LitePoint Design Test Solutions looks at radio frequency design tradeoffs in IoT wireless designs
As “internet of things” devices become essential in our lives and in industry, so too will their quality and reliability. From door locks to industrial sensors to medical equipment, a wireless device that works 95% of the time might as well not work at all. The wireless functionality makes these products far more useful, but it also makes it that much more critical that they never fail.
For consumers, dependability of their IoT products is necessary and expected. For example, a malfunctioning smart door lock would not only be frustrating and inconvenient for a consumer, but also have a negative impact on their opinion of the brand. As homes become filled with smart devices such as refrigerators, lights, temperature regulators and washing machines, the old adage “zero defects” is more imperative than ever.
Making IoT design tradeoffs
IoT devices use a wide variety of networking technologies, ranging from Bluetooth and Zigbee on the low end to cellular technologies such as 4G and various iterations of LTE on the high end. To choose the right technologies, consider a number of factors as noted in the first article in this series: battery requirements, the range that your device will need to cover and the amount of data that you will have to transfer.
Bluetooth and Bluetooth Low Energy
Bluetooth is a technology designed to transmit data over short distances using 79 one-megahertz channels in the unlicensed 2.4 GHz ISM band. Typically, the range is 10 meters, but some devices have a range of 100 meters. Data rates top out at about 2.1 megabits per second.
Bluetooth Low Energy, sometimes called Bluetooth Smart, is part of the latest Bluetooth specification and is targeted at battery-powered devices that don’t require a high data rate. The maximum range of a Bluetooth low energy device is 50 meters and the maximum data rate is only 270 kilobits per second. A good example of an IoT device that might use Bluetooth low energy is a smartwatch. Using Bluetooth low energy, a battery in a smartwatch could last months.
Another wireless standard that’s widely used for IoT devices is Zigbee. Like Bluetooth, Zigbee uses the unlicensed 2.4 GHz band, has a range of 10 to 100 meters, and like Bluetooth low energy consumes very little power and has a relatively low data rate (200 kbps). Its implementation, however, is quite different from Bluetooth. Zigbee devices use multihop mesh networking to eliminate single points of failure and expand the reach of networks.
IoT devices that need a range of up to 250 meters generally use Wi-Fi. Depending on which version of the Wi-Fi standard (IEEE 802.11) a device supports, it may operate in the unlicensed ISM bands at 900 MHz, 2.4 GHz or 5.4 GHz. In addition to greater range, Wi-Fi technology offers higher data rates than Bluetooth or Zigbee, ranging from 11 Mbps for 802.11b devices to 1.3 gigabits per second for devices that will support 802.1ac in the future. Of course, greater range and higher data rates come at the price of high-energy consumption. Using a battery to supply power for one of these Wi-Fi devices would be impractical.
To address battery-powered applications and IoT applications, the Wi-Fi Alliance recently announced Wi-Fi HaLow, aka 802.11ah, which operates in the 900 MHz band, giving it a range of up to 500 meters, but the data rate is slow at only 100 kbps.
For IoT applications that require more range, devices will use cellular technologies such as 4G (LTE, LTE-Advanced) and 5G. These devices use licensed spectrum and offer both high data rates (300 Mbps for LTE and 1 Gbps for LTE-A) and long range, but there are disadvantages as well. They rely on the cellular network for connectivity, meaning that carrier data costs could become prohibitive. Also, long battery life for mobile devices is limiting.
The tradeoff between design and performance
Perhaps the biggest tradeoff IoT device manufacturers face is the issue of product design and radio frequency performance. Great product design sells, but it can be difficult to make a product look good and also perform well. And, if a product is not rigorously tested while still in development, costly wireless design flaws will not be caught until a product goes into mass production.
A big example of something that can go wrong is poor antenna design and placement. Antennas are crucial to wireless performance, and designing and positioning the antenna in such a way that it fails to radiate properly will limit an IoT device’s performance. This is especially true when designers have chosen a metal enclosure for the device. Unless the antenna is properly positioned, a metal enclosure will act as a shield, limiting the amount of RF energy the device can radiate or receive and ultimately limit the range of the IoT device.
Another design tradeoff IoT device manufacturers must make is to whether to use RF modules or chip-on-board RF designs. The advantage of using RF modules is the module manufacturers have in general rigorously tested their designs and you can be fairly sure that the design will function as specified. The advantage of designing your own RF interface, using ICs from the leading chipset makers is that the cost will be less than using an RF module.
The importance of testing
In either case, extensive design verification testing will need to be done. If opting to use an RF module, tests will need to ensure that the module works with the rest of the design and the antenna selected. If you’ve designed your own RF interface, you’ll be testing the functionality of the RF circuitry as well as the system as a whole.
In today’s multitrillion-dollar IoT market, establishing a test-oriented environment – especially with the rapid proliferation phase – is a critical investment in the preproduction process and will differentiate brands in terms of quality and reliability. If problems arise in the hands of the consumer, the reality of product rework, retest and warranty claims, reinspection and after-the-sale customer service costs will place a hard hit on profits. And no company wants to incur the additional costs and long-term damage associated with a tarnished brand. As IoT products become a necessary fixture in our daily lives, our reliance on their quality is paramount.
Chris Ziomek is the VP and GM of LitePoint Design Test Solutions. This division is focused on wireless design verification and RFIC testing, helping customers bring their wireless electronic products to the market. Ziomek has 30 years of experience in the test-equipment industry as an instrument designer, engineering manager, entrepreneur and business unit manager.
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