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In this model, the shadowing fading factor is not considered.
Therefore, for a unique distance, the *Pr* is a
determinstic value.
Usually, tworayground has two formulas:

- when d is less than the crossing distance: Free Space model is used.
- when d is larger than the crossing distance: the follownig formula is applied:

P_{r} = P_{t}G_{t}G_{r}h_{t}^{2}h_{r}^{2}
/ (Ld^{4})

Based on the default settings in ns-2, we can derive a relationship between Pr and distance

Default parameter in ns-2:

- Pt = 0.28183815
- L = 1
- Antenna Gain : 1
- Antanna height 1.5m

Distance | Pr |

15m | 2.81838e-5 |

20m | 8.91754e-6 |

22m | 6.0908e-6 |

30m | 1.7615e-6 |

60m | 1.1009e-7 |

120m | 6.8808e-9 |

200m | 8.9175e-10 |

210m | 7.3365e-10 |

220m | 6.908e-10 |

230m | 5.0986e-10 |

240m | 4.3005e-10 |

250m | 3.6526e-10 |

300m | 1.7615e-10 |

350m | 9.5081e-11 |

400m | 5.5735e-11 |

450m | 3.4795e-11 |

500m | 2.2829e-11 |

550m | 1.5592e-11 |

600m | 1.1009e-11 |

650m | 7.993e-12 |

700m | 5.9425e-12 |

750m | 4.5094e-12 |

In reality, path loss index is only 2 in near distance. Therefore, for near-distance (<25m) , the above formula does not apply. When distance is less than ~25 meter, the Friss model will be used. Check tworayground.cc for detail