IoTSensor.io lists IoT devices for the following output protocols: Bluetooth, Ethernet, LoRa™, NB-IoT, Sigfox, WiFi, Z-Wave, Zigbee. Bluetooth, Z-Wave, Zigbee are short range wireless while LoRa™, NB-IoT, Sigfox are long range.
The main factors to consider when choosing a protocol are:
- Throughput – Most IoT specefic protocols are designed to send small amounts of data infrequently while general purpose protocols such as WiFi support much greater data throughput.
- Cost of Data – Whether a data subscription is required or is free to use.
- Cost of Sensor – The complexity of the hardware required to support the protocol affects the cost of the sensor.
- Latency – The time to initially connect and the time to get data from A to B.
- Efficiency – Protocols that send small amounts of data quickly are more efficient and make better use of the bandwidth.
- Reliability – Protocols have different reliability when it comes to contention with other sensors and receiving devices.
- Interference – There’s varying susceptibility to wireless interference across protocols.
- Availability – Some types of sensor are only available with particular protocols and some protocols are only available in some countries.
- Receiver – Protocols have specific requirements for receiving hardware and software that can have their own varying costs and availability.
- Distance – The protocols have different ranges and some of them can be meshed to increase range.
- Scalability – The number of sensor devices supported.
- Security – Security varies across protocols, both for the sensor itself and the data in transit.
- Power Source – Some protocols are optimised for use on battery.
- Interoperabilty – How devices and receivers can be interchanged or second-sourced varies across protocols.
Bluetooth was designed for power efficient transfer of small pieces of information, relatively slowly at typically hundreds of Kbits/s. There’s no cost to use the wireless spectrum and sensors are inexpensive, down to $10, due to the use of System on a Chip (SoC) provided by four manufacturers, Dialog, Nordic, Texas Instruments and NXP. Latency is low and of the order of tens to hundreds of milliseconds. The protocol is very efficient with Bluetooth 4.0 advertising typically taking only 1ms. The protocol uses multiple frequency channels and doesn’t rely carrier sense multiple access (CSMA) thus making it suitable for electrically noisy environments. There’s a wide range of sensor types. Key strengths of Bluetooth are that it can be battery powered and is that it can be detected using a wide range of devices including smartphones, gateways, desktops, laptops and single board computers such as the Raspberry Pi. Bluetooth is low range, typically up to 50m but there are devices that can achieve hundreds of meters. Bluetooth can be meshed to send data across longer ranges across a site. The maximum number of devices in the same say 50m2 area, depends very much on how often they are set to advertise. This can be from every few hundred milliseconds to multiple hours leading to scalability of tens to thousands of devices. Most sensors send sensor data unencrypted. Bluetooth mesh uses double encryption.
Few IoT devices use Ethernet. It supports relatively high throughput and being wired is reliable. It’s fast at up to 100 megabits per second and has low latency. The required hardware is moderately complex for simple sensors so device costs are moderate. Ethernet IoT devices usually need to be mains powered. The range is 100m but this can be extended site wide using extenders.
LoRa™ is a patented protocol while LoRaWAN® is a higher level communication protocol that runs on top of LoRa that provides extra features. Most sensors use LoRaWAN and a few LoRa. LoRa has a low bandwidth of typically between 300bit/s and 50kbit/s and is designed for small amounts of data sent infrequently. LoRaWAN has different classes of devices with different power vs latency tradeoffs. LoRa uses the ISM bands that are 868 MHz in Europe, 915 MHz in North America and 433 MHz in Asia. LoRa and LoRaWAN are license exempt but this doesn’t mean you can use this frequency as you like. For example, in Europe, EU ETSI EN300.220 (pdf) defines a duty cycle for how long a transmitter can transmit. LoRaWAN® imposes extra, more strict, duty rules and also requires the use of a LoRaWAN® server. The duty cycle rules reduce wireless contention and usually ensure reliability. LoRa uses chirp spread spectrum (CSS) modulation that spreads a narrow-band signal over a wider channel bandwidth resulting in a signal with high electrical noise immunity. There’s a wide range of sensors with moderate cost. The range is 10Km but can be more in line-of-sight applications and substantially less, 5Km to 7Km in urban environments. LoRaWAN packets are 128bit end-to-end encrypted. LoRa sensors can be battery powered. LoRa has good scalability of typically maximum 50 thousand nodes per receiver.
Narrowband Internet of Things (NB-IoT) has been developed by 3GPP and is typically provided by traditional cellular operators. As such, it requires a subscription. It’s designed for low power, low throughput up to 127 kbit/s and has a latency of 1.6s to 10s. Being a commercial, paid service it has high reliability. The data is encrypted using standard LTE encryption. There’s no maximum duty cycle or maximum messages per day. NB-IoT has very high scalability of the order of 100K devices per cellular base station. Coverage is poor in some countries where it has has yet to rollout. The maximum range to a base station is typically 10Km but depends on the terrain. While NB-IoT can be battery powered, it uses more power than LoRa and Sigfox due to synchronous communication, QoS handling and OFDM/FDMA access modes that require more battery current. The relatively few available sensor devices currently tend to be complex and costly.
Sigfox runs a complete, commercial, IoT solution in tens of countries and is under continual rollout worldwide. Proprietary base stations with software-defined radios connect to the servers using an IP-based network. Throughput is around 100 bps. Sigfox uses the same unlicensed ISM bands, 868 MHz in Europe, 915 MHz in North America and 433 MHz in Asia as LoRa. It uses ultra-narrow band and short communications to provide for a high interference immunity. Sigfox has good scalability of typically 50 thousand devices per base station and an excellent range of up to 40Km. There’s a good range of sensor devices. Sigfix sensors can be battery powered.
Few IoT devices use WiFi. It uses similar 2.4GHz frequency bands as Bluetooth so has a similar range of up to 50m. However, WiFi uses carrier sense multiple access (CSMA) that listens to the channel before transmitting and waits until a free channel is observed which can produce very long latency in congested areas. WiFi requires significant power and can’t be battery powered for longer periods of time. Look out for future devices using a new WiFi standard, 802.11ah, named it HaLow™ that operates on the 900MHz band.
Z-Wave is a popular wireless technologies used for home IoT products and provides throughput up to 100kbit/s. It has a range of up to 40 meters and uses unlicensed industrial, scientific and and medical (ISM) bands. It operates at 868.42MHz in Europe, 908.42MHz in North America and other frequencies in other countries depending on their specific regulations. Z-Wave networks can have a maximum of 232 devices and is a proprietary design using AES-encryption. It can relay data to form a mesh. Z-Wave chips are optimised for battery power.
Zigbee uses similar 2.4Ghz bands as WiFi and Bluetooth and hence has a similar range of 50m to 100m. Zigbee can form a mesh network to relay data over larger area. It has a low power, low maximum data rate of rate of 250 Kbit/s. Data is secured using 128-bit encryption. Latency is low, typically 40ms to 200ms and remains low for mesh. The Zigbee network can address up to 65536 different devices but large networks require repeaters to ensure connectivity. Devices must have a battery life of at least two years to pass ZigBee certification.