Table of Contents:

• 1.  For LoRaWAN Network
  • 1.1  How does LoRa wireless work?
  • 1.2  Traffic for a single End Node.
  • 1.3  Capacity for Gateway
  • 1.4  Conclusion

1.  For LoRaWAN Network

1.1  How does LoRa wireless work?

LoRa transmission is a broadcast protocol. There is no fix connection between gateway and end node.

For uplink steam:          Each End node will broadcast the uplink message and all-around gateways will get this message and forward to LoRaWAN Server.

For Downlink Stream:   Gateway will get instruction from LoRaWAN server and then broadcast this message to LoRaWAN End Node.

1.2  Traffic for a single End Node.

If we consider using LHT65N as an example to calculate the traffic, we can get a rough idea for how many messages are there:

• Uplink Traffic:
  • 1~ several messages for OTAA Join Request. // Once the Device joins successful, there is no such traffic.
  • 1 message to uplink sensor value / every 20 minutes // Default uplink interval is 20 minutes for LHT65N. In case user set LHT65N to work in Confirmed Uplink Mode, each uplink might uplink up to 3~8 messages if the sensor doesn't get any ACK from Server
  • up to several messages per day.
  • So every day, LHT65N might send an average 100 or less messages. Every uplink message last between 200ms to 1 second and they are in different frequencies point ( For example, 868.1Mhz, 868.3Mhz).

• Downlink Traffic:
  • several per day for each sensor, Unless end-node sends CONFIRMED UPLINK, in this case, each uplink message will require one downlink message from the server.

1.3  Capacity for Gateway

A general LoRaWAN gateway such as LPS8N uses a multi-channel LoRaWAN Concentrator. which supports 10 rx channels and 1 tx channel.

• RX channel is used to received Uplink from Sensor. User can pre-set max 10 different frequencies on rx. For example, in EU868, 8 channels are use, they are as below:
  • 868.1 - SF7BW125 to SF12BW125
  • 868.3 - SF7BW125 to SF12BW125 and SF7BW250
  • 868.5 - SF7BW125 to SF12BW125
  • 867.1 - SF7BW125 to SF12BW125
  • 867.3 - SF7BW125 to SF12BW125
  • 867.5 - SF7BW125 to SF12BW125
  • 867.7 - SF7BW125 to SF12BW125
  • 867.9 - SF7BW125 to SF12BW125
  • 868.8 - FSK

When two sensors send uplink in different frequencies, for example, 868.1 nad 868.3. both packets can arrive at the gateway, and the gateway will forward to LoRaWAN Server. Normally, we can consider the gateway support 8 packets per second ( The packets are of different frequencies).

• TX channel frequency is flexible and defined by each downstream from LoRaWAN Server. Please notice when the gateway is in TX mode, RX won't be able to receive packets. So If there are too many downstream in the network. RX capacity will be highly effected.

1.4  Conclusion

When we check the capacity for the LoRaWAN network, we need to check how the sensor work. We can't simply say how many nodes the gateway can support because nodes' uplink frequency is very important.

In a network with low transmission frequency end node, for example, several hundred LHT65N, transmit every 20 minutes.  can be easily supported by a LoRaWAN gateway.

but for a high-frequency application, for example, a tracker sends a message every 3 second, you wil then see packet loss for dozens of units. 

Accordiing to the tech spec, simply add Gateways, listening the same frequencies can't improve a lot the capacity.

Above is a simple calculation with rough idea. For more precise, please check this LoRaWAN Capacitor White Paper