Making sense of wireless connectivity options for IOT applications

Rapid advances and massive growth in internet-connected devices has driven development in the range of connectivity standards and internet protocols that are now available to developers. Which protocol you build-in is entirely dependent on the needs of the device you’re designing – in terms of range, coverage and data rates. This article compares some of today’s key protocols to help you select the best fit for your application, and highlights some forthcoming developments to watch out for.

Firstly, you need to consider the range your device requires as it’s pretty much the most important factor in determining the right connectivity option. Take a look at our IoT Wireless Radio Standards table (above, and linked as a downloadable file at the end of this article) to compare protocol ranges at a glance. Lots of devices transfer data to and from the Cloud using a gateway with a broadband connection. Gateways are ideal for using short-range protocols operating at reasonably low transmit power levels, but in many cases it will be too difficult or expensive to implement a gateway. This might be where a set of sensors are deployed along a length of train track, or around a large reservoir for example. For these sorts of applications the sensors would be too widely dispersed to access a gateway reliably.

At the moment, widely dispersed sensors or meters are more likely to make use of cellular connections, or use proprietary protocols such as 868MHz in the unlicensed sub-gigahertz bands. This is an area in which major changes are taking place due to the need for specific standards for IoT connectivity and the strategic changes that are being made by cellular operators. Operators are looking to get the most out of their licensed spectrum allocation and are expected to switch existing sub-gigahertz GSM networks over to supporting LTE due to its higher spectral efficiency.

LTE bands

With requirements for IoT and M2M communications ramping up rapidly, several LTE-based cellular protocols have been proposed to provide support, but these are changing and evolving frequently.

Cat-M offers a less complex type of LTE that is suitable for IoT devices in the shorter-term, offering access to the already widespread cellular network with data rates of up to 1Mbit/s. However, the 3GPP-defined Narrowband-IoT (NB-IoT) is likely to provide support to IoT networks at lower operational costs over the coming two to three years. This will improve access to difficult locations, like underground meters, and will use lower data rates of around 200kbit/s, so it is well worth keeping NB-IoT in mind as a longer-term option.

LoRa® and SIGFOX

Moving into the sub-1GHz range and operating primarily in the unlicensed spectrum, SIGFOX and LoRa® offer alternative options to cellular connections in both transceiver design and cost/pricing models. Instead of charging on a data-usage basis like traditional cellular operators, commercial operators supporting the unlicensed spectrum offer flat-rate models as low as $1 per device per year.

LoRa® technology was developed by Semtech and allows IoT users to access the internet using a network of base stations. This offers more control and the potential for lower operating costs, but does incur hardware costs to get set up. The open source nature of LoRa® provides huge flexibility however, and opens up opportunities to share costs and benefits. Take ‘The Things Network’ in Amsterdam for example. This is a LoRa® network providing long range internet access city-wide and was set up in just six weeks through crowd-funding. The exercise is being repeated in cities around the world, with gateways being placed by community members to expand the network and increase coverage. Anyone – business or individual – can place a gateway and in less than a year since The Things Network Amsterdam was launched, 100 cities worldwide now have The Things Network present.

LoRa® technology is supported by devices manufactured by STMicroelectronics, Microchip and Semtech, and offers access to below-ground devices like water or parking meters, unlike traditional radio systems. LoRa® has a transmit range of 5km in urban areas, and up to some 15km in rural environments. Its spread-spectrum modulation scheme makes it resilient to interference from other unlicensed band users and LoRa® data rates range from 300bit/s to 50kbit/s making data transfer speed similar to that of existing GPRS connections. LoRa® overcomes one of the major issues for M2M communications in IoT applications, enabling communications over long ranges using very low power levels.

In contrast, SIGFOX uses an ultra-narrow band transmission technique to reduce and limit power, allowing for a wider range of up to 50km in urban areas with lower data rates of between 10bit/s and 1kbit/s. SIGFOX offers a unidirectional link in contrast to most other protocols which can be used to minimise power consumption of the IoT node. This is because the RF transceiver doesn’t need to wake up and listen for incoming communication, but it also means node software can’t be updated remotely with a conventional SIGFOX transceiver, another radio will be required. However, because the requirements of SIGFOX transmissions are relatively simple, a number of RF transceivers designed for the unlicensed ISM band are able to handle them.

In terms of manufacturer take up, SIGFOX is used for IoT connectivity by onsemi  AX- SIGFOX single chip solution and Arrow Electronic’s SmartEverything prototyping development board for M2M and IoT applications.

IEEE 802.15.4

Possibly better known for the popular protocols that use this channel, Wi-Fi in particular, the 2.4GHz unlicensed band has become the primary choice for wireless networking. This band provides the spectrum for a number of newer protocols designed specifically for the IoT including Thread, 6LoWPAN, Zigbee and Wireless HART.

The underlying standard for these protocols is IEEE 802.15.4 which supports a transmit range of up to 10m with a transfer rate of 250kbit/s. The core IEEE 802.15.4 can operate on sub-gigahertz unlicensed bands in addition to 2.4GHz.

The 6LoWPAN protocol effectively adds an extra set of upper layer protocols to the core IEEE 802.15.4 standard to make it compatible with the Internet Protocol (IP), allowing standard IP-based cloud communication to reach IoT edge devices using a range of standards, including HTTP, TCP, MQTT and COAP. 6LoWPAN uses header compression and other data encapsulation techniques to minimise protocol overhead on IoT data transfers.

6LoWPAN supports mesh networking to increase the maximum distance between nodes and a gateway. Using a mesh networking topology allows nodes that are too far away from the gateway to relay packets through devices until they can reach the gateway directly. Mesh networks have the added benefit of automatically configuring new devices to leverage usage patterns already learned by the system because they analyse the routability of the network dynamically.

Thread builds further security functionality like encryption and authentication needed for some IoT applications on top of 6LoWPAN. Usually a simple software upgrade is all that’s needed to run Thread on devices supporting IEEE 802.15.4, including devices from Silicon Labs, a founding board member of the Thread Group.

Bluetooth

Another key standard to consider is Bluetooth. With its abundant support in tablets, smartphones and laptops it already provides a key mechanism for configuring and controlling IoT devices via apps. The standard has seen enhancements allowing Bluetooth to become a key protocol even for IoT applications that don’t rely on smartphone connectivity. Bluetooth Smart supports nodes with greatly reduced power consumption for transfers of small amounts of data making the short-range network protocol better suited to IoT applications. In addition, a change is expected to be made to the Bluetooth Smart specification this year (2016) that will quadruple the normal transmit range, trading off improved range against bitrate. Bluetooth Smart has a standard bandwidth of 1Mbit/s and the new, adaptive protocol will allow nodes that are closer together to employ higher bitrates to as much as double the standard bandwidth available.

Mesh networking could help Bluetooth devices communicate over longer distances too. Version 4.1 released in 2013 introduced the Scatternet concept and the mesh networking planned for Bluetooth expands this further. Scatternet allows each node to switch between slave and master modes in order to pass packets to other slaves/masters until they can reach the destination transceiver. In addition, recent changes to the Bluetooth protocol allows interaction with devices using the 6LoWPAN wireless protocol which will help to extend the coverage of a network.

IEEE 802.11ah

Lastly, what is next for Wi-Fi? Wi-Fi as we know it supports much higher data rates than most of the IoT protocols, but these can be harnessed and used for things like the transmission of security videos.

The Working Group of the IEEE responsible for Wi-Fi is working on a new version – IEEE 802.11ah – that will massively reduce power consumption, extending the transmission range in exchange for lower data rates – around 100kbit/s over a distance of 1km is expected.

To sum up, there is a rich variety of protocols already available to IoT developers, with some great advances to come in the not-too-distant future. Whatever device you’re designing today – or dreaming about inventing tomorrow – there’s a protocol just right for your application now, plus the latest set of next generation protocols are only just around the corner.