JP6560605B2 - Wireless communication system and wireless terminal - Google Patents

Description

  The present invention relates to a radio communication system and radio terminals constituting the system.

  With the downsizing and cost reduction of wireless devices, the development of information processing devices and the increase in storage capacity, the demand for sensor network systems that provide services using information collected from a large number of wireless sensor terminals has increased. Yes. At the same time, there is an increasing demand for lower power consumption of wireless sensor terminals for the purpose of reducing maintenance costs caused by battery replacement. In particular, in an ad hoc network that realizes a wide communication area by relaying communication between wireless terminals, the power consumption of a wireless terminal that relays communication from another wireless terminal is larger than the power consumption of a general wireless terminal. Tend to be. For this reason, high expectations are placed on the technology for reducing the power consumption of wireless terminals used in ad hoc networks.

  In an ad hoc network, RIT (Receiver Initiated Transmission) is one of the techniques for reducing the power consumption of a wireless terminal that relays communication. In this method, all wireless terminals start intermittently, broadcast a request signal to the surroundings at a timing at which they can be relayed, and the wireless terminal that receives the request signal returns a data signal to another wireless terminal. Relay the data signal from Thereby, the start-up time of the wireless terminal that relays the data signal is suppressed as much as possible, and the power consumption is reduced.

JP 2009-206624 A

En-Yi A. Lin, Jan M. Rabaey, Sven Wiethoelter, Adam Wolisz, “Receiver Initiated Rendezvous Schemes for Sensor Networks”, In Proc. Of IEEE Globecom 2005, Nov. 2005

  In the RIT scheme, only one wireless terminal that first transmitted a data signal among wireless terminals that have received a request signal from a wireless terminal that relays communication (hereinafter referred to as “relay terminal”) communicates with the relay terminal. forgiven. For this reason, the relay terminal needs to transmit request signals as many as the number of wireless terminals connected to the relay terminal. When the system is introduced, the number of request signal transmissions is set in each relay terminal in consideration of the arrangement status of wireless terminals and the frequency of occurrence of communication. When the number of request signal transmissions is smaller than the required number, wireless terminals that cannot communicate with each other are generated. Conversely, when the number of request signal transmissions is greater than the required number, the power consumption of the relay terminal increases. For this reason, for smooth operation of the system, it is necessary to frequently adjust the transmission frequency and interval of request signals by an administrator who is well versed in wireless technology, leading to an increase in cost and burden on the person in charge.

  In a wireless communication system in which a wireless terminal moves and a wireless communication system that employs a rank routing method in which a relay route is not determined in advance, the number of wireless terminals connected to each relay terminal always changes. For this reason, it is difficult to always maintain the number of request signal transmissions at an appropriate number, and it has been difficult to smoothly operate the system while taking advantage of the characteristics (low power consumption) of the RIT method.

  In order to solve the above problems, the present invention employs, for example, the configurations described in the claims. The present specification includes a plurality of means for solving the above-described problems. For example, the first wireless terminal that transmits a data signal as a response to the request signal after receiving the broadcasted request signal. And a second wireless terminal that automatically changes the number of transmissions for transmitting the request signal within a predetermined time based on the communication status of the first wireless terminal.

  As another example, “the first wireless terminal that transmits a data signal as a response to the request signal after receiving the broadcast request signal, and the transmission interval of the request signal is set to the first wireless terminal. A wireless communication system having a second wireless terminal that automatically changes based on the communication status of the wireless terminal.

  According to the present invention, it is possible to automatically set the number of transmissions or the transmission interval of request signals by the relay terminal to a value according to the actual situation. Problems, configurations, and effects other than those described above will become apparent from the following description of embodiments.

1 is a diagram illustrating a configuration of a sensor network system according to a first embodiment. The figure which shows the example of a communication sequence. The figure which shows the example of allocation of communication possible time. 3 is a flowchart illustrating an example of an operation sequence of the relay terminal according to the first embodiment. FIG. 3 is a diagram illustrating a structure example of a data signal used in the first embodiment. 1 is a diagram illustrating a functional configuration of a wireless terminal according to Embodiment 1. FIG. The figure which shows the example of a message sequence which concerns on Example 1 (example which reduces the frequency | count of transmission of a request signal). The figure which shows the example of a message sequence which concerns on Example 1 (example which increases the frequency | count of transmission of a request signal). FIG. 6 is a diagram illustrating a structure example of a data signal used in the second embodiment. 9 is a flowchart illustrating an example of an operation sequence of the relay terminal according to the second embodiment. FIG. 10 is a diagram illustrating a functional configuration of a wireless terminal according to a third embodiment. 9 is a flowchart illustrating an example of an operation sequence of the relay terminal according to the third embodiment. 10 is a flowchart illustrating an example of an operation sequence of the relay terminal according to the fourth embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiment of the present invention is not limited to the examples described later, and various modifications are possible within the scope of the technical idea. The communication system described below means, for example, IEEE802.11a system, IEEE802.11b system, ZigBee (registered trademark) system, UWB (Ultra Wideband) system, and ISA100.11A system of wireless LAN (Local Area Network). It is assumed that all wireless terminals and base stations that make up the wireless communication system have a common time axis that is time synchronized.

  Hereinafter, a sensor network system that transmits measurement results of a vibration sensor, a temperature sensor, and the like attached to a device such as a motor to a server through a wireless terminal to manage the operation status of the device and detect an abnormality will be described. However, the application of the present invention is not limited to the sensor network system, but can also be applied to an energy management system that controls the output by measuring the power consumption of the device, an operation management system that manages the state and position of the vehicle, and the like.

(1) Example 1
(1-1) System Configuration FIG. 1 shows a configuration example of a sensor network system (hereinafter referred to as “the present system”) according to the present embodiment. This system includes a base station 1 that aggregates information and a plurality of wireless terminals 2 (2A to 2E) that transmit or relay information to the base station 1. Both the base station 1 and the wireless terminal 2 have a wireless communication module compliant with the communication method used. The wireless communication module incorporates a microprocessor that controls a communication operation described later. The antenna may be built in the apparatus main body or may be externally attached. A detailed functional configuration of the wireless terminal 2 will be described later.

  Communication between the plurality of wireless terminals 2 is hierarchized, and the hierarchy (rank) to which the wireless terminals 2 belong is defined by the relationship with the base station 1. The rank of the wireless terminal 2 that can directly communicate with the base station 1 is rank 1, the rank of the wireless terminal that requires one relay by another wireless terminal 2 for communication with the base station 1 is rank 2, and the base station 1 The rank of the wireless terminal 2 that requires (N-1) relays for communication is assumed to be rank N. The wireless terminals 2 belonging to each hierarchy are referred to as rank 1 wireless terminal 2, rank 2 wireless terminal 2,... Rank N wireless terminal 2. The number of wireless terminals 2 belonging to each rank is arbitrary.

  Each wireless terminal 2 operates intermittently to suppress power consumption. When information to be transmitted to the base station 1 is generated, each wireless terminal 2 transmits the information as a data signal 10 to the wireless terminal 2 that is one rank higher than itself. The higher rank wireless terminal 2 aggregates the received information of the one or more data signals 10 and transmits the information as the data signal 10 to the wireless terminal 2 of the rank one higher than itself. This relay operation is repeatedly executed with the wireless terminal 2 belonging to a higher rank. Finally, the rank 1 wireless terminal 2 transmits a data signal 10 to the base station 1. As a result, information on all the wireless terminals 2 is collected in the base station 1.

  Below, the case where a rank routing system is applied to the communication in this system is demonstrated. In the rank routing method, the transfer route is not defined in advance, and the wireless terminal 2 that is first able to transfer data among the plurality of wireless terminals 2 that have received the request signal 20 is the wireless terminal 2 having the higher rank. This is a communication method for communication. However, the communication technique described in the present embodiment can be applied to other routing methods in which a transfer route is defined in advance.

(1-2) Communication Sequence FIG. 2 shows an example of a communication sequence used when the rank-2 radio terminal 2 transmits information (data signal) to the rank-1 radio terminal 2. FIG. 2 shows a communication sequence in the case where the wireless terminal 2C and the wireless terminal 2D of rank 2 transmit the data signal 10 to the wireless terminal 2A of rank 1. All the higher rank wireless terminals 2A periodically broadcast the request signal 20 (indicated as “RQ transmission” in FIG. 2). Note that carrier sense (shown as “CS” in FIG. 2) is performed before transmission of the request signal, and transmission of the request signal 20 is permitted when the presence of another carrier is not confirmed.

  The wireless terminal 2C and the wireless terminal 2D receive the request signal 20 from the rank-1 wireless terminal 2A. The rank-2 wireless terminals 2C and 2D that are scheduled to transmit the data signal 10 perform the carrier sense for a predetermined time after receiving the request signal 20. When a radio signal from another radio terminal 2 is not detected during carrier sense, the radio terminals 2C and 2D transmit a data signal to the rank-1 radio terminal 2A. In the case of the present embodiment, the carrier sense time of each wireless terminal 2 is set to a different value. However, each time the request signal 20 is received, each wireless terminal 2 may set the carrier sense time at random. In this case, the wireless terminal 2 sets the carrier sense time using a random number generator installed.

  In the example of FIG. 2, the carrier sense time of the wireless terminal 2C is shorter than the carrier sense time of the wireless terminal 2D. For this reason, the wireless terminal 2C that has finished carrier sense first succeeds in transmitting the data signal 10C. The wireless terminal 2 </ b> A of rank 1 waits for reception of the data signal 10 after transmitting the request signal 20. When the wireless terminal 2A successfully receives the data signal 10C transmitted from the wireless terminal 2C during this standby period, the wireless terminal 2A transmits an ACK signal (confirmation signal) 30 to the wireless terminal 2C. By receiving this ACK signal 30, the wireless terminal 2C confirms that the transmission of the data signal 10C to the wireless terminal 2A of rank 1 is successful. In this example, since the data signal 10C to be transmitted does not remain, the wireless terminal 2C does not enter a data signal transmission waiting state and does not perform carrier sense.

  On the other hand, the wireless terminal 2D that has failed to transmit the data signal 10D waits for reception of the next request signal 20. At this time, the wireless terminal 2D does not record the transmission failure of the data signal 10D. The wireless terminal 2D resumes the transmission wait state for the data signal 10D after a predetermined time from the end of the previous carrier sense, and waits for reception of the request signal 20 from the wireless terminal 2A again. In this case, the wireless terminal 2D does not detect a wireless signal from another wireless terminal 2 at the end of the carrier sense. Therefore, the wireless terminal 2D transmits the data signal 10D to the wireless terminal 2A of rank 1 and confirms its success. If the request signal 20 is not received even after waiting for transmission of the data signal 10D for a predetermined time or longer, the wireless terminal 2D increments the number of transmission failures of the data signal 10D and records it in a memory (not shown). The number of transmission failures is cleared when the data signal 10 is successfully transmitted.

  The rank-one wireless terminal 2A describes information regarding the transmission time and transmission interval of the request signal 20 to be transmitted. On the other hand, the rank-2 wireless terminals 2C and 2D that have received the request signal 20 synchronize with the system time based on the information included in the received request signal 20.

(1-3) Allocation of communicable time FIG. 3 shows an example of allocation of communicable time. All the wireless terminals 2 constituting this system are synchronized with a common time axis, and the time during which communication is permitted only between specific ranks is repeated at regular intervals T. In the example of FIG. 3, the time T2 for communication from the rank 2 radio terminal 2 to the rank 1 radio terminal 2 is arranged after the time T1 for communication from the rank 3 radio terminal 2 to the rank 2 radio terminal 2. Furthermore, a time T3 for communicating from the rank-1 wireless terminal 2 to the base station 1 is arranged.

  Each allocation time is repeated at intervals of the period T. Each wireless terminal 2 may perform communication at any timing as long as communication within the rank of the wireless terminal 2 is permitted. In addition, each wireless terminal 2 prevents the communication order between the wireless terminals from being fixed by changing the transmission timing for each period T so that the communication is not repeated at the same timing within each allocation time. Thereby, the occurrence of a situation in which some of the wireless terminals 2 cannot always receive the request signal 20 is avoided.

  Referring to the example of FIG. 2, the rank 1 wireless terminal 2A, with respect to the rank 2 wireless terminal 2D, the time from the start time of the allocation time to the transmission of the request signal 20, the period T of the allocation time, the length of the allocation time This information is included in the request signal 20 and sent. The wireless terminal 2D that has received the request signal 20 calculates the reception time of the request signal 20 based on the acquired information, and synchronizes with the system time based on the time.

(1-4) Operation Sequence during Relaying FIG. 4 shows an example of an operation sequence when the higher rank wireless terminal 2 relays the data signal 10 from the lower rank wireless terminal 2. Note that the operation shown in FIG. 4 is executed through a control operation of a microprocessor mounted on the wireless terminal 2. The higher rank wireless terminal 2 starts up according to the time allocation shown in FIG. 3 and then broadcasts the request signal 20 (step S1). The data signal 10 from the lower rank wireless terminal 2 that receives the request signal 20 is transmitted. Waiting for reception (step S2).

  When the higher rank wireless terminal 2 has received the data signal 10 within a predetermined time after transmitting the request signal 20 (yes in step S3), the number of transmission failures described in the received data signal 10 Is read (step S4). The number of transmission failures is information indicating how many times the wireless terminal 2 that is the transmission source of the data signal 10 has failed to transmit the data signal 10. This information is described by the wireless terminal 2 that transmits the data signal 10. For example, when the lower rank wireless terminal 2 cannot transmit the data signal 10 during the allocation cycle twice, information indicating that the data signal 10 transmitted in the next cycle cannot be transmitted twice continuously. (For example, “1”) is described.

  The upper rank wireless terminal 2 that has read the information on the number of transmission failures is the number of transmissions of the request signal 20 that it transmits from the next startup if the previous number of failures is two or more (if yes in step S5). The setting is changed so as to increase once (step S6). That is, the wireless terminal 2 increases the number of transmissions of the request signal 20 to be transmitted within a certain time, and proceeds to step S10. On the other hand, if the number of previous failures is 1 or less (in the case of no in step S5), the wireless terminal 2 proceeds to step S10 as it is.

  If the upper radio terminal 2 cannot receive the data signal 10 from the lower rank radio terminal 2 within the standby time started after transmission of the request signal 20 (in the case of no in step S3), the fact is not yet confirmed. The received information is recorded in its own memory (not shown) (step S7). At this time, the higher rank wireless terminal 2 that is the transmission source of the request signal 20 checks the recorded unreceived information, and checks whether there was no unreceived at the time of previous activation (step S8).

  If no reception has occurred continuously more than the specified number of times (in the case of yes in step S8), the wireless terminal 2 determines that the number of transmissions of the request signal 20 is large and uses it at the next start-up. The setting is changed so that the number of transmissions of the request signal 20 is reduced by one (step S9). That is, the wireless terminal 2 decreases the number of transmissions of the request signal 20 to be transmitted within a certain time, and proceeds to step S10. On the other hand, if there has been no unreceived record that has continued for a predetermined number of times (in the case of no in step S8), the wireless terminal 2 continuously determines whether the cause of unreceived is a sudden unreceived cause. Therefore, the process proceeds to step S10 without changing the number of transmissions of the request signal 20.

  The upper rank wireless terminal 2 that has proceeded to step S10 determines whether or not the request signal has been transmitted a specified number of times. If the number of transmissions has not reached the specified number (in the case of no in step S10), the wireless terminal 2 waits for a predetermined interval (step S11) and then returns to step S1. That is, the wireless terminal 2 transmits the next request signal 20. On the other hand, when the number of transmissions reaches the specified number (if yes in step S10), the wireless terminal 2 sleeps until the next allocation time.

(1-5) Structure of Data Signal FIG. 5 shows a structure example of the data signal 10 transmitted by the wireless terminal 2. The data signal 10 includes a header 11 indicating information necessary for communication, data 12 to be transmitted to the base station 1, and information on success / failure of transmission so far (transmission failure information) 13. Information indicating the number of transmission failures described above is recorded in the transmission failure information 13.

(1-6) Functional Configuration of Wireless Terminal FIG. 6 shows a functional configuration of the wireless terminal 2. The wireless terminal 2 includes a device main body 200 and an antenna 201. The control unit 202 corresponds to the above-described wireless communication module. The control unit 202 controls communication operations (startup operation, sleep operation, request signal 20 transmission operation, etc.) through execution of a program by the microprocessor. The transmission / reception unit 203 transmits / receives a radio signal via the antenna 201. For transmission / reception of wireless signals, a communication method that the device itself complies with is used. The message recording unit 204 records the received data signal 10 and the data signal 10 to be transmitted.

  The request signal transmission frequency determination unit 205 determines the validity of the transmission frequency of the request signal 20. The request signal transmission number determination unit 205 determines the number of transmissions in accordance with, for example, the processing procedure shown in FIG. The transmission failure information recording unit 206 records information such as the number of times the transmission of the data signal 10 from the own device to the higher rank wireless terminal 2 has failed. The message recording unit 204 and the transmission failure information recording unit 206 may be different memories or different recording areas on the same memory. Note that the message recording unit 204 and the request signal transmission frequency determination unit 205 are not required in the case of the wireless terminal 2 that is determined in advance not to operate as a relay terminal.

(1-7) Message Sequence (1-7-1) When Decreasing the Number of Request Signal Transmissions FIG. 7 shows an example of a message sequence when reducing the number of request signal transmissions. In FIG. 7, the N-1 rank radio terminal 2C relays the data signal 10A from the N rank radio terminal 2A and the data signal 10B from the N rank radio terminal 2B to the N-2 rank radio terminal 2D. Assume a case. In addition, there is no transmission of the data signals 10A and 10B from the lower rank wireless terminals 2A and 2B (no response) with respect to the previous transmission of the request signal 20C, and no reception has already been recorded when the previous request signal 20C is transmitted. It shall be. Here, it is assumed that the wireless terminal 2 </ b> C has a rule that reduces the number of transmissions of the request signal 20 </ b> C from the next time when non-reception is detected twice consecutively.

  When the communication time allocated to communication from the N rank to the N-1 rank starts, both the N rank wireless terminals 2A and 2B and the N-1 rank wireless terminal 2C are activated. The activated N-1 rank wireless terminal 2C broadcasts a request signal 20C. The N rank wireless terminal 2A and wireless terminal 2B that have received the request signal 20C both have the data signal 10 (10A and 10B) to be transmitted. However, when the wireless terminal 2A and the wireless terminal 2B transmit the data signals 10A and 10B at the same time, congestion occurs. Therefore, each of the wireless terminal 2A and the wireless terminal 2B performs carrier sensing for a random time, and checks whether the data signal 10 is transmitted from another wireless terminal 2.

  The wireless terminal 2 that has confirmed that there is no transmission of the data signal 10 from the other wireless terminal 2 transmits its own data signal 10. On the other hand, the wireless terminal 2 that has confirmed transmission of the data signal 10 from the other wireless terminal 2 does not transmit its own data signal 10 and waits for reception of the next request signal 20C. In the example of FIG. 7, the wireless terminal 2B transmits the data signal 10B to the first request signal 20C, and the wireless terminal 2A transmits the data signal 10A to the second request signal 20C.

  However, in the example of FIG. 7, there is no response to the third request signal 20C. Therefore, the N rank wireless terminal 2 </ b> C records that the data signal 10 has not been received. As described above, in the wireless terminal 2C, the non-reception of the data signal 10 is recorded even when the previous request signal 20C is transmitted. For this reason, the non-reception of the data signal 10 at the wireless terminal 2C is continuous twice. Therefore, the wireless terminal 2C performs a setting change to reduce the number of transmissions of the request signal 2C in the subsequent communication times from 3 times to 2 times. This operation is performed based on the operation sequence (step S9) shown in FIG. When the communication time allocated for communication from the N rank to the N-1 rank elapses, the wireless terminals 2A, 2B, and 2C all enter a sleep state.

  Next, the communication time allocated for communication from the N-1 rank to the N-2 rank arrives. Then, both the N-1 rank wireless terminal 2C and the N-2 rank wireless terminal 2D are activated. The wireless terminal 2D transmits the request signal 20D, and the wireless terminal 2C receives the request signal 20D. Next, the wireless terminal 2C transmits a data signal 10C obtained by combining the previously received data signals 10A and 10B to the wireless terminal 2D. Thereafter, both the wireless terminal 2C and the wireless terminal 2D enter the sleep state. Eventually, the communication time allocated for communication from N rank to N-1 rank arrives. As described above, in the previous communication time, the number of transmissions of the request signal 20C by the wireless terminal 2C is changed to two. Therefore, the wireless terminal 2C broadcasts the request signal 20C only twice this time.

(1-7-2) Increasing the number of request signal transmissions FIG. 8 shows an example of a message sequence for increasing the number of request signal transmissions. In FIG. 8, the N-1 rank radio terminal 2C relays the data signal 10A from the N rank radio terminal 2A and the data signal 10B from the N rank radio terminal 2B to the N-2 rank radio terminal 2D. Assume a case. In the figure, the N-2 rank wireless terminal 2D is omitted. Note that it is assumed that the wireless terminal 2A has already failed once in transmission of the data signal 10A during communication for the previous allocation time.

  When the communication time allocated for communication from the N rank to the N-1 rank starts, both the N rank wireless terminals 2A and 2B and the N-1 rank wireless terminal 2C are activated. The activated N-1 rank wireless terminal 2C broadcasts a request signal 20C. The N rank wireless terminal 2A and wireless terminal 2B that have received the request signal 20C both have the data signal 10 (10A and 10B) to be transmitted. In this allocation time, the wireless terminal 2B transmits the data signal 10B first. Therefore, the wireless terminal 2A waits for reception of the next request signal 20C.

  However, the number of request signal transmissions in the current allocation time is “1”. For this reason, the wireless terminal 2C can transmit the request signal 20C only once at the first allocation time of FIG. For this reason, the wireless terminal 2A cannot receive the request signal 20C within the current allocation time, and records a failure in data transmission. The wireless terminal 2A updates the number of transmission failures to “2”. Thereafter, the wireless terminals 2A, 2B, and 2C are all in the sleep state.

  At the next allocation time, the wireless terminal 2A first transmits the data signal 10A to the wireless terminal 2C because of the carrier sense time set at random. At this time, in the data signal 10A transmitted by the wireless terminal 2A, transmission failure information 13 indicating that the transmission of the data signal 10A has failed twice in succession is described. This time, the transmission failure of the transmission data 10B is recorded in the wireless terminal 2B. Based on the transmission failure information 13, the wireless terminal 2C that has received the data signal 10A confirms that the wireless terminal 2A has failed to transmit the data signal 10A at least twice. As a result, the wireless terminal 2C changes the setting to increase the number of request signal transmissions used at the next activation from one to two. This operation is performed based on the operation sequence (step S6) shown in FIG. As a result, at the next activation, both the wireless terminal 2A and the wireless terminal 2B can transmit the data signals 10A and 10B after receiving the request signal 20C.

  The wireless terminal 2C operating as the relay terminal transmits the request signal 20 once more immediately (within the current allocation time) immediately after receiving the data signal 10 in which two or more transmission failures are recorded. However, the number of transmissions of the request signal 20 may be changed according to whether or not there is a response to the response.

(1-8) Summary At least the wireless terminal 2 functioning as a relay terminal reads the transmission failure information 13 included in the data signal 10 that is a response to the request signal 20 of the own device, and the validity of the number of transmissions of the request signal 20 Equipped with a function to examine the sex. When the wireless terminal 2 belonging to a rank lower than the own device often cannot transmit the data signal 10 to the own device, the wireless terminal 2 functioning as a relay terminal has insufficient number of transmissions of the request signal 20. And increase the number of request signal transmissions. On the other hand, when no response to the request signal 20 transmitted by the own device continues, the wireless terminal 2 functioning as a relay terminal determines that the request signal 20 is transmitted too many times and reduces the request signal transmission frequency.

  For this reason, the number of individual request signal transmissions in each wireless terminal 2 operating in the RIT system can be automatically set to an appropriate value according to the actual situation. This eliminates the need for a person in charge of radio technology to diagnose the communication status of each radio terminal 2 and set the number of request signal transmissions individually, greatly reducing the cost of introducing and maintaining the radio communication system. can do. Further, even in a system in which movement and addition of the wireless terminal 2 frequently occur, smooth operation can be realized as compared with the conventional case.

(2) Example 2
In this embodiment, a case where a data signal having a structure different from that in Embodiment 1 is used for wireless communication will be described. The system configuration of this embodiment is the same as that of the first embodiment. FIG. 9 shows a structural example of the data signal 10 used in this embodiment. In FIG. 9, parts corresponding to those in FIG. The data signal 10 of this embodiment includes information (remaining message information) 14 indicating the number of messages remaining in the transmission buffer of the wireless terminal 2 that is the transmission source, instead of the transmission failure information 13.

  FIG. 10 shows an example of an operation sequence when the higher rank wireless terminal 2 relays the data signal from the lower rank wireless terminal 2. 10, parts corresponding to those in FIG. 4 are denoted by the same reference numerals. The operation sequence of this embodiment is different from that of the first embodiment in the content of the operation that is executed when the data signal 10 is received (in the case of yes in step S3). Specifically, steps S21 and S22 are executed instead of steps S4 to S6 in FIG.

  In step S21, the wireless terminal 2 reads the remaining message information 14 included in the data signal 10 received as a response to the request signal 20 of the own device. The remaining message information 14 is information indicating how many messages remain in the transmission buffer of the lower rank wireless terminal 2. The remaining message information 14 is recorded by the wireless terminal 2 that is the transmission source of the data signal 10 based on the management information of its own transmission buffer.

  In this embodiment, it is assumed that one message can be transmitted by one data signal 10. For example, when three messages remain in the transmission buffer, two messages remain in the transmission buffer of the wireless terminal 2 that is the transmission source. Therefore, “2” is recorded in the remaining message information 14. In this case, the wireless terminal 2 functioning as a relay terminal changes the setting to increase the number of transmissions of the request signal 20 to be transmitted at the next activation by the number of messages indicated by the remaining message information 14 (step S22). For example, when the number of request signal transmissions during the current activation period is two, the number of request signal transmissions at the next activation is set to four.

  The increase in the number of request signal transmissions may be an added value of the plurality of remaining message information 14 recorded in the plurality of received data signals 10. Further, when the number of times of increase is limited, the upper limit value may be added to the next number of request signal transmissions. Even if the number of messages temporarily remaining in the transmission buffer increases, the transmission of these messages can be completed in a short time.

(3) Example 3
In the two embodiments described above, as shown in FIG. 3, the case where the communicable time is allocated for each specific rank has been described. In this embodiment, a system is assumed in which there is no such assignment and all the wireless terminals 2 can transmit the data signal 10 at an arbitrary timing. FIG. 11 shows a functional configuration of the wireless terminal 2 in the present embodiment. In FIG. 11, parts corresponding to those in FIG.

  In this embodiment, a request signal transmission interval determination unit 207 is used instead of the request signal transmission frequency determination unit 205. The request signal transmission interval determination unit 207 changes the next and subsequent request signal transmission intervals based on the transmission failure information 13 included in the received data signal 10 and the non-reception of the transmission data 12. Detailed operation will be described later.

  FIG. 12 shows an example of an operation sequence when the higher rank wireless terminal 2 relays the data signal 10 from the lower rank wireless terminal 2. In FIG. 12, parts corresponding to those in FIG. The operation sequence of the present embodiment is different from that of the first embodiment in that the transmission interval of the request signal 20 is changed instead of the number of transmissions of the request signal 20. Specifically, step S31 is executed instead of step S6 of FIG. 4, and step 32 is executed instead of step S9 of FIG. Further, since the number of transmissions of the request signal 20 is not managed, steps S10 and S11 in FIG. 4 are not executed.

  In the case of the present embodiment, the wireless terminal 2 operating as a relay terminal broadcasts the request signal 20 to the lower-ranked wireless terminals 2 every predetermined period T1 seconds. When the data signal 10 can be received within a predetermined time from the transmission of the request signal 20 (yes in step S3), the wireless terminal 2 operating as a relay terminal transmits the transmission failure information described in the received data signal 10 13 is read (step S4).

  When the transmission failure information 13 is twice or more (in the case of yes in step S5), the wireless terminal 2 determines a transmission interval (that is, cycle T seconds) of the request signal 20 after the next activation in advance (see FIG. 12 is shortened by Δt seconds). That is, the wireless terminal 2 operating as a relay terminal transmits a request signal 20 every (T−Δt) seconds after the next activation. Thereby, the waiting time until the lower rank wireless terminal 2 can receive the request signal 20 is shortened. The shortening of the period T substantially leads to an increase in the number of transmissions of the request signal 20. In addition, immediately after receiving the data signal 10 in which two or more transmission failures are recorded (within the current allocation time), the request signal 20 is additionally transmitted once, depending on whether there is a response to the request signal 20, The transmission interval of the request signal 20 may be changed.

  On the other hand, when the data signal 10 cannot be received within a predetermined time from the transmission of the request signal 20 (in the case of no in step S3), the wireless terminal 2 operating as the relay terminal uses its own memory as unreceived information to that effect. To record. Thereafter, the wireless terminal 2 confirms the previous unreceived information, and checks whether there was no unreceived at the time of previous activation (step S8). If no reception has occurred continuously more than the specified number of times (N times), the wireless terminal 2 operating as a relay terminal determines that the transmission interval of the request signal 20 is short, and after the next activation The transmission interval of the request signal 20 is increased by a predetermined time (Δt seconds in FIG. 12).

  That is, the wireless terminal 2 operating as a relay terminal transmits a request signal 20 every (T + Δt) seconds after the next activation. This increase in the period T substantially leads to a decrease in the number of transmissions of the request signal 20. Thereby, the transmission interval of the request signal 20 transmitted by the wireless terminal 2 is optimized. If there is no continuous non-reception record (in the case of no in step S8), the wireless terminal 2 determines whether the cause of the non-reception is a sudden non-reception or a continuous request signal 20 remaining. Cannot be judged. For this reason, the wireless terminal 2 does not change the transmission interval of the request signal 20 at this time, and postpones the determination after the next activation. Even if it does in this way, the effect similar to Example 1 is realizable.

(4) Example 4
As in the third embodiment, this embodiment also describes a system in which no communication time is allocated between terminals and all wireless terminals 2 can transmit signals at an arbitrary timing. The request signal transmission interval determination unit 207 of this embodiment changes the transmission interval of the request signal based on the remaining message information 14 described in the data signal 20.

  FIG. 13 shows an example of an operation sequence when the higher rank wireless terminal 2 relays the data signal 10 from the lower rank wireless terminal 2 in this embodiment. In FIG. 13, parts corresponding to those in FIG. Also in the case of the present embodiment, the transmission interval of the request signal 20 is changed as in the case of the third embodiment. Specifically, steps S41 and S42 are executed instead of steps S4 to S6 of FIG. 4, and step S43 is executed instead of step S9 of FIG. Further, since the number of transmissions of the request signal 20 is not managed, steps S10 and S11 in FIG. 4 are not executed.

  Also in the case of the present embodiment, the wireless terminal 2 operating as a relay terminal broadcasts the request signal 20 to the lower rank wireless terminal 2 every predetermined period T seconds. If the data signal 10 can be received within a certain time from the transmission of the request signal 20 (yes in step S3), the wireless terminal 2 operating as a relay terminal receives the remaining message information described in the received data signal 10 14 is read (step S41).

  Here, it is assumed that one message can be transmitted by one data signal 10. For example, when three messages remain in the transmission buffer, two messages remain in the transmission buffer of the wireless terminal 2 that is the transmission source. Therefore, “2” is recorded in the remaining message information 14. In this case, the wireless terminal 2 functioning as a relay terminal changes the setting so as to shorten the transmission interval of the request signal 20 transmitted at the next activation by the number of messages indicated by the remaining message information 14 (step S42). When changing the time interval in units of Δt seconds, the wireless terminal 2 changes the transmission interval of the request signal 20 to (T−2 × Δt) only the next time. This shortening of the period T substantially leads to an increase in the number of transmissions of the request signal 20.

  On the other hand, when a negative result is obtained in step S3, the wireless terminal 2 records the fact as unreceived information in its own memory (not shown) (step S7). At this time, the higher-level wireless terminal 2 that has transmitted the request signal 20 confirms the recorded unreceived information, and checks whether there has been no unreceived at the time of previous activation (step S8).

  If no reception has occurred continuously more than the specified number of times (in the case of yes in step S8), the wireless terminal 2 determines that there is a margin in the transmission interval of the request signal 20, and at the next and subsequent startups. The setting is changed to widen the transmission interval of the request signal 20 to be used by Δt seconds (step S43). This extension of the period T substantially leads to a decrease in the number of transmissions of the request signal 20. Even if it does in this way, the effect similar to Example 1 is realizable.

(5) Other Embodiments The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and it is not necessary to provide all the configurations described. In addition, a part of one embodiment can be replaced with the configuration of another embodiment. Moreover, the structure of another Example can also be added to the structure of a certain Example. In addition, with respect to a part of the configuration of each embodiment, a part of the configuration of another embodiment can be added, deleted, or replaced.

  Each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them, for example, with an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by the processor interpreting and executing a program that realizes each function (that is, in software). Information such as programs, tables, and files that realize each function can be stored in a storage device such as a memory, a hard disk, and an SSD (Solid State Drive), or a storage medium such as an IC card, an SD card, and a DVD. Control lines and information lines indicate what is considered necessary for the description, and do not represent all control lines and information lines necessary for the product. In practice, it can be considered that almost all components are connected to each other.

1 ... Base station,
2 ... wireless terminal,
10: Data signal,
11 ... Header 12 ... Data,
13 ... Transmission failure information,
14 ... remaining message information,
20 ... Request signal,
30 ... Ack signal,
200 ... device main body,
201 ... antenna,
202 ... control unit,
203 ... transmitting / receiving unit,
204 ... Message recording unit,
205... Request signal transmission frequency determination unit,
206 ... transmission failure information recording section,
207 ... Request signal transmission interval determination unit.

Claims (6)

A first wireless terminal that transmits a data signal in response to the request signal after receiving the broadcast request signal;
A second wireless terminal that automatically changes the number of transmissions for transmitting the request signal within a predetermined time based on the communication status of the first wireless terminal;
Have
The second wireless terminal reads the number of transmission failures of the first wireless terminal from the data signal, and automatically changes the number of transmissions of the request signal based on the read number of transmission failures. Wireless communication system. A first wireless terminal that transmits a data signal in response to the request signal after receiving the broadcast request signal;
A second wireless terminal that automatically changes the number of transmissions for transmitting the request signal within a predetermined time based on the communication status of the first wireless terminal;
Have
The second wireless terminal reads the number of messages remaining in the first wireless terminal from the data signal, and automatically changes the number of transmissions of the request signal based on the read number of messages. A wireless communication system. A first wireless terminal that transmits a data signal in response to the request signal after receiving the broadcast request signal;
A second wireless terminal that automatically changes a transmission interval of the request signal based on a communication status of the first wireless terminal;
Have
The second wireless terminal reads the number of transmission failures of the first wireless terminal from the data signal, and automatically changes the transmission interval of the request signal based on the read number of transmission failures. Wireless communication system. A first wireless terminal that transmits a data signal in response to the request signal after receiving the broadcast request signal;
A second wireless terminal that automatically changes a transmission interval of the request signal based on a communication status of the first wireless terminal;
Have
The second wireless terminal reads the number of messages remaining in the first wireless terminal from the data signal, and automatically changes the transmission interval of the request signal based on the read number of messages. A wireless communication system. A first communication control unit for transmitting a first data signal to the first wireless terminal as a response to the first request signal when receiving a first request signal broadcast from the first wireless terminal; ,
When broadcasting the second request signal, the number of transmissions of transmitting the second request signal within a predetermined time or the transmission interval of the second request signal is set as a response to the second request signal. A second communication control unit that automatically changes based on the communication status of the second wireless terminal that transmits the data signal of
Have
The second communication control unit automatically changes the number of transmissions or the transmission interval based on the number of transmission failures of the second wireless terminal read from the second data signal. Wireless terminal. A first communication control unit for transmitting a first data signal to the first wireless terminal as a response to the first request signal when receiving a first request signal broadcast from the first wireless terminal; ,
When broadcasting the second request signal, the number of transmissions of transmitting the second request signal within a predetermined time or the transmission interval of the second request signal is set as a response to the second request signal. A second communication control unit that automatically changes based on the communication status of the second wireless terminal that transmits the data signal of
Have
The second communication control unit automatically changes the number of transmissions or the transmission interval based on the number of messages remaining in the second wireless terminal read from the second data signal. Features wireless terminal.

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