Most of the current machine-to-machine (M2M) connectivity is working over the 2G GPRS standard, requiring 2G EDGE coverage and SIM cards. As operators phase out some 2G networks, in part to reduce cost, new standards have emerged in the past five years: Zigbee, LoRa, LTE-M, Wi-Fi 802.11ah (HaLow) and 802.11af (White-Fi).
Depending on the application, security needs and cost factors, some are better than others.
Here are the most popular standards, their features and advantages:
Zigbee: proprietary, short-range, inexpensive and basically secure
The Zigbee trademark is owned by the Zigbee Alliance, a group of companies that maintain and publish the Zigbee standard. The alliance publishes application profiles that enable the creation of interoperable products using the specification.
According to their website, hundreds of millions of devices using Zigbee technology are deployed worldwide, with over 2,200 products certified. Zigbee was conceived in 1998, standardized in 2003 and revised in 2006. Its name comes from the waggle dance of the honey bee.
Zigbee is a very popular option for IoT device manufacturers. It provides most of the basic features (connectivity, range, security) that they look for and, as an open-industry standard, it allows interoperability with any Zigbee-certified device.
The biggest complaint from OEMs is the cost of joining the alliance, the certification and lack of open GPL license. OEMs must become members of the alliance to use its technology.
Zigbee is a low-power, low-data-rate, close-proximity ad hoc wireless network, supporting mesh network topology. It is especially suited for home and office applications, where devices are located in a small area. It only works in distances from 10 to 100 meters line-of-sight. It uses the IEEE 802.15 WPAN specification, providing data rates of 250 kbps, 40 kbps and 20 kbps.
The low data rates and proximity allow devices using smaller batteries to last for years rather than weeks. And with Zigbee Pro’s Green Power feature, it is possible to operate battery-less devices, such as door locks, switches and environmental sensors.
Last year, Zigbee celebrated its 15th anniversary and launched its anticipated IoT basic language, Dotdot, which makes it possible for smart objects to work together on any network. Dotdot is not limited to Zigbee; it can work together on Zigbee, IP and other networks. Recently, the Zigbee Alliance also announced Dotdot over Thread, an IPV6 protocol to connect home devices.
LoRa: proprietary, long-range, inexpensive and secure
Similar to Zigbee, LoRaWan is a proprietary technology, open global standard, defined and controlled by the LoRa Alliance, a nonprofit organization.
The main difference is that, while Zigbee is a short-range IoT protocol aimed at connecting a number of devices in close proximity, LoRa focuses on wide-area networks.
Especially suited for long-range communications, LoRa uses unlicensed sub-gigahertz radio frequency bands like 169 MHz, 433 MHz, 868 MHz (Europe) and 915 MHz (North America). The low bands allow for data rates from 0.3 kbps to 50 kbps.
LoRa is the preferred choice for deploying a large number of non-critical sensors and control devices in large areas. Its use of unlicensed radio makes it the perfect choice for city-wide environmental sensors, streetlamp control and monitoring, basic control units for agricultural farms and monitoring of small objects.
The LoRa Alliance argues that the standard can also be used for critical infrastructure. Confidential personal data or critical functions for society need secure communication. That is why the protocol can use 64-bit and 128-bit keys for network, application and device encryption.
Marketed as the new standard for most M2M applications, its use of unlicensed radio based on picocells and gateways that can be installed independently of the cellular carriers makes LoRa very attractive to OEMs deploying IoT devices in a wide area.
Like Zigbee, LoRaWan is not a fully open protocol and requires membership in the LoRa Alliance to be used.
Its main drawback is the lack of hardware security. M2M devices have been using cellular carrier’s Subscriber Identity Modules (SIM) chips that can be used to store and certify encryption keys. LoRaWan uses software-based encryption.
Also, interoperability between LoRa devices is not guaranteed, as every OEM can implement the radio features of the standard in its own operating system.
LTE-M: the cellular carrier’s solution to replace M2M
Long-Term Evolution for Machines (LTE-M) is the M2M industry answer to IoT using secured cellular networks for long-range communications. It is a cellular carrier’s wireless system, backed by the industry association GSMA and the 3GPP standards organization. (LTE is what is commonly known as 4G cellular networks.)
One of the main advantages of LTE-M is the potential for worldwide connectivity, and it is the only system suitable for tracking moving objects over long distances.
According to the GSMA: “The technology provides improved both indoor and outdoor coverage, supports massive numbers of low throughput devices, low delay sensitivity, ultra-low device cost, low device power consumption and optimised network architecture.”
Because it is working over cellular networks, LTE-M can be used to monitor, control and receive information from IoT devices loaded into most forms of transportation, such as trucks, trains, boats, etc. When an LTE network is not available, the system can fall back to WCDMA (3G) or GPRS/EDGE (2G) to maintain connectivity.
LTE-M also provides location services, based on cell-tower positioning, without the need of using satellite-based systems such as GPS or Galileo. This feature is an important cost savings for OEMs that need a basic location system for their devices.
The biggest advantage of LTE-M, however, is security. Cellular-connected devices need to be fitted with a SIM chip. It can be embedded in the circuit board and provisioned at the factory or receive the carrier keys and signature later. Once the SIM is provisioned with the embedded keys, it is not possible to modify those keys without having physical access to the device.
SIMs are secure modules that can provide NSA Suite B AES-256 encryption and Identity Certification.
Another advantage is the ability to remain connected even during a power failure. As it is connected to cellular networks, it doesn’t require an Access Point (AP) and, as long as the IoT device battery is functioning, it can remain connected.
That’s why cellular-based IoT connectivity is widely used for critical applications such as power grids, home and office security, fleet management, etc.
The only catch is ongoing costs. To use the system, a subscription with one of the cellular carriers is required, and a SIM needs to be present in every connected device.
White-Fi and HaLow: low-cost, unlicensed spectrum, extended range, but low-security
IEEE 802.11af (White-Fi) and IEEE 802.11ah (HaLow) are the most sought-after solutions for connectivity. Both use previously licensed spectrum and do not interfere with traditional Wi-Fi signals in the 2.4-GHz and 5-GHz bands nor with 2G and 3G cellular networks. Some of the spectrum is shared with some LTE channels used in the United States.
White-Fi makes use of the digital dividend of frequencies freed up when broadcast television moved to digital terrestrial and some of the previous UHF channels ceased to operate. The use of the digital dividend spectrum is regulated differently in the U.S. and Europe, and the connected devices need to look for available frequencies at regular intervals.
HaLow extends Wi-Fi into the 900-MHz band, enabling the low power connectivity necessary for applications, including sensors and wearables. Because this frequency is freely available for basic communications, HaLow is the preferred Wi-Fi standard for IoT.
The biggest problem for HaLow is that unlicensed spectrum is not harmonized across the globe: HaLow operates at 900 MHz in the U.S., 850 MHz in Europe and 700 MHz in China and does not even have operating spectrum in many countries.
Due to the nature of the low-frequency bands, neither technology is suitable for high-speed or high-volume data transmission. They can be used, however, to provide connectivity for a significant number of devices deployed in a wide area.
Low speeds are acceptable over these distances because of the lack of interference. HaLow provides for data rates as low as 150 Kbps.
Sub-1-GHz connectivity is also critical for the new generation of low-power-consumption devices, with a battery life of several years instead of weeks. That battery performance is necessary for the billions of sensors and monitoring devices deployed in cities around the world.
HaLow also offers several power-saving features, such as Target Wake Time (TWT) and Traffic Indication Map (TIM), enabling the IoT devices to communicate at selected intervals, thus saving battery power.
Last year, the IEEE introduced another Wi-Fi standard for IoT: 802.11ax. Its advantage over HaLow is the use of the 2.4-GHz and 5-GHz frequency bands, common on most Wi-Fi access points.
Overall, 802.11ax is better-suited to local-range IoT than HaLow. The expectations for 802.11ax are high due to its network access enhancements, which will naturally provide secondary benefits of IoT enablement.
Security is the biggest issue. Wi-Fi lacks the protection of the secure element and hardware encryption provided by SIMs on cellular networks. To deploy hundreds or thousands of wireless sensors in a wide area, however, White-Fi and HaLow can provide low-cost connectivity and good performance.
What is the best option for you?
It depends. If you’re looking for a low-cost solution to connect non-critical devices in close proximity, then Zigbee or White-Fi are the probably the best options. Zigbee’s DotDot software will help you develop a solution compatible with other Zigbee devices, but you’ll have to join the Zigbee Alliance to use it.
For long-range applications, Lo-RaWan or LTE-M are the best options.
LTE-M is the most robust and secure, as well as being backed by cellular networks, but it’s probably the most expensive. It is the only standard that guarantees truly worldwide connectivity and can be used for cargo and fleet management.
LoRa is a good solution for local medium-range networks that don’t require positioning services or NSA-grade security.
