Hi all,
I had been using the TwoRayGround model for a while and tried using the
Shadowing model and discovered something I need help. Well, my packet
delivery success rate had greatly reduce from 100% to 30% when i switch from
Freespace or Tworayground for path loss exponent =2 (same as free space) and
shadowing deviation = 1. I checked that if my shadowing deviation is 0, the
model give same result as free space model.
I dug in further and found out a criteria where packets were being dropped.
It is in the wpan/p802_15_4mac. cc.
Line no 1031:
if ((wph->rxTotPower-p->txinfo_.RxPr) > 0.0)
if (p->txinfo_.RxPr/(wph->rxTotPower-p->txinfo_.RxPr) <
p->txinfo_.CPThresh)
{
drop(p,"LQI");
return;
}
I understand here that the power receive is checked to see if it is more
thatn CPthresh times the power of interfering packets and if yes, the
packets are dropped.
In my scenerio, there is only two nodes with node 0 transmitting to node 1
only. When I use the TwoRayGround propagation, the value of power of
interfering packets are always 0 and hence no packets are ever dropped for
this reason but in Shadowing model, there is always some interfering power
with some packets getting dropped due to the fact that the power due to
interference high enough for the frame to be considered corrupted, and for
shadowing deviation =1, it is 70% of all transmitted packet. The condition
for both transmission is same and I am sure there is no interfering packets.
Another interesting thing that I noted was that the power received of the
packet with the TwoRayGround model is always the same and in the order of
10^(-12) and the interfering power is 0 while for shadowing model, the
received power of that packet is in the variation from 10^(-9) to 10^(-11)
with the interfering power also in the same order of magnitude.
Could someone please help explain me the shadowing model and also maybe why
there is interference when there is supposed to be none? Also, any other
explanation to help explain what values are the usual standards for
shadowing model will alsobe appreciated.
Thank you.
Sincerely,
Ravit Sachasiri
