A ubiquitous Internet of Things (IoT) depends upon wireless connectivity, but there are many options for wireless and not every device is IP addressable – a requisite feature for IoT. What’s more, RF design is inherently difficult. Few companies are equipped with the appropriate skills to implement RF and antenna design, and even when done, keeping that design up to date with the latest standards and getting it through FCC compliance is time-consuming.
For designers, there is a very solid and proven option for wireless connectivity and IoT. That option is Wi-Fi and the use of modules. This feature will explain why, offer some design solutions, discuss soon-to-arrive upgrades to IEEE 802.11 protocols, and show how to bridge ZigBee to Wi-Fi for native IP addressability.
There are many wireless interface options, Bluetooth Low Energy (BLE), ZigBee, Z-Wave, Wi-Fi and RFID, each with their own unique balance of power, range, data rates, mesh networking, interference immunity, and ease of use. However, some interfaces are not yet native-IP enabled, so cannot be addressed directly or exchange data with other devices and servers over the Internet. These then require a separate gateway, adding expense and complexity to the final solution.
This is where Wi-Fi stands out: it is based on the IEEE 802.11 standards with native IP addressability, is ubiquitous, well understood, and can scale well in terms of data rates to optimize for power consumption. According to the Wi-Fi Alliance, there are more than 6.8 billion installed Wi-Fi-capable devices, so the odds are pretty high that there is a local Wi-Fi access point available (Figure 1). Note too that 802.11 standards are also IPv6 compliant, so there’s almost no limit to the number of unique addresses.
Easing wireless development
After selecting Wi-Fi for an IoT application, the designer often faces the daunting challenge of building a custom RF implementation, which requires time, money and expertise. Design requirements for developing a wireless device include, at a minimum, direct RFIC integration and the ability to specify components such as filters, amplifiers, clocks, capacitors, inductors, crystal oscillators, and the antennas that need to be on the board, as well as their placement. There also needs to be network-matching circuitry to ensure that the radio and antenna are well matched to avoid signal loss. Other knowledge areas include system layout, software stack development, device security, connection reliability, signal interference and degradation, and last but surely not least, FCC certification.
How does this task get done within typical time to market parameters given that RF design expertise is not something readily available to every electronics company? An increasingly common way to add Wi-Fi capability is to use a pre-packaged module. This approach greatly simplifies the process. Modules are supplied tested, calibrated and pre-certified to the required standards by the module vendor, and therefore can provide companies with a fast, easy route to market with what is, essentially, a plug-and-play solution, reducing the need for software development. What is more, manufacturers who design and build the Wi-Fi modules can be your RF consultants during the design integration stage.
The Wi-Fi module generally contains two main parts: a Wi-Fi chip and an application host processor. The Wi-Fi subsystem includes an 802.11 radio physical layer (PHY), baseband, media access control (MAC), and perhaps a crypto engine for a fast, secure Internet connection. The application host processor has an internal or external flash, ROM, and RAM. The module generally also comes with I/Os for timers, serial communication interfaces, analog comparators, analog-to-digital converter (ADC), digital-to-analog converter (DAC), crystal oscillators, and a debug interface.
The power management subsystem includes integrated DC-DC converters supporting a wide range of supply voltages. It enables low-power consumption modes, such as hibernate with real-time clock (RTC) mode. A module may offer an integrated antenna or provide an RF connector for an external antenna. The software package included with a Wi-Fi module usually includes a device driver, an integrated 802.11 security layer, and a management and monitoring utility.
In designing a Wi-Fi IoT solution, the starting point is an understanding that IEEE 802.11 represents a family of standards that until just recently operated only in the 2.4 GHz (IEEE 802.11b/g/n) and 5 GHz (IEEE 802.11a/n/ac) unlicensed bands. There are three key factors to consider when evaluating these protocols: data rate, range, and power requirements. When you compare the different Wi-Fi protocols, 802.11b/g has the advantage in compatibility with installed devices and power requirements while 802.11n and 802.11ac have the advantage of higher data throughput for multimedia applications such as video streaming.