Long range wireless solutions: Wireless technologies for IoT networks
Long-range IoT wireless technologies form the basis for a low power wide area network (LPWAN). In these types of networks, end devices with low energy consumption – typically sensors – are connected to gateways that transmit data to other devices and network servers. The network devices assess the received data and control the end devices. Accordingly, the protocols are specially designed for long-range capabilities, low-power devices, and reduced operating costs.
For a long time, cellular wireless technologies have had a monopoly position in long-range applications that can connect a device directly to the Internet without a gateway. Thanks to the well-established infrastructure of base stations worldwide, end products only require a SIM card to communicate with the cloud. After successful initialization and registration with the network provider, data can be sent and received.
Further development of cellular wireless technologies in the past generally focused on increasing data transmission rates. LTE Advanced, for instance, now enables a transmission rate of up to 3.9 Gbps in the downlink and 1.5 Gbps in the uplink. However, most things in the IoT do not transmit such huge amounts of data (the majority of them require less than 100 bpm) and higher data rates result in higher power consumption for end devices. The focus of successful communication technology is therefore on long ranges, reliable communication, and low power consumption for extended battery life.
With these goals in mind, the Third Generation Partnership Project (3GPP) has created the LTE machine-type communications (LTE-M) standard. LTE-M transmits in the licensed sub-GHz band at between 700 MHz and 900 MHz. The downlink and uplink data rates are roughly 1 Mbps. The low power consumption approach could help to extend the life of battery-powered end devices up to between 10 and 20 years. LTE-M also uses the existing cellular wireless infrastructure, providing excellent coverage, and operates on the well-known licensed spectrum, making it more safe and robust – ideal for services with high quality requirements.
One disadvantage of LTE-M, however, is the high cost of utilizing licensed cellular wireless networks. In this case, each end device requires its own SIM card, which results in added installation and maintenance costs, as well as running expenses that are, on average, significantly higher than those for comparable technologies. Moreover, the current SIM card service for LTE-M is comparatively complicated. This problem could be addressed in the future by the embedded SIM (eSIM) card, which, as the name suggests, is embedded in the end device and can be easily reprogrammed without having to open the actual device.
SigFox is a tailor-made solution for long ranges (30-50 km in rural areas, 3-10 km in urban areas), low data rates (12 bytes per message, max. 140 messages a day per end device), and preferably low power operation. SigFox uses the sub-GHz band (868 MHz in Europe) and employs BPSK modulation with ultra-narrowband technology. End devices equipped with SigFox technology transmit data to SigFox base stations, which then forward the data to SigFox cloud servers. This is where the data are processed before the results are sent back to the respective end devices for visualization.
Unlike LTE, the SigFox infrastructure is still under construction. The company works with large network operators around the globe and continues to deploy and operate its own networks in various regions, such as France and the USA. SigFox currently offers service coverage in France, Portugal, Spain, the Netherlands, and the UK. The company is further ramping up its rollout plans for Belgium, Denmark, Germany, Ireland, Italy, Luxembourg, and the USA. In the USA alone, it plans to expand from 10 to 50 cities in just six months. Nevertheless, the technology is not yet recommendable for countrywide or international projects.
A SIM card is not required for SigFox. The price depends on how many messages are sent per day and the volume of these messages. Customers generally pay between one and ten euros a year to keep an individual end device active.
LoRa is very similar to the SigFox technology, as LoRa also uses the sub-GHz band (868 MHz in Europe), achieves similar ranges (up to approx.15 km), and is economical due to low data rates ranging from 0.3 to 22 kbps. In contrast to SigFox, LoRa utilizes chip spread spectrum technology to set the ratio between bandwidth and bitrate.
The LoRa Alliance was established in 2015 to standardize and further develop LoRa. Besides the LoRa developer Semtech, numerous chip and module manufacturers, software businesses, and network operators are now members of the LoRa Alliance.
To equip end products with LoRa, an annual license fee of $3,000 must be paid to the LoRa Alliance. There are no other fees payable on top of this, and LoRa, just like SigFox, does not require a SIM card.
In terms of infrastructure, the situation for both newcomers is about the same: The LoRa Alliance members are working intensively on expanding coverage, particularly in Europe and the USA, but also in large Russian cities. Thanks to an interactive network, each user can help to expand the LoRa infrastructure. And users who do not want to wait for improved coverage can also set up a private network using LoRa technology, if the application enables it.
Compared to LTE-M, both LoRa and SigFox offer cost benefits: At present, the hardware for a module costs about €10. Added to this is the $3,000 annual license fee for LoRa, while SigFox users can expect to pay between one and ten euros a year for each end device. The hardware costs alone for LTE-M are much higher than those for SigFox and LoRa, and added to this are the running expenses for the SIM cards and the costs for replacement items.
The LoRa and SigFox wireless modules for end devices ensure very low power operation and can transmit over large distances with strong in-building penetration characteristics. The biggest stumbling block for both technologies is, however, the infrastructure, which is still a work in progress.
It has turned into a neck-and-neck race between LoRa and SigFox, and it will be interesting to see who wins, or what new competitors might enter the fray. The ability to allow the creation of private networks is obviously particularly advantageous to LoRa. It might not be suitable for every application, but ensures LoRa a certain degree of independence no matter what the outcome of the race.