DESCRIPTION
WIRELESS MASTER STATION, WIRELESS SLAVE STATION, WIRELESS COMMUNICATION SYSTEM, AND WIRELESS COMMUNICATION METHOD
Field
[0001] The present invention relates to a wireless master station, a wireless slave station, a wireless communication system, and a wireless communication method used in an industrial network.
Background
[0002] In an industrial network, in a field network, a controller has been a master device and various 10 (Input Output) devices and measuring devices have been slave devices. The master device and the slave devices have been connected in a one-to-mulbi relation. Cyclic communication is performed between the master device and the slave devices at a time interval set in advance. Such a technology is disclosed in Non-Patent Literature 1 described below. Concerning a CC-Link (Control & Communication Link) IE field network, it is disclosed that frames called tokens are exchanged to sequentially circulate a transmission opportunity in a plurality of slave devices. A scheme in which a device that ends transmission of a data frame transmits a token frame to the next device last and determines a device that transmits the data frame is called token passing scheme.
[0003] Concerning the industrial network, it is demanded to make a network wireless for the purpose of reducing costs required for laying the network. In making the network wireless, it is inconvenient in terms of convenience of use to use a special apparatus and use a

frequency that requires a license. Therefore, it is possible to reduce procurement cost and development cost of hardware by realizing the wireless network in a form similar to the existing wireless LAN (Local Area Network) standard.
[0004] In the industrial network, to realize fixed periodicity of communication between the master device and the slave devices, schedule management for preventing collision in a wireless section is requested. In the wireless LAN standard, there is an HCCA (Hybrid Coordination Function Controlled Channel Access) scheme for centrally managing communication in an access point according to the IEEE (Institute of Electrical and electronics Engineers) 802.lie standard that specifies communication taking into account QoS (Quality of Service)
(Non-Patent Literature 2 described below).
[0005] In the wireless industrial network, it is conceivable to adopt the HCCA scheme and carry out wireless polling in the order of devices present in the network. The polling is a control scheme in which, in the network, one device inquires another device whether the other device has data that can be periodically transmitted in order and, when the other device has the data, the other device transmits the data and, when the other device does not have the data, the other device notifies that the data is absent.
[0006] Specifically, when the CC-Link IE field network is made wireless, the master device is connected to a wireless master apparatus and the slave devices are respectively connected to wireless slave apparatuses. The master device performs communication with the slave devices via the wireless master apparatus and the wireless slave apparatuses. A section between the master device and the wireless master apparatus is a wired communication section.

Sections between the wireless master apparatus and the wireless slave apparatuses are wireless communication sections. Sections between the wireless slave apparatuses and the slave devises are wired communication sections. Because the wireless communication sections are independent, a plurality of kinds of communication can be performed at the same time. However, in the wired communication sections, only one kind of communication can be performed at the same time. The token passing scheme is adopted in the wireless communication sections. The control scheme by polling is adopted in the wireless communication sections. [0007] The master device transmits a data frame and a token frame from the wireless master apparatus to all the wireless slave apparatuses through wireless communication. The wireless slave apparatuses transmit the received frames to the slave devices. The slave devices, which receive the token frame, return the data frame and the token frame to the wireless slave apparatuses. When the wireless master apparatus has no data, the wireless master apparatus executes polling to the wireless slave apparatuses. When the wireless slave apparatuses have transmittable data, the wireless slave apparatuses transmit a data frame including the data to the wireless master apparatus. When the wireless slave apparatuses do not have transmittable data, the wireless slave apparatuses notify the wireless master apparatus that data is absent. When the wireless master apparatus receives the data frame from the wireless slave apparatuses, the wireless master apparatus transfers the received data frame to the master device and re-distributes the data frame to the wireless slave apparatuses in the wireless communication sections.

Non-Patent Literature
[0008] Non-Patent Literature 1: Tatsuhiko Naito, Osamu Watanabe "Introduction to Industrial Ethernet (registered trademark)" CQ Publishing Co., Ltd. May 2009
Non-Patent Literature 2: IEEE Std 802.11e-2005 "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications Amendment 8: Medium Access Control (MAC) Quality of Service Enhancements"
Summary
Technical Problem
[0009] However, according to the conventional technology, the wire.1 ess master apparatus is connected to the slave dev;i ces that do not receive the token frame and also executes the polling to the wireless slave apparatuses that do not have transmittable data. Therefore, there is a problem in that invalid processing occurs and communication efficiency is deteriorated. There is also a problem in that an interval of a communication cycle for cyclically performing communication between the master device and the slave devices is long.
[0010] The present invention has been devised in view of the above, and an object of the present invention is to obtain, when the token passing scheme is set as a host network and polling is executed in a wireless communication section of a subordinate network, a wireless master station capable of improving communication efficiency while realizing fixed cycle communication in the host network.
Solution to Problem
[001].] To solve the problems and achieve the object, the present invention is a wireless master station connected to a master device that performs transmission and reception of

data with slave devices according to a token passing scheme, the wireless master station performing wireless communication with wireless slave stations connected to the slave devices. The wireless master station includes a token-circulation-route-information retaining unit to hold information concerning a token circulation route in which order of the slave devices and the master device that receive a token frame is shown. The wireless master station includes a wireless transmission unit to execute, on the basis of the information concerning the token circulation route, polling of wireless communication to the wireless slave station connected to the slave device corresponding thereto according to the order of the slave devices that receive the token frame.
Advantageous Effects of Invention
[0012] The wireless master station according to the present invention achieves an effect that, when the token passing scheme is set as a host network and polling is executed in a wireless communication section of a subordinate network, it is possible to improve communication efficiency while realizing fixed cycle communication in the host network.
Brief Description of Drawings
[0013] F'IG. 1 is a diagram showing a configuration example of an industrial network including a wireless communication system according to a first embodiment.
FIG. 2 is a diagram showing an industrial network by wired communication obtained by excluding the wireless communication system from the configuration example of the industrial network shown in FIG. 1 in the first embodiment.
FIG. 3 is a diagram showing a protocol stack of the

industrial network, according to the first embodiment.
FIG. 4 is a block diagram showing a configuration example of a wireless master apparatus and a wireless slave apparatus configuring the wireless communication system according to the first embodiment.
FIG. 5 is a flowchart showing operation in which a wireless transmission unit performs polling according to the first embodiment.
FIG. 6 is a flowchart showing operation until a circulation-route-information retaining unit retains information concerning a token circulation route according to the first embodiment.
FIG. 7 is a flowchart showing operation for determining polling of a wireless reception unit according to the first embodiment.
FIG. 8 is a flowchart showing operation for the polling of the wireless transmission unit according to the first embodiment.
FIG. 9 is a flowchart showing processing in which the wireless master apparatus executes polling and the wireless slave apparatus responds according to the first embodiment.
FIG. 10 is a sequence chart showing frames transmitted and received among devices or apparatuses when polling is executed without taking into account the order of a token circulation route in an industrial network according to a comparative example.
FIG. 11 is a sequence chart showing frames transmitted and received among devices or apparatuses when polling is executed on the basis of the order of the token circulation route in the industrial network according to the first embodiment.
FIG. 12. is a block diagram showing a configuration example of a wireless master apparatus and a wireless slave

apparatus configuring a wireless communication system according to a second embodiment.
FIG. 13 is a flowchart showing processing in which a token omitting unit generates master omission information according to the second embodiment.
FIG. 14 is a flowchart showing processing at the time when a wireless transmission unit receives a token frame according to the second embodiment.
FIG. 15 is a flowchart showing processing in which a token generating unit generates the token frame according to the second embodiment.
FIG. 16 .is a flowchart showing processing for receiving a data frame in which the master omission information is stored and transmitting the token frame in a wireless reception unit according to the second embodiment.
FIG. 17 is a flowchart showing processing in which the wireless master apparatus omits transmission of the token frame and the wireless slave apparatus generates the token frame according to the second embodiment.
FIG. 18 a sequence chart showing frames transmitted and received among devices or apparatuses when the wireless master apparatus omits the token frame in an industrial network according to the second embodiment.
FIG. 19 is a block diagram showing a configuration example of a wireless master apparatus and a wireless slave apparatus configuring a wireless communication system according to a third embodiment.
FIG. 20 is a flowchart showing processing in which a token generating unit generates a token frame according to the third embodiment.
FIG. 21 is a flowchart showing processing for receiving a data frame in which slave omission information is stored and transmitting the token frame in a wireless

reception unit according bo the bhird embodiment.
FIG. 22 is a flowcharb showing processing in which a token omitting unit generates slave omission information according to the third embodiment.
FIG. 23 is a flowchart showing processing at the time when a wireless transmission unit receives the token frame according to the third embodiment.
FIG. 24 is a sequence chart showing frames transmitted and received among devices or apparatuses when the wireless master apparatus and the wireless slave apparatus omit the token frame in an industrial network according to the third
embodiment.
FIG. 25 is a diagram showing an example of a hardware configuration of a wireless communication unit of the wireless master apparatus or the wireless slave apparatus according to the first to third embodiments.
Description of Embodiments
[0014] A wireless master station, a wireless slave station, a wireless communication system, and a wireless communication method according to embodiments of the present invention are explained in detail below with reference to the drawings. Note that the present invention is not limited by bhe embodiments. [0015] First Embodiment.
In this embodiment, a method of executing polling according to the order of receiving a token frame in a wireless master apparatus is explained. [0016] FIG. 1 is a diagram showing a configuration example of an industrial network including a wireless communication system according to the first embodiment of the present invention. The industrial network includes an industrial master device Nl, which is a controller of the

industrial network, industrial slave devices N101, N102, N103, , and NlOO+m, which are various 10 devices, measuring devices, and the like, in the industrial network, a wireless master apparatus N201 that is a wireless communication apparatus functioning as a wireless master station connected bo the industrial master device Nl by wire to perform wireless communication with the industrial slave devices N101, N102, N103, , and NlOO+m side, and wireless slave apparatuses N301, N302, N303, , and N300-l-m, which are wireless communication apparatuses functioning as a wireless slave station connected to the industrial slave devices N101, N102, N103, , and NlOO+m in a one-to-one relation by wire to perform wireless communication with the industrial master device Nl side. [0017] The wireless communication system is configured by the wireless master apparatus N201 and the wireless slave apparatuses N301, N302, N303, , and N300+m. In the wireless communication system, control communication performed at a fixed cycle in the past is performed by wireless communication between the wireless master apparatus N201 connected to one industrial master device Nl and the wireless slave apparatuses N301, N302, N303, , and N300+m connected to m industrial slave devices N101, N102, N103, , and NlOO+m.
[0018] FIG. 2 is a diagram showing a configuration example of an industrial network by wired communication obtained by excluding the wireless communication system from the configuration example of the industrial network shown .in FIG. 1 in the first embodiment. The industrial master device Nl and the industrial slave devices N101, N102, N103, , and NlOO+m perform operation in cooperation with each other in an interval of the control communication performed at the fixed cycle. A connection

topology is a daisy chain. However, this is an example and the connection topology can be a star, bus, or ring configuration. As shown in FIG. 1, a topology in a wireless communicabion system after being made wireless applied in bhe embodiments of the present invention is a tree type. However, the present invention is not limited to this.
[0019] FIG. 3 is a diagram showing a protocol stack of the industrial network according to the first embodiment. On a wired side, Ethernet is adopted in a physical layer and a data link layer and a token passing scheme is adopted in a network layer. On a wireless side, a standard such as IEEE802.Ha/b/g/n/ac is adopted in a physical layer and a procedure of the present invention explained below is adopted in addition to a standard indicated by IEEE802.il in a data link layer. On the wireless side, the token passing scheme is adopted as on the wired side. In FIG. 1 and FIG. 2, the industrial slave devices N101, N102, N103, , and NIOO-lm, which are the slave devices, and the industrial master device Nl, which is the master device, are performing transmission and reception of data according to the token passing scheme.
[0020] Subsequently, the configurations of the wireless master apparatus N201 and the wireless slave apparatuses N301, N302, N303, , and N300+m are explained. FIG. 4 is a block diagram showing a configuration example of the wireless master apparatus N201 and the wireless slave apparatus N301 configuring a wireless communication system 30 according to the first embodiment. Because the wireless slave apparatuses N301, N302, N303, , and N300+m have the same configuration, the wireless slave apparatus N301 is referred to in the following explanation. [0021] In the industrial network, a section connected by

wire between the industrial master device Nl and the wireless master apparatus N201 is set as a wired section SI. A wirelessly connected section between the wireless master apparatus N201 and the wireless slave apparatuses N301, N302, N303, , and N300+m is set as a wireless section S2. A section connected by wire between the wireless slave apparatuses N301, N302, N303, , and N300+m and the industrial slave devices N101, N102, N103, , and NlOO+m is set as a wired section S3. Note that it is assumed that speed in the wired sections SI and S3 is sufficiently high compared with speed in the wireless section S2. For example, it is assumed that a data transfer rate of the wired sections SI and S3 is 1 Gbps and a data transfer rate of the wireless section S2 is 1 Mbps to 100 Mbps. [0022] The wireless master apparatus N201 includes a wired communication unit 11 that transmits and receives a signal oU fixed cycle communication in the conventional industrial network in the wired section Si between the wired communication unit 11 and the industrial master device Nl and a wireless communication unit 12 that performs transmission and reception of a wireless signal in the wireless section S2 between the wireless communication unit 12 and the wireless slave apparatuses N301 to N300+m. The wired communication unit 11 transmits and receives, specifically, a data frame and a token frame between the wired communication unit 11 and the industrial master device Nl. The wireless communication unit 12 includes a wireless transmission unit 13, a circulation-route-information retaining unit 14, and a wireless reception unit 15. The wireless transmission unit 13 changes a signal from the industrial master device Nl input from the wired communication unit 11 to a wireless signal and transmits the wireless signal to the wireless slave

apparatuses N301 to N300+m through the wireless section S2. The wireless transmission unit 13 transmits, specifically, a daba frame, a token frame, and the like to the wireless slave apparatuses N301 to N300+m through the wireless section S2. The circulation-route-information retaining unit 14 retains information concerning a token circulation route in which the order of the industrial slave devices N101, N102, N103, , and NIOO+m and the industrial master device Nl that receive the token frame in the industrial network is shown. The wireless reception unit 15 receives a wireless signal from the wireless slave apparatuses N301 to N300+m through the wireless section S2 and outputs the received wireless signal.to the wired communication section 11. Note that the circulation-route-information retaining unit 14 can be included'in the inside of the wireless transmission unit 13.
[0023] The wireless transmission unit 13 executes, on the basis of the information concerning the token circulation route retained by the circulation-route-info.rmat.ion retaining unit 14, polling of wireless communication to a wireless slave apparatus connected to an industrial slave device corresponding thereto according to the order of industrial slave devices that receive a token frame. Specifically, the wireless transmission unit 13 transmits a polling frame to a destination wireless slave apparatus. FIG. 5 is a flowchart showing operation in which the wireless transmission apparatus 13 performs polling according to the first embodiment. The wireless transmission unit 13 reads out the information concerning the token circulation route retained by the circulation-route-information retaining unit 14 (step ST1) and executes, on the basis of the read-out information concerning the token circulation route, polling of wireless communication

* to a wireless slave apparatus connected to an industrial slave device corresponding thereto according to the order of an industrial slave device that receives the token frame (step ST2). Note that, when executing the polling on the basis of the information concerning the token circulation route, the wireless transmission unit 13 can synchronize timing of the transmission of the token frame and timing of the execution of the polling by setting, as a trigger, a token frame received from the industrial master device Nl connected to the wireless master apparatus N201. For example, it is assumed that the order of the token circulation route is the order of the industrial master device Nl, the industrial slave device N102, the industrial slave device N101, and the industrial slave device N103 and the token circulation route thereafter returns to the industrial master device Nl. When receiving a token frame addressed to the industrial slave device N102 from the industrial master device Nl, the wireless transmission unit 13 transmits the token frame addressed to the industrial slave device N102. After transmitting the token frame addressed to the industrial slave device N102, the wireless transmission unit 13 executes, on the basis of the information concerning the token circulation route, polling to the wireless slave apparatus N302 connected to the industrial slave device N102. That is, the wireless transmission unit 13 starts polling from the wireless slave apparatus N302 connected bo the industrial slave device N102. Consequently, the wireless transmission unit 13 can synchronize timing of the transmission of the token frame and timing of the execution of the polling. The wireless transmission unit 13 can synchronize the timing of the transmission of the token frame and the timing of the execution of the polling by performing the processing every

time the wireless transmission unit 13 receives the token frame from the industrial master device Nl connected to the wireless master apparatus N201. When deviation occurs between the timing of the transmission of the token frame and the timing of the execution of the polling, the wireless transmission unit 13 can avoid a situation in which the deviation is accumulated to increase. The same applies in the following explanation. [0024] As a method of acquiring the information concerning the token circulation route in the circulation-route-information retaining unit 14, for example, an administrator or the like can manually set the information concerning the token circulation route in the circulation-route-information retaining unit 14 during initial setting of the industrial network or the circulation-route-information retaining unit 14 can automatically learn the order of destinations of the token frame flowing in the industrial network and acquire the information concerning the token circulation route. In general, when a token frame is transmitted and received among a plurality of apparatuses, the apparatuses receive the token frame in order. Therefore, the circulation-route-information retaining unit 14 is capable of automatically learning and acquiring, without manual setting, the order of the apparatuses that receive the token frame, that is, the information concerning the token circulation route. FIG. 6 is a flowchart showing operation until the circulation-route-information retaining unit 14 retains the information concerning the token circulation route according to the first embodiment. The circulation-route-information retaining unit 14 acquires the information concerning the token circulation route according to the setting by the administrator or by automatically learning the order of the

destinations of the token frame flowing in the industrial network (step STll) and stores and retains the acquired information concerning the token circulation route in a storing unit incorporated in the circulation-route-information retaining unit 14 (step ST12). [0025] The wireless slave apparatus N301 includes a wired communication unit 21 that transmits and receives a signal of fixed cycle communication in the conventional industrial network in the wired section S3 between the wired communication unit 21 and the industrial slave device N101 and a wireless communication unit 22 that performs transmission and reception of a wireless signal in the wireless section S2 between the wireless communication unit 22 and the wireless master apparatus N201. The wired communication unit 21 transmits and receives, specifically, a data frame, a token frame, and the like between the wired communication unit 21 and the industrial slave device N101. The wireless communication unit 22 includes a wireless transmission unit 23 and a wireless reception unit 24. The wireless transmission unit 23 changes a signal from the industrial slave device N101 input from the wired communication unit 21 to a wireless signal and transmits the wireless signal to the wireless master apparatus N201 through the wireless section S2. The wireless transmission unit 23 transmits, specifically, a data frame, a token frame, and the like to the wireless master apparatus N201 through the wireless section S2. The wireless reception unit 24 receives the wireless signal from the wireless master apparatus N201 through the wireless section S2 and outputs the received wireless signal to the wired communication unit 21.
[0026] The wireless reception unit 24 determines whether polling from the wireless master apparatus N201 is polling

to the wireless slave apparatus N301. In the case of the polling to the wireless slave apparatus N301, when the wireless slave apparatus N301 has transmittable data, the wireless transmission unit 23 transmits a data frame including the transmittable data to the wireless master apparatus N201. When the wireless slave apparatus N301 has no transmittable data, the wireless transmission unit 23 notifies the wireless master apparatus N201 that data is absent. Note that, when receiving a polling frame addressed to another wireless slave apparatus from the wireless master apparatus N201, the wireless slave apparatus N301 ends the processing without performing anything. FIG. 7 is a flowchart showing operation for determining polling of the wireless reception unit 24 according to the first embodiment. When the polling from the wireless master apparatus N201 is the polling to the wireless slave apparatus N301 (Yes at step ST21), the wireless reception unit 24 notifies the wireless transmission unit 23 that the polling from the wireless master apparatus N201 is addressed to the wireless slave apparatus N301 (step ST22). When the polling from the wireless master apparatus N201 is addressed to another wireless slave apparatus (No at step ST21), the wireless reception unit 24 ends the processing without performing anything. FIG. 8 is a flowchart showing operation on polling by the wireless transmission unit 23 according to the first embodiment. When receiving, from the wireless reception unit 24, the notification that the polling is the polling to the wireless slave apparatus N301 (step ST31), the wireless transmission unit 23 checks whether the wireless slave apparatus N301 has transmittable data (step ST32). When the wireless slave apparatus N301 has transmittable data (Yes at step ST32), the wireless

transmission unit 23 transmits a data frame including the transmittable data to the wireless master apparatus N201 (step ST33). When the wireless slave apparatus N301 has no transmittable data (No at step ST32), the wireless transmission unit 23 notifies the wireless master apparatus N201 that data is absent (step ST34).
[0027] Subsequently, a wireless communication method in which the wireless master apparatus N201 executes polling and the wireless slave apparatus N301 responds in the industrial network including the wireless communication system is explained. FIG. 9 is a flowchart showing processing in which wireless master apparatus N201 executes polling and the wireless slave apparatus N301 responds according to the first embodiment. Processing at steps Sll and S12 is processing of the wireless master apparatus N201. Processing at steps S13 to S16 is processing of the wireless slave apparatus N301.
[0028] First, in the wireless master apparatus N201, the circulation-route-information retaining unit 14 acquires information concerning a token circulation route (step Sll') . A method of acquiring the information concerning the token circulation route in the circulation-route-information retaining unit 14 is as explained below. In the wireless master apparatus N201, the wireless transmission unit 13 executes, on the basis of the information concerning the token circulation route retained by the circulation-route-information retaining unit 14, polling of wireless communication to a wireless slave apparatus connected to an industrial slave device corresponding thereto according to the order of industrial slave devices that receive a token frame (step S12).
[0029] In the wireless slave apparatus N301, the wire].ess reception unit 24 determines whether the polling

from the wireless master apparatus N201 is polling to the wireless slave apparatus N301 (step S13). When the polling is not the polling to the wireless slave apparatus N301 (No at step S13), the wireless slave apparatus N301 ends the processing. When bhe polling is the polling to the wireless slave apparatus N301 (Yes at step S13), that is, when the wireless reception unit 24 receives a polling frame addressed to the wireless slave apparatus N301, the wireless transmission unit 23 checks whether the wireless slave apparatus N301 23 has data transmittable to the wireless master apparatus N201 (step S14). When the wireless slave apparatus N301 has transmittable data (Yes at step S14), the wireless transmission unit 23 transmits a data frame including the transmittable data to the wireless master apparatus N201 (step S15). When the wireless slave apparatus N301 has no transmittable data (No at step S14), the wireless transmission unit 23 notifies the wireless master apparatus N201 that data is absent (step S16). [0030] A difference in the length of a communication cycle for performing transmission of data in all devices of the industrial network is explained concerning, as in this embodiment, the time when the wireless master apparatus N201 executes polling to a wireless slave apparatus connected to an industrial slave device that receives a token frame according to order of receiving the token frame on the basis of a token circulation route and the time when the wireless master apparatus N201 executes the polling without taking into account the token circulation route. [0031] FIG. 10 is a sequence chart showing frames transmitted and received among devices or apparatuses when polling is executed without taking into account the order of a token circulation route in an industrial network according to a comparative example. As an example, it is

assumed that the number of wireless slave apparatuses and industrial slave devices is three. For convenience of explanation, the industrial master device Nl, the wireless master apparatus N201, the wireless slave apparatuses N301, N302, and N303, and the industrial slave devices N101, N102, and N103 denoted by reference signs same as the reference signs .in the first embodiment are referred to in the following explanation. However, bhe function of the circulation-route-information retaining unit 14 is not used in the wireless master apparatus N201.
[0032] First, the industrial master device Nl transmits a data frame to the wireless master apparatus N201 (step S101) and transmits, to the wireless master apparatus N201, a token frame addressed to the industrial slave device N102 (step S102) .
[0033] The wireless master apparatus N201 transmits the data frame received from the industrial master device Nl to the wireless slave apparatuses N301 to N303 (step S103). The wireless slave apparatuses N301 to N303 transmit the data frame received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S104). The wireless master apparatus N201 transmits, to the wireless slave apparatuses N301 to N303, the token frame addressed to the industrial slave device N102 received from the industrial master device Nl (step S105). The wireless slave apparatuses N301 to N303 transmit the token frame addressed to the industrial slave device N102 received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S106).
[0034] When receiving the token frame addressed to the industrial slave device N102, the industrial slave device

N102 transmits the data frame to the wireless slave apparatus N302 (step S107 and transmits the token frame addressed to the industrial slave device N101 to the wireless slave apparatus N302 (step S108). [0035] The wireless master apparatus N201 executes polling to bhe wireless slave apparatus N301 (step S109). Because the wireless slave apparatus N301 has no transmittable data, the wireless slave apparatus N301 notifies the wireless master apparatus N201 that data is absent (step S110). Note that it is also conceivable that the wireless slave apparatuses N302 and N303 actually receive a polling frame from the wireless master apparatus N201. However, as explained above, when the polling is not polling to the wireless slave apparatuses N302 and N303, the wireless slave apparatuses N302 and N303 do not perform any processing. Therefore, in the sequence chart, to simplify description, arrows indicating execution of polling only to a destination wireless slave apparatus are described concerning execution of polling by the wireless master apparatus N201. The same applies in the following explanation.
[0036] Subsequently, the wireless master apparatus N201 executes polling to the wireless slave apparatus N302 (step Sill). The wireless slave apparatus N302 receives the data frame from the industrial slave device N102 (step S107) and has transmittable data. Therefore, the wireless slave apparatus N302 transmits the data frame to the wireless master apparatus N201 (step S112).
[0037] The wireless master apparatus N201 transmits the data frame received from the wireless slave apparatus N302 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (steps S113 and S114). When a destination of the received data frame is not limited to

the industrial master device Nl, for example, in the case of broadcast, multicast, or unicast communication of a device other than the industrial master device Nl, the wireless master apparatus N201 transmits the received data frame to the wireless slave apparatuses N301 to N303. The same applies in the following explanation. The wireless slave apparatuses N301 to N303 transmit the data frame received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S115). Note that the wireless slave apparatus N302 transmits the data frame to the wireless master apparatus N201 only once. However, this is an example. When a data size of the data frame received from the industrial slave device N102 is large, the wireless slave apparatus N302 transmits the data frame to the wireless master apparatus N201 a plurality of times. The same applies in the following explanation.
[0038] The wireless master apparatus N201 executes poJling to the wireless slave apparatus N302 (step S116). After the transmission of the data frame, because the wireless slave apparatus N302 receives the token frame from the industrial slave device N102 (step S108), the wireless slave apparatus N302 transmits the token frame addressed to the industrial slave device N101 to the wireless master apparatus N201 (step S117).
[0039] The wireless master apparatus N201 transmits the token frame addressed to the industrial slave device N101 received from the wireless slave apparatus N302 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (steps S118 and S119). The wire.1 ess s l.ave apparatuses N301 to N303 transmit the token frame addressed to the industrial slave device N101 received from the wireless master apparatus N201 to the

industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S120). [0040] When receiving bhe token frame addressed to the industrial slave device N101, the industrial slave device N101 transmits the data frame to the wireless slave apparatus N301 (step S121) and transmits the token frame addressed to the industrial slave device N103 to the wireless slave apparatus N301 (step S122) .
[0041] Subsequently, the wireless master apparatus N201 executes polling to the wireless slave apparatus N303 (step S123). Because the wireless slave apparatus N303 has no transmittable data, the wireless slave apparatus N303 notifies the wireless master apparatus N201 that data is absent (step S124) .
[0042] Subsequently, the wireless master apparatus N201 executes polling to the wireless slave apparatus N301 (step S125). The wireless slave apparatus N301 receives the data frame from the industrial slave device N101 (step S121) and has bransmittable data. Therefore, the wireless slave apparatus N301 transmits the data frame to the wireless master apparatus N201 (step S126).
[0043] The wireless master apparatus N201 transmits the data frame received from bhe wireless slave apparatus N301 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (step S127 and S128) . The wireless slave apparatuses N301 to N303 transmit the data frame received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S129). [0044] The wireless master apparatus N201 executes polling to the wireless slave apparatus N301 (step S130). The wireless slave apparatus N301 receives the token frame from the industrial slave device N101 (step S122).

Therefore, the wireless slave apparatus N301 transmits the token frame addressed to the industrial slave device N103 to the wireless master apparatus N201 (step S131).
[0045] The wireless master apparatus N201 transmits the token frame addressed to the industrial slave device N103 received from the wireless slave apparatus N301 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (steps S132 and S133) . The wireless slave apparatuses N301 to N303 transmit the token frame addressed to the industrial slave device N103 received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S134).
[0046] When receiving the token frame addresses to the industrial slave device N103, the industrial slave device N103 transmits the data frame to the wireless slave apparatus N303 (step S135) and transmits the token frame addressed to the industrial master device Nl to the wireless slave apparatus N303 (step S136).
[0047] Subsequently, the wireless master apparatus N201 executes polling to the wireless slave apparatus N302 (step S137). Because the wireless slave apparatus N302 has no transmittable data, the wireless slave apparatus N302 notifies the wireless master apparatus N201 that data is absent (step S138).
[0048] Subsequently, the wireless master apparatus N201 executes polling to the wireless slave apparatus N303 (step S139). The wireless slave apparatus N303 receives the data frame from the industrial slave device N103 (step S135) and has transmittable data. Therefore, the wireless slave apparatus N303 transmits the data frame to the wireless master apparatus N201 (step S140).
[0049] The wireless master apparatus N201 transmits the

data frame received from the wireless slave apparatus N303 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (steps S141 and S142) . The wireless slave apparatuses N301 to N303 transmit the data frame received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S143) . [0050] The wireless master apparatus N201 executes polling to the wireless slave apparatuses N303 (step S144). The wireless slave apparatus N303 receives the token frame from the industrial slave device N103 (step S136). Therefore, the wireless slave apparatus N303 transmits the token frame addresses to the industrial master device Nl to the wireless master apparatus N201 (step S145). [0051] The wireless master apparatus N201 transmits the token frame addressed to the industrial master device Nl received from the wireless slave apparatus N303 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (steps S146 and S147) . The wireless slave apparatuses N301 to N303 transmit the token frame addressed to the industrial master device Nl to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S148). [0052] The industrial master device Nl transmits the data frame to the wireless master apparatus N201 (step S101) and transmits the token frame addressed to the industrial slave device N102 (step S102). The subsequent processing is as explained above.
[0053) In this way, order of receiving the token frame, that is, a token circulation route is the order of industrial master device Nl, the industrial slave device N102, the industrial slave device N101, and the industrial slave device N103. On the other hand, order of execution

of polling by the wireless master apparatus N201 is the order of the wireless slave apparatus N301, the wireless slave apparatus N302, and the wireless slave apparatus N303. Even if the wireless master apparatus N201 executes polling to a wireless slave apparatus connected to an industrial slave device that does not receive the token frame, absence of data is notified. Therefore, the execution of the polling is useless processing. Therefore, a communication cycle from the execution of the polling by the wireless master apparatus N201 until all of the wireless slave apparatuses, that is, the wireless slave apparatuses N301 to N303 end the transmission of the data increases. [0054] FIG. 11 is a sequence chart showing frames transmitted and received among devices or apparatuses when polling is executed on the basis of the order of the token circulation route in the industrial network according to the first embodiment. As in FIG. 10, the industrial master device Nl, the wireless master apparatus N201, the wireless slave apparatuses N301, N302, and N303, and the industrial slave devices N101, N102, and N103 are referred to in the following explanation. The wireless master apparatus N201 uses the function of the circulation-route-information retaining unit 14. It is assumed that the circulation-route-information retaining unit 14 already retains the information concerning the token circulation route. The information of the token circulation route, which is the order of receiving the token frame, in this embodiment specifically indicates the order of the industrial master device Nl, the industrial slave device N102, the industrial slave device N101, and the industrial slave device N103 and indicates that the token circulation route thereafter returns to the industrial master device Nl. The order of receiving the token frame indicated by the information

concerning the token circulation route is the same as the case of the sequence chart shown in FIG. 10. [0055] First, the industrial master device Nl transmits a data frame to the wireless master apparatus N201 (step S201) and transmits a token frame addressed to the industrial slave device N102 (step S202) .
[0056] The wireless master apparatus N201 transmits the data frame received from the industrial master device Nl to the wireless slave apparatuses N301 to N303 (step S203). The wireless slave apparatuses N301 to N303 transmit the data frame received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S204). The wireless master apparatus N201 transmits the token frame addressed to the industrial slave device N102 received from the industrial master device Nl to the wireless slave apparatuses N301 to N303 (step S205). The wireless slave apparatuses N301 to N303 transmit the token frame addressed to the industrial slave device N102 received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wire],ess slave apparatuses N301 to N303 (step S206). [0057] When receiving the token frame addressed to the industrial slave device N102, the industrial slave device N102 transmits the data frame to the wireless slave apparatus N302 (step S207) and transmits the token frame addressed to the industrial slave device N101 to the wireless slave apparatus N302 (step S208). [0058] In the wireless master apparatus N201, the wireless transmission unit 13 executes, on the basis of the information concerning the token circulation route retained by the circulation-route-information retaining unit 14, polling to the wireless slave apparatus N302 connected to

the industria] slave device N102 that receives the token frame following the industrial slave device N102 (step S209). The wireless slave apparatus N302 receives the data frame from the industrial slave device N102 (step S207) and has transmittable data. Therefore, the wireless slave apparatus N302 transmits the data frame to the wireless master apparatus N201 (step S210).
[00591 The wireless master apparatus N201 transmits the data frame received from the wireless slave apparatus N302 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (steps S211 and S212). The wireless slave apparatuses N301 to N303 transmit the data frame received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S213). [0060] The wireless master apparatus N201 executes polling to the wireless slave apparatus N302 (step S214). The wireless slave apparatus N302 receives the token frame from the industrial slave device N102 (step S208). Therefore, the wireless slave apparatus N302 transmits the token frame addressed to the industrial slave device N101 to the wireless master apparatus N201 (step S215). [0061] The wireless master apparatus N201 transmits the token frame addressed to the industrial slave device N101 received from the wireless slave apparatus N302 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (step S216 and S217). The wireless slave apparatuses N301 to N303 transmit the token frame addressed to the industrial slave device N101 received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S218). [0062] When receiving the token frame addressed to the

industrial slave device N101, the industrial slave device N101 transmits the data frame to the wireless slave apparatus N301 (step S219) and transmits the token frame addressed to the industrial slave device N103 to the wireless slave apparatus N301 (step S220). [00631 Subsequently, in the wireless master apparatus N201, the wireless transmission unit 13 executes, on the basis of the information concerning the token circulation route retained by the circulation-route-information retaining unit 14, polling to the wireless slave apparatus N301 connected to the industrial slave device N101 that receives the token frame following the wireless master apparatus N201 (step S221). The wireless slave apparatus N301 receives the data frame from the industrial slave device N101 (step S219) and has transmittable data. Therefore, the wireless slave apparatus N301 transmits the data frame to the wireless master apparatus N201 (step S222) .
[0064] The wireless master apparatus N201 transmits the data frame received from the wireless slave apparatus N301 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (steps S223 and S224). The w.i reless slave apparatuses N301 to N303 transmit the data frame received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S225). [0065] The wireless master apparatus N201 executes polling to the wireless slave apparatus N301 (step S226). The wireless slave apparatus N301 receives the token frame from the industrial slave device N101 (step S220). Therefore, the wireless slave apparatus N301 transmits the token frame addressed to the industrial slave device N103 to the wireless master apparatus N201 (step S227) .

[00661 The wireless master apparatus N201 transmits the token frame addressed to the industrial slave device N103 received from the wireless slave apparatus N301 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (steps S228 and S229) . The wireless slave apparatuses N301 to N303 transmit the token frame addressed to the industrial slave device N103 received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S230). [0067] When receiving the token frame addressed to the industrial slave device N103, the industrial slave device N103 transmits the data frame to the wireless slave apparatus N303 (step S231) and transmits the token frame addressed to the industrial master device Nl to the wireless slave apparatus N303 (step S223). [0068] Subsequently, in the wireless master apparatus N201, the wireless transmission unit 13 executes, on the basis of the information concerning the token circulation route retained by the circulation-route-information retaining unit 14, polling to the wireless slave apparatus N303 connected to the industrial slave device N103 that receives the token frame following the wireless master apparatus N201 (step S233). The wireless slave apparatus N303 receives the data frame from the industrial slave device N103 (step S231) and has transmittable data. Therefore, the wireless slave apparatus N303 transmits the data frame to the wireless master apparatus N201 (step S234) .
[0069] The wireless master apparatus N201 transmits the data frame received from the wireless slave apparatus N303 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (steps S235 and S236). The

wireless slave apparatuses N301 to N303 transmit the data frame received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301 to N303 (step S237). [00701 The wireless master apparatus N201 executes polling to the wireless slave apparatus N303 (step S238). The wireless slave apparatus N303 receives the token frame from the industrial slave device N103 (step S232). Therefore, the wireless slave apparatus N303 transmits the token frame addressed to the industrial master device Nl to the wireless master apparatus N201 (step S239). [0071] The wireless master apparatus N201 transmits the token frame addressed to the industrial master device Nl received from the wireless slave apparatus N303 to the industrial master device Nl and the wireless slave apparatuses N301 to N303 (steps S240 and S241). The wire].ess slave apparatuses N301 to N303 transmit the token frame addressed to the industrial master device Nl received from the wireless master apparatus N201 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N30l'to N303 (step S242).
[0072] The industrial master device Nl transmits the data frame to the wireless master apparatus N201 (step S20]) and transmits the token frame addressed to the industrial slave device N102 (step S202). The subsequent processing is as explained above.
[0073] In the wireless master apparatus N201, the wireless transmission unit 13 executes, on the basis of the information concerning the token circulation route retained by the circulation-route-information retaining unit 14, polling of wireless communication to a wireless slave apparatus connected to an industrial slave device cor [responding thereto according to the order of industrial

slave devices that receive the token frame. The wireless master apparatus N201 does not execute the polling on a wire]ess slave apparatus connected to an industrial slave device that does not receive the token frame. Therefore, it is possible to avoid useless processing and improve communication efficiency and reduce a communication cycle compared with the processing shown in FIG. 10. It is possible to set the communication cycle shown in FIG. 11 to a fixed cycle.
[0074] As explained above, according to this embodiment, in a wireless communication system in which a wireless master apparatus connected to an industrial master device and wireless slave apparatuses connected to industrial slave devices in a one-to-one relation and as many as the industrial slave devices perform wireless communication in a communication network in which communication is performed at each communication cycle between one industrial master device and one or a plurality of industrial slave devices, the wireless master apparatus executes polling to the wireless slave apparatuses taking into account token order of the token passing scheme, which is a host network, when determining polling order in sections of the wireless communication, which is a subordinate network. Consequently, there is an effect that it is possible to prevent a situation in which polling is executed on a wireless slave apparatus that has no transmittable data and an invalid procedure occurs, achieve both of high reliability and high communication efficiency, reduce a communication cycle of control communication performed at a fixed cycle, and effectively use frequency resources. [0075] A communication cycle of the industrial network is not decided when the polling order in the sections of the wireless communication and the token order in the token

passing scheme are unrelated. However, there is an effect that it is easy to grasp bhe communication cycle by matching the polling order to the token order. [0076] Note that, in the explanation in this embodiment, the wireless master apparatus N201 is connected to one industrial master device Nl and the wireless slave apparatuses N301, N302, N303, , and N300+m are connected to the industrial slave devices N101, N102, N103, , and NIOO+m in a one-to-one relation. However, the present invention is not limited to this. Depending on the configuration of the industrial network, the wireless master apparatus N201 can be connected to a plurality of industrial master devices Nl belonging to a different industrial network. In the wireless slave apparatuses N301, N302, N303, , and N300+m, one wireless slave apparatus can be connected to a plurality of industrial slave devices. The same applies in embodiments explained below. [0077] Second Embodiment.
In this embodiment, a method of omitting transmission of a token frame in a wireless master apparatus is explained.
[0078] FIG. 12 is a block diagram showing a configuration example of a wireless master apparatus N201a and a wireless slave apparatus N301a configuring a wireless communication system 30a according to the second embodiment. In the second embodiment, in the configuration of the industrial network shown in FIG. 1, the wireless master apparatus N201 is replaced with the wireless master apparatus N201a and the wireless slave apparatuses N301, N302, N303, , and N300-l-m are replaced with wireless slave apparatuses N301a, N302a, N303a, , and N(300+m)a. In the second embodiment, the wireless communication system is configured by the wireless master apparatus N201a and

the wireless slave apparatuses N301a, N302a, N303a, , and N(300-Hm)a. The wireless slave apparatuses N301a, N302a, N303a, , and N(300+m)a have the same configuration. Therefore, the wireless slave apparatus N301a is referred to in the following explanation.
[0079] The wireless master apparatus N201a includes the wi red communication unit 11 and a wireless communication unit 12a that performs transmission and reception of a wireless signal in the wireless section S2 between the wireless communication unit 12a and the wireless slave apparatuses N301a to N(300+m)a. The wireless communication unit 12a includes a wireless transmission unit 13a, the circulation-route-information retaining unit 14, a token omitting unit 16, and the wireless reception unit 15. [0080] When the wireless transmission unit 13a receives a token frame from the industrial master device Nl through the wired communication unit 11 and an un-transmitted data frame to the wireless slave apparatuses N301a, N302a, N303a, , and N(300+m)a is present, the token omitting unit 16 generates master omission information indicating that transmission of the token frame from the wireless master apparatus N201a is omitted. FIG. 13 is a flowchart showing processingi in which the token omitting unit 16 generates the master omission information according to the second embodiment. When receiving notification that an un-transmitted data frame is present from the wireless transmission unit 13a that receives the token frame (step ST41), the token omitting unit 16 generates master omission information (step ST42) and outputs the generated master omission information to the wireless transmission unit 13a (step ST43).
[0081] In addition to the function of the wireless transmission unit 13, when the data frame is transmitted to

the wireless section S2 a plurality of times, the wireless transmission unit 13a further stores the master omission information generated by the token omitting unit 16 in a data frame transmitted last and transmits the master omission information. The wireless transmission unit 13a stores the master omission information in a header or payload portion of the last data frame and transmits the master omission information. The master omission information can be represented by information concerning a form such as "0" or "1" by, for example, defining the master omission information in advance in the wireless master apparatus N201a and the wireless slave apparatuses N301a to N(300+m)a configuring the wireless communication system 30a. FIG. 14 is a flowchart showing processing at the time when the wireless transmission unit 13a receives the token frame according to the second embodiment. When receiving the token frame from the industrial master device Nl through the wired communication unit 11 (step ST51), when an un-transmitted data frame is present (Yes at step ST52), the wireless transmission unit 13a notifies the token omitting unit 16 that the un-transmitted data frame is present (step ST53), acquires the master omission information from the token omitting unit 16 (step ST54), and stores the master omission information in the data frame transmitted last and transmits the master omission information (step ST55). When the un-transmitted data frame is absent (No at step ST52), the wireless transmission unit 13a transmits the token frame separately from the data frame (step ST56).
[0082] Note that the circulation-route-information retaining unit 14 and the token omitting unit 16 can be present on the inside of the wireless transmission unit 13a. [0083] The wireless slave apparatus N301a includes the

wired communication unit 21 and a wireless communication unit 22a that performs transmission and reception of a wireless signal in the wireless section S2 between the wireless communication unit 22a and the wireless master apparatus N201a. The wireless communication unit 22a includes the wireless transmission unit 23, a wireless reception unit 24a, and a token generating unit 25. [0084] The token generating unit 25 retains information concerning a token circulation route. When the master omission information is stored in the data frame from the wireless master apparatus N201a received by the wireless reception unit 24a, the token generating unit 25 generates, on the basis of the information concerning the token circulation route, the token frame, the transmission of which is omitted in the wireless master apparatus N201a. The information concerning the token circulation route is the same as the information retained by the circulation-roLite-information retaining unit 14 in the first embodiment. [0085] As a method of acquiring the information concerning the token circulation route in the token generating unit 25, as in the circulation-route-information retaining unit 14, an administrator or the like can manually set the information concerning the token circulation route in the token generating unit 25 during initial setting of the industrial network or the token generating unit 25 can automatically learn the order of destinations of the token frame flowing in the industrial network and acquire the information concerning the token circulation route. Note that, when the token generating unit 25 automatically learns the order of the destinations of the token frame flowing in the industrial network, the token generating unit 25 cannot, generate the token frame until the learning ends. Therefore, for example, a

specified fixed period after a start of operation of the industrial network is set as a learning period of the token generating unit 25. The transmission of the token frame is not omitted in the wireless master apparatus N201a in the learning period. FIG. 15 is a flowchart showing processing in which the token generating unit 25 generates the token frame according to the second embodiment. The token generating unit 25 acquires the information concerning the token circulation route according to the setting by the administrator or by automatically learning the order of the destinations of the token frame flowing in the industrial network (step ST61) and stores and retains the acquired information concerning the token circulation route in a storing un.i t incorporated in the token generating unit 25 (step ST62). When receiving, from the wireless reception unit 24a that receives the data frame, notification that the master omission information is stored (step ST63), the token generating unit 25 generates the token frame on the basis of the information concerning the token circulation route (step ST64) and outputs the generated token frame to the wireless reception unit 24a (step ST65). Note that the token generating unit 25 performs the processing at steps ST61 and ST62 only for the initial time. When the token generating unit 25 already retains the information concerning the token circulation route, the token generation unit 25 omits the processing at steps ST61 and ST62 .
[0086] When receiving, from the wireless master apparatus N201a, the data frame in which master omission information is stored, the wireless reception unit 24a extracts the master omission information from the data frame and transmits the data frame, from which the master omission information is extracted, to the industrial slave

device N101 through the wired communication unit 21. Thereafter, the wireless reception unit 24a transmits the token frame generated by the token generating unit 25 to the industrial slave device N101 through the wired communication unit 21. The wired reception unit 24a can transmit the data frame to the industrial slave device N101 without extracting the master omission information from the data frame. FIG. 16 is a flowchart showing processing in which the wireless reception unit 24a receives the data frame in which the master omission information is stored and transmits the token frame according to the second embodiment. When receiving, from the wireless master apparatus N201a, the data frame in which the master omission information is stored (step ST71), the wireless reception unit 24a notifies the token generating unit 25 that the master omission information is stored (step ST72), acquires the token frame from the token generating unit 25 (step ST73), and transmits the acquired token frame (step ST7 4).
[0087] Note that the token generating unit 25 can be present on the inside of the wireless reception unit 24a. [0088] Subsequently, a wireless communication method is explained in which the wireless master, apparatus N201a omits the transmission of the token frame and the wireless slave apparatus N301a generates the token frame in the industrial network including the wireless communication system. FIG. 17 is a flowchart showing processing in which the wireless master apparatus N201a omits the transmission of the token frame and the wireless slave apparatus N301a generates the token frame according to the second embodiment. Processing at steps S21 to S24 and S29 is processing of the wireless master apparatus N201a. Processing at steps S25 to S28 and S30 is processing of the

wireless slave apparatus N301a. It is assumed that, in the token generating unit 25, the information concerning the token circulation route is already set by the administrator or the like.
[0089] First, in the wireless master apparatus N201a, the wireless communication unit 12a receives a token frame from the industrial master device Nl through the wireless communication unit 11 (step S21). In the wireless communication unit 12a, the tome omitting unit 16 checks whether an un-transmitted data frame to the wireless slave apparatus N301a is present in the wireless transmission un.it 13a (step S22) .
[0090] When the un-transmitted data frame is present (Yes at step S22), the token omitting unit 16 generates the master omission information (step S23). The wireless transmission unit 13a stores the master omission information in a last data frame among data frames transmitted to the wireless slave apparatus N301a and transmits the master omission information to the wifeless slave apparatus N301a (step S24).
[0091] In the wireless slave apparatus N301a, the wireless reception unit 24a receives, from the wireless master apparatus N201a, the data frame in which the master omission information is stored (step S25). Because the master omission information is stored in the data frame received in the wireless reception unit 24a, the token generating unit 25 generates, on the basis of the information concerning the token circulation route, the token frame to the industrial slave device N101 (step S26). [0092] The wireless reception unit 24a transmits the data frame, from which the master omission information is extracted, to the industrial slave device N101 through the wired communication unit 21 (step S27) and transmits the

token frame generated by the token generating unit 25 to the industrial slave device N101 through the wired communication unit 21 (step S28).
[0093] Note that, in the wireless master apparatus N201a, when an un-transmit ted data frame to the wireless slave apparatus N301a is absent in the wireless transmission unit 13a (No at step S22), the wireless transmission unit 13a transmits the token frame received from the industrial master device Nl to the wireless slave apparatus N301a (step S29). In the wireless slave apparatus N301a, when receiving the token frame (step S30), the wireless reception unit 24a transmits the token frame to the industrial slave device N101 through the wireless communication unit 21 (step S28).
[0094] A difference in a communication cycle for performing transmission of data in all devices of the industrial network is explained concerning the time when the wireless master apparatus N201a omits the token frame as in this embodiment and the time when the wireless master apparatus N2 01a does not omit the token frame as in the first embodiment.
[0095] FIG. 18 is a sequence chart showing frames transmitted and received among devices or apparatuses when the wireless master apparatus N201a omits the token frame in the industrial network according to the second embodiment. The industrial master device Nl, the wireless master apparatus N201a, the wireless slave apparatuses N301a, N302a, and N303a, and the industrial slave devices N101, N102, and N103 are referred to in the following explanation. It is assumed that the token generating units 25 of the wireless slave apparatuses N301a to N303a already retain the information concerning the token circulation route. The information concerning the token circulation

route, which is the order for receiving the token frame, in this embodiment is information indicating the order of the industrial master device Nl, the industrial slave device N102, the industrial slave device N101, and the industrial slave device N103 and indicating that thereafter the token circulation route returns to the industrial master device Nl as in the first embodiment.
[00961 First, the industrial master device Nl transmits a data frame to the wireless master apparatus N201a (step S301) and transmits a token frame addressed to the industrial slave device N102 (step S302). [0097] In the wireless master apparatus N201a, the wireless transmission unib 13a transmits the data frame to the wireless slave apparatuses N301a to N303a (step S303). At this point, in bhe wireless master apparatus N201a, the token omitting unib 16 generates the master omission .information and the wireless transmission unit 13a stores the master omission information in a last data frame among data frames transmitted to the wireless slave apparatuses N301a to N303a and transmits the master omission information bo the wireless slave apparatuses N301a to N303a.
[0098] The wireless slave apparatuses N301a to N303a transmit the data frame received from the wireless master apparatus N201a to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301a to N303a (step S304). When bransmitting the data frame to the industrial slave devices N101 to N103, the wireless reception units 24a of the wireless slave apparatuses N301a to N303a can extract the master omission information from the data frame and transmit the master omission information or can transmit the master omission information while keeping the master omission information stored in the data

frame. The same applies in the following explanation. [0099] At this point, in the wireless apparatuses N301a to N303a, because the wireless reception units 24a receive the data frame in which the master omission information is stored, the token generating units 25 generate the token frame on the basis of the information concerning the token circulation route. In the wireless slave apparatuses N301a to N303a, because the master omission information is stored in the data frame received from the wireless master apparatus N201a, the token generating units 25 can determine that the industrial master device Nl connected to the wireless master apparatus N201a has received the token frame. As explained above, in the order of the token circulation route, the industrial slave device N102 follows the .industrial master device Nl. Therefore, the token generating units 25 generate, on the basis of the information concerning the token circulation route, the token frame addressed to the industrial slave device N102. [01001 In the wireless slave apparatuses N301a to N303a, the wireless reception units 24a transmit the token frame addressed to the industrial slave device N102 generated by the token generating units 25 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301a to N303a (step S305).
[0101] Respective kinds of processing at the following steps S306 to S341 are the same as the respective kinds of processing at steps S207 to S242 shown in the sequence chart of FIGS. 11 in the first embodiment. Therefore, explanation of the processing is omitted.
[0102] In the wireless master apparatus N201a, when the wireless transmission unit 13a transmits the data frame a plurality of times, the wireless transmission unit 13a stores the master omission information generated by the

token omitting unib 16 in a data frame transmitted last and transmits the master omission information. In the wireless slave apparatuses N301a to N303a, the token generating units 25 generate the token frame, the transmission of wh.i ch is omitted in the wireless master apparatus N201a, and transmit the token frame to the industrial slave devices N101 to N103. As a result, when the sequence chart of F'IG. 18 in the second embodiment and the sequence chart of FTG. 11 in the first embodiment are compared, it is possible to set a communication cycle shorter in the second embodiment than in the first embodiment.
[0103] AS explained above, according to this embodiment, in a wireless communication system in which a wireless master apparatus connected to an industrial master device and wireless slave apparatuses connected to industrial slave devices in a one-to-one relation and as many as the industrial slave devices perform wireless communication in a communication network in which communication is performed at each communication cycle between one industrial master device and one or a plurality of industrial slave devices, in wirelessly transmitting a token frame, when an ury-transmitted data frame is present in a wireless section, the wireless master apparatus stores master omission information indicating that the transmission of the token frame is omitted in transmitting a last data frame and transmits the master omission information. The wireless slave apparatus generates the token frame, the transmission of which is omitted, and transmits the token frame to the industrial slave device. Consequently, there is an effect that it is possible to reduce a time for exchanging the token frame in a wireless section having a narrower communication band than a wired section, achieve both of high reliability and high communication efficiency, reduce

a communication cycle of control communication performed at a fixed cycle, and effectively use frequency resources.
[0104] Third Embodiment.
In the second embodiment, the method of omitting transmission of a boken frame in a wireless master apparatus is explained. In this embodiment, a method of omitting transmission of a token frame in a wireless slave apparatus as well as a wireless master apparatus is explained.
[0105] FIG. 19 is a block diagram showing a configuration example of a wireless master apparatus N201b and a wireless slave apparatus N301b configuring a wireless communication system 30b according to the third embodiment. In the third embodiment, in the configuration of the industrial network shown in FIG. 1, the wireless master apparatus N201 is replaced with the wireless master apparatus N201b and the wireless slave apparatuses N301, N302, N303, , and N300+m are replaced with wireless slave apparatuses N301b, N302b, N303b, , and N(300+m)b. In the third embodiment, the wireless communication system is configured by the wireless master apparatus N201b and the wireless slave apparatuses N301b, N302b, N303b, , and N(300+m)b. The wireless slave apparatuses N301b, N302b, N303b, , and N(300+m)b have the same configuration. Therefore, the wireless slave apparatus N301b is referred to the following explanation.
[0106] The wireless master apparatus N20lb includes the wired communication unit 11 and a wireless communication unit 12b that performs transmission and reception of a wireless signal in the wireless section S2 between the wireless communication unit 12b and the wireless slave apparatuses N301b to N(300fm)b. The wireless communication section 12b includes the wireless transmission unit 13a,

the circulation-route-information retaining unit 14, the token omitting unit 16, a wireless reception unit 15a, and a token generating unit 17.
[0107] When slave omission information indicating that transmission of a token frame from the wireless slave apparatuses N301b to N303b is omitted is stored in a data frame from the wireless slave apparatuses N301b to N303b received by the wireless reception unit 15a, the token generating unit 17 generates, on the basis of information concerning a token circulation route, the token frame, the transmission of which is omitted in the wireless slave apparatuses N301b to N303b. The information concerning the token circulation route is the same as the information retained by the circulation-route-information retaining unit 14 in the first embodiment. In the wireless master apparatus N201b, the token generating unit 17 can retain the information concerning the token circulation route and can use the information concerning the token circulation route retained by the circulation-route-information retaining unit 14 without retaining the information concerning the token circulation route.
[0108] Concerning a method of acquiring the information concerning the token circulation route in the token generating unit 17, as in the circulation-route-information retaining unit 14, an administrator or the like can manually set the information concerning the token circulation route in the token generating unit 17 during initial setting of the industrial network or the token generating unit 17 can automatically learn the order of destinations of the token frame flowing in the industrial network and acquire the information concerning the token circulation route. Note that, when the token generating unit 17 automatically learns the order of the destinations

of the token frame flowing in the industrial network, the token generating unit 17 cannot generate the token frame unti] the learning ends. Therefore, for example, a specified fixed period after a start of operation of the industrial network is set as a learning period of the token generating unit 17. The transmission of the token frame is not omitted in the wireless slave apparatuses N301b to N303bl in the learning period. FIG. 20 is a flowchart showing processing in which the token generating unit 17 generates the token frame according to the third embodiment. The token generating unit 17 acquires the information concerning the token circulation route according to the setting by the administrator or by automatically learning the order of the destinations of the token frame flowing in the industrial network (step ST81) and stores and retains the acquired information concerning the token circulation route in a storing unit incorporated in the token generating unit 17 (step ST82). When receiving, from the wireless reception unit 15a that receives the data frame, notification that the slave omission information is stored (step ST83), the token generating unit 17 generates the token frame on the basis of the information concerning the token circulation route (step ST84) and outputs the generated token frame to the wireless reception unit 15a (step ST85). Note that the token generating unit 17 performs the processing at steps ST81 to ST82 only for the initial time. When the circulation-route-information retaj.ning unit 14 already retains the information concerning the token circulation route, the token generation unit 17 can omit the processing at steps ST81 and ST82 from the initial time.
[01091 When receiving, from the wireless slave apparatuses N301b to N303b, the data frame in which the

slave omission information is stored, the wireless reception unit 15a extracts the slave omission information from the data frame and transmits the data frame, from which the slave omission information is extracted, to the industrial master device Nl through the wired communication un.it 11. Thereafter, the wireless reception unit 15a transmits the token frame generated by the token generating unit 17 to the industrial master device Nl through the wired communication unit 11. The wireless reception unit 15a can transmit the data frame to the industrial master device Nl without extracting the slave omission information from the data frame. FIG. 21 is a flowchart showing processing in which the wireless reception unit 15a receives the data frame in which the slave omission information is stored and transmits the token frame according to the third embodiment. When receiving, from the wireless slave apparatuses N301b to N303b, the data frame in which the slave omission information is stored (step ST91), the wireless reception unit 15a notifies the token generating unit 17 that the slave omission information is stored (step ST92), acquires the token frame from the token generating unit 17 (step ST93), and transmits the acquired token frame (step ST94). [0110] Note that the token generating unit 17 can be present on the inside of the wireless reception unit 15a. [0111J The wireless slave apparatus N301b includes the wired communication unit 21 and a wireless communication unit 22b that performs transmission and reception of a wireless signal in the wireless section S2 between the wireless communication unit 22b and the wireless master apparatus N201b. The wireless communication unit 22b includes a wireless transmission unit 23a, a token omitting unit 26, the wireless reception unit 24a, and the token

generating unit 25.
[0112] When the token omitting unit 2 6 receives the token frame from the industrial slave device N101 through the wired communication unit 21 and an un-transmitted data frame to the wireless section S2 is present in the wireless transmission unit 23a, the token omitting unit 26 generates slave omission information indicating that the transmission of the token frame from the wireless slave apparatus N301b is omitted. FIG. 22 is a flowchart showing processing in which the token omitting unit 26 generates the slave omission information according to the third embodiment. When receiving, from the wireless transmission unit 23a that receives the token frame, notification that the un-transmitted data frame is present (step ST101), the token omitting unit 2 6 generates the slave omission information
(step ST102) and outputs the generated slave omission information to the wireless transmission unit 23a (step ST103) .
[0113] In addition to the function of the wireless transmission unit 13, when the data frame is transmitted to the wireless section S2 a plurality of times, the wireless transmission unit 23a further stores the slave omission information generated by the token omitting unit 26 in a data frame transmitted last and transmits the slave omission information. The wireless transmission unit 23a stores the slave omission information in a header or payload portion of the last data frame and transmits the slave omission information. The slave omission information can be represented by information concerning a form such as "0" or "1" by, for example, defining the slave omission information in advance in the wireless master apparatus N201b and the wireless slave apparatuses N301b to N(300+m)b configuring the wireless communication system 30b. FIG. 23

is a flowchart showing processing at the time when the wireless transmission unib 23a receives the token frame according to the third embodiment. When receiving the token frame from the industrial slave device N101 through the wired communication unit 21 (step STlll), when an un-transmitted data frame is present (Yes at step ST112), the wireless transmission unit 23a notifies the token omitting unit 26 that the un-transmitted data frame is present (step ST113), acquires the slave omission information from the token omitting unit 26 (step ST114), and stores the slave omission information in the data frame transmitted last and transmits the slave omission information (step ST115). When the un-transmitted data frame is absent (No at step ST112), the wireless transmission unit 23a transmits the token frame separately from the data frame (step ST116). [0114] When the master omission information indicating that the transmission of the token frame from the wireless master apparatus N201b is omitted is stored in the data frame from the wireless master apparatus N201b received by the wireless reception unit 24a, the token generating unit 25 generates, on the basis of the information concerning the token circulation route, the token frame, the transmission of which is omitted in the wireless master apparatus N201b. When the slave omission information indicating that the transmission of the token frame from the wireless slave apparatuses N301b to N303b is omitted is stored in the data frame from the wireless slave apparatuses N301b to N303b transferred from the wireless master apparatus N201b, the token generating unit 25 generates, on the basis of the information concerning the token circulation route, the token frame, the transmission of which is omitted in the wireless slave apparatuses N301b to N303b. The information concerning the token circulation

route is the same as the information retained by the circulation-route-information retaining unit 14 in the fi rs b embodiment.
[0115 J No be thab the boken omitting unit 2 6 can be present on the inside of bhe wireless transmission unit 23a. [0116] In the industrial network including the wireless communication system in this embodiment, a wireless communication method in which the wireless slave apparatus N301b omits the transmission of the token frame and the wi reless master apparatus N201b generates the token frame is the same as the respective kinds of processing of the flowchart shown in FIG. 17 in the second embodiment, although a flow of the frames are in the opposite direction. Therefore, detailed explanation of the wireless communication method is omitted.
[OKI 7] A communication cycle at the time when the wireless master apparatus N201b and the wireless slave apparatuses N301b to N303b omit the token frame as in bhis embodiment is explained. FIG. 24 is a sequence chart showing frames transmitted and received among devices or apparatuses when the wireless master apparatus N201b and the wireless slave apparatuses N301b to N303b omit the token frame in the industrial network according to the third embodiment. The industrial master device Nl, the wireless master apparatus N201b, the wireless slave apparatuses N301b, N302b, and N303b, and the industrial slave devices N101, N102, and N103 are referred to in the following explanation. The token generating unit 17 of the wireless master apparatus N201b already retains the information concerning the token circulation route or can use the information concerning the token circulation route. The information concerning the token circulation route, which is the order of receiving the token frame, in this

embodiment is information indicating the order of the industrial master device Nl, the industrial slave device N102, the industrial slave device N101, and the industrial slave device N103 and indicating that the token circulation route thereafter returns to the industrial master device Nl as in the first embodiment.
[0118] First, the industrial master device Nl transmits a daba frame to the wireless master apparatus N201b (step S401) and transmits a token frame addressed to the industrial slave device N102 (step S402). [0119] In the wireless master apparatus N201b, the wireless transmission unit 13a transmits the data frame to the wireless slave apparatuses N301b to N303b (step S403). At this point, in the wireless master apparatus N201b, the token omitting unit 16 generates master omission information. The wireless transmission unit 13a stores the master omission information in a last data frame among data frames transmitted to the wireless slave apparatuses N301b to N303b and transmits the master omission information to the wireless slave apparatuses N301b to N303b. [0120] The wireless slave apparatuses N301b to N303b transmit the data frame received from the wireless master apparatus N201b to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301b to N303b (step S404) . When transmitting the data frame to the industrial slave devices N101 to N103, the wireless reception units 24a of the wireless slave apparatuses N301b to N303b can extract the master omission information from the data frame and transmit the master omission information or can transmit the master omission information while keeping the master omission information stored in the data frame. The same applies in the following explanation. [0121] At this point, in the wireless slave apparatuses

N301b to N303b, the wireless reception units 24a receive the data frame in which the master omission information is stored. Therefore, the token generating units 25 generate the token frame on the basis of the information concerning the token circulation route. In the wireless slave apparatuses N301b to N303b, because the master omission information is stored in the data frame received from the wireless master apparatus N201b, the token generating units 25 can determine that the industrial master device Nl connected to the wireless master apparatus N201b has received the token frame. As explained above, in the order of the token circulation route, the industrial slave device N102 follows the industrial master device Nl. Therefore, the token generating units 25 generate, on the basis of the information concerning the token circulation route, the token frame addressed to the industrial slave device N102. [0122] In the wireless slave apparatuses N301b to N303b, the wireless reception units 24a transmit the token frame addressed to the industrial slave device N102 generated by the token generating units 25 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301b to N303b (step S405).
[0123] When receiving the token frame addressed to the industrial slave device N102, the industrial slave device N102 transmits the data frame to the wireless slave apparatus N302b (step S406) and transmits the token frame addressed to the industrial slave device N101 to the wireless slave apparatus N302b (step S4 07) . [0124] In the wireless master apparatus N201b, the wireless transmission unit 13a executes, on the basis of the information concerning the token circulation route retained by the circulation-route-information retaining unit 14, polling to the wireless slave apparatus N302b

connected to the industrial slave device N102 that receives the token frame following the wireless master apparatus N201b (step S408) . The wireless slave apparatus N302b receives the data frame from the industrial slave device N102 (step S406) and has transmittable data. Therefore, the wireless slave apparatus N302b transmits the data frame to the wireless master apparatus N201b (step S409). [0125] At this point, in the wireless slave apparatus N302b, the token omitting unit 26 generates slave omission information. The wireless transmission unit 23a stores the slave omission information in a last data frame among data frames transmitted to the wireless master apparatus N201b and transmits the slave omission information to the wireless master apparatus N201b.
[0126] The wireless master apparatus N201b transmits the data frame received from the wireless slave apparatus N302b to the industrial master device Nl and the wireless slave apparatuses N301b to N303b (steps S410 and S412) . When transmitting the data frame to the industrial master device Nl, the wireless reception unit Iba of the wireless master apparatus N201b can extract the slave omission information from the data frame and transmit the slave omission information or can transmit the slave omission information while keeping the master omission information stored in the data frame. The same applies in the following explanation. Note that, when transmitting the data frame to the wireless slave apparatuses N301b to N303b, the wireless reception unit 15a of the wireless master apparatus N201b transmits the data frame while keeping the slave omission information stored in the data frame. The same applies in the fol "I owing explanation.
[0127) At this point, in the wireless master apparatus N201b, the wireless reception unit 15a receives the data

frame in which the slave omission information is stored. Therefore, the token generating unit 17 generates the token frame on the basis of the information concerning the token circulation route. In the wireless master apparatus N201b, because the slave omission information is stored in the data frame received from the wireless slave apparatus N302b, the token generating unit 17 can determine that the industrial slave device N102 connected to the wireless slave apparatus N302b has received the token frame. As explained above, in the order of the token circulation route, the industrial slave device N101 follows the Indusbrial slave device N102. Therefore, the token generating unit 17 generates, on the basis of the information concerning the token circulation route, the token frame addressed to the industrial slave device N101. [03 28 1 In the wireless master apparatus N201b, the wireless reception unit 15a transmits the token frame addressed to the industrial slave device N101 generated by the token generating unit 17 to the industrial master device Nl connected to the wireless master apparatus N201b (step S411).
[03 29 J ' The wireless slave apparatuses N301b to N303b transmit the data frame received from the wireless master apparatus N201b to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301b to N303b (step S413). At this point, in the wireless slave apparatuses N301b to N303b, the wireless reception units 24a receive the data frame in which the slave omission information is stored. Therefore, the token generating units 25 generate the token frame on the basis of the information concerning the token circulation route. A method of generating the token frame addressed to the industrial slave device N101 in the token generating unit

25 is the same as the method in the token generating unit 17.
[03 30] In the wireless slave apparatuses N301b to N303b, the wireless reception units 24a transmit the token frame addressed to the industrial slave device N101 generated by the token generating unit 25 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301b to N303b (step S414).
[0131] When receiving the token frame addressed to the industrial slave device N101, the industrial slave device N101 transmits the data frame to the wireless slave apparatus N30]b (step S415) and transmits the token frame addressed to the industrial slave device N103 to the wireless slave apparatus N301b (step S416). [0132] In the wireless master apparatus N201b, the wireless reception unit 15a receives, from the wireless slave apparatus N302b, the data frame in which the slave omission information is stored. Therefore, the wireless reception unit 15a determines that the wireless slave apparatus N302b has no trame and notifies the wireless transmission unit 13a that the wireless slave apparatus N302b has no frame. In the wireless master apparatus N201b, the wireless transmission unit 13a executes, on the basis of the information concerning the token circulation route retained by the circulation-route-information retaining unit 14, polling to the wireless slave apparatus N301b connected to the industrial slave device N101 that receives the token frame following the wireless master apparatus N201b (step S417). The wireless slave apparatus N301b receives the data frame from the industrial slave device N101 (stop S415) and has transmittable data. Therefore, the wireless slave apparatus N301b transmits the data frame to the wireless master apparatus N201b (step S418).

[0133] At this point, in the wireless slave apparatus N301b, the token omitting unit 26 generates the slave omission information. The wireless transmission unit 23a stores the slave omission information in a last data frame among data frames transmitted to the wireless master apparatus N2 01b and transmits the slave omission information to the wireless master apparatus N201b. [0134] The wireless master apparatus N201b transmits the data frame received from the wireless slave apparatus N301b to the industrial master device Nl and the wireless slave apparatuses N301b to N303b (steps S419 and S421). At this point, in the wireless master apparatus N201b, the wireless reception unit 15a receives the data frame in which the sJave omission information is stored. Therefore, the token generating unit 17 generates the token frame on the basis of the information concerning the token circulation route. [0135] In the wireless master apparatus N201b, because the slave omission information is stored in the data frame received from the wireless slave apparatus N301b, the token generation unit 17 can determine that the industrial slave device N101 connected to the wireless slave apparatus N301b has received the token frame. As explained above, in the order of the 'token circulation route, the industrial slave device N103 follows the industrial slave device N101. Therefore, the token generating unit 17 generates, on the basis of the information concerning the token circulation route, the token frame addressed to the industrial slave device N103.
[0136] In the wireless master apparatus N201b, the wireless reception unit 15a transmits the token frame addressed to the industrial slave device N103 generated by the token generating unit 17 to the industrial master device Nl connected to the wireless master apparatus N201b

(step S420).
[0137] The wireless slave apparatuses N301b to N303b transmit the data frame received from the wireless master apparatus N201b to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301b to N303b (step S422). At this point, in the wireless slave apparatuses N301b to N303b, the wireless reception units 24a receive the data frame in which the slave omission information is stored. Therefore, the token generating units 25 generate the token frame on the basis of the information concerning the token circulation route. A method of generating the token frame addressed to the industrial slave device N103 in the token generating unit 25 is the same as the method in the token generating unit 17.
[0138] In the wireless slave apparatuses N301b to N303b, the wireless reception units 24a transmit the token frame addressed to the industrial slave device N103 generated by the token generating unit 25 to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301b to N303b (step S423).
[0139] When receiving the token frame addressed to the industrial slave device N103, the industrial slave device N103 transmits the data frame to the wireless slave apparatus N302b (step S424) and transmits the token frame addressed to the industrial master device Nl to the wireless slave apparatus N303b (step S425).
[0140] In the wireless master apparatus N201b, the wireless reception unit 15a receives, from the wireless slave apparatus N301b, the data frame in which the slave omission information is stored. Therefore, the wireless reception unit 15a determines that the wireless slave apparatus N301b has no frame and notifies the wireless

transmission unit 13a that the wireless slave apparatus N301b has no frame. In the wir-eless master apparatus N201b, the wireless transmission unit 13a executes, on the basis of the information concerning the token circulation route retained by the circulation-rout-information retaining unit 14, polling to the wireless slave apparatus N303b connected to the industrial slave device N103 that receives the token frame following the wireless master apparatus N201b (step S42.6) . The wireless slave apparatus N303b receives the data frame from the industrial slave device N103 (step S424) and has transmittable data. Therefore, the wireless slave apparatus N303b transmits the data frame to the wireless master apparatus N201b (step S427). [0141] At this point, in the wireless slave apparatus N303b, the token omitting unit 2 6 generates the slave omission information. The wireless transmission unit 23a stores the slave omission information in a last data frame among data frames transmitted to the wireless master apparatus N201b and transmits the slave omission information to the wireless master apparatus N201b. [0142] The wireless master apparatus N201b transmits the . data frame received from the wireless slave apparatus N303b to the industrial master device Nl and the wireless slave apparatuses N301b to N303b (step S428 and S430). At this point, in the wireless master apparatus N201b, the wireless reception unit 15a receives the data frame in which the slave omission information is stored. Therefore, the token generating unit 17 generates the token frame on the basis of the information concerning the token circulation route. [0143] In the wireless master apparatus N201b, because the slave omission information is stored in the data frame received from the wireless slave apparatus N303b, the token generating unit 17 can determine that the industrial slave

device N103 connected to the wireless slave apparatus N303b has received the token frame from the industrial slave device N103 connected to the wireless slave apparatus N303b. As explained above, in the order of the token circulation route, the industrial master device Nl follows the industrial slave device N103. Therefore, the token generating unit 17 generates, on the basis of the information concerning the token circulation route, the token frame addressed to the industrial master device Nl. [0144] In the wireless master apparatus N201b, the wireless reception unit 15a transmits the token frame addressed to the industrial master device Nl generated by the token generating unit 17 to the industrial master device Nl connected to the wireless master apparatus N201b (step S429) .
[0145] The wireless slave apparatuses N301b to N303b transmit the data frame received from the wireless master apparatus N201b to the industrial slave devices N101 to N103 connected to the wireless slave apparatuses N301b to N303b (step S431). At this point, in the wireless slave apparatuses N301b to N303b, the wireless reception units 24 receive the data frame in which the slave omission information is stored. Therefore, the token generating units 25 generate the token frame on the basis of the information concerning the token circulation route. A method of generating the token frame addressed to the industrial master device Nl in the token generating unit 25 is the same as the method in the token generating unit 17. [0146] In the wireless slave apparatuses N301b to N303b, the wireless reception units 24a transmit the token frame addressed to the industrial master device Nl generated by the token generating unit 25 to the industrial slave devices N101 to N103 connected to the wireless slave

apparatuses N301b to N303b (step S432).
[0147] The industrial master device Nl transmits the data frame bo the wireless master apparatus N201b (step S401) and transmits the token frame addressed to the industrial slave device N102 (step S402). The subsequent processing is as explained above.
[0148] As explained above, in this embodiment, in addition to the wireless master apparatus N201b, the wireless slave apparatuses N301b to N303b omit the transmission of the token frame. Therefore, it is possible to reduce a communication cycle compared with the second embodiment.
[0149] As explained above, according to this embodiment, in a wireless communication system in which a wireless master apparatus connected to an industrial master device and wireless slave apparatuses connected to industrial slave devices in a one-to-one relation and as many as the industrial slave devices perform wireless communication in a communication network in which communication is performed at each communication cycle between one industrial master device and one or a plurality of industrial slave devices, exchange of a token frame is omitted between the wireless master apparatus and the wireless slave apparatus. Invalid polling is omitted even when polling is sequentially executed. Consequently, there is an effect that it is possible to reduce a time for exchanging the token frame in a wireless section having a narrower communication band than a wired section, achieve both of high reliability and high communication efficiency, reduce a communication cycle of control communication performed at a fixed cycle, and effectively use frequency resources.
[0150] A hardware configuration for realizing the components of the wireless master apparatus and the

wireless slave apparatus shown in FIGS. 4, 12, and 19 is explained. The wired communication unit 11 of the wireless master apparatus and the wired communication unit 21 of the wireless slave apparatus are realized by an interface card of wired communication. Similarly, the wireless communication unit of the wireless master apparatus and the wireless communication unit of the wireless slave apparatus are realized by an interface card of wireless communication. Note that, in the wireless master apparatus and the w.ire.1 ess slave apparatus shown in FIGS. 4, 12, and 19, a part of the components of the wireless communication unit can be configured by software. FIG. 25 is a diagram showing an example of a hardware configuration of the wireless communication unit of the wireless master apparatus or the wireless slave apparatus according to the first to third embodiments.
[0151] In the wireless communication units 12, 12a, and 12b, the wireless transmission units 13 and 13a are realized together with a transmitter 93 by a processor 91 executing programs for the components stored in a memory 92. In the wireless communication units 12, 12a, and 12b, the ci rculat.i on-route-inf ormation retaining unit 14 is realized together with the memory 92 by the processor 91 executing a program for the circulation-route-information retaining unit 14 stored in the memory 92. In the wireless communication units 12, 12a, and 12b, the wireless reception units 15 and 15a are realized together with a receiver 94 by the processor 91 executing the programs for components stored in the memory 92. In the wireless communication units 12a and 12b, the token omitting unit 16 is realized by the processor 91 executing a program for the token omitting unit 16 stored in the memory 92. In the wireless communication unit 12b, the token generating unit

17 is realized by the processor 91 executing a program for the token generating unit 17 stored in the memory 92. The token generating unit 17 is realized together with the memory 92 by the processor 91 executing a program for the token generating unit 17 stored in the memory 92.
[0152] In the wireless communication units 22, 22a, and 22b, the wireless transmission units 23 and 23a are realized together with the transmitter 93 by the processor 91 executing the program for the components stored in the memory 92. In the wireless communication units 22, 22a, and 22b, the wireless reception units 24 and 24a are realized together with the receiver 94 by the processor 91 executing the program for the components stored in the memory 92. In the wireless communication units 22a and 22b, the token generating unit 25 is realized together with the memory 92 by the processor 91 executing a program for the token generating unit 25 stored in the memory 92. In the wireless communication unit 22b, the token omitting unit 26 is realized by the processor 91 executing a program for the token omitting unit 26 stored in the memory 92.
[0153] The processor 91, the memory 92, the transmitter 93, and the receiver 94 are connected by the system bus 95. A plurality of processors 91 and a plurality of memories 92 can execute the functions of the components in cooperation with each other.
[0154] The configurations explained in the embodiments above indicate an example of the contents of the present invention. The components can be combined with other publicly-known technologies. A part of the configurations can be omitted or changed in a range not departing from the spirit of the present invention.
Reference Signs List

[0155] 11, 21 wired communication unit
12, 12a, 12b, 22, 22a, 22b wireless communication unit
13, 13a, 23, 23a wireless transmission unit
14 circulation-route-information retaining unit
15, 15a, 24, 24a wireless reception unit
16, 2 6 token omitting unit
17, 25 token generating unit
30, 30a, 30b wireless communication system Nl .industrial master device
N101, N102, N103, , NlOO+m industrial slave device N201, N201a, N201b wireless master apparatus N301, N302, N303, , N300+m, N301a, N302a, N303a, N301b, N302b, N303b wireless slave apparatus

CLAIMS
1. A wireless master station connected to a master device
that performs transmission and reception of data with a
slave device according to a token passing scheme, the
wireless master station performing wireless communication
with a wire].ess slave station connected to the slave device,
the wire.1 ess master station comprising: a circulation-route-information retaining unit to retain information concerning a token circulation route in which order of the slave device and the master device that receive a token frame is indicated; and
a wireless transmission unit to execute, on the basis of: the information concerning the token circulation route, polling of the wireless communication to the wireless slave station connected to the slave device corresponding thereto according to the order of the slave device that receives the token frame.
2. The wireless master station according to claim 1,
further comprising a token omitting unit to, when the token
frame is received from the master device and an un-
transm.it ted data frame to the wireless slave station is
present in the wireless transmission unit, generate master
omi ssion information indicating that transmission of the
token frame received from the master device is omitted,
wherein
the wireless transmission unit stores the master omission information in a last data frame to the wireless slave station and transmits the master omission information.
3. The wireless master station according to claim 1 or 2,
further comprising:
a token generating unit to generate the token frame on

the basis of the information concerning the token circulation route when slave omission information indicating that transmission of the token frame received from the slave device is omitted is stored in a data frame received from the wireless slave station; and
a wireless reception unit to transmit the token frame generated by the token generating unit to the master device.
4. A wireless slave station connected to a slave device
that performs transmission and reception of data with a
master device according to a token passing scheme, the
wireless slave station performing wireless communication
with a wireless master station connected to the master
device,
the wireless slave station comprising: a token generating unit to retain information concerning a token circulation route in which order of the slave device and the master device that receive a token frame is indicated and, when master omission information indicating that transmission of the token frame received from the master device is omitted is stored in a wireless data frame received from the wireless master station, generate the token frame on the basis of the information concerning the token circulation route; and
a wireless reception unit to transmit the token frame generated by the token generating unit to the slave device.
5. The wireless slave station according to claim 4,
further comprising:
a token omitting unit to receive the token frame from the slave device and, when an un-transmitted data frame to the wireless master station is present, generate slave omission information indicating that transmission of the

token frame received from the slave device is omitted; and
a wireless transmission unit to store the slave omission .information in a last data frame to the wireless master station and transmit the slave omission information.
6. A wireless communication system comprising:
a wireless master station connected to a master device that performs transmission and reception of data with a slave device according to a token passing scheme; and
a wireless slave station connected to the slave device, wherein
the wireless master station includes:
a circulation-route-information retaining unit to retain information concerning a token circulation route in which order of the slave device and the master device that receive a token frame is indicated; and
a wireless transmission unit to execute, on the basis of the information concerning the token circulation route, polling of the wireless communication to the wireless slave station connected to the slave device corresponding thereto according to the order of the slave device that receives the token frame, and the wireless slave station includes:
a wire].ess reception unit to determine whether the polling is polling to the wireless slave station; and a wireless transmission unit to, in case of the polling to the wireless slave station, when the wireless slave station has transmittable data, transmit a data frame including the transmittable data to the wireless master station and, when the wireless slave station does not have the transmi ttable data, notify the wireless master station that data is absent.

7. A wireless communication method in a wireless communication system including a wireless master station connected to a master device that performs transmission and reception of data with a slave device according to a token passing scheme and a wireless slave station connected to the slave device,
the wireless communication method comprising:
a circulation-route-information retaining step in which the wireless master station acquires and retains information concerning a token circulation route in which order of the slave device and the master device that receive a token frame is indicated;
a polling step in which the wireless master station executes, on the basis of the information concerning the token circulation route, polling of the wireless communication to the wireless slave station connected to the slave device corresponding thereto according to the order of the slave device that receives the token frame;
a determining step in which the wireless slave station determines whether the polling is polling to the wireless slave station; and
a responding step in which, in case of the polling to the wireless slave station, when the wireless slave station has transmittable data, the wireless slave station transmits a data frame including the transmittable data to the wireless master station and, when the wireless slave station does not have the transmittable data, the wireless slave station notifies the wireless master station that data is absent,