JP2005184423A - Wireless communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless communication method capable of reducing probability of convergence and drop in throughput, and alleviating processing on a transmission request frame and a transmission permission frame. <P>SOLUTION: In the wireless communication method for constituting an ad hoc network in which a plurality of wireless terminals can directly communicate with one another, the transmission request frame not containing information of an access inhibited period to a channel and an address of a transmission source and the transmission permission frame not containing the information of the access inhibited period to the channel and the address of a destination are transmitted/received. Thus, while the frames are transmitted/received between a pair of wireless terminals, the wireless terminal which can access the channel of at least one of the transmitting/receiving wireless terminals and has received either the transmission request frame or the transmission permission frame conducts virtual carrier sensing to inhibit the access to the channel of the other wireless terminal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wireless communication method, and more particularly to a CSMA / CA wireless communication method.

  For example, the wireless communication method standardized by the IEEE 802.11 committee established by the Institute of Electrical and Electronics Engineers (IEEE) for the purpose of standardizing wireless LANs is as follows. Communication is performed by transmitting and receiving (see Non-Patent Document 1). A frame is transmitted from a certain wireless terminal. A frame transmitted from this wireless terminal may be received by a plurality of wireless terminals, not limited to the wireless terminal that wants to communicate. Each wireless terminal that has received the frame determines whether the destination address included in the frame is addressed to itself, and if it is addressed to itself, transmits a confirmation response frame. The wireless terminal that has transmitted the frame confirms that the data frame has been transmitted to the wireless terminal at the designated address by receiving the confirmation response frame transmitted from the wireless terminal that has received the frame. Therefore, the destination address is also included in the confirmation response frame. If the wireless terminal that transmitted the frame cannot receive the acknowledgment frame, it is determined that the data frame has not arrived due to space conditions or a frame collision, and processing such as retransmission is performed.

  In an environment in which an ad hoc network in which a plurality of wireless terminals directly communicate with each other is configured in this manner, another wireless terminal can transmit a data frame while another wireless terminal transmits a data frame. There is sex. If the frames collide with each other in this way, normal communication cannot be performed. This is called a collision. In IEEE 802.11, this collision is avoided by using an access method called a carrier sense multiple access method with collision avoidance (hereinafter referred to as “CSMA / CA method”). In this method, in order to perform communication in a space where a plurality of wireless terminals exist, a wireless terminal that transmits a data frame uses a method called physical carrier sense to transmit the surrounding space before transmitting the data frame. In the case where other wireless terminals are communicating, the transmission is suspended until the communication is completed. Also, for example, when there is a short period in which communication is not performed during frame exchange, such as exchange of a data frame and its acknowledgment response frame, if it is less than a certain period, other communication terminals It is assumed that the communication is continued, the communication is not started, and the communication is considered to be completed when a certain period is exceeded. That is, when frames are exchanged within a certain period, other wireless terminals do not interrupt the communication and can communicate normally.

  However, when there are multiple other wireless terminals waiting for the end of communication of a certain wireless terminal, immediately after the end of the previous communication, a plurality of other wireless terminals attempt to start transmission at the same time. A collision occurs. In order to avoid this, the following method called random back-off is used. Each wireless terminal does not perform transmission immediately after communication is completed, and generates a random value. The generated random value decreases at regular intervals, and the wireless terminal that has become 0 can acquire the right to transmit and perform transmission. Since the random values generated by the wireless terminals are different from each other, the possibility of starting transmission at the same time decreases. When the random value of any wireless terminal becomes 0 and transmission is started, another wireless terminal whose random value is not 0 suspends transmission again. When this communication is completed and transmission is possible, the wireless terminal that has forgotten transmission does not generate a random value again, but decreases from the remaining random value generated earlier. Since there are few remaining random values of wireless terminals that have forgotten communication, there is a higher possibility that transmission can be performed earlier than wireless terminals that newly generate other random values. In this way, the state in which the same wireless terminal cannot transmit is prevented from continuing for a long time. However, even with this method, the probability of collision increases as the number of wireless terminals increases. So, if the frame sent after waiting for the generated random value collides, generate a random value again and wait for that period, but the maximum value of the random value generated at that time is first Double the maximum value of the set random value. Further, every time a collision occurs, the maximum random value generated in the same manner is doubled. If the specified maximum value is exceeded, the specified maximum value is set as the maximum random value. As the range of random values increases, the possibility that each wireless terminal generates the same random value decreases, and as a result, the possibility of collisions decreases. If transmission is successful, the maximum random value is returned to the initial state.

  However, even in such a system, it is inevitable that frames transmitted simultaneously from different wireless terminals collide. Also, because of wireless communication, the wireless terminal that transmitted the frame cannot detect that a collision has occurred, and cannot stop frame transmission when the collision occurs. Since there is no response from the communication partner within a certain period after the frame transmission is completely completed, it is detected that a collision has occurred for the first time, and retransmission processing is performed. This is the greater overhead the longer the collided frame is.

  In addition to the above, there is a possibility of frame collision called a hidden node problem. FIG. 6 is a diagram for explaining the possibility of this type of frame collision. In FIG. 6, 601, 602, and 603 are wireless terminals, 611 is a range where radio waves of the wireless terminal 601 can reach, 612 is a range where radio waves of the wireless terminal 602 are received, and 613 is a range where radio waves of the wireless terminal 603 are received. Yes. When the wireless terminal 601 transmits a frame to the wireless terminal 602, the radio wave does not reach the wireless terminal 603. Therefore, the physical carrier sense of the wireless terminal 603 cannot detect that another terminal is communicating, and starts transmission. The radio wave of the wireless terminal 603 reaches the wireless terminal 602 that may be in the process of receiving a frame from the wireless terminal 601, so even if the transmission is not directed to the wireless terminal 602, The communication of the terminal 602 is obstructed.

  In order to solve the above hidden node problem, a transmission request frame, a transmission permission frame, and a virtual carrier sense are used. A wireless terminal having a virtual carrier sense mechanism includes a kind of counter called a network allocation vector (hereinafter referred to as “NAV”) that decreases at a uniform rate. This NAV is for suppressing communication. When the count value is other than 0, the channel of the wireless terminal is in an access prohibited state, and only when the count value is 0, the access prohibited state is released and communication is performed. Allow to do. By using this, it is avoided that another wireless terminal transmits to the wireless terminal performing communication. The NAV is set by a transmission request frame and a transmission permission frame. In the IEEE 802.11 specification, a transmission request frame is called an RTS frame, a transmission permission frame is called a CTS frame, and an acknowledgment frame is called an ACK frame.

  FIG. 7 shows the configuration of a transmission request frame and a transmission permission frame used in the conventional wireless communication method. Reference numeral 701 denotes a configuration of a transmission request frame, and reference numeral 702 denotes a configuration of a transmission permission frame. Frame type fields 701a and 702a indicate what frame the frame is. In this case, a frame type field 701a 701 represents a transmission request frame, and a frame type field 702a 702 represents a transmission permission frame. The prohibition period information fields 701b and 702b contain information for setting the NAV. This information is created by calculating the time required for the end of communication. The destination address fields 701c and 702c represent the addresses of the wireless terminals that are the transmission destinations of the respective frames. The transmission source address field 701d represents the address of the transmission source wireless terminal of the transmission request frame 701. FCS (Frame Check Sequence) fields 701e and 702e are called frame check sequences, and are used by a wireless terminal that has received these frames to check whether the contents of the frames are correct.

  FIG. 8 is an example of communication using the transmission request frame and the transmission permission frame. Reference numerals 201, 202, 203, and 204 denote wireless terminals, and 211, 212, 213, and 214 denote NAVs of the wireless terminals 201, 202, 203, and 204, respectively. In this state, the access to the channel is prohibited, and the white part indicates that the counter value is 0, and the access prohibition state to the channel is released and communication is possible. Yes. The NAV decreases to 0 at a predetermined speed as time passes. FIG. 8 shows that the count number decreases as time goes to the right. Further, the wireless terminal 201 is in a position where radio waves reach the wireless terminal 202, the wireless terminal 202 is in a position where radio waves reach the wireless terminals 201 and 203, and the wireless terminal 203 is in contact with the wireless terminals 202 and 204. On the other hand, it is assumed that the radio terminal 204 is in a position where radio waves reach the radio terminal 203 at a position where radio waves reach. 801 is the time until the transmission of the transmission request frame is completed, 802 is the time until the transmission of the transmission permission frame is completed, 223 is the time until the transmission of the data frame is completed, 224 is the transmission of the acknowledgment frame Each time is shown.

  In order to set the NAV of a wireless terminal other than the communication partner, the wireless terminal that is to perform communication transmits a transmission request frame prior to transmission of the data frame. If the wireless terminal that has received the transmission request frame is not transmitted from the destination address of the transmission request frame to itself, the wireless terminal must set the prohibition period information in its own NAV. In the example illustrated in FIG. 8, the wireless terminal 202 transmits a transmission request frame 701. The destination address 701c of the transmission request frame 701 indicates the address of the wireless terminal 203, which indicates that the wireless terminal 202 communicates with the wireless terminal 203. Immediately after receiving the transmission request frame 701, the wireless terminal 201 sets the NAV 211 to a designated count value other than 0 based on the prohibition period information 701b, thereby setting the access prohibited state. The wireless terminal 203 transmits the transmission permission frame 702 to the wireless terminal 202 while keeping the count value of the NAV 213 at 0 after a predetermined time after receiving the transmission request frame 701. Similar to the transmission request frame 701, the transmission permission frame 702 sets the NAV 214 of the wireless terminal 204 that has received the frame to a specified count value other than 0, thereby prohibiting access. As a result, the count value of the NAV 214 of the wireless terminal 204 within the range where the transmission request frame 701 does not reach is also set to a count value other than 0, which solves the hidden node problem. By receiving the transmission permission frame 702 addressed to itself, the wireless terminal 202 considers that the communication permission has been granted, and transmits the data frame to the wireless terminal 203 after a certain period of time. At this time, since the transmission permission frame 702 is addressed to itself, the count value of the NAV 212 is kept at 0. The wireless terminal 203 that has received the data frame addressed to itself transmits an acknowledgment frame to the wireless terminal 202 after a predetermined time after receiving the data frame, indicating that the data has been received. The prohibition period information 701a and 702a of the transmission request frame 701 and the transmission permission frame 702 are created by calculating the time until the acknowledgment frame is completely transmitted. The NAV 211 of the terminal 201 has a count value of 0, the access prohibited state is canceled, and communication is possible. Further, the NAV 214 of the wireless terminal 204 that has received the confirmation response frame has a count value of 0, the access prohibition state is canceled, and communication is enabled. Even if the acknowledgment frame is not received for some reason, since the transmission permission frame 702 including the prohibition period information 702b is received, the count value of the NAV 214 is set to 0 at the time when the acknowledgment frame is transmitted. Will return. In this way, the virtual carrier sense accesses a wireless terminal other than the wireless terminal that is performing communication during the period until the communication is completed by setting the NAV count value in the transmission request frame 701 and the transmission permission frame 702. As a prohibited state, normal communication can be performed. In general, the data frame has a long frame length, and the transmission request frame and the transmission permission frame having a short frame length are exchanged prior to the transmission, thereby reducing the overhead when a collision occurs. When the transmission request frame and the transmission permission frame are successfully exchanged, the data frame is transmitted / received without colliding.

  FIG. 10 is a flowchart illustrating an example of the operation of the wireless terminal that has received the transmission request frame. The wireless terminal that has received the transmission request frame determines whether the transmission request frame is addressed to itself or another person from the destination address. If it is addressed to itself, it transmits a transmission permission frame and waits for a data frame to be sent. When the data frame is received, the communication is terminated by transmitting an acknowledgment frame to the wireless terminal that has transmitted the transmission request frame. On the other hand, when the transmission request frame is addressed to another person, a designated count value other than 0 is set in the NAV from the prohibition period information of the transmission request frame. The NAV decreases in count value at regular intervals, and is in an access-prohibited state until the count value becomes 0, and does not perform communication. This communication is terminated when the NAV count value becomes zero.

  As another conventional example, there is a wireless communication method in which only a transmission permission frame is transmitted without exchanging a transmission request frame and a transmission permission frame. FIG. 9 shows an example of the communication method. Reference numerals 201, 202, 203, and 204 denote wireless terminals, and 211, 212, 213, and 214 denote NAVs of the wireless terminals 201, 202, 203, and 204, respectively. In this state, the access to the channel is prohibited, and the white part indicates that the counter value is 0, and the access prohibition state to the channel is released and communication is possible. Yes. The NAV decreases to 0 at a predetermined speed as time passes. FIG. 9 shows that the time passes and the count number decreases as going to the right. Further, the wireless terminal 201 is in a position where radio waves reach the wireless terminal 202, the wireless terminal 202 is in a position where radio waves reach the wireless terminals 201 and 203, and the wireless terminal 203 is in contact with the wireless terminals 202 and 204. On the other hand, it is assumed that the radio terminal 204 is in a position where radio waves reach the radio terminal 203 at a position where radio waves reach. Reference numeral 802 denotes a time until the transmission of the transmission permission frame is completed, 223 indicates a time until the transmission of the data frame is completed, and 224 indicates a time until the transmission of the confirmation response frame is completed. In order to set the NAV count value of another wireless terminal, the wireless terminal that is to perform communication transmits a transmission permission frame prior to transmission of the data frame, and then transmits the data frame after a predetermined time. The destination address of the transmission permission frame is set to its own address. In this example, the wireless terminal 202 transmits a transmission permission frame to the wireless terminal 202, and continuously transmits a data frame after a predetermined time. After receiving the transmission permission frame 702, the wireless terminal 201 sets the count value of the NAV 211 to a value other than 0 to make the access prohibited state. The wireless terminal 203 receives the data frame addressed to itself, resets the counter value of the NAV 213 to 0, and transmits an acknowledgment frame to the wireless terminal 202 after a predetermined time. In this method, the overhead is small because the transmission request frame 701 is not used, but the hidden node problem cannot be solved.

FIG. 11 is a flowchart illustrating an example of the operation of the wireless terminal that has received the transmission permission frame. The wireless terminal that has received or transmitted the transmission permission frame determines whether the transmission permission frame is addressed to itself or another person from the destination address. If it is addressed to itself, it transmits a data frame and waits for an acknowledgment frame. If the confirmation response frame is received, this communication is terminated. On the other hand, when the transmission permission frame is addressed to another person, a designated count value other than 0 is set in NAV from the prohibition period information of the transmission permission frame. If the data frame is not received or is received but is addressed to another person, the NAV is decremented every fixed time, and the access is prohibited until the count value becomes 0, and communication is not performed. This communication is terminated when the NAV count value becomes zero. On the other hand, if a data frame is received and addressed to itself, NAV is set to 0, an acknowledgment frame is transmitted, and this communication is terminated.
IEEE Edition, `` IEEE Standards 802.11gTM ... IEEE Standard for Information technology- Telecommunications and information exchange between system- Local and metropolitan area networks- Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY ) specifications Amendment4: Further Higher Data Rate Extension in the 2.4GHz Band "(USA), July 27, 2003

  The communication of the transmission request frame and the transmission permission frame as described above is merely an overhead when no collision occurs, which causes a reduction in communication efficiency. However, if these frames are not used, the overhead when a collision occurs is even greater, so these frames have to be used. In particular, when the hidden node problem occurs, the possibility that the transmission request frame and the transmission permission frame collide with each other increases as the frame length increases. There is a problem that the possibility of congestion increases by repeating retransmission due to this collision. Also, the source address and prohibition period information in the transmission request frame, and the destination address and prohibition period information in the transmission permission frame are not necessarily required. Processing for calculating the prohibition period information and when creating a frame There are problems such as processing burden and increase in frame length.

  In order to solve the above problems, the present invention improves the transmission request frame and the transmission permission frame, reduces the possibility of congestion and a decrease in throughput, and reduces the processing related to the transmission request frame and the transmission permission frame. An object of the present invention is to provide a wireless communication method.

  In order to achieve the above object, the invention according to claim 1 of the present application is directed to a wireless communication method for configuring an ad hoc network in which a plurality of wireless terminals can directly communicate with each other. At least during transmission / reception of a frame between a set of wireless terminals, by transmitting / receiving a transmission request frame not including information and a transmission permission frame not including information on a channel access prohibition period and a destination address A wireless terminal that can access the channel of one wireless terminal that is transmitting / receiving, and the wireless terminal that has received either the transmission request frame or the transmission permission frame prohibits access to the channel of the other wireless terminal It is characterized by performing virtual carrier sense.

  The invention according to claim 2 of the present application is the wireless communication method according to claim 1, wherein the virtual carrier sense is obtained by transmitting / receiving only a transmission permission frame not including information on a channel access prohibition period and a destination address. It is characterized by performing.

  The invention according to claim 3 of the present application is directed to a wireless communication method for configuring an ad hoc network in which a plurality of wireless terminals can directly communicate with each other. The second wireless terminal that has transmitted the transmission request frame not including the address and has received the transmission request frame addressed to itself transmits the transmission permission frame not including the information on the channel access prohibition period and the destination address, After receiving the data frame transmitted by the first wireless terminal, the third wireless terminal that transmits the acknowledgment frame to the first wireless terminal and receives the transmission request frame not addressed to itself is at least the first wireless terminal. The access to the channel of one wireless terminal is prohibited for a preset time, and when the preset time has elapsed, the access is When the third wireless terminal that releases the prohibited state and receives the data frame transmitted by the first wireless terminal when the third wireless terminal in the access prohibited state has received a time shorter than the preset time, the access The prohibited state is canceled.

  The invention according to claim 4 of the present application is the wireless communication method according to claim 3, wherein the fourth wireless terminal that does not receive the transmission request frame and receives the transmission permission frame transmitted by the second wireless terminal is provided. The access is prohibited at least for a preset time to the channel of the second wireless terminal, and when the preset time has elapsed, the access prohibited state is canceled and the access is prohibited. When the terminal receives the confirmation response frame transmitted from the second wireless terminal, the access prohibited state is canceled when a time shorter than the preset time has elapsed.

  The invention according to claim 5 of the present application is directed to a wireless communication method for configuring an ad hoc network in which a plurality of wireless terminals can directly communicate with each other, wherein the fifth wireless terminal includes information on a channel access prohibition period and a destination address. After transmitting the transmission permission frame that does not include the data, the sixth wireless terminal that transmits the data frame and receives the transmission permission frame transmitted by the fifth wireless terminal is at least sent to the channel of the fifth wireless terminal. When the preset time elapses, the access prohibition state is canceled when the preset time has elapsed, and the sixth radio terminal in the access prohibition state is the fifth radio terminal addressed to itself. The data frame transmitted by the fifth wireless terminal addressed to another person, when the data prohibition state is received, the access prohibition state is canceled. When receiving, when it said shorter than the preset time has elapsed, and cancels the access prohibition state.

  The invention according to claim 6 of the present application is the wireless communication method according to any one of claims 3 to 5, wherein the wireless terminal is placed in an access prohibited state by setting a count value of a network allocation vector of the wireless terminal to a maximum value. The access prohibition state is canceled by setting the count value to zero, and the access prohibition state is set when a time shorter than the preset time has elapsed by setting the counter value to a value other than the maximum value. It is characterized by canceling.

  In the present invention, the information on the channel access prohibition period and the information on the access prohibition period on the channel and the destination, which are shorter than the conventional transmission request frame and the transmission permission frame, are used as the transmission request frame. A frame that does not include the address is used as a transmission permission frame, and a wireless terminal that has received either a transmission request frame or a transmission permission frame performs a virtual carrier sense that prohibits access to the channel of another wireless terminal. , The probability of collisions can be reduced and further the possibility of congestion can be reduced. Further, since the time required for communication is shortened by shortening the transmission request frame and the transmission permission frame, there is an effect that the throughput is improved.

  Furthermore, if communication is performed using only the transmission permission frame that does not include information on the channel access prohibition period and the destination address, there is an effect that the possibility of collision is reduced and the throughput is further improved.

  By setting the count value of the network allocation vector of the wireless terminal to the maximum value, the wireless terminal becomes in an access prohibited state, and by setting the count value to zero, the access prohibited state is canceled or set to a value other than the maximum value. By shortening the access prohibition period that is set by setting the count value to the maximum value, and after the elapse of a predetermined time according to the set value, it is configured to cancel the access prohibition state, Even when there is no prohibition period information in the transmission request frame and the transmission permission frame, it is possible to set the transmission request frame and the transmission permission frame so that the wireless terminal that is not communicating can be in the access prohibited state or the access prohibited state can be released. Processing, calculating the prohibition period information, and reading the prohibition period information from the frame, There is also an effect that the processing for setting the cement value is reduced.

  Examples of the present invention will be described in detail below. FIG. 1 shows the configuration of a transmission request frame and a transmission permission frame used in the wireless communication method of the present invention. 101 indicates a transmission request frame, and 102 indicates a transmission permission frame. The frame type fields 101a and 102a indicate what frame the frame is. In this case, the frame type field 101 represents a transmission request frame, and the frame type field 102 represents a transmission permission frame. The destination address field 101c indicates the transmission destination of this transmission request frame. The FCS fields 101e and 102e are used by the wireless terminal that has received this frame to check whether the contents of the frame are correct.

  Compared to the conventional transmission request frame 701 described in FIG. 7, the transmission request frame 101 used in the present invention has prohibition period information (corresponding to 701b in FIG. 7) and a transmission source address (corresponding to 701d in FIG. 7). The transmission permission frame 102 of the present invention is different from the conventional transmission permission frame in that there is no prohibition period information (corresponding to 702b in FIG. 7) and destination address (corresponding to 702c in FIG. 7). The transmission source address of the conventional transmission request frame is necessary because the wireless terminal that has received the transmission request frame uses it as a destination address to which the transmission permission frame is sent back. However, the transmission permission frame 102 of the present invention is not necessary because it is not transmitted toward a specific destination wireless terminal. This is because it is only necessary to know that only the wireless terminal that has made the transmission request is permitted for the request. In addition, when a data frame includes a transmission source address and a transmission source address is required, the transmission source address of the data frame can be used. For example, the confirmation response frame may be sent back with the transmission source address of the data frame as the destination address. That is, even if there is no destination address, it can be determined that only the wireless terminal that has made a transmission request is a transmission permission frame addressed to itself. As a result, it is understood that the transmission source address of the transmission request frame and the destination address of the transmission permission frame are not necessary.

  In the present invention, there is no prohibition period information. The prohibition period information is the conventional transmission request frame, and the prohibition period is (the time necessary for receiving the transmission permission frame + the time necessary for transmitting the data frame + necessary for receiving the acknowledgment frame. Time). Wireless terminals that do not participate in communication set the NAV count value to a specified value using this information. However, this is because, in a wireless terminal that does not participate in communication, after receiving the transmission request frame 101, the NAV count value is set to the maximum value, and after receiving the data frame, the acknowledgment frame is received. An equivalent function can be performed by resetting the NAV count value at a required time or by setting the NAV to 0 by receiving an acknowledgment frame. Data frames are generally variable length, but acknowledgment frames are generally fixed length. For this reason, it is only necessary to reset a certain value as the NAV count value without performing calculation like the prohibition period information. Also, the wireless terminal that has received the transmission request frame 101 addressed to itself does not set the NAV count value as in the conventional case. By using the above method, it is not necessary to calculate and add prohibition period information to the transmission request frame.

  Similarly, in the transmission permission frame, the prohibition period is (time necessary for receiving the data frame + time necessary for transmitting the acknowledgment frame). Wireless terminals that do not participate in communication set NAV using this information. However, this is also the time required for receiving the acknowledgment frame after receiving the data frame after setting the maximum value in the NAV by receiving the transmission permission frame 102 in the wireless terminal that does not participate in communication. By setting NAV to 0 or resetting NAV to 0 by receiving an acknowledgment frame, a function equivalent to the conventional operation can be achieved.

  By using the method as described above, the prohibition period information can be removed from the transmission request frame and the transmission permission frame. Note that the maximum value of the count value set in the NAV can be arbitrarily set. However, any length of the data frame length is sufficient to prevent communication until the acknowledgment frame is transmitted. .

  Hereinafter, the first embodiment will be described in detail. FIG. 2 is an explanatory diagram of a wireless communication method using the transmission request frame 101 and the transmission permission frame 102. 201, 202, 203, and 204 represent wireless terminals, 211, 212, 213, and 214 represent NAVs of wireless terminals 201, 202, 203, and 204, respectively. In this state, the access to the channel is prohibited, and the white part indicates that the counter value is 0, and the access prohibition state to the channel is released and communication is possible. ing. As the time elapses, the NAV counts down to 0 at a predetermined speed. FIG. 2 shows that the count value decreases as time elapses toward the right. Further, the wireless terminal 201 is in a position where radio waves reach the wireless terminal 202, the wireless terminal 202 is in a position where radio waves reach the wireless terminals 201 and 203, and the wireless terminal 203 is in contact with the wireless terminals 202 and 204. On the other hand, it is assumed that the radio terminal 204 is in a position where radio waves reach the radio terminal 203 at a position where radio waves reach. 221 is the time until the transmission of the transmission request frame 101 is completed, 222 is the time until the transmission of the transmission permission frame 102 is completed, 223 is the time until the transmission of the data frame is completed, 224 is the transmission of the acknowledgment frame Represents the time to complete each.

  A wireless terminal that performs communication transmits a transmission request frame 101 prior to transmission of a data frame in order to place a wireless terminal other than the communication partner in an access prohibited state. A wireless terminal that has received the transmission request frame 101 sets a preset maximum value as a count value of its own NAV when the frame is not addressed to itself. In the example illustrated in FIG. 2, the wireless terminal 202 transmits the transmission request frame 101. The transmission request frame 101 of the wireless terminal 202 is addressed to the wireless terminal 203, which indicates that the wireless terminal 202 is going to communicate with the wireless terminal 203. Immediately after receiving the transmission request frame 101, the wireless terminal 201 that has received the transmission request frame 101 addressed to another person sets the maximum value preset in the NAV 211 as a count value. The wireless terminal 203 that has received the transmission request frame 101 addressed to itself transmits the transmission permission frame 102 while keeping the count value of the NAV 213 at a predetermined time after the reception of the transmission request frame 101 is completed. Similar to the transmission request frame 101, the transmission permission frame 102 sets the count value of the NAV 214 of the wireless terminal 204 to the maximum value. As a result, the NAV 214 of the wireless terminal 204 within the range where the transmission request frame 101 does not reach can be set to the access prohibited state, that is, the virtual carrier sense can be performed, and the hidden node problem can be dealt with. On the other hand, even if the wireless terminal 202 receives the transmission permission frame 102 without the destination address by transmitting the transmission request frame 101, the wireless terminal 202 regards that the data transmission permission has been granted and keeps the count value of the NAV 212 at 0. The data frame is transmitted after a certain period. The wireless terminal 203 that has received the data frame addressed to itself transmits an acknowledgment frame 202 after a certain period of time after receiving the data frame, indicating that the data has been received. On the other hand, when the wireless terminal 201 receives the data frame, the wireless terminal 201 resets the count value of the NAV 211 to a value necessary for receiving the acknowledgment frame. The count value set here is smaller than the previously set maximum value. As a result, after the communication between other wireless terminals is completed (after transmission / reception of the acknowledgment frame is completed), the count value of the NAV 211 becomes 0, the access prohibited state is released, and communication is possible. The wireless terminal 203 that has received the data frame transmits an acknowledgment frame after a certain period. The wireless terminal 204 that has received the confirmation response frame sets the count value of the NAV 214 to 0, and the access prohibited state is released. The wireless terminal 202 determines that the communication has been normally completed by receiving the confirmation response frame.

  FIG. 4 is a flowchart illustrating an example of the operation of the wireless terminal that has received the transmission request frame 101. The wireless terminal that has received the transmission request frame 101 determines whether or not the frame is addressed to itself from the destination address. If it is addressed to itself, it transmits a transmission permission frame 102 and waits for a data frame to be sent. When the data frame is received, the communication is terminated by transmitting an acknowledgment frame. On the other hand, if the transmission request frame 101 is not addressed to itself, the maximum count value is set in the NAV. The NAV count value decreases at regular intervals and repeats until it reaches zero. During that time, transmission is not possible. By receiving the data frame, the designated count value corresponding to the time required for receiving the acknowledgment frame is reset to the NAV. When the NAV count value becomes 0, it is determined that the communication of another wireless terminal is completed.

  FIG. 5 is a flowchart illustrating an example of the operation of the wireless terminal that has received the transmission permission frame 102. The wireless terminal that has received the transmission permission frame 102 determines whether or not the frame is addressed to itself depending on whether or not the transmission request frame 101 has been transmitted immediately before. If the transmission request frame 101 has been transmitted, it is determined that the transmission permission frame 102 is addressed to itself, transmits a data frame, and waits for an acknowledgment frame to be transmitted. This communication is terminated by receiving the confirmation response frame. On the other hand, if the transmission request frame 101 is not transmitted when the transmission permission frame 102 is received, the maximum count value is set in the NAV. After that, when an acknowledgment frame is received without receiving a data frame, the count value 0 is set in the NAV and it is recognized that the communication is completed. Even when the confirmation response frame is not received, when the count value becomes 0, it is recognized that the communication is completed, and the access prohibition state is released.

As described above, in the first embodiment of the present application, a transmission request data frame that does not include information on a channel access prohibition period and a transmission source address, and a transmission permission that does not include information on a channel access prohibition period and a destination address. Even when only frames are used, communication that solves the hidden node problem is possible.

  Next, a second embodiment will be described. There is a wireless communication method in which only the transmission permission frame 102 is transmitted without performing communication between the transmission request frame 101 and the transmission permission frame 102 described in the first embodiment. FIG. 3 is an explanatory diagram thereof. 201, 202, 203, and 204 represent wireless terminals, 211, 212, 213, and 214 represent NAVs of wireless terminals 201, 202, 203, and 204, respectively. The white part indicates that the counter is zero. NAV decreases at a predetermined speed as time passes, but never decreases to 0 or less. In FIG. 3, the time elapses as it goes to the right, and the count value set in the NAV decreases. Further, the wireless terminal 201 is in a position where radio waves reach the wireless terminal 202, the wireless terminal 202 is in a position where radio waves reach the wireless terminals 201 and 203, and the wireless terminal 203 is in contact with the wireless terminals 202 and 204. On the other hand, it is assumed that the radio terminal 204 is in a position where radio waves reach the radio terminal 203 at a position where radio waves reach. 222 represents the time until the transmission of the transmission permission frame 102 is completed, 223 represents the time until the transmission of the data frame is completed, and 224 represents the time until the transmission of the acknowledgment frame is completed. In order to set the NAV of another wireless terminal, the wireless terminal that is to perform communication transmits the transmission permission frame 102 prior to transmission of the data frame, and then transmits the data frame after a certain period. In this example, the wireless terminal 202 transmits a transmission permission frame 102 and transmits a data frame continuously after a certain period. The wireless terminal 201 sets the NAV 211 to the maximum value immediately after receiving the transmission permission frame. The wireless terminal 203 once sets the maximum value in the NAV 213, but receives the data frame. If the data frame is addressed to itself, the wireless terminal 203 resets the NAV to 0 and transmits an acknowledgment frame after a certain period. The wireless terminal 202 that has received the confirmation response frame ends the communication. This method does not deal with the hidden node problem, but the overhead is reduced by not using the transmission request frame.

  FIG. 5 is a flowchart illustrating an example of the operation of the wireless terminal that has received the transmission permission frame 102. If the transmission request frame 101 is not transmitted when the transmission permission frame 102 is received, the maximum value is set in the NAV. After that, when the data frame is received, if the data frame is addressed to itself, it is determined that the communication uses only the transmission permission frame 102 in FIG. 3 and NAV is set to 0, and then an acknowledgment frame is transmitted to communicate. Exit. If the data frame is not addressed to itself, the count value corresponding to the time required to receive the acknowledgment frame is reset to NAV, and the loop is repeated until the NAV count value becomes zero. If no data frame is received, the NAV decreases at regular intervals and loops until it reaches zero. If an acknowledgment frame is received, the NAV count value is set to zero. When the NAV count value becomes 0, it is determined that the communication is completed.

  As described above, in the second embodiment of the present application, even when only the transmission permission frame not including the channel access prohibition period information and the destination address is used, the conventional channel access prohibition period information and Communication equivalent to the case where only the transmission permission frame including the destination address is used can be performed.

It is a figure explaining the transmission request frame and transmission permission frame used for the radio | wireless communication method of this invention. It is a figure explaining the 1st Example of this invention. It is a figure explaining the 2nd Example of this invention. It is a flowchart explaining the radio | wireless communication method of this invention. It is a flowchart explaining the radio | wireless communication method of this invention. It is a figure explaining the conventional radio | wireless communication method. It is a figure explaining the conventional transmission request frame and transmission permission frame. It is a figure explaining the conventional radio | wireless communication method. It is a figure explaining another conventional radio | wireless communication method. It is a flowchart explaining the conventional radio | wireless communication method. It is a flowchart explaining the conventional radio | wireless communication method.

Explanation of symbols

101, 701: Transmission request frame, 102, 702: Transmission permission frame, 201, 202, 203, 204, 601, 602, 603: Wireless terminal, 211, 212, 213, 214: NAV

Claims (6)

  In a wireless communication method that constitutes an ad hoc network in which a plurality of wireless terminals can directly communicate with each other, a transmission request frame that does not include channel access prohibition period information and a transmission source address, and a channel access prohibition period By transmitting and receiving a transmission permission frame that does not include information and a destination address, a wireless that can access at least the channel of one wireless terminal that is transmitting and receiving while transmitting and receiving frames between a pair of wireless terminals A wireless communication method, wherein a wireless terminal that has received either the transmission request frame or the transmission permission frame performs virtual carrier sense for prohibiting access to a channel of another wireless terminal.   The wireless communication method according to claim 1, wherein the virtual carrier sense is performed by transmitting / receiving only a transmission permission frame not including information on a channel access prohibition period and a destination address. Method. In a wireless communication method for configuring an ad hoc network in which a plurality of wireless terminals can directly communicate with each other,
The first wireless terminal transmits a transmission request frame that does not include information on the channel access prohibition period and the source address,
A second wireless terminal that has received the transmission request frame addressed to itself transmits a transmission permission frame that does not include information on a channel access prohibition period and a destination address, and the first wireless terminal transmits a data frame Is transmitted, an acknowledgment frame is transmitted to the first wireless terminal,
When the third wireless terminal that has received the transmission request frame not addressed to itself is in an access-prohibited state for at least a preset time to the channel of the first wireless terminal, the access is performed when the preset time has elapsed. Release the prohibited state,
When the third wireless terminal in the access prohibited state receives a data frame transmitted by the first wireless terminal, the access prohibited state is canceled when a time shorter than the preset time has elapsed. A wireless communication method characterized by the above. 4. The wireless communication method according to claim 3, wherein the fourth wireless terminal that has received the transmission permission frame transmitted by the second wireless terminal without receiving the transmission request frame is at least the second wireless terminal. Access to the channel is prohibited for a preset time, and when the preset time has elapsed, the access prohibition state is canceled,
When the fourth wireless terminal in the access prohibited state receives an acknowledgment frame transmitted by the second wireless terminal, the access prohibited state is canceled when a time shorter than the preset time has elapsed. A wireless communication method. In a wireless communication method for configuring an ad hoc network in which a plurality of wireless terminals can directly communicate with each other,
The fifth wireless terminal transmits a data frame after transmitting a transmission permission frame that does not include the channel access prohibition period information and the destination address,
The sixth wireless terminal that has received the transmission permission frame transmitted by the fifth wireless terminal is in an access prohibited state for at least a preset time to the channel of the fifth wireless terminal, and the preset time is When the time has elapsed, the access prohibition state is canceled,
When the sixth wireless terminal in the access prohibited state receives a data frame transmitted by the fifth wireless terminal addressed to itself, the sixth wireless terminal releases the access prohibited state,
When the data frame transmitted by the fifth wireless terminal addressed to another person is received, the access prohibition state is canceled when a time shorter than the preset time elapses.   6. The wireless communication method according to claim 3, wherein the wireless terminal is placed in an access prohibited state by setting a count value of a network allocation vector of the wireless terminal to a maximum value, and the count value is set to zero. The access prohibition state is canceled by the above-mentioned, and the access prohibition state is canceled when a time shorter than the preset time elapses by setting the counter value to a value other than the maximum value. Communication method.

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