In this video series different topics will be explained which will help you to understand LoRa/LoRaWAN.
It is recommended to watch each video sequentially as I may refer to certain LoRa/LoRaWAN topics explained earlier.
In this tutorial I will give a simplified explanation of what the parameters mean in the global and local JSON configuration files.
The Semtech UDP Packet Forwarder is configured by the global configuration file global_conf.json.
It has two sections: the radio settings (SX1301_conf) and server settings (gateway_conf).
The radio settings (SX1301_conf) should contain the parameters for the Lora concentrator board.
The server settings (gateway_conf) should contain the gateway parameters.
If parameters are defined in both the global and local configuration file, the local definition overwrites the global definition.
Recommended is to make changes in the local configuration file (local_conf.json).
Listen-Before-Talk (LBT) is a mandatory requirement in some countries, such as South Korea.
LBT prevents end devices from transmitting at the same time on the same channel.
LBT means the end device checks (=Listen) if the intended channel is free.
If the channel is not free, the end device changes to another channel and repeats the LBT procedure.
If the channel is free it transmits (=Talk).
The SX1257/55 radios captures the LoRa uplink packets and sends the digital signal to the SX1301 digital baseband chip which demodulates the signal.
This processed signal is used by the Micro Controller Unit (MCU).
The SX1257 chip can be configured to any frequency inside the 868/900 MHz ISM band.
The SX1255 chip can be configured around the 433MHz ISM band.
In the global_conf.json file you can find the Intermediate Frequency channels (IF).
All gateways must comply to certain rules and regulations when using the ISM band frequencies.
These rules and regulations determines how the Intermediate Frequency channels came about.
In the LoRaWAN 1.0.2 Regional Parameters Revision B (2017 Feb), for the EU863-870 ISM band the following is specified:
- The EU863-870 ISM Band channel frequencies applies to any region where the ISM radio spectrum use is defined by the ETSI 300220 standard.
- For the EU863-870 ISM frequency band a maximum of 16 channels is supported.
- Three default channels must be implemented in every EU868MHz end-device.
Those channels are the minimum set that all network gateways should always be listening on.
- The remaining 13 channels can be freely attributed by the network operator.
A list of frequency plan definitions used by The Things Network, see:
https://www.thethingsnetwork.org/docs...
These frequency plans are based on what is specified in the LoRaWAN regional parameters document.
In the most basic form a LoRaWAN gateway is just a digital radio transceiver.
How a digital radio transceiver works:
- The digital data that contains the information that needs to be transmitted.
- The Digital-to-Analog Converter (DAC) converts the digital data to an analog signal.
- The Low Pass Filter (LPF) filters out the noise, etc from the analog signal.
- A Local Oscillator (LO) generates a carrier signal and modulates the carrier signal onto the analog signal thus creating an RF signal.
- The power amplifier boost the RF signal.
- The Transmit/Receive (TR) switch sends the amplified RF signal to the transmitting antenna.
A maximum of 16 power settings can be configured.
These settings are board specific and have been selected during calibration for each concentrator.
The network server is in charge of requesting transmit powers.
The gateway extracts the proposed RF power from the txpk JSON object.
The proposed RF powers are in fact EIRP values.
The antenna_gain is subtracted from the proposed RF power to stay within the legal limits:
rf_power (dBm) = powe (dBm) - antenna_gain (dBi)
The gateway searches the LUT for rf_power.
If the rf_power is not found in the LUT than an error will be logged, the downlink packet will be rejected and de facto the packet is lost.
EIRP= rf_power + antenna_gain (+ cable losses)
It is important to specify the antenna_gain in the global_conf.json file, otherwise the EIRP does not comply with the regulations.