Path Loss is the attenuation a signal experiences when propagating through space and is therefore primarily modeled to calculate link budgets or cell coverages. There are various analytical as well as empirical models for all kinds of environments, the most prominent one being the free space loss [2].
The 802.11n path loss model [3] includes breakpoint distances $d_{\mathrm{bp}}$ for 6 different scenarios defining the distance up to which a Line-of-Sight (LOS) channel with free space loss is assumed. After the breakpoint distance the channel is assumed to be Non-Line-of-Sight (NLOS) with a path loss exponent of 3.5. Mathematically, this two slope model can be described as $$ L(d)(\mathrm{dB}) = \begin{cases} 20\log{\left(\frac{\lambda}{4\pi d}\right)} & d \le d_{\mathrm{bp}} \\ 20\log{\left(\frac{\lambda}{4\pi d}\right)} + 35\log{\left(\frac{d}{d_{\mathrm{bp}}}\right)} & d \ge d_{\mathrm{bp}} \\ \end{cases} $$ where
- $\lambda$ denotes the signal wave length
- $d$ denotes the the distance between transmitter and receiver
- $d_{\mathrm{bp}}$ is the breakpoint distance
| scenario | $\mathbf{d_{\mathrm{bp}}}$ in m |
| Flat-Fading | 5 |
| Typical residential environment | 5 |
| Typical residential or small office environment | 5 |
| Typical office environment | 10 |
| Typical large open space and office environments | 20 |
| Large open space (indoor and outdoor) | 30 |