# small-scale propagation models ## Physical cause  Due to the multiple paths, there can be huge fluctuations in the received signal power. We transmit modulated sine waves, so moving a small amount dramatically changes the received signal.  ## Effects 1. Signal attenuation (up to 30dB or 1000x! ^[20dB means 100x, 30dB means 1000x, multiplier of 10 in dB is the number of zeros in linear]) 2. Varies rapidly within a distance of a few wavelengths ^[If a carrier wavelength is 1GHz, then the signal wavelength is 30cm] ## Examples [Multipath Fading](Multipath%20Fading.md) ## Description Describes the signal variation on the scale of the wavelength. ## Uses 1. [Resource allocation](Resource%20Allocation.md) algorithm design 2. Transceiver architecture design 3. [Coding](Coding.md) 4. [Modulation](Modulation.md) 5. [Interleaving](Interleaving.md) ## Other notes Small-scale fading is also called [Rayleigh](Rayleigh%20distribution.md) fading because when the number of versions of the transmitted signal which arrive at slightly different times is large, the envelope of the received signal is statistically described by a [rayleigh distribution](Rayleigh%20distribution.md) if there is no line-of-sight component. If there is a line-of-sight component, it is then described by a [Rician](Ricean.md) distribution. # References 1. [Science Direct](https://www.sciencedirect.com/topics/engineering/scale-fading#:~:text=Small%2Dscale%20fading%20refers%20to,distance%20(a%20few%20wavelengths).)