 to 3,
The first transmission means includes
For each predetermined time, at a transmission timing different from the multicast CTS, a multicast communication frame in which data to each of the plurality of wireless terminals is multiplexed is transmitted,
The second receiving means includes
A wireless communication system, wherein the wireless communication system receives the multicast communication frame and extracts data addressed to the wireless terminal from the frame. An access point that performs wireless communication with a plurality of wireless terminals,
Transmitting means for transmitting data to the plurality of wireless terminals;
Receiving means for receiving data from the plurality of wireless terminals,
The transmission means includes
A multicast CTS (Clear to Send) that defines the data transmission timing of each of the plurality of wireless terminals is transmitted every predetermined time, and the plurality of wireless terminals are transmitted at a transmission timing different from the multicast CTS every the predetermined time. Send a multicast communication frame with multiplexed data to each terminal,
The receiving means includes
In response to the multicast CTS, a communication frame is received from each of the plurality of wireless terminals,
The duration period included in the multicast CTS is:
An access point characterized in that it is a period obtained by multiplying the number of wireless terminals that can be simultaneously connected to its own access point by a predetermined period as a period for transmitting data per wireless terminal. A wireless terminal that performs wireless communication with an access point,
Transmitting means for transmitting data to the access point;
Receiving means for receiving data from the access point;
The receiving means includes
Receiving a multicast communication frame in which data from the access point to each of the plurality of wireless terminals is multiplexed, extracting data addressed to the own wireless terminal from the frame, and each of the plurality of wireless terminals from the access point Receives multicast CTS (Clear to Send) that defines the data transmission timing,
The transmission means includes
When the receiving means receives the multicast CTS, the communication means addressed to the access point is transmitted according to the transmission timing of the own wireless terminal defined by the multicast CTS,
The duration period included in the multicast CTS is:
A wireless terminal characterized in that it is a period obtained by multiplying the number of wireless terminals that can be simultaneously connected to the access point by a predetermined period as a period for transmitting data per wireless terminal. An access control method for a wireless communication system having a plurality of wireless terminals and an access point,
The access point is
After transmitting a multicast CTS (Clear to Send) that defines the data transmission timing of each of the plurality of wireless terminals at predetermined time intervals, receiving a communication frame from each of the plurality of wireless terminals,
Each of the plurality of wireless terminals is
When the multicast CTS is received, a communication frame addressed to the access point is transmitted according to the transmission timing of the own wireless terminal defined by the multicast CTS,
The duration period included in the multicast CTS is:
An access control method characterized in that it is a period obtained by multiplying the number of wireless terminals that can be simultaneously connected to the access point by a predetermined period as a period for transmitting data per wireless terminal.

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