Welcome to the Wireless Menagerie: RF Bands and Protocol Choices for Embedded Developers, Part 1


Editor’s Note: Part 1 of this two part series discusses the various wireless connectivity options available to embedded system designers and provides some relevant examples. Part 2 will discuss the characteristics of wireless modules in more detail, along with insight on how to go about using them effectively.

Embedded devices and systems have historically been standalone with plug-in wired interfaces for data exchange and maintenance. Now designers are under increasing pressure to add some sort of wireless interface to connect their system or device to other systems, or to the Internet of Things (IoT).

While silicon advancements and new interfaces have made the addition of wireless connectivity more practical and cost effective, the downside is that there is an expanding and confusing array of available protocols, range capabilities, and data rates to choose from. This makes it difficult for designers to make the right choice for a specific application.

To help narrow the field more quickly to a practical solution, this article compares and summarizes ten wireless networking options for embedded designs and provides examples of three very different wireless modules.

Wireless interface evaluation criteria

Range, cost, and power consumption are perhaps the most important criteria for most embedded designs. In terms of range, wireless options vary widely:

Near field communications (NFC) only carries across a few centimeters. Bluetooth and Zigbee are designed to cross a few meters using extremely low power. 802.11-based Wi-Fi radios have a range in the hundreds of meters and tap directly into the ubiquitous Internet infrastructure. Narrowband IoT (NB-IoT) uses licensed cellular infrastructure to carry wireless data over many kilometers. LoRaWAN and Sigfox are low-power, long-range wireless options for IoT devices that also cover many kilometers but operate in unlicensed bands.

Figure 1 is a simple drawing that places several of these protocols on the bandwidth/range plane.

Conceptual diagram of range (in meters to kilometers) versus bandwidth (in bits per second to megabits per second)

Figure 1: A conceptual diagram of range (in meters to kilometers) versus bandwidth (in bits per second to megabits per second) for several wireless protocols. (Image source: Digi-Key Electronics)

There are two additional criteria to consider in addition to range, cost, and power consumption. The first is whether or not the application calls for an on-board application processor. Some wireless modules emulate the operation of, and use the same development tools as popular development boards such as the Arduino Uno. Others have their own architectures and their own development ecosystems. Still others have no on-board processing at all.

If the wireless module will only implement communications for a host processor, then the interface between the host processor and the wireless module becomes an important factor. Here there are many choices including serial protocols such as I2C, SPI, or UART. Another possibility is the Arduino I/O header - many modules are available as Arduino shields. However, these slower serial interfaces and the Arduino I/O header will not support higher data rates. Much faster data rates call for much faster interfaces like PCIe, for example.

The following alphabetical table lists ten common choices and basic selection criteria for various wireless networking protocols suited to embedded designs.

Wireless Standard Power Transmission Range (typical) Data Rates
Bluetooth Medium 1 to 100 m 1 to 3 Mbps
Bluetooth LE Lower >100 m 125 kbps to 2 Mbps
LoRaWAN Low 10 km 0.3 to 50 kbps
NB-IoT Low <35 km 20 kbps to 5 Mbps
NFC Low <10 cm 106 to 424 kbps
Sigfox Low 3 to 50 km 100 to 600 bps
6LoWPAN Low 100 m 0 to 250 kbps
802.11/Wi-Fi Medium 100 m to several km (with boosters) 10 to 100+ Mbps
802.15.4/Zigbee Low 10 to 100 m 20 to 250 kbps
Z-Wave Low 15 to 150 m 9.6 to 40 kbps

Table 1: Comparison of various standards for embedded wireless communications. (Image source: Digi-Key Electronics)

Some of these wireless protocols such as Wi-Fi, Bluetooth, Bluetooth low energy (LE), and NFC are already in wide use in mobile phones and laptop computers. Shipping in the hundreds of millions, the RF ICs and modules needed to implement these protocols have become relatively inexpensive. Here are brief summaries for each of the wireless standards listed in the table above:

Bluetooth: Developed initially to wirelessly link companion devices to mobile phone handsets, Bluetooth has become a useful wireless protocol for low-power applications that need relatively short range and moderate data bandwidth of 1 to 3 megabits per second (Mbps). Because of the extensive data protocols and profiles already developed, Bluetooth RF modules are relatively easy to integrate into an embedded application.

Bluetooth LE: Bluetooth LE considerably reduces power consumption and cost compared to Classic Bluetooth while maintaining a similar communication range. It’s aimed at new applications in healthcare, fitness, location beacons, security, and home entertainment.

LoRaWAN: Intended for wireless battery-operated devices in a regional, national, or global network, LoRaWAN targets key IoT requirements of providing secure, low-power, bi-directional communication with mobility and localization services over a wide area. The LoRaWAN specification is a media access control (MAC) layer that can be overlaid on a variety of physical layer (PHY) protocols from satellite networks like Globalsat to terrestrial public and private networks. LoRaWAN provides seamless, long range interoperability among IoT devices without the need for local network support.

Narrowband IoT: Developed to connect a wide range of devices and enable services using cellular telecommunications bands, Narrowband IoT (NB-IoT) is one of a range of Mobile IoT (MIoT) technologies standardized by the 3rd Generation Partnership Project (3GPP). NB-IoT is deployed “in-band” within the cellular spectrum allocated to 4G LTE cellular networks using resource blocks within a normal LTE carrier, or in the unused resource blocks within an LTE carrier’s guard band.

NFC: For portable devices like mobile phones, NFC provides a standardized set of communication protocols that enable two electronic devices to communicate in close proximity (usually less than 10 centimeters (cm)), so it’s strictly a short-range connection. It’s often used for financial transactions such as contactless payment systems and electronic mobile ticketing. Due to NFC’s short range, one of the two NFC communicating devices is usually handheld and portable. Otherwise, a simple pair of wires usually provides a cheaper, simpler communications link.

Sigfox: Low-power objects such as electricity meters or smartwatches that need to be intermittently switched on and need to operate on battery power for years or even decades, can use Sigfox’s proprietary long-range radio interface to occasionally send small amounts of data to the cloud.

6LoWPAN: 6LoWPAN is an acronym of “IPv6 over Low-Power Wireless Personal Area Networks”, and is based on the idea that the Internet protocol (IP) could and should be applicable to even the smallest devices. The 6LoWPAN protocol allows low-power devices with limited processing capabilities to participate in the IoT by defining mechanisms that allow IPv6 packets to be sent and received over radio networks based on the less complex PHY and MAC layers of IEEE 802.15.4 (which also serves as the basis for Zigbee low power RF mesh networks, and several others).

802.11/Wi-Fi: Ubiquitous, fast, and with native support of IP, Wi-Fi radios are relatively easy to integrate into an embedded design to connect a device directly to the IoT.

802.15/Zigbee: The IEEE 802.15.4 standard specifies the PHY and MAC for low data rate wireless personal area networks (WPANs). Zigbee builds on the 802.15.4 standard with a wireless protocol designed to build medium or large mesh networks that link sensors and controllers. More than 2,500 products are now Zigbee certified, and more than 300 million of these products have been shipped.

Z-Wave: Z-Wave was developed as a simple to implement, low-speed wireless protocol that allows a variety of home electronics devices to intercommunicate using a reliable, low-power wireless protocol that easily travels through walls, floors, and cabinets. Z-Wave is a proprietary protocol developed by one vendor and requires a use license. There are now more than 700 member companies in the Z-Wave Alliance offering more than 2400 wirelessly connected, “intelligent” products such as appliances, window shades, thermostats and home lighting.

Most of these wireless protocols are now in ready-to-use modules that are certified to regional standards, making life much easier for embedded designers who need to add wireless communications to their designs. While Part 2 of this article will provide examples and descriptions of many such modules, here are three quite different wireless protocol modules to whet the appetite:

ESP-WROOM-32 from Espressif Systems

The ESP-WROOM-32 is a Wi-Fi/Bluetooth/Bluetooth LE module with a built-in processor that targets a wide variety of applications ranging from low-power, low data rate sensor networks to more demanding tasks operating at higher data rates, including voice encoding, music streaming, and MP3 decoding. The module measures only 25.2 x 18 millimeters, yet comes with a 32-bit dual core processor, allowing it to act as a host controller where necessary. It can also wirelessly enable another CPU operating as a slave, using a variety of interfaces including SPI and I2C.

Image of Espressif Systems’ ESP-WROOM-32 Wi-Fi-BT-BLE MCU module

Figure 2: Espressif Systems’ ESP-WROOM-32 Wi-Fi-BT-BLE MCU module operates at speeds to 150 Mbps. (Image source: Espressif Systems)

EWM-W151H01E 802.11b/g/n 1T Mini PCIe card from Advantech Corp.

The half-size EWM-W151H01E 1T Mini PCIe card implements the IEEE 802.11b/g/n Wi-Fi standards and operates at data rates up to150 Mbps. The card’s plug-in Mini PCIe form factor, along with drivers for Windows and Linux, means that this card module is most suited to embedded PC (x86 processor) designs.

Image of Advantech EWM-W151H01E 1T half-size Mini PCIe card

Figure 3: The Advantech EWM-W151H01E 1T half-size Mini PCIe card implements the IEEE 802.11b/g/n Wi-Fi standards. (Image source: Advantech)

XBC-V1-UT-001 XBee cellular LTE Cat 1 module from Digi International

The XBC-V1-UT-001 cellular LTE Cat 1 module from Digi International’s XBee series of programmable RF modules connects to Verizon’s LTE cellular network for a few dollars per month. It can serve as a wireless embedded control processor that’s programmed in MicroPython. It can also serve as a simple cellular modem with a UART connection for other embedded CPUs. Digi International also offers the XKC-V1T-U XBee 4G cellular dev kit that includes the cellular modem, cables, a power supply, and a carrier board that breaks out the modem’s ports to connectors.

Image of Digi International’s XBC-V1-UT-001 XBee cellular LTE Cat 1 radio module

Figure 4: Digi International’s XBC-V1-UT-001 XBee cellular LTE Cat 1 radio module puts an embedded system on Verizon’s cellular communications network for a few dollars per month. (Image source: Digi International)

Conclusion

Designers continue to respond to demand for some form of wireless connectivity for their embedded system designs. However, the number of wireless options continues to expand causing a certain degree of confusion.

To cut through this confusion, a designer must first develop a clear picture of the design requirements. So, armed, they can use the above discussion to quickly match those requirements to the various wireless connectivity profiles of range, power, and data rate. This can greatly simplify and accelerate the process of selecting from the ever-growing wireless menagerie.

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