JP2013219687A - Radio communication device, and radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress control data for STAs to simultaneously transmit.SOLUTION: The radio communication device, used for a radio communication system that performs carrier sense and exchange of a transmission request signal and a transmission permission signal in performing radio communication, includes a control part that transmits a transmission permission signal that specifies a plurality of terminals after carrier sense in a state where no transmission request signal is received.

Description

  The present invention relates to wireless communication technology.

  A CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) method is widely used as an access method when configuring a wireless network, and is also used in IEEE802.11 which is one of the wireless LAN standards. CSMA / CA uses carrier sense prior to transmission, and then uses random backoff to avoid collisions. RTS (Request To Send) is also used to solve the hidden terminal problem. / CTS (Clear To Send, sometimes referred to as transmission permission) may be exchanged, and IEEE802.11 uses it in a form that includes RTS / CTS exchange.

  An example of communication based on the access method used in IEEE802.11 will be described with reference to FIG. In FIG. 14, an AP (Access Point, also referred to as a wireless control device) communicates with two STAs (STAtion, also referred to as a wireless terminal device), and communication is performed from STA1 to AP and immediately thereafter from STA2 to AP. It is the figure shown using the timing chart about an example in the case of being called.

  First, STA1 waits for AP 140 or any STA transmission 1401 to end. After the transmission is completed, the RTS 1403 is transmitted to the AP after waiting for a DIFS (Distributed coordination function InterFrame Space) time 1402. DIFS is a waiting time for DCF (Distributed Coordination Function), which is a time in which a basic time longer than SIFS described later is set and a random backoff time is added. When the RTS 1403 has been successfully received, the AP waits for a SIFS (Short InterFrame Space) time 1404 and transmits a CTS 1405 to the STA 1 assuming that no STA is using radio resources. SIFS is the minimum required time for the AP and STA to perform the next transmission, and is specified so that it is not interrupted by other STAs when sending important packets such as ACK (ACKnoledge), RTS, and CTS. Is the time. The DIFS or the like for starting the DCF access has a longer time than the SIFS, so that important packets can be preferentially transmitted. Subsequently, STA1 receiving CTS 1405 waits for SIFS time 1406 on the assumption that the transmission right has been obtained, and then transmits DATA1 1407 to the AP. The AP that has received DATA1 1407 waits for SIFS time 1408, and transmits ACK1 to STA1. Upon receiving ACK1, STA1 determines that transmission of DATA1 1407 has been completed, and does not perform subsequent transmission.

  STA2 receives the communication between STA1 and AP, and waits for DIFS time 1410 from the timing when all transmissions are completed, and then transmits RTS 1411 to AP. When the RTS 1411 is successfully received, the AP waits for the SIFS time 1412 and transmits CTS 1413 to the STA 2 assuming that no STA is using radio resources. The STA2 that has received the CTS 1413 transmits the DATA2 1415 to the AP after waiting for the SIFS time 1414 assuming that the transmission right has been obtained. The AP that has received DATA2 1415 normally waits for SIFS time 1416 and transmits ACK2 1417 to STA2. Upon receiving ACK2 1417, STA2 determines that transmission has been completed, and does not perform subsequent transmission. Thereafter, when the DIFS time 1418 elapses, another DCF access 1419 becomes possible.

  Through the above procedure, IEEE802.11 avoids packet collision and enables data transmission between a plurality of STAs.

JP 2010-130625 A

IEEE 802.11-2007

  When transmission control is performed using the CSMA / CA method, since random backoff is used, the transmission timing of each STA cannot be known by other STAs. For this reason, it is difficult for multiple STAs to transmit in synchronization when using multiple user-multi input multi output (MU-MIMO) technology to improve radio wave usage efficiency. It was difficult to introduce.

  In addition, JP 2010-130625 has been proposed as a technique for synchronization between a plurality of STAs, but in order to achieve synchronization between a plurality of terminals, it is necessary to exchange a plurality of data corresponding to RTS / CTS, There is a problem in compatibility because there is a problem that the overhead becomes large and data that does not exist in the conventional method needs to be transmitted.

  An object of the present invention is to suppress control data for the STA to perform simultaneous transmission while maintaining compatibility with the conventional system as much as possible.

  According to one aspect of the present invention, a wireless communication apparatus used in a wireless communication system that performs carrier sense and exchange of a transmission request signal and a transmission permission signal when performing wireless communication, and receiving a transmission request signal A wireless communication apparatus is provided that includes a control unit that performs transmission of a transmission permission signal designating a plurality of terminals after carrier sense in a state in which communication is not performed.

  The method for designating the plurality of terminals is preferably a method for designating a group address of the group obtained by dividing the plurality of terminals into a plurality of groups.

  At the time of transmission of the transmission permission signal, a network may be identified, it may be identified as an extended CTS (extend Clear To Send: eCTS), and a note field used for transmitting periodic data may be included. In the note field, the bit corresponding to the U / L bit may be 1.

In the note field, the bit corresponding to the I / G bit may be 1.
The note field may start with 01-00-5e.
The method of designating the plurality of terminals may be a broadcast method.

  A transmission prohibition section for prohibiting data communication of other terminals is notified when the transmission permission signal is transmitted, and the transmission prohibition section is determined based on information on a transmission time notified in advance by a wireless communication device included in the group. It is good to do so.

  At the time of transmission of the transmission permission signal, a transmission prohibited section shorter than a predetermined time that can be determined as extended CTS may be notified.

  The present invention is a wireless communication device used in a wireless communication system that performs carrier sense and exchange of a transmission request signal and a transmission permission signal when performing wireless communication, and does not transmit a transmission request signal The transmission permission signal is transmitted when there is transmission data for the wireless communication device that has transmitted the transmission permission signal when the reception of the transmission permission signal in which the group address including the own wireless communication device is specified is confirmed. The wireless communication device starts transmitting data immediately after receiving the transmission permission signal.

  Here, after receiving the transmission permission signal, transmission of data without confirming transmission of another STA is started. When the reception of the transmission permission signal is confirmed, a note field for identifying a network may be confirmed. The group address may be a broadcast address. When transmitting the data, a pre-assigned preamble pattern may be used.

  Prior to the transmission of the data, the transmission prohibited period notified together with the transmission permission signal is compared with the time required for the data transmission, and the transmission prohibited period is longer than the time required for the data transmission. Sometimes data may be transmitted.

  According to another aspect of the present invention, there is provided a wireless communication method in a wireless communication system that performs carrier sense and exchange of a transmission request signal and a transmission permission signal when performing wireless communication, and receives a transmission request signal. In this state, a wireless communication method is provided that includes a step of transmitting a transmission permission signal designating a plurality of terminals after carrier sense.

  In addition, the present invention is a wireless communication method in a wireless communication system that performs carrier sense and exchange of a transmission request signal and a transmission permission signal when performing wireless communication, and does not transmit a transmission request signal The transmission permission signal is transmitted when there is transmission data for the wireless communication device that has transmitted the transmission permission signal when the reception of the transmission permission signal in which the group address including the own wireless communication device is specified is confirmed. A wireless communication method comprising a step of starting data transmission immediately after receiving the transmission permission signal to the wireless communication apparatus.

  The present invention may be a program for causing a computer to execute the wireless communication method described above, or a computer-readable recording medium for recording the program.

  In addition, the present invention is an integrated circuit used in a wireless communication apparatus used in a wireless communication system that performs carrier sense and exchange of a transmission request signal and a transmission permission signal when performing wireless communication, the transmission request signal This is an integrated circuit characterized by having a control circuit that transmits a transmission permission signal designating a plurality of terminals after carrier sense in a state in which no signal is received.

  According to the present invention, it is possible to suppress control data for the STA to perform simultaneous transmission while maintaining compatibility with the conventional system as much as possible.

6 is a timing chart when STAs (STA1, STA2, and STA3) included in a group having a Group ID of 1 perform transmission simultaneously. It is a figure which shows an example which performed group assignment according to the period of the data transmitted. It is a figure which shows the example of 1 structure of extended CTS. It is a functional block diagram which shows one structural example of AP. It is a functional block diagram which shows one structural example of STA. It is a timing chart which shows an example when AP and STA operate | move. It is a figure which shows the example of 1 structure of a wireless network. It is a flowchart figure when STA connects to a network. It is a flowchart figure of the process which AP receives a connection request from STA. [Fig. 10] Fig. 10 is a flowchart for transmitting periodic data to an STA included in a group assigned by an AP using extended CTS. FIG. 10 is a flowchart diagram in which an STA included in a group assigned by an AP transmits periodic data according to the extended CTS transmitted from the AP. It is a figure which shows the procedure which AP transmits period data to STA in the state in which AP and STA were set. It is a flowchart figure of STA. An example of an AP (Access Point, also referred to as a wireless control device) communicating with two STAs (STAtion, also referred to as a wireless terminal device), where communication is performed from STA1 to AP and immediately thereafter from STA2 to AP It is the figure shown about using the timing chart. It is a figure which shows the structural example of a packet.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
The radio communication system according to the first embodiment of the present invention will be described in detail. In the wireless communication system according to the present embodiment, eight STAs are divided into a plurality of groups, and the number of STAs in one group is configured to be 4 or less. An example will be described in which a plurality of STAs included in each group generate transmission data in a predetermined cycle and simultaneously transmit from the STAs to improve radio wave utilization efficiency.

  The wireless communication system according to the present embodiment is configured by a wireless network including an access point (hereinafter referred to as AP) for managing a network and a plurality of wireless stations (hereinafter referred to as STA) connected to the AP. FIG. 7 is a diagram illustrating a configuration example of such a wireless network. As shown in FIG. 7, the wireless network according to the present embodiment includes one AP 701 and eight STAs 702-1-8 from STA1 to STA8.

  FIG. 4 is a functional block diagram illustrating a configuration example of the AP. As shown in FIG. 4, the AP is attached to the AP housing 401, the antenna 401 composed of four antennas attached to the housing 401 for transmitting and receiving RF signals, and the connection destination of the antenna portion 402. Switch (SW) unit 403 that switches between receiving unit 404 and transmitting unit 410 according to an instruction from unit 407, converts the received RF signal into a baseband signal, performs carrier sense on the baseband signal, and results Is received by the control unit 407, and a receiving unit 404 that inputs a baseband signal to the demodulating unit 405 is provided. Demodulation section 405 demodulates the input baseband signal based on information preset from control section 407. When MIMO demodulation is set, the preamble pattern added to the head of the received signal is also set at the same time, and the transfer function between multiple transmit antennas and AP antenna unit 402 is estimated based on the set preamble pattern. And demodulate. The preamble pattern and other transmission signals are based on the IEEE802.11n standard, and the MIMO preamble pattern (HT-LTF) used in the IEEE802.11n standard is used. In this embodiment, the MIMO demodulation method is not particularly defined, but various methods such as a ZF (zero forcing) method, an MMSE (Minimum Mean Square Error) method, and an MLD (Maximum Likelihood Detection) method can be used. In the present embodiment, it is assumed that signals of up to 4 streams (up to 4 STAs when STA is 1 antenna) can be demodulated using 4 antennas. Since a preamble pattern similar to that in the IEEE802.11n MIMO transmission is used, transfer functions from four different STAs at maximum can be estimated. The estimated transfer function is used for demodulation and input to the control unit 407. The demodulation result is input to the packet identification unit 406. When MIMO demodulation is performed, the demodulated streams are separately input to the packet identification unit 406.

  Here, a configuration example of a packet used in the present embodiment will be described with reference to FIG. The packet uses a configuration conforming to the IEEE802.11 system. First, a packet header 1501 is arranged, followed by a payload part 1504 including a data body, and finally an FCS part 1505 for error detection is arranged. The packet header 1501 is further divided into several fields. First, a control field 1502 is arranged, followed by other fields 1503. Depending on the contents of the control field 1502, the types of fields included in the other fields 1503 may change. The payload portion 1504 may not be included depending on the contents of the packet header 1501. The payload portion 1504 may include a predetermined value depending on the type of packet header, or may include a packet used in an upper layer as it is. When the payload unit 1504 includes a packet used in the upper layer, the data length is included in the packet used in the upper layer. FCS section 1505 includes CRC of packet header 1501 and payload section 1504, calculates CRC of packet header 1501 and payload section 1504 at the time of reception, and compares with FCS section 1505 to determine whether there is an error in the received packet. Can do.

  Returning to FIG. 4, the packet identification unit 406 detects the packet header 1502 from the signal demodulated by the demodulation unit 405, acquires the payload unit 1504 and further the FCS unit 1505 based on the contents of the packet header 1502, and the packet header 1502 and the payload unit The CRC including 1504 is calculated, and if the CRC is different from the FCS unit 1505, it is a reception error, and if the CRC matches the FCS unit 1505, the packet header unit 1501 and the payload unit 1504 are regarded as successful reception. Send to. When reception of a packet including communication data is successful, the payload portion 1504 is also output to the outside as received data.

  The control unit 407 is a block that controls and manages the AP and the entire network. When a signal is to be received, the switch unit 403, the reception unit 404, and the demodulation unit 405 are set to prepare for signal reception. When transmission data is input or when transmission data for network management is generated in the control unit 407, the packet generation unit 408, the modulation unit 409, the transmission unit 410, and the switch unit 403 are set to transmit data. I do. Network management will be described later.

  When the transmission data is input from the outside, the packet generation unit 408 notifies the control unit 409 to that effect, and then adds a packet header 1502 in the format specified by the control unit 407, and transmits the transmission data to the payload unit 1504. And the CRC of the header part 1502 and the payload part 1504 are calculated, and then the FCS part 1505 is added. When the transmission data is long, fragmentation may be instructed by the control unit 407. In this case, the transmission data is classified according to the instructed content, and a packet header 1502 and an FCS unit 1505 are added to each. The transmission packet to which the packet header 1502 and the FCS unit 1505 are added is input to the modulation unit 409 as specified by the control unit 407. It is assumed that the modulation unit 409 can simultaneously generate a maximum of four pieces of modulation data according to instructions from the control unit 407. Further, it is assumed that the modulation unit 409 can generate a preamble of a format specified by the control unit 407 prior to performing modulation on the input data according to an instruction from the control unit 407. Modulation section 409 modulates the input data by the modulation method instructed by control section 407 after transmitting the preamble, and transmits it to transmission section 410. The transmission unit 410 is a block that converts the modulation data input from the modulation unit 409 into a baseband signal, converts the baseband signal into an RF signal in response to an instruction from the control unit 407, and outputs the RF signal. Up to 4 RF signals can be output. The output from the transmission unit 410 is transmitted from the antenna unit 402 via the switch unit 403.

  Next, a configuration example of the STA is shown in FIG. The configuration of the STA is basically the same as that of the AP, but the number of antennas in the antenna unit is 1. The STA includes a housing 501 of the STA, an antenna unit 502 that is attached to the outside of the housing 501 and includes one antenna for transmitting and receiving an RF signal, and a receiving unit that receives an antenna connection destination according to an instruction from the control unit 507 Switch (SW) unit 503 that switches between 504 and transmission unit 510, converts the received RF signal into a baseband signal, performs carrier sense on the baseband signal, and notifies the control unit 507 of the result, The demodulator 505 includes a receiver 504 that inputs a baseband signal. Further, it includes a demodulation unit 505, a packet identification unit 506, a control unit 507, a packet generation unit 508, a modulation unit 509, and a transmission unit 510.

  Demodulation section 505 demodulates the input baseband signal based on information preset from control section 507. It is assumed that the transfer function between the AP transmission antenna and the STA antenna 502 is estimated by the preamble added to the head of the received signal, and demodulated. The estimated transfer function is used for demodulation and input to the control unit 507. The demodulation result is input to the packet identification unit 506.

  The packet identification unit 506 detects the packet header 1502 from the signal demodulated by the demodulation unit 507, acquires the payload unit 1504 and further the FCS unit 1505 according to the contents of the packet header 1502, and includes the packet header 1502 and the payload unit 1504 The CRC is calculated, and if the CRC is different from the FCS unit 1505, it is a reception error. If the CRC matches the FCS unit 1505, the packet header unit 1501 and the payload unit 1504 are transmitted to the control unit 507 as reception success. When the packet including the communication data is successfully received, the payload portion is output to the outside as received data.

  The control unit 507 is a block that controls and manages the STA and the entire network. When a signal is to be received, the control unit 507 sets a switch unit 503, a reception unit 504, and a demodulation unit 505, and prepares for reception of the signal. When data is input or when transmission data for network management is generated in the control unit 507, the packet generation unit 508, the modulation unit 509, the transmission unit 510, and the switch unit 503 are set to transmit data. Do. Network management will be described later.

  When the transmission data is input from the outside, the packet generation unit 508 notifies the control unit 509 to that effect, and then adds a packet header 1502 in a format specified by the control unit 509 and sends the transmission data to the payload unit 1504. After calculating the CRC of the header part 1502 and the payload part 1504, the FCS part 1505 is added. If the transmission data is long, fragmentation may be instructed by the control unit 509. In this case, the transmission data is classified according to the instructed content, and a packet header 1502 and an FCS unit 1505 are added to each. The transmission packet to which the packet header 1502 and the FCS unit 1505 are added is input to the modulation unit 509 as specified by the control unit 507. It is assumed that the modulation unit 509 can generate a preamble of a format specified by the control unit 507 prior to performing modulation on the input data according to an instruction from the control unit 507. Modulation section 509 modulates the input data by the modulation method instructed by control section 507 after transmitting the preamble, and transmits it to transmission section 510. The transmission unit 510 is a block that uses the modulation data input from the modulation unit 509 as a baseband signal, converts the baseband signal into an RF signal, amplifies it, and outputs it in response to an instruction from the control unit 507. An output from the transmission unit 510 is transmitted from the antenna unit 502 via the switch unit 503.

  First, the procedure for configuring the STA group will be described. In the present embodiment, the network management uses a method according to the IEEE 802.11 standard, and the procedure necessary for the embodiment of the present invention will be described in more detail. The group structure is assumed to be grouped whenever the STA is connected to the network.

  FIG. 8 is a flowchart when the STA connects to the network. In step S801, a connection request is made to the connection target AP. This corresponds to an association request in the IEEE802.11 standard. In step S802, connection completion is received from the STA. This corresponds to receiving an association response in the IEEE802.11 standard. In step S803, it is determined whether the connection request has been made normally. If not, the process returns to step S801 to make a connection request again. If the connection request is normally received, the process proceeds to step S804, and STA transmits to the AP that periodic data is generated. At this time, the generation period of the periodic data, the amount of information generated at a time, and the modulation method at the time of transmitting the periodic data are transmitted. It is assumed that data is transmitted in the same manner when there are multiple types of data. In step S805, a group ID, an index (also referred to as an intra-group number or simply a number), and a signature (also referred to as a note) are received from the AP. The Group ID, Index, and Signature are used to identify an extended CTS (extend Clear To Send: eCTS), which will be described later, and transmit periodic data. When assigned to multiple groups, multiple Group IDs and Indexes are notified. The above is the connection process on the STA side.

  FIG. 9 is a flowchart of processing in which the AP receives a connection request from the STA. In step S901, a connection request is received from the STA. The connection request corresponds to an IEEE 802.11 association request. In step S902, the STA that has transmitted the connection request is registered in the network, and in step S903, connection completion is transmitted to the STA that has transmitted the connection request. This corresponds to an IEEE802.11 association response. Subsequently, in step S904, it is determined whether information related to generation of periodic data is transmitted from the STA that transmitted the connection request. If there is no transmission after waiting for a certain time, it is determined that no periodic data is generated from the STA, and the connection request processing is terminated. When information related to the generation of periodic data is transmitted from the STA within a certain time, the process proceeds to step S905 to perform group assignment for the STA.

  Various methods can be considered for group assignment. Considering the radio wave utilization efficiency, it is desirable that the number of STAs close to the allowable number of STAs transmit on the occasion of allowing simultaneous transmission of STAs. In addition, it is desirable that transmission times when transmitting simultaneously are as equal as possible. Considering these points, it is desirable that the AP assigns a group each time an STA that notifies generation of periodic data is connected to the network.

  FIG. 2 is a diagram illustrating an example in which group assignment is performed in accordance with the cycle of data to be transmitted. A numerical value 0 in FIG. 2 indicates that the corresponding STA is not included in the group, and a numerical value other than 0 indicates the intra-group Index of the corresponding STA. As a result, STA1, STA2, and STA3 are included in Group 1, STA4 and STA5 are included in Group 2, STA6, STA7, and STA8 are included in Group 3, and STA1, STA4, STA5, and STA8 are included in Group 44. Indicates that an Index has been assigned. As a result of group assignment, STAs included in each group generate data in the same cycle.

  The result of group assignment by the method as described above is sent to the STA that sent the connection request in step S906, and signature is also sent at the same time. The signature is used for transmission of the extended CTS, and is used for distinguishing from the extended CTS transmitted by other APs by transmitting together with the group ID of a group that allows simultaneous transmission. The extended CTS will be described later. Subsequently, the newly configured group assignment result is transmitted to the STA connected to the network other than the STA that transmitted the connection request in step S907, and the connection request processing is terminated.

  Regarding the connection request processing described above, both transmission from the AP side and transmission from the STA side are performed by a method based on IEEE802.11 DCF.

  Next, a flowchart for transmitting period data to the STA included in the group assigned by the AP using the extended CTS will be described with reference to FIG.

  As shown in FIG. 10, the AP determines whether or not it is time for transmission data to occur in the STA in the group assigned in step S1001, and if transmission data does not occur, the AP returns to step S1001 again, and the STA in which transmission data is generated. If there is, the process proceeds to step S1002. In step S1002, a group ID of a group including an STA in which transmission data is generated is specified, and an extended CTS in which a NAV (to be described later) matching the STA having the longest transmission time is set among the STAs included in the group is transmitted. At this time, in order to confirm that no other STA is transmitting, it waits for DIFS time before transmitting.

  The extended CTS uses the format shown in FIG. 3A in order to maintain compatibility with the CTS (Clear To Send) packet used in IEEE802.11. A frame control field 301 indicating a CTS packet at the beginning of the packet, and then a NAV (Network Allocation Vector, also referred to as a transmission-prohibited interval) that is set so that other STAs do not transmit when data is transmitted by STAs included in the specified group ) Including a value field, a signature field 311 and a group ID field 306 are placed in a field 303 where an RA (Receiving station Address) is placed in IEEE802.11, and finally a group ID field from the frame control field. FCS field 307 including up to CRC is arranged.

  The signature is preferably a bit string that can be distinguished from other APs. It is desirable that the U / L bit (Universal / Local bit) of the IEEE MAC address is 1 so that it can be distinguished from the MAC addresses assigned to the AP and STA. Also, it is desirable that the I / G bit (Individual / Group bit) of the IEEE MAC address is 1 to indicate that it is addressed to a plurality of STAs. For these reasons, the signature can use a 5-octet bit string whose first octet starts with “xxxxxx11” (x is an arbitrary bit). Bits other than U / L bits and I / G bits may be any bit string as long as they can be distinguished from other APs. Therefore, a method of using a part of the MAC address of the AP as it is may be used.

  As a method for assigning a signature, a method according to an IEEE multicast address may be used. An example of this case is shown in FIG. In this example, the bit sequence 01-00-5e of the multicast MAC address that specifies IEEE from the first octet to the third octet of the signature is used, followed by the PAD field 305 of 2 octets, and then the Group An ID field 306 is arranged. In order to distinguish from the extended CTS transmitted from other APs, it is desirable to use an AP-specific bit string in the PAD field. That is, the PAD field can have a meaning as a note. As an example, a method using the lower 16 bits of the AP MAC address, a method using a 16-bit hash value of the AP MAC address (the hash function to be used is arbitrary), or the like can be used.

  The NAV set when transmitting an extended CTS is the largest amount of information generated at one time that the STA included in the target group has notified when a connection request is made, and the transmission time determined from the modulation method at the time of periodic data transmission. Assume that a value is set by adding the SIFS time and the time required to transmit one ACK to the long transmission time. As a result, it is possible to prevent STAs not included in the group from starting data transmission by DCF at the time of transmission of the STA in the group transmitted following the extended CTS. An ACK may be transmitted multiple times from the AP, but since the ACK is transmitted at SIFS time intervals, other STAs cannot start transmission by DCF during that time. The procedure for transmitting multiple ACKs will be described later.

  Subsequently, in step S1003, a signal transmitted by a plurality of STAs included in the group with the Group ID designated when transmitting the extended CTS is received. Each STA waits for the SIFS time after receiving the extended CTS and transmits a signal at the same timing, so the AP can perform MIMO demodulation.

  In step S1004, a packet having the format shown in FIG. 15 is detected from the signal after MIMO demodulation. If no packet is detected, the process returns to step S1001. When one or more packets are detected, in step S1005, CRC is calculated from the packet header 1501 and payload part 1504 of the detected packet and compared with the FCS part 1505 to detect whether the detected packet is correct. ACK is sent to the STA that sent the packet if it is correct, and NACK is sent if it is not correct. At this time, SIFS time is waited from the timing when transmission of all STAs is completed, and then ACK / NACK is transmitted at SIFS intervals. Subsequently, if at least one NACK has been transmitted in step S1006, the process returns to step S1002 to transmit the extended CTS again to perform retransmission to the STA, and when all ACKs have been transmitted, all data has been successfully received. As a result, the process returns to step S1001.

  Next, a flow in which the STA included in the group assigned by the AP transmits period data according to the extended CTS transmitted from the AP will be described with reference to FIG.

  The STA determines whether or not the extended CTS including the Group ID assigned to the STA in step S1101 has been received. If the extended CTS including the assigned Group ID cannot be received, the STA returns to step S1101 and is assigned. If the extended CTS including the Group ID is received, the process proceeds to step S1102. In step S1102, it is determined whether there is periodic data to be transmitted to the AP in its own STA. If there is no data to be transmitted, the process returns to step S1101, and if there is data to be transmitted, the process proceeds to step S1103. In step S1103, data is transmitted to the AP. At this time, after reception of the extended CTS transmitted from the AP is completed, data is transmitted after waiting for CIFS time. Also, the preamble pattern used is the preamble pattern (HT-LTF) used during IEEE802.11n MIMO transmission, and the preamble pattern used by the spatial stream of the Index value in the group assigned to the own STA. Use to send. Since different index values are assigned to all STAs in the group, all STAs that transmit simultaneously use different preamble patterns. Subsequently, in step S1104, it is determined whether or not ACK is transmitted from the AP. When ACK is received, the process proceeds to step S1106, and when ACK cannot be received, the process proceeds to step S1105. In step S1105, it is determined whether or not the periodic data to be transmitted is too old to be valid. If it is not valid, the process proceeds to step S1106. If it is valid, the process returns to step S1101 and waits for the extended CTS to be transmitted from the AP. In step S1106, the periodic data to be transmitted is discarded, and then the process returns to step S1101 to wait for the extended CTS to be transmitted.

  By performing the above flow between the AP and each STA, it becomes possible to transmit periodic data from a plurality of STAs at the same time and perform MIMO demodulation at the AP, thereby improving radio wave use efficiency compared to the conventional method. As an example of this flow, FIG. 1 shows a timing chart in the case where STAs (STA1, STA2, and STA3) included in a group with Group ID 1 perform transmission simultaneously. First, reference numeral 101 indicates that transmission is being performed from the AP or any STA. After waiting for the DIFS time 102 from the end of transmission, the extended CTS 103 is transmitted from the AP. Waiting for SIFS time 104 from the timing when transmission of the extended CTS 103 is completed, STA1 to DATA1 105, STA2 to DATA2 106, and STA3 to DATA3 107 are transmitted. The AP transmits ACK1 109 to STA1 after the reception of DATA2 106 having the longest transmission time among the data transmitted from the STA group, waits for SIFS time 108, and SIFS from the transmission end timing of ACK1 109. ACK2 111 is transmitted to STA2 after waiting for time 110, and ACK3 113 is transmitted to STA3 after SIFS time 112 from the timing when transmission of ACK2 111 is completed, and data transmission from the STA group is completed. Thereafter, another data transmission starts from 115 after waiting for the DIFS time 114.

  In this embodiment, SIFS is inserted between ACKs when continuously transmitting ACKs to a plurality of STAs. However, only ACKs may be continuously transmitted without inserting SIFS.

  As described above, a plurality of STAs connected to the AP are divided into several groups including a plurality of terminals, and a plurality of STAs included in each group generate transmission data in a predetermined cycle, and an extended CTS By simultaneously transmitting data according to the frequency, the use efficiency of radio waves is improved. At this time, only the transmission of the extended CTS is necessary for synchronization, and the extended CTS can be realized by changing part of the data used in the conventional method. Therefore, the compatibility with the conventional method is high and the introduction is easy. Become.

(Second Embodiment)
In the first embodiment, the STA group is divided into a plurality of groups, and the number of STAs in the group is managed so as not to exceed the maximum number of streams that can be demodulated by the AP. In the second embodiment, when the frequency at which the STA generates periodic data is low and the possibility that the periodic data is transmitted at the same time is low, simultaneous transmission from the STA is performed with less overhead by opportunistic control. An example of improving the utilization efficiency will be shown.

  The basic configuration is the same as that of the first embodiment, and is applied to a wireless network including one AP 701 and a plurality of STAs 702 as shown in FIG. As with the first embodiment, the AP device configuration shown in FIG. 4 can be applied, and the STA configuration shown in FIG. 5 can be applied.

  When the probability that each STA generates periodic data per unit time is α, the time period when the AP transmits the extended CTS is β, and the number of STAs accommodated in the AP is n, when the AP transmits the extended CTS The number of STAs (expected value) transmitted at the same time is αβn. Β is controlled so that this number does not exceed the number of streams that can be demodulated simultaneously. For example, in the AP configuration shown in FIG. 4, MIMO demodulation of a maximum of 4 streams is possible, so that β is set so that the value of αβn is 3 or less with a margin. In order to distinguish between periodic data and data used in normal communication (for example, assuming that the data transmitted at once is large in general TCP / IP communication such as HTTP), the size of the periodic data is Limit to a sufficiently short size (eg 500 octets or less).

  Furthermore, a preamble pattern used when responding to the extended CTS is assigned to the STA accommodated in the AP. In the case of the STA configuration shown in FIG. 5, it is possible to output four types of preamble patterns defined in IEEE802.11n, assuming that each STA generates periodic data uniformly, It is desirable that the preamble pattern allocation is not biased among STAs accommodated in the AP. As an example of the allocation method, the AP receives a connection request from the STA, and each time a connection completion is transmitted to the STA, a different preamble pattern is sequentially allocated, or connection completion (association response) is transmitted by IEEE802.11. A method for selecting a preamble pattern based on 2-bit information using an AID (Association ID) included in the information sent to the STA and applying a hash function (optional) to the AID, the MAC address of the STA For example, a selection method based on 2-bit length information to which a hash function (arbitrary) is applied can be used. Except when transmitting to the extended CTS, transmission is performed using a preamble pattern used when one IEEE802.11n antenna is used. STA shall transmit with probability of initial value 1 when extended CTS is transmitted from AP when there is data to transmit. Hereinafter, this probability is referred to as a transmission probability.

  A procedure for the AP to transmit period data to the STA in a state where the AP and STA are set as described above will be described with reference to the drawings.

  First, the AP flow will be described with reference to FIG. In step S1201, it is determined whether it is time to transmit the extended CTS. If it is not time to transmit, the process returns to step S1201, and if it is time to transmit, the process proceeds to step S1202. In step S1202, the NAV set in the extended CTS is set for short period data transmission. Here, the total of the time required for the STA to transmit 500 octets of data and the time required to transmit ACK for the data is set. In step S1203, after confirming that no STA is transmitting, the extended CTS is transmitted after waiting for the DIFS time. At this time, the group ID to be specified is set to a value that means broadcast. For example, a method of setting ff having all bits of 1 as a broadcast is conceivable. If the Group ID is not used, it is possible to specify the value ffffff in which all bits that mean broadcast are 1 in the IEEE MAC address as the meaning of the extended CTS in the field that specifies the signature and group ID of the extended CTS. It is done. In step S1204, a signal transmitted from the STA is received. At this time, MIMO demodulation is performed assuming that all preamble patterns are used. In step S1205, the CRC of the demodulated signal header part and payload part is calculated, and error detection is performed by comparing with the FCS part. Subsequently, in step S1206, ACKs are sequentially transmitted to the STA that has received the packet normally without error. Subsequently, in step S1207, it is determined whether an error is included in the received packet. If no error is included, the process proceeds to step S1208, and a reception error occurs due to a preamble pattern colliding at the time of transmission. In the case, the process proceeds to step S1209. In step S1208, if the transmission cycle of the extended CTS is different from the initial value, the cycle is returned to the original, and the process returns to step S1201. In step S1209, the transmission period of the extended CTS is shortened, and the process returns to step S1201. It is difficult to determine the optimum value because it depends on factors such as the number of STAs accommodated in the AP and the transmission probability of STAs, but the number of STAs to be retransmitted increases due to the occurrence of errors and congestion occurs. Since the purpose is to respond to what is done, it is effective if the cycle is shortened. As an example, a method of halving the cycle every time an error occurs can be considered.

  Next, the STA flow will be described with reference to FIG. First, in step S1301, the process waits for the extended CTS to be transmitted from the AP. When the extended CTS is not transmitted, the process returns to step S1301, and when the extended CTS is received, the process proceeds to step S1302. When ffffffff is used for the signature and group ID fields as an extended CTS, the format is the same as that of a normal broadcast-addressed CTS. However, if the NAV setting is a short value, it can be determined as an extended CTS. In step S1302, it is determined whether there is periodic data to be transmitted to the local STA. If there is no transmission data, the process returns to step S1301, and if there is transmission data, the process proceeds to step S1303. In step S1303, if a uniform random number of 0 to 1 is subtracted and the random number is larger than the set transmission probability (N), the process returns to step S1301, and if it is less than the set transmission probability (Y) Advances to step S1304.

  In step S1304, after the extended CTS is received, only SIFS is waited, and data is transmitted using the assigned preamble pattern. In step S1305, it is determined whether an ACK is transmitted from the AP to the own STA. If an ACK is received, the process proceeds to step S1306. If an ACK is not received, the process proceeds to step S1307. In step S1306, the transmission data is discarded, the transmission probability is returned to 1, and the process returns to step S1301. In step S1307, the transmission data is left unchanged, the value of the transmission probability is decreased, and the process returns to step S1301. As an example, a method of halving the transmission probability is conceivable. The transmission probability is reduced because the STA assigned with the same preamble pattern that causes the same communication error generates transmission data at the same time and copes with a packet collision. This is to avoid a collision of newly transmitted packets and to succeed in sequential packet transmission. When an error occurs, the AP transmits the extended CTS at a shorter cycle, so even if the transmission opportunity is temporarily reduced, data transmission is not completely impossible.

  An example when the AP and STA operate in the above procedure will be described with reference to the timing chart of FIG. This shows a case where STA1 and STA3 transmit extended CTS from the AP when periodic data for the AP is generated, and normal long transmission data is generated in STA2 almost simultaneously. The part indicated by the first reference numeral 601 means that AP or any STA is transmitting data. After the transmission indicated by reference numeral 601 is completed, the AP waits for the DIFS time 602, confirms that there is no STA being transmitted, and then transmits the extended CTS 603. The NAV 604 set in the extended CTS 603 is set to the short value described above. After receiving the extended CTS 603, the STA1 waits for the SIFS time 605, and then confirms that the value obtained by adding the length of the DATA1 605 to be transmitted, the length of the ACK to be returned, and the SIFS time is shorter than the NAV, and transmits the DATA1 605. Similarly, STA3 transmits DATA3 608. STA2 tries to send DATA2 607 because extended CTS 603 is addressed to the broadcast. However, if the length of DATA2 607, the time required for ACK return, and the SIFS time are added, the NAV will be exceeded. Is not sent. After receiving DATA1 605 and DATA3 608, the AP waits for SIFS time 609, then sends ACK1 610 to STA1, waits for SIFS time 611 after sending, sends ACK3 612 to STA3, and a series of procedures Exit. After the last transmission of ACK3 612, after waiting for DIFS time 613, transmission 614 by another DCF may be started.

  By performing the flow as described above between the AP and the STA, it is possible to simultaneously transmit periodic data from a plurality of STAs using the extended CTS, and to perform MIMO demodulation at the AP, thereby improving radio wave utilization efficiency. In addition, since the extended CTS is a format that is highly compatible with the conventional IEEE802.11 standard, it can be easily introduced into an existing system.

  In the above-described embodiment, the configuration and the like illustrated in the accompanying drawings are not limited to these, and can be changed as appropriate within the scope of the effects of the present invention. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  Each component of the present invention can be arbitrarily selected, and an invention having a selected configuration is also included in the present invention.

  In addition, a program for realizing the functions described in the present embodiment is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed to execute processing of each unit. May be performed. The “computer system” here includes an OS and hardware such as peripheral devices.

  Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.

  The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case, and a program that holds a program for a certain period of time are also included. The program may be a program for realizing a part of the above-described functions, or may be a program that can realize the above-described functions in combination with a program already recorded in a computer system. At least a part of the functions may be realized by hardware such as an integrated circuit.

  The present invention is applicable to a wireless communication device.

401 ... AP housing, 402 ... antenna unit, 403 ... switch (SW) unit, 404 ... reception unit, 405 ... demodulation unit, 406 ... packet identification unit, 407 ... control unit, 408 ... packet generation unit, 409 ... modulation Unit, 410 ... transmission unit, 501 ... STA housing, 502 ... antenna unit, 503 ... switch (SW) unit, 504 ... reception unit, 505 ... demodulation unit, 506 ... packet identification unit, 507 ... control unit, 508 ... Packet generator, 509 ... modulator, 510 ... transmitter.

Claims (18)

A wireless communication device used for a wireless communication system that performs carrier sense and exchange of a transmission request signal and a transmission permission signal when performing wireless communication,
A wireless communication apparatus comprising: a control unit configured to transmit a transmission permission signal designating a plurality of terminals after carrier sense in a state where a transmission request signal is not received.   The radio communication apparatus according to claim 1, wherein the method of designating the plurality of terminals is a method of designating a group address of the group obtained by dividing the plurality of terminals into a plurality of groups.   The transmission permission signal includes a signature field that is used to identify a network, identify an extended CTS (extend Clear To Send: eCTS), and transmit periodic data. Or the radio | wireless communication apparatus of 2.   The wireless communication apparatus according to claim 3, wherein the note field has a bit corresponding to a U / L bit of 1.   The radio communication apparatus according to claim 3, wherein the note field has a bit corresponding to an I / G bit of 1.   The wireless communication apparatus according to claim 3, wherein the note field starts with 01-00-5e.   The wireless communication apparatus according to claim 1, wherein the method of specifying the plurality of terminals is a broadcast method.   A transmission prohibition section for prohibiting data communication of other terminals is notified when the transmission permission signal is transmitted, and the transmission prohibition section is determined based on information on a transmission time notified in advance by a wireless communication device included in the group. The wireless communication apparatus according to claim 2.   1. A wireless communication apparatus according to claim 1, wherein at the time of transmission of the transmission permission signal, the wireless communication apparatus notifies a transmission prohibited section shorter than a predetermined time that can be determined as an extended CTS. A wireless communication device used for a wireless communication system that performs carrier sense and exchange of a transmission request signal and a transmission permission signal when performing wireless communication,
When transmission of a transmission request signal is confirmed and reception of a transmission permission signal in which a group address including its own wireless communication device is specified is confirmed, transmission data to the wireless communication device that has transmitted the transmission permission signal is not received. In some cases, the wireless communication apparatus starts transmitting data immediately after receiving the transmission permission signal to the wireless communication apparatus that has transmitted the transmission permission signal.   11. The wireless communication apparatus according to claim 10, wherein when confirming reception of the transmission permission signal, a note field for identifying a network is confirmed.   The wireless communication apparatus according to claim 10, wherein the group address is a broadcast address.   The wireless communication apparatus according to any one of claims 10 to 12, wherein a preamble pattern assigned in advance is used when transmitting the data. Prior to the transmission of the data, the transmission prohibition interval notified with the transmission permission signal is compared with the time required for the transmission of the data,
The wireless communication apparatus according to any one of claims 10 to 13, wherein data transmission is performed when the transmission prohibited section is longer than a time required for the data transmission. In performing wireless communication, a wireless communication method in a wireless communication system that performs carrier sense and exchange of a transmission request signal and a transmission permission signal,
A wireless communication method comprising a step of transmitting a transmission permission signal designating a plurality of terminals after carrier sense in a state where a transmission request signal is not received. In performing wireless communication, a wireless communication method in a wireless communication system that performs carrier sense and exchange of a transmission request signal and a transmission permission signal,
When transmission of a transmission request signal is confirmed and reception of a transmission permission signal in which a group address including its own wireless communication device is specified is confirmed, transmission data to the wireless communication device that has transmitted the transmission permission signal is not received. In some cases, the wireless communication method includes a step of starting data transmission immediately after receiving the transmission permission signal to the wireless communication apparatus that has transmitted the transmission permission signal.   A program for causing a computer to execute the wireless communication method according to claim 15 or 16. In performing wireless communication, an integrated circuit used in a wireless communication device used in a wireless communication system that performs carrier sense and exchange of a transmission request signal and a transmission permission signal,
An integrated circuit comprising: a control circuit that transmits a transmission permission signal designating a plurality of terminals after carrier sense in a state where a transmission request signal is not received.

Images