Spreadsheet for LoRa airtime calculation

42

Thanks for this spreadsheet!
I have a question about downlink Toa…
The only difference between uplink and downlink is the CRC field, right?

"Downlink messages use the radio packet explicit mode in which the LoRa physical header 377 (PHDR) and a header CRC (PHDR_CRC) are included*.

*No payload integrity check is done at this level to keep messages as short as possible with minimum impact on any duty-cycle limitations of the ISM bands used." [lorawan specification]

If yes, I can use this spreadsheet for the Toa Downlink computation but I have to subtract 16 bit of CRC. I’m right?

Thanks in advance for replies and for your help.

43

If there is at least 13 bytes in a packet, I often see in the papers that the data packets of physical payload size such as 9 bytes and 10 bytes are launched. How do they do it?

44

A LoRaWAN\TTN packet has a length of 13 bytes plus payload.

Are ‘the papers’ referring to plain LoRa packets ?

45

I think So.

Only LoRaWAN will add extra data.

Thanks.

46

I think it’s explicit vs implicit header. Academic, not relevant to TTN.

47

I dont see how the type of header would affect the payload size ?

48

I’m sorry to disturb you again.

Can’t the gateway receive plain LoRa packets? After a round of asking, I found that the gateway can only accept LoRaWAN packets

49

Why would you want it to ?

50

Just to collect data.

The P2P communication provided by some nodes can only communicate between two nodes.

51

This forum is focussed on TTN and by extension LoRaWAN implementations. LoRa only/LoRaP2P is out of scope. There are LoRa ‘Gateways’ which you may be thinking of - effectively single channel or dual channel LoRa packet forwarders…there are disruptive to LoRaWAN networks and should not be connected to them and should NOT be conneceted to TTN. You should look to other forums and othe LoRa RF Library instances for support on these. A LoRaWAN GW will ‘hear’ LoRa only transmissions but will not action or handle the traffic and it will be ignored/dropped at the GW.

52

I thought the question from @haowong was bad expressed. Of course the payload is something else. It can be also zero. In that context the question is meaningless to me.

53

Hello,

can you please tell me what is the meaning of these equations that I found them in a code and where is the reference for these equations?. I only found the equation of the number of symbols in a packet but it doesn’t contain +5 like in the code

message_chr = convertStringsToChars(message) ;
message_dbl = uint8(message_chr) ;
N_pld = (SF == 7).*1 + (SF == 8).*2 + (SF == 9).*3 + (SF == 10).*4 + (SF == 11).*5 + (SF == 12).6 ;
n_packet = 8 + max([ceil((8(length(message_dbl) + 5) - 4.*SF + 28 + 16.CRC_pld - 20.imp)/(4.(SF - 2.opt))).(CR + 4) 0]) ;
n_wht = SF . floor((n_packet-8)/(4 + CR)) + N_pld - 1 ;
n_pld = ceil((n_wht + (SF == 7).*0 + (SF == 8).*1 + (SF == 9).*2 + (SF == 10).*3 + (SF == 11).*4 + (SF == 12).*5)/2) ;
n_pad = n_pld - 5 - length(message_dbl) - CRC_pld.2 ;
%% Create payload message
CRC_dbl = CRC_pld.[1 1] ; % CRC is not working atm
pad_dbl = zeros(1,n_pad + N_pld - 1) ; % padding
pld_dbl = [255 255 0 0 message_dbl 0 CRC_dbl pad_dbl] ; % LoRa payload

54

  1. Not sure if you should expect a reply - as far as I can tell @assia_b has not been seen on the forum for>7 years! And was only active for <2 months :frowning:

  2. Dont expect others to go searching in ancient code and posts; please be explicit where you are looking for this illusive “+5” and why you think it should be there - epsicially with something that is so old…otherwise suspect you are on your own to go digging into historic forensics…you might get lucky with a response but :man_shrugging: