Load Shedding for Battery-Powered Devices

Abstract

The apparatus includes a radio (302) that operates according to a predetermined schedule and a battery (304) configured to provide power for radio operation of the radio (302). A radio controller (306) is configured to control the radio operation. A voltage indicator circuit (308) monitors the voltage of the battery (304) and provides an output signal (424) that indicates sufficient battery voltage for radio operation. When the output signal (424) is active, the radio controller (306) operates the radio (302) according to the predetermined schedule. When the output signal (424) is inactive, the radio controller (306) adjusts the operation of the radio (302) to maintain radio operation.

Description

[Background technology]

[0001] A typical time-synchronized radio has a predetermined schedule for when it must transmit or receive. This operation requires a certain amount of power, the amount of which is highly dependent on the schedule. In battery-powered devices, a point will come when the battery can no longer provide enough power to sustain the required radio operation, causing the voltage level to drop. At this point, the available voltage will fall below the radio's reset voltage, creating a risk that the radio will reset and be unable to perform the required operation. If multiple resets occur, especially within a short period of time, the radio may not be able to recover from the reset state and may fail, even though the battery still has sufficient power remaining.

[0002] Radio load affects battery operation over temperature and time. Under certain conditions, or as the battery ages, there may not be enough power available to fully execute a predetermined transmit or receive schedule. Low battery power may cause the device to reset or go offline without warning. Summary of the Invention [Means for solving the problem]

[0003] The apparatus of the present invention includes a radio that operates according to a predetermined schedule and a battery configured to provide power for radio operation of the radio. A radio controller is configured to control the radio operation. A voltage indicator circuit monitors the battery voltage and provides an output signal indicating that the voltage required for radio operation is available. When the output signal is active, the radio controller operates the radio according to the predetermined schedule. When the output signal is inactive, the radio controller regulates the operation of the radio to maintain radio functionality.

[0004] The radio load reduction method of the present invention includes monitoring available power from a device's battery and controlling radio frequency (RF) operation of a radio based on that power. Controlling RF operation includes operating the radio according to a known transmit or receive schedule when the battery has sufficient power to perform scheduled RF operation, and adjusting RF operation to maintain radio functionality when the battery does not have sufficient power. [Brief explanation of the drawings]

[0005] [Figure 1] 1 is a block diagram of a location-aware system in which embodiments of the present disclosure may be implemented. [Figure 2] 1 is a graph of radio operation in a prior art system; [Figure 3] 1 is a block diagram of a load suppression device according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a circuit diagram of the load suppression device of FIG. 3. [Figure 5] 1 is a graph of radio activity in a system employing an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0006] This disclosure provides embodiments of methods for radio load mitigation in location-aware systems. While such systems are described, radio mitigation according to various embodiments of the invention can also be applied to other devices with battery-operated and limited-power radios. Examples include wireless field devices used in industrial process monitoring and control.

[0007] In devices with radios, the amount of power consumed by the radio varies depending on the number of transmits (TX) and receives (RX). Battery-powered devices are limited by the amount of power they can provide. One example is the Rosemount WirelessHART location anchor, which uses a time-synchronized radio to communicate with location tags and is battery-powered.

[0008] 1 is a block diagram of a location system 100 to which embodiments of the present disclosure may be applied. The location-aware system 100 includes a host 102 that connects to multiple gateways 104. The gateways operate a gateway network 110 that connects to multiple anchors 106. The anchors 106, in one embodiment, are connected to the gateways 104 over a WirelessHART network 110. Each anchor 106 connects to a tag 108 to perform ranging and determine the location of each tag. The system operates based on synchronized time clocks and communicates according to a schedule of wireless communications powered by batteries within the tags and anchors.

[0009] In this type of system, each anchor 106 synchronizes to the WirelessHART network 110, and each tag 108 synchronizes to an anchor 106. To keep the tags 108 synchronized, anchors 106 near the tags 108 periodically transmit beacon messages using location radios. The tags 108 use the messages to synchronize their clocks and extract location ranging information, which is transmitted back to the receiving anchor 106 and then forwarded to the host system 102. In this type of system 100, keeping the anchors online and operational is important to keeping the tags 108 connected to the location system 102.

[0010] With global time synchronization, each location anchor 106 executes a radio schedule during which it transmits beacons or receives data from tags 108. This schedule repeats at frame intervals (e.g., 16-20 seconds, but may vary without departing from the scope of this disclosure), and the number of scheduled receives within a frame depends on the number of tags 108 that the anchor 106 is listening to. Therefore, the load on the anchor 106 varies from device to device, making it difficult to design a power supply that can handle all conditions.

[0011] An embodiment of the present disclosure is provided to prevent the anchor's radio consumption from exceeding the range that a normal battery can provide. Under these conditions, the battery maintains its voltage and powers the radio load. However, this type of system can face problems when the battery is depleted or the ambient temperature drops. As the battery deteriorates, its internal resistance increases, causing a voltage drop when drawing a large current. If the voltage drop increases, the system becomes inoperable and the device resets. Unless the power consumption changes significantly, the device may not fully recover until the battery is replaced. In the case of an anchor, resetting the device disconnects it from the WirelessHART network and loses connection with nearby tags.

[0012] In addition to battery degradation, low temperatures can have a similar effect. In either case, resetting is undesirable and can occur before the battery is completely depleted, rendering it unusable even if there is still some charge remaining, and reducing its actual lifespan.

[0013] This situation is illustrated in the graph of FIG. 2. Wireless RF activity is shown by line 200, and battery voltage is shown by line 202. The voltage indicator signal is shown by line 204, and the device's micro-reset signal is shown by line 206. When wireless RF activity begins at time 200a, the battery voltage also begins to drop, eventually reaching and falling below threshold voltage 210 at point 200b. At point 200b, the voltage drop associated with the radio's RF activity causes the voltage indicator signal to change from active to inactive, indicating that the battery voltage is below threshold voltage 210. A large load current, such as a wireless RF receiver, causes the voltage drop. At time 200c, the battery voltage drops to low voltage limit 211. At this point, the battery cannot provide enough voltage to power the device, and the device resets. As a result, the device disconnects from the network and RF activity ceases. When voltage recovers, the device emerges from reset and rejoins the network at time 200d. RF operation resumes at time 200e, but because the voltage has only partially recovered, it quickly reaches the low voltage limit 211 and resets again at time 200f. This process may repeat as long as the device successfully reconnects. As a result, the device may operate erratically and performance may degrade, even if sufficient battery power remains. When the device does recover, this is often when changes in ambient conditions improve battery output. However, excessive resets may cause the device to permanently disconnect from the network and be unable to reconnect. In such cases, the battery may still have available power, but the remaining battery power is rendered unusable by the high radio load.

[0014] Radio load throttling embodiments of the present disclosure are used to extend battery life and reduce the likelihood of device resets. Instead of implementing a fixed transmit and receive schedule, the anchor controls radio RF operation based on the power available to the device. When the device has a good power source, the radio follows a full schedule. However, if the power supply drops, the device senses this drop and automatically adjusts its scheduled RF operation to compensate.

[0015] Location systems, particularly tags and anchors, located in remote locations and powered by internal batteries are susceptible to power loss due to battery degradation, aging, ambient conditions, etc. As shown in FIG. 3, a block diagram of an anchor 106 or tag 108 is shown as a radio-suppressed device. Device 300 includes a radio 302 that, in one embodiment, operates on a predetermined schedule and a battery 304 that provides power for the radio operation. A radio control unit 306 is connected to radio 302 and controls the radio operation. A voltage indicator circuit 308, connected to the battery and further to the radio control unit, monitors the battery voltage and provides an output signal indicating that the required voltage for radio operation is available.

[0016] When battery power is sufficient, the output signal from the voltage indicator circuit 308 is active, causing the radio controller 306 to operate the radio 302 according to a predetermined schedule. When battery power falls below a threshold and is insufficient for full scheduled RF operation, the output signal becomes inactive. In this case, the radio controller 306 adjusts the operation of the radio 302 to maintain a supply voltage above the reset voltage of the radio 302. One adjustment involves disabling radio operation when the output signal is inactive, preventing a reset. Disabling the radio disconnects it from the network and prevents it from reconnecting. Another adjustment involves adjusting the radio operation by changing the schedule to operate the radio less frequently when the output signal is inactive. Furthermore, in one embodiment, the radio controller is configured to provide a low voltage warning when the output signal is inactive.

[0017] As long as the battery provides sufficient voltage for normal operation, the radio controller is configured to follow a predetermined schedule, checking the battery voltage before each transmit and receive and shed load if the output signal is inactive. Battery voltage checking is performed at the start of every scheduled RF operation. In one embodiment, monitoring continues after RF operation has begun. If the battery voltage falls below a threshold required for safe operation of the radio, RF operation is shed when the output signal changes to inactive.

[0018] Referring to Figure 4, a circuit 400 according to the embodiment of Figure 3 is shown in more detail in schematic form. The circuit 400 includes a radio 302 having an antenna 402, a battery 304, a radio control unit 306, and a voltage indicator circuit 308. Other components include a voltage regulator 404, a power sharing resistor 406, a bulk power storage component 408, and a decoupling capacitor 410.

[0019] The voltage indicator circuit 308 includes a sense resistor 412 connected between the positive battery terminal and the non-inverting input of a comparator 414 (e.g., an operational amplifier connected as a positive voltage comparator), providing an input voltage to the comparator 414 at node 426. A voltage divider 416 provides a reference voltage, with its midpoint 418 (i.e., threshold voltage) connected to the inverting input of the comparator 414. With this configuration, when the battery voltage at node 426 exceeds the reference voltage at node 418, the output signal 424 is active (high). Conversely, when the voltage at node 426 is below the voltage at node 418, the output signal is inactive.

[0020] The threshold voltage at node 418 is determined by a portion of the voltage Vreg output by voltage regulator 404. One end of voltage divider 416 is supplied with Vreg and the other end is connected to ground. Thus, the voltage supplied to midpoint node 418 is a percentage of Vreg, and by selecting the values ​​of resistors 420 and 422, the voltage at node 418 is adjusted to the threshold voltage. When the positive terminal of the battery, i.e., the battery voltage, falls below the voltage at node 418, amplifier output signal 424 becomes inactive. When signal 424 becomes inactive, radio control unit 306 inhibits RF operation.

[0021] Other low voltage detection circuits may be used without departing from the scope of this disclosure.

[0022] The operation of an embodiment of the present disclosure is illustrated in graphical form in FIG. 5. Wireless RF operation is shown on line 500, battery voltage on line 502, a voltage indicator signal on line 504, and a device micro-reset signal on line 506. When wireless RF operation is initiated at time 500a, the battery voltage also begins to drop. Voltage indicator signal 504 is determined by a voltage indicator circuit, such as circuit 308, and indicates voltage monitoring. When the voltage drops to a low voltage threshold 510 (voltage level Vt) for safe operation, the voltage indicator circuit deactivates voltage indicator signal 504 at time 500b. This signal instructs the wireless controller to inhibit RF operation, resulting in control of RF operation at time 500c.

[0023] As yet another additional configuration of embodiments of the present disclosure, a bulk storage component (e.g., a supercapacitor) can be added to assist in situations where radio activity is heavy. This reduces the duty cycle and allows full capacity even with a low-voltage battery. In one embodiment, bulk storage component 408 is added so that the initial current of the radio load is fully or nearly supplied by bulk storage component 408. This allows a certain number of radio tasks to be performed without duty cycle control, even when the battery is weak. The bulk storage component is charged by the battery during RF standby. When radio activity exceeds the charge stored in the bulk storage component, the battery provides additional current, and radio load throttling is activated as described above. The use of a supercapacitor allows power to be drawn from a low-voltage battery as it is charged during RF standby, thereby extending the available battery life.

[0024] The bulk storage component 408 and its use are described below. In one embodiment, the bulk storage component 408 is used to smooth out power consumption spikes that would otherwise cause the battery voltage to droop. In one embodiment, the bulk storage component 408 comprises a bulk capacitor or a bank of bulk capacitors. The bulk storage component 408 is connected across the terminals of the battery 304, and its operation is smoothed by a power sharing resistor 406. The bulk storage component 408 charges when RF operation is on standby, and the stored energy provides initial power when RF operation is to occur.

[0025] Specifically, this embodiment maintains the battery load as low and stable as possible. High current loads, especially during wireless transmission, shorten the battery's usable life. This problem worsens as the battery ages and its equivalent series resistance (ESR) increases. To reduce the battery's peak load, a power sharing resistor 406 and a bulk storage component 408 are used before the voltage regulator 404. The power sharing resistor 406 serves two purposes: it buffers the current required to recharge the bulk storage component 408 during RF standby periods and allows the bulk storage component 408 to absorb most of the peak current during RF transmission. The voltage indicator circuit 308 monitors the battery 304 voltage via a sense resistor 412 and a comparator 414 to determine whether the battery can support RF operation. If the battery voltage begins to drop, the wireless controller receives an inactive output signal 424 and inhibits RF operation to prevent the battery voltage from dropping. During the inhibit period, a warning is notified to the user, and in one embodiment, this is communicated via the wireless interface.

[0026] The radio can operate in several modes of operation. Two example modes are 1) a single message transmit and receive mode, and 2) a timed continuous receive mode (usually lasting a few seconds). Mode 1 is scheduled receive, where the radio is active only when a receive is scheduled. Mode 2 is open listen, where the receiver is enabled and waits for an incoming message. Open listen can last for several minutes, but is usually scheduled for no more than approximately 16 seconds. Transmissions are all scheduled or very short. Continuous transmissions are not permitted by Federal Communications Commission (FCC) regulations.

[0027] Mode 1 is typically used when all devices in a system are time-synchronized. In this configuration, devices operate on a time schedule that repeats every frame time (e.g., 16 seconds). The radio is turned on only when a transmit or receive is scheduled, transmitting or receiving a single message. In this case, the radio's on-time is typically 4-8 milliseconds per message. In this configuration, battery voltage is checked only immediately before a transmit or receive operation. Within a frame time, hundreds of transmits and receives may occur relatively quickly, with approximately 20 milliseconds of off-time between each transmit and receive. Battery voltage is checked immediately before each transmit and receive, and if it is above a threshold, operation continues. If not, load shedding is initiated.

[0028] Load throttling can take several different forms without departing from the scope of this disclosure, such as delaying transmit and receive schedules, i.e., reducing the frequency of transmit and receive, etc. In one embodiment, all wireless RF activity is stopped and no activity occurs until the battery voltage is above a threshold.

[0029] In Mode 2, the receiver is enabled for a longer period of time (e.g., 10 seconds or so), so a single voltage check at the start may not fully account for the current consumed by the radio while receiving. In this case, in one embodiment, voltage checks are performed continuously while the radio is receiving. If the battery voltage drops to a threshold during reception, voltage throttling is performed, such as shutting down the radio until power is restored.

[0030] In one embodiment, when the output signal drops, an alert is generated by the wireless controller. A status alert flag is set to indicate that RF suppression has been activated. This status flag is periodically transmitted to the host system using WirelessHART additional status command 48. The host system can monitor the flag to determine when a battery change is required.

[0031] The disclosed wireless load reduction allows power-limited devices to adjust their power consumption based on available power, thereby extending overall battery life and enabling devices to operate for longer periods of time. Reducing the wireless load can prevent device resets, maintain connectivity to the WirelessHART network, and provide advance warning to users for battery replacement. During this time, the device maintains connectivity to the location system and reduces impact on surrounding tags and devices.

[0032] Embodiments of the present disclosure provide a radio load reduction device and method that dynamically adjusts radio power consumption depending on the power available from the device's battery. This helps maintain battery voltage and prevent device resets, thereby extending battery life and providing early notification to the user that the device is nearing the end of its life.

[0033] As a result of embodiments of the present disclosure, the device can transmit and receive as much as possible based on the available power. As the battery weakens due to aging or temperature effects, it will be unable to keep up with the current demands of the radio. In this case, radio operation will be throttled back to reduce the average current load to prevent a system reset.

[0034] Embodiments of the present disclosure offer several advantages over existing systems, including, by way of example, reduced average radio current, prevention of device resets when batteries become weak, increased device runtime / battery life, increased likelihood of reporting critical battery conditions to the user, and reduced anchor downtime by allowing the user time to plan for battery replacement. Additionally, they also reduce positioning errors of nearby tags caused by anchors going offline.

Claims

1. a radio that operates according to a predetermined schedule; a battery configured to provide power for operation of the radio; a radio control unit that controls the operation of the radio; a voltage indicating circuit configured to monitor the voltage of the battery and provide an output signal indicative of whether the battery voltage is sufficient for operation of the radio; Equipped with When the output signal is active, the radio control unit operates the radio according to the predetermined schedule; When the output signal is inactive, the radio control unit adjusts operation of the radio to maintain operation of the radio. Device.

2. 10. The apparatus of claim 1, wherein maintaining operation of the radio comprises maintaining a supply voltage greater than a reset voltage of the radio.

3. The apparatus of claim 1 , wherein the radio control regulates operation of the radio by disabling the radio when the output signal is inactive.

4. 2. The apparatus of claim 1, wherein the radio control adjusts operation of the radio by changing the radio to a schedule that operates less frequently when the output signal is inactive.

5. The device of claim 1 , wherein the wireless control is configured to provide a low voltage warning when the output signal is inactive.

6. The wireless control unit checking the voltage of the battery according to the predetermined schedule and before each transmission or reception in the predetermined schedule; configured to perform load shedding when the output signal is inactive; 10. The apparatus of claim 1.

7. 2. The apparatus of claim 1, wherein the radio control unit is further configured to monitor the output signal during transmission and reception of the radio, and inhibit transmission and reception when the output signal switches to inactive.

8. 10. The device of claim 1, further comprising: a mass storage component coupled between the battery and the wireless control unit and configured to provide power prior to using the battery for transmission and reception.

9. 9. The apparatus of claim 8, wherein the mass storage component is charged with power from the battery when the radio is in standby mode.

10. the bulk storage component comprises a bulk capacitor charged by the battery; when transmitting or receiving according to the predetermined schedule, power for the radio is provided by enabling the ultra-capacitor to provide transmit or receive power; 9. The apparatus of claim 8.

11. 11. The apparatus of claim 10, wherein the bulk storage component further comprises a power sharing resistor coupled between the battery and the bulk capacitor.

12. The voltage indicating circuit a comparator having an inverting input, a non-inverting input, and an output; a sense resistor connected between the positive terminal of the battery and the non-inverting input of the comparator; a voltage divider providing a reference voltage and connected to the inverting input of the comparator; Equipped with The comparator is configured to output an active output signal when the battery voltage exceeds the reference voltage and to output an inactive output signal when the battery voltage falls below the reference voltage.

10. The apparatus of claim 1.

13. Monitor the available power from the device's battery; controlling radio frequency (RF) operation of a radio based on available power from the battery of the device; This includes: The control of the RF operation includes: if the battery has sufficient power for scheduled RF operation, operating the radio according to a known transmit and receive schedule; If the battery does not have sufficient power for scheduled RF operation, adjust the RF operation to maintain operation of the radio. A method for reducing wireless load in an apparatus, comprising:

14. 14. The method of claim 13, wherein controlling RF operation to maintain operation of the radio includes protecting the radio from an over-the-air reset.

15. monitoring the available power The voltage indicator circuit detects the battery voltage, comparing the sensed battery voltage to a low voltage threshold; providing an output signal that is active when the battery has sufficient power and inactive when the battery does not have sufficient power; The method of claim 13, comprising:

16. Control of RF operation of the radio is performed by a radio control unit; the radio controller receives the output signal and adjusts operation of the radio by disabling the radio when the output signal is inactive.

16. The method of claim 15.

17. 16. The method of claim 15, wherein controlling RF operation of the radio is performed by changing the radio to a schedule that operates less frequently when the output signal is inactive.

18. sensing the battery voltage before each transmission or reception in the predetermined schedule; performing load shedding when the output signal is inactive; The method of claim 15 further comprising:

19. monitoring the output signal while the radio is transmitting and receiving; inhibiting the transmission and reception when the output signal is switched to an inactive state; The method of claim 15 further comprising:

20. 14. The method of claim 13, further comprising charging a bulk storage component configured to provide power for transmission and reception during the standby period of RF operation.

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