Author Topic: What is the shortest frame/packet that can be sent and still received?  (Read 2625 times)

WhiteHare

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Re: What is the shortest frame/packet that can be sent and still received?
« Reply #15 on: March 12, 2017, 06:17:50 PM »
So, is that the recommended number of preamble bits for 300kbps?  4 bytes worth?  I seem to be getting pretty good results with just one byte of preamble.

It sounds like one rounds up from the desired number of bits to the nearest number of bytes?  For instance, if the DS says the preamble is 12 bits (which is obviously not an even multiple of 8-bit bytes), then when setting the preamble length, do I need to make it 2 bytes?  That part I'm still unclear about.
« Last Edit: March 12, 2017, 06:33:25 PM by WhiteHare »

perky

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Re: What is the shortest frame/packet that can be sent and still received?
« Reply #16 on: March 12, 2017, 09:09:34 PM »
Well it's 12 bits plus the TS_RE time minimum, and since you can only select the preamble in units of bytes (i.e. 8 bits) you have to round up.

Edit: My maths I think is wrong, the Trssi times are part of the preamble itself (see figure 18 in the sx1231h spec), so it's actually TS_RE plus 8 bits, which actually makes it 3 bytes minimum for the preamble.

Mark.
« Last Edit: March 12, 2017, 09:17:39 PM by perky »

joelucid

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Re: What is the shortest frame/packet that can be sent and still received?
« Reply #17 on: March 13, 2017, 01:51:36 AM »
Experimentally 3 bytes are required at 300kbit even without AGC.

WhiteHare

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Re: What is the shortest frame/packet that can be sent and still received?
« Reply #18 on: March 14, 2017, 07:58:18 AM »
Thanks, guys, for your great input on this.  Makes sense.  I'm now sold on using a longer preamble and more sync bytes.   :)