Knowledge Base

Receiver polling

Hi, I am new to this forum so apologies if this is not the correct place to post.

I am using a SX1272 on a field device which has to respond to an action from a base station (turn on a motor as and when required). The field device is battery powered and I want to maximise battery life. I am using a spreading factor of 12 with a bandwidth of 125kHz.

My packet is 27 symbols (including 8 pre-amble symbols).

I want to wake up the receiver on the field device, look for a valid packet and if I can't see one, go back to sleep. I need the field device to respond within 1 minute to any trigger and at the moment I am waking-up the receiver every 30 seconds. When I need to control my field device, the base station repeatedly transmits packets for about 60 seconds.

My questions are:-

1.For how many symbols should I keep the receiver on once I have placed it in receive mode?
2.Is this the best scheme to use?
3.Should I consider waking up using CAD detection?

Thanks in advance for any thoughts and help.


Hi Chris,

From your question, I would consider implementing CAD to detect LoRa preamble in the channel as described in Section 4.1.3 of the SX1272 DS. You don't state whether your base station is DC power-constrained, but I would consider experimenting with increasing the number of transmitted preamble symbols to ensure a long enough sequence so that CAD can detect activity and in full RX mode the LoRa modem can similarly detect sufficient symbols (you may need to increase RX preamble detection size so as to ensure correct operation if CAD is asserted at the start of the TX sequence).

Semtech Applications