LoRaMac Node with OTAA + ADR - Current Consumption


(Silas Valera) #1

Hi All ,

My node based on EFM32PG custom board + SX1276 works just fine from operation point - i…e uplink and downlink working as expected. Sleep current between transmissions is about 28uA

I am now trying to analyze some data like rssi, power and current consumption. Here is some info:

ADR is set as 1,
Current while transmitting is 55mA (measured as max hold on multimeter).
When the node is about 2 meters (LoS) from gateway - rssi = -40
When the node is about 15 meters (non LoS - through walls)from gateway - rssi = -70
When away, the transmitting current is still 55mA.
Questions:

  1. My understanding is that when the node is close to gateway, it will use least possible power so that it will use less current, and when farther it will try to send more powerful signal, this is to conserve battery, is that expected behavior?
  2. The transmitting current is 55mA - that seems pretty high, should it be lower? what power level does LoRaMac code would start with? Can I limit this to lower value by now allowing higher power output levels?
  3. Has anyone some guide line numbers for distance vs rssi, distance vs transmitting current or something similar, which can give an idea that the overall RF performance of node is ok or near ok? or is there any other result which can indicate the same?

Thanks


(Cslorabox) #2

In addition to controlling power, ADR will control the spreading factor as well. Each increase in the spreading factor doubles the transmit time, which will nearly double the integrated power cost of a transmission.

There are transmit power levels that will result in even higher current than you are seeing, but if you want to study power consumption you need to measure duration as well as magnitude. And keep in mind that the longer the range you operate, typically the more all the sources of energy cost increase - higher power, slower data rate, and more transmission attempts for the same number of messages successfully moved.