A calculator of the time on air (ToA) of LoRa/LoRaWAN PHY frame in Python.
This script refers to the section 4.1.1.6. LoRa Packet Structure, [SX1276/77/78/79 Datasheet rev.5][http://www.semtech.com/images/datasheet/sx1276.pdf].
The default parameters of the equation is based on LoRaWAN AS923 in the LoRaWAN regional parameters v1.1.
The default value of Explicit Header is enable. It is guessed from the PHY frame format though there is no explit text in the LoRaWAN specification.
The value of LowDataRateOptimization is set automatically when the symbol duration exceeds 16ms. Because the datasheet requires that it must be used when the symbol duration exceeds 16ms. This is the case below:
- SF=12 and 11 in 125 kHz.
- SF=12 in 250 kHz.
You can disable this feature by the --disable-auto-ldro option. The LDRO is disabled by default if you disable the auto LDRO. If you want to enable the LDRO, you can specify the --enable-ldro option.
In the downlink stream, the CRC at the tail of the PHY frame is not used. To calculate the ToA for the downlink stream, the --downlink option should be specified.
lorawan_toa.py [-h] [--band-width NUMBER] [--disable-auto-ldro]
[--enable-ldro] [--disable-eh] [--downlink]
[--disable-crc] [--cr NUMBER] [--preamble NUMBER]
[--duty-cycle NUMBER] [-v] [-d]
SF SIZE
LoRa Time on Air calculator.
positional arguments:
SF Spreading Factor. It should be from 7 to 12.
SIZE PHY payload size in byte. It's equal to the MAC payload
+ 5.
optional arguments:
-h, --help show this help message and exit
--band-width NUMBER bandwidth in kHz. default is 125 kHz.
--disable-auto-ldro disable the auto LDRO and disable LDRO.
--enable-ldro This option is available when the auto LDRO is
disabled.
--disable-eh disable the explicit header.
--downlink disable the CRC field, which is for the LoRaWAN
downlink stream.
--disable-crc same effect as the --downlink option.
--cr NUMBER specify the CR value. default is 1 as LoRaWAN does.
--preamble NUMBER specify the preamble. default is 8 for AS923.
--duty-cycle NUMBER specify the duty cycle in percentage. default is 1 %.
-v enable verbose mode.
-d increase debug mode.
with the -v option, it shows the ToA as well as the related information. below example, it show detail information in SF 12, 64 bytes of PHY payload, 125 kHz bandwidth, preamble 8.
% python lorawan_toa.py 12 64 -v
PHY payload size : 16 Bytes
MAC payload size : 11 Bytes
Spreading Factor : 7
Band width : 125 kHz
Low data rate opt. : disable
Explicit header : enable
CR (coding rate) : 1 (4/5)
Symbol Rate : 976.562 symbol/s
Symbol Time : 1.024 msec/symbol
Preamble size : 8 symbols
Packet symbol size : 38 symbols
Preamble ToA : 12.544 msec
Payload ToA : 38.912 msec
Time on Air : 51.456 msec
Duty Cycle : 1 %
Min span of a cycle : 5 sec
Max Frames per day : 16791 frames
without the -v option, it simply shows the ToA.
% python lorawan_toa.py 12 64
2793.472
It makes a set of figures about Time on Air and PHYPayload size,
especially LoRaWAN AS923 using matlib like below.
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