From using batteries to battery-free, do you know the tricks for developing low-power wireless IoT applications?

The Internet of Things (IoT) has been a hot topic in recent years, and many Internet operators are predicting that this field will see significant growth over the next decade. Data from Statista shows that the global IoT end-user solutions market grew to $212 billion by the end of 2019. In 2017, revenue from this market reached $100 billion for the first time, and this number is expected to grow to around $1.6 trillion by 2025.

The Internet of Things (IoT) has been a hot topic in recent years, and many Internet operators are predicting that this field will see significant growth over the next decade. Data from Statista shows that the global IoT end-user solutions market grew to $212 billion by the end of 2019. In 2017, revenue from this market reached $100 billion for the first time, and this number is expected to grow to around $1.6 trillion by 2025.

In IoT applications such as smart homes, smart warehouses, wearable health monitoring equipment, and logistics, in many cases, terminal devices and sensors need to rely entirely on batteries to work. At this time, the length of battery life basically determines the service life of the entire system.

In fact, battery life often depends on how long the device remains “awake”. The longer the device sleeps, the longer the battery will last, at the expense of performance. Therefore, we can argue that there is a contradiction between maintaining long battery life and achieving high performance of IoT devices.

On the other hand, wireless connection technology, which is an important part of the Internet of Things, usually requires devices to consume more energy to achieve faster data transmission. That said, low latency often comes at the expense of high power consumption, and there is a contradiction between the two.

Well, here comes the question. How to solve the above two contradictions to create a low-power, low-latency, high-performance, battery-powered or battery-free IoT system? Next, we will start from two aspects of finding suitable wireless connection technology and realizing ultra-low power IoT design to find the answer.

Choosing the Right Wireless Technology for IoT Applications

To build a low-power, low-latency IoT network, it is important to choose a suitable short-range wireless connection technology, and the considerations are best from the following aspects:

One is cost. Since many devices (sensors) are low-cost small devices, the wireless connectivity technology of choice for IoT cannot add much additional cost to the overall bill of materials (BOM). Even, in many cases, the wireless connectivity technology and user equipment are better off sharing a single MCU.

The second is power consumption. Low power consumption is a prerequisite for IoT applications such as battery power or utilizing energy harvesting technology as a power source, so the lower the power consumption of wireless technologies used for network connectivity, the better.

The third is security. Wireless connectivity technologies must adequately support security requirements such as authentication and encryption, and sometimes end-to-end security from sensors to web services.

The fourth is coverage. This is well understood. Each wireless technology has its maximum working radius. When choosing, it must ensure sufficient coverage without increasing the system cost too much.

The fifth is the ecosystem. A good ecosystem construction will be very beneficial to the development of IoT systems, shorten the time to market of products, and make technology development costs easier to control.

Since IoT is a wide variety of application areas, it is difficult to find a one-size-fits-all communication solution. The six most common IoT wireless technologies listed below, each solution has its own advantages and disadvantages in different network standards. Sometimes a complex IoT communication system is even a combination of multiple wireless technologies. In a word, there is always one that suits you.

From using batteries to battery-free, do you know the tricks for developing low-power wireless IoT applications?
Figure 1: Performance comparison of multiple wireless technologies (Source: BehrTech)

LPWAN

Low-Power Wide-Area Network (LPWAN) can connect all types of IoT sensors, however, it can only send small data blocks at low rates and, therefore, is more suitable for applications that do not require high bandwidth and are not time-sensitive.

Zigbee and other mesh protocols

Zigbee is a short-range, low-power wireless standard (IEEE802.15.4) typically deployed in mesh topologies to extend coverage by relaying sensor data across multiple sensor nodes. Compared to LPWAN, Zigbee offers higher data rates, but at the same time it is much less energy efficient due to the mesh configuration.

Since the coverage is less than 100 meters, Zigbee and similar mesh protocols (such as Z-Wave, Thread, etc.) are ideal for mid-range IoT applications where nodes are evenly distributed and very close together. Zigbee is often seen as the perfect complement to Wi-Fi, especially for a variety of home automation applications such as smart lighting, heating ventilation and air conditioning (HVAC) control, security and energy management.

Bluetooth and Bluetooth Low Energy (BLE)

As a short-range wireless communication technology, the application of Bluetooth is mainly located in the consumer market. Classic Bluetooth was originally used for point-to-point or point-to-multipoint data exchange between consumer devices. After optimizing power consumption, BLE technology was introduced later to solve the power consumption problem of small consumer IoT. Today, BLE is widely integrated into fitness and medical wearables and smart home devices such as smart watches, blood glucose meters, pulse oximeters, smart door locks, and more.

Wi-Fi

Wi-Fi has played an important role in providing high-throughput data transmission for enterprise and home environments. However, in the IoT field, Wi-Fi has not been widely adopted due to its limitations in coverage, scalability and power consumption. Especially for battery-powered IoT sensor networks and industrial IoT applications, Wi-Fi is not suitable.

Wi-Fi 6 is the latest generation of Wi-Fi technology with amazing network bandwidth (RFID

Radio Frequency Identification (RFID) uses radio waves to transmit small amounts of data from an RFID tag to a card reader over a short distance. At the same time, the technology has brought about a major change in retail and logistics. By attaching RFID tags to various products and equipment, businesses can track inventory and assets in real time, enabling better inventory and production planning and optimized supply chain management. As IoT adoption continues to increase, RFID will continue to have a place in retail.

Cellular Communication (3G/4G/5G)

Cellular networks provide reliable broadband communications for a variety of voice calling and video streaming applications. On the downside, they have very high operating costs and power requirements. While cellular networks are not suitable for most IoT applications such as battery-powered sensor networks, they are well suited for specific use cases such as fleet management in transportation and logistics. In-vehicle infotainment, traffic routing, advanced driver assistance systems (ADAS), and fleet telematics and tracking services are among the best use cases for ubiquitous high-bandwidth cellular communications.

In particular, there are three well-known wireless communication technologies in the 2.4 GHz ISM band: Wi-Fi, Bluetooth and Zigbee.

♦ Wi-Fi is probably the best known, offering the fastest communication rates and ideal for computer connectivity, but it cannot be used for very low power operation, battery powered applications, etc.

♦ Bluetooth technology is ideal for low-power, battery-powered devices designed primarily to provide short-range, medium-speed wireless connectivity within 10 meters of cell phones, headsets, and other handheld consumer devices.

♦ Zigbee was designed from the outset to provide low-speed, short-range (20m to 100m) wireless connectivity for months to years for devices using small batteries, especially in terms of power consumption.

To sum up, each IoT vertical application has its own unique network requirements. When choosing the best wireless technology, we often need to make trade-offs in coverage, bandwidth, QoS, security, power consumption, and network management. Only in this way can an efficient network connection be established.

Low-Power Design in IoT Devices

After selecting the appropriate wireless technology, the next thing to do is to achieve long-term stable operation of battery-powered or battery-free IoT devices through low-power design.

While IoT systems for consumer and industrial applications may appear similar on the surface, there are distinct differences in power, connectivity, and robustness requirements. Generally, industrial applications require a large number of small-sized, battery-operated sensors that may be in difficult-to-reach places for maintenance personnel due to altitude or harsh operating conditions, and sometimes battery-free solutions through energy harvesting. Equipment powered by batteries needs to commit to a predictable battery life so that implementation and subsequent maintenance can be planned in advance. For consumer IoT, although it is relatively easy to replace the battery, if the device consumes too much power and the standby time is too short, it will seriously affect the user experience.

The best solution to these challenges is to use low-power designs.

Low-power designs generally follow a key concept: use as few hardware resources as possible to process data. In other words, the purpose of reducing power consumption is achieved by reducing the number of hardware. This approach seems simple in theory, but in many cases there is a trade-off between performance and power consumption in hardware and software.

Choosing the right battery is another important factor in achieving long life for IoT devices. While low-power designs are important, end users are often equally interested in system longevity and total cost of ownership. Choosing the right battery size and technology is an important step in this process.

Energy harvesting is a hot topic in recent years and has been widely deployed in IoT applications. While energy harvesting will not replace batteries in all applications, they are still an important solution for extending battery life in many cases.

In the real design scheme of IoT, reducing the number of peripherals by integrating more functions to achieve high performance and low power consumption of the product is the most common method used by semiconductor companies today. Listed below are some of the more popular solutions on the market.

♦ NXP multi-protocol wireless MCU maximizes battery life

As the choice of wireless technologies continues to increase, so does the need for ultra-low-power connectivity in the smart home. NXP’s K32W061 and K32W041 multi-protocol wireless microcontrollers (MCUs), which use the IEEE 802.15.4 wireless standard, support Thread and Zigbee network protocols, BLE 5.0 and integrated NFC NTAG (K32W061), are ideal for IoT The wireless interconnect provides ultra-low power performance, maximizing the performance of single coin cell battery devices in the smart home and IoT.

From using batteries to battery-free, do you know the tricks for developing low-power wireless IoT applications?
Figure 2: NXP K32W061/41 block diagram (Image source: NXP)

♦ Cypress Wearables Solutions

Cypress has a series of wearable device solutions, from the basic version PSoC 6-BLE ultra-low power MCU to an upgraded version consisting of a PSoC 6 chip + a dual-mode BLE 5.0 chip (CYW20719). The solution is very suitable for the increasing demand for Bluetooth audio on the bracelet. The biggest features of the solution are high integration, high performance, low power consumption, and small size. In addition, in order to support a large number of data transmission applications (such as downloading songs and background upgrades through Wi-Fi), Cypress also provides an advanced solution – with CYW43012 Wi-Fi + Bluetooth combo chip, which can support 802.11 ac at the same time Wi-Fi and BLE 5.0 wireless connection.

We mentioned earlier that Wi-Fi is very unsuitable for battery-powered IoT applications. The development of technology is always unimaginable. Today, the author will share with you a piece of good news about the progress of Wi-Fi technology. After a careful search, we found that electrical engineers at UC San Diego announced in February 2020 that they had developed a new ultra-low-power Wi-Fi product that could power IoT devices. Comes with ultra-low-power Wi-Fi connectivity. The chip package is smaller than a grain of rice and consumes only 28 microwatts of power to transmit data at a rate of 2Mb/s per second (a connection strong enough to stream music and most YouTube videos) over a range of 21 meters, while IoT devices can communicate with existing Wi-Fi networks using 5,000 times less power than today’s Wi-Fi. At that point, our phones, smart devices, and even small cameras or various sensors can be connected to this chip, which can send data from these devices directly to a nearby Wi-Fi access point. Of course, we don’t yet know when it will be officially commercialized.

Energy harvesting allows IoT devices to save batteries

Battery-free and maintenance-free terminals are increasingly present in IoT deployments. These battery-free devices with smart sensors will harvest energy from the environment, using energy harvesting to charge themselves.

The so-called energy harvesting technology mainly refers to recovering and converting the energy generated by thermoelectricity, vibration, motion, solar energy, etc. into electrical energy, instead of batteries to power equipment. A key point to achieve battery-free power supply through energy harvesting is that IoT devices must choose ultra-low-power wireless communication technologies, such as BLE, Zigbee, etc., combined with energy harvesting and low-power design to save batteries. As for how to achieve it, there is no need to worry, semiconductor manufacturers have already prepared solutions for us.

♦ Energy harvesting power IC for wireless sensor nodes

This is another important product of Cypress in the IoT field, the S6AE101A Energy Harvesting Power Management IC (PMIC) is mainly used for small solar powered wireless sensors in IoT applications. According to Cypress, the S6AE101A is a single-chip energy harvesting PMIC with ultra-low power consumption in the industry, which can be used with solar cells as small as 1cm2. The startup power of the S6AE101A is only 1.2μW and the current consumption is as low as 250nA. This low-power performance maximizes the power available to the sensing, processing and communication functions of the target application. This PMIC is a fully integrated device ideal for use in batteryless wireless sensor nodes (WSNs) for monitoring physical and environmental conditions in smart homes, commercial buildings, factories, infrastructure, and agriculture.

From using batteries to battery-free, do you know the tricks for developing low-power wireless IoT applications?
Figure 3: Block diagram of the S6AE101A energy harvesting power management IC (Image source: Mouser Electronics)

♦ ON Semiconductor Bluetooth Low Energy Switch Reference Design

ON Semiconductor’s design is based on BLE 5.0, combined with ZF Friedrichshafen AG’s energy harvesting technology, by capturing the energy transmitted when the user presses a button and converting it into electromagnetic energy and ultimately electricity , stored for the RSL10 chip.

The RSL10 is a Bluetooth 5.0 certified wireless single-chip SoC with a fully integrated antenna and all passive components with extremely low power consumption. In deep sleep, the power consumption is only 62.5 nW, and the receive power consumption is as low as 7 mW. Every time the user presses the button, the energy harvesting scheme generates 300μJ of energy, which can fully meet the power consumption requirements of the RSL10. This Bluetooth low energy switch reference design works with harvested energy, enabling true self-powered IoT applications.

Epilogue

In today’s active advocacy of green environmental protection, no matter what industry, low energy consumption is an eternal topic. IoT is more sensitive to the power consumption of devices due to the particularity of its application scenarios. In order to achieve battery-powered or battery-free operation, and at the same time ensure a long service life of the device, choosing the appropriate wireless connection technology is a prerequisite for the success of the solution. The highly integrated MCU or SoC that integrates multiple wireless protocols provides a strong technical guarantee for the establishment of low-power, high-performance IoT systems.

According to Gartner’s latest forecast, IoT connections in the enterprise and automotive markets alone will grow 21% over 2019, reaching a staggering 5.8 billion endpoints in 2020. More IoT development milestones will be ushered in the future as new wireless standards become more widely used based on existing technologies.

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