The Things Network

The Things Network (TTN) is a global, community-driven and open-source LoRaWAN network. It provides an infrastructure for connecting own devices free of charge.

Table of contents

1. What is LoRaWAN
2. Network Components of a LoRaWAN
3. Whats special about TTN?
4. Differences to other LoRaWAN networks
5. Typical range of transmission
6. RSSI and SNR
   1. RSSI (Received Signal Strength Indicator)
   2. SNR (Signal-to-Noise Ratio)
   3. What are good values?
7. Security

What is LoRaWAN

LoRaWAN (Long Range Wide Area Network) is generally a wireless technology that allows devices such as sensors to send data over long distances. These devices are not directly connected to the Internet. They send the data at regular intervals via the LoRaWAN to a so-called gateway. This gateway then forwards the data to the Internet.

LoRaWAN is perfect for connecting devices that need to send small amounts of data, like temperature readings, air quality information, or water level measurements. These devices can be placed anywhere, no internet connection or power supply is needed. Normally these devices are battery powered and have a long lifetime.

Network Components of a LoRaWAN

In a LoRaWAN, the setup involves the following components

• Sensors/Devices/Nodes
  These are the end devices equipped with sensors that collect data, such as temperature, humidity, or motion. They are also called LoRa Nodes.
• Gateway
  Gateways act as communication hubs in the network. They receive data from the devices over long distances and forward it to a central network server in the internet.
• Network Server
  The network server manages the entire LoRaWAN network. It processes data received from gateways, deduplicates telegrams, manages device registrations, handles security, and routes data to the appropriate applications.
• Application Server
  The application server is where data is sent after passing through the network server. Here, the data is processed, stored, and integrated with other systems or applications.
• End User Application
  The end user application is for example a dashboard where the transmitted data gets processed and visualized. The data can also get transmitted to an automation system.

The data flow is as follows

1. The sensor sends data
2. The gateway(s) in the receiving area receive the data and forward them to the network server
3. The network server validates, deduplicate and decrypts the data, determines the appropriate application, and sends it to the respective application server
4. The application server processes and stores the data, making it available for analysis or integration with other services
5. The End User application receives the data from the application server and may process and/or visualize it

Whats special about TTN?

This public network is free of charge and built on the principle of shared infrastructure, meaning that users can benefit from existing gateways deployed by others in the community. As long as there are TTN gateways within the reception range of your sensor device, you can utilize the network without the need to deploy your own gateway.

Differences to other LoRaWAN networks

In Switzerland, for example, the company Swisscom offers a similar network, although there is a charge for it. Here, Swisscom maintains the entire network infrastructure and you only have to integrate your own sensor devices. With the TTN, every individual can contribute to this infrastructure and install a gateway at home, for example. This gateway then not only forwards LoRa telegrams from one’s own devices, but also from other users to the Internet.

Typical range of transmission

The typical range for LoRaWAN devices is a few hundred meters to a few kilometers in urban areas and several kilometers in rural or open environments. It is as well possible to place devices in buildings and have the next gateway somewhere outside.

However, the actual range can vary depending on several factors

• Distance to the Gateway
  The farther the sensor device is from the gateway, the weaker the signal, impacting communication reliability.
• Obstacles and Environment
  Physical obstacles like buildings, walls, windows and trees can weaken or block the signal, affecting signal strength and range.
• Gateway Density
  More gateways nearby improve coverage and increase the chances of successful communication. That has as well an effect on battery life. The better the reception, the faster the device can transmit, the shorter its airtime.
• Transmit Power of the Sensor Device
  Higher transmit power allows for longer range but consumes more energy.
• Environmental Factors
  Weather, humidity, and atmospheric conditions can influence signal strength.
• Interference
  Electronic noise or interference from other devices can impact reception and as well battery life.
• Antenna Quality
  The quality of antennas on both the sensor device and gateway affects range and reception quality.
• Sensor Device Orientation
  Each antenna has a designed orientation. Refer to the sensor device datasheets to see how you orient best the devices.

RSSI and SNR

In the LoRaWAN network, the Received Signal Strength Indicator (RSSI) and the Signal-to-Noise Ratio (SNR) are important metrics for evaluating the communication quality between LoRa devices and gateways.

RSSI (Received Signal Strength Indicator)

RSSI measures the strength of the received signal in decibels relative to 1 milliwatt (dBm). The values for RSSI in the LoRaWAN can typically range from around -120 dBm to -40 dBm. A value of -120 dBm indicates a very weak signal that is close to the reception limit, while a value of -40 dBm indicates a very strong signal.

SNR (Signal-to-Noise Ratio)

SNR is a measure of how much stronger the signal is than the background noise. It is measured in decibels (dB). The SNR values in the LoRaWAN can range from around -20 dB to +10 dB.

• A negative SNR means that the noise is stronger than the signal, which typically occurs at very long distances or in poor environmental conditions.
• A positive SNR indicates that the signal is stronger than the noise, which is necessary for effective communication.

What are good values?

To assess the quality, the two values must be considered together!

• The radio link can be described as GOOD if RSSI > -115dB and SNR > -7dB
• The radio link is POOR (range limit) if RSSI <= -120 dB or SNR <= -13dB

If RSSI is good (> -115dB), but SNR is poor (<= -13dB), this means that the environment is very noisy

The SNR must be checked over several days to be sure that the radio link is stable enough to receive all messages.

If RSSI is poor (<=-120dB) but SNR is good (> -7dB), this means that the device is probably far away from the gateway.

Security

LoRaWAN networks are designed with robust security measures, for example including encryption, device authentication and message integrity checks. Overall LoRaWAN networks are considered secure for various IoT applications.