JP5559753B2 - Base station apparatus and radio communication method - Google Patents

Description

  The present invention relates to wireless communication technology.

  In recent years, the IEEE802.11g standard, the IEEE802.11a standard, and the like are remarkable as high-speed wireless access systems using the 2.4 GHz band or the 5 GHz band. These systems use an Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme, which is a technique for stabilizing characteristics in a multipath fading environment, and realize a physical layer transmission rate of 54 Mbps at the maximum. (For example, refer nonpatent literature 1).

  However, the transmission rate here is the transmission rate on the physical layer, and the transmission efficiency in the MAC (Medium Access Control) layer is actually about 50 to 70%, so the upper limit of the actual throughput is 30 Mbps. If the number of communication stations that intend to transmit information increases, this characteristic further deteriorates. On the other hand, in a wired LAN (Local Area Network), a 100 Mbps high-speed line has been introduced due to the widespread use of FTTH (Fiber to the home) using an optical fiber in each home, including the Ethernet (registered trademark) 100Base-T interface. Provision is widespread, and further increase in transmission speed is demanded in wireless LAN.

  As a technique for this purpose, a MIMO (Multiple Input Multiple Output) technique has been introduced as a spatial multiplexing transmission technique in the IEEE 802.11n standard. Furthermore, in IEEE802.11ac, a multiuser MIMO (MU-MIMO) transmission method to which space division multiple access (SDMA) is applied has been studied (for example, see Non-Patent Document 2).

  In the wireless LAN system compliant with IEEE802.11, each communication station adopts an access control procedure based on CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance), and each communication station detects a signal collision with another communication station. To avoid. A communication station that has made a transmission request first monitors the state of the wireless medium for a predetermined sensing period (DIFS: Distributed Inter-Frame Space), and if there is no transmission signal from another communication station during this period, a random back Do off. The communication station continues to monitor the wireless medium during the random back-off period, but if there is no transmission signal from another communication station during this period, the exclusive channel use transmission right (TXOP) over a predetermined period : Transmission Opportunity), frames can be transmitted continuously within the TXOP period.

  As a method for solving the hidden terminal problem in wireless communication, “virtual carrier sense” can be cited. Specifically, if the communication station describes Duration (sustained use time) information for reserving a wireless medium in a received frame not addressed to the local station, the communication station is in the medium for the period corresponding to the Duration information. Is used (virtual carrier sense), and this period is set as a transmission suspension period (NAV: Network Allocation Vector). This guarantees exclusive use of the channel in TXOP.

  In IEEE802.11n, an RD (Reverse Direction) protocol is introduced in order to further improve the efficiency of data transmission in TXOP (see, for example, Non-Patent Document 3). In the conventional technique, only one-way data transmission is performed in which the communication station that has acquired the TXOP transmits a data frame and receives a reply frame in response thereto. On the other hand, in the RD protocol, the communication station that acquired the TXOP permits “RDG (RD Grant) = 1” in a specific field in the MAC frame when transmitting data, that is, permits data transmission in the reverse direction. By transmitting information indicating that (reverse direction permission information), the data receiving station transmits a data frame in the reverse direction destined to the communication station (TXOP holder) that acquired the TXOP within the same TXOP. Can do.

  FIG. 20 is a time chart showing an example of frame transmission timing when the conventional RD protocol in IEEE 802.11n is applied and data is transmitted and received in both directions. In the illustrated example, AP (Access Point: base station) and WT (Wireless Terminal: wireless terminal) 1 to WT 3 transmit frames. In the illustrated example, data is transmitted from the AP to the WT 1 and data is transmitted from the WT 1 to the AP. Thereafter, data is transmitted from the AP to the WT 3, and data is transmitted from the WT 3 to the AP. Thereafter, data is transmitted from the WT 3 to the AP. Thereafter, an example in which data is transmitted from the AP to the WT 3 is shown.

  First, the AP transmits data with the destination set to WT1 and RDG = 1, notifying that transmission by RD is possible. At this time, a response by BA (Block Ack) can be requested by setting BAR (Block Ack Request). The WT 1 that has received the data knows that the data can be transmitted to the AP because the RDG in the received data is 1, and there is data to be transmitted by RD by returning the BA with RDG = 1. Let them know. And WT1 transmits data addressed to AP after SIFS. Note that WT1 sets the RDG in the data to be transmitted to 0, thereby notifying the TXOP holder (AP) that it is the last frame to be transmitted. With this, AP returns BA to WT1.

  Next, the AP transmits data in which the destination is WT3 and RDG = 1. The WT 3 that has received the data transmits a piggyback packet that combines the BA and the data. Thus, it is also possible to transmit data together with the BA by RD. Note that the RDG of the piggyback packet is 0 because it is the last frame to be transmitted. The AP that has received the piggyback packet with RDG = 0 transmits the BA with the destination set to WT3 and RDG = 1 in order to further grant the transmission right to WT3. The WT 3 that has received the BA transmits further data to the AP. The WT 3 informs the TXOP holder (AP) that it is the last frame to be transmitted by setting the RDG in the data to be transmitted to 0. With this, AP returns BA to WT3. Thereafter, frames are transmitted and received at the timing shown in the figure, and AP and WT1 to WT3 perform bidirectional data transmission and reception.

  In order to further improve the MAC efficiency and system throughput, there is a MU-RD (Multi-user RD) method that applies the above-mentioned RD protocol defined in IEEE 802.11n to a communication system that performs space division multiple access. Conceivable. In this method, when the base station acquires TXOP, the base station performs space division multiplexing, and performs data transmission with a plurality of wireless terminals as destinations in the downlink. Then, in the remaining TXOP period, the wireless terminals are caused to perform transmission with the AP as the destination. That is, a plurality of wireless terminals that have received reverse direction permission information from the AP simultaneously transmit data to the AP through space division multiple access.

  FIG. 21 is a time chart showing an example of frame transmission timing when data is transmitted and received by a conventionally known MU-RD method. In the example shown in the figure, the timing at which the AP and the WT1 to WT3 transmit frames is shown. Further, the illustrated example shows an example in which data destined for WT1 and WT3 is generated in the AP. When data destined for WT1 and WT3 occurs in the AP, the AP simultaneously transmits data in which GID (Group ID) indicating WT1 and WT3 as transmission destinations is set. At this time, in order to make it known that data transmission on the uplink is possible, RDG = 1 is set for each of the data transmitted simultaneously. By setting RDG = 1, each wireless terminal (WT1, WT3) acquires a transmission right that allows data transmission on the uplink. WT1 and WT3 which acquired the transmission right transmit data simultaneously by UL MU-MIMO. At this time, WT1 and WT3 can piggyback BA. WT1 and WT3 can also add padding bits in order to align the length of data to be transmitted simultaneously.

Supervised by Masahiro Morikura, Shuji Kubota, “802.11 High-Speed Wireless LAN Textbook”, revised third edition, Impress R & D Co., Ltd. IEEE, “Proposed specification framework for TGac,” doc .: IEEE 802.11-09 / 0992r21, Jan. 2011. IEEE, “IEEE Std 802.11n-2009”

  However, in the conventional RD method and MU-RD method, only the wireless terminals (WT1 and WT3 in the examples of FIGS. 20 and 21) that are the destinations of data in the terminal (TXOP holder) that has obtained the access right are in the reverse direction. Since permission information (RDG) is given, data can be exchanged only with the same wireless terminal in the downlink and uplink. That is, it is not possible to change the wireless terminal that gives permission to transmit data within the remaining TXOP period.

  As described above, in the conventional RD method and MU-RD method, the wireless terminals or wireless terminal groups (a plurality of wireless terminals) that transmit and receive data on the downlink and the uplink are the same. Therefore, it is not possible to designate a specific wireless terminal or a group of wireless terminals in accordance with the access right acquisition status of the wireless terminal, the data accommodation status in the buffer, or the priority of the wireless terminal, and transmit the data. For example, there is a problem in that it is difficult to ensure data quality because it is impossible to transmit data to a wireless terminal (terminal having difficulty in transmission), which is difficult to obtain access rights due to interference from adjacent communication cells.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique for improving the quality assurance of traffic.

One aspect of the present invention is a base station apparatus that performs radio communication with a plurality of radio terminals, a transmission right acquisition unit that acquires a transmission right for transmitting data, and an adjacent communication cell among the radio terminals. A transmission difficult terminal management means for detecting and storing a transmission difficult terminal that is a wireless terminal that is less likely to detect an empty channel by carrier sense due to interference from the radio terminal, when acquiring the transmission right, the transmission difficulties terminal management unit determines the presence of the transmission difficulties terminal for storing, when there is the transmission difficulties terminal, transmission right grant giving the transmission right to those the transmission difficulties terminal And a transmission means for transmitting a signal.

  Further, one aspect of the present invention is the above base station apparatus, wherein the transmission right acquisition unit transmits to the base station with reverse direction permission information destined for the base station transmitted by the wireless terminal. The transmission right is acquired by receiving data describing permission.

  Further, one aspect of the present invention is the base station apparatus described above, wherein the transmission unit transmits a control signal to the transmission difficult terminal and transmits a response to the control signal before transmitting the data. If received, after transmitting the data, transmit the transmission right grant signal, or send the data including the transmission right grant signal, and when not receiving a response to the control signal, After transmitting the data, when the control signal is transmitted again and a response to the control signal is received, the transmission right grant signal is transmitted to the terminal having difficulty in transmission.

One embodiment of the present invention is a wireless communication method between a plurality of wireless terminals and a base station apparatus that performs wireless communication with the wireless terminal, and the base station acquires a transmission right for transmitting data. A transmission right acquisition step for performing transmission, and the base station receives interference from an adjacent communication cell among the wireless terminals, and it is difficult to detect an empty channel by carrier sense, so there is an opportunity to acquire the transmission right. A transmission difficulty terminal management step of detecting and storing a transmission difficulty terminal which is a reduced wireless terminal, and the transmission difficulty terminal management means storing the transmission difficulty terminal management means when the base station has acquired the transmission right. determines the presence of, wherein when there is transmission difficulties terminal includes a transmission step of transmitting a transmission right grant signal providing the transmission right to those the transmission difficulties terminal, said transmission difficulties terminal, before When receiving the transmission right grant signal transmitted from the base station, a wireless communication method and a step of transmitting data to the base station.

  According to the present invention, the transmission right acquisition means acquires a transmission right for transmitting data. Further, the transmission difficulty terminal management means detects and stores a transmission difficulty terminal which is a wireless terminal having a reduced opportunity to acquire a transmission right among the wireless terminals. In addition, when the transmission right is acquired, the transmission means determines whether there is a transmission difficult terminal stored by the transmission difficult terminal management means. If there is a transmission difficult terminal, the transmission means transmits the data to the transmission difficult terminal. A transmission right grant signal for giving a transmission right is transmitted. As a result, since a transmission right can be given to a terminal having difficulty in transmission, traffic quality assurance can be improved.

1 is a configuration diagram illustrating a network configuration of a wireless communication system according to a first embodiment. It is the block diagram which showed the structure of AP in 1st Embodiment. It is the block diagram which showed the structure of WT in 1st Embodiment. It is the flowchart which showed the operation | movement procedure of AP in 1st Embodiment. It is a time chart which showed the timing which AP and WT in 1st Embodiment transmit / receive a radio frame. It is the flowchart which showed the operation | movement procedure of AP in 2nd Embodiment. FIG. 10 is a time chart showing the timing at which APs and WTs transmit and receive radio frames when a CTS is replied to the first RTS transmission in the second embodiment. FIG. 10 is a time chart showing the timing at which APs and WTs transmit and receive radio frames when a CTS is replied to the first RTS transmission in the second embodiment. In the second embodiment, when there is no CTS response to the first RTS transmission and there is a CTS response to the retransmitted RTS, the AP and WT transmit / receive radio frames. It is a time chart. In 2nd Embodiment, it is a time chart which showed the timing which AP and WT transmit / receive a radio | wireless frame in the case of performing RTS / CTS exchange in order for every WT. In 2nd Embodiment, it is a time chart which showed the timing which AP and WT transmit / receive a radio | wireless frame in case a some WT returns CTS continuously with respect to one RTS about RTS / CTS exchange. . In the second embodiment, RTS / CTS exchange is performed when AP and WT transmit / receive radio frames when all WTs return CTS at once using UL MU-MIMO for one RTS. It is the time chart shown. In 2nd Embodiment, it is a time chart which showed the timing which AP and WT transmit / receive a radio | wireless frame in case WT transmits data simultaneously. In 2nd Embodiment, it is a time chart which showed the timing which AP and WT transmit / receive a radio | wireless frame in case WT transmits data simultaneously. In 2nd Embodiment, it is a time chart which showed the timing which AP and WT transmit / receive a radio | wireless frame in case WT transmits data simultaneously. In 2nd Embodiment, it is a time chart which showed the timing which AP and WT transmit / receive a radio | wireless frame in case WT transmits data simultaneously. It is the schematic which showed the structure of the preamble part of the flame | frame used in 2nd Embodiment. It is the flowchart which showed the operation | movement procedure of AP in 3rd Embodiment. It is a time chart which showed the timing which AP and WT in 3rd Embodiment transmit / receive a radio frame. It is the time chart which showed the example of the transmission timing of the frame at the time of applying the RD protocol in IEEE802.11n known conventionally and transmitting / receiving data bidirectionally. It is the time chart which showed the example of the transmission timing of the flame | frame at the time of performing transmission / reception of the data by a conventionally known MU-RD method.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a network configuration of a wireless communication system in the present embodiment. In the illustrated example, the wireless communication system is composed of two adjacent cells that transmit and receive data using the same frequency band. Cell A is composed of one AP 10 (access point, base station) and three WTs 1 to 3 (wireless terminals). Note that the cell A is a cell of interest (target cell) in this embodiment. Cell B is composed of three interfering stations 20 (AP or WT).

  Since the cell A and the cell B transmit and receive data using the same frequency band, interference occurs in the cell A by the interference station 20 configuring the cell B. In the example shown in the figure, WT2 belonging to cell A receives interference from adjacent cell B, and as a result, WT2 becomes an exposed terminal, making it difficult to access the wireless medium. That is, WT2 is a transmission difficult terminal.

  At this time, the AP 10 does not receive any reply (CTS, ACK, Block Ack: BA) for the RTS or data frame transmitted to the WT 2 and exceeds a predetermined threshold within a certain period. It can be detected that transmission / reception is difficult due to the influence (a state in which the opportunity to acquire a transmission right is reduced). In addition, for example, in a signal transmitted by WT2, information indicating that transmission is difficult (indicating that interference from adjacent cells is received, that a large amount of data is accumulated in the buffer provided in WT2, or accumulated AP10 can determine that it is difficult for the WT 2 to acquire the access right based on such information. In this embodiment, the AP 10 is characterized in that the WT 2 that is difficult to transmit is identified as a terminal having difficulty in transmission, and the transmission right is given to the terminal having difficulty in transmission by the RD method.

  Specifically, the AP 10 detects a transmission difficulty terminal in advance by the above method and records it as a transmission difficulty terminal list in a memory provided in the AP 10 (in the example of FIG. 1, WT2 is registered in the transmission difficulty list). In this state, it is assumed that data to be transmitted occurs in the AP 10 and the destination of the data is WT1. Here, in order to transmit data addressed to WT1, the AP 10 performs CSMA / CA and attempts to acquire an access right. When the AP 10 determines that there is no data transmission by another WT during the CSMA / CA implementation period and can transmit a frame to the wireless medium, first, the name of the wireless terminal registered in the difficult-to-transmit terminal list (example in FIG. 1) Then, WT2) is acquired. And AP10 transmits the data which arose, and gives a transmission right with respect to WT2 by RDG. As a result, the WT 2 to which the transmission right is granted can transmit data during the TXOP period.

  Next, the configuration of the AP 10 will be described. FIG. 2 is a block diagram showing the configuration of the AP 10 in the present embodiment. In the illustrated example, the AP 10 includes a transmission right acquisition unit 101 (transmission right acquisition unit), a transmission difficulty terminal management unit 102 (transmission difficulty terminal management unit), and a transmission / reception unit 103 (transmission unit).

  The transmission right acquisition unit 101 acquires the transmission right by CSMA / CA. The transmission difficulty terminal management unit 102 detects a terminal whose opportunity to acquire a transmission right is reduced, and stores information specifying the detected WT2 in the transmission difficulty terminal list. The transmission difficulty terminal management unit 102 includes a storage unit, and the transmission difficulty terminal list may be stored in the storage unit included in the transmission difficulty terminal management unit 102. The terminal list may be stored. The transmission / reception unit 103 transmits / receives signals to / from other devices. The control unit 104 controls each unit included in the own device.

  Next, the configuration of WT1 to WT3 will be described. FIG. 3 is a block diagram showing a configuration of WTs 1 to 3 in the present embodiment. In the illustrated example, the WTs 1 to 3 include a terminal transmission / reception unit 201 and a terminal control unit 202. The terminal transmission / reception unit 201 transmits / receives signals to / from other devices. The terminal control unit 202 controls each unit included in the own device.

  Next, the operation procedure of the AP 10 will be described. FIG. 4 is a flowchart showing an operation procedure of the AP 10 in the present embodiment. Note that it is assumed that the transmission difficult terminal management unit 102 sequentially detects a terminal whose opportunity to acquire a transmission right is reduced and stores information indicating the detected WT2 in the transmission difficult terminal list. The method for detecting WT2 in which the opportunity to acquire the transmission right is reduced is as described above.

  (Step S101) The transmission right acquisition unit 101 of the AP 10 tries to acquire the transmission right by CSMA / CA when data to be transmitted occurs. When it is confirmed that the channel is free for a predetermined period, the transmission right acquisition unit 101 determines that data can be transmitted and acquires the transmission right. Thereafter, the process proceeds to step S102.

  (Step S102) When the transmission right acquisition unit 101 acquires the transmission right, the transmission / reception unit 103 stores information indicating a transmission difficult terminal in which the opportunity to acquire the transmission right is reduced in the transmission difficult terminal list. Determine whether or not. If the transmission / reception unit 103 determines that information indicating a transmission difficulty terminal is not stored in the transmission difficulty terminal list (the transmission difficulty terminal does not exist), the process proceeds to step S103, and the transmission difficulty terminal is added to the transmission difficulty terminal list. If the transmitting / receiving unit 103 determines that the indicated information is stored (there is a terminal that is difficult to transmit), the process proceeds to step S104.

(Step S103) The transmission / reception unit 103 transmits the data generated in step S101, receives the ACK or BA for this data transmission, and ends the process.
(Step S104) The transmission / reception unit 103 transmits the data generated in step S101, receives ACK or BA for this data transmission, and then proceeds to the process of step S105.
(Step S105) The transmission / reception unit 103 acquires information indicating the transmission difficulty terminal stored in the transmission difficulty terminal list, and transmits null data (transmission right grant signal) in which RDG = 1 is set to the transmission difficulty terminal. . Thereafter, the process ends.

  By this operation, WT2, which is a transmission difficult terminal, receives null data in which RDG = 1 is set. WT2, which has received null data in which RDG = 1 is set, transmits this data to AP 10 when data is accumulated. In this way, by determining whether or not there is a transmission difficulty terminal using the AP 10 as a trigger to acquire the transmission right and granting the transmission right to the transmission difficulty terminal subsequent to the original data transmission, the transmission difficulty terminal Within the acquired TXOP, data can be transmitted without contention with other WT1 and WT3.

  Next, the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames will be described. FIG. 5 is a time chart illustrating the timing at which the AP 10 and the WTs 1 to 3 in the present embodiment transmit and receive radio frames. In the example shown in the figure, the AP 10 and the WTs 1 to 3 show the timing at which frames are transmitted. Further, in the illustrated example, the transmission difficult terminal management unit 102 detects WT 2 as a transmission difficult terminal, and data for WT 1 is generated in the AP 10 in a state where information indicating WT 2 is stored in the transmission difficult terminal list. An example of the case is shown.

  When data addressed to WT1 occurs, the AP 10 performs carrier sense over the DIFS + Backoff period, and acquires a transmission right by detecting that it is an empty channel. Subsequently, the AP 10 acquires information indicating the transmission difficulty terminal stored in the transmission difficulty terminal list, and sets a TXOP including a period until the WT 2 that is the transmission difficulty terminal transmits data. Here, TXOP is set within a predetermined upper limit (TXOPLimit). Subsequently, the AP 10 transmits data to the WT 1. The WT 1 transmits the BA for the data transmitted from the AP 10 to the AP 10.

  When the AP 10 receives the BA, the AP 10 transmits a null packet in which RDG = 1 is set to the WT 2 in order to allow the WT 2 to perform RD transmission. Thereby, RD transmission can be permitted to WT2. Since WT 2 is permitted to transmit RD, WT 2 transmits data to AP 10. AP 10 transmits the BA for the data transmitted from WT 2 to WT 2.

  As described above, according to the present embodiment, the transmission difficult terminal management unit 102 of the AP 10 detects WT 2 which is a transmission difficult terminal among the WTs 1 to 3 where the opportunity to acquire the transmission right is reduced, and transmission difficult. Store in the terminal list. Further, the transmission right acquisition unit 101 of the AP 10 acquires the transmission right, and the transmission / reception unit 103 transmits data within the period of the transmission right acquired by the transmission right acquisition unit 101, and further sets RDG = 1. A null packet is transmitted to WT2, which is a terminal that is difficult to transmit. Thereby, WT2 which is a transmission difficult terminal among WT1-3 can transmit data with respect to AP10 within the transmission period which AP10 acquired, and can improve the quality assurance of traffic.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. The network configuration of the wireless communication system, the configuration of the AP 10, and the configurations of the WTs 1 to 3 in the present embodiment are the same as the configurations in the first embodiment. The difference between this embodiment and the first embodiment is that, in this embodiment, the AP 10 transmits an RTS prior to data transmission, and the WTs 1 to 3 that have received the RTS return a CTS. As a result, the AP 10 receives the CTS for the RTS transmitted to the WT 2 that is the transmission difficult terminal, confirms the communication with the WT 2 that is the transmission difficult terminal, and then transmits the null data in which RDG = 1 is set. It can transmit to WT2 which is a transmission difficult terminal.

  Next, the operation procedure of the AP 10 will be described. FIG. 6 is a flowchart showing an operation procedure of the AP 10 in the present embodiment. The example shown in the figure is an example in which the RTS is transmitted twice at the maximum to the WT2, which is a difficult-to-transmit terminal, and the TXOP section is terminated when both fail. It is assumed that the transmission difficult terminal management unit 102 sequentially detects WT2 in which the opportunity to acquire a transmission right is reduced, and stores information indicating the detected WT2 in the transmission difficult terminal list. The WT2 detection method in which the opportunity to acquire the transmission right is reduced is the same method as in the first embodiment.

The processing from step S201 to step S203 is the same processing as the processing from step S101 to step S103 in the first embodiment.
(Step S204) The transmission / reception unit 103 of the AP 10 acquires information indicating a transmission difficulty terminal stored in the transmission difficulty terminal list, and transmits an RTS to the WT2 which is a transmission difficulty terminal. Thereafter, the process proceeds to step S205.

  (Step S205) The transmission / reception unit 103 determines whether or not a CTS has been returned from the WT2, which is a transmission difficult terminal that has transmitted the RTS in step S204. If it is determined that the CTS has been returned from the WT2, which is a transmission difficult terminal, the process proceeds to step S206. If it is determined that the CTS has not been returned, the process proceeds to step S207.

(Step S206) The transmission / reception unit 103 transmits the data generated in step S201, receives ACK or BA for this data transmission, and then proceeds to the process of step S210.
(Step S207) The transmission / reception unit 103 transmits the data generated in step S201, and after receiving the ACK or BA for this data transmission, proceeds to the process of step S208.
(Step S208) The transmission / reception unit 103 acquires information indicating the transmission difficulty terminal stored in the transmission difficulty terminal list, and transmits the RTS to the WT2 that is the transmission difficulty terminal. Thereafter, the process proceeds to step S209.

  (Step S209) The transmission / reception unit 103 determines whether or not a CTS has been returned from the WT2, which is a transmission difficult terminal that has transmitted the RTS in step S208. If it is determined that a CTS has been returned from the WT2, which is a transmission difficult terminal, the process proceeds to step S210. If it is determined that a CTS has not been returned, the process ends.

  (Step S210) The transmission / reception unit 103 acquires information indicating a transmission difficulty terminal stored in the transmission difficulty terminal list, and null data (transmission right grant signal) in which RDG = 1 is set for WT2 which is a transmission difficulty terminal Send. Thereafter, the process ends.

  With this operation, the AP 10 transmits null data in which RDG = 1 is set to the WT 2 that is difficult to transmit after confirming that it can communicate with the WT 2 that is difficult to transmit. WT2, which has received null data in which RDG = 1 is set, transmits this data to AP 10 when data is accumulated.

  In this way, after confirming that the AP 10 can communicate with the WT 2 that is the transmission difficult terminal, the AP 10 transmits the null data in which RDG = 1 is set to the WT 2 that is the transmission difficult terminal. On the other hand, null data in which RDG = 1 is set can be transmitted more reliably. In addition, it is determined whether or not there is a terminal having difficulty in transmission by using the AP 10 as a trigger to acquire the transmission right, and the transmission right is granted to the terminal having difficulty in transmission following the original data transmission. Within TXOP, data can be transmitted without contention with other WT1, WT3.

  When there is no CTS reply from WT2 which is a difficult transmission terminal and AP 10 transmits RTS again, the destination of RTS does not necessarily have to be the same transmission difficult terminal as the transmission difficult terminal which transmitted the previous RTS. For example, when there are a plurality of transmission difficulty terminals, the RTS may be transmitted to a transmission difficulty terminal different from the transmission difficulty terminal that transmitted the RTS last time. In addition, when there are a plurality of terminals that are difficult to transmit, there is no particular method for selecting a terminal that performs data transmission using RDG. Further, as long as data transmission / reception can be accommodated within the TXOP section, RTS may be transmitted three times or more instead of twice as described above. In addition, when data transmission with the WT 2 which is a difficult transmission terminal is completed and the TXOP period remains, the AP can also give the remaining TXOP period to other terminals.

  Next, the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames will be described with reference to FIGS. FIG. 7 is a time chart showing the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames when a CTS is replied to the first RTS transmission to the transmission difficult terminal WT2 in this embodiment. It is.

  When data addressed to WT1 occurs, the AP 10 performs carrier sense over the DIFS + Backoff period, and acquires a transmission right by detecting that it is an empty channel. Subsequently, the AP 10 transmits an RTS to the WT 1 that is a data transmission destination. The WT 1 that has received the RTS transmits a CTS to the AP 10. Subsequently, the AP 10 acquires information indicating the transmission difficulty terminal stored in the transmission difficulty terminal list, and transmits the RTS to the WT2 that is the transmission difficulty terminal. The WT 2 that has received the RTS transmits a CTS to the AP 10.

  Since AP 10 has received CTS from WT 1, it transmits data to WT 1. The WT 1 transmits the BA for the data transmitted from the AP 10 to the AP 10. Subsequently, since the AP 10 has received the CTS from the WT 2, the AP 10 transmits a null packet in which RDG = 1 is set to the WT 2 in order to allow WT transmission to the WT 2. Thereby, RD transmission can be permitted to WT2. Since WT 2 is permitted to transmit RD, WT 2 transmits data to AP 10. AP 10 transmits the BA for the data transmitted from WT 2 to WT 2. Thereafter, the AP 10 transmits CF-END.

  FIG. 8 is a time chart showing the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames when a CTS is replied to the first RTS transmission to the transmission difficult terminal WT2 in this embodiment. It is. The difference between FIG. 7 and FIG. 8 is that in FIG. 8, the AP 10 designates the WT2 data transmission start time in the new RTS that is transmitted to the WT2 that is a transmission difficult terminal, and permits the data transmission of the WT2. It is. This eliminates the need to transmit a call frame from the AP 10 to the WT 2 as shown in FIG.

  When data addressed to WT1 occurs, the AP 10 performs carrier sense over the DIFS + Backoff period, and acquires a transmission right by detecting that it is an empty channel. Subsequently, the AP 10 transmits an RTS to the WT 1 that is a data transmission destination. The WT 1 that has received the RTS transmits a CTS to the AP 10. Subsequently, the AP 10 acquires information indicating the transmission difficulty terminal stored in the transmission difficulty terminal list, and transmits a new RTS to the WT 2 that is the transmission difficulty terminal. In this frame, the data transmission start time of WT2 is designated. The WT 2 that has received the new RTS transmits a CTS to the AP 10.

  Since AP 10 has received CTS from WT 1, it transmits data to WT 1. The WT 1 transmits the BA for the data transmitted from the AP 10 to the AP 10. Subsequently, since there is an instruction that the data may be transmitted at this time in the new RTS frame transmitted from the AP 10, the WT 2 transmits the data to the AP 10. AP 10 transmits the BA for the data transmitted from WT 2 to WT 2. Thereafter, the AP 10 transmits CF-END.

  FIG. 9 shows a case where there is no CTS response to the first RTS transmission to the transmission difficult terminal WT2 in this embodiment, and there is a CTS response to the retransmitted RTS. 5 is a time chart showing the timing for transmitting and receiving a radio frame.

  When data addressed to WT1 occurs, the AP 10 performs carrier sense over the DIFS + Backoff period, and acquires a transmission right by detecting that it is an empty channel. Subsequently, the AP 10 transmits an RTS to the WT 1 that is a data transmission destination. The WT 1 that has received the RTS transmits a CTS to the AP 10. Subsequently, the AP 10 acquires information indicating the transmission difficulty terminal stored in the transmission difficulty terminal list, and transmits the RTS to the WT2 that is the transmission difficulty terminal. However, in this example, the WT 2 that has received the RTS cannot transmit the CTS to the AP 10 due to a communication failure or the like.

  Since AP 10 has received CTS from WT 1, it transmits data to WT 1. The WT 1 transmits the BA for the data transmitted from the AP 10 to the AP 10. Subsequently, since the AP 10 has not received the CTS from the WT 2, the AP 10 transmits the RTS again to the WT 2. The WT 2 that has received the RTS transmits a CTS to the AP 10.

  Since the AP 10 has received the CTS from the WT 2, the AP 10 transmits a null packet in which RDG = 1 is set to the WT 2 in order to permit the WT transmission to the WT 2. Thereby, RD transmission can be permitted to WT2. When the AP 10 cannot receive the CTS from the WT 2, the AP 10 completes the TXOP, retransmits the RTS to the WT 2, or communicates with a different terminal.

  Since WT 2 is permitted to transmit RD, WT 2 transmits data to AP 10. AP 10 transmits the BA for the data transmitted from WT 2 to WT 2. Thereafter, the AP 10 transmits CF-END.

  As described above, it is possible to reliably give a transmission right to WT2, which is a difficult-to-transmit terminal, by preliminarily reserving a period for transmission and reception between AP 10 and WT2, which is a difficult-to-transmit terminal, through RTS / CTS exchange. it can.

  In the above-described example, the RTS / CTS exchange is performed in order for each WT1 to WT3. However, it is not always necessary to sequentially perform the exchange, and a plurality of WT1 to 3 continuously reply CTS to one RTS. Alternatively, all WTs 1 to 3 may return CTS at a time using UL MU-MIMO for one RTS.

  FIG. 10 is a time chart illustrating the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames when the RTS / CTS exchange is sequentially performed for each of the WTs 1 to 3. When data occurs, the AP 10 performs carrier sense over a DIFS + Backoff period, and acquires a transmission right by detecting that the channel is an empty channel. Subsequently, the AP 10 transmits an RTS to the WT 1. The WT 1 that has received the RTS transmits a CTS to the AP 10. Subsequently, the AP 10 transmits an RTS to the WT 2. The WT 2 that has received the RTS transmits a CTS to the AP 10. Subsequently, the AP 10 transmits an RTS to the WT 3. WT3 which received RTS transmits CTS with respect to AP10.

  FIG. 11 is a time chart showing the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames when a plurality of WTs 1 to 3 continuously send back CTSs to one RTS for RTS / CTS exchange. is there. When data occurs, the AP 10 performs carrier sense over a DIFS + Backoff period, and acquires a transmission right by detecting that the channel is an empty channel. Then, AP10 transmits RTS with respect to WT1-3. The WT 1 that has received the RTS transmits a CTS to the AP 10. Subsequently, the WT 2 that has received the RTS transmits a CTS to the AP 10. Subsequently, the WT 3 that has received the RTS transmits a CTS to the AP 10.

  FIG. 12 shows the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames when all the WTs 1 to 3 return CTS at a time using UL MU-MIMO for one RTS in the RTS / CTS exchange. It is the time chart which showed. When data occurs, the AP 10 performs carrier sense over a DIFS + Backoff period, and acquires a transmission right by detecting that the channel is an empty channel. Then, AP10 transmits RTS with respect to WT1-3. The WTs 1 to 3 that have received the RTS transmit CTS to the AP 10 at once using UL MU-MIMO.

  In the example shown in FIGS. 7 to 9, WT1 and WT2 transmit frames in order. However, the present invention is not limited to this, and a plurality of WTs 1 to 3 transmit frames simultaneously using UL MU-MIMO. You may do it. FIG. 13 is a time chart showing the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames when the WT 1 and WT 2 transmit data simultaneously in the present embodiment. In this example, the length of the data frame transmitted from the WT 1 to the AP 10 and the length of the data frame transmitted from the WT 2 to the AP 10 are the same.

  When data addressed to WT1 occurs, the AP 10 performs carrier sense over the DIFS + Backoff period, and acquires a transmission right by detecting that it is an empty channel. Subsequently, the AP 10 transmits an RTS to the WT 1 that is a data transmission destination. The WT 1 that has received the RTS transmits a CTS to the AP 10. Subsequently, the AP 10 acquires information indicating the transmission difficulty terminal stored in the transmission difficulty terminal list, and transmits the RTS to the WT2 that is the transmission difficulty terminal. The WT 2 that has received the RTS transmits a CTS to the AP 10.

  Since AP 10 has received the CTS from WT 1 and WT 2, AP 10 transmits data to WT 1 and WT 2. The contents of the VHT PLCP preamble of this data are GID = WT1, WT2, and Nsts = 1, 1 (WT1, WT2). Also, the contents of the MAC header of this data are RDG = 1 and RA = WT1. That is, this data includes a transmission right grant signal, permits RD transmission to WT1 and WT2, and indicates that the data is destined for WT1 and WT2 discards the received packet.

  The WT 1 transmits the BA for the data transmitted from the AP 10 to the AP 10. Subsequently, since WT1 and WT2 are permitted to perform RD transmission, they transmit data to the AP 10. Note that WT 1 does not transmit any data unless there is data to be transmitted to AP 10. AP 10 transmits the BA for the data transmitted from WT 1 and WT 2 to WT 1 and WT 2. Thereafter, the AP 10 transmits CF-END.

  FIG. 14 is a time chart showing the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames when the WT 1 and WT 2 transmit data simultaneously in the present embodiment. The difference from FIG. 13 is that the length of the data frame transmitted from WT1 to AP 10 is shorter than the length of the data frame transmitted from WT 2 to AP 10. Other than that is the same as the example shown in FIG. Therefore, in the example shown in FIG. 14, padding is added to the data frame transmitted from the WT 1 to the AP 10, and the length is the same as the length of the data frame transmitted from the WT 2 to the AP 10. Thereby, even when the length of the data frame transmitted from WT1 to AP10 and the length of the data frame transmitted from WT2 to AP10 are different, data is simultaneously transmitted to AP10 using UL MU-MIMO. Can do. Note that the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames is the same as the timing illustrated in FIG.

  FIG. 15 is a time chart showing the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames when the WT 1 and the WT 2 transmit data simultaneously in the present embodiment. In this example, WT1 and WT2 set an example in which the timing for transmitting a data frame to AP 10 is set.

  When data addressed to WT1 occurs, the AP 10 performs carrier sense over the DIFS + Backoff period, and acquires a transmission right by detecting that it is an empty channel. Subsequently, the AP 10 transmits an RTS to the WT 1 that is a data transmission destination. The WT 1 that has received the RTS transmits a CTS to the AP 10. Subsequently, the AP 10 acquires information indicating the transmission difficulty terminal stored in the transmission difficulty terminal list, and transmits the RTS to the WT2 that is the transmission difficulty terminal. The WT 2 that has received the RTS transmits a CTS to the AP 10.

  Since AP 10 has received the CTS from WT 1 and WT 2, AP 10 transmits data to WT 1 and WT 2. The contents of the VHT PLCP preamble of this data are GID = WT1, WT2, Nsts = 1, 0 (WT1, WT2), and RD Start Time = X. Note that X indicates a time interval from when the preamble is received until frame transmission is started. As a result, WT1 and WT2 transmit a frame X X after receiving the preamble. Also, the contents of the MAC header of this data are RDG = 1 and RA = WT1. That is, this data includes a transmission right grant signal, and RD transmission is permitted to WT1 and WT2, indicating that the data is destined for WT1 and WT2 discards the packet.

  WT1 and WT2 transmit a frame X X after receiving the preamble. Specifically, the WT 1 transmits the BA for the data transmitted from the AP 10 to the AP 10 X X after receiving the preamble. In addition, WT2 transmits data to the AP 10 X X after receiving the preamble. AP 10 transmits the BA for the data transmitted from WT 1 and WT 2 to WT 1 and WT 2. Thereafter, the AP 10 transmits CF-END.

  FIG. 16 is a time chart showing the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames when the WT 1 and WT 2 transmit data simultaneously in the present embodiment. In this example, WT1 and WT2 set an example in which the timing for transmitting a data frame to AP 10 is set. Further, an example in which there is data to be transmitted from WT1 to AP10 is shown. When there is data to be transmitted from the WT 1 to the AP 10, as shown in the figure, the BA and the data are transmitted to the AP 10 by piggybacking the BA with respect to the data transmitted from the AP 10. Other than that, it is the same as the example shown in FIG.

  Next, the frame format used in this embodiment will be described. FIG. 17 is a schematic diagram illustrating a configuration of a preamble portion of a frame used in the present embodiment. In the illustrated example, VHT Preamble includes L-STF, L-LTF, L-SIG, VHT-SIG-A, VHT-STF, VHT-LTF, and VHT-SIG-B. Yes. The VHT-SIG-A of the first example includes BW, Resvd, STBC, GID, NSTS, TXOP_PS_NOT_ALW, Resvd, and RD Start Time. In this embodiment, the timing at which WT1 and WT2 transmit a data frame to AP 10 is set using RD Start Time. The RD Start Time stores a time interval X from the reception of the preamble to the start of frame transmission.

  The VHT-SIG-A of the second example includes RD MCS in addition to BW, Resvd, STBC, GID, NSTS, TXOP_PS_NOT_ALW, Resvd, and RD Start Time. The RD MCS stores information specifying an MCS code to be used in RD transmission.

  As described above, in this embodiment, after exchanging RTS / CTS with WT1 and WT2, the AP 10 sets a GID including WT2 and sets RDG = 1 when transmitting data addressed to WT1. Thus, it is possible to notify WT1 and WT2 that TXOP has been granted. In this case, the AP 10 does not need to send null data in order to cause the WT 2 to transmit data.

  In normal data communication, when the AP 10 transmits data addressed to WT1, the address of only WT1 is set in GID. However, in this case, a GID in which the addresses of both the terminals WT1 and WT2 are selected is selected and the GID is written. Since the data itself is addressed to WT1, the MAC address information of WT1 is entered in the destination address field of the MAC header.

  By setting in this way, both the terminals WT1 and WT2 receive data signals from the AP 10. Since the data itself is addressed to WT1, WT2 reads only the MAC header and discards the data part. In addition, since WT1 and WT2 have RDG in the MAC header of 1, data is transmitted to AP 10 after reception of data transmitted from AP 10 is completed. If both the WT1 and WT2 terminals transmit data to the AP 10, the communication is based on UL MU-MIMO using SDMA. The MCS code used by WT1 and WT2 during UL MU-MIMO using SDMA may be predetermined by the AP 10 or may use the lowest MCS code.

  AP 10 transmits RTS prior to data transmission, and WTs 1 to 3 that have received RTS return CTS. As a result, the AP 10 receives the CTS for the RTS transmitted to the WT 2 that is the transmission difficult terminal, confirms the communication with the WT 2 that is the transmission difficult terminal, and then transmits the null data in which RDG = 1 is set. It can transmit to WT2 which is a transmission difficult terminal. Thereby, WT2 which is a transmission difficult terminal among WT1-3 can transmit data with respect to AP10 within the transmission period which AP10 acquired, and can improve the quality assurance of traffic.

(Third embodiment)
Next, a third embodiment of the present invention will be described. The network configuration of the wireless communication system, the configuration of the AP 10, and the configurations of the WTs 1 to 3 in the present embodiment are the same as the configurations in the first embodiment. The difference between this embodiment and the first embodiment is that, in this embodiment, not only the AP 10 acquires the transmission right by itself, but also the TX 10 is difficult to transmit using the TXOP based on the transmission right acquired by the WT 1 and WT 3. This is a point of granting a transmission right to the terminal WT2. As a result, even when WT1 and WT3 acquire the transmission right, the transmission right is given to WT2, which is a difficult-to-transmit terminal, thereby increasing the chance that WT2, which is a difficult-to-transmit terminal, can transmit data.

  Next, the operation procedure of the AP 10 will be described. FIG. 18 is a flowchart showing an operation procedure of the AP 10 in the present embodiment. The illustrated example shows an example in which a transmission right is given to WT2, which is a transmission difficult terminal, using TXOP based on the transmission right acquired by WT1 and WT3. In addition, it is assumed that the transmission difficulty terminal management unit 102 sequentially detects WT1 to WT3 in which the opportunity to acquire the transmission right is reduced, and stores information indicating the detected WT1 to 3 in the transmission difficulty terminal list. . The detection method of WT1 to 3 in which the opportunity to acquire the transmission right is reduced is the same method as in the first embodiment.

  Note that, when data to be transmitted occurs, the WTs 1 to 3 try to acquire a transmission right by CSMA / CA. When it is confirmed that the channel is free for a predetermined period, the transmission right acquisition unit 101 determines that the data can be transmitted, acquires the transmission right, and transmits the data to the AP 10. At this time, if the AP 10 is permitted to transmit the remaining TXOP within the TXOP period of the transmission due to, for example, no accumulated data, RDG = 1 is set and the data is transmitted to the AP 10.

(Step S301) The transmission / reception unit 103 of the AP 10 receives data transmitted from the WT1 and WT3, and determines whether or not the RDG of the received data is 1. If the RDG of the received data is 1, and the transmission / reception unit 103 determines that the transmission source terminal is a terminal (TXOPHolder) that has acquired the access right, the process proceeds to step S303; otherwise, the transmission / reception unit When 103 determines, it progresses to the process of step S302.
(Step S302) The transmission / reception unit 103 transmits ACK or BA for the data received in step S301. Thereafter, the process ends.

(Step S303) The transmission / reception unit 103 determines whether or not information indicating a transmission difficult terminal that is WT2 in which the opportunity to acquire a transmission right is reduced is stored in the transmission difficult terminal list. If the transmission / reception unit 103 determines that information indicating a transmission difficulty terminal is not stored in the transmission difficulty terminal list (the transmission difficulty terminal does not exist), the process proceeds to step S304, and the transmission difficulty terminal is added to the transmission difficulty terminal list. If the transmission / reception unit 103 determines that the indicated information is stored (there is a terminal that is difficult to transmit), the process proceeds to step S305.
(Step S304) The transmission / reception unit 103 of the AP 10 transmits ACK or BA for the data received in the process of step S301. Thereafter, the process ends.

(Step S305) The transmission / reception unit 103 of the AP 10 transmits ACK or BA for the data received in the process of step S301. Thereafter, the process proceeds to step S306.
(Step S306) The transmission / reception unit 103 acquires information indicating the transmission difficulty terminal stored in the transmission difficulty terminal list, and transmits null data (transmission right grant signal) in which RDG = 1 is set to the transmission difficulty terminal. . Thereafter, the process ends.

  Next, the timing at which the AP 10 and the WTs 1 to 3 transmit and receive radio frames will be described. FIG. 19 is a time chart showing the timing at which the AP 10 and the WTs 1 to 3 in the present embodiment transmit and receive radio frames. In the example shown in the figure, the AP 10 and the WTs 1 to 3 show the timing at which frames are transmitted. Further, in the illustrated example, the transmission difficult terminal management unit 102 detects WT2 as a transmission difficult terminal, stores information indicating WT2 in the transmission difficult terminal list, and data addressed to the AP 10 is generated in WT1. An example is shown.

  When data addressed to the AP 10 occurs, the WT 1 performs carrier sense over the DIFS + Backoff period, and acquires a transmission right by detecting that it is an empty channel. Subsequently, WT 1 transmits data in which RDG = 1 is set to AP 10. AP 10 transmits a BA for the data transmitted from WT 1 to WT 1.

  Subsequently, since the RDG set in the data transmitted from the access right acquisition terminal (TXOPHolder) WT1 is 1, the AP 10 acquires information indicating the transmission difficulty terminal stored in the transmission difficulty terminal list, WT2 is specified as a terminal having difficulty in transmission. And AP10 transmits the null packet which set RDG = 1 with respect to WT2 in order to permit RD transmission with respect to WT2. Thereby, RD transmission can be permitted to WT2. Since WT 2 is permitted to transmit RD, WT 2 transmits data to AP 10. AP 10 transmits the BA for the data transmitted from WT 2 to WT 2.

  As described above, according to the present embodiment, when permitting the AP 10 to transmit in the remaining TXOP, the terminal sets RDG = 1 and transmits data. In addition, the AP 10 that has received the data in which RDG = 1 is set from the WT 1 that is the TXOP Holder transmits null data in which the RDG = 1 is set to the WT 2 that is a transmission difficult terminal. WT2, which is a transmission difficult terminal, receives null data for which RDG = 1 is set. WT2, which has received null data in which RDG = 1 is set, transmits this data to AP 10 when data is accumulated.

  In this way, the AP 10 determines whether or not there is a transmission difficult terminal using the reception of data in which RDG = 1 is set from the WTs 1 to 3 as a trigger, and grants a transmission right to the transmission difficult terminal, whereby the transmission difficult terminal Can transmit data in the TXOP acquired by the other WTs 1 to 3 without contention with the other WTs 1 to 3. Thereby, WT2 which is a transmission difficulty terminal among WT1-3 can transmit data with respect to AP10 within the transmission period which other WT1-3 acquired, and can improve the quality assurance of traffic. .

  It should be noted that all or some of the functions of the units included in the AP 10 and WTs 1 to 3 in the present embodiment described above are recorded on a computer-readable recording medium and a program for realizing these functions. You may implement | achieve by making a computer system read the program recorded on the medium and executing it. Here, the “computer system” includes an OS and hardware such as peripheral devices.

  The “computer-readable recording medium” refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, and a CD-ROM, and a storage unit such as a hard disk built in the computer system. Further, 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 inside a computer system that serves as a server or a client in that case may also be included that holds a program for a certain time. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

  1-3 ... WT (wireless terminal), 10 ... AP (access point, base station), 20 ... Interfering station, 101 ... Transmission right acquisition unit, 102 ... Difficult to transmit terminal management unit , 103 ... transmission / reception unit, 201 ... terminal transmission / reception unit, 202 ... terminal control unit

Claims (4)

A base station device that performs wireless communication with a plurality of wireless terminals,
A transmission right acquisition means for acquiring a transmission right for transmitting data;
Among the wireless terminals, it is difficult to detect a vacant channel by carrier sense due to interference from an adjacent communication cell, so that it is difficult to detect a transmission difficult terminal that is a wireless terminal having a reduced opportunity to acquire the transmission right. A transmission difficulty terminal management means for storing;
When acquiring the transmission right, the transmission to determine the presence or absence of the transmission difficulties terminal for storing difficulty terminal management unit, wherein when there is transmission difficulties terminal transmission right which gives the transmission right to those the transmission difficulties terminal A transmission means for transmitting the grant signal;
A base station apparatus comprising: The transmission right acquisition means acquires the transmission right by receiving data indicating that transmission is permitted to the base station with reverse direction permission information destined for the base station transmitted by the wireless terminal. The base station apparatus according to claim 1. The transmission means transmits a control signal to the terminal that is difficult to transmit before transmitting the data, and when receiving a response to the control signal, the transmission right grant signal after transmitting the data Or when the data including the transmission right grant signal is transmitted and a response to the control signal is not received, the control signal is transmitted again after transmitting the data, and the control signal is transmitted. The base station apparatus of Claim 1. When the response with respect to is received, the said transmission right grant signal is transmitted to the said said transmission difficult terminal. A wireless communication method between a plurality of wireless terminals and a base station apparatus that performs wireless communication with the wireless terminals,
A transmission right acquisition step for the base station to acquire a transmission right to transmit data;
Transmission in which the base station is a wireless terminal that receives interference from an adjacent communication cell among the wireless terminals and has a reduced opportunity to acquire the transmission right because it is difficult to detect an empty channel by carrier sense. A transmission difficulty terminal management step for detecting and storing a difficulty terminal; and
Said base station, when having acquired the transmission right, the transmission difficulties terminal management unit determines the presence of the transmission difficulties terminal for storing, when there is the transmission difficulties terminal, said to those the transmission difficulties terminal A transmission step of transmitting a transmission right grant signal for giving a transmission right;
When the transmission difficulty terminal receives the transmission right grant signal transmitted from the base station, transmitting data to the base station;
A wireless communication method.

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