FIELD OF THE INVENTION

This invention relates to wireless networks, and more particularly to battery optimization of network end devices.

BACKGROUND OF THE INVENTION

Common wireless networks have ranges limited to under 100 meters for WiFi and a few meters for Bluetooth. Network standards such as LoRaWAN (Long Range Wide Area Network) may have a much wider geographical area, such as 5 km in an urban area, or 15 km in a rural area with fewer obstructions.

Wireless networks having battery-operated end devices are widely deployed. The end devices can be Internet-of-Things (IoT) devices having relatively low data needs, allowing a battery to power an end device for as long as a few years before the battery needs replacement or recharge. Long-range networks such as LoRaWAN can enhance IoT device power savings by using techniques such as chirp spread spectrum modulation.

FIG. 1shows a prior art long-range network. End devices10are small battery-powered devices that communicate wirelessly with gateways20. End devices10can monitor various appliances or systems. For example, end device10could be attached to a pet collar to track the pet and periodically send a data packet to gateway20with the pet's geographical location. End device10could be part of a smart trash can, periodically sending a data packet indicating if the can is full. Other end devices10could send water-meter reading data, smoke alarm status, or vending machine sales data, as just a few of many examples. There can be thousands of end devices10of many types and purposes. Each end device10may send data to gateway20only a few times per day, such as 10 time per day, thus reducing battery drain.

End devices10may be spread over a wide geographical area, such as 5 km in an urban area, or 15 km in a rural area with fewer obstructions. Several gateways20may be placed throughout a large area to provide better coverage. Gateways20can connect over backhaul network18, such as cellular networks, Ethernet, or other network links to network server22, which can access application server24over Internet26.

Networks such as LoRaWAN can allow end devices to have adaptive data rates. End devices10that are physically closer to gateway20may use a higher data rate and may consume less energy, prolonging their battery life.

FIG. 2is a table of data rates and configurations in a long range network. In this example, data can be transmitted from end device10to gateway20over a 125 kHz channel or over a 250 kHz channel for a higher data rate. Gateway20has no power limitations and can use a much higher 500 kHz channel when transmitting to end devices10. Using low frequencies such as 125 kHz can lower power requirements since power amplifiers can have high efficiency for these low frequencies.

End devices10that are farther from gateway20or that have obstructions that cause Radio Frequency (RF) interference can use a larger Spreading Factor (SF) to reduce transmission errors. Higher Spreading Factors (SF) have a given symbol spread out over more chirps or groups of physical bits transmitted. Thus higher SF settings have more redundancy and are more robust for transmitting data over poor connections. However, the data rate is reduced for higher SF settings with the increased redundancy.

For example, data rate configuration0has a SF of 12 and transmits only 250 bps, while data rate configuration4has a SF of 8 and transmits 3125 bps. Close end devices10can support the highest data rate of 50,000 bps using Frequency Shift Keying (FSK) for data rate configuration7. Based upon the strength of the received signal, network server22determines the optimal node data rate including the spreading factor. Network server22configures the data rate of the end devices through gateway20, and other servers such as application server24, can change the data rate of the end devices with the help of network server22. Each end device10is configured to a specific data rate configuration based on factors such as the physical distance to the nearest gateway20. The assigned configuration can be downgraded when data transmission errors surpass a threshold.

FIG. 3shows a long range network. End devices10are physically located and different distances from gateway antenna21for gateway20. End device14is farther from gateway antenna21than end device12. End device14will require more energy to transmit a fixed amount of data to the gateway than does end device12. This higher transmission energy will tend to deplete the battery of end device14faster than for end device12. End device14may be expected to deplete its battery and fail or require battery replacement sooner than end device12.

FIG. 4is a graph of battery lifetime for a long range network. This histogram shows a wide range and dispersion of battery lifetimes in a long range network. Some end devices such as end device12are close to the gateway and require little energy to transmit data, so their batteries last as long as 10,000 or 11,000 days until battery depletion when battery replacement is needed. Other end devices such as end device14are far from the nearest gateway and require relatively larger amounts of energy to transmit data. These remote end devices may deplete their batteries in only 2,000 days. Such uneven battery consumption is undesirable.

Battery replacement can be an annoyance for end users when they discover that their end device is no longer functioning. Notices could be sent to end users when a battery is nearing depletion, or a service provider could send a technician out to replace the battery or the entire end device. Each service call is expensive. It would be better if all batteries needed replacement at about the same time, to reduce the frequency of expensive service calls or the annoyance of end users.

What is desired is to reduce early battery failures of remote end devices in a long range network. It is desired to spread battery usage over several end devices to extend the battery life of a remote end device. A long range network with transmission-energy load-balanced end devices is desired.

