CODEWITHSUNDEEP
raspberry-piloralorawan
Intern USMC
Intern USMC

Reputation: 1

Single channel gateway only detect first message

My gateway uses the Raspi and RFM95 configuration and operates at 915 MHz. I am using the single channel packet forwarder code by tfelkamp (https://github.com/tftelkamp/single_chan_pkt_fwd).

My gateway only the detects the first message it received and ignores the all messages afterwards. It is still connected to the TTN server but does not receive any more messages.

Can anyone explain what might be the cause of this? Might it because the RFM95 sleeping or the code no longer forwarding the message from the transceiver.

Thanks

Upvotes: 0

Views: 856

Answers (3)

Chris
Chris

Reputation: 913

If you're using the LMIC-Arduino library for your node then yes, by default it is transmitting in a range and the single_chan_pkt_fwd gateway is only receiving on the frequency you specify in the global_conf.json or the .cpp source (depending on your chosen library).

With the assumption that you're using the arduino-lmic library, make the changes/additions mentioned in the this TTN forum post linked by Rainer which is the same I ran into.

Also... you'll find this further down the thread: in src > lmic > lmic.c edit the following:

void LMIC_disableChannel (u1_t channel) {
    if( channel < 72+MAX_XCHANNELS )
        //LMIC.channelMap[channel>>4] &= ~(1<<(channel&0xF)); // comment this one
        LMIC.channelMap[channel/16] &= ~(1<<(channel&0xF)); // add this one
}

Then pick a frequency on channel 0 and set that for both node and packet forwarder. Here's a table snip from this page. I went with 902300000 and it's working fine.

"freq": 902300000,
"spread_factor": 7,

enter image description here

Upvotes: 0

arminb
arminb

Reputation: 2103

This sounds like your transmitter sends the messages using frequency-hopping, while your receiver does not handle it correctly (or the other way around).

Definition of frequency-hopping found in chapter 4.1.1.8 of Semtech's SX1272 datasheet:

Frequency hopping spread spectrum (FHSS) is typically employed when the duration of a single packet could exceed regulatory requirements relating to the maximum permissible channel dwell time. This is most notably the case in US operation where the 902 to 928 MHz ISM band which makes provision for frequency hopping operation. [...]

Upvotes: 0

Rainer
Rainer

Reputation: 11

I experienced a similar issue. Please note your sender is using different channels, but starts with channel(0). This is the first successful message you receive. Your single channel receiver is just able to receive channel(0). There is a work around for this issue for your sender explained here

Upvotes: 1

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