Patent Application
20110310748
The present application claims priority from Japanese patent application JP 2010-138422 filed on Jun. 17, 2010, the content of which is hereby incorporated by reference into this application.
The present invention relates to a coordinator, wireless node, and wireless communication system for same, and relates in particular to an ad hoc wireless communication device and wireless communication system for sending data from nodes by way of multiple intermediate nodes to access points.
The continued spread of wireless communication systems oriented toward personal uses as wireless LAN and cellular telephones has led to increased demand for wireless communications in the industrial field. In the manufacturing field for example such as in industrial plants, much equipment is currently controlled by cables. However adding a new machine requires more cable installation work in order to convey control information to this new machine. Along with the cost of the new machine, there are also expenses for cable installation work and losses from having to halt the production line during the installation period. However, if the control information could be sent by wireless then a huge reduction in costs could be attained. Achieving wireless communication in the industrial field requires attaining reliability that is the same or higher than in communication by conventional cables.
The technology disclosed in Japanese Unexamined Patent Application Publication No. 2007-195179 reveals a scheme for achieving reliability to prevent communication stoppages by utilizing route diversity to send the same data contents over multiple paths.
The technology in Japanese Unexamined Patent Application Publication No. 2008-148299 and Japanese Unexamined Patent Application Publication No. 2004-538690 attain reliability by boosting redundancy through communications by changing the code symbols for the plural paths. Moreover the Japanese Unexamined Patent Application Publication No. 2010-35068 discloses technology for switching routes according to the status of the communication path to deal with rapid fluctuations in the communication path environment.
Wireless or radio communication of the related art includes no scheme for ensuring reliability when communication errors occur due to effects on the overall communication frequency band used for wireless communications in the area used by the wireless communication system from effects of electromagnetic noise such as from household electrical appliances, trains, industrial equipment or interference from other wireless schemes, or physical blockages due to the intrusion of objects in the communication path and so on. The route diversity method for example that conveys data utilizing plural paths (with no geographic points in common) cannot achieve sufficient reliability due to effects on all routes when a failure occurs that exerts effects on the entire communication system. Moreover even in systems that change communication parameters such as the dispersion factor and code symbols used between routes, there is still the problem of communications stoppages when a communication error occurs on the overall frequency band being used since the frequency, channels or modulation method of the wireless standard itself are not changed.
In view of these problems, an object of the present invention is to provide a coordinator and wireless communication system capable of ensuring high reliability wireless communications in ad hoc systems even when large-scale trouble occurs that effects the overall wireless standard.
A typical example of the present invention is given as follows. The wireless communication system according to one aspect of the present invention includes nodes, intermediate nodes and access points each equipped with multiple wireless standards; is further an ad hoc wireless communication system comprising at least one coordinator including a function for setting the communication route between each node and the access point; and in which a feature of the coordinator is a function to set multiple communication routes utilizing wireless standards of different frequencies and modulation methods according to the status of the communication path on the applicable communication route from the node to the access point by way of the intermediate node; and perform wireless communication between each node and the access point on the communication routes specified by the applicable coordinator, and transmit the same information from the node to the access point.
The ad hoc wireless communication system of the present invention is capable of conveying data without causing communication stoppages even in cases where a failure has occurred over a wide range spanning one entire system because the same data is jointly sent by wireless standards utilizing different frequencies and modulation methods. High reliability wireless communication matching that of cable communications can in this way be achieved while also shortening the installation period and lowering costs for installing communication cables which also allows flexible expansion of the system.
The wireless communication system of the present invention sets a plurality of routes between the node and the access point, and transmits data with the same contents in ad hoc communication between a node and access points by way of plural intermediate nodes in systems where the nodes, intermediate nodes and access points are each equipped with multiple wireless standards. By selecting a wireless standard according to the status of the communication paths to relay data on the respective routes, the system of this invention always conveys the communication (data) even if a large-scale communication error occurs that exerts effects over the entire communication system. The coordinator that finds that communication path status on each intermediate node, provides instructions on setting routes and wireless standards for communication by each intermediate node, and each intermediate node then conveys the information while complying with those instructions. The system of this invention moreover avoids use of redundant multiple routes between intermediate nodes and so prevents communication stoppages due to intermediate node breakdowns and blocking.
If there are plural coordinators within the same area in this system then the adjacent coordinators share data and give appropriate route instructions by having all coordinators within the same area find the status on all communication paths within the area.
Also, each intermediate node obtains the communication path status in the vicinity of its own node, and sets the optimal transfer destination and wireless standard for use to achieve route diversity utilizing multiple wireless standards without a coordinator.
The embodiments of the present invention are described next while referring to the drawings. The wireless communication standards described below are for example the IEEE802.11a system and IEEE802.11b system for wireless LAN, the ZigBee and UWE (Ultra Wideband) system, and ISA100.11a systems. Specially designated energy-saving wireless may also be utilized.
The following description assumes the sending and receiving of measurement data for temperature, pressure, gas concentrations, light and sound, etc. The ad hoc wireless communication system of this invention can in this way be applied to municipal central monitoring networks, emergency monitoring systems such as for power equipment and industrial plants, energy-saving monitor equipment, failure prediction systems at work sites, traffic facility operation management systems, building air conditioning and light control equipment, building entry/exit control systems and alarm systems etc. However, the present invention is not limited to the above applications and can also be applied to industrial equipment inside factories and medical treatment equipment such as in hospitals; all types of control actuators and position sensing and so on; and sending and receiving of machine control information.
All devices such as the node 100, intermediate nodes (300A-300C), and access point 200 within the wireless communication system contains a “communication environment measurement function” that measures and monitors the communication path status in the vicinity of its own node and sends “communication path information” 500 to the coordinator 400 if a change occurs. Other communication path parameters required by this “communication environment measurement function” are the received signal strength indicator (RSSI), and the noise power, the link quality indicator (LQI: Link Quality Identifier), the communication path effective throughput, and the latency, etc. These information items are utilized to decide if the transmission method is suitable for that communication path.
The coordinator 400 registers the reported results from this “communication path information” 500 in the communication path status DB406 as shown in
The coordinator 400 for example sets the route judged as a high-reliability A route as the communication route for usage per to the communication route status decision results, and instructs each device accordingly. The structure of the coordinator 400 including the communication path status DB406 is described in
In the ad hoc communication system, the coordinator 400 constantly maintains plural routes between the node 100 and the access point 200 that satisfy the specified criteria based on the “communication path information” 500 and exerts control to allow transmitting the same data. The coordinator 400 sets plural optimal wireless standards that fully utilize the features of each wireless standard among the devices according to the status and the physical communication environment such as the relative length of the distance between the access points, the intermediate node and nodes.
When a communication error has occurred due to effects such as from electromagnetic radio waves from another wireless standard or electromagnetic noise from equipment in a state where using the ZigBee system at 2.4 GHz as shown in
The node 100 sends the measurement data 503 to the access point 200 according to the plurality of paths specified by the coordinator 400.
As one example, the access point 200 is a robot arm within the factory and the node 100 is a temperature sensor. The node 100 sends the same “measurement data” or in other words data measured by the same temperature sensor by wireless communication utilizing multiple wireless standards along plural routes at specified time periods to the access point 200. The measurement data that is sent includes information with the temperature sensor measurement time.
In the present invention, data of the same type or category measured on the same node such as data or information relating to temperature or pressure is respectively defined as the “same information” or “same data” relating to the temperature or pressure. The data rate or baud rate of the “measurement data” varies according to the wireless standard so that even if the “measurement data” relates to temperatures measured by the node 100 at specified times, there is a high probability that the data will reach the access point 200 at different times after passing through the multiple repeaters (intermediate zones). The access point 200 summarizes this plural “same data” from the different time periods into one “measurement data” such as temperature at each measurement time period and sends it over the wide band network 209 to the upstream control device 220.
Examples of plural wireless standards and their carrier wave frequencies and modulation methods utilized in the wireless communication system of this embodiment include the following. The IEEE 802.11a system (or wireless standard) operates on the 5 GHz frequency band, the IEEE 802.11b system on the 2.4 GHz frequency band. In the IEEE 802.11a system, eight channels are allocated to the 5.150-5.350 GHz frequency band. In the IEEE 802.11b system a total of 14 channels are allocated at 5 MHz each in the 2.400-2.4835 GHz frequency band. The IEEE 802.11a system utilizes Orthogonal Frequency Division Multiplexing (OFDM) as the modulation method. The IEEE 802.11b system utilizes any of the Binary Phase-Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), or the Complementary Code Keying (CCK) modulation methods to transmit the data after first diffusing the signal with Direct Sequence Spread Spectrum (DSSS) phase modulation.
The ZigBee system is utilized on the three frequency bands which of 868 MHz, 916 MHz and 2.4 GHz. On the 915 MHz band for example used by the ZigBee system, the frequency band from 902 MHz through 928 MHz is subdivided in two megahertz each and allotted to ten channels. The modulation method is Offset Quadrature Phase-shift Keying (OQPSK), and others.
The UWB (Ultra Wideband) system sends and receives over a wide frequency band from 3.1 GHz to 10.6 GHz. Amongst other systems is the NFC system that is utilized on the 13.56 MHz frequency band.
In the wireless communication system of the present invention, the coordinator 400 selects the path (plural repeaters) between each device, and one or plural wireless standards for these paths, or namely selects a combination of frequency band and modulation method as needed, and changes the combination as needed when a failure occurs to constantly maintain an optimal communication path within the system.
As shown in the example in
The node 100 directly sends a “node registration request” 501 to the coordinator 400 by way of the intermediate node 300 immediately after startup. The node 100 afterwards receives a “communication route instruction” 502 from then coordinator 400 showing the route (plural repeaters) to the access point 200. The node 100 then sends the “measurement data” 503 to the access point 200 utilizing the instructed route. The node 100 also monitors the status of the communication path environment in the vicinity of the node and if a change has occurred, sends a “communication path information” 500 to the coordinator 400. The route is changed when the coordinator 400 sends a “route change instruction” according to changes in the communication path environment in the vicinity of the node 100 and intermediate node 300.
The access point 200 provides “measurement data” 503 received from the node 100 to each external application over the network as needed. The communication environment measurement unit 211 measures the propagation path environment in the vicinity of its own node by way of the connected communication equipment and transmits the “communication path information” 500 to the coordinator 400.
The intermediate node 300 forwards the “measurement data” 503 sent from the node 100 and other intermediate nodes 300 along communication paths specified by the coordinator 400. The communication environment measurement unit 306 measures the propagation path environment of its own node by way of the connected communication devices and sends the “communication path information” 500 to the coordinator 400.
The coordinator 400 receives a “node registration request” 501 from the node 100 and sends a “communication route instruction” 502 showing the communication route from the node 100 to the access point 200 for connecting to the node 100. Moreover, the coordinator 400 judges the contents of the “communication path information” 500 sent from the node 100, the access point 200, and intermediate node 300, and sends a “route change instruction” to the node 100 when a change in the communication route is required.
Next,
The node 100 sends the “node registration request” 501 to the nearest coordinator 400 (S002) at startup (S001). At this time, instead of the node 100 sending a “node registration request” 501 directly to the coordinator 400, another method may be used where the node 100 makes a broadcast to the nearest intermediate node 300, the intermediate node 300 checks that the message content from the node 100 is a “node registration request” 501 and forwards the message to the coordinator 400. The coordinator 400 that accepted this “node registration request” 501 from the node 100, sets the access point 200 for connecting to that node 100, establishes plural communication routes linking the node 100 and the access point 200 based on the estimated node positions (S3003), and sends a “communication route instruction” 502 showing those contents to the node 100 (S004).
The communication route described here is an instruction combining the route from the node 100 to the access point 200 via the intermediate node 300; and the wireless standard used on that communication path. In one example of a route instruction for connecting from the node 100 to the access point 200 by way of the intermediate node A (300A), the instruction combines the path and the wireless standard so that communication from the node to the intermediate node A utilizes ZigBee, and communication from the intermediate node A to the access point uses IEEE802.11b. The method for establishing this route is related separately in detail.
The node 100 that received the “communication route instruction” 502 from the coordinator 400 sends the “measurement data” 503 having the same contents, along the plural specified communication routes (S005). This “measurement data” 503 contains routing information. The intermediate node 300 that received it, transfers this “measurement data” 503 from the node 100 to the access point 200 based on the routing information within the “measurement data” 503. The same contents, namely the plural measurement data 503-1, 503-2, and so on having an identical measurement time, or plural “measurement data” at different time periods due to difference in wireless standards are sent so the access point 200 checks the contents of this plural “measurement data” and integrates the same data or in other words type data having the same measurement times such as temperature to form the “measurement data” 503 (S006). The coordinator resets the route if a change has occurred in the communication path environment within the route (S007). If the node 100 has stopped operating then a “registration delete request” 505 is sent to the coordinator 400 by the same method as at startup (S008). The coordinator 400 that received the “registration delete request” 505 then deletes the communication path information relating to that node 100 (S009).
During notification of routing information to the intermediate node 300 as shown in
The node 100 that received instructions for plural routes 1-N, may also divide up the data contents to send to the access point 200, and may send them along the plural routes, and sends the data; and the access point receiving the data may unify this data, demodulate the contents, and then integrate it. This process will prevent the outflow of data during the communication process.
The number of routes set between the node 100 and the access point 200 by the coordinator 400 is an optional number set by the system administrator according to the environment where the node 100 is installed. The number of routes may be increased or decreased according to the priority of data sent from the node 100.
To set up a route between the node 100 and the access point 200, the coordinator 400 first of all selects one default route from the route information DB407 (S304). The information on the communication paths included in this default route are checked by the communication path status DB406, and after a usage judgment process, is registered and rewritten in the communication path status DB406, and a communication path whose judgment values fall below a fixed standard value are tagged (S305). The system sets criteria values according to the priority of the communications.
Examples of criteria values for judging and selecting whether or not the wireless standard is suitable for that communication path are given as follows. The route generator 405 selects a wireless standard that simultaneously satisfies any one or plural conditions in these examples as a wireless standard suitable for the communication path.
(1) Received signal power that is higher than a specified value.
(2) Noise power that is lower than a specified value.
(3) Packet error rate that is lower than a specified value.
(4) Propagation delay is smaller than a specified value.
(5) Signal power to noise power ratio (SN ratio) is larger than a specified value.
(6) The differential between the number of sent packets and number of Ack signals for those packets is smaller than a specified value.
The communication path status DB406 next searches for another communication path as a substitute for the tagged communication path (S306).
When a communication error occurs for example due to a problem along the communication path joining the intermediate node 300A and intermediate node 300B as shown in
The route generator 405 for the coordinator 400 in this case searches the default routes stored in the route information DB407, and decides on utilizing a detour route combining communication paths where IEEE802.11a joins the intermediate node 300A and the intermediate node 300C; and IEEE802.11b joins the intermediate node 300C and the intermediate node 300B as a combination detour route as a default route that is substitutable and satisfies the above criteria values for the communication paths using ZigBee to join the intermediate node 300A and intermediate node 300B. If a substitute path can be set in the same way for all tagged communication paths then this substitute path can be set as a single route from the node 100 to the access point 200.
The coordinator 400 next selects another default route from the route information DB407 (S310). Communication paths included among the previously set routes are tagged for this communication path (S309). The coordinator 400 sets alternate paths for these tagged communication routes in the same way (S309), and also checks the information included in these routes on the communication path status DB406, and tags communication paths whose judgment values are below a fixed standard value (S305). The coordinator 400 also sets an alternate communication path for these (tagged) routes in the same way (S306), and moreover repeats this task until the required number of routes has been obtained (S307).
After obtaining the required number of routes, the coordinator 400 notifies the node 100 of those contents in the form of a “communication route instruction” 502 (S311).
Moreover when the coordinator 400 sets the route, the plural intermediate nodes 300 that initially receive transmissions from a certain node 100 may be set on the plural routes in directions as seen from that node 100 that are greater than a specified angle so that even if an incident occurs that blocks a portion of the vicinity of that node 100 due to an obstruction or problem then the communication will not be completely cut off.
The route change procedures used when a change has occurred along the communication path within the route are described next while referring to
One more method that may be employed at this time when there are no suitable alternate paths within the applicable communication system due to reason such as occurrence of a large communication error is temporarily switching over data transmission to a public communication system or a separate communication system, and then resetting the route when the system recovers from the failure.
The processing used when a communication stoppage has occurred between the node 100 and the intermediate node 300 or between the node 100 and the access point 200 is described next using
The node 100 may at this time send the broadcast to the coordinator 400 by way of the intermediate node 300 and access point 200 without sending the broadcast directly to the coordinator 400.
The coordinator 400 searches the default routes registered in the route information DB407 and sends a “route change instruction” to the node 100 to set an alternate path for the communication path where the problem occurred. The node 100 then communicates on that new route (S505) after receiving the “route change instruction” from the coordinator 400. If the node has not received a “route change instruction” within a specified period after sending the “route change request” then the wireless standard is changed and sends the “route change request” again. The node repeats this process until a route change instruction is received.
The present embodiment therefore is capable of configuring a wireless standard capable of sending the same data that can be jointly utilized on wireless standards having different frequency bandwidths and modulation methods and sent simultaneously along plural paths, even when a wide-scale failure has occurred that effects not only a portion but the entire wireless communication system. This embodiment can therefore continuously transmit data without causing a communication stoppage even if a wide-scale failure occurs. This embodiment can moreover also achieve wireless communication with high reliability equivalent to that of cable communications. Moreover, this embodiment is a wireless method so the cost of installing communications cable is reduced and the construction period for the installation can be significantly shortened. Another advantage is that flexible system expansion can be achieved.
The present embodiment sends data to plural intermediate nodes 300 the same as in the first embodiment, and ultimately the “measurement data” 503 is simultaneously transferred over plural routes to the access point 200. This second embodiment configures a wireless communication system capable of simultaneously sending the same data along plural paths by jointly utilizing another wireless standard having different frequency bandwidths and modulation methods, and therefore the data can be transmitted without causing a communication stoppage even when a wide-scale failure has occurred. This embodiment can therefore achieve wireless communication with high reliability equivalent to that of cable communications. Further, all the coordinators 400 share the same communication path status content so communication between the node 100 and the access point 200 is possible even over long distances and over a wide range. The embodiment can also select the ideal route from many potential routes. In addition even if a failure occurs on any one of the coordinators 400, the other coordinators can maintain those functions.
The node 100 sends data towards the plural intermediate nodes 510 the same as in the first embodiment and ultimately transfers the “measurement data” 503 simultaneously over plural routes to the access point 200. During data transfer if one intermediate node 510 received the same data two or more times along different routes, then it attached information indicating the information was already included in other routes and sends the message back to the intermediate node that was the transmit source. The intermediate node the received the returned message then selects another communication path and once again transfers the data
This embodiment is therefore capable of configuring a wireless communication system capable of simultaneously sending the same data on plural paths by jointly utilizing separate wireless standards having different frequency bandwidths and modulation methods, and is moreover capable of continuously transmitting data without causing a communication stoppage even if a wide-scale failure occurs. This embodiment can therefore achieve wireless communication with high reliability equivalent to that of cable communications. Moreover, communication is achievable over a wide range without coordinators.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-138422 | Jun 2010 | JP | national |
