Adjusting ACK_TIME with lower bitrates

[hneiraf]

Hi all,

#define ACK_TIME     50 works for 56kbps
I have changed the bitrate to lower values, and I have seen the moteinos reporting ACK fail.
As I understand I have to increase the 50ms time for the ACK_TIME in order to get ACK OK with lower bitrate. Is there a rule?
Or just test and test... ?

Best,

HN

[Felix]

Lower bitrate means longer time to transmit the message. I suppose there is a bitrate-transmit time relationship but not sure how to best determine it.
The simple way is to just increase it until you feel it's a good timeframe to catch any expected ACK.

[jbeale]

You can make a quick sketch to measure and print out the actual time for an ACK. The code I posted in this message does that, among other things:
http://lowpowerlab.com/forum/index.php/topic,160.msg623.html#msg623

Excerpt from its output:

Code Select Expand

Sending[1]: - wait 12 On try 1 ACK after 9 msec. Packets: 79301 Retries: 271
Sending[25]: - wait 18 On try 1 ACK after 16 msec. Packets: 79350 Retries: 271

With the default datarate and 1 byte of data, you can see that the ACK happened in 9 msec (although I allowed for 12 msec), and with 25 bytes of data, it took 16 msec (although I allowed 18 msec).  You can use similar code to measure the actual ACK time with whatever bitrate you configured, then set the ACK timeout to a few msec longer just in case.  That assumes your timing is determined only by the radio module Tx/Rx time, and your receiving unit is not delaying its ACK reply further with other local processing prior to replying.

[hneiraf]

Thank you Jbeale