Sigfox uses ultra-narrowband transmission to extend its range to as much as 50 km in rural areas. Whereas LoRA is designed to support bidirectional communication, Sigfox is optimised for low-datarate transfers in one direction – usually from the sensor node to the server. Datarates range from 10 b/s to 1 kb/s. Sigfox is not completely unidirectional: the protocol supports acknowledgement packets so the sensor node can determine whether a communication has been received, supporting applications such as security alarms.
One advantage of Sigfox’s focus on one-way data transfers is that it can help preserve power on the sensor node, thus extending battery life. If the node only has to wait for acknowledgements, which are received very quickly after transmission, there is no need for the node to wake on a regular cycle to listen for downlinks from the gateway.
Whereas LoRA provides the option for users to operate their own gateways, all communications on Sigfox pass through the company’s own gateways. Although it has less operational flexibility this has the benefit of providing users with a single supplier that provides network support in a large number of countries.
Cellular connectivity is already widely used for machine-to-machine applications. In recent years, the industry has augmented the basic GPRS offerings with a variety of protocols that support either higher datarates or lower-power operation. A key advantage of cellular connectivity is that operators are able to manage congestion and interference much more readily than is possible with unlicensed spectrum, which improves long-term reliability. The open nature of the protocols themselves provides a rich array of compatible silicon and RF modules.
The first change came with Enhanced Coverage GSM, which improves the ability of cellular signals to reach more distant nodes or connect to buried sensor nodes. EC-GSM can handle signals that are 20 dB weaker than standard GPRS and supports datarates up to 10 kb/s.