sandeepmistry / arduino-LoRa

An Arduino library for sending and receiving data using LoRa radios.

MIT License

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What is the length of thepreamble? #373

Closed Portia-Lin closed 4 years ago

Portia-Lin commented 4 years ago

Hello. I want to calculate data rate in bps.

I used the following lora settings Spread Factor: 12 Bandwidth: 62.5 The table shows that the data rate will be 146 bits per seconds.

Table 10

The structure of the package is shown in the figure:

Packet Structure

Now i want to calculate how many seconds my message will be transmitted. I need to know the programmed length of the preamble. What is it for your library? And maybe you can tell me how to calculate the length of the header. Then I will be able to know the length of the whole packet and calculate the transmission time

Portia-Lin commented 4 years ago

In the library, I found tapes that are responsible for the length of the preamble:

define REG_PREAMBLE_MSB 0x20

define REG_PREAMBLE_LSB 0x21

But I still don't understand the length ...

IoTThinks commented 4 years ago

Check here https://www.loratools.nl/#/airtime

Portia-Lin commented 4 years ago

Thank you, there is a standard length 8 symbols. 0x20 and 0x21 are listed in the library. What is the length of 0x20? I don`t understand this

morganrallen commented 4 years ago

Those are the address location for the preamble length setting. Unfortunately we do not provide a way to read that back yet, but if you have not changed it, it will stay at the default of 0.

Section 4.1.1.7 explains how to calculate airtime.

Portia-Lin commented 4 years ago

Therefore, the length of the preamble is 0?

Portia-Lin commented 4 years ago

I tried to calculate it and I don't understand what max(numeric, 0) means. And I don't know if I'm doing it right.

IoTThinks commented 4 years ago

The preamble should be > 0 as it is used to detect if a signal is the beginning of a LoRa packet. You can set it here: https://github.com/sandeepmistry/arduino-LoRa/blob/master/API.md#preamble-length.

The wording says: Supported values are between 6 and 65535.

I believe transferring a preamble bit or a normal data bit take the same period of time.

Portia-Lin commented 4 years ago

But how to calculate the function max ()

Portia-Lin commented 4 years ago

Now i want to use the center frequency of channel 4 of LPD433 - 433.150 MHz. I inserted the following code:

LoRa.begin(433.150E6)

Everything works, but does it really work at this frequency?

IoTThinks commented 4 years ago

I checked with my SDR. This library really sets the frequency correctly with LoRa AI-Thinker.

Portia-Lin commented 4 years ago

I checked with my SDR.

Thank you very much!