By: Richard Emmerson
Senior Consultant, Communications Systems

3rd May 2017

So you have a great idea for an internet connected ‘Thing’. You’ve done the business plan, you’ve raised some investment, or maybe you’re staking your own money. All you have to do now is connect your ‘Thing’ to ‘The Internet of Things (IoT)’ and get the product into the market.

Well, there are a few things you should consider before you jump in.

How will the ‘Thing’ connect?

Surely that’s simple, everyone’s using LoRa (long-range, low-power radio), so I can buy some LoRa modules, connect them to my ‘Thing’ and I’m done.

Well, yes and no.

Range, Data Rate & Power Consumption

With any communications system, there is a direct trade-off between range, data rate and power consumption. LoRa is potentially a great system for IoT. When properly designed, it can achieve long range (typically 2 km in urban areas and line of sight in rural areas) and have a battery life that can last for years. However, data rates are limited to between 0.3 kbps to 50 kbps; with the longest range achieved at the lowest data rate. In the EU 868 MHz band, the duty cycle is also limited to 1%, meaning, at the lowest data rate, only 51 user bytes can be sent every 245 seconds. This is fine for a smoke alarm but unsuitable for a security camera.

For higher data rate applications, a 3G or 4G modem module may be a better choice, provided the power is available. For power limited systems, there is also the Narrowband IoT system, which uses the 4G mobile network with data rates between 20-250 kbps and offers impressive battery life.

What about base stations?

LoRa can be used in a peer-to-peer mode (communication between nodes). To connect to the internet though requires some kind of base station. This could be a local base station installed in the home or office, or a wide area base station (LoRa-WAN). You might choose to supply customers with their own low-cost base stations, or take advantage of public networks such as ‘The Things Network’.

An alternative may be to use the ’Sigfox’ system. This has similar performance to LoRa but for a small subscription fee accesses an international network of base stations owned and managed by Sigfox. Unlike Sigfox and cellular systems, LoRa has the advantage that if there is no coverage then you can simply add your own base station.

What about the Antenna?

The antenna is a key part of any wireless system and is an area where many developers face problems. In order to work efficiently, antennas need an effective area which is made up of the antenna itself and the circuit board it is connected to. Look carefully at the datasheet for that tiny 868 MHz ‘chip’ antenna and you are likely to see that it requires a PCB of approximately 90 mm length.

However, this poses a problem for small devices operating at 868 MHz, as the antenna is unlikely to be efficient, and that 2km range you expected just reduced to 500 m or less. The antenna may also become de-tuned by the presence of breaks in the PCB ground plane, nearby components and caseworks require a matching network to compensate for these effects. For really small devices, it may be worth considering Bluetooth, which with its higher operating frequency of 2.4 GHz requires a smaller PCB, and, with the release of Bluetooth 5, can be used for local area networks.

So that’s it?

Well, not quite. LoRa and Sigfox use the licence free 868 MHz ISM band in Europe and 915 MHz band in the US. Both of which are prone to interference from other users. There is also the platform, encryption, data ownership, and regulatory approvals to consider.