Spreadsheet for LoRa airtime calculation

[Sylvain_M]

Hopping I’m not off-topic

@arjanvanb

LoRaWAN might have a fixed coding rate of 1? (So, CR=1.) I cannot find that in the specification. Even more: it does mention it explicitly for transmission of Class B beacons, so I doubt it’s also fixed for other operations?

Beware that disabling the Forward Error Correction code comes with a significant penalty when it comes to sensitivity/range. The trade-of, a small increase in data-rate vs a significant loss in sensitivity, is not worth it, except in very special cases like class B beacon when it was done on purpose for specific reasons.

Always use a 4/5 (in “nice” environments) or 4/6 (in environments with bursted interferes) redundancy for data transmission.

[CHAPINONG (Kasper S)]

Hi,
i don’t understand why you, in the “payloadSymbNb” equation write “… 20*(1-Header) …”.

in the Semtech LoRa design guide (page 7), the equation for Payload symbol number is:

but in you’r spreadsheet’s you write it like:

That doesn’t make any sense to me, when i use the first formula, with no header (H = 1) i get payloadSymbNb=23, and with header (H = 0) i get 28… thats also what i would expect.

Why do you do as you do, have i missed something ?!?

Thanks

[robg66]

Took a little time but I get why.
If you look add page 7 it says:
H = 0 when the header is enabled and H = 1 when no header is present.

In spreadsheet in column B9:
“=if(C9=“yes”,1,0)”
Yes == 1.
This is the opposite of what Semtech Describes.
1-H simply inverts 1 to 0 (just as Semtech wants).

if you would change the value of B9 to
“=if(C9=“yes”,0,1)”
Then you can use the same formula as Semtech.

I hope you can follow it

[assia_b]

hello matthijs

Thank you for the spreadsheet, it does explain better the LoRa symbol / bit conversion.

I would like to ask you about the 8 mandatory symbols in the payloadnb symbol. I searched everywhere to explain their utility, since it’s not representing the preamble length. A payload has at least 8 symbols, what are those representing?

Thank you,

[BoRRoZ]

LoRa: Symbol Generation

[assia_b]

Hello BoRRoZ,
Thank you for the reply,

Still the 8 symbols i’m talking about aren’t those of the preamble. As you see:

Time on Air = T preamble + T payload
with
Tpreamble= (NbPreamble (8) + (symbols added by radio)4,25) x Tsymbol
and
Tpayload = NbPayloadSymbol x Tsymbol
And according to LoRa calculator, the NbPayloadSymbols is calculated with this formula:

I am looking for the meaning of those 8 symbols (red circle). In the formulas of the calculator the nPayload is independant from the 8+4.25 symb of the preamble.

[james_L]

In the Loramac-node project, the low data rate optimization is set not just for SF12BW125 and SF11BW125, but also for SF12BW250. Not sure where this stuff is supposed to be documented… I can’t find anything in the LoRaWAN standard. Doesn’t look like any regions actually use this setting though.

[maranza]

Hey everyone i just want to ask how to calculate or get packet error rate for LoRa???

[BoRRoZ]

@maranza

packet error rate

search (right top corner)

[maranza]

i did search the is no clear discussion about it.

@maranza

i did search the is no clear discussion about it.

[ben_dg]

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.

[haowong]

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?

[LoRaTracker]

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

Are ‘the papers’ referring to plain LoRa packets ?

[haowong]

I think So.

Only LoRaWAN will add extra data.

Thanks.

[clv]

@haowong

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?

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

[LoRaTracker]

@clv

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

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

[haowong]

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

[LoRaTracker]

@haowong

Can’t the gateway receive plain LoRa packets?

Why would you want it to ?

[haowong]

Just to collect data.

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