Re: Collision detection and recovery

[Marcus Müller]

Hi Nitin,

not involved in gr-ieee802-15-4, I can maybe still comment on the collision 
detection part:

On 12.06.22 09:13, Nitin Shivaraman wrote:
> Since the preamble detection happens after the clock recovery mechanism, I want to know 
> how the collision can be detected using correlation. 

Yep!

> To detect collision, I intend to 
> receive the collided packet and subtract part of the correctly received packet to recover 
> both packets correctly.

You don't even need to subtract! You're correlating, and correlation is a linear 
operation. When correlating for the preamble of the second packet, which lies within the 
first packet, you simply get as correlation the sum of the autocorrelation at timeshift 0, 
i.e. the energy, of the preamble (what you actually want to detect) and its 
autocorrelation with the first packet at the timeshift between the two packets

By design, preambles typically have high autocorrelation at \tau=0 and low for other 
timeshifts \tau. So, this should actually be pretty reliable, even without subtracting the 
other packet first! You *will* get some interference, yes, and strictly speaking, this 
should put your detection threshold a bit higher.


Best regards,
Marcus