Purpose of SF12 and SF11 if Join-Accept is SF10? (AU915)

LoRaWAN LoRaWAN Discussions
1

Reading the LoRaWAN Regional Parameters 1.0.4 for the AU915 frequency plan, I note the following on lines 955 to 958 (page 50):

If using the over-the-air activation procedure, the end-device SHALL broadcast the Join Request message alternatively on a random 125 kHz channel amongst the 64 channels defined using DR2 (SF10 uplink) and on a 500 kHz channel amongst the 8 channels defined using DR6 (SF8 downlink). The end-device SHOULD change channel for every transmission.

  1. If a device were to have its payloads successfully received when transmitting on SF11 or SF12 but not when on SF10, does this mean such a device would never connect?

  2. Why is DR6 defined if it is the same as DR12, both being SF8 at 500 kHz with bit rate of 12,500 bits per second?

  3. Why does the downlink get transmitted at SF8 if the uplink is transmitted at SF10? Is there not a 1:1 correlation between downlink and uplink SF?

2

This is answered only a few lines later in the spec on lines 997/998:

Note: DR6 is purposely identical to DR12. DR8 to DR13 refer to data rates that are only used for downlink messages.

3

You sure are quick @stevencellist!

Note : DR6 is purposely identical to DR12. DR8 to DR13 refer to data rates that are only used for downlink messages.

Is there any logic behind this or is this another one of those “accept it for what it is”?

Also, any chance you know the answers to questions #1 and #3?

4

That is what is called a design decision. Apparently the decision was to define a separate set of DRs for downlinks. Why? Ask the committee members that worked on the design.