Multiple master nodes for wireless battery management system robustness

Abstract

A system (500) includes a first plurality of secondary devices (550), each secondary device (550) of the first plurality of secondary devices including a first wireless transmitter and a battery monitor integrated circuit (IC). The battery monitor IC is configured to obtain battery data from at least one battery cell, and the first wireless transmitter is configured to wirelessly transmit the battery data. A first primary device (502) has a second wireless transmitter wirelessly coupled to the first wireless transmitter of the first plurality of secondary devices via a first wireless network. The second master device (506) has a second wireless transmitter. The second primary device (506) is configured to detect a failure of the first primary device and, in response to detecting the failure, establish a second wireless network with the first plurality of secondary devices.

Description

Background Art

[0001] Increasingly, battery packs are being integrated into systems that are not traditionally powered by batteries, such as cars, homes, and even parts of the electrical grid. In addition to becoming more common, battery packs are also becoming larger and more complex. For example, a modern battery pack may include hundreds or thousands of battery cells. Monitoring the health and status of individual cells in such battery packs helps ensure continued proper operation of the systems powered by such battery packs. Summary of the invention

[0002] A system includes a first plurality of slave devices, each of the first plurality of slave devices including a first wireless transmitter and a battery monitor integrated circuit (IC). The battery monitor IC is configured to obtain battery data from at least one battery cell, and the first wireless transmitter is configured to wirelessly transmit the battery data. A first master device has a second wireless transmitter wirelessly coupled to the first wireless transmitter of the first plurality of slave devices via a first wireless network. A second master device has a second wireless transmitter. The second master device is configured to detect a failure of the first master device, and in response to detecting the failure, establish a second wireless network with the first plurality of slave devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] To describe various examples in detail, reference is now made to the accompanying drawings, in which:

[0004] Figure 1 is a block diagram of a battery management system (WBMS) having a master node and slave nodes according to an example illustration.

[0005] Figure 2 is another block diagram illustrating a WBMS according to an example.

[0006] Figure 3 is a block diagram of radios available in a primary node and a secondary node of a WBMS according to an example.

[0007] Figure 4 is a diagram of a superframe for WBMS according to an example.

[0008] Figure 5 is a block diagram of a WBMS system according to an example having a master node, a backup master node, and a memory shared between the master node and the backup master node.

[0009] Figure 6 is a block diagram of a WBMS system having a master node and a backup master node without using a shared memory according to an example.

[0010] Figure 7 is a block diagram of a WBMS system having a master node and a backup master node according to yet another example.

[0011] Figure 8 is a block diagram of a WBMS system having a master node and a backup master node according to another example.

[0012] The same reference numbers or other reference designators are used in the drawings to indicate the same or similar features (functionally and / or structurally). DETAILED DESCRIPTION

[0013] Some systems are battery operated and include a large number of battery cells. A subset of battery cells may be packaged together in a battery module. A group of interconnected battery modules represents a battery pack. Thus, a battery pack may have multiple battery cells, and in some cases may have hundreds or more battery cells. For example, an electric vehicle (EV) includes a rechargeable battery pack to operate the motor of the EV and power various electronic components within the vehicle. In the case of an EV, the battery pack may provide a voltage of 400V, 800V, or another voltage. Monitoring individual battery cells to obtain information such as voltage, current, temperature, register settings, etc. helps ensure the health and function of the entire battery pack. For example, battery cells may differ in capacity and discharge (and / or charge) rate. Cell-to-cell variations may result in an imbalance in the state of charge between battery cells. Balancing techniques (e.g., passive cell balancing, active cell balancing) may be used to more evenly balance the load (and / or power) across cells and help improve the available capacity of the battery pack and increase its usable life. Passive cell balancing may dissipate excess charge in a given cell through a bleed resistor. Active cell balancing redistributes charge between individual cells during charge and discharge cycles. Where it may be useful, a battery management system may be included to monitor and adjust the system's battery pack (eg, cell balancing).

[0014] Figure 11 is a block diagram illustrating a wireless battery management system (WBMS) 100 according to aspects of the present disclosure. The WBMS 100 is operable to provide power to a system such as an EV. In addition to the WBMS 100, the system also includes a motor 118 (e.g., an electric motor that moves the EV) and an electric control unit (ECU) 124. The WBMS 100 includes battery modules 104A, 104B, ..., 104N (collectively referred to as battery modules 104) and a battery pack controller 114. The battery pack controller 114 communicates wirelessly with each battery monitor 104. Each battery monitor 104 monitors and controls a corresponding group of battery cells 102. Each instance of a battery cell 102 includes one or more cells (6 cells, 9 cells, 18 cells, etc.), and a connected group of battery cells 102 represents a battery pack for a system (e.g., an EV). Each group of battery cells 102 is coupled to a battery module 104. In other embodiments, the battery cells 102 are contained within the battery module 104 and are part of the battery module. The number N of battery modules 104 depends on the number of individual battery cells 102 that each module can monitor. Each group of battery cells can be coupled in series to produce a substantially high voltage (e.g., 400V, 800V, etc.). The battery pack controller 114 includes an interface (e.g., a controller area network (CAN) bus) to the ECU 124.

[0015] Each battery module 104 includes a battery monitor 106. Each battery monitor 106 may include an analog front end coupled to a corresponding battery cell 102 to measure and collect information about the battery cell 102 (e.g., voltage, current, state of charge, temperature, etc.). In this example, each battery monitor 106 is wirelessly coupled to a battery pack controller 114. A microcontroller 112 within the battery pack controller 114 may process the battery cell information for some or all of the cells 102 and may provide the battery cell information to the ECU 124.

[0016] Each battery monitor 106 collects and digitizes information about its corresponding battery cell 102, and wirelessly transmits the digital information to the battery pack controller 114 for receipt by the microcontroller 112. The microcontroller 114 may also be coupled to control the input of a switch 116 that couples the battery cells 102 to one or more motors 118 or other load devices. The microcontroller 112 may also be coupled to one or more other sensors, such as a current sensor 120, which may monitor the current supplied by the battery pack to the motor 118. In this example, the battery pack controller 114 is powered by a battery 122 that is separate from the battery cells 102. The battery 122 may be, for example, a relatively low voltage battery, such as a 12V battery, while the voltage generated by the series-connected group of battery cells 102 may be a higher voltage (e.g., 400V, 800V, etc.).

[0017] The battery monitor 104 wirelessly transmits its battery data to the battery pack controller 114. The battery pack controller 114 and / or the ECU 124 can monitor the status of individual cells and perform various actions as needed. For example, the ECU 124 can detect that the voltages of certain cells 102 are different from each other and respond by performing a cell balancing process such as a passive or active cell balancing process. If the battery pack controller 114 malfunctions or is otherwise unable to receive battery data from the battery monitor 104, the ability to monitor the battery cells of the battery pack and respond appropriately to the cell status may not be available.

[0018] Embodiments described herein relate to the inclusion and use of a backup battery pack controller.Due to a failure of a currently operating battery pack controller 114, a failover process may be performed whereby the backup battery pack controller takes over the functionality of the now failed battery pack controller.

[0019] Figure 2 1 is a block diagram illustrating an embodiment of a WBMS 100 in accordance with aspects of the present disclosure. The WBMS 100 includes a master node 202 that functions in a manner similar to the battery pack controller 114. The master node 202 includes a microcontroller 204 that is coupled to the ECU 124 via, for example, a CAN bus 203. The microcontroller 204 can operate in a substantially similar manner to the microcontroller 112. The microcontroller 204 is coupled to a radio 206 via a digital communication interface 207, such as a universal asynchronous receiver-transmitter (UART) interface, a serial peripheral interface (SPI), a shared memory, or the like. The radio 206 is wirelessly coupled to a slave node 210. The slave node 210 represents Figure 1 Each secondary node 210 includes a radio 208 for communicating with the radio 206 of the primary node. Each secondary node 210 also includes one or more battery monitoring systems (BMS) 212, which are coupled to the corresponding radio 208 via a UART or other type of electrical interface. Figure 2 Two BMSs 212 are shown in each battery module 210 in the embodiment, but any suitable number of BMSs may be included in any given battery module (e.g., one or more). The radio devices 206 and 208 are capable of radio frequency (RF) wireless transmission. Each secondary node 210 may be manufactured as a printed circuit board (PCB) with a BMS 212 and a radio 208 mounted thereon. In this configuration, each BMS 212 is manufactured as an integrated circuit (IC), and each radio device 208 is also manufactured as an IC.

[0020] The BMS 212 may be similar to the battery monitor 106 and may include an analog front end coupled to the battery cells 204 to measure and collect information about the battery cells (e.g., voltage, current, etc.). This information may be sent to the respective radios 208 of the slave nodes 210 via a digital communication interface. The radio 208 of each slave node 210 then wirelessly transmits the information to the master node 202. In some cases, this wireless transmission may be performed according to a wireless battery management protocol, such as the WBMS protocol.

[0021] The wireless battery management protocol may define a set of wireless channels and a set of rules about how information may be wirelessly transmitted to monitor and manage the battery cells 102. In some cases, the wireless battery management protocol may utilize unlicensed frequency bands, such as the 2.4 GHz, 5.8 GHz, and other frequency bands. Typically, frequency bands such as the 2.4 GHz unlicensed frequency band may be divided into a set of channels, where each channel includes a set of frequency resources within a certain set of frequencies. The number of channels and the size of the channels may be determined based on the protocol. For example, the WBMS protocol may divide the 2.4 GHz unlicensed frequency band into a set of 40 channels, where each channel is 2 MHz wide. As another example, an IEEE 802.11 wireless network may divide the same 2.4 GHz unlicensed frequency band into a set of 11 channels, where each channel is 20 MHz wide.

[0022] Figure 3 300, which may be used to implement either or both of the radio 206 of the secondary node 210 and the radio 208 of the primary node 202. In this example, the radio 300 includes an RF transceiver 302, a microcontroller 304, and a memory 306. The microcontroller 304 is coupled to the RF transceiver 302 and the memory 306. The memory 306 may store software 308 that may be executed by the microcontroller 304. The creation of the mesh network in the examples described herein may be implemented by the microcontroller 302 of the radios 206 and 208 when executing the software 308. The software 308 provided in the radio 208 of the secondary node 210 may implement different functions than the software provided in the radio 206 of the primary node 202.

[0023] The master node 202 and the slave node 210 exchange information according to a "superframe". Figure 4 4 is a superframe diagram 400 of a WBMS superframe 450 in the case where the system in which the WBMS is operating is on and therefore the battery pack controller 114 (primary node 202) is on and is able to receive wireless battery data from the battery monitor 106 (secondary node 210). The left side of the superframe diagram 400 lists the primary node 402 and a plurality of secondary nodes 404A, 404B, ..., 404N (collectively referred to as secondary nodes 404). The primary node 402 may include or be Figure 1The battery pack controller 114 or Figure 2 The secondary node 404 may include or be Figure 1 The battery monitor 106 or Figure 2 The auxiliary node 210 of .

[0024] Along with the channel size design, the WBMS protocol also defines how communication between nodes can be performed. A WBMS network is led by a master node 402, which coordinates communication between a set of N slave nodes 404. In one example, the master node 402 defines the communication interval and uses Figure 4 The superframe 450 structure illustrated in the example of FIG. 4 allocates the intervals to coordinate communications of the WBMS network. The superframe 450 includes a downlink allocation 406 for the master node 402 and an uplink allocation 408A, 408B, ..., 408N (collectively referred to as uplink allocations 408) for the secondary nodes 404A, 404B, ..., 404N in the set of secondary nodes 404. In this example, the superframe 450 also includes a guard interval 416 before the downlink transmission 410, which, together with the switching interval 418, provides time for the node to switch from a receive mode to a transmit mode or from a transmit mode to a receive mode. The superframe interval 414 is the amount of time to complete all transmissions of the superframe 450, including the guard interval 416. The duration of the superframe interval 414 may vary from WBMS network to WBMS network based on the number of secondary nodes 404 in the WBMS network.

[0025] The master node 402 transmits (410) to the slave node 404 allocation information regarding an uplink allocation 408 for the slave node 404 during the downlink allocation 406. The allocation information may include a set of channels that may be used for the WBMS network (e.g., as indicated by a bitmap), and a per-slave node uplink allocation indicating when the respective slave node 404A, 404B, ..., 404N may transmit 412A, 412B, ..., 412N to the master node 402. In some cases, the allocation information may include additional information, such as an acknowledgement of an uplink transmission from a previous superframe, an indication of when the next superframe may begin, an adaptive frequency hopping countdown, etc. In some cases, a personalized uplink allocation 408 is provided to each slave node 404 wirelessly coupled to the master node 402 to transmit information regarding a battery cell associated with the respective slave node 404.

[0026] Each secondary node 404 collects information about its respective battery unit and wirelessly transmits 412 such information to the primary node 402 during the uplink interval 408 assigned to the secondary node. For example, secondary node 2 404B receives 420 a downlink transmission 410 from the primary node 402 during a downlink allocation 406. In some cases, the secondary node 404 may determine the downlink allocation 406 time based on an indication from a previous superframe. The uplink transmission 412 (and retransmission, if any) of the secondary node 404 is completed within its respective uplink allocation 408, but the uplink transmission may not occupy the entire uplink allocation 408.

[0027] After receiving the downlink transmission 410 from the master node 403, each secondary node 404 may parse the allocation information received from the master node 402 to determine the timing information of the secondary node's uplink allocation 408 allocated to the secondary node. In some cases, information about how to locate the timing information associated with a particular secondary node may be exchanged during the WBMS network formation process.

[0028] Figure 5 5 is a block diagram of a WBMS 500 including two master nodes 502 and 506, a shared memory 510, and a plurality of slave nodes 550. In this example, the master node 502 is designated as a "primary" master node, and is therefore used to exchange information with the slave nodes 550 according to the superframe structure described above. The master node 506 can be an instance of the same master node device as the master node 502, but functions in a backup role for the master node 502 (and is therefore referred to as a "backup" master node). If the primary master node 502 fails (e.g., becomes unable to send packets to or receive packets from the slave node 550, is unable to process packets received from the slave node 550, etc.), the backup master node 506 can assume the role of the primary master node.

[0029] When operating to communicate with the secondary nodes, the primary master node 502 and the backup master node 506 function in a manner similar to the battery pack controller 114 described above. Each secondary node 550 may include a battery monitor (e.g., battery monitor 506) and be coupled to or coupled to one or more battery cells. The shared memory 510 may include volatile storage (e.g., random access memory) or non-volatile storage (e.g., programmable read-only memory).

[0030] When the primary master node 502 is actively functioning to exchange packets with the secondary node 550, the primary master node 502 stores network data in the shared memory 510. Such network data may include timing information, such as scheduling downlink allocations (e.g., the number of downlink time slots), uplink allocations (e.g., the number of uplink time slots), frequency hopping tables, superframe construction, security keys, encryption keys, device identifiers of devices forming the network, etc.

[0031] The primary master node 502 includes a fault detection capability. For example, the microcontroller of the primary master node may output a "heartbeat" signal to the fault detection circuit. The fault detection circuit may be configured to expect to receive a heartbeat signal every n milliseconds (e.g., every 1 millisecond). The failure of the heartbeat signal to occur in a timely manner may indicate that the microcontroller is in an error state and cannot function as expected. Regardless of the mechanism used to detect a fault of the primary master node 502, the primary master node (e.g., its fault detection circuit) outputs a fault line interrupt signal to the backup master node 506 to indicate the occurrence of a fault condition of the primary master node 502.

[0032] After receiving the asserted fault line interrupt signal, the backup master node 506 reads the network data from the shared memory 510 and uses the network data to take on the role of the primary master node. To assume the role of the primary master node, the backup master node re-forms and synchronizes the network. For example, the backup master node may initiate a network formation similar to that which would occur in a power-on sequence.

[0033] Figure 6 6 is a block diagram of a WBMS 500 including two master nodes 602 and 606 and a plurality of slave nodes 550. As described above, the master node 602 is designated as a "primary" master node and is therefore used to exchange information with the slave nodes 550 according to the superframe structure described above. The master node 606 can be an instance of the same master node device as the master node 602, but functions in a backup role for the master node 602. If the primary master node 602 fails (e.g., becomes unable to send packets to or receive packets from the slave node 550, is unable to process packets received from the slave node 550, etc.), the backup master node 606 can assume the role of the primary master node. When operating to communicate with the slave nodes, the primary master node 602 and the backup master node 606 function in a manner similar to the battery pack controller 114 described above. This embodiment does not contain the shared memory 510 described above.

[0034] As described above, the primary master node 602 includes a fault detection capability (e.g., a fault detection circuit configured to expect a heartbeat signal from the microprocessor of the primary master node every n milliseconds (e.g., every 1 millisecond). The failure of the heartbeat signal to occur in a timely manner may indicate that the microcontroller is in an error state and cannot function as expected. As described above, the primary master node 602 (e.g., its fault detection circuit) outputs a fault line interrupt signal to the backup master node 606 to indicate the occurrence of a fault condition of the primary master node 602.

[0035] Due to the failure of the primary master node 602, the secondary nodes 550 will stop receiving downlink packets from the primary master node. Each secondary node 550 has timing data previously provided to it by the primary master node 602, whereby each such secondary node can determine when a downlink packet from the primary master node is expected. Each secondary node 550 responds to the absence of the expected downlink packet by transitioning to a scanning mode in which the secondary node waits for a network creation packet from the primary node. Rather than using network data from a shared memory, the standby master node 606 reconstructs the network with the secondary nodes 550. In one example, the network reconstruction process is performed by any of a plurality of different methods, which may include performing a rejoin operation with an encryption key exchange packet to reauthenticate and establish the network.

[0036] The backup master node 606 now operates as the primary master node. The backup master node 606 may have the same fault detection capabilities as the previous primary master node 602. The failed primary master node 602 may be repaired or replaced in the WBMS 600 and may again assume the role of the primary master node if, for example, the backup master node 606 subsequently fails.

[0037] Figure 7 700 and a plurality of secondary nodes 550. As described above, the primary node 702 is designated as a "primary" master node and is therefore used to exchange information with the secondary nodes 550 according to the superframe structure described above. The primary node 706 can be an instance of the same master node device as the primary node 702, but functions in a backup role for the primary node 702. If the primary master node 702 fails (e.g., becomes unable to send packets to or receive packets from the secondary node 550, is unable to process packets received from the secondary node 550, etc.), the backup master node 706 can assume the role of the primary master node. When operating to communicate with the secondary nodes, the primary master node 702 and the backup master node 706 function in a manner similar to the battery pack controller 114 described above. This embodiment does not contain both the shared memory 510 and the fault line interrupt capability described above.

[0038] In this embodiment, the standby master node independently decides to reestablish the network with the secondary node 550 based on the absence of packet transmission for a time period exceeding a threshold time period. For example, the standby master node 706 can be phase-synchronized to the primary master node 702 in the configuration channel and continue to follow the primary master node 702 in the connection mode. In this embodiment, the standby master node is able to observe the network configuration in the configuration channel to determine the timing and size design of the network. Subsequently, the standby master node tracks the active network behavior in the connection mode to maintain synchronization with the primary master node over time. After the initial synchronization, the standby master node 706 can monitor the primary master node 702 at periodic intervals (e.g., once every minute, once every 5 minutes, etc.). The length of the periodic interval can be programmable in the standby master node 706. If the standby master node 706 is unable to receive packets from the primary master node 702, the standby master node 706 can determine that the primary master node 702 has failed. In response to the cessation of packets from the primary master node 702, the standby master node 706 can initiate a process of establishing its own network with the secondary node 550. The secondary node 550, which also has not received a packet from the primary master node 702, participates in the network establishment process described above.

[0039] Figure 8 Yet another embodiment of the WBMS 800 is shown, which includes two main master nodes 802 and 806, both of which actively communicate with secondary nodes. In this example, the main master node 802 has established a network with the secondary node 850, and the main master node 806 has established a network with the secondary node 860. The two networks operate simultaneously. The main master node and the secondary node can be implemented as described above. Each main master node 802, 806 is programmed with a unique identifier (e.g., address) of the secondary node of each such main master node to establish its network. Therefore, the main master node 802 is programmed with the address of the secondary node 850, and the main master node 806 is programmed with the address of the secondary node 860. In addition, each main master node is programmed with the address of the secondary node with which another main master node has established a network, for use in the event of a failure of the other main master node. That is, each main master node is programmed with the address of its own secondary node and the secondary node within the network of the other main master node.

[0040] Periodically (e.g., once every 5 minutes), each primary master node 802 and 806 scans for packets from another primary master node. In the event that the primary master node does not detect any packets from another primary master node, the primary master node determines that the other master node may have failed and performs a process of establishing a network with all secondary nodes 850 and 860. The primary master node 802 or 806 attempting to establish a network with all secondary nodes 850 and 860 may extend the length of the superframe to include the time slots allocated for the uplink of the currently larger number of secondary nodes 850, 860. Due to the larger number of secondary nodes accommodated per superframe, the latency of each node secondary node 850 and 860 transmitting its battery data to the surviving primary master node may increase, but the WBMS 800 has redundancy to handle the failure of the primary master node.

[0041] In this description, the term "coupled" may encompass connections, communications, or signal paths that enable a functional relationship consistent with this description. For example, if device A generates a signal to control device B to perform an action, then: (a) in a first instance, device A is coupled to device B through a direct connection; or (b) in a second instance, device A is coupled to device B through an intermediate component C, provided that the intermediate component C does not change the functional relationship between device A and device B, so that device B is controlled by device A through the control signal generated by device A.

[0042] A device "configured to" perform a task or function may be configured (e.g., programmed and / or hardwired) to perform the function when manufactured by a manufacturer, and / or may be configurable (or reconfigurable) by a user after manufacture to perform the function and / or other additional or alternative functions. The configuration may be performed through firmware and / or software programming of the device, through the construction and / or layout of hardware components and interconnection of the device, or a combination thereof.

[0043] Modifications in the described embodiments are possible, and other embodiments are possible, within the scope of the claims.

Claims

1. A system comprising: a first plurality of slave devices, each slave device of the first plurality of slave devices comprising a first wireless transmitter and a battery monitor integrated circuit (IC), the battery monitor IC being configured to obtain battery data from at least one battery cell, and the first wireless transmitter being configured to wirelessly transmit the battery data; a first master device having a second wireless transmitter wirelessly coupled to the first wireless transmitters of the first plurality of slave devices via a first wireless network; as well as A second master device has a second wireless transmitter, the second master device being configured to detect a failure of the first master device and to establish a second wireless network with the first plurality of slave devices in response to detecting the failure. 2 . The system of claim 1 , wherein the first master device is configured to transmit an interrupt signal to the second master device to indicate the failure of the first master device.

3. The system according to claim 1 further includes a shared memory accessible by the first host device and the second host device, the first host device is configured to store second data corresponding to the first wireless network in the shared memory, and the second host device is configured to access the second data in the shared memory to establish the second wireless network. The system of claim 3 , wherein the second data comprises timing data of the first wireless network.

5. The system of claim 1, wherein the second master device is configured to periodically monitor transmissions from the first master device and detect a failure of the first master device following an absence of an expected transmission from the first master device.

6. The system according to claim 1 further includes a second plurality of slave devices, the second master device is configured to wirelessly couple to the second plurality of slave devices via a second wireless network, and wherein after detecting the failure of the first master device, the second master device is configured to establish a third wireless network with the first and second plurality of slave devices.

7. The system of claim 6, wherein each slave device within the first plurality of slave devices and each slave device within the second plurality of slave devices comprises a unique identifier, and the second master device comprises the unique identifiers of the slave devices in the first and second pluralities of slave devices.

8. The system of claim 6, wherein after establishing the third wireless network, the second master device allocates uplink allocations to each slave device in the first and second pluralities of slave devices.

9. A system comprising: a plurality of battery cells; a first plurality of slave devices, each slave device of the first plurality of slave devices comprising a first wireless transmitter and a battery monitor integrated circuit (IC), the battery monitor IC coupled to a subset of the plurality of battery cells, the battery monitor IC configured to obtain battery data from a respective subset of battery cells, and the first wireless transmitter configured to wirelessly transmit the battery data, the battery data comprising at least one of voltage or current; a first master device having a second wireless transmitter wirelessly coupled to the first wireless transmitters of the first plurality of slave devices via a first wireless network; as well as A second master device has a second wireless transmitter, the second master device being configured to detect a failure of the first master device and to establish a second wireless network with the first plurality of slave devices in response to detecting the failure.

10. The system of claim 9, wherein the first master device is configured to transmit an interrupt signal to the second master device to indicate the failure of the first master device.

11. The system of claim 9, further comprising a shared memory accessible by the first host device and the second host device, the first host device being configured to store network data corresponding to the first wireless network in the shared memory, and the second host device being configured to access the network data in the shared memory to establish the second wireless network.

12. The system of claim 11, wherein the network data comprises timing data for the first wireless network.

13. The system of claim 9, wherein the second master device is configured to detect the failure of the first master device in the absence of a transmission from the first master device.

14. The system according to claim 9 further includes a second plurality of slave devices, the second master device is configured to wirelessly couple to the second plurality of slave devices via a second wireless network, and wherein after detecting the failure of the first master device, the second master device is configured to establish a third wireless network with the first and second plurality of slave devices.

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