JP4189330B2 - Data communication method and data communication system - Google Patents

Description

The present invention relates to a data communication method and a data communication system for performing a delivery confirmation response in a data communication network including a center station device that transmits broadcast data to a terminal device and a plurality of terminal devices that receive the broadcast data.

  Generally, when data is transmitted in a data communication network, delivery confirmation is performed to confirm whether or not the transmission data has been correctly received by the other party. If a delivery confirmation response indicating that correct data has not been received is returned from the other side, the transmitting side retransmits the same data. By repeating such retransmission by the delivery confirmation response, the receiving side can receive correct data even if the network line is not necessarily a high-quality line.

  However, when the same data is transmitted from the center station device to a number of terminal devices in a broadcast manner, if the center station device attempts to perform individual delivery confirmation with all the terminal devices, the center station device has a large number of delivery confirmations. Responses are sent back almost simultaneously, and the inbound (outside to inside) line to the center station apparatus becomes congested. For this reason, the center station apparatus takes a long time for the delivery confirmation process, or the center station apparatus cannot receive the delivery confirmation responses from all the terminal apparatuses due to a timeout.

Therefore, in the data communication system disclosed in Patent Document 1, a large number of terminal devices are grouped in advance, a representative terminal device is defined for each group, and only the representative terminal device initially receives a delivery confirmation response to the center station device. To be sent back. Then, the non-representative terminal device monitors the delivery confirmation response transmitted from the representative terminal device to the center station device, the delivery confirmation response of the non-representative terminal device is different from the delivery confirmation response of the representative terminal device, and negative Only when it is a delivery confirmation response, a delivery confirmation response is returned to the center station apparatus. As described above, in the data communication system of Patent Document 1, congestion of the inbound line is avoided by reducing the number of delivery confirmation responses returned by the terminal device.
JP-A-11-196041 (paragraphs 0018 to 0042, FIGS. 3 to 8)

  In recent years, for example, a data communication system that provides traffic information and the like to a terminal device mounted on a traveling vehicle has been put into practical use. In such a data communication system for providing information, in order to ensure communication reliability, it is essential to confirm the delivery between the center station device and the terminal device and perform retransmission as necessary. It is a requirement. However, in such a case, since the number of terminal devices may range from tens of thousands to hundreds of thousands or more, there naturally occurs a problem that the inbound line of the center station device is congested. In addition, since each terminal device moves and communication between the center station device and the terminal device is performed wirelessly, it is possible to define a representative terminal device as in the data communication system of Patent Document 1, The terminal device delivery confirmation response cannot be monitored. That is, in such a data communication system, the method of avoiding inbound line congestion as disclosed in Patent Document 1 cannot be applied.

  Therefore, in the present invention, in a data communication system that transmits the same data from a center station device to a large number of terminal devices, the center station according to the delivery confirmation response of the terminal device can be used without determining the representative terminal device in advance. It is an object to be solved to provide means capable of avoiding congestion of an inbound line of a device and capable of reliably and efficiently retransmitting data to a terminal device.

  In order to solve the above-described problems, the present invention provides a data communication method in a data communication system comprising a center station device that mainly transmits broadcast data to a terminal device and a large number of terminal devices that mainly receive broadcast data. (1) a broadcast data transmission step in which the center station apparatus transmits broadcast data to a number of terminal apparatuses; and (2) a broadcast apparatus in which the terminal apparatus receives broadcast data transmitted from the center station apparatus. A broadcast data reception step, (3) a delivery confirmation response determination step in which the terminal device determines whether or not to perform a delivery confirmation response to the received broadcast data, and (4) a response in the delivery confirmation response determination step. A delivery confirmation response step in which the terminal device determined to transmit a delivery confirmation response to the center station device; and (5) the center station device is a part of a large number of terminal devices. A delivery confirmation response evaluation step for evaluating the status of a delivery confirmation response transmitted from all of a large number of terminal devices based on a delivery confirmation response transmitted from the terminal device; and (6) the center station device performs a delivery confirmation response evaluation step. When it is determined that the evaluation result does not satisfy the predetermined condition, a data retransmission step for retransmitting broadcast data to a large number of terminal devices, and (7) the evaluation result of the delivery confirmation response evaluation step by the center station device Is determined to satisfy a predetermined condition, a communication mode transition step for transitioning the communication mode between the center station apparatus and a large number of terminal apparatuses to the individual communication mode is provided.

  Further, in the present invention, based on data transmission means for transmitting broadcast data to a number of terminal devices to a center station device, and a delivery confirmation response transmitted from some of the number of terminal devices. And a delivery confirmation response evaluating means for evaluating the status of delivery confirmation responses transmitted from a large number of terminal devices, and receiving broadcast data transmitted from the center station device to the terminal device. A delivery confirmation response determining means for deciding whether or not to make a delivery confirmation response to the received broadcast data, and delivery to the center station apparatus when it is decided to respond by the delivery confirmation response determination means. A delivery confirmation response means for transmitting a confirmation response, and the center station apparatus determines that the evaluation result by the delivery confirmation response evaluation means does not satisfy a predetermined condition. The retransmit the broadcast data to, if it is determined that satisfies the predetermined condition, and so as to shift the mode of communication between a number of terminal devices to the individual communication mode.

  As described above, in the present invention, since the terminal device includes the delivery confirmation response determination unit, it is possible to determine whether or not the terminal device itself makes a delivery confirmation response and to make a delivery confirmation response. Therefore, it is not necessary to determine a representative terminal in advance. In addition, since only some of the terminal devices make a delivery confirmation response, the number of delivery confirmation responses transmitted to the center station device can be reduced, and congestion of the inbound line of the center station device can be avoided. . On the other hand, the center station apparatus evaluates how many of the terminal devices have not yet received the correct data based on the status of the delivery confirmation response of some terminal devices by the delivery confirmation response evaluation means. can do. Based on the result, when there are many terminal devices that have not yet received the correct data, the data is retransmitted by broadcast communication, and when the number is small, the data is retransmitted by individual communication.

  According to the present invention, in a data communication system that transmits the same data from a center station device to a large number of terminal devices, it is possible to reduce delivery confirmation responses from the terminal devices without defining a fixed representative terminal. The congestion of the inbound line of the center station apparatus can be avoided. Also, it is possible to efficiently and reliably retransmit data to the terminal device.

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

FIG. 1 is an example of an overall configuration diagram of a communication system using an artificial satellite to which the present invention is applied.
The communication system of FIG. 1 includes a terminal group 3a including a center station 1, an artificial satellite 2, and a large number of terminal devices 3 as main components. Here, the center station 1 and each terminal device 3 are connected to the outbound line 4 from the center station 1 via the artificial satellite 2 to the terminal group 3a, and from the terminal group 3a via the artificial satellite 2 to the center station 1 It is connected by the inbound line 5 which goes to. Also, a part of the terminal device 3 may be connected to the center station 1 via the terrestrial Internet 8 directly or by a wireless LAN (Local Area Network) 7. Further, another part of the terminal device 3 may be connected to the center station 1 via the mobile phone line 6, the mobile phone base station 6 a and the Internet 8 or the dedicated line 9. The center station in this embodiment is an abbreviation for the center station apparatus in the claims.

  In the communication system of FIG. 1, the center station 1 transmits various types of information as broadcast data to a terminal group 3a composed of a large number of terminal devices 3 via an outbound line 4 using the artificial satellite 2 as a relay station. For example, many of the terminal devices 3 are mounted on a traveling vehicle, and the center station 1 provides information such as the congestion status of roads as broadcast data to the terminal device 3 on the vehicle. Also, in this communication system, unlike the one-way satellite broadcasting, when the terminal device 3 causes a reception error, the terminal device 3 means that the center station 1 fails to receive via the inbound line 5. Requesting retransmission of data by sending a message of acknowledgment. By retransmitting data, the reliability of data transmission / reception can be improved.

  In the communication system of FIG. 1, for example, TDM (Time Division Multiplexing) is used as the communication method of the outbound line 4. In TDM, scheduling of communication operations can be controlled entirely by the center station 1 or the artificial satellite 2. Accordingly, the center station 1 can arbitrarily set and change a method such as data retransmission control and redundancy. If the outbound line 4 is a TDM line, all the terminal devices 3 can receive all the transmission data. Therefore, the center station 1 can easily transmit broadcast data to a large number of terminal devices 3 by TDM.

  On the other hand, since communication is performed individually on the inbound line 5, that is, the line from the terminal device 3 to the center station 1, it is necessary to use a competitive access method by a large number of terminal devices 3. Here, the communication method of the inbound line 5 is, for example, FDMA (Frequency Division Multiple Access). In FDMA, the number of lines for simultaneous access is limited depending on the carrier band. Therefore, when many terminal apparatuses 3 access the center station 1 at the same time, the inbound line 5 is congested.

  In the configuration of the communication system in FIG. 1, the terminal device 3 may be a fixed terminal such as a personal computer as well as a mobile terminal mounted on a vehicle, or a mobile terminal such as a PDA (Personal Digital Assistant). It may be. Further, the center station 1 is not necessarily a ground station, and may be one mounted on the artificial satellite 2. Further, although the inbound line 5 from the terminal device 3 to the center station 1 is an FDMA line, part or all of the inbound line 5 uses a terrestrial wireless communication line such as a mobile phone line 6 or a PHS (Personal Handy phone System) line. However, via a terrestrial wireless communication line such as wireless LAN (IEEE802.11b, a and its successor standard, compatible standard), Bluetooth (IEEE802.15 and its successor standard, compatible standard), UWB (Ultra Wide Band), etc. Also good. Further, in the case of the fixed terminal device 3, a wired communication line may be used. The transmission data in the inbound direction via these ground communication lines may be transmitted to the center station 1 via the Internet 8 or directly to the center station 1 via the dedicated line 9 or the like.

  Next, the configuration of the communication device in each of the center station 1 and the terminal device 3 in this embodiment and the communication operation performed between them will be described with reference to FIGS. Here, FIG. 2 is a diagram illustrating an example of a block configuration of the communication device in each of the center station 1 and the terminal device 3, and FIG. 3 is a sequence of communication performed between the center station 1 and the terminal group 3a. It is the figure which showed the example of.

  In FIG. 2, the center station communication device 10 includes a transmission data storage unit 11, a communication control mode designation unit 12, a transmission control unit 13, a transmission conversion unit 14, a reception conversion unit 15, a reception control unit 16, and a delivery confirmation response evaluation unit 17. Etc. The terminal communication device 20 includes a reception conversion unit 21, a reception control unit 22, a delivery confirmation response determination unit 23, a transmission control unit 24, a transmission conversion unit 25, a communication control mode designation unit 26, a terminal position detection unit 27, and the like. .

  As shown in FIG. 3, the communication sequence in the embodiment of the present invention is characterized in that the center station 1 initially performs data communication with the terminal group 3a in the broadcast communication mode, and the center station 1 transmits the terminal group. When it is determined that the number of negative delivery confirmation responses (NAK) transmitted from 3a is equal to or smaller than a certain reference value (S145: detailed later), the data communication mode is switched to the individual communication mode. Further, in the broadcast communication mode, only a part of the terminal devices 3 transmits a delivery confirmation response to the center station 1 with respect to the broadcast data transmitted from the center station 1 (S120a etc .: detailed later). All terminal devices 3 transmit a delivery confirmation response to the center station 1 only in the individual communication mode. By doing so, the number of delivery confirmation responses transmitted by the terminal group 3a for the broadcast data transmitted by the center station 1 can be limited, and congestion of the inbound line 5 associated with the delivery confirmation response can be avoided. it can. In FIG. 3, the delivery confirmation response is described as ACK (Acknowledgement: positive acknowledgment response) or NAK (Negative Acknowledgement), and also in this specification, ACK or NAK notation is used.

  Next, returning to FIG. 2, the function and operation of each block will be described. First, the center station 1 transmits target data as broadcast data to the terminal group 3a. Here, the target data refers to the main body of data that the center station 1 intends to transfer to the terminal device 3, and refers to a block of data having a predetermined data amount such as a file. Although the target data is generally transmitted and received by a plurality of packets, in the following description, it is assumed that the target data is transmitted and received by one packet. Further, data transmitted and received between the center station 1 and the terminal device 3 includes a control message in addition to target data. The control message refers to transmission / reception data used for controlling communication between the center station 1 and the terminal device 3, and the delivery confirmation response is also included in the control message.

  The target data input to the center station communication device 10 is supplied by an upper layer system such as a computer. The input target data is stored in the transmission data storage unit 11 in preparation for retransmission processing, and the transmission control unit 13 reconstructs a data frame or performs encoding for error detection / correction. To do. Further, the target data is packetized into a predetermined format in the transmission control unit 13, and modulation and frequency conversion conforming to the specification of the outbound line 4 is added in the transmission conversion unit 14 such as a modem, and the terminal is connected via an antenna or the like. Sent to group 3a. Note that when the center station 1 and the terminal device 3 are connected by wire, a connector connected to, for example, a LAN cable instead of an antenna corresponds to this. In addition, the transmission control part 13 can produce | generate various control messages with respect to the terminal device 3, and can send those messages toward the terminal group 3a via the transmission conversion part 14 similarly to the objective data.

  The terminal communication device 20 receives a signal transmitted from the center station 1 via an antenna or a connector, and the received signal is demodulated by a reception conversion unit 21 such as a modem and converted into a digital signal. The reception control unit 22 disassembles the digitized received data packet, performs predetermined error detection / correction processing, and restores the target data. In the error detection / correction process, the target data that has no reception error is output to a higher-layer system such as a display control device (not shown) included in the terminal device 3, for example.

  The reception control unit 22 notifies the delivery confirmation response determination unit 23 of the result of the predetermined error detection / correction processing. The delivery confirmation response determination unit 23 that has received the notification determines whether or not it should make a delivery confirmation response based on a predetermined determination method (detailed later). As a result, when it is determined that a delivery confirmation response should be made, the delivery confirmation response determination unit 23 sends a delivery confirmation response (ACK / NAK) indicating success or failure of reception to the center station 1 to the transmission control unit 24. To send. According to the instruction, the transmission control unit 24 transmits ACK / NAK to the center station 1 and requests retransmission of the target data by NAK transmission. The ACK / NAK message is packetized at the time of transmission, modulated by the transmission conversion unit 25 according to the specifications of the inbound line 5, and transmitted from the antenna or connector of the terminal communication device 20. Note that the terminal communication device 20 can transmit target data and can also transmit control messages other than ACK / NAK.

  Next, the center station communication device 10 receives a signal transmitted from the terminal communication device 20 via an antenna or a connector, and the received signal is demodulated by a reception conversion unit 15 such as a modem and converted into a digital signal. Is done. The reception control unit 16 disassembles the packet of the digitized reception signal, performs predetermined error detection / correction, and restores control data such as target data or ACK / NAK.

  Here, the delivery confirmation response evaluation unit 17 monitors a delivery confirmation response (ACK / NAK) message returned from the terminal group 3a, and how many terminal devices 3 of the terminal devices 3 of the terminal group 3a are the center. It is estimated by evaluating whether the target data (broadcast data) transmitted from the station 1 is correctly received. As a result, when the number of terminal devices 3 that have not received correct target data is greater than a predetermined number, the delivery confirmation response evaluation unit 17 instructs the transmission control unit 13 to retransmit the target data, When the number of terminal devices 3 that have not received the correct target data becomes smaller than a predetermined number, the delivery confirmation response evaluation unit 17 notifies the communication control mode designating unit 12 to that effect.

  In response to the notification, the communication control mode designating unit 12 instructs the transmission control unit 13 to transmit an instruction message for shifting to the individual communication mode. The transmission control unit 13 performs processing such as packetization for transmission of the message for instructing transition to the individual communication mode. Further, the transmission conversion unit 14 modulates the signal and transmits it from the antenna or the connector to the terminal group 3a. Send to. When the transmission ends, the communication control mode designating unit 12 switches the communication mode of the transmission control unit 13 to the individual communication mode.

  In the terminal communication device 20, the message for instructing the transition to the individual communication mode received via the reception conversion unit 21 is interpreted as a control message by the reception control unit 22, and that is the communication control mode designation unit 26. Will be notified. Upon receiving the notification, the communication control mode designating unit 26 switches the communication mode of the reception control unit 22 to the individual communication mode.

  Next, an example of a sequence of communication performed between the center station 1 and the terminal group 3a will be described with reference to FIG. 3 and with reference to FIG. 2 as appropriate. Note that, since this communication sequence example is an example of the operation for explanation, the sequence flow in the decision branch block branches according to one branch direction according to the situation of the explanation. In FIG. 3, the operation of the terminal device 3 of the terminal group 3a is described by using the terminal A and the terminal B as representatives.

  First, the center station 1 transmits the target data to the terminal group 3a as broadcast data (S110). Terminal A and terminal B receive the transmitted target data (S110a, S110b), and each reception control unit 22 checks whether there is any reception error. As a result, if there is no error, a positive delivery confirmation response (ACK) is transmitted to the center station 1, and if there is an error, a negative delivery confirmation response (NAK) is transmitted. That is, ACK means successful reception of target data, and NAK means failure of receiving target data. Here, NAK is transmitted assuming that there is a reception error in both terminal A and terminal B (120a, 120b). In this embodiment, if it is determined in advance as a rule, during the broadcast communication mode, both ACK / NAK may be responded, or only ACK or NAK may be responded.

  Next, the center station 1 receives a delivery confirmation response (ACK / NAK) transmitted from the terminal group 3a (S120). At this time, if transmission of ACK / NAK is performed from all the terminal devices 3 in the terminal group 3a, the inbound line 5 is immediately congested. Therefore, in the present embodiment, the terminal communication device 20 is provided with the delivery confirmation response determination unit 23 (see FIG. 2), and only the terminal device 3 that has decided to respond with the delivery confirmation response by its own delivery confirmation response determination unit 23. Then, a delivery confirmation response (ACK / NAK) is transmitted to the center station 1. By doing so, the number of ACK / NAK transmissions can be reduced, and congestion of the inbound line 5 can be avoided.

  Here, whether or not the delivery confirmation response determination unit 23 should perform the delivery confirmation response can be uniquely determined according to, for example, its own device number or a randomly generated random number. However, the center station 1 designates a reply rate to the terminal device 3 in advance in order to determine the approximate number of terminal devices 3 that respond to the delivery confirmation. The reply rate is the probability that the terminal device 3 will respond to the delivery confirmation. For example, when 1% is specified as the reply rate, the terminal device 3 may generate a random number, for example, and a delivery confirmation response may be made when the last two digits of the random number are “23”, for example. . Then, the terminal device 3 transmits a delivery confirmation response at a rate of about 1 in 100. Note that the reference number such as “23” may be a random number or may be the last two digits of the device number. Further, the reply rate can be transmitted to the terminal device 3 as dedicated control message data or as additional information in the header portion of the target data.

  The center station 1 can directly specify the terminal device 3 to which a delivery confirmation response should be made by polling. When the outbound line 4 is TDM, the center station 1 can transmit a polling message by designating a plurality of terminal devices 3 or as broadcast transmission data. In this case, the target terminal device 3 is designated by data attached to the polling message. For example, if geographical information such as a prefecture name is included in a polling message, the terminal device 3 that has received the polling message is, for example, a position obtained by a terminal position detection unit 27 such as a GPS (Global Positioning System). Based on the information, it is determined whether or not a delivery confirmation response should be made. In addition, the terminal device 3 should just transmit a delivery confirmation response, when a polling message is received and made into the object of a delivery confirmation response.

  In FIG. 3, the terminal A and the terminal B are examples of the terminal device 3 that is determined by the delivery confirmation response determination unit 23 to be a delivery confirmation response. Here, both transmit NAK (S120a, S120b). However, if the terminal A and the terminal B are determined to be not the delivery confirmation response, they are NAKs in steps S120a and S120b. Is not sent.

  Next, when the center station 1 receives the delivery confirmation response (ACK / NAK) transmitted from the terminal group 3a (S120), whether or not the number of received NAKs is equal to or less than the reference value in the delivery confirmation response evaluation unit 17 Is determined (S125). This determination is made by estimating how many terminal devices 3 that have not successfully received the target data transmitted from the center station 1 remain, and the remaining terminal devices 3 receive a delivery confirmation response ( It is intended to determine whether or not the inbound line 5 is congested when ACK / NAK) is transmitted.

  For example, if the congestion of the inbound line 5 does not occur in communication with the terminal device 3 having 1000 or less, and the total number of terminal devices 3 is 100,000, the initial response rate is 1%. There is a need. In this case, since the ACK / NAK response can be expected from 1000 terminal apparatuses 3, the reference value of the number of received NAKs is 10. Therefore, if 5% of the terminal devices 3 fail to receive and the actual number of received NAKs is 50, the determination condition of step S125 is not satisfied. If estimated from the reception failure rate of 5%, there are still 5000 terminal devices 3 that could not receive correct data as a whole.

Therefore, the center station 1 retransmits the target data to the terminal group 3a (S130). Since terminal A and terminal B have failed to receive the previous target data, they receive the retransmitted target data (S130a, S130b). Here, the terminal device 3 that has successfully received the target data does not need to receive the target data to be retransmitted.
Next, the terminal A and the terminal B inspect whether there is a reception error (S135a, S135b). When the delivery confirmation response determining unit 23 determines to perform the delivery confirmation response, the delivery confirmation response is transmitted to the center station 1. Here, since there is a reception error, terminal A transmits a NAK to center station 1 (S140a), and since terminal B has no reception error, terminal A transmits an ACK to center station 1 (S140b). ) The reception operation has been completed.

  According to the above example, 5000 terminal devices 3 that could not receive correct data remain, and congestion of the inbound line 5 does not occur until communication with the terminal device 3 of 1000 or less. The reply rate that can be determined is 20%. In this case, the center station 1 can expect an ACK / NAK response from the 1000 terminal devices 3 as before. Therefore, if there is no change in the communication conditions and environment, the reference value for the number of received NAKs can be 200.

  Next, the center station 1 receives again the delivery confirmation response (ACK / NAK) transmitted from the terminal group 3a (S140). If the reception failure rate of the terminal device 3 remains 5%, the number of received NAKs is 50. Therefore, the number of received NAKs is below the reference value (S145). At this time, the number of terminal apparatuses 3 that have not successfully received the target data is estimated to be 250. This number of terminal devices 3 no longer congest the inbound line 5.

  Therefore, the center station 1 transmits a message for instructing the transition to the individual communication mode to the terminal group 3a in order to shift the communication mode between the center station 1 and the terminal device 3 from the broadcast communication mode to the individual communication mode. (S150). The terminal A receives the message for instructing transition to the individual communication mode (S150a), and transitions the communication mode to the individual communication mode (S155a). Here, among the terminal devices 3 of the terminal group 3a, the terminal device 3 that has not yet successfully received the target data similarly receives the message for instructing the transition to the individual communication mode, and sets the communication mode to the individual communication mode. Transition to mode. Note that there are cases where it is not necessary to distinguish between the broadcast communication mode and the individual communication mode depending on the communication method as in the case of TDM or the like. In that case, transmission of the transition instruction message to the individual communication mode (S150) is unnecessary.

  On the other hand, if the number of received NAKs is not less than the reference value in step S145, the center station 1 and terminal A perform the operations from step S130 to step S145, and the number of received NAKs is less than the reference value. Repeat until. That is, the retransmission of the target data is repeated until the terminal device 3 that has not successfully received the target data does not congest the inbound line 5 even if individual communication is performed.

  Next, when the communication mode shifts to the individual communication mode, the terminal device 3 that has not yet successfully received the target data, including the terminal A, transmits a retransmission request message of the target data to the center station 1 (S160a). The center station 1 receives the retransmission request message for the target data (S160). At this stage, since the number of terminal devices 3 that have not received the target data correctly is sufficiently small, the inbound line 5 is not congested by this transmission. The target data retransmission request message may be a NAK as a delivery confirmation response, or may be a control message independent of the NAK.

  Receiving the target data retransmission request message, the center station 1 individually retransmits the target data to the terminal device 3 that transmitted the message (S170). Upon receiving the retransmission, the terminal device 3 receives the target data (S170a), checks whether there is a reception error (S170b), and if there is an error, transmits the NAK to the center station 1 and re-purposes the target data. Data retransmission is requested (not shown). Also, the presence or absence of a reception error is checked (S175a). If there is no error, ACK is transmitted to the center station 1 (S180a), and the reception operation is completed. On the other hand, the center station 1 receives the ACK transmitted from the terminal device 3 (S180), confirms that the ACK has been received from all the terminal devices that have performed the individual communication operation (S185), and performs a series of transmissions. Complete the operation.

  As described above, in this embodiment, the delivery confirmation response determination unit 23 is provided for the target data transmitted from the center station 1 by providing the delivery confirmation response determination unit 23 in the terminal communication device 20 of the terminal device 3. Only the terminal device 3 that has determined to receive a delivery confirmation response transmits a delivery confirmation response (ACK / NAK) to the center station 1. Therefore, even if the number of terminal devices 3 communicating with the center station 1 is a large number exceeding, for example, several hundred thousand, for example, if the return rate is set to about 0.1%, a delivery confirmation response (ACK / NAK) The number can be reduced to about several hundreds. Therefore, the inbound line 5 is not congested due to a delivery confirmation response (ACK / NAK) transmitted from the terminal device 3 to the center station 1.

  Further, since the delivery confirmation response evaluation unit 17 is provided in the center station communication device 10, the center station 1 can evaluate the number of delivery confirmation responses (ACK / NAK) transmitted from the terminal device 3. Thereby, the center station 1 can estimate the number of terminal devices 3 that have not successfully received the target data. Therefore, when the estimated value becomes a predetermined number or less, in other words, when the number of received NAKs becomes a predetermined number or less, the center station 1 sets the communication mode with the terminal device 3 individually. Switch to communication mode and start communication. By doing so, the terminal device 3 requesting the target data can reliably receive the target data without error without congesting the inbound line 5.

  As mentioned above, although one Embodiment of this invention was described, this Embodiment is further supplemented and demonstrated using FIGS. Here, FIG. 4 is a diagram illustrating an example of a sequence of communication performed between the center station 1 and the terminal group 3a when the center station 1 polls the terminal device 3 to which a delivery confirmation response should be made. 5 shows an example of a sequence of communication performed between the center station 1 and the terminal group 3a when the center station 1 transmits a communication control mode change message to the terminal group 3a. FIG. 6 is an example of a flowchart showing the communication operation of the center station communication device 10 in the broadcast communication mode, and FIG. 7 is an example of a flowchart showing the communication operation of the terminal communication device 20 in the broadcast communication mode. It is.

  FIG. 4 is a diagram illustrating an example of a sequence of communication performed between the center station 1 and the terminal group 3a when the center station 1 polls the terminal device 3 to which a delivery confirmation response should be made. FIG. 4 is a diagram for correcting a part of FIG. 3. Therefore, in FIG. 4, the same reference numerals are assigned to blocks showing the same operation corresponding to FIG. 3. In FIG. 4, the terminal B is not shown.

  In FIG. 4, the center station 1 first transmits target data to the terminal group 3a as broadcast data (S110). Terminal A receives the transmitted target data (S110a), and the reception control unit 22 checks whether there is any reception error. Next, the center station 1 designates the terminal device 3 as the terminal A, for example, and transmits a polling message (S117). The terminal A receives the polling message (S117a), and transmits a delivery confirmation response (ACK / NAK) to the center station 1 based on the result of the previously checked reception error. In the example of FIG. 4, NAK is transmitted (S120a). The terminal device 3 that has not received the polling message, or the terminal device 3 that has not been targeted even after receiving the polling message, needs to transmit a delivery confirmation response (ACK / NAK) to the center station 1. Absent.

  The center station 1 receives the delivery confirmation response (ACK / NAK) transmitted as described above (S120), and evaluates whether or not the number of received NAKs is equal to or less than the reference value (S125). Depending on the result, the target data is retransmitted (S130) or the individual communication mode is entered, but the subsequent operation is the same as the communication sequence shown in FIG.

The method in which the center station 1 polls and selects the terminal device 3 that responds to the delivery confirmation response is effective when it is desired to transmit the target data more reliably.
For example, when it is desired to reliably deliver information to the affected area at the time of a disaster, the terminal device 3 in the affected area is designated by intensive polling. In this case, the terminal device 3 compares the position information acquired by the terminal position detection unit 27 with the polling target area specified by the center station 1 to determine whether the terminal device is the polling target. to decide.

Further, for example, when the target data is map partial update data, the terminal device 3 existing in the vicinity of the updated map may be polled with increasing specific gravity.
In addition, in the satellite line, the received radio wave may be attenuated due to rain or the like, so the terminal device 3 in the rainy area may be intensively polled. Conversely, by polling without the terminal device 3 in the rainy region, it is possible to improve the estimation accuracy of the reception error rate of the entire terminal group 3a. Further, when polling is performed by excluding the terminal device 3 in the rain region, the target data can be transmitted more efficiently by repeating the retransmission after the rain is canceled than when repeating the retransmission in the rain with a high reception error rate. it can.

  Next, FIG. 5 shows an example of a sequence of communication performed between the center station 1 and the terminal group 3a when the center station 1 transmits a communication control mode change message to the terminal group 3a. However, this is a diagram for correcting a part of FIG. Therefore, in FIG. 5, the same reference numerals are given to blocks showing the same operation corresponding to FIG. 3. Further, in FIG. 5, illustration of the terminal B is omitted.

  In FIG. 5, the center station 1 transmits the target data (S110), the terminal A receives the target data (S110a), checks whether there is a reception error (S115a), and there is a reception error. A NAK is transmitted to the center station 1 as a delivery confirmation response (S120a). The center station 1 receives a delivery confirmation response (ACK / NAK) transmitted from the terminal group 3a including the terminal A (S120), evaluates the reception status, and determines whether or not the number of received NAKs is equal to or less than a predetermined reference value. Is determined (S125). Up to this point, the communication sequence is the same as that shown in FIG.

  Next, when the number of received NAKs is equal to or greater than a predetermined reference value and the center station 1 attempts to retransmit the target data, the center station 1 transmits a communication control mode change message to the terminal group 3a prior to the retransmission (S127). ). Here, changing the communication control mode means changing the communication protocol between the center station 1 and the terminal device 3, for example, changing the error correction code of the target data to a stronger one or the same. Increasing the number of consecutive packets or increasing the depth of interleaving is performed. Here, continuous transmission refers to transmitting the same frame multiple times in the same session in order to increase the survival rate of the frame, and is distinguished from retransmission in which the same data transmission session is repeated multiple times.

  Such a change in the communication control mode is performed in order to efficiently retransmit the target data. For example, when the number of received NAKs is abnormally large due to rain or the like, that is, when there are many terminal devices 3 that have failed to receive the target data, it is difficult to cause an error in communication at the time of retransmission. Change to a communication method that is easy to correct even if a problem occurs. In this case, the number of terminal devices 3 that fail to receive the target data decreases faster than normal retransmission.

  Conversely, when the number of received NAKs is small and the number of terminal devices 3 that failed to receive the target data is less than expected, the probability that the terminal device 3 makes a delivery confirmation response, that is, the response rate is increased. A control message may be sent. This procedure can be applied only when the terminal apparatus 3 transmits only NAK as a delivery confirmation response. However, since the delivery confirmation responses from a larger number of terminal apparatuses 3 can be collected, the target data has been successfully received. The number of terminals that are not available can be estimated more accurately.

  In FIG. 5, when the center station 1 transmits a communication control mode change message (S127), the center station 1 changes the communication control mode in the communication control mode designating unit 12 (S128). The terminal device 3 receives the communication control mode change message (S127a), and changes the communication control mode in the communication control mode designating unit 26 (S128a). Thus, according to the changed communication control mode, the center station 1 transmits the target data (S130), and the terminal device 3 receives the target data (S130a).

  FIG. 6 is an example of a flowchart showing the communication operation of the center station communication device 10 in the broadcast communication mode, which integrates the communication operations of the center station 1 in FIGS. Therefore, the description of FIG. 6 slightly overlaps with the description of FIGS. 3 to 5, but will be described again including supplements. For convenience of explanation, in FIG. 6 and FIG. 3 to FIG. 5, the reference numerals of the blocks indicating the operations are given different reference numerals even in the same operation blocks.

  In FIG. 6, the center station communication apparatus 10 inputs target data supplied from a host system such as a computer (S210), stores it in the transmission data storage unit 11 (S220), and toward the terminal group 3a. Transmit (S230). When polling is used to designate the terminal device 3 that responds to the delivery confirmation (Yes in S240), the center station 1 designates the terminal device 3 toward the terminal group 3a and transmits a polling message (S250). ). Next, the center station 1 sends out a delivery confirmation response (ACK / NAK) transmitted from the terminal device 3 that spontaneously determines the delivery confirmation response at a predetermined reply rate in the terminal group 3a or the terminal device 3 designated by polling. ) (S270), and the reception status of the ACK / NAK is evaluated (S280).

  Here, the evaluation of the ACK / NAK reception status means that the correct target data is still received among the terminal devices 3 of the entire terminal group 3a from the actual number of ACK / NAK received from some terminal devices 3. This means estimating the number of terminal devices 3 that are not connected and the ratio thereof. The simplest estimation model is as illustrated in the description of FIG. In that model, the total number of terminal devices 3, the maximum number of terminal devices 3 that do not cause congestion of the inbound line 5, the reply rate, and the number of received NAKs are used. Using information such as the ratio of the model improves the accuracy of the model. Some of the terminal devices 3 are non-operating and exist in a non-communication area (for example, in a tunnel), but the total number of terminal devices 3 is actually calculated based on the number of ACK receptions and the number of NAK receptions. It can be obtained as the number of terminal devices 3 in operation. Further, in the line via the artificial satellite 2, the line state is greatly influenced by the weather. Such weather information or the like can be reflected in the reply rate.

  Here, the same model as described in FIG. 3 is assumed. Therefore, the center station 1 obtains the maximum number of terminal devices 3 that do not cause congestion of the inbound line 5, and determines the maximum number of NAK receptions determined by the maximum number, the total number of terminal devices 3, and the reply rate. Use the reference value. The number of NAKs actually received is compared with the reference value (S290). As a result, when the number of received NAKs is larger than the reference value (No in S290), the center station 1 retransmits the target data to the terminal group 3a (S340). In this way, if the retransmission of the target data to the terminal group 3a is repeated several times, the number of received NAKs becomes less than the reference value. When the number of received NAKs is equal to or less than the reference value (Yes in S290), the center station 1 transmits a message for instructing the transition to the individual communication mode to the terminal group 3a (S300) and still successfully receives the correct target data. The terminal device 3 that is not connected is individually communicated.

  In FIG. 6, steps S <b> 310 and S <b> 320 are optional operations that are performed when the communication control mode is changed in resending the target data. For example, in the case of a satellite line, the line state deteriorates due to rain or the like. Therefore, a strong error correction method is used, and during retransmission, it is difficult to cause an error in communication, or an error is corrected. Change to an easy communication method. Therefore, when changing the communication control mode (Yes in S310), the center station 1 transmits a communication control mode change message to the terminal group 3a (S320), and changes the communication control mode of the communication control mode designating unit 12. (S330). These operations are described in detail in FIG.

  FIG. 7 is an example of a flowchart showing the communication operation of the terminal communication device 20 in the broadcast communication mode, which integrates the communication operation of the terminal device 3 in FIGS. Accordingly, the description of FIG. 7 slightly overlaps with the description of FIGS. 3 to 5, but will be described again including supplements. For convenience of explanation, in FIG. 7 and FIG. 3 to FIG. 5, the reference numerals of the blocks indicating the operations are different even in the same operation blocks.

  In FIG. 7, the terminal device 3 receives data transmitted from the center station 1 (S410), and checks whether there is an error in the received data (S420). As a result, if there is an uncorrectable reception error (Yes in S420) and there is a need for a delivery confirmation response (Yes in S430), a NAK is transmitted as a delivery confirmation response (S440). If there is no uncorrectable reception error (No in S420) and there is a need for a delivery confirmation response (Yes in S430a), an ACK is transmitted as a delivery confirmation response (S440a).

  Next, when there is no reception error in the received data (No in S420), the data is sorted. If the received data is the target data (Yes in S450), the receiving operation is completed. If the received data is an instruction message for switching to the individual communication mode (Yes in S460), the communication control mode designating unit 26 of the terminal communication device 20 is changed to the individual communication mode, and the individual communication mode is shifted to. If the received data is a polling message (Yes in S470), a polling response message is transmitted (S480). The polling response message may be ACK / NAK or a special message. If the received data is a communication control mode change message (Yes in S490), the communication control mode of the communication control mode designating unit 26 is changed (S500), and the communication from the center station 1 is performed according to the communication control mode. Enable transmission data to be received.

  When receiving the data, the terminal device 3 basically transmits either ACK / NAK as a response to the center station 1 (S440, S440a). However, as described above, in the broadcast communication mode, both ACK / NAK may be responded, or only ACK or NAK may be responded. The method for responding may be determined in advance in consideration of the likelihood of occurrence of reception errors. Further, even when the retransmission operation is being repeated depending on the number of ACK / NAK actually received, the response method may be switched. Furthermore, when the target data is unnecessary for the terminal device 3, an ACK may be transmitted regardless of whether there is a reception error. In this case, there is an advantage that the center station 1 can grasp the degree of demand for the transmitted target data. In addition, as a result, the number of terminal devices 3 that have not been successfully received quickly becomes equal to or less than the reference value, so that the transition to the individual communication mode can be made early. Further, in addition to ACK (successful reception) and NAK (reception failure), a response message that explicitly indicates that reception is unnecessary may be used.

In FIG. 7, a delivery confirmation response (ACK / NAK) is transmitted for the control message as well as the target data. However, in FIGS. 3 to 6, the ACK / NAK transmission operation and control message for the control message are transmitted. The description is omitted. This is because the explanation is avoided.
Also, the control message has a role of setting the state of the terminal device 3 such as the communication control mode to a state instructed by the center station 1. Therefore, it is necessary to transmit the control message more reliably. Therefore, the transmission of the control message may be repeatedly performed a plurality of times regardless of the ACK / NAK delivery confirmation response. Since the control message has a smaller data amount than the target data, the influence on communication efficiency is small.

  In the above embodiment of the present invention, all the terminal devices 3 are assumed to have a delivery confirmation response function, but it is not always necessary that all the terminal devices 3 have a delivery confirmation response function. Therefore, only a part of the terminal devices 3 may have a delivery confirmation response function, and the other terminal devices 3 may not have the delivery confirmation response function. When the number of terminal devices 3 as the terminal group 3a is large, the reception error status of the remaining terminal devices 3 is estimated from the delivery confirmation responses from some terminal devices 3 having a delivery confirmation response function. Can do. Further, in this case, all of the terminal devices 3 having the delivery confirmation response function may transmit the delivery confirmation response, or a part thereof may transmit the delivery confirmation response. Thus, by deleting the delivery confirmation response function of the terminal device 3 and further deleting the transmission function itself, the manufacturing cost and power consumption cost of the terminal device 3 can be reduced.

It is an example of the whole block diagram of the communication system using the artificial satellite to which this invention is applied. It is the figure which showed the example of the block configuration of the communication apparatus in each of the center station and terminal device in embodiment of this invention. It is the figure which showed the example of the sequence of the communication performed between the center station and terminal group in embodiment of this invention. In the embodiment of the present invention, it is a diagram showing an example of a sequence of communication performed between the center station and a terminal group when the center station polls a terminal device to which a delivery confirmation response should be made. In the embodiment of the present invention, when the center station transmits a communication control mode change message to the terminal group, it is a diagram illustrating an example of a sequence of communication performed between the center station and the terminal group. In the embodiment of the present invention, it is an example of a flowchart showing the communication operation of the center station communication device in the broadcast communication mode. In embodiment of this invention, it is an example of the flowchart which shows the communication operation | movement of the terminal communication apparatus at the time of broadcast communication mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Center station 3 Terminal device 3a Terminal group 4 Outbound line 5 Inbound line 10 Center station communication apparatus 12 Communication control mode designation | designated part 13 Transmission control part 14 Transmission conversion part 15 Reception conversion part 16 Reception control part 17 Delivery confirmation response evaluation part 20 Terminal Communication device 21 Reception conversion unit 22 Reception control unit 23 Delivery confirmation response determination unit 24 Transmission control unit 25 Transmission conversion unit 26 Communication control mode designation unit

Claims (6)

A data communication method in a data communication system mainly composed of a center station device that transmits broadcast data to a terminal device and a large number of terminal devices that mainly receive broadcast data,
The center station device is
Broadcast data transmission step of transmitting broadcast data consisting of a plurality of packets to the multiple terminal devices,
A delivery confirmation response receiving step for receiving a delivery confirmation response to the broadcast data transmitted from some of the plurality of terminal devices among the multiple terminal devices that have received the broadcast data;
Based on the delivery confirmation response transmitted from some of the plurality of terminal devices received in the delivery confirmation response receiving step, the reception status of the broadcast data in the entire number of terminal devices is determined. A delivery acknowledgment evaluation step to evaluate;
When the evaluation result by the delivery confirmation response evaluation step does not satisfy a predetermined condition, a data retransmission step of retransmitting the broadcast data to the multiple terminal devices;
A communication mode transition step for shifting a communication mode between the center station device and the multiple terminal devices to an individual communication mode when an evaluation result in the delivery confirmation response evaluation step satisfies a predetermined condition;
With
The terminal device is
Broadcast data receiving step for receiving the broadcast data transmitted from the center station device;
A delivery confirmation response determining step for determining whether or not to perform a delivery confirmation response to the broadcast data after receiving the broadcast data in the broadcast data receiving step;
A data communication method comprising: a delivery confirmation response step of transmitting a delivery confirmation response to the center station apparatus when it is determined in the delivery confirmation response determination step that a delivery confirmation response is made . When the evaluation result of the delivery confirmation response evaluation step does not satisfy a predetermined condition, the center station device may communicate with the terminal device before retransmitting the broadcast data to the multiple terminal devices. A center station apparatus communication control mode change step of transmitting to the terminal apparatus a message to change the communication control mode of communication performed in the above, and changing the communication control mode of the own apparatus to the communication control mode
Further comprising
When the terminal device receives a message to change the communication control mode from the center station device, the terminal device communication control mode changing step of changing the communication control mode of the own device to the communication control mode specified by the message The data communication method according to claim 1, further comprising: In the delivery confirmation response determination step, the terminal device determines whether to make a delivery confirmation response based on information included in the polling message when receiving the polling message transmitted from the center station device. The data communication method according to claim 1 or 2 . A center station device which mainly transmits the broadcast data to the terminal device, a data communication system comprising a plurality of terminal devices mainly receive broadcast data,
The center station device is
Broadcast data transmission means for transmitting broadcast data consisting of a plurality of packets to the multiple terminal devices;
A delivery confirmation response receiving means for receiving a delivery confirmation response to the broadcast data transmitted from a plurality of terminal devices among the plurality of terminal devices that have received the broadcast data;
Based on the delivery confirmation response transmitted from some of the plurality of terminal devices received by the delivery confirmation response receiving means, the reception status of the broadcast data in the entire multiple terminal devices is determined. A delivery confirmation response evaluating means for evaluating,
When the evaluation result by the delivery confirmation response evaluation unit does not satisfy a predetermined condition, the broadcast data is retransmitted to the multiple terminal devices,
When the evaluation result by the delivery confirmation response evaluation unit satisfies a predetermined condition, the communication mode between the center station device and the multiple terminal devices is shifted to the individual communication mode ,
The terminal device is
Broadcast data receiving means for receiving the broadcast data transmitted from the center station device;
A delivery confirmation response determining means for determining whether or not to send a delivery confirmation response to the broadcast data after receiving the broadcast data by the broadcast data receiving means;
A delivery confirmation response means for transmitting a delivery confirmation response to the center station apparatus when it is determined by the delivery confirmation response determination means to be a delivery confirmation response;
Data communication system, characterized in that it comprises a. When the evaluation result by the delivery confirmation response evaluating unit does not satisfy a predetermined condition , the center station device may contact the terminal device before retransmitting the broadcast data to the multiple terminal devices. The center station apparatus communication control mode changing means for transmitting a message to the terminal apparatus to change the communication control mode of communication performed in the terminal apparatus and changing the communication control mode of the own apparatus to the communication control mode.
Further comprising
When the terminal device receives a message to change the communication control mode from the center station device, the terminal device communication control mode changing means changes the communication control mode of the own device to the communication control mode specified by the message. further data communication system according to claim 4, characterized in that it comprises a. The delivery confirmation response determining unit is a delivery confirmation response determining unit that determines whether to perform a delivery confirmation response based on information included in the polling message when a polling message transmitted from the center station apparatus is received. data communication system according to claim 4 or claim 5, characterized in that.

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