What is LoRa

LoRa / LoRaWAN - Long Range Wide Area Network

LoRa is an open radio standard for a Low Power Wide Area Network (LPWAN) for only small amounts of data and a long range. Semtech chips are used exclusively in all LoRa transmitters and receivers, which is why the operation of such a network is dependent on a single manufacturer.

LoRaWAN is the name for a wireless network based on LoRa. LoRa and uses frequency bands from the license-free ISM bands. This means that a LoRaWAN can be an alternative or supplement to the classic mobile network with a central network operator. A LoRaWAN is also referred to as a 0G network to distinguish it from classic mobile communications.

Since LoRa is an open radio standard, anyone can set up a LoRaWAN as an IoT or M2M network with bidirectional communication or use a community-based solution.

Note: It should be noted that LoRaWAN in the USA is not the same as LoRaWAN EU. This has an influence on the transmission rate and thus also on the energy consumption.

properties

  • Connection: uplink-oriented, bidirectional, acknowledgment operation possible
  • Modulation: Chirp Spread Spectrum and FSK
  • Network architecture: The end devices communicate with gateways, which transmit the data packets to a server. The server has interfaces for connection to IoT platforms and applications.
  • Frequency ranges: In Europe 868 MHz (863–870 MHz, divided into several sub-bands) and in the USA 915 MHz. In many countries, the service life of the sewer is limited by regulations (working cycle).
  • Range: Depending on the topography, up to 2 km in urban areas and up to 15 km in rural areas. A good penetration of buildings is achieved in this way.
  • Energy consumption: Between 10 mA and 100 nA in sleep mode. Depending on the application, the battery life is 2 to 15 years.
  • Radio channel bandwidth: 125 kHz
  • Sensitivity: -137 dBm
  • Transmission power: +20 dBm or a maximum of 25 mW
  • Data packets: EU: max. 51 bytes / USA: max. 11 bytes of user data per packet
  • Transmission rate: between 250 bit / s and 50 kBit / s

Transmission technology

In order to achieve high efficiency in data transfer and energy consumption, LoRaWAN uses frequency spreading. In this way, interference can be avoided as far as possible and narrow-band interference can be bypassed.

The transmission method is called "Chirp Spread Spectrum". The signal is transmitted as a kind of chirping. The chirp pulse is spread over a wide frequency range. The bandwidth can optionally be used for a high data rate or a robust transmission. The spread factor and the bandwidth determine how high the data rate can be and how high the reception probability is.

Signals that are modulated with different spreading factors and transmitted over the same frequency channel do not interfere with one another. The orthogonality of the spreading factors enables multiple terminals to be sent simultaneously in the same channel.
The LoRa signals are very robust against in-band and out-of-band interference. Their insensitivity to multi-path reception or fading ensures a long range in urban areas.

LoRaWAN network architecture

The LoRaWAN network architecture consists of many end devices in the form of sensors and actuators, several gateways and a central network server. The end devices communicate with the gateways. And the gateways are connected to the network server. The network server communicates via various protocols (e.g. REST, MQTT, etc.) with an application that is operated, for example, as an application in the cloud.

In a LoRaWAN, gateways are the receivers for the radio signals at 868 MHz. This is where the LoRa chips receive the chirp signals. On the other hand, the gateways are connected to the internet.
The gateways of a LoRaWAN ideally form a close-knit network and can be distributed all over the world.

A message can be received by one or more gateways. The gateways forward this to the network server without any further intervention.
In a LoRaWAN, the network servers are responsible for identifying the sender and forwarding the package to an application server.
Among other things, the network server ensures that a message only arrives once at the application server, regardless of how many gateways it has received.

Private or Community Network

Basically everyone can operate their own LoRaWAN. Since LoRa works in the frequency range that is not allocated, no license costs are required for frequencies.
If you only have to set up a LoRaWAN in a limited area, it can make sense to operate your own gateways and servers.
However, if you rely on an extensive wireless network, you can also participate in the community-based network “The Things Network (TTN)”. With this participation network, you only operate your own gateway, which speaks to the TTN servers via the Internet. In terms of security, you only have to trust the network server to deliver the received data packets and the application server, which can decrypt the content.

Range

LoRa has a high sensitivity of -137 dBm, which increases the availability of the network. The signals penetrate building walls without any problems and thus also reach basement rooms or other so-called deep indoor locations, for example.

The range between the transmitter and receiver is approx. 3 km (city), approx. 6 km (suburbs) and up to 13 km (rural areas), depending on the surroundings and buildings.
How large the distance between LoRa transmitter and receiver can be depends on the spreading factor, the bandwidth, the selected transmission power of the LoRaChip and the antenna used.

Transfer rate

To maximize the battery life and control the overall network capacity (limited by regulatory requirements), LoRa controls the data rate and the RF output using an adaptive data rate (ADR) individually for each end device.
The communication between the end device and the gateway takes place on different frequency channels with different data rates. The data rates range from 0.3 to 50 kbit / s. The physical packet size is 64 bytes gross. 13 bytes are required for the header. This leaves 51 bytes for the user data.

Note: In the USA, the maximum channel occupancy time is limited to 400 ms. This means that only a maximum of 11 bytes of user data can be transmitted per packet.

The SF12 (spreading factor) at 125 kHz (bandwidth) only comes to 250 bit / s (data rate). In return, the receiver perceives the chirp impulse with a very high probability, because it is comparatively easy for it to distinguish the signals from the noise.
The fastest combination specified is SF7 at 250 kHz bandwidth. This brings you to 11,000 bit / s.

power consumption

The LoRa modulation method enables optimal transmission power with the lowest possible power consumption by the transmitter. The low energy consumption enables a battery life of up to 15 years.
This simplifies handling and is inexpensive because no separate power supply is required.

Terminal classes

LoRa differentiates between different classes of end devices, whereby only class A is of interest for applications in the Internet of Things. The end device is in a battery-saving state and only sends briefly when the state changes. Something can then only be sent to the terminal during this time.
Together with the radio module, these terminals are very inexpensive because of their simplicity and are also suitable for meeting high demand.
If end devices are to be addressed outside of this period, device class B or C must actually be selected, which greatly increases power consumption and, depending on the network, is not supported at all.

Applications

LoRa is primarily made for static sensor applications. Typical applications are to collect, query and exchange status information. With sensors located at any location, information can be determined or obtained that can be easily integrated into an application.

  • Smart home
  • Smart city
  • Smart Factory
  • Smart farming
  • Smart transportation

The Things Network (TTN)

"The Things Network" (TTN) is a community-based initiative to establish a global IoT wireless network based on LoRa. The idea is to be in range of a TTN gateway anywhere in the world.
The provision, construction and support of the gateways is in the hands of volunteers or participants in the network. Anyone who plans their own LoRaWAN project and operates a TTN gateway always supplies their environment. This makes LoRaWAN interesting for hobbyists and commercial users alike. The organization operates network servers and application servers for this purpose.

Overview: IoT radio systems

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