Patent Application
20090290511
This disclosure relates generally to wireless networks and more specifically to a system and method for merging clusters of wireless nodes in a wireless network.
Processing facilities are often managed using process control systems. Example processing facilities include manufacturing plants, chemical plants, crude oil refineries, and ore processing plants. Among other operations, process control systems typically manage the use of motors, valves, and other industrial equipment in the processing facilities. Process control systems routinely include one or more wireless networks containing various wireless devices, such as wireless sensors and wireless actuators.
Devices in wireless networks (such as wireless networks in process control systems, batch control systems, or building HVAC control systems) may need to be synchronized in time with one another. This may be necessary or desirable for various reasons, such as to ensure that one wireless node transmits data at a time when another wireless node is prepared to receive the data. However, robust and accurate time synchronization is often very difficult to achieve, particularly in large wireless networks. This problem is exacerbated by the dynamic nature of wireless links between the wireless devices.
This disclosure provides a system and method for merging clusters of wireless nodes in a wireless network.
In a first embodiment, a system includes a first cluster having multiple first wireless nodes. One first node is configured to act as a first cluster master, and other first nodes are configured to receive time synchronization information provided by the first cluster master. The system also includes a second cluster having one or more second wireless nodes. One second node is configured to act as a second cluster master, and any other second nodes configured to receive time synchronization information provided by the second cluster master. The system further includes a manager configured to merge the clusters into a combined cluster. One of the nodes is configured to act as a single cluster master for the combined cluster, and the other nodes are configured to receive time synchronization information provided by the single cluster master.
In a second embodiment, an apparatus includes an interface configured to receive information identifying a link between first and second clusters of wireless nodes in a wireless network. Each cluster includes one wireless node configured to act as a cluster master, and each cluster master is configured to provide time synchronization information for use by any other wireless nodes in that cluster. The apparatus also includes a controller configured to merge the clusters into a combined cluster, where one of the wireless nodes in the combined cluster is configured to act as a cluster master for the combined cluster and to provide time synchronization information for use by the other wireless nodes in the combined cluster.
In a third embodiment, a method includes providing time synchronization information from a wireless node acting as a first cluster master to other wireless nodes in a first cluster. The method also includes providing time synchronization information from a wireless node acting as a second cluster master to any other wireless nodes in a second cluster. The method further includes merging the wireless nodes in the first and second clusters into a combined cluster. In addition, the method includes providing time synchronization information from one of the wireless nodes acting as a single cluster master to the other wireless nodes in the combined cluster.
Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims.
For a more complete understanding of this disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:
In this example embodiment, the process control system 100 includes one or more process elements 102. The process elements 102 represent components in a process system that perform any of a wide variety of functions. For example, the process elements 102 could represent sensors, actuators, or any other or additional industrial equipment in a processing environment. Each process element 102 includes any suitable structure for performing one or more functions in a process system. Also, a process system may represent any system or portion thereof configured to process one or more materials in some manner.
A controller 104 is coupled to the process elements 102. The controller 104 controls the operation of one or more of the process elements 102. For example, the controller 104 could receive information associated with the process system, such as sensor measurements from some of the process elements 102. The controller 104 could use this information to provide control signals to others of the process elements 102, thereby adjusting the operation of those process elements 102. The controller 104 includes any hardware, software, firmware, or combination thereof for controlling one or more process elements 102. The controller 104 could, for example, represent a computing device executing a MICROSOFT WINDOWS operating system.
A network 106 facilitates communication between various components in the system 100. For example, the network 106 may communicate Internet Protocol (IP) packets, frame relay frames, Asynchronous Transfer Mode (ATM) cells, or other suitable information between network addresses. The network 106 may include one or more local area networks, metropolitan area networks, wide area networks (WANs), all or a portion of a global network, or any other communication system or systems at one or more locations.
In
The infrastructure nodes 108a-108e and the leaf nodes 110a-110e engage in wireless communications with each other. For example, the infrastructure nodes 108a-108e may receive data transmitted over the network 106 (via the node 112) and wirelessly communicate the data to the leaf nodes 110a-110e. Similarly, the leaf nodes 110a-110e may wirelessly communicate data to the infrastructure nodes 108a-108e for forwarding to the network 106 (via the node 112). In addition, the infrastructure nodes 108a-108e may wirelessly exchange data with one another. In this way, the nodes 108a-108e form a wireless network capable of providing wireless coverage to leaf nodes and other devices in a specified area, such as a large industrial complex.
In this example, the nodes 108a-108e and 110a-110e are divided into infrastructure nodes and leaf nodes. The infrastructure nodes 108a-108e typically represent routing devices that can store and forward messages for other devices. Infrastructure nodes 108a-108e are typically line-powered devices, meaning these nodes receive operating power from an external source. Infrastructure nodes 108a-108e are typically not limited in their operations since they need not minimize power consumption to increase the operational life of their internal power supplies. On the other hand, the leaf nodes 110a-110e are generally non-routing devices that do not store and forward messages for other devices. Leaf nodes 110a-110e typically represent devices powered by local power supplies, such as nodes that receive operating power from internal batteries or other internal power supplies. Leaf nodes 110a-110e are often more limited in their operations in order to help preserve the operational life of their internal power supplies.
The nodes 108a-108e and 110a-110e include any suitable structures facilitating wireless communications, such as radio frequency (RF) frequency hopping spread spectrum (FHSS) transceivers. The nodes 108a-108e and 110a-110e could also include other functionality, such as functionality for generating or using data communicated over the wireless network. For example, the leaf nodes 110a-110e could represent wireless sensors used to measure various characteristics within an industrial facility. The sensors could collect and communicate sensor readings to the controller 104 via the node 112. The leaf nodes 110a-110e could also represent actuators that receive control signals from the controller 104 and adjust the operation of the industrial facility. In this way, the leaf nodes may include or operate in a similar manner as the process elements 102 physically connected to the controller 104. The leaf nodes 110a-110e could further represent handheld user devices (such as INTELATRAC devices from HONEYWELL INTERNATIONAL INC.), mobile stations, programmable logic controllers, or any other or additional devices. The infrastructure nodes 108a-108e may also include any of the functionality of the leaf nodes 110a-110e or the controller 104.
The gateway infrastructure node 112 communicates wirelessly with, transmits data to, and receives data from one or more infrastructure nodes and possibly one or more leaf nodes. The node 112 may convert data between protocol(s) used by the network 106 and protocol(s) used by the nodes 108a-108e and 110a-110e. For example, the node 112 could convert Ethernet-formatted data transported over the network 106 into a wireless protocol format (such as an IEEE 802.11a, 802.11b, 802.11g, 802.11n, 802.15.3, 802.15.4, or 802.16 format) used by the nodes 108a-108e and 110a-110e. The node 112 could also convert data received from one or more of the nodes 108a-108e and 110a-110e into Ethernet-formatted data for transmission over the network 106. In addition, the node 112 could support various functions, such as network creation and security, used to create and maintain a wireless network. The gateway infrastructure node 112 includes any suitable structure for facilitating communication between components or networks using different protocols.
In particular embodiments, the various nodes in the wireless network of
A global slot manager 114 facilitates the identification and assignment of time slots to nodes in the wireless network. For example, communications between the nodes could occur during multiple time slots, and at least two wireless nodes may communicate during a slot. The global slot manager 114 determines which time slots are assigned to a node for communications with other nodes. The global slot manager 114 includes any hardware, software, firmware, or combination thereof for managing time slots used for wireless communications. The global slot manager 114 could, for instance, include at least one processor 116 and at least one memory 118 configured to store instructions and data used, collected, or generated by the at least one processor 116. The global slot manager 114 could also include at least one network interface 120 for communicating over at least one wired or wireless network, such as an RF transceiver.
A time synchronization manager 122 facilitates the synchronization of nodes in a wireless network. For example, nodes can be grouped into clusters, where nodes in a cluster are substantially synchronized with one another. The time synchronization manager 122 can help maintain synchronization of nodes and control merging of clusters. The time synchronization manager 122 includes any hardware, software, firmware, or combination thereof facilitating synchronization of wireless network nodes. The time synchronization manager 122 could, for instance, include at least one processor 124 and at least one memory 126 configured to store instructions and data used, collected, or generated by the at least one processor 124. The time synchronization manager 122 could also include at least one network interface 128 for communicating over at least one wired or wireless network, such as an RF transceiver.
A wireless configuration and OLE for Process Control (OPC) server 130 can configure and control various aspects of the process control system 100. For example, the server 130 could configure the operation of the nodes 108a-108e, 110a-110e, and 112. The server 130 could also support security in the process control system 100, such as by distributing cryptographic keys or other security data to various components in the process control system 100 (like the nodes 108a-108e, 110a-110e, and 112). The server 130 includes any hardware, software, firmware, or combination thereof for configuring wireless networks and providing security information.
In one aspect of operation, various nodes in the wireless network (such as the nodes 108a-108e) can be divided into clusters, and time synchronization occurs among nodes in each of the clusters. Also, different clusters can be merged if the wireless coverage areas of the clusters overlap. Additional details regarding these functions are provided below.
Although
As shown here, the node 200 includes a controller 202, which controls the overall operation of the node 200. For example, the controller 202 may receive or generate data to be transmitted, and the controller 202 could provide the data to other component(s) in the node 200 for transmission over a wired or wireless network. The controller 202 could also receive data over a wired or wireless network and use or forward the data. As a particular example, the controller 202 in a sensor leaf node could provide sensor data for transmission, and the controller 202 in an actuator leaf node could receive and implement control signals (the leaf node could represent a combined sensor-actuator device). As another example, the controller 202 in an infrastructure node could receive data transmitted wirelessly, determine a next hop for the data (if any), and provide the data for transmission to the next hop (if any). As a third example, the controller 202 in a gateway infrastructure node 112 could receive data from a wired network and provide the data for wireless transmission (or vice versa). The controller 202 includes any hardware, software, firmware, or combination thereof for controlling operation of the node 200. As particular examples, the controller 202 could represent a processor, microprocessor, microcontroller, field programmable gate array, or other processing or control device.
A memory 204 is coupled to the controller 202. The memory 204 stores any of a wide variety of information used, collected, or generated by the node 200. For example, the memory 204 could store information received over a network that is to be transmitted over the same or other network. The memory 204 includes any suitable volatile and/or non-volatile storage and retrieval device(s).
The node 200 also includes a wireless transceiver 206 coupled to an antenna 208. The transceiver 206 and antenna 208 can be used to communicate wirelessly with other devices. For example, in a leaf node, the transceiver 206 and antenna 208 can be used to communicate with infrastructure nodes. In an infrastructure or gateway infrastructure node, the transceiver 206 and antenna 208 can be used to communicate with leaf nodes or other infrastructure nodes. One or more additional transceivers 210 could also be used in the node 200. For instance, in an infrastructure or gateway infrastructure node, the additional transceiver(s) 210 could be used to communicate with Wi-Fi or IEEE 802.11 devices (such as wireless controllers or hand-held user devices) or other infrastructure or gateway infrastructure nodes. The additional transceivers 210 may be coupled to their own antennas 212 or share one or more common antennas (such as antenna 208). Each transceiver includes any suitable structure for transmitting and/or receiving wireless signals. In some embodiments, each transceiver represents an RF transceiver, such as an RF FHSS transceiver. Also, each antenna could represent an RF antenna. It may be noted that any other suitable wireless signals could be used to communicate. In addition, each transceiver could include a transmitter and a separate receiver.
If the node 200 represents a gateway infrastructure node, the node 200 may further include one or more wired network interfaces 214. The wired network interfaces 214 allow the node 200 to communicate over one or more wired networks, such as the network 106 (as shown in
Although
As shown here, the wireless nodes in the cluster 300 are arranged in a hierarchy, where one or more nodes in one level pass time synchronization information to one or more nodes in a lower level. The cluster 300 includes a single wireless node 302, which represents a cluster master, in its highest level. The cluster master represents the wireless node that generates or receives (possibly from a source that is not in the cluster) a clock signal and then sends out timing information to other nodes in the cluster 300. The wireless node 302 could receive a clock signal from any suitable source, such as an atomic clock, a global positioning system (GPS) clock, or other source that is not a member of the cluster.
During operation, the wireless node 302 provides time synchronization information (such as information based on the clock signal) to nodes 304a-304c in the next level of the cluster 300. The wireless nodes 304a and 304c pass the time synchronization information to wireless nodes 306a-306c and 306d, respectively, in the next level of the cluster 300. The wireless node 306c provides the time synchronization information to wireless nodes 308a-308b in the last level of the cluster 300. In this configuration, the nodes form a spanning tree with the cluster master as the root of the spanning tree. The levels of the cluster 300 could be numbered, such as when the cluster master is level zero, the next level is level one, and so on. In general, a node providing time synchronization information is called a “master” or “parent,” while a node receiving time synchronization information is called a “child.”
Each of the wireless nodes 304a-308c could synchronize its internal clock with the time synchronization information it receives. In this way, the wireless nodes 304a-308c can be substantially synchronized with the wireless node 302. The wireless nodes 304a-308c could be “substantially” synchronized with the cluster master because there is some delay in receiving the time synchronization information (such as due to electromagnetic propagation of wireless signals and the inaccuracy associated with relaying time synchronization information using wireless messages). However, these delays could be ignored by the wireless nodes or estimated and taken into account when adjusting the nodes' internal clock. In general, the synchronization is adequate for the particular application requiring time synchronization such as to allow time-coordinated communications between wireless nodes, where transmitting nodes transmit data at specified times (such as assigned time slots) and receiving nodes are prepared to receive data in those time slots.
While a single cluster 300 is shown in
Although
In some embodiments, communications between nodes in a wireless network could occur as follows. A hyperperiod can be defined as a thirty second (or other) periodic cycle. Within each hyperperiod is a discovery time period (DTP), such as a ten second period. The DTP is subdivided into repeating frames, an example of which is shown in
Nodes engage in various handshaking and other operations during the discovery subframe 402. For example, infrastructure nodes 108a-108e could broadcast beacon signals during the discovery subframe 402, allowing other nodes to identify the infrastructure nodes. This may allow new nodes coming online in the wireless network to identify potential infrastructure nodes that can communicate with the new nodes. The operation subframe 404 then allows the nodes to exchange data being transported through the wireless network, such as sensor data sent from leaf nodes or actuator data sent to leaf nodes.
In the operation subframe 404, various slots 406 could represent Guaranteed Leaf Access (GLA) slots, or slots 406 where normal data traffic (such as sensor and actuator data) is sent. The GLA-designated slots also represent time slots 406 when periodic time synchronization can occur. For example, infrastructure nodes (except cluster masters) can receive GLA messages during “receive GLA slots,” where the GLA messages contain time synchronization information. The infrastructure nodes can use the information in the GLA messages to synchronize with parent nodes. Infrastructure nodes can also transmit GLA messages in “transmit GLA slots,” and nodes receiving those messages can synchronize with masters. This allows various nodes to receive time synchronization information and to adjust their internal clocks to be substantially synchronized with the clock in the cluster master.
The GLA slots could have a specified periodicity, such as once every five seconds. Also, GLA slots could have a fixed periodicity or be random. With fixed GLA slots, the first slot 406 in the operation subframe 404 of each frame 400 could be a dedicated GLA slot. As a particular example, the first slot 406 in one frame 400 could be used to receive a GLA message, while the first slot 406 in the next frame 400 could be used to transmit a GLA message. With random GLA slots, random slots 406 can be used to exchange GLA messages between pairs of infrastructure nodes.
The structure of the frame 400 shown in
power up and discovery: operations performed when a node first comes online;
cluster election: operations performed when a node selects a cluster to join;
time synchronization: operations performed to synchronize nodes in a cluster;
recovery: operations performed when a cluster master fails or when a link with a cluster master is lost; and
merging: operations performed when two clusters are merged into a single larger cluster.
Although
When a new node comes online in a wireless network, the node has no sense of the current system time. As a result, the new node does not know if the system is in the discovery period (DSF 402) or the operational period (OSF 404) of a frame 400. The node can therefore take one or several steps to synchronize with the boundary of the frames 400. For example, the node could select a particular frequency and wait to receive a message, such as a beacon-like broadcast message or a regular message intended for another node, that contains time synchronization information.
Another approach is shown in
Once a new node 502 has figured out the current system time, the new node 502 can use the discovery subframes 402 in subsequent frames 400 to discover neighboring nodes (such as neighboring infrastructure nodes) without interfering with normal system communications carried out during the OSF 404 of the frames 400. For example, as shown in
Once the new node 502 has a list of its neighboring infrastructure nodes, the new node 502 can rank the neighboring infrastructure nodes and select the top neighboring infrastructure nodes (such as the top four or five). For example, the new node 502 can rank all neighboring infrastructure nodes having at least a minimum RSSI value in order of increasing cluster level. A message 606 could then be sent to one of the infrastructure nodes 506a during a subsequent time slot 608 (such as a time slot temporarily assigned to the new node 502). The message 606 identifies the top neighboring infrastructure nodes selected by the new node 502 (and may or may not identify the infrastructure node 506a). The infrastructure node 506a could represent the “best” infrastructure node identified by the new node 502, such as the infrastructure node with at least the minimum RSSI value and the lowest cluster level.
The message 606 is passed to the global slot manager 114 (shown in
As shown in
At this point, the new node 502 knows which infrastructure node(s) it should communicate with and the time slot(s) during which those communications should occur. As shown in
This process could occur for any node coming online in a wireless network. This process allows the node to synchronize with the frame boundary in a particular cluster of nodes in the wireless network. It also allows the node to identify the best or other infrastructure nodes around the node. It further allows the node to receive a slot assignment and to communicate with at least one of the infrastructure nodes around the node. In this way, the node can join and be synchronized with a cluster.
The messages transmitted in
A response to a message 504 (provided by an infrastructure node) could represent a clock sync acknowledgement, which can have the form:
Messages 602-604 could represent RSSI beacon requests that have the same form as the clock sync beacon shown above. RSSI beacon acknowledgements (sent by infrastructure nodes in response to the RSSI beacon requests) could have the form:
The “slot_number,” “INDSFFHPhase,” “tx_gla_slot,” and “INOSFFHPhase” allow the new node to communicate with the responding infrastructure node (at least temporarily). The “parent_list” identifies the chain of clock sync parents of the infrastructure node sending the RSSI beacon acknowledgement. The “parents” refer to all nodes (including the cluster master) through which time synchronization information passes to reach the infrastructure node sending the beacon acknowledgement.
The messages 606 could represent a slot requests having the form:
The “duty_cycle” value identifies the reporting period of a leaf node (and can be set to zero for infrastructure nodes). The “freq_seed” value identifies how the frequency of the new node 502 can be determined.
Slot request acknowledgements can be sent by infrastructure nodes receiving the slot requests and can have the form:
A slot request ping (used to ping an infrastructure node to verify that a prior slot request was received) can have a similar form (without the “clock_fix” and “freq” fields).
Once a time slot is selected by the global slot manager 114, a slot request response is sent to the new node 502. The slot request response could have the form:
Data can then be sent from the new node 502 to the identified infrastructure node(s). The data could be contained in data messages having the form:
The “QoSTag_fields” defines the desired quality of service for the data message.
Data messages received by an infrastructure node can be acknowledged using data acknowledgements, which could have the form:
This acknowledgement contains timing data (ticks_left, slot_number, hyperPeriodNumber) that allows a node to maintain synchronization with the infrastructure node. If data messages require certain qualities of service, the data acknowledgements could have the form:
The “QoSTag_fields” contains various data regarding the QoS being provided. A CCQ ping could have the same form as the CCQ data acknowledgement.
Finally, as noted above, GLA time slots can be used to pass time synchronization information between nodes. The messages transmitted during the GLA slots could represent GLA messages having the form:
This GLA time sync message contains timing data (ticks_left, slot_number, hyperPeriodNumber) that allows a node to maintain synchronization with the parent node. The “curINFHFreqChannel” represents a change in the infrastructure node's frequency hopping pattern, which allows nodes to update information about the infrastructure node when the infrastructure node is used as a backup master (described below). The “new_gla_slot” is used to identify a new GLA slot that is going to be used by the infrastructure node after the number of GLA transmissions identified by the “old_gla_countdown” value occurs. As described in more detail below, the “hpWait,” “hpDelta,” and “delta” are used to adjust the time of nodes in a cluster that is being merged.
Although
In
As shown here, node I5 ordinarily receives time synchronization information from node I2. However, in this example, a communication link 902 between nodes I2 and I5 is interrupted. This could be due to various reasons, such as a failure of node I2, a change in location or operation of node I2, or new construction around node I2. Whatever the cause, node I5 loses contact with its master, preventing node I5 from receiving information from that master.
As described in more detail below, a node can identify both a master and at least one backup master. During normal operation, the node can receive time synchronization information from its master via a uni-directional time sync message transmission. When communications with its master are lost, the node can begin using time sync information provided by one of its backup masters. In
With the loss of communication link 902 and the active use of communication link 904, the shape of the cluster 900 changes. As a result, the cluster 900 may now be less wide than desired or more deep than desired. When this occurs, the cluster 900 can be “pivoted” to make a different node act as the cluster master. An example of this is shown in
Note that reducing the number of levels in a cluster improves the accuracy of time synchronization across the cluster, so it may be desirable to reduce the number of levels in a cluster. Also note that the pivoting of a cluster can be initiated in any suitable manner. For example, a cluster could be reorganized based on user input or automatically. Regarding automatic triggering of a pivot, the global slot manager 114 or the time synchronization manager 122 could monitor the operation of the nodes and determine when a cluster pivot is desirable. For instance, the global slot manager 114 or the time synchronization manager 122 could compute a PivotFunction value for each node i of a cluster:
PivotFunction(i)=CurrentMaxLevel−MaxLeveli.
Here, CurrentMaxLevel represents the number of levels in a cluster, and MaxLeveli represents number of levels that would exist if node i was acting as the cluster master. If node i has a PivotFunction value greater than zero, node i represents a more optimal node to act as the cluster master. The global slot manager 114 or the time synchronization manager 122 could therefore select the node with the largest PivotFunction value and cause that node to become the cluster master of the cluster.
In the example shown in
As another example, a delay (such as a random delay and/or a deterministic delay) could be implemented in each node I2 and I3. After its delay, each node I2 and I3 could determine whether it hears from another “level 1” node. The first node to detect another “level 1” node could make that “level 1” node its master. As a particular example, if node I3 ends its delay first, it could detect node I2 and make node I2 its master. Node I2 becomes the new cluster master, and nodes I3 and I5 represent the new “level 1” nodes of the cluster.
As a third example, when a node in “level 1” loses contact with its cluster master, the node can send RSSI beacons in discovery subframes 402 to discover neighboring infrastructure nodes. If neighboring infrastructure nodes with equal cluster levels (sibling nodes) or higher cluster levels are found, one of the siblings can be selected as the new cluster master (such as the sibling with the lowest network address). If only neighboring infrastructure nodes with higher cluster levels are found, the “level 1” node can become a cluster master for those higher-level nodes. If only higher-level neighbors belonging to a different cluster are found, the neighbor with the lowest level is selected, and a cluster merge (described below) can be initiated. If a higher-level node (“level 2” or above) loses contact with its master and a neighboring infrastructure node with a lower cluster level is found, the higher-level node can make that neighboring infrastructure node its new master. For example, in
In any event, once a new cluster master is selected for all or a portion of the cluster 950, the nodes in the cluster 950 can be updated. For example, nodes below the new cluster master can have their cluster levels adjusted accordingly. In addition, some leaf nodes may be affected if their primary and secondary infrastructure nodes split into different clusters, which could happen if a node is forced to become a cluster master. In this case, a leaf node could remain connected with the infrastructure node in the same cluster as the leaf node and a new infrastructure node can be assigned to the leaf node.
Although
Various clusters of wireless nodes can sometimes overlap, which could be due to changes in wireless network topology, the dynamic nature of wireless links, or other causes. For example, infrastructure nodes in two different clusters could provide wireless coverage to the same physical area. When this occurs, it may be necessary or desirable to merge the clusters into a single larger cluster. This process is referred to as a “cluster merge.” Cluster merges could be initiated in any suitable manner, such as in response to user input or automatically (like when a node in one cluster detects a node in another cluster).
Take, for instance, the example shown in
In this example, there are four connecting nodes, and the time synchronization manager 122 could select the link between nodes I8 and I11 as the basis for the merge. One of these nodes (in this case, node I8) is then made the cluster master of its cluster as shown in
At this point, a decision can be made whether to pivot the cluster 1000c so that the cluster master is placed in a more appropriate location. In this example, node I7 may make a more suitable cluster master than the current cluster master (node I16). This is due to the long path from node I16 to node I9 in cluster 1000c. As a result, the flow of time synchronization information between the existing cluster master (node I16) and the new cluster master (node I7) is reversed as shown in
The infrastructure node can transition to a “become cluster master” state 1104, such as when the time synchronization manager 122 wishes for the infrastructure node to become a cluster master to facilitate a cluster merge. In this state 1104, a timer can be started in substate 1 to define a period in which the infrastructure node can become the cluster master (such as a period of two hyperperiods). If the timer expires without necessary conditions being met, the infrastructure node returns to state 1102 (without having become a cluster master). Otherwise, if the necessary conditions are met (such as a determination that the infrastructure node is a parent to its current master), the infrastructure node becomes a cluster master in substate 2. Here, the infrastructure node clears its parent list, sets its level to zero, initializes its cluster identifier (such as to its unique network identifier), and clears its cluster master changing flag. It could also clear a backup master list.
The infrastructure node can also transition to a state 1106 when a node in another cluster is detected. This transition may require that no cluster master change is occurring. In this state 1106, the infrastructure node informs the time synchronization manager (TSM) 122 of its detection of the other cluster. The infrastructure node can also inform the time synchronization manager 122 of a time delta or time difference between the two clusters. The infrastructure node can then transition back to state 1102. It is then up to the time synchronization manager 122 to determine whether a cluster merge is initiated.
The infrastructure node can further transition to a “reverse link” (rLink) state 1108 when an rLink request is received. The rLink request causes the infrastructure node at some point to reverse the flow of time synchronization information with a neighboring node, such as when a cluster master is being moved. In this case, a second timer is started in substate 1. If the timer expires without necessary conditions being met, the infrastructure node returns to state 1102 without reversing the link. Otherwise, if the infrastructure node is to become a cluster master due to the link reversal, the proper settings are cleared and set in the infrastructure node during substate 2. If the infrastructure node is not to become a cluster master (or once substate 2 is complete), the infrastructure node waits for a transmit (Tx) GLA message from its new master in substate 3. If it does not receive one, a timeout occurs, the cluster master changing flag is cleared, and the infrastructure node returns to state 1102. If a transmit GLA message is received from the infrastructure node's new master (and if the infrastructure node does not appear in the parent list of its new master), the infrastructure node updates its information during substate 4. Once substate 4 is complete, the infrastructure node transitions back to state 1102. During this transition, the new master of the infrastructure node is not dropped even if its change cluster master bit is set (as long as the nodes in the new master's parent list have a cleared change cluster master bit).
The infrastructure node can also transition to a “jump correction” state 1110. The jump correction refers to a change in the infrastructure node's time when the node is being merged into a cluster with a different measure of time. Here, substate 1 can be entered when a cluster master receives a jump request from the time synchronization manager 122 or when a GLA message with a jumping flag is received. In either case, the infrastructure node sets its jumping flag and determines a jump time. The jump time can be based on a waitHyperPeriod value, which identifies the number of hyperperiods that should pass before the jump occurs. The waitHyperPeriod value and an HPDelta value (the difference between the infrastructure node's current hyperperiod boundary and another cluster's hyperperiod boundary) are set in the infrastructure node's GLA message, which can be broadcast during the infrastructure node's transmit GLA slot.
Once the current time reaches the boundary of the hyperperiod where the jump occurs, the infrastructure node transitions to substate 2, where the hyperperiod is adjusted and the current time is set to equal the delta value. This adjusts the time of the infrastructure node in one single jump or change, and the jumping flag is cleared. If the infrastructure node is a cluster master, it also listens for a transmit GLA message from a new master (in the cluster into which the node is being merged). If a GLA message is received, the infrastructure node becomes a child of the new master and notifies the time synchronization manager 122 that the jump is complete in substate 3. Otherwise, the infrastructure node moves to substate 4 and continues with normal operation (and it remains the cluster master of an unmerged cluster).
In state 1204, the time synchronization manager 122 waits to see if other “cluster detect” messages are received from nodes in the same pair of clusters. This allows the time synchronization manager 122 to identify various links between the two clusters. It also allows the time synchronization manager 122 to identify the time difference between the two clusters.
After a specified time period (such as 30 seconds), the time synchronization manager 122 transitions to state 1206. State 1206 can also be entered directly from state 1202 when a request to rebalance a cluster is received. Rebalancing a cluster involves moving the cluster master to reduce the number of levels in a cluster. In state 1206, the time synchronization manager 122 attempts to move the cluster master in a cluster. The cluster could represent one of the clusters involved in a merge or the cluster being rebalanced. In either case, the time synchronization manager 122 sends rLink messages to appropriate nodes and continues collecting data regarding the time difference between clusters. Also, no updates could be processed or used in state 1206.
If a timeout (such as two hyperperiods) occurs, a cluster master change fails, or a rebalance request succeeds, the time synchronization manager 122 returns to state 1202. Otherwise, the cluster master change succeeds, and the time synchronization manager 122 enters state 1208. In state 1208, the time synchronization manager 122 is ready to initiate a merge of two clusters. If a timeout occurs (such as after 15 minutes), the time synchronization manager 122 returns to state 1202 without completing the cluster merge. The time synchronization manager 122 is waiting here to receive an update on the time difference between the two clusters being merged.
If an update is less than a specified amount of time in age (such as five seconds) or if another “cluster detect” message is received with a time delta value, the time synchronization manager 122 enters state 1210 and triggers the cluster merge. The cluster merge is initiated by instructing the cluster master of the cluster being merged into another cluster to jump time. If a timeout (such as four hyperperiods) occurs or the jump is not successful, the time synchronization manager 122 returns to state 1202, and the cluster merge is not completed. If the jump is successful, the time synchronization manager 122 has successfully synchronized the nodes in the two clusters. As long as the cluster master in one cluster becomes the child of any node in the other cluster, the two clusters are successfully merged. The time synchronization manager 122 can therefore update its internal tables or other data structures with the merge results and return to state 1202. Note that the time-shifting to achieve synchronization between the two clusters could occur gradually or as a jump correction depending on the application requirements.
If the Master_of function returns a non-NULL value (indicating that node C is a child of another node) and the connecting node is not the cluster master, the time synchronization manager 122 transitions to state 1304 and sets a retryrLink value to an initial value (such as three). In state 1304, the time synchronization manager 122 sends an rLink request to node Node_id, which was identified using the Master_of function. If the rLink request is successful, the time synchronization manager 122 sets node C equal to Node_id and returns to step 1302 (to update the value of Node_id and repeat the process). If the rLink request is not successful, the retryrLink value is decremented, and the time synchronization manager 122 can reenter state 1304 or transition to state 1310. If the time synchronization manager 122 reenters state 1304, the time synchronization manager 122 can again transmit an rLink message. If the time synchronization manager 122 enters state 1310, the move cluster master operation fails.
If the Master_of function returns a NULL value but the connecting node is still not the cluster master, the time synchronization manager 122 transitions to state 1306 and sets a retryBCM value to an initial value (such as three). “BCM” refers to “become cluster master,” and state 1306 involves sending a become cluster master request to the connecting node. This request causes the connecting node to begin operating as a cluster master. If the request is not successful, the retryBCM value is decremented, and the time synchronization manager 122 can reenter state 1306 or transition to state 1310. If the time synchronization manager 122 reenters state 1306, the time synchronization manager 122 can again attempt to cause the connecting node to become the cluster master. If the time synchronization manager 122 enters state 1310, the move cluster master operation fails. If the request is successful, the time synchronization manager 122 transitions to state 1308.
In
The connecting node in the first cluster can calculate the delta value and report it to the time synchronization manager 122. At time 1550 (which represents a hyperperiod boundary), the nodes in the first cluster set their current time equal to the delta value. In effect, rather than starting a hyperperiod at time T=0, the nodes in the first cluster are pushed ahead and start the hyperperiod at time T=Δ. This shortens the hyperperiod so that the nodes in both clusters are synchronized at the end of the first cluster's shortened hyperperiod.
The messages used during a cluster merge could have any suitable format. For example, updates can be periodically sent to the time synchronization manager 122, such as every five minutes and could have the form:
A “cluster detect” message sent to the time synchronization manager 122 when a node detects another cluster could have the form:
An rLink message could have the form:
A cluster master change status message can be sent to indicate whether a cluster master has been changed successfully. This message could have the form:
A start jump message for initiating a time jump in a cluster could have the form:
The status of the time jump can be reported using a jump complete status message, which could have the form:
Although
In
In
The node then determines if the discovery subframe is currently occurring at step 1806. If so, the node changes to the next hopping frequency at step 1808, transmits an RSSI beacon message at step 1810, and determines if any response is received at step 1812. If a response is received, the node records information associated with a neighboring infrastructure node at step 1814. The information could include the RSSI, cluster identifier, cluster level, transmit GLA slot, and response slot.
The method 1800 then proceeds to step 1816, where a determination is made whether the timer exceeds the length of a discovery time period. If not, the method 1800 returns to step 1806. If so, the node selects its master at step 1818 and at least one backup master (if available) at step 1820. This could include examining the information recorded at step 1814 to identify the neighboring infrastructure node with the lowest cluster level (as long as the neighboring infrastructure node has at least a minimum RSSI value). The backup masters could represent other neighboring infrastructure nodes having at least a minimum RSSI value. At this point, the node (if it is an infrastructure node) selects a transmit GLA time slot at step 1822. The transmit GLA time slot is selected to not interfere with the transmit GLA time slots of the identified master or backup master(s).
If no clock synchronization information (no acknowledgement) is received, a failure has occurred at step 1908, and a determination is made whether to retry at step 1910. This could include, for example, determining if the “retry count” value exceeds a threshold (such as three). If not, the “retry count” value is incremented, and the method 1900 returns to step 1904. Otherwise, the node becomes a cluster master at step 1912 and selects its own transmit GLA slot at step 1914. In this case, the node cannot join any clusters and starts its own cluster.
If clock synchronization information is received at step 1906, a success is identified at step 1908 The “retry count” value is reset to zero, and the node attempts to join the cluster in which the neighboring node that provided the clock synchronization information resides. The node attempts to obtain RSSI beacon acknowledgements from neighboring nodes at step 1916. This could include transmitting RSSI beacon messages during discovery subframes 402 and forming a list of infrastructure nodes that respond. The infrastructure nodes in the list could be those that meet threshold RSSI requirements and that have the same cluster identifier as the one contained in the clock sync acknowledgement. If at least one neighboring node is found at step 1918, a master and at least one backup master (if available) are selected at step 1920. The master could represent the neighboring node with the lowest cluster level or, if multiple neighboring nodes exist on the same level, the neighboring node with the highest RSSI value. A transmit GLA slot is selected at step 1922. The transmit GLA slot could be selected randomly (as long as it does not occur during the master and backup masters' transmit GLA slots). The transmit GLA slot could also be selected using a circular allocation of slots based on level (such as when slots 0-4 are assigned to “level 1” nodes and slots 5-9 are assigned to “level 2” nodes). Also, clock corrections are performed during the GLA slots of the node's master at step 1924.
If no neighboring nodes are found at step 1918, a decision is made whether to retry the attempt at step 1926 in
If the GLA slot does not represent a transmit GLA slot at step 2102, a determination is made whether the slot represents a receive GLA slot at step 2114. If so, the node performs a GLA receive process at step 2116, an example of which is shown in
If the GLA slot is not a transmit GLA slot for a backup master at step 2118, the node listens on the OSF frequency hopping pattern at step 2122. Here, the node attempts to detect other nodes that could act as its backup master. The node determines whether it receives a GLA message from a transmitting node in the same cluster at step 2124. If so, the node determines whether it has identified a maximum number of backup masters (such as three) at step 2126. If not, the node determines whether its address appears in the parent list of the transmitting node at step 2128. A determination is also made whether the node and the transmitting node share the same parent at step 2130. If neither condition is true, the transmitting node is added to a list of potential backup masters at step 2132, and information about the transmitting node is recorded at step 2134. The information could include the transmitting node's GLA frequency and phase information.
Step 2128 is performed so that the selection of potential backup masters does not create loops. A loop could be created when a parent node selects one of its children nodes as a backup master. To avoid looping, a node's backup master cannot be one of that node's children. Other tests or criteria could also be enforced here. For example, a node's backup master should not have selected that node as its backup master. Also, if a node's backup master changes its cluster or changes its level to be greater than the node, that backup master can be dropped.
If a GLA message is not received at step 2204, the node increments its master's GLA frequency at step 2222 and attempts to receive a GLA message at step 2224. If received, the method returns to step 2206 to process the received GLA message. If not received, the node decrements the error count value at step 2226 and determines if the error count value equals a minimum value (such as zero) at step 2228. If so, the node performs a “sync to new master” process at step 2230, an example of which is shown in
Otherwise, the node sets its orphan bit at step 2408, which indicates that the node is no longer part of a cluster. With the orphan bit set, the node does not reply to any RSSI beacon messages until the node has a master or it becomes a cluster master. A random delay is implemented at step 2410, which can help to avoid collisions when multiple nodes lose their master at the same time. The delay could be between [0,5*BEACON_TIME], where BEACON_TIME equals one discovery time period (such as 10 seconds). The node then attempts to locate any neighboring nodes at step 2412. If found, a decision is made whether any of the neighboring nodes are children of the node at step 2414 (such as by using the parent lists of the neighboring nodes). If not, the orphan bit is cleared, and the node becomes a cluster master at step 2416.
If a non-child neighboring node of the same cluster is found, a new master and at least one backup master (if available) are selected at step 2418. A transmit GLA slot is selected at step 2420, and the node synchronizes with its new master at step 2422. A decision is made whether the new master's transmit GLA slot equals the node's transmit GLA slot at step 2424. If so, the node selects a new transmit GLA slot at step 2426. In either case, the node listens during its new master's transmit GLA slot and corrects its clock at step 2428.
If a backup master is present at step 2404, the node implements a random delay at step 2430 (which may or may not equal the random delay of step 2410). The node begins using its backup master as its new master at step 2432. If necessary, the node changes its cluster level based on the cluster level of its new master at step 2434.
Using these various methods, nodes in a wireless network can join together into clusters and share time synchronization information. The nodes can also enter and leave clusters as communications with master nodes are found and lost.
Although
In
If a cluster detect message is received at step 2608, a mark for merge process can be performed at step 2610, an example of which is shown in
A master of node M is identified at step 2810. Initially, node M may represent the connecting node that received the merge response. An rLink message is sent to the identified master of node M at step 2812. The rLink request could include the transmit GLA slot of node M and node M's phase delta. The rLink request can be used to facilitate reversal of one of the links that exists between the connecting node and the current cluster master of the connecting node. In this example, rLink requests are first sent to the current cluster master and to the nodes between the connecting node and the current cluster master. Also, in this particular example, most of the rLink requests do not result in the immediate reversal of the directional link between two nodes.
If node M does not successfully receive the rLink message at step 2814, the cluster merge fails at step 2816. Note that this could actually involve sending multiple rLink messages to node M (such as three messages as shown in
Although
In some embodiments, various functions described above are implemented or supported by a computer program that is formed from computer readable program code and that is embodied in a computer readable medium. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory.
It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term “couple” and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. The terms “transmit,” “receive,” and “communicate,” as well as derivatives thereof, encompass both direct and indirect communication. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like.
While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.
This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/055,817 filed on May 23, 2008, which is hereby incorporated by reference.
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of a contract awarded by the Department of Energy.
| Number | Date | Country | |
|---|---|---|---|
| 61055817 | May 2008 | US |
