LoRa, Large Packet

[Jin ho An]

Posted on January 31, 2018 at 09:04

HI.

I am testing with ST Discovery LoRa Kit, PingPong.

There is no problem sending / receiving 64 bytes.However, the size of 64 bytes or more can not be transmitted or received.Semtech says that 128 bytes are possible, but why not?

[Tesla DeLorean]

Posted on January 31, 2018 at 10:57

The max is closer to 255 bytes. You are likely sending just fine, there is a setting on the receiving side to reject packets beyond a certain size.

[Andrew Neil]

Posted on January 31, 2018 at 17:42

Note that the maximum size of packet depends on the the data rate you're using; eg, 

for the European 863-870MHz band, the

applicationpacket size varies between 51 bytes for the slowest data rate, and 222 bytes for faster rates.

[Tesla DeLorean · Accepted solution]

Posted on January 31, 2018 at 18:40

I think the issue as observed here is the rejection of large packets where the receiver could be distracted from reception by large corrupt packets. The size is in the header burst as I recall.

The use case for the radio could be small control channel packets, where the radio only keys on these packets and the micro stays in deep sleep states ignoring larger bulk packets not destine for it.

The radio software in the LRWAN explicitly configures the default max to 64 bytes, although this may be changed later programmatically.

    { MODEM_LORA, REG_LR_PAYLOADMAXLENGTH, 0x40 }

[Jin ho An]

Posted on February 01, 2018 at 10:02

 Hi Clive One

Thank you for your reply.

I have modified the REG_LR_PAYLOADMAXLENGTH value and it seems to be receiving to some extent. If it is set to 0x80 (128) byte, it will be received only up to about 115 bytes.If 0x100 (256) byte is set, no reception is possible.I need to know only this information.

[Tesla DeLorean]

Posted on February 01, 2018 at 14:23

It is an 8-bit register so 0xFF would be the maximal setting. Not sure if it includes header bytes or just payload too, had assumed it was payload