As LoRa is actually rising in France with different announce from 2 of the main cellular operators deploying the network, it is a good time to have a post on what it is, how it works and what differs compared with SigFox.
LoRa has been created by a french startup Cycleo (cocoricco) and was acquired by semtech in 2012 according to wikipedia LoRa wan post. LoRa is a communication technology : it means you can compare LoRa to Wifi, Bluetooth, Ethernet : it is a way to move information from point A to point B. LoRa is a radio-frequency solution allowing long distance communications (couple of miles – 1x km) with a minimum of power.
You can use LoRa at a low level mode making point to point communication based on the radio stage (like you can do with Ethernet or Wifi technologies) at this level you can benefit a long range radio solution for private use. The main use of LoRa is to use it in a LoRaWAN environment.
LoRaWAN is a structured network where with an operator managing this network. We can imagine LoRa wan as an Wifi environment with access point and gateways to Internet. LoRaWAN 1.0 has been released on June 2015
LoRa is based on opened radio-frequency communications, different frequencies are used depend on locations:
- 430 Mhz – valid for Asia
- 780 Mhz – valid for China
- 433 Mhz – valid for Europe
- 866 Mhz – valid for Europe
- 915 Mhz – valid for USA
LoRa supports different Data Rates and offer a large radio link budget over 160dB. The power consumption is about 40mA during transmission and 10mA during reception. It allows a wide coverage : about 2.5Km from antenna inside a city and up to 15km in a countryside.
LoRa is based on a Spead Spectrum technology this technology helps to reach long distance over noise boosting up to 10x the distances obtains with classical transmission systems. It also have a good shifting frequency immunity. LoRa sound to have good results on movement. It uses wide-band linear frequency modulated pulses. Frequency increase or decrease to encode the information.
The key point of the LoRaWAN network is the GatewayHost, this component is like a Wifi Access Point for the network. It manages the remote devices (sensors, things…) distributing channels and data-rates from 0.3Kbs to 50Kbps based on the quality of the signal. The Gateway Host also manage encryption in the device to network communication with 3 level of keys : Network / App / Device. This sounds a device will have to manage encryption keys in its communication depends on network it is connected to ; keys are managed over the air.
DataRate is driven by the network but should make sense in a mobile environment as based on historical transmissions so device and lock that feature to low bandwidth on movement but activate it when fixed to reduce transmission time to its minimum and preserve batteries.
Device address is managed by the network and depends on the network your are connected to. The global address of the device is a 25b device number + a 7b network number. A device contains an application identifier, hardcoded in the device corresponding to the application and by-the-way to the owner of the device.
Every device have its own device Id based on IEEE EUI64 address space.
LoRaWan defines 3 class of communications ; all are bidirectional :
- Class A : sound like a sigfox device : the device will transmit data (uplink) on its own timing then listen for a downlink messages. Downlink messages are queued until the next device uplink communication. This mode is power saving.
There are two downlink windows after an uplink, the time between the end of uplink and start of downlinks and the duration of the downlink slots are network parameters. The timing starts and duration is configured over the air by some specifi frames. The default are 1 second after transmit then 1 second after the first receive window.
An uplink message can be sent with a acknowledgment request or not. The network is able to indicates it have some pending downlink message to transmit.
- Class B : sound like a beacon device : the device will listen for downlink data on regular basis and predictable periods. That way is is possible to send it data on predefined time-slot. This way we can optimize battery consumption by not having to emit unnecessary messages and consume too much power.
Time synchronization as given by the gateway on regular basis. A beacon is regularly sent by the network to sync the clock, the device will switch in reception expecting a ping message but will stop listening as soon as it get network sync and no ping. On a predefined windows the device will receive a ping it will be able to answer. The device may adapt the received window based on the last synchronization time and risk of clock variations. Beacon period is 128s beacon duration is about 5 seconds.
This mode support multicast messages to reach multiple devices in a time.
The beacon frame content contains the GPS coordinate of the gateways in a 48bits encoding enabling many capabilities for the device to locate itself.
- Class C : is a continuous listening mode making sense for device that are connected to the electrical network. In this mode the network can at anytime transmit downlink message to the device. The device can transmit as in Class A mode.
The risk of loss of a message is not managed by the protocol (in Sigfox you have 3 emits on different frequencies to statistically avoid transmission issues) but the acknowledgment capability allows you to retransmit your message based on device own choices.
Frequencies uses depends on countries and operators. Network can request device to open or close some channel of communications. Gateways must always listen on some common frequencies depends on zone. Device will use these one to connect then being configured by network.
- Europe : common channels 868.10, 868.30, 868.50Mhz with a 125KHz bandwidth
- Europe : joinReq broadcast channels add 864.10,864.30,864.50Mhz
- See also 433Mhz channels.
Datarates in Europe
- from 250bps to 5470bps based on LoRa / 125Kpbs bandwidth
- at 11kbps based on LoRa / 250Kpbs bandwidth
- at 50kbps based on FSK
Payload size depends on data rate
- 51B from 250bps to 980bps
- 115B at 1760bps
- 222B upper
Getting start with LoRa
Different modules are now available to get start on LoRa but the main issue is the network. Even if some network operators have announced network deployment like bouygues telecom we still have no public offer and date of a sufficient network coverage for deploying products.
Some module are actually available at price around 10-15$ like
- Nemeus MM002 – implementing LoRa Wan 1.0 ClassA distributed by ProRep
- Microship RN2483 – implementing LoRa Wan 1.0 Class A 434/868Mhz
Chips are mainly produced by semtech but other provider like HopeRF also have devices under semtech IP.
Understand LoRa vs Sigfox
LoRa is a technology, SigFox is a network based on a proprietary technology. That said most is said – the business proposal is totally different.
LoRa is owned by one manufacturer – Semtech and deployed by many network operators (Bouygues Telecom, Orange, KPN, Swisscom, proximus…) one or more in every country. It offers some advantages based on a larger competition and allow to build your own network infrastructure to get YOUR private LoRa network. It also create some negative aspects – roaming condition are uncertain, backend integration could depend on each operator, coverage will depend of each operator strategy and Semtech will a be single point of failure.
LoRa provides more mode than sigfox to feet many more need, the specification is young but I assume it get benefits of the sigfox experience and the more mature industry on IoT. The bandwidth allow larger communication rate to get faster communication and it enable more application thanks to the capability to transport more data in the 1% duty cycle rules. By-the way it won’t enable application like sound or video as we are still talking about hundreds of bits per seconds.. not more
SigFox is a world wide IoT network operator (direct or indirect), it actually own the technology using the same name but it will be able to provide different technologies to serve the same objective in the next years (like satellites). Object can roam to any covered country (USA not yet totally clear) without any extra fee. As a consequence you won’t be able deploy a private SigFox network and you are in a dependency with SigFox operator for any commercial conditions.
The BIG question
LoRa is based on opened frequencies where according to the legal rules you should not use more than 1% of the time. SigFox is fully time emitting predictable and these rules are driving any SigFox design. LoRa is fully not predictable as the protocol have many variable frame length, transmission time is data-rate dependent when data-rate is controlled by network, not device. Device can decide to restart to emit when ack did not received. According to the documentation the rules is to block device emission after each communication the needed time to ensure the duty-cycle rules.
So the frequency of data transfer will be linked on the quality of the network, the noise around, the distance … This means it opens many opportunities in terms of quantity of data to transmit but this depends on external element your are not managing.
What the norms does not details is the average transfer rate or average needed re-emit to get a success – and it make sense as it is link with environment. The consequence is that to go to LoRa you need to already have a large experience of this network to design your communication properly.