110 lines
4.0 KiB
Markdown
110 lines
4.0 KiB
Markdown
LoRa/LoRaWAN Time on Air calculator
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===================================
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(28-Aug-2020) Python2 has sunset already. For Python3, toa.py has been added. Don't worry. lorawan_toa.py is not changed for backward compatibility.
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A calculator of the time on air (ToA) of LoRa/LoRaWAN PHY frame in Python.
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This script refers to the section 4.1.1.6. LoRa Packet Structure,
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[SX1276/77/78/79 Datasheet rev.5][http://www.semtech.com/images/datasheet/sx1276.pdf].
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The default parameters of the equation is based on LoRaWAN AS923
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in the LoRaWAN regional parameters v1.1.
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## Note
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The default value of Explicit Header is enable.
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It is guessed from the PHY frame format
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though there is no explit text in the LoRaWAN specification.
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The value of LowDataRateOptimization is set automatically
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when the symbol duration exceeds 16ms.
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Because the datasheet requires that it must be used
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when the symbol duration exceeds 16ms.
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This is the case below:
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- SF=12 and 11 in 125 kHz.
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- SF=12 in 250 kHz.
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You can disable this feature by the --disable-auto-ldro option.
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The LDRO is disabled by default if you disable the auto LDRO.
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If you want to enable the LDRO, you can specify the --enable-ldro option.
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In the downlink stream, the CRC at the tail of the PHY frame is not used.
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To calculate the ToA for the downlink stream,
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the --downlink option should be specified.
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## Usage
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```
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usage: toa.py [-h] [--band-width NUMBER] [--disable-auto-ldro] [--enable-ldro]
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[--disable-eh] [--downlink] [--disable-crc] [--cr NUMBER]
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[--preamble NUMBER] [--duty-cycle NUMBER] [-v] [-d]
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SF SIZE
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LoRa Time on Air calculator.
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positional arguments:
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SF Spreading Factor. It should be from 7 to 12.
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SIZE PHY payload size in byte. Remember that PHY payload
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(i.e. MAC frame) is consist of MHDR(1) + MAC payload +
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MIC(4), or MHDR(1) + FHDR(7) + FPort(1) + APP + MIC(4).
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For example, SIZE for Join Request is going to be 23.
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If the size of an application message (APP) is 12, SIZE
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is going to be 25.
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optional arguments:
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-h, --help show this help message and exit
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--band-width NUMBER bandwidth in kHz. default is 125 kHz.
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--disable-auto-ldro disable the auto LDRO and disable LDRO.
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--enable-ldro This option is available when the auto LDRO is
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disabled.
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--disable-eh disable the explicit header.
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--downlink disable the CRC field, which is for the LoRaWAN
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downlink stream.
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--disable-crc same effect as the --downlink option.
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--cr NUMBER specify the CR value. default is 1 as LoRaWAN does.
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--preamble NUMBER specify the preamble. default is 8 for AS923.
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--duty-cycle NUMBER specify the duty cycle in percentage. default is 1 %.
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-v enable verbose mode.
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-d increase debug mode.
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```
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## Examples
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with the -v option, it shows the ToA as well as the related information.
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below example, it show detail information in SF 12, 64 bytes of PHY payload,
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125 kHz bandwidth, preamble 8.
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% python toa.py 12 64 -v
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PHY payload size : 16 Bytes
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MAC payload size : 11 Bytes
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Spreading Factor : 7
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Band width : 125 kHz
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Low data rate opt. : disable
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Explicit header : enable
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CR (coding rate) : 1 (4/5)
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Symbol Rate : 976.562 symbol/s
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Symbol Time : 1.024 msec/symbol
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Preamble size : 8 symbols
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Packet symbol size : 38 symbols
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Preamble ToA : 12.544 msec
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Payload ToA : 38.912 msec
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Time on Air : 51.456 msec
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Duty Cycle : 1 %
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Min span of a cycle : 5 sec
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Max Frames per day : 16791 frames
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without the -v option, it simply shows the ToA.
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% python toa.py 12 64
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2793.472
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## graph_as923.py
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It makes a set of figures about Time on Air and PHYPayload size,
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especially LoRaWAN AS923 using matlib like below.
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