LoRa P2P implementation cross talk? and security

Regarding the RAK4200 or any other RAK lora module how is P2P implementif ed. i use LoRaWAN no problem but have an appplication now for P2P.

my questions are
how is P2P set up ?
how does the node know to accept a message?

for example there are 4 nodes A B C D
Nodes A → B communicate
Nodes C-> D communicate

if there are all in range with eachother what stops the messages from node A being recieved by node D?

and how does node A and B know to accept messages from eachother?


LoRa P2P is very basic per definition. One node is sending a packet and all other nodes that are listening on the same frequency will receive it.

In LoRa P2P you have to implement node addressing within your application and add it to the packet by yourself.
In addition, LoRa P2P is sending data unencrypted. If you need data encryption you have to add it within your application.

As an example, you give your nodes A … D addresses
A ==> 0x00
B ==> 0x01
C ==> 0x02
D ==> 0x03
When node A sends a packet and it wants node B to process it, it adds the node address to the data packet like <0x01><data bytes>
When the other nodes receive the packet, they check the first byte. If the first byte is matching it’s node address, they process the data, if the address doesn’t match, they ignore it.

Thanks that makes sense now

Another option, if always the same two modules are talking to each other, you can use different frequencies for the pairs.

Like node A and B use 916.1 MHz and node C and D use 916.5 MHz.

how is that set and how many frequency variation channels are there ?

It depends on your country.
For me, the ISM frequencies are between 916.6 and 918 MHz. I can select any frequency in this range. But to avoid conflicts with the frequencies that LoRaWAN uses, I would avoid the following frequencies and select the ones in between:

LoRaWAN Channel Frequency
0 916600000
1 916800000
2 917000000
3 917200000
4 917400000
5 917600000
6 917800000
7 918000000

So I would select for example 916.7 and 917.9 MHz for the two pairs.

I have an overview of the frequencies that LoRaWAN uses for the different regions in Channels

But better to look into the official LoRa Alliance regional parameters

ok thanks
approximately what communication speeds are achievable for P2P for ~10bytes with reasonable SNR
I know you cant give an exact figure but for example is 10 byte packets every second possible?

It depends on the range you want to achieve. Lower Spreading factor, higher bandwidth and the coding rate influence the air-time, beside of other factors like preamble length.

With an SF of 12, BW 500kHz and CR 4/5, standard Preamble length of 8 symbols and a payload length of 10 bytes you get an Time on Air of ~250ms.

You can get the SX1261 Calculator tool from Semtech

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