Communication apparatus and communication system

Abstract

To provide a communication apparatus and a communication system capable of effectively reducing a communication delay on the occurrence of re-transmission in wireless communication employing the TDMA system.SOLUTION: A communication device includes a transmission unit 53, a reception unit 55, a determination unit 61, and a calculation unit 63. The reception unit 55 does not receive the retransmission request, and overhears another response to the retransmission request transmitted by another child device 5 of the retransmission target included in the plurality of child devices 5. In this case, the determination unit 61 determines whether or not the own device needs to transmit a response to the retransmission request, based on the slave unit reception information included in the other response. When the determination unit 61 determines that it is necessary to transmit the response, the calculation unit 63 calculates the second transmission timing based on the slave unit reception information included in the other response. The transmission unit 53 transmits the response to the master unit 3 at the second transmission timing.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a communication device and a communication system. [Background technology]

[0002] A conventional technique for wireless communication using a time division multiple access (TDMA) system is known. In the TDMA system, one wireless channel is divided into multiple TDMA frames at a fixed time period, and each TDMA frame is divided into multiple time slots.

[0003] Multiple users can communicate using the same channel by assigning each user a specific time slot.

[0004] In the wireless communication system disclosed in Patent Document 1, when a master device broadcasts a request to transmit sensor data, all slave devices sequentially transmit the sensor data using the time slots assigned to them in the TDMA frame.

[0005] If the master unit fails to receive sensor data from multiple slave units within the TDMA frame, it generates instruction data instructing only those slave units to retransmit the sensor data. When the master unit broadcasts a retransmission request including the instruction data, each of the multiple slave units retransmits the sensor data using the time slot assigned to it within the next TDMA frame. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-162792 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the wireless communication system disclosed in Patent Document 1, if a specific slave device among multiple slave devices fails to receive a retransmission request from the master device, it does not retransmit sensor data to the master device. In this case, the master device repeatedly sends retransmission requests, causing a communication delay.

[0008] Therefore, in wireless communications using the TDMA system, further improvements are desired in order to effectively reduce communication delays when retransmissions occur.

[0009] The present invention has been made in view of the problems inherent in the conventional techniques, and an object of the present invention is to provide a communication device and a communication system that can effectively reduce communication delays when retransmissions occur in wireless communication using the TDMA method. [Means for solving the problem]

[0010] A communication device according to a first aspect of the present invention operates as a slave device included in a plurality of slave devices in a communication system in which wireless communication using TDMA is performed between a master device and a plurality of slave devices. The communication device includes: a receiver capable of receiving a retransmission request from the master device, the retransmission request including slave device information specifying a slave device to be retransmitted; a determiner configured to determine, when the receiver receives the retransmission request, whether the slave device itself needs to transmit a response to the retransmission request based on the slave device information; a calculator configured to calculate a first transmission timing based on the slave device information if the determiner determines that the response needs to be transmitted; an extractor configured to extract the slave device information from the retransmission request; and a transmitter configured to transmit the response including the extracted slave device information to the master device at the first transmission timing. When the receiver does not receive the retransmission request and overhears another response to the retransmission request transmitted by another slave device to be retransmitted, the determiner determines, when the receiver does not receive the retransmission request and overhears the other response, the determiner determines, when the receiver does receive the retransmission request, whether the slave device itself needs to transmit the response based on the slave device information included in the other response. When the determination unit determines that the response needs to be transmitted, the calculation unit calculates a second transmission timing based on the child device information included in the other response. The extraction unit extracts the child device information from the other response. The transmission unit transmits a response including the extracted child device information to the parent device at the second transmission timing.

[0011] A communication system according to a second aspect of the present invention includes a master unit and a plurality of communication devices according to the first aspect that perform wireless communication with the master unit using TDMA. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a communication device and a communication system that can effectively reduce communication delays when retransmissions occur in wireless communication using the TDMA system. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing the overall schematic configuration of a communication system according to this embodiment. [Figure 2] FIG. 2 is a diagram showing an example of a slave unit number table according to the present embodiment. [Figure 3] FIG. 3 is a diagram illustrating an example of a communication sequence according to this embodiment. [Figure 4] FIG. 4 is a diagram illustrating an example of the configuration of a communication frame according to this embodiment. [Figure 5] FIG. 5 is a block diagram showing an example of the functional configuration of the parent device according to this embodiment. [Figure 6] FIG. 6 is a block diagram showing an example of the functional configuration of the slave unit according to this embodiment. [Figure 7] FIG. 7 is a block diagram showing an example of the hardware configuration of the parent device and the child device according to this embodiment. [Figure 8] FIG. 8 is a diagram illustrating an example of the configuration of a communication frame of a transmission request according to this embodiment. [Figure 9] FIG. 9 is a diagram illustrating an example of the configuration of a communication frame of a response to a transmission request according to this embodiment. [Figure 10] FIG. 10 is a diagram illustrating an example of a communication sequence when a retransmission request occurs according to this embodiment. [Figure 11] FIG. 11 is a diagram illustrating an example of the configuration of a communication frame for a retransmission request according to this embodiment. [Figure 12] FIG. 12 is a diagram illustrating an example of the configuration of a communication frame in response to a retransmission request according to this embodiment. [Figure 13] FIG. 13 is a diagram illustrating an example of the operation of the communication system when the slave unit according to this embodiment fails to receive a retransmission request. [Figure 14] FIG. 14 is a diagram illustrating another example of the operation of the communication system when the slave unit according to the present embodiment fails to receive a retransmission request. [Figure 15] FIG. 15 is a diagram showing an example of an operation flowchart of the parent device according to this embodiment. [Figure 16A]FIG. 16A is a diagram showing an example of an operation flowchart of the slave device according to this embodiment. [Figure 16B] FIG. 16B is a diagram showing an example of an operation flowchart of the slave device according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] The communication device and communication system according to the present embodiment will be described in detail below with reference to the drawings. Note that the same or similar reference numerals are used to designate the same functions and configurations, and descriptions thereof will be omitted as appropriate.

[0015] [Communication system configuration] First, the configuration of a communication system 1 according to this embodiment will be described. Fig. 1 is a schematic diagram of the entire configuration of the communication system 1. As shown in Fig. 1, the communication system 1 includes a master unit 3 and a plurality of slave units 5 (slave units 5a to 5h). The master unit 3 is also called a wireless master unit. The slave units 5 are also called wireless slave units or communication devices.

[0016] The master device 3 periodically broadcasts a transmission request to the slave devices 5a to 5h in order to acquire information to be transmitted from the slave devices 5a to 5h. The information to be transmitted is, for example, sensor data that each of the slave devices 5a to 5h periodically acquires from a sensor device (not shown) communicatively connected to the slave device itself.

[0017] If there is one or more slaves 5a to 5h from which the master 3 was unable to receive the information to be transmitted in response to the transmission request, the master 3 broadcasts a retransmission request to the slaves 5a to 5h. The retransmission request includes slave reception information indicating whether the master 3 received the information to be transmitted from each of the slaves 5a to 5h.

[0018] The slave units 5a to 5h are arranged within a range where they can communicate with the master unit 3. Each of the slave units 5a to 5h is arranged within a range where it can overhear (intercept) communication frames transmitted by the other slave units. In this embodiment, the number of slave units is eight, but is not limited to this, and may be seven or less or nine or more.

[0019] When each of the slave devices 5a to 5h receives a transmission request broadcast from the base device 3, it transmits the information to be transmitted that it possesses to the base device 3 in response to the transmission request. When each of the slave devices 5a to 5h receives a retransmission request broadcast from the base device 3, it determines whether or not it is a slave device to be retransmitted based on the slave device reception information included in the retransmission request. When each of the slave devices 5a to 5h determines that it is a slave device to be retransmitted, it transmits the information to be transmitted that it possesses to the base device 3 in response to the retransmission request.

[0020] Each of the slave units 5a to 5h is assigned a different slave unit number in advance. Each slave unit number is specified, for example, by firmware installed in the slave unit. FIG. 2 is a diagram showing an example of a slave unit number table. In this embodiment, as shown in FIG. 2, slave units 5a to 5h are assigned slave unit numbers 1 to 8, respectively. The slave unit numbers are also called terminal numbers or terminal IDs.

[0021] In the communication system 1, wireless communication is performed between the base station 3 and the slave stations 5a to 5h using a time division multiple access (TDMA) method. Specifically, in the communication system 1, one wireless channel is divided into a plurality of TDMA frames at a fixed time period. Each TDMA frame is divided into a plurality of time slots. The plurality of time slots have the same slot length (time length). A guard time exists between adjacent time slots. The guard time has a time length that can be set arbitrarily, taking into consideration the communication time, the deviation of the internal clocks of the slave stations 5a to 5h, and the like.

[0022] In each TDMA frame, the multiple time slots are classified into downstream communication time slots for transmitting communication frames from the base unit 3 to the slave units 5a to 5h, and upstream communication time slots for transmitting communication frames from the slave units 5a to 5h to the base unit 3. In this embodiment, in each TDMA frame, the multiple time slots are arranged in the order of downstream communication time slots and upstream communication time slots.

[0023] 3 is a diagram illustrating an example of a communication sequence. As shown in FIG. 3, in each TDMA frame, a time slot TD for downstream communication is assigned to the master unit 3. The master unit 3 communicates with the slave units 5a to 5h using the assigned time slot TD.

[0024] Each of the slave units 5a to 5h selects a time slot to be used by itself from the time slots TU1 to TU8 for upstream communication for each TDMA frame. Each of the slave units 5a to 5h communicates with the master unit 3 using the selected time slot.

[0025] In this embodiment, when the master device 3 broadcasts a communication frame of a transmission request using the time slot TD, each of the slave devices 5a to 5h, upon receiving the communication frame of the transmission request, independently selects a time slot to be used by itself.

[0026] Specifically, in the TDMA frame in which the transmission request is broadcast, the time slots TU1 to TU8 for upstream communication are linked to the slave unit numbers 1 to 8, respectively. Each of the slave units 5a to 5h selects a time slot linked to its own slave unit number from the time slots TU1 to TU8. Therefore, the slave units 5a to 5h can independently select different time slots even if the transmission request does not include information specifying the transmission timing of the slave units 5a to 5h.

[0027] With this configuration, the slave units 5a to 5h each select a time slot TU1 to TU8, and sequentially transmit communication frames including information to be transmitted to the master unit 3 as a response to the transmission request using the selected time slots TU1 to TU8. In this embodiment, the number of time slots for upstream communication is N (8 <N)である。

[0028] Figure 4 is a diagram illustrating an example of the configuration of a communication frame. As shown in Figure 4, the communication frame is composed of a preamble field, a header field, a data field, and an FCS (Frame Check Sequence) field.

[0029] The preamble field contains a specific bit sequence that the destination device uses to synchronize with the communication frame, and the header field contains the destination address and the source address.

[0030] The data field may include data types DT1 to DT4, child device reception information, and data body. Data types DT1 to DT4 are information indicating the type of communication frame. Specifically, data type DT1 is information indicating that the communication frame is a transmission request. Data type DT2 is information indicating that the communication frame is a response to a transmission request. Data type DT3 is information indicating that the communication frame is a retransmission request. Data type DT4 is information indicating that the communication frame is a response to a retransmission request.

[0031] The data types DT1 to DT4 are represented by two-bit values, for example, "00," "01," "10," and "11," respectively.

[0032] As will be described later, the slave reception information is information indicating, among the slaves 5a to 5h, the slaves from which the master 3 has received the information to be transmitted, and the slaves from which the master 3 has not received the information to be transmitted (i.e., the slaves to be retransmitted). The data body is the information to be transmitted, etc.

[0033] In this embodiment, the data field of a communication frame for a transmission request contains only a data type DT1 (see FIG. 8). The data field of a communication frame for a response to a transmission request contains a data type DT2 and a data body (see FIG. 9). The data field of a communication frame for a retransmission request contains a data type DT3 and child device reception information (see FIG. 11). The data field of a communication frame for a response to a retransmission request contains a data type DT4, child device reception information, and a data body (see FIG. 12).

[0034] The FCS field contains a bit string that the destination device uses to determine whether or not there is an error in the communication frame.

[0035] Hereinafter, when there is no need to distinguish between the slave units 5a to 5h, they will be simply referred to as "slaves 5."

[0036] [Functional configuration of the parent unit] Next, we will explain the functional configuration of the base unit 3. Fig. 5 is a block diagram showing an example of the functional configuration of the base unit 3. As shown in Fig. 5, the base unit 3 includes a control unit 11, a transmission unit 13, a reception unit 15, a storage unit 17, an acquisition unit 19, an update unit 21, a retransmission determination unit 23, and a creation unit 25.

[0037] The control unit 11 controls the overall processing in the base unit 3. Specifically, the control unit 11 controls the operation of each of the transmission unit 13, the reception unit 15, the storage unit 17, the acquisition unit 19, the update unit 21, the retransmission determination unit 23, and the creation unit 25.

[0038] The transmitter 13 transmits various signals. For example, the transmitter 13 broadcasts a transmission request and a retransmission request. The signals are also called communication frames or messages.

[0039] The receiving unit 15 receives various signals, such as a response to a transmission request and a response to a retransmission request.

[0040] The storage unit 17 stores information to be transmitted received from each of the slave units 5a to 5h. The storage unit 17 stores the address of the own unit, the addresses of the slave units 5a to 5h, and the broadcast address. The storage unit 17 stores a slave unit number table. The storage unit 17 stores data types DT1 to DT4. The storage unit 17 stores slave unit received information.

[0041] The acquiring unit 19 acquires the data type from the communication frame received by the receiving unit 15 within the TDMA frame that broadcast the transmission request. Specifically, when the receiving unit 15 receives a communication frame, the acquiring unit 19 acquires the data type from the communication frame. When the acquiring unit 19 acquires the data type DT2 from the communication frame, the acquiring unit 19 identifies the communication frame as a response to the transmission request.

[0042] When the acquisition unit 19 identifies the communication frame as a response to a transmission request, it acquires the sender address and the information of the transmission target from the communication frame. From the acquired sender address, the acquisition unit 19 identifies the slave unit 5 that sent the information of the transmission target from among the multiple slave units 5. The acquisition unit 19 associates the information of the transmission target with the slave unit number of the identified slave unit 5 and stores the information in the storage unit 17.

[0043] The acquiring unit 19 acquires the data type from the communication frame received by the receiving unit 15 within the TDMA frame that broadcast the retransmission request. Specifically, when the receiving unit 15 receives a communication frame, the acquiring unit 19 acquires the data type from the communication frame. When the acquiring unit 19 acquires the data type DT4 from the communication frame, the acquiring unit 19 identifies the communication frame as a response to the retransmission request.

[0044] When the acquisition unit 19 identifies that the communication frame is a response to a retransmission request, it acquires the source address and the information of the transmission target from the communication frame. The acquisition unit 19 identifies the slave unit 5 that transmitted the information of the transmission target among the plurality of slave units 5 from the acquired source address. The acquisition unit 19 associates the information of the transmission target with the slave unit number of the identified slave unit 5 and stores it in the storage unit 17. Note that the acquisition unit 19 is also referred to as a data acquisition unit.

[0045] The update unit 21 updates the slave unit reception information based on the slave unit number of the slave unit 5 identified by the acquisition unit 19. The slave unit reception information is composed of a bit string in which bits are arranged as many as the number of slave units 5. In the present embodiment, since the number of slave units 5 is 8, the slave unit reception information is an 8-bit bit string. Note that the slave unit reception information is also referred to as slave unit information.

[0046] In the slave unit reception information, information regarding the slave unit 5 to which the slave unit number n is assigned is set at the n-th (0 < n) bit position counted from the most significant bit position (leftmost bit position). Specifically, at the n-th bit position, information indicating whether or not the master unit 3 has received the information of the transmission target from the slave unit 5 to which the slave unit number n is assigned is set.

[0047] Note that the slave unit reception information is not limited to the above-described setting, and information regarding the slave unit 5 to which the slave unit number n is assigned may be set at the n-th (0 < n) bit position counted from the least significant bit position (rightmost bit position).

[0048] [[ID=**16**]]In the present embodiment, when the master unit 3 receives the information of the transmission target, the bit value "1" is set, and when the master unit 3 fails to receive the information of the transmission target, the bit value "0" is set. Note that the setting of the bit value is not limited to this, and when the master unit 3 receives the information of the transmission target, the bit value "0" may be set, and when the master unit 3 fails to receive the information of the transmission target, the bit value "1" may be set.

[0049] As the initial value of the handset reception information, a bit value of "0" is set in all bit positions. Based on the handset number of the handset 5 identified by the acquisition unit 19, the update unit 21 updates the bit value of "0" set in the bit position in the handset reception information corresponding to the handset number of the identified handset 5 to a bit value of "1". The update unit 21 is also referred to as a receiving handset update unit.

[0050] The retransmission determination unit 23 determines the slave units 5 from which the base unit 3 was unable to receive the information to be transmitted in the TDMA frame in which the transmission request was broadcast as slave units to be retransmitted. Specifically, the retransmission determination unit 23 determines, based on the slave unit reception information updated by the update unit 21, the slave units 5 from which the base unit 3 was unable to receive the information to be transmitted, among the multiple slave units 5. The retransmission determination unit 23 identifies bit positions in the slave unit reception information where the bit value "0" is set, and determines the slave unit 5 to which the slave unit number corresponding to that bit position is assigned as the slave unit to be retransmitted. The retransmission determination unit 23 is also referred to as a retransmission slave unit confirmation unit.

[0051] Here, the bit value set in the nth bit position of the slave reception information when the base unit 3 fails to receive the information to be transmitted can be rephrased as information indicating that the slave 5 to which slave number n is assigned is the target for retransmission. Similarly, the bit value set in the nth bit position of the slave reception information when the base unit 3 receives the information to be transmitted can be rephrased as information indicating that the slave 5 to which slave number n is assigned is not the target for retransmission.

[0052] The bit value that is set when the base unit 3 fails to receive the information to be transmitted is also referred to as a first value. Similarly, the bit value that is set when the base unit 3 receives the information to be transmitted is also referred to as a second value.

[0053] The creation unit 25 creates a communication frame for a transmission request and a communication frame for a retransmission request. When creating a communication frame for a transmission request, the creation unit 25 sets a broadcast address and the address of the parent device 3 in the destination address and source address of the header field, respectively, and sets a data type DT1 in the data field. When creating a communication frame for a retransmission request, the creation unit 25 sets a broadcast address and the address of the parent device 3 in the destination address and source address of the header field, respectively, and sets a data type DT3 and child device reception information in the data field. The creation unit 25 is also referred to as a transmission data creation unit.

[0054] [Functional configuration of the slave unit] Next, a description will be given of the functional configuration of the slave unit 5. Fig. 6 is a block diagram showing an example of the functional configuration of the slave unit 5. As shown in Fig. 6, the slave unit 5 includes a control unit 51, a transmission unit 53, a reception unit 55, a storage unit 57, an acquisition unit 59, a determination unit 61, a calculation unit 63, an extraction unit 65, an update unit 67, and a creation unit 69.

[0055] The control unit 51 controls the overall processing in the slave unit 5. Specifically, the control unit 51 controls the operation of each of the transmission unit 53, the reception unit 55, the storage unit 57, the acquisition unit 59, the determination unit 61, the calculation unit 63, the extraction unit 65, the update unit 67, and the creation unit 69.

[0056] The transmitter 53 transmits various signals. The transmitter 13 transmits, for example, a response to a transmission request and a response to a retransmission request at a transmission timing described later. The signals are also called communication frames or messages.

[0057] The receiving unit 55 receives various signals. For example, the receiving unit 55 receives a transmission request and a retransmission request. The receiving unit 55 overhears a response to a retransmission request transmitted by another slave unit 5.

[0058] The storage unit 57 stores the slave unit number of the own device and a slave unit number table. The storage unit 57 stores the address of the own device, the address of the parent device 3, and the addresses of other slave units 5. The storage unit 17 stores data types DT1 to DT4. The storage unit 17 stores slave unit reception information. The storage unit 57 stores sensor data acquired from sensor devices connected to the own device.

[0059] The acquisition unit 59 acquires the data type DT1, DT3, or DT4 from the communication frame received or overheard by the receiving unit 55 within the TDMA frame that broadcasts the transmission request or retransmission request. When acquiring the data type DT3 or DT4 from the communication frame, the acquisition unit 59 reads the slave unit reception information from the communication frame.

[0060] The acquisition unit 59 acquires sensor data from a sensor device connected to the device itself. The acquisition unit 59 stores the acquired sensor data in the storage unit 57. The acquisition unit 59 is also referred to as a data acquisition unit and an external data acquisition unit.

[0061] When the acquisition unit 59 acquires the data type DT1 (i.e., when the receiving unit 55 receives a transmission request), the determination unit 61 determines that it is necessary to transmit the information to be transmitted that the device has to the base unit 3 in response to the transmission request. When the acquisition unit 59 acquires the data type DT3 or DT4 (i.e., when the receiving unit 55 receives a retransmission request or overhears a response to the retransmission request), the determination unit 61 determines, based on the child device reception information read by the acquisition unit 59, whether it is necessary to transmit the information to be transmitted that the device has to the base unit 3 in response to the retransmission request.

[0062] Specifically, the determination unit 61 determines whether or not the bit value set in the bit position corresponding to the handset number of the own device is set to "0" in the handset reception information. If the bit value set in the bit position corresponding to the handset number of the own device is set to "0," the determination unit 61 determines that the base unit 3 has not received the information to be transmitted that it possesses, and determines that it is necessary to transmit the information to be transmitted to the base unit 3. On the other hand, if the bit value set in the bit position corresponding to the handset number of the own device is not set to "0," the determination unit 61 determines that the base unit 3 has received the information to be transmitted that it possesses, and determines that it is not necessary to transmit the information to be transmitted to the base unit 3.

[0063] The calculation unit 63 calculates the transmission timing at which the transmission unit 53 transmits the communication frame. Three methods for calculating the transmission timing by the calculation unit 63 will be described below.

[0064] The first calculation method is a calculation method for the transmission timing when the acquisition unit 59 acquires the data type DT1 (i.e., the reception unit 55 receives a transmission request) and the determination unit 61 determines that a response to the transmission request needs to be transmitted. In this case, the calculation unit 63 calculates the transmission timing of the own device based on the following equation (1).

[0065] Formula (1): Own device transmission timing = (Own device number - 1) x Guard time

[0066] In the above formula (1), for example, the transmission timing of the slave device 5a assigned slave device number 1 is "0." In this case, after receiving a transmission request from the base device 3, the slave device 5a immediately transmits a response to the transmission request in time slot TU1. Also, in the above formula (1), the transmission timing of the slave device 5b assigned slave device number 2 is "1 x guard time." In this case, after receiving a transmission request from the base device 3, the slave device 5b transmits a response to the transmission request in time slot TU2 after one guard time has elapsed.

[0067] In addition, if it is necessary to take into account the time length of the time slot for uplink communication when calculating the transmission timing of the own device, the calculation unit 63 adds the correction term "(own device's slave device number - 1) x time length of the time slot" to the above formula (1).

[0068] As a result, the slave devices 5a to 5h sequentially transmit communication frames in response to the transmission request in the order of the slave device numbers 1 to 8 assigned to them, using the time slots TU1 to TU8 for upstream communication within the TDMA frame in which the transmission request was broadcast.

[0069] The second calculation method is a calculation method for the transmission timing when the acquisition unit 59 acquires the data type DT3 (i.e., the reception unit 55 receives a retransmission request) and the determination unit 61 determines that a response to the retransmission request needs to be transmitted. In this case, the calculation unit 63 refers to the slave device reception information.

[0070] The calculation unit 63 acquires the number (retransmission number) of the bit position corresponding to the handset number of the own device, counting from the leftmost bit position set to bit value "0" among all bit positions set to bit value "0" in the handset reception information. After acquiring the retransmission number, the calculation unit 63 calculates the transmission timing of the own device based on the following equation (2).

[0071] Equation (2): Own device's transmission timing = (own device's retransmission number - 1) x guard time

[0072] In the above equation (2), for example, the transmission timing of the slave device 5 to which retransmission number 1 is assigned is "0." In this case, after receiving a retransmission request from the master device 3, the slave device 5 immediately transmits a response to the retransmission request in time slot TU1. Also, in the above equation (2), the transmission timing of the slave device 5 to which retransmission number 2 is assigned is "1 x guard time." In this case, after receiving a retransmission request from the master device 3, the slave device 5 transmits a response to the retransmission request in time slot TU2 after one guard time has elapsed.

[0073] In addition, if it is necessary to take into account the time length of the time slot for uplink communication when calculating the transmission timing of the own device, the calculation unit 63 adds a correction term "(own device's retransmission number - 1) x time length of the time slot" to the above equation (2).

[0074] As a result, the slave devices to be retransmitted transmit communication frames in response to the retransmission request in the order of the retransmission numbers, using the time slots for uplink communication within the TDMA frame in which the retransmission request was broadcast. The transmission timing calculated using the second calculation method is also called the first transmission timing.

[0075] The third calculation method is a method for calculating the transmission timing when the acquisition unit 59 acquires the data type DT4 without acquiring the data type DT3 (i.e., the receiving unit 55 overhears a response to a retransmission request without receiving a retransmission request), and the determination unit 61 determines that a response to the retransmission request needs to be transmitted. In this case, the acquisition unit 59 acquires the source address from the communication frame. The determination unit 61 identifies another slave unit 5 that transmitted the communication frame from among the multiple slave units 5, from the acquired source address.

[0076] The determination unit 61 determines whether the handset number of the identified other handset 5 is smaller or larger than the handset number of the own handset. When the determination unit 61 determines that the handset number of the identified other handset 5 is smaller than the handset number of the own handset, the calculation unit 63 acquires the number (resend number) of the bit position corresponding to the handset number of the own handset, counting from the bit position to the right of the bit position corresponding to the handset number of the identified other handset 5, which is initially set to the bit value "0", among all bit positions in the handset reception information where the bit value "0" is set.

[0077] That is, the calculation unit 63 counts the number of bit values ​​"0" in the handset reception information from the bit position corresponding to the handset number of the identified other handset 5 toward the lowest bit position to the bit position corresponding to the handset number of its own handset, and sets the value as the retransmission number.

[0078] When the calculation unit 63 acquires the retransmission number, it calculates the transmission timing of its own device based on the transmission timing of the identified other handset 5, based on the following equation (3).

[0079] Equation (3): Own device transmission timing = (own device retransmission number) × guard time

[0080] In addition, if it is necessary to take into account the time length of the time slot for uplink communication when calculating the transmission timing of the own device, the calculation unit 63 adds a correction term "(retransmission number of the own device) x time length of the time slot" to the above equation (3).

[0081] If the determination unit 61 determines that the handset number of the identified other handset 5 is greater than the handset number of the own handset, the calculation unit 63 acquires the number of the bit position (retransmission number) corresponding to the handset number of the own handset, counting from the leftmost bit position set with a bit value of "0" among all bit positions set with a bit value of "0" in the handset reception information. The calculation unit 63 further calculates the number of bit positions set with a bit value of "0" that exist to the right of the bit position corresponding to the handset number of the identified other handset 5 among all bit positions set with a bit value of "0". The calculation unit 63 adds the calculated number to the retransmission number to correct the retransmission number.

[0082] That is, the calculation unit 63 counts the number of bit values ​​"0" in the handset reception information from the most significant bit position to the bit position corresponding to the handset number of the own handset. The calculation unit 63 further counts the number of bit values ​​"0" in the handset reception information from the bit position corresponding to the handset number of the identified other handset 5 to the least significant bit position. The calculation unit 63 adds the former number to the latter number, and determines the value as the retransmission number.

[0083] After calculating the retransmission number, the calculation unit 63 calculates the transmission timing of its own device based on the transmission timing of the identified other handset 5, based on the above formula (3). The transmission timing calculated by the third calculation method is also called the second transmission timing.

[0084] As described above, in the second and third calculation methods, when the determination unit 61 determines that the information to be transmitted that the device has needs to be transmitted to the base device 3 in response to the retransmission request, the calculation unit 63 calculates the transmission timing based on the handset reception information acquired by the acquisition unit 59. Specifically, the calculation unit 63 calculates the transmission timing based on the bit position in the handset reception information that corresponds to the handset number of the device itself and other bit positions to which the bit value "0" is set. The calculation unit 63 is also referred to as a transmission timing calculation unit.

[0085] When the acquisition unit 59 acquires the data type DT3 (i.e., the receiving unit 55 receives a retransmission request) and the determination unit 61 determines that it is necessary to transmit a response to the transmission request, the extraction unit 65 extracts the handset reception information from the received communication frame. When the acquisition unit 59 acquires the data type DT4 without acquiring the data type DT3 (i.e., the receiving unit 55 overhears a response to the retransmission request without receiving a retransmission request) and the determination unit 61 determines that it is necessary to transmit a response to the transmission request, the extraction unit 65 extracts the handset reception information from the received communication frame. The extraction unit 65 stores the extracted handset reception information in the storage unit 57.

[0086] The update unit 67 updates the handset reception information extracted by the extraction unit 65. Specifically, when the acquisition unit 59 acquires the data type DT3 (i.e., the reception unit 55 receives a retransmission request) and the determination unit 61 determines that a response to the retransmission request needs to be transmitted, the update unit 67 rewrites the bit value "0" set in the bit position corresponding to the handset number of the own device in the extracted handset reception information to a bit value "1."

[0087] When the acquisition unit 59 acquires data type DT4 without acquiring data type DT3 (i.e., the receiving unit 55 overhears a response to a retransmission request without receiving a retransmission request), and the judgment unit 61 determines that a response to the retransmission request needs to be sent, the update unit 67 rewrites the bit value "0" set in the bit position corresponding to the handset number of the own device in the extracted handset reception information to the bit value "1".

[0088] If the acquisition unit 59 acquires the data type DT4 before the transmission unit 53 transmits a response to the retransmission request (i.e., if the reception unit 55 overhears the response to the retransmission request), the update unit 67 acquires the source address from the communication frame. The update unit 67 identifies another handset 5 that transmitted the communication frame from among the multiple handset units 5, based on the acquired source address. Based on the handset reception information acquired by the acquisition unit 59, the update unit 67 rewrites the bit value "0" set in the bit position corresponding to the handset number of the identified other handset unit 5 in the handset reception information already extracted by the extraction unit 65 to a bit value "1".

[0089] The creation unit 69 creates a communication frame in response to a transmission request and a communication frame in response to a retransmission request. When creating a communication frame in response to a transmission request, the creation unit 69 sets the address of the base unit 3 and its own address in the destination address and source address of the header field, respectively, and sets the data type DT2 and information on the transmission target in the data field. When creating a communication frame in response to a retransmission request, the creation unit 69 sets the address of the base unit 3 and its own address in the destination address and source address of the header field, respectively, and sets the data type DT4, updated child unit reception information, and information on the transmission target in the data field. The creation unit 69 is also referred to as a transmission data creation unit.

[0090] [Hardware configuration of parent and child units] Next, a description will be given of the hardware configuration of the parent device 3 and the child device 5. Fig. 7 is a block diagram showing an example of the hardware configuration of the parent device 3 and the child device 5. As shown in Fig. 7, each of the parent device 3 and the child device 5 is configured by a computer, and includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 105, storage 107, an antenna 109, a transmission / reception circuit 111, a clock circuit 113, and an external interface 115.

[0091] The CPU 101 executes a program stored in the ROM 103. The CPU 101 performs arithmetic processing on data loaded into the RAM 105 in accordance with the program, and comprehensively controls each part of the parent device 3 or the child device 5. The CPU is also called a processor.

[0092] ROM 103 stores programs and the like executed by CPU 101. In this embodiment, ROM 103 stores at least programs for controlling a transmission request procedure, a retransmission request procedure, an operation flow of parent device 3, and an operation flow of child device 5, which will be described later. RAM 105 temporarily holds calculation data when CPU 101 executes the programs stored in ROM 103. ROM 103 and RAM 105 are also referred to as non-volatile memory and volatile memory, respectively.

[0093] Storage 107 stores control parameters necessary for wireless communication, a transmission request procedure, a retransmission request procedure (to be described later), various information necessary for the operation flow of parent device 3, and the operation flow of child device 5. CPU 101 controls reading and writing of data from and to storage 107 in accordance with a program stored in ROM 103. Storage 107 is, for example, a hard disk drive (HDD) or a solid state drive (SSD), and storage 107 may be a combination of an HDD and an SSD. Storage 107 may also be provided as a database outside parent device 3 or child device 5.

[0094] Antenna 109 transmits and receives radio waves under the control of CPU 101. Transmitting and receiving circuit 111 performs modulation processing, demodulation processing, etc. under the control of CPU 101. Clock circuit 113 generates a clock for synchronizing time slots between parent device 3 and multiple child devices 5.

[0095] The external interface 115 is connected to an external device 200. The CPU 101 transmits and receives data to and from the external device via the external interface 115. The external device is, for example, a sensor device. In this case, the CPU 101 transmits and receives sensor data to and from the external device via the external interface 115.

[0096] [Transmission request procedure] Next, a description will be given of a transmission request procedure performed between the base unit 3 and multiple slave units 5. As shown in Fig. 3, when the base unit 3 acquires information to be transmitted from the slave units 5a to 5h, it broadcasts a transmission request communication frame to the slave units 5a to 5h in the time slot TD in the TDMA frame.

[0097] 8 is a diagram illustrating the configuration of a communication frame for a transmission request. As shown in Fig. 8, in the communication frame for a transmission request, the base unit 3 sets the broadcast address and the address of the base unit 3 in the destination address and the source address of the header field, respectively, and sets the data type DT1 in the data field.

[0098] Each of the slaves 5a to 5h receives a communication frame from the base unit 3, checks the data type DT1 set in the communication frame, and then calculates its own transmission timing for transmitting a communication frame in response to the transmission request based on the above-mentioned formula (1). When its own transmission timing arrives, each of the slaves 5a to 5h transmits a communication frame in response to the transmission request to the base unit 3.

[0099] 9 is a diagram illustrating the configuration of a communication frame in response to a transmission request. As shown in FIG. 9, each of the slaves 5a to 5h sets the address of the master 3 and its own address in the destination address and source address of the header field in the communication frame in response to the transmission request, respectively, and sets the data type DT2 and the data body in the data field.

[0100] In this way, the slave units 5a to 5h sequentially transmit the information to be transmitted that they have to the master unit 3 in response to the transmission request, in the time slots TU1 to TU8 in the same TDMA frame, respectively.

[0101] When the base unit 3 receives a response to the transmission request from each of the slave units 5a to 5h, it updates the bit value "0" in the slave unit reception information "00000000" at the bit position corresponding to each of the slave units 5a to 5h to a bit value "1". When the base unit 3 receives a response to the transmission request from all of the slave units 5a to 5h, it rewrites the slave unit reception information from "00000000" to "11111111". The base unit 3 waits until it is time to send the next transmission request.

[0102] [Retransmission request procedure] Next, a description will be given of a retransmission request procedure performed between the parent device 3 and multiple child devices 5. In the following description, as operation example 1, a case will be described in which all child devices 5 targeted for retransmission have received the retransmission request, and as operation examples 2 and 3, a case will be described in which one child device 5 among the child devices 5 targeted for retransmission has not received the retransmission request.

[0103] [Example 1] First, operation example 1 will be described. Fig. 10 is a diagram illustrating an example of a communication sequence when a retransmission request occurs. In operation example 1, as shown in Fig. 10, it is assumed that as a result of performing the above-mentioned retransmission request procedure, the master unit 3 fails to communicate with the slave units 5c, 5e, and 5h. Since there is one or more slave units among the slave units 5a to 5h from which the master unit 3 was unable to receive the information to be transmitted in response to the transmission request, the master unit 3 performs the retransmission request procedure.

[0104] In this case, in the transmission request procedure, the base unit 3 has failed to communicate with the slave units 5c, 5e, and 5h, and therefore the slave unit reception information has been rewritten from "00000000" to "11010110".

[0105] The base station 3 broadcasts a retransmission request communication frame to the slave stations 5a to 5h in time slot TD within the next TDMA frame. FIG. 11 is a diagram illustrating the configuration of the retransmission request communication frame. As shown in FIG. 11, the base station 3 sets the broadcast address and the address of the base station 3 in the destination address and source address of the header field of the retransmission request communication frame, respectively, and sets the data type DT3 and slave station reception information in the data field. In operation example 1, "11010110" is set as the slave station reception information.

[0106] Each of the slaves 5a to 5h receives a communication frame from the base unit 3 and checks the data type DT3 and slave unit reception information set in the communication frame. If a bit value of "1" is set in the bit position corresponding to the slave unit 5a to 5h in the slave unit reception information, each of the slaves 5a to 5h recognizes that the base unit 3 has received the information to be transmitted and determines that there is no need to transmit the information to the base unit 3. In this case, the slaves 5a to 5h do nothing.

[0107] On the other hand, when the bit value "0" is set in the bit position corresponding to the slave device 5a to 5h in the slave device received information, the slave device 5 determines that the base device 3 was unable to receive the information to be transmitted and determines that the information to be transmitted needs to be transmitted to the base device 3. In this case, the slave device 5 calculates its own transmission timing for transmitting a communication frame in response to the retransmission request based on the above-mentioned equation (2). In the operation example 1, each of the slave devices 5c, 5e, and 5h transmits a communication frame in response to the retransmission request to the base device 3 when its own transmission timing arrives.

[0108] When determining that the information to be transmitted needs to be transmitted to the base unit 3, the handset 5 updates the bit value "0" set in the bit position corresponding to the handset in the handset reception information to a bit value "1." In the first operation example, for example, the handset 5c rewrites the handset reception information from "11010110" to "11110110."

[0109] 12 is a diagram illustrating the configuration of a communication frame in response to a retransmission request. As shown in FIG. 12, each of the slaves 5c, 5e, and 5h sets the address of the master 3 and its own address in the destination address and source address of the header field in the communication frame in response to the retransmission request, respectively, and sets the data type DT4, slave reception information, and data body in the data field.

[0110] In this way, the slave units 5c, 5e, and 5h each sequentially transmit the information to be transmitted that they have to the master unit 3 in response to the retransmission request in the time slots TU1 to TU3 in the next TDMA frame.

[0111] When the base unit 3 receives a response to the retransmission request from each of the slave units 5c, 5e, and 5h, the base unit 3 waits until the timing for transmitting the next transmission request.

[0112] [Example 2] Next, an operation example 2 will be described. Fig. 13 is a diagram illustrating an operation example of the communication system in a case where one of the slave units 5 to be retransmitted fails to receive a retransmission request. In the operation example 2, as shown in Fig. 13, the master unit 3 transmits a communication frame of a retransmission request to the slave units 5a to 5h, but among the slave units 5c, 5e, and 5h to be retransmitted, the slave unit 5e fails to receive the communication frame and overhears a communication frame in response to the retransmission request transmitted by the slave unit 5c.

[0113] In this case, the sub-units 5c and 5h receive a retransmission request communication frame from the parent unit 3 and send a response communication frame to the retransmission request, but the sub-unit 5e does nothing because it cannot receive a retransmission request communication frame from the parent unit 3.

[0114] In this state, when the slave 5e overhears the communication frame in response to the retransmission request transmitted by the slave 5c in time slot TU1, the slave 5e checks the data type DT4 and the slave reception information "11110110" set in the communication frame. Since the bit value "0" is set in the bit position corresponding to the slave 5e in the slave reception information "11110110," the slave 5e determines that the master 3 was unable to receive the information to be transmitted and determines that the information to be transmitted needs to be transmitted to the master 3.

[0115] In this case, the slave device 5e acquires the source address from the communication frame, identifies the slave device 5c from the acquired source address, and determines that the slave device number 3 of the slave device 5c is smaller than the slave device number 5 of the slave device 5e itself.

[0116] Based on this determination, of all the bit positions in the slave unit reception information "11110110" where the bit value "0" is set, the bit position corresponding to slave unit number 5 of the slave unit 5e itself (the fifth bit from the left) is the first bit position to the right of the bit position corresponding to slave unit number 3 of slave unit 5c (the third bit from the left) where the first bit value "0" is set, so slave unit 5e acquires retransmission number 1.

[0117] When the slave device 5e acquires the retransmission number 1, it calculates its own transmission timing based on the transmission timing of the slave device 5c, for transmitting a communication frame in response to the retransmission request, based on the above-described formula (3). When its own transmission timing arrives, the slave device 5e transmits the communication frame in response to the retransmission request to the master device 3 in time slot TU2.

[0118] In this way, even if the slave unit 5e is unable to receive a retransmission request from the master unit 3, it can overhear the communication frame in response to the retransmission request sent from the slave unit 5c and transmit the communication frame in response to the retransmission request in time slot TU2, just as if it had received a retransmission request from the master unit 3.

[0119] [Example 3] Next, an operation example 3 will be described. Fig. 14 is a diagram illustrating another operation example of the communication system in a case where one of the slave units 5 to be retransmitted fails to receive a retransmission request. In the operation example 3, as shown in Fig. 14, the master unit 3 transmits a communication frame of a retransmission request to the slave units 5a to 5h, but among the slave units 5c, 5e, and 5h to be retransmitted, the slave unit 5e fails to receive the communication frame and overhears a communication frame in response to the retransmission request transmitted by the slave unit 5h.

[0120] In this case, similarly to the second operational example, the slaves 5c and 5h receive a retransmission request communication frame from the master 3 and transmit a response communication frame to the retransmission request, but the slave 5e does nothing because it cannot receive the retransmission request communication frame from the master 3. Also, let us assume that the slave 5e was unable to overhear the response communication frame to the transmission request transmitted by the slave 5c.

[0121] In operation example 3, in order for the slave unit 5h to overhear the communication frame in response to the transmission request sent by the slave unit 5c, the slave unit reception information received by the slave unit 5h from the master unit 3 is updated from "11010110" to "11110110".

[0122] In this state, when slave unit 5e overhears the communication frame in response to the retransmission request transmitted by slave unit 5h in time slot TU3, it checks the data type DT4 and slave unit reception information "11110111" set in the communication frame. Since the bit value "0" is set in the bit position corresponding to slave unit 5e in the slave unit reception information "11110111," slave unit 5e determines that base unit 3 was unable to receive the information to be transmitted and determines that it is necessary to transmit the information to base unit 3.

[0123] In this case, the slave device 5e acquires the source address from the communication frame. The slave device 5e identifies the slave device 5h from the acquired source address and determines that the slave device number 8 of the slave device 5h is greater than the slave device number 5 of the slave device 5e itself.

[0124] Based on this determination, of all the bit positions in the slave unit reception information "11110111" where the bit value "0" is set, counting from the leftmost bit position where the bit value "0" is set, the bit position corresponding to slave unit number 5 of the slave unit 5e (the fifth bit from the left) is the first, so slave unit 5e acquires retransmission number 1. Note that in operation example 3, there is no bit value to the right of the bit position corresponding to the slave unit number of slave unit 5h, so the number of bit positions to the right of that bit position where the bit value "0" is set is not calculated.

[0125] When the slave device 5e acquires the retransmission number 1, it calculates its own transmission timing based on the transmission timing of the slave device 5h, at which it transmits a communication frame in response to the retransmission request, based on the above-described formula (3). When its own transmission timing arrives, the slave device 5e transmits the communication frame in response to the retransmission request to the master device 3 in time slot TU4.

[0126] In this way, even if the slave unit 5e is unable to receive a retransmission request from the master unit 3, it can overhear the communication frame in response to the retransmission request sent from the slave unit 5h, and can transmit the communication frame in response to the retransmission request without waiting for the retransmission request to be sent in the time slot TD in the next TDMA frame.

[0127] [Operation flow of parent unit] Next, the operation flow of the base unit 3 in the transmission request procedure and the retransmission request procedure will be described. Fig. 15 is a diagram showing an example of the operation flowchart of the base unit 3.

[0128] 15, the control unit 11 determines whether it is time to send a transmission request (step S11). If the control unit 11 determines that it is time to send a transmission request, the creation unit 25 creates a communication frame of the transmission request (step S13). When the transmission timing arrives, the transmission unit 13 transmits the communication frame of the transmission request (step S15), and the operation flow ends.

[0129] If the control unit 11 determines that it is not time to send a transmission request, it determines whether or not a communication frame in response to the transmission request or retransmission request has been received (step S17). If the control unit 11 determines that a communication frame in response to the transmission request or retransmission request has been received, the acquisition unit 19 acquires information to be transmitted from the communication frame (step S19). When the acquisition unit 19 acquires the information to be transmitted, the update unit 21 updates the slave unit reception information (step S21).

[0130] When the update unit 21 updates the slave unit reception information, the retransmission determination unit 23 determines whether or not the information to be transmitted has been received from all slave units 5 (step S23). If the retransmission determination unit 23 determines that the information to be transmitted has been received from all slave units 5, the operation flow ends. If the retransmission determination unit 23 determines that the information to be transmitted has not been received from all slave units 5, the creation unit 25 creates a communication frame for a retransmission request (step S25). When the transmission timing arrives, the transmitter 13 transmits the communication frame for a retransmission request (step S27), and the operation flow ends.

[0131] [Operation flow of the child device] Next, an operational flow of the slave device 5 in the transmission request procedure and the retransmission request procedure will be described.

[0132] 16A, the control unit 51 determines whether the receiving unit 55 has received or overheard a communication frame (step S51). If the control unit 51 determines that the receiving unit 55 has received or overheard a communication frame, the acquisition unit 59 acquires the data type from the communication frame (step S53). If the control unit 51 determines that the receiving unit 55 has not received or overheard a communication frame, the process returns to step S51.

[0133] When the acquisition unit 59 acquires the data type, the determination unit 61 determines whether the data type is DT1 (step S55). If the determination unit 61 determines that the data type is DT1, the calculation unit 63 calculates the transmission timing (step S57). When the calculation unit 63 calculates the transmission timing, the creation unit 69 creates a communication frame in response to the transmission request (step S59). When the transmission timing arrives, the transmission unit 53 transmits the communication frame in response to the transmission request (step S61), and the operation flow ends.

[0134] If the determination unit 61 determines that the data type is not DT1, it determines whether the data type is DT3 (step S63). If the determination unit 61 determines that the data type is DT3, it determines whether the base unit 3 has received the information to be transmitted by its own device based on the child device reception information included in the communication frame (step S65). If the determination unit 61 determines that the base unit 3 has received the information to be transmitted by its own device, it ends the operation flow.

[0135] If the determination unit 61 determines that the parent device 3 has not received the information to be transmitted by the parent device, the calculation unit 63 calculates the transmission timing (step S67). When the calculation unit 63 calculates the transmission timing, the extraction unit 65 extracts the child device reception information included in the communication frame. When the extraction unit 65 extracts the child device reception information, the update unit 67 updates the child device reception information (step S69). When the update unit 67 updates the child device reception information, the creation unit 69 creates a communication frame in response to the retransmission request (step S71). When the transmission timing arrives, the transmission unit 53 transmits the communication frame in response to the retransmission request (step S73), and the operation flow ends.

[0136] 16B, when the determination unit 61 determines that the data type is not DT3, it determines whether or not the data type is DT4 (step S75). When the determination unit 61 determines that the data type is DT4, it determines whether or not the parent device 3 has received the information to be transmitted by the parent device based on the child device reception information included in the communication frame (step S77). When the determination unit 61 determines that the parent device 3 has received the information to be transmitted by the parent device, it ends the operation flow. When the determination unit 61 determines that the data type is not DT4, it ends the operation flow.

[0137] If the determination unit 61 determines that the parent device 3 has not received the information to be transmitted by the parent device 3, the calculation unit 63 calculates the transmission timing (step S79). When the calculation unit 63 calculates the transmission timing, the extraction unit 65 extracts the child device reception information included in the communication frame. When the extraction unit 65 extracts the child device reception information, the update unit 67 updates the child device reception information (step S81). When the update unit 67 updates the child device reception information, the creation unit 69 creates a communication frame in response to the retransmission request (step S83). When the transmission timing arrives, the transmission unit 53 transmits the communication frame in response to the retransmission request (step S85), and the operation flow ends.

[0138] [Actions and Effects] According to this embodiment, the communication device operates as a slave 5 included in multiple slaves 5 in a communication system 1 in which wireless communication using the TDMA method is performed between a parent unit 3 and multiple slaves 5, and is equipped with a transmitter 53, a receiver 55, a judgment unit 61, a calculation unit 63, and an extraction unit 65.

[0139] The receiving unit 55 can receive a retransmission request from the base unit 3, including handset reception information specifying the handset 5 to which the retransmission is to be made. When the receiving unit 55 receives a retransmission request, the determining unit 61 determines whether the device itself needs to transmit a response to the retransmission request, based on the handset reception information. When the determining unit 61 determines that the response needs to be transmitted, the calculating unit 63 calculates a first transmission timing based on the handset reception information. The extracting unit 65 extracts the handset reception information from the retransmission request. The transmitting unit 53 transmits the response, including the extracted handset reception information, to the base unit 3 at the first transmission timing.

[0140] When the receiving unit 55 does not receive a retransmission request and overhears another response to the retransmission request transmitted by another slave unit 5 that is a retransmission target and is included in the multiple slave units 5, the determining unit 61 determines whether the slave unit 5 itself needs to transmit the response based on the slave unit reception information included in the other response. When the determining unit 61 determines that the response needs to be transmitted, the calculating unit 63 calculates a second transmission timing based on the slave unit reception information included in the other response. The extracting unit 65 extracts the slave unit reception information from the other response. The transmitting unit 53 transmits a response including the extracted slave unit reception information to the base unit 3 at the second transmission timing.

[0141] With this configuration, even if the communication device cannot receive a retransmission request from the base unit 3, it can overhear other responses to the retransmission request sent by other slave units 5 that are the retransmission targets, and determine whether or not it needs to transmit a response to the retransmission request based on the slave unit reception information included in the other responses. Therefore, even if the communication device cannot receive a retransmission request from the base unit 3, it can transmit a response to the retransmission request.

[0142] Therefore, in wireless communication using the TDMA system, communication delays when retransmissions occur can be effectively reduced.

[0143] According to this embodiment, the plurality of slave devices 5 are sequentially assigned slave device numbers starting from 1. In the slave device reception information, at the n-th (0 < n) bit position, a first value indicating that the slave device 5 to which the slave device number n is assigned is a retransmission target, or a second value indicating that it is not a retransmission target is set. The calculation unit 63 calculates the first transmission timing or the second transmission timing based on the bit position corresponding to the slave device number of its own device in the slave device reception information and the other bit positions where the first value is set.

[0144] With such a configuration, only the slave device 5 that is the retransmission target has the transmission timing and transmits a response to the retransmission request to the master device 3. Therefore, the time taken for retransmission can be shortened, and the communication delay at the time of retransmission can be more effectively reduced.

[0145] According to this embodiment, the communication device further includes an update unit 67 that updates the slave device reception information. When the reception unit 55 receives a retransmission request and the determination unit 61 determines that it is necessary to transmit a response to the retransmission request, the update unit 67 rewrites the first value set at the bit position corresponding to the slave device number of its own device in the extracted slave device reception information to the second value. The transmission unit 53 transmits the response including the updated slave device reception information to the master device 3 at the first transmission timing.

[0146] With such a configuration, when another slave device 5 overhears the response to the retransmission request transmitted by the communication device, it is possible to identify the slave device 5 that has not transmitted a response to the retransmission request at the time of overhearing by simply referring to the slave device reception information included in the response. Therefore, the communication delay at the time of retransmission can be effectively reduced while reducing the data amount.

[0147] According to this embodiment, when the transmitting unit 53 overhears another response to the retransmission request before transmitting a response to the retransmission request to the base unit 3 at the first transmission timing, the updating unit 67 updates the extracted handset reception information by rewriting the first value set in the bit position corresponding to the handset number of the other handset 5 to a second value based on the handset reception information contained in the other response.

[0148] With this configuration, when another handset 5 overhears a response to a retransmission request sent by a communication device, it can efficiently identify handset 5 that has not sent a response to the retransmission request at the time of overhearing by simply referring to the handset reception information included in the response.

[0149] According to this embodiment, when the receiving unit 55 receives a retransmission request and the bit position number corresponding to the handset number of the own device, counted from the leftmost bit position where the first value is set, among all bit positions where the first value is set in the handset reception information, is the mth bit position (1≦m), the calculation unit 63 calculates the mth time slot as the first transmission timing.

[0150] With this configuration, the slave device 5 to be retransmitted can calculate its own transmission timing simply by referring to the slave device reception information included in the retransmission request. This reduces the amount of data and more effectively reduces communication delays when retransmission occurs.

[0151] According to this embodiment, the communication device further includes an update unit 67 that updates the handset reception information. When the receiver 55 does not receive a retransmission request but overhears another response to the retransmission request, the determiner 61 determines that a response to the retransmission request needs to be transmitted, and the extractor 65 extracts the handset reception information included in the other response, the update unit 67 rewrites the first value set in the bit position corresponding to the handset number of the communication device itself in the extracted handset reception information with a second value. The transmitter 53 transmits the response including the updated handset reception information to the base unit 3 at the second transmission timing.

[0152] With this configuration, when another slave device 5 overhears a response to a retransmission request transmitted by the communication device, it can identify a slave device 5 that has not transmitted a response to the retransmission request at the time of overhearing it simply by referring to the slave device reception information included in the response. This makes it possible to reduce the amount of data and effectively reduce communication delays when retransmission occurs.

[0153] According to this embodiment, when the receiving unit 55 does not receive a retransmission request but overhears another response sent by another handset 5, the judgment unit 61 judges whether the other handset 5 has been assigned a handset number that is smaller or larger than the handset number of the own device.

[0154] If the judgment unit 61 determines that the other handset 5 has been assigned a handset number smaller than the handset number of the own device, the calculation unit 63 calculates the kth time slot as the second transmission timing when the number of the bit position corresponding to the handset number of the own device, counted from the bit position to the right of the bit position corresponding to the other handset 5 and having the first value set, among all bit positions having the first value set in the handset reception information included in the other response, is kth (1≦k).

[0155] If the judgment unit 61 determines that the other handset 5 has been assigned a handset number greater than the handset number of the own device, the calculation unit 63 calculates the s+tth time slot as the second transmission timing when the bit position number corresponding to the handset number of the own device, counted from the leftmost bit position where the first value is set, among all bit positions where the first value is set in the handset reception information included in the other response, is sth (1≦s) and the number of bit positions where the first value is set and which are located to the right of the bit position corresponding to the handset number of the other handset 5 among all bit positions where the first value is set is t (0≦t).

[0156] With this configuration, the slave device 5 to be retransmitted can calculate its own transmission timing simply by referring to slave device reception information included in another response to a retransmission request sent by another slave device 5 to be retransmitted. This makes it possible to reduce the amount of data and more effectively reduce communication delays when retransmission occurs.

[0157] According to this embodiment, the multiple slave units 5 are assigned slave unit numbers in order starting from 1. The receiver 55 receives a transmission request from the master unit 3 by broadcast. The calculator 63 calculates the transmission timing based on the slave unit number of the own device. The transmitter 53 transmits a response to the transmission request at the transmission timing.

[0158] With this configuration, the timing at which slave device 5 transmits a response to a transmission request can be determined independently by slave device 5, rather than being specified by master device 3. This makes it possible to reduce the amount of data in the transmission request transmitted by master device 3.

[0159] According to this embodiment, the communication system 1 includes a base unit 3 and the plurality of communication devices described above that perform wireless communication with the base unit 3 using the TDMA system.

[0160] With this configuration, communication delays when retransmissions occur can be effectively reduced in wireless communications using the TDMA system.

[0161] [Variations] In the above-described embodiment, the transmission of the communication frame of the transmission request and the transmission of the communication frame of the response to the transmission request are performed within the same TDMA frame, but this is not limiting. The transmission of the communication frame of the transmission request and the transmission of the communication frame of the response to the transmission request may be performed within different TDMA frames.

[0162] In the above-described embodiment, the transmission of the retransmission request communication frame and the transmission of the response communication frame to the retransmission request are performed within the same TDMA frame, but this is not limiting. The transmission of the retransmission request communication frame and the transmission of the response communication frame to the retransmission request may be performed within different TDMA frames.

[0163] In the above-described embodiment, the slave device 5 to be retransmitted updates the slave device reception information when transmitting a response to a retransmission request, but this is not limited to this. The slave device 5 to be retransmitted does not need to update the slave device reception information when transmitting a response to a retransmission request. In this case, when another slave device 5 to be retransmitted does not receive the retransmission request but overhears the response, it determines the transmission timing based on the sender address of the response and the slave device reception information.

[0164] In the above-described embodiment, the slave unit reception information is composed of a bit string, but is not limited to this. The slave unit reception information may be composed of the terminal numbers of the slave units 5 from which the base unit 3 was unable to receive the information to be transmitted, and the terminal numbers of the slave units 5 from which the base unit 3 received the information to be transmitted.

[0165] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment. [Explanation of symbols]

[0166] 1. Communication Systems 3 Base unit 5 Handsets 53 Transmitter 55 Receiving unit 61 Judgment section 63 Calculation Unit 65 Extraction part 67 Update section

Claims

1. In a communication system in which wireless communication using a TDMA system is performed between a master unit and a plurality of slave units, a communication device that operates as a slave unit included in the plurality of slave units, a receiving unit capable of receiving a retransmission request from the parent device, the retransmission request including child device information specifying a child device to which the retransmission is to be made; a determination unit that determines, when the receiving unit receives the retransmission request, whether or not the device itself needs to transmit a response to the retransmission request based on the child device information; a calculation unit that calculates a first transmission timing based on the slave device information when the determination unit determines that the response needs to be transmitted; an extraction unit that extracts the child device information from the retransmission request; a transmitting unit that transmits the response including the extracted child device information to the parent device at the first transmission timing; Equipped with When the receiving unit does not receive the retransmission request and overhears another response to the retransmission request transmitted by another slave device that is a retransmission target and is included in the plurality of slave devices, the determining unit determines whether or not the own device needs to transmit the response based on slave device information included in the other response; When the determination unit determines that the response needs to be transmitted, the calculation unit calculates a second transmission timing based on the child device information included in the other response; The extraction unit extracts the child device information from the other response, The communication device, wherein the transmitting unit transmits a response including the extracted child device information to the parent device at the second transmission timing.

2. The plurality of handset units are assigned handset numbers in order starting from 1, In the child device information, a first value indicating that a child device to which a child device number n is assigned is the subject of the retransmission or a second value indicating that the child device is not the subject of the retransmission is set in an n-th (0<n) bit position.

2. The communication device according to claim 1, wherein the calculation unit calculates the first transmission timing or the second transmission timing based on a bit position in the handset information corresponding to the handset number of the own device and another bit position to which the first value is set.

3. an update unit that, when the receiving unit receives the retransmission request and the determining unit determines that the response needs to be transmitted, updates the handset information by rewriting the first value set in the bit position corresponding to the handset number of the own device in the extracted handset information with the second value; The communication device according to claim 2 , wherein the transmission unit transmits the response including the updated handset device information to the master device at the first transmission timing.

4. 4. The communication device according to claim 3, wherein when the transmitting unit overhears the other response before transmitting the response to the base unit at the first transmission timing, the updating unit updates the extracted handset information by rewriting the first value set in a bit position corresponding to the handset number of the other handset to the second value based on the handset information included in the other response.

5. 4. The communication device according to claim 3, wherein when the receiving unit receives the retransmission request and the bit position number corresponding to the handset number of the device itself, counted from the leftmost bit position where the first value is set, is m (1≦m) among all bit positions in the handset information where the first value is set, the calculation unit calculates the mth time slot as the first transmission timing.

6. an updating unit that, when the receiving unit does not receive the retransmission request but overhears the other response, the determining unit determines that the response needs to be transmitted, and the extracting unit extracts the handset information included in the other response, rewrites the first value set in a bit position corresponding to the handset number of the own device in the extracted handset information with the second value, thereby updating the handset information; The communication device according to claim 2 , wherein the transmission unit transmits the response including the updated handset device information to the master device at the second transmission timing.

7. When the receiving unit does not receive the retransmission request and overhears the other response transmitted by the other slave unit, the determining unit determines whether the other slave unit is assigned a slave unit number that is smaller or larger than the slave unit number of the own device; When the determination unit determines that the other slave device is assigned a slave device number smaller than the slave device number of the own device, the calculation unit calculates the kth time slot as the second transmission timing when the bit position number corresponding to the slave device number of the own device is kth (1≦k), counting from the bit position to the right of the bit position corresponding to the slave device number of the other slave device, among all bit positions to which the first value is set, in the slave device information included in the other response, and which is set with the first value, 7. The communication device according to claim 6, wherein when the determination unit determines that the other handset is assigned a handset number greater than the handset number of the own device, the calculation unit calculates the s+tth time slot as the second transmission timing when, among all bit positions in the handset information included in the other response in which the first value is set, the bit position number corresponding to the handset number of the own device, counted from the leftmost bit position in which the first value is set, is s (1≦s) and the number of bit positions in which the first value is set that are to the right of the bit position in which the first value is set is t (0≦t).

8. The plurality of handset units are assigned handset numbers in order starting from 1, The receiving unit receives a transmission request from the parent device by broadcast, the calculation unit calculates a transmission timing based on the slave unit number of the own device; The communication device according to claim 1 , wherein the transmitting unit transmits a response to the transmission request at the transmission timing.

9. The parent unit and A communication system comprising: a plurality of communication devices according to claim 1, which perform wireless communication with the master unit using a TDMA system.

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