New-Tech Europe Magazine | April 2019

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

Figure 2: BLE modules like the MBN52832 device can support the most demanding Bluetooth low energy IoT applications

buried sensor nodes. EC-GSM can handle signals that are 20 dB weaker than standard GPRS and supports datarates up to 10 kb/s. The arrival of Long Term Evolution (LTE) has brought with it several options for IoT connectivity, thanks to the 4G protocol’s more efficient use of RF spectrum. The first to arrive was Cat-M, which supports 1Mb/s datarates for both the uplink and downlink using half-duplex communication. Cat-M also provide energy-saving enhancements. Compared to the core LTE protocol used by mobile phones, Cat-M can operate with fewer updates from the base station. The frequency of updates can be reduced to the point where the sensor node only has to wake up every ten minutes or so, which can greatly preserve battery life for devices that monitor slow- changing conditions, such as soil moisture. Narrowband-IoT (NB-IoT) provides further enhancements to energy efficiency. NB-IoT uses a much narrower transmission band than

full LTE:1.4 MHz rather than 20 MHz. This is accompanied by a reduction in transmit power to further improve battery life. In an ongoing process of enhancements, Release 14 of the LTE standard by 3GPP, has further improved efficiency by supporting techniques to allow nodes to disconnect rapidly after a transmission to reduce leakage power. Datarates of 50 kb/s on the downlink and 20 kb/s on the uplink are possible, extending to 50 kb/s if multi-tone signalling is employed for the uplink. Thanks to the rich selection of protocols suitable for IoT use, whether operating in a short-range or wide-range scenario, developers and integrators can be sure to find one that fits the application. Independent module suppliers such as Murata can advise on which makes sense for each situation and provide solutions based on the best available silicon on the market.

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