The present invention relates to a wireless communication device, a wireless communication system, and a wireless communication method in which wireless communication is performed with one or more other wireless communication devices during a predetermined time within a given cycle.
A multi-hop wireless network is known in which not only do wireless communication devices communicate directly with each other, each wireless communication device can also communicate with a wider range of wireless communication devices via other wireless communication devices. In the multi-hop wireless network, when individual wireless communication devices perform wireless communications at respective timings, communications interference occurs when the timing of transmissions accidentally coincide. Interference between communications precludes normal transmission and reception of data, resulting in the need to retransmit data. As a technique for preventing interference between communications, a time-division synchronous communication scheme is known.
The time-division synchronous communication scheme is a scheme in which wireless communication devices joining in communication perform transmission or reception only during a predetermined time. This scheme enables avoiding communication interference among wireless communication devices in the same network. This allows suppression of an unexpected extension of a communication duration involved in retransmission resulting from communication interference.
The time-division synchronous communication scheme has been increasingly frequently applied in the field of, for example, a wireless network for a control system involving a constraint on a data update cycle.
When available wireless channels (wireless communication bands) in the entire network based on the time-division synchronous communication scheme are limited to one band, the entire single multi-hop wireless network needs to share a single schedule. Under this condition, a total duration during which the schedule for the multi-hop wireless network is complete (the duration is hereinafter referred to as one cycle time) is determined based on “one cycle time=the number of all communication tasks in the network×an allotment unit time. Communication data on the network is updated every cycle time, and thus, a data update period=one cycle time.
Many of the systems adopting the time-division synchronous communication scheme are intended to complete transmitting data held by individual wireless communication devices to other devices within a given limit time (maximum update cycle). To achieve this, a mechanism is needed which allows the time from the final communication before occurrence of an error until the first communication after restoration (the maximum update cycle for error occurrence) to be prevented from exceeding a given limit time. Therefore, a communication device provided in such a system needs to have the capability of restoring communication within a given time unless the communication device is malfunctioning.
In general, according to an embodiment, a wireless communication device is applicable to a wireless communication system having a plurality of wireless communication devices. The wireless communication device includes a wireless section, a storage, a communication controller, a response confirmer and a schedule modifier. The wireless section executes a communication task in which the wireless communication device transmits and receives a wireless signal to and from another wireless communication device. The storage stores schedule information indicative of a time when the communication task is permitted to be executed. The communication controller controls execution of the communication task based on the schedule information. The response confirmer confirms a reception response from the another wireless communication device. The schedule modifier modifies the schedule information based on a result for the reception response from the response confirmation section.
A wireless communication device, a wireless communication system, and a wireless communication method according to the present embodiment will be described below with reference to the drawings.
As illustrated in
A tree-type topology centered around the wireless communication device A is illustrated in
Input/output devices, sensors and motors for example, are connected to the wireless communication devices A to J.
For example, control devices in the external network 30 collect sensor information from the wireless communication devices A to J via the external network 30. The control devices may transmit control signals to the wireless communication devices A to J via the external network 30 based on the collected sensor information, allowing the motors and the like to be controlled.
The wireless section 11 transmits and receives, via the antenna section 15, wireless signals to and from other wireless communication devices that are present within the radio wave coverage range of the wireless communication device 11. The schedule storage section 13 stores schedule information indicative of execution timings (times) for communication tasks in the wireless signals.
The schedule information is shared among the wireless communication devices A to J belonging to the system. In other words, all the wireless communication devices in the multi-hop wireless network hold common schedule information.
The clock section 14 generates a reference time used to control the execution timings for the communication tasks in the wireless signals, based on a common clock used in the entire system. The reference time is assumed to be synchronous among the wireless communication devices A to J belonging to the system.
The control section 12 includes a communication control section 121, a schedule modification section 123, and a response confirmation section 125. The communication control section 121 manages one cycle time needed to execute all the communication tasks recorded in the schedule information, and performs fixed-cycle transmission utilizing a time allotted to the communication control section 121.
The response confirmation section 125 allows the wireless communication device to communicate with a wireless communication device adjacent to the wireless communication device (adjacent device) to acquire information on the adjacent device in order to confirm the status of communication between the wireless communication device 10 and the adjacent device.
The schedule storage section 123 allots a free time in the schedule information to the communication task of the adjacent device to modify the schedule information based on the information of the adjacent device acquired by the response confirmation section 125.
The wireless communication device 10A has an external network section 17 in addition to the wireless section 11, the control section 12, the schedule storage section 13, the clock section 14, and the antenna section 15. The external network section 17 is a connection interface between the wireless network and the external network 30. The wireless communication device 10A with the external network section 17 functions as a gateway that mediates data transmission and reception between the wireless network and the external system.
The control section 12 of the wireless communication device 10A includes a setting reception section 126 in addition to the communication control section 121, the schedule modification section 123, and the response confirmation section 125. The setting reception section 126 receives settings such as the maximum update cycle from the maintenance terminal 60 and the like. The setting of the maximum update cycle is indicative of a constraint condition for one cycle time needed to execute all the communication tasks recorded in the schedule information.
Next, a time negotiation procedure in the wireless communication system configured as above will be described. The wireless communication devices 10 and 10A perform wireless communication with no communication interference using the time negotiation procedure for embedding the communication task of each wireless communication device in the schedule information shared among the wireless communication devices.
In this case, the “time” in the time 51 corresponds to a period of time of a predetermined length, for example, a time slot or a time frame.
Furthermore, the wireless communication devices 10 and 10A recognize wireless communication paths constructed by a wireless network constructing function via communications among the wireless communication devices provided by the wireless network constructing function, before time negotiation is executed. The wireless communication device 10A functioning as the main device recognizes all the wireless paths in the wireless network.
For example, in
In the time negotiation procedure, first, the wireless communication device A operating as the main device performs allotment of the times 51 in the schedule information 50. The schedule modification section 123 of the wireless communication device 10A allots unallotted times in the schedule information to the communication tasks between the wireless communication device 10A and the wireless communication devices (in
For example, the order of allotment is such that, in a downlink direction in which transmitted data from the wireless communication device A is transmitted to a terminal device in the wireless network, the devices are recorded in order of increasing distance to the wireless communication device A on the paths. In an uplink direction in which data is transmitted from each of the wireless communication devices to the wireless communication device A, the devices are recorded in order of decreasing distance to the wireless communication device A on the paths.
Thus, in a wireless communication system in which data is transferred among nodes similar to a bucket brigade, downlink data from the wireless communication device A is smoothly transferred down to the terminal of the wireless network similar to a bucket brigade as long as the times are allotted to the nodes in order of increasing distance to the wireless communication device A.
Uplink data toward the wireless communication device A is smoothly transferred up to the terminal of the wireless network similar to a bucket brigade as long as the times are allotted to the nodes in order of decreasing distance to the wireless communication device A.
The wireless communication device A further allots the times 51 specified in the schedule information 50 to bypass node information as information on bypass paths. In the example illustrated in
As illustrated in
For example, in
For recording in the schedule information 50, besides one-to-one communication, broadcast transmission from a single source device to a plurality of nodes within a signal coverage range from the source device is allowed.
In
Upon completing all the communication tasks and allotment of the bypass node information, the wireless communication device 10A functioning as the main device transmits the schedule information to all of the wireless communication devices having wireless communication paths to the wireless communication device 10A. After a fixed-cycle (hereinafter fixed-cycle) communication performed at predetermined cycles is started, if communication tasks associated with each wireless communication device 10 and the wireless communication device 10A are recorded for the times described in the schedule information, the wireless communication device 10 and 10A execute relevant transmitting and receiving processes.
As described above, the first embodiment enables autonomous creation of a transmission and reception schedule that allows communication interference in the multi-hop wireless network to be avoided. Moreover, a wireless communication system can be implemented in which the recorded bypass node information allows, even if a certain fault occurs in communication, data transmission to be reliably achieved via the bypass path.
So, there is provided a wireless communication device, a wireless communication system, and a wireless communication method which enable autonomous creation of a transmission and reception schedule that helps to avoid communication interference in the network, and it is allowed that the maximum update cycle to be prevented from exceeding a given limit time without interrupting communications even when any wireless communication device fails or a communication error occurs.
A wireless communication system according to a second embodiment has a path switching function accomplished within a given time and allowing the fixed-cycle communications in the entire system to continue even when a wireless communication device located at a relay point on a communication path fails or a communication error occurs. In the second embodiment, bypass nodes are pre-recorded in the schedule information as described in the first embodiment.
Each wireless communication device detects an error in the source communication device during a receiving operation of the wireless communication device.
On the other hand, in the above-described receiving process, if an error is recorded for the destination device, the wireless communication device checks the schedule information for bypass node information for the corresponding time to determine whether or not a bypass path is available (step S24).
In this case, if bypass node information is recorded (for example, data other than “0” is recorded in the bypass node information in
By way of example,
At the time number 05 during the second cycle, the device A recognizes that no normal reception has been obtained from the device C to detect a failure in the device C. Then, the device A provides, to the device B, a transmission otherwise provided to the device C during a time (time number 01) in the third cycle involving the device C specified as the destination device. Moreover, the device B detects at that time a failure in the device C, which is the original destination, because of reception from a communication source that is not in the schedule. The device B provides transmission to the device G rather than to the device C during the time (time number 02) for transmission from the device C to the device G. The device G detects at that time a failure in the device C, which is the original destination, because of reception from the communication source B that is not in the schedule. In this manner, the failure in the device C is transmitted to all the nodes on the paths, completing path switching.
As illustrated in
As described above, the second embodiment can implement a wireless communication system that allows a communication interruption time involved in communication path switching to be prevented from exceeding two cycles of fixed-cycle transmission even when a wireless communication device located at a relay point on a communication path fails, or a communication error occurs.
In a third embodiment, the wireless communication device 10A operating as the main device provides an operation setting function to the maintenance terminal 60 outside the wireless network. The wireless communication device 10A has the setting reception section 126, illustrated in
The wireless communication device 10A is connected to the maintenance terminal 60 via the external network 30 using the external network section 17. The setting reception section 126 provides the operation setting function of the wireless communication device 10A to the maintenance terminal 60. Using the operation setting function and the path switching function accomplished within the given time as described in the second embodiment, the present system enables the fixed-cycle communications in the entire system to continue without exceeding the maximum update cycle for when an error occurs set by a user even when the wireless communication device fails, or a communication error occurs.
Specifically, the setting reception section 126 is implemented as an HTTPd (Web server) or a similar function. In response to a request from the maintenance terminal 60, the setting reception section 126 transmits information on the wireless communication device 10A and the entire wireless network to the maintenance terminal 60. The setting reception section 126 performs operation setting on the wireless communication device 10A in conjunction with an operation performed by the maintenance terminal 60.
The setting screen illustrated in
The maximum update cycle is the total duration from the last data transmission (or reception) until the latest data transmission (or reception) by a certain device during fixed-cycle communication when focus is placed on each of the wireless communication devices 10 and 10A.
The maximum update cycle for when an error occurs is the maximum update cycle for cases including a communication error, and means the maximum duration from the final data transmission (or reception) by a certain device immediately before a failure occurs in the system until the first data transmission (or reception) after recovery of the fixed-cycle communication.
In the third embodiment, the schedule modification section 123 of each of the wireless communication devices 10 and 10A determines whether or not the total duration in the schedule information exceeds the maximum update cycle. Furthermore, the schedule modification section 123 of each of the wireless communication devices 10 and 10A determines whether or not the maximum duration including a time needed to replace the communication task exceeds the maximum update cycle for when an error occurs.
As illustrated in
If the calculated value for the maximum update cycle for when an error occurs exceeds the set value for the maximum update cycle for when an error occurs, the wireless communication device records, in the schedule storage section 13 of the wireless communication device (step S34), an error in the source specified in the schedule.
That is, the schedule modification section 123 of each of the wireless communication devices 10 and 10A does not record the determination of an error in the source in the path switching process simply based on a reception error during the single corresponding time during the corresponding cycle (reception obtained from an device different from the source set for the corresponding time, or a failure in reception) as in the second embodiment.
In the third embodiment, the schedule modification section 123 determines to not record an error in the source, even if a reception error occurs during the corresponding time during the corresponding cycle to the extent that the maximum update cycle expected, based on an error in reception from the same source, does not exceed the maximum update cycle for error occurrence—one cycle. In this case, the maximum update cycle means that, assuming an error is recorded during the current cycle, an expected duration from the last successful reception until a successful reception is followed by completion of path switching during the next cycle.
In other words, the schedule modification section 123 in the third embodiment increases a communication frequency used for communication error determination for the wireless communication device to the extent that the predicted maximum cycle is equal to or shorter than the maximum update cycle for when an error occurs.
As described above, in the third embodiment, even if the system has a constraint on the maximum update cycle for when an error occurs, the wireless communication device does not perform communication error determination until the needed cycle time from occurrence of a reception error until restoration of communication resulting from path switching exceeds the maximum update cycle for when an error occurs. Thus, if a communication error temporarily occurs in the device but the communication is quickly restored, then the device can join the fixed-cycle communication immediately after the restoration without performing path switching.
Consequently, a wireless communication system for the multi-hop wireless network having a constraint on the maximum update cycle can be provided which allows, in regard to a short-time communication error, the fixed-cycle communication to be resumed within one cycle after restoration from the error without violating the constraint on the maximum update cycle for when an error occurs set by the user.
Furthermore, the setting reception section 126 of the wireless communication device 10A in the third embodiment has a function to transmit the maximum update cycle and the maximum update cycle for when an error occurs set by the user, the maximum update cycle for when an error occurs calculated by the schedule modification section 123 (calculated value), and the number of cycles needed for the error determination to the maintenance terminal 60 as illustrated in
Consequently, the user can check whether the update cycle calculated by the system is shorter or longer than the condition for the set value of the maximum update cycle, the number of cycles needed for the error determination, and other types of information.
Therefore, the third embodiment can present, for the multi-hop wireless network involving a constraint on the maximum update cycle, a criterion to allow the user to determine whether the fixed-cycle communication based on the schedule information created by the present system satisfies an operating environment desired by the user.
A wireless communication device that has been restored from a communication error or replaced with a normal unit can acquire schedule information upon receiving the presence check message from the response confirmation section 125. The communication control section 121 of the restored wireless communication device resumes fixed-cycle transmission utilizing a time allotted to the wireless communication device before a failure occurs, based on the acquired schedule information.
A wireless communication device having received data through the resumed fixed-cycle transmission recognizes that the failing device has been restored (“Node A detects return of C” at a time number 05 during the fifth cycle in
As described above, in the fourth embodiment, when a wireless communication device is restored for which communication has been interrupted due to a failure or a fault in communication, the restored wireless communication device can rejoin the fixed-cycle communication without interrupting or delaying the fixed-cycle communications in the entire wireless network.
The several embodiments have been described. The embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes may be made to the embodiments without departing from the spirit of the invention. The embodiments and variations thereof are included in the scope and spirit of the inventions set forth in the claims and equivalents thereof.
Furthermore, the following can be implemented as hardware such as integrated circuits: the wireless section 11, the control section 12, the schedule storage section 13, the clock section 14, the external network section 17, the communication control section 121, the schedule modification section 123, the response confirmation section 125, and the setting reception section 126. These sections can also be implemented as software programs modularized as software.
Number | Date | Country | Kind |
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2013-270322 | Dec 2013 | JP | national |
This application is a Continuation Application of PCT Application No. PCT/JP2014/084586, filed Dec. 26, 2014 and based upon and claiming the benefit of priority from prior Japanese Patent Application No. 2013-270322, filed Dec. 26, 2013, the entire contents of all of which are incorporated herein by reference.
Number | Date | Country | |
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Parent | PCT/JP2014/084586 | Dec 2014 | US |
Child | 15188657 | US |