JP2010050882A - Communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To guarantee a data packet transmission opportunity to each terminal while avoiding the problem of a so-called hidden terminal. <P>SOLUTION: A communication apparatus includes: a non-transmission period setting section 15 for setting a data packet non-transmission period within a fundamental cycle; a transmission timing control section 18 for determining whether or not a data packet can be transmitted at a time out of the non-transmission period within the fundamental cycle; and a transmission circuit 19 for periodically transmitting a data packet while no carrier is detected in a case where it is determined that any data packet cannot be transmitted. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a communication device.

  2. Description of the Related Art Conventionally, there has been proposed a wireless system that transmits information by broadcasting (broadcasting) individual wireless terminal devices to surrounding wireless terminal devices without using a control station such as a base station. As an example of realizing such a communication form, in a CSMA (Carrier Sense Multiple Access) method, which is one of communication methods used in a wireless LAN, a terminal (node) that wants to transmit data is a packet of another terminal. The communication status is monitored (carrier sense), and transmission is started when the channel is free.

  In such a wireless system, for example, the terminal A monitors the communication status of a terminal that exists within a range where radio waves around it reach by carrier sense.

  For this reason, when there are many other terminals in the vicinity, there is a case where the timing for transmitting own data cannot be obtained and the data transmission is greatly delayed. For this reason, there is a problem that reliability cannot be guaranteed when the number of terminals and communication traffic increase.

  Furthermore, when there are many other terminals where direct carrier sense is not possible outside the radio wave reachable range, the communication status of these terminals cannot be detected, and when the terminal A itself transmits data, When colliding with communication (so-called hidden terminal problem) occurs. The wireless LAN has means for avoiding this communication collision using a method called RTS / CTS (Request To Send / Clear To Send). Although this method is effective when it is desired to communicate with a specific terminal, it cannot be applied in the case of broadcast communication, and thus there is a problem that it is impossible to avoid the collision of the packet communication.

  Therefore, in order to solve the above problem, a method of accessing a frame by dividing it into n slots in time is proposed (see Patent Document 1). The wireless terminal device described in Patent Document 1 monitors slot occupancy information in units of frames, and exchanges information with other terminals by embedding slot occupancy information in a transmission packet in addition to transmission data of the terminal itself. To do. The frame is composed of, for example, 100 ms, and each slot is occupied by a different terminal.

  Also, with respect to the so-called hidden terminal problem, the technique of Patent Document 1 embeds frame information indicating various occupation states of slots in a packet, and based on the reception status of the packet and the frame information of the packet, Packet collision is avoided in consideration of existence. However, since the technique of Patent Document 1 is based on the premise that frame information exists in a packet, the transmission target data in one packet cannot be increased.

  Further, as one method for avoiding the hidden terminal problem, a MACA (Multiple Access Collision Avoidance) method has been proposed. However, when the MACA method is used, there is a problem that communication between neighboring terminals is stopped more than necessary.

Therefore, Patent Document 2 discloses a wireless communication system that does not stop communication with neighboring terminals more than necessary. In the wireless communication system of Patent Document 2, when a terminal other than the transmission source terminal and the transmission destination terminal receives a communication request packet, the terminal temporarily stops transmitting a wireless signal and receives a communication permission packet. Temporarily stops transmitting radio signals.
JP 2007-28550 A JP 2008-85505 A

  However, in the wireless communication system of Patent Document 2, when a terminal other than the transmission source terminal and the transmission destination terminal receives a large number of communication request packets or communication permission packets, it must stop transmitting the wireless signal many times. As a result, the packet to be transmitted cannot be transmitted. As a result, there is a problem that a fair transmission opportunity is not given to each terminal and the system does not function.

  The present invention has been proposed to solve the above-described problems, and provides a communication device that can guarantee a transmission opportunity of a data packet to each terminal while avoiding a so-called hidden terminal problem. Objective.

  A communication apparatus according to the present invention includes a transmission prohibition period setting unit that sets a transmission prohibition period of a data packet within a basic period, and a transmission determination that determines whether a data packet can be transmitted at a time other than the transmission prohibition period within the basic period Means, a transmission prohibition period determination means for determining whether the current timing is a transmission prohibition period, a carrier detection determination means for determining whether a carrier is detected at the current timing, and the transmission determination means to transmit a data packet When it is determined that it is possible, when a predetermined determination result is obtained by the transmission prohibition period determination unit and the carrier detection determination unit, respectively, or when it is determined by the transmission determination unit that a data packet cannot be transmitted A data packet is periodically transmitted when a predetermined determination result is obtained by the carrier detection determination means. It includes a Tapaketto transmitting means.

  If the data packet cannot be transmitted in a time other than the transmission prohibition period within the basic period and the data packet transmission is stopped as it is, there is no opportunity to transmit the data packet, and communication with other terminals cannot be performed at all.

  Therefore, in the above invention, when it is determined that the data packet cannot be transmitted, the data packet is periodically transmitted when a predetermined determination result is obtained by the carrier detection determination means. As a result, the above-described invention can be achieved by transmitting data packets even if packet collision may occur. Can be sent to.

  Here, the transmission determination means, based on the comparison result between the transmission prohibition period or the time other than the transmission period with respect to the basic period and a predetermined threshold, the data packet is transmitted at a time other than the transmission prohibition period within the basic period. It may be determined whether transmission is possible.

  Further, the transmission determination means determines whether the data packet can be transmitted in a time other than the transmission prohibition period within the basic period, based on the number of times the reply packet from the other terminal for the data packet has been received within the basic period. May be.

  Further, when it is determined that the data packet can be transmitted by the transmission determination unit, the data packet transmission unit determines that the current timing is not the transmission prohibition period by the transmission prohibition period determination unit, and the carrier detection determination unit The data packet may be transmitted when it is determined that the carrier is not detected at the timing.

  The data packet transmitting means transmits the data packet when the carrier determining means determines that the carrier is not detected at the current timing when the data determining means determines that the data packet cannot be transmitted. May be.

  According to the communication device of the present invention, even when it is determined that the data packet cannot be transmitted in a time other than the transmission prohibition period within the basic period, when a predetermined determination result is obtained by the carrier detection determination unit By periodically transmitting the data packet, it is possible to avoid that the data packet cannot be transmitted.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration of a communication device of a wireless communication network according to the first embodiment of the present invention. The wireless communication network is dynamically configured by each communication device broadcasting a packet. Here, the basic period is divided into a plurality of slots, and each communication apparatus occupies one of the slots and transmits a data packet. Hereinafter, as necessary, a communication device to be described is referred to as an own terminal, and a communication device around the own terminal is referred to as a peripheral terminal or another terminal.

  The communication device receives a packet transmitted from another wireless terminal device via the reception antenna 11, and a packet that detects a received packet and detects at which slot (at which timing) the received packet is transmitted. A detection unit 13, a packet demodulation unit 14 that demodulates data transmitted from the detected packet to generate reception information, and a transmission prohibition period setting that sets a transmission prohibition period based on timing information of the detected packet Part 15.

  Further, the communication apparatus includes a packet generator 16 that generates a packet based on the transmission information, a reply packet generator 17 that generates a reply packet based on the demodulated packet, and a transmission timing controller 18 that controls transmission timing. And a transmission circuit 19 that transmits the generated packet via the antenna 20 and a control circuit 30 that controls the overall operation.

  The reply packet generator 17 determines whether the packet is normally detected based on the packet demodulated by the packet demodulator 14, and only when the packet is normally detected indicates that the packet is normally detected. A reply packet is generated. Thus, in this embodiment, there is one type of reply packet generated by the reply packet generator 17.

  The transmission timing control unit 18 controls the transmission timing of the data packet generated by the packet generation unit 16 and the return packet generated by the return packet generation unit 17 with respect to the transmission circuit 19. In particular, for a reply packet, the transmission timing control unit 18 controls the transmission circuit 19 so as to be surely transmitted after a predetermined period after the reception of the data packet is completed. The predetermined time is common to all terminals. Therefore, when a large number of terminals are crowded around, reply packets from the terminals collide. Although this will be described in detail later, this is used for detecting a hidden terminal by intentionally colliding a reply packet.

  FIG. 2 is a diagram illustrating a configuration of a basic period transmitted and received by n communication apparatuses. A data packet and a reply packet indicate one transmission / reception combination. That is, in this embodiment, there are only two types of packets. One basic period is set to 100 msec, for example, and there are n slots.

  FIG. 3 is a state transition diagram of the communication apparatus. The communication apparatus transits the states of “reception standby state”, “data packet transmission process”, “reply packet reception process for data of own terminal”, “signal reception process”, and “reply packet transmission process”.

  Specifically, in a reception standby state, the communication apparatus shifts to a data packet transmission process when there is no reception signal and there is data to be transmitted, and shifts to a signal reception process when a reception signal is detected.

  When the data packet cannot be transmitted in the data packet transmission process, the communication apparatus shifts to a reception standby state. When the data packet transmission process is completed, the communication apparatus shifts to a reply packet reception process for the data of the terminal itself. Then, in the reply packet reception process for the data of the terminal itself, the communication apparatus shifts to a reception standby state when the process is completed or when a predetermined period has elapsed.

  On the other hand, in the signal reception process, the communication apparatus shifts to a reception standby state when the process is completed, and shifts to a reply packet transmission process when the process is completed and a return packet needs to be transmitted. Then, when the processing is completed in the reply packet transmission processing, the communication device shifts to a reception standby state. Hereinafter, the data packet transmission process, the data packet transmission process of the own terminal, the signal reception process, and the reply packet transmission process will be described.

(Data packet transmission processing)
When there is no reception signal and there is data to be transmitted in the reception standby state, the communication apparatus shifts to a data packet transmission process and executes the next process.

  FIG. 4 is a flowchart showing the processing routine of “data packet transmission processing”. In step S1, the transmission timing control unit 18 determines whether the data packet can be transmitted in a time (gap time) other than the transmission prohibition period within the next basic period.

  FIG. 5 is a diagram illustrating the relationship between the basic transmission cycle Tcycle, the transmission prohibition period (NAV period), and the clearance time. As shown in the figure, the gap time becomes shorter as the set number of transmission prohibition periods increases, and if the gap time is too short, data packets may not be transmitted.

  Therefore, the transmission timing control unit 18 determines whether the data packet can be transmitted in the gap time, and the transmission prohibition period setting ratio (TNAV / Tcycle) with respect to the time until the next basic period is less than the predetermined threshold value α. Determine whether. Note that TNAV is the total time of the transmission prohibition period (NAV period) within the basic transmission period Tcycle. If the determination is affirmative (TNAV / Tcycle <α), the process proceeds to step S2 to determine transmission of the data packet by both the transmission prohibition period and carrier sense. In the case of negative determination (TNAV / Tcycle ≧ α), the process proceeds to step S3 in order to determine transmission of the data packet only by carrier sense.

  In step S2, the transmission timing control unit 18 determines whether the current timing is the transmission prohibition period set by the transmission prohibition period setting unit 15. If the determination is affirmative, the transmission timing control unit 18 is in a state of “there is data to be transmitted”. If the determination is negative, the process proceeds to step S3.

  In step S3, the transmission timing control unit 18 measures the reception sensitivity of each slot based on the detection result of the reception circuit 12 or the packet detection unit 13, and determines whether or not a carrier is detected at the current timing. When the determination is affirmative, the state shifts to the reception standby state while the state of “data to be transmitted” remains, and when the determination is negative, the processing proceeds to step S4.

  In step S4, the transmission timing control unit 18 controls the transmission circuit 19 to transmit the data packet generated by the packet generation unit, and ends this routine. Thereby, the data packet is transmitted to each terminal via the antenna 20. And it transfers to the reply packet reception process with respect to the data of the own terminal.

  In addition, when it is not a transmission prohibition period (determination determination of step S1) and the condition of carrier non-detection (determination determination of step S2) is not satisfied, there is “data to be transmitted”, but “reception standby state” and “ It goes back and forth between “data packet transmission processing”. In this case, when it is time to transmit the next data packet, processing for discarding the previous data to be transmitted and transmitting new data is performed.

  As described above, when it is determined that the data packet cannot be transmitted in a time other than the transmission prohibition period of the basic cycle (determination determination in step S1), the transmission timing control unit 18 performs the same operation as in normal CSMA / CA operation. If no carrier is detected at the current timing, a data packet is transmitted (steps S3 and S4).

  For this reason, there is a possibility that a packet collision with a hidden terminal may occur. However, since a data packet is transmitted while avoiding a packet collision with a terminal within a range where the own terminal can detect a carrier, It is possible to avoid being unable to transmit.

  That is, the communication apparatus can transmit a data packet with strong power to a terminal that is in a relatively close range from the own terminal, although packet collision may occur with the hidden terminal. Therefore, assuming an application for a safety device, there is an advantage that it is possible to communicate with a terminal close to its own terminal even if packet collision occurs when communication traffic is high and communication to all terminals is not successful. is there.

  In step S1, the transmission timing control unit 18 compares (TNAV / Tcycle) with α in order to determine whether the data packet can be transmitted with the gap time of the basic cycle, but the present invention is not limited to this. is not.

  For example, the transmission timing control unit 18 counts the number of times that a reply packet from another terminal for the data packet is received within the basic period, and if this count value exceeds a predetermined threshold, If it is determined that the packet cannot be transmitted, and the count value does not exceed a predetermined threshold, it may be determined that the data packet can be transmitted in the gap time of the basic period.

(Return packet reception processing)
FIG. 6 is a flowchart showing a processing routine of “reply packet reception processing for data of own terminal”. In step S11, the transmission timing control unit 18 determines whether a predetermined period has elapsed after the data packet transmission in step S3 described above. If the determination is affirmative, this routine is terminated and the process proceeds to a reception standby state. In this case, the process proceeds to step S22.

  In step S12, the packet receiving unit 13 determines whether reply packets for the data of the terminal itself have been received from all the peripheral terminals. If the determination is affirmative, the process proceeds to step S13. If the determination is negative, the process returns to step S11. . In addition, when the reply packet is received within a predetermined period after the transmission of the data packet of the own terminal, it is regarded as a reply packet to the own terminal, and when it is received during the other period It is regarded as a reply packet to the hidden terminal.

  In step S13, the transmission prohibition period setting unit 15 sets a transmission prohibition period to reserve the next transmission timing.

  FIG. 7 is a timing chart for explaining the transmission prohibition period. Here, after the terminal transmits a data packet, all peripheral terminals transmit a reply packet to the data packet.

  At this time, when the transmission prohibition period setting unit 15 receives a reply packet for the data packet of the own terminal from all peripheral terminals, the transmission prohibition period setting unit 15 determines 100 msec after the transmission timing of the data packet of the own terminal as the next scheduled transmission timing of the own terminal. Then, the period from the current timing to the next scheduled transmission timing is set as a transmission prohibition period, and this routine ends. As a result, the next scheduled transmission timing of the terminal is reserved. Then, the state shifts to a reception standby state.

(Signal reception processing)
Further, when the communication apparatus detects a reception signal in the “reception standby state”, the communication apparatus shifts to “signal reception process” and executes the next process.

  FIG. 8 is a flowchart showing the processing routine of “signal reception processing”. In step S21, the receiving circuit 12 shown in FIG. 1 receives a packet of another terminal (peripheral terminal), the packet detection unit 13 detects the packet, and the process proceeds to step S22.

  In step S22, the transmission prohibition period setting unit 15 determines the type of the packet detected by the packet detection unit 13. If the packet is a data packet, the process proceeds to step S23. If the packet is a reply packet, the process proceeds to step S24.

  In step S23, the transmission prohibition period setting unit 15 waits for a predetermined period, ends this routine, and proceeds to a reply packet transmission process.

  In step S24, since a reply packet that is not a reply to the data packet of the terminal itself has been detected, it can be seen that there is a hidden terminal. Therefore, the transmission prohibition period setting unit 15 sets the transmission prohibition period as follows.

  FIG. 9 is a timing chart for explaining the transmission prohibition period. Here, a transmission packet of a hidden terminal (a terminal that is detected in the peripheral terminal but not detected in the own terminal) is transmitted every basic transmission cycle (for example, 100 msec), but is not detected in the own terminal. It is assumed that the reply packet of the peripheral terminal is detected by the own terminal.

  When a reply packet is detected, the transmission prohibition period setting unit 15 predicts 100 msec after the reply packet detection timing as the reception timing of the next reply packet, and from the predicted timing to the time before the predetermined period, Set as the transmission prohibition period.

  There is a possibility that the return packet is a packet transmitted from a peripheral terminal in response to a data packet transmitted from a hidden terminal. Therefore, the transmission prohibition period setting unit 15 sets a period during which the hidden terminal may transmit the next data packet as the transmission prohibition period based on the detection timing of the return packet. Then, after setting the transmission prohibition period, this routine is ended and a transition is made to a reception standby state.

(Reply packet transmission process)
FIG. 10 is a flowchart showing the processing routine of “reply packet transmission processing”. In step S31, the transmission timing control unit 18 controls the transmission circuit 19 to transmit a reply packet after a predetermined period from the completion of reception of the data packet, and proceeds to step S32. As a result, when the data packet is normally received, a reply packet is always transmitted after a predetermined period has elapsed from completion of reception.

  In step S32, the transmission prohibition period setting unit 15 sets a transmission prohibition period so that the own terminal does not transmit at the next transmission schedule timing of another terminal.

  FIG. 11 is a timing chart for explaining the transmission prohibition period. Here, the transmission prohibition period setting unit 15 sets the next transmission timing and the expected period as the transmission prohibition period so that the own terminal does not transmit at the next transmission scheduled timing of the other terminal. Specifically, the transmission prohibition period setting unit 15 sets a transmission prohibition period that ends after 100 msec (basic transmission period) after the terminal transmits a reply packet and starts from the end to a predetermined time before. . Thereby, the next transmission timing of the other terminal is included in the transmission prohibition period, and it is possible to prevent the own terminal from transmitting the data packet at the next transmission timing of the other terminal. Then, when the setting of the transmission prohibition period is completed, this routine is terminated and a transition is made to a reception standby state.

  As described above, when the communication apparatus according to the present embodiment cannot transmit a data packet in a time other than the transmission prohibition period within the basic period, the transmission prohibition period is ignored and the carrier is not detected at the current timing. If so, the data packet is forcibly transmitted.

  As a result, even if the communication device cannot communicate with all terminals due to packet collision, it can communicate with a terminal within a range close to its own terminal. As well as a fair transmission opportunity. As a result, it is possible to avoid the failure of the system due to data transmission.

  It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can also be applied to a design modified within the scope described in the claims.

It is a block diagram which shows the structure of the communication apparatus of the radio | wireless communication network which concerns on embodiment of this invention. It is a figure which shows the structure of the basic transmission period transmitted / received by a communication apparatus. It is a state transition diagram of a communication apparatus. It is a flowchart which shows the process routine of a "data packet transmission process". It is a flowchart which shows the process routine of the "reply packet reception process with respect to the data of the own terminal." It is a timing chart for demonstrating a transmission prohibition period. It is a flowchart which shows the processing routine of a "signal reception process". It is a timing chart for demonstrating a transmission prohibition period. It is a flowchart which shows the processing routine of a "reply packet transmission process". It is a timing chart for demonstrating a transmission prohibition period. It is a timing chart for demonstrating a transmission prohibition period.

Explanation of symbols

12 reception circuit 13 packet detection unit 14 packet demodulation unit 15 transmission prohibition period setting unit 16 packet generation unit 17 reply packet generation unit 18 transmission timing control unit 19 transmission circuit

Claims (5)

A transmission prohibition period setting means for setting a transmission prohibition period of the data packet within the basic period;
Transmission determination means for determining whether a data packet can be transmitted in a time other than the transmission prohibition period within the basic period;
A transmission prohibition period determination means for determining whether the current timing is a transmission prohibition period;
Carrier detection determination means for determining whether a carrier is detected at the current timing;
When it is determined that the data packet can be transmitted by the transmission determination unit, when a predetermined determination result is obtained by the transmission prohibition period determination unit and the carrier detection determination unit, respectively, or data is transmitted by the transmission determination unit When it is determined that a packet cannot be transmitted, when a predetermined determination result is obtained by the carrier detection determination unit, a data packet transmission unit that periodically transmits a data packet;
A communication device comprising: The transmission determination unit transmits a data packet at a time other than the transmission prohibited period within the basic period based on a comparison result between a transmission prohibition period or a time other than the transmission period with respect to the basic period and a predetermined threshold value. The communication device according to claim 1, wherein it is determined whether or not it is possible. The transmission determination unit determines whether or not the data packet can be transmitted in a time other than the transmission prohibition period within the basic period based on the number of receptions of the reply packet received from another terminal within the basic period for the data packet. Item 4. The communication device according to Item 1. The data packet transmission means determines that the current timing is not a transmission prohibition period by the transmission prohibition period determination means when the transmission determination means determines that the data packet cannot be transmitted, and the carrier detection determination means The communication apparatus according to any one of claims 1 to 3, wherein a data packet is transmitted when it is determined that a carrier is not detected at the current timing. The data packet transmission means transmits the data packet when the carrier determination means determines that the carrier is not detected at the current timing when the transmission determination means determines that the data packet can be transmitted. The communication device according to any one of claims 1 to 3.

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