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