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# ⌘ B3-Multipath Propagation

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B-Antennas and Propagation
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Multipath Propagation, Reflection, Diffraction
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# ⌘Multipath and how to use it

 Multipath propagation can be used through ) specific receivers (rake receivers) ) Multiple-input, multiple-output antenna systems (MIMO)

Note: The mobile phone users will typically not have a direct link between the mobile phone and the antennas of the base station in a typical environment. Such a situation, where the mobile communication has to go "around a building" or "around the corner" are called NLOS, non Line-of-Sight connection. As compared to a Line-of-Sight LOS connection the signal is typically reduced by some 20-30 dB.

# ⌘ Boundary conditions

• What is happening on electrical walls, magnetic walls?

Scattering, reflection and diffraction (explain differences) are the three major components in wave propagation. Ideal reflection environments are characterised through $|r| =1,\ \ \phi_r=180\deg$

 Receiver characteristics for usage of reflections in impulse response sliding 16 mu s window and integration of power in this window (typical GSM) Rake receiver, where each finger of the receiver points to one reflection (typical enhanced GSM, UMTS) MIMO (Multiple input, multiple output) or smart antenna arrays. Here we use spatial filtering, assuming that radiation comes in from different directions (typical 802.11n, smart antennas for UMTS)

## ⌘ Reflection

 Reflection at a perfectly plane gives a reflection coefficient r= -1. When the surface gets rougher, reflection is still in the main direction, but the reflected power is spread around the main reflection angle. Assuming that no absorption takes place, then the total reflected power is constant. When the surface becomes extremely rough, and with roughness >> lambda, then the reflected wave will be scattered into any direction.

## Related physics

Free Space impedance $Z_0$ as connection of permeability $\mu_0$ and permittivity $\varepsilon_0$.

$\mu_0=4 \pi \cdot \10^{-7} N/A^2$. The unit of $\mu_0$ is $Newton/Ampere^2 = N/A^2 = kg m/s^2 1/A^2$

$\varepsilon_0=\frac{1}{\mu_0 c^2}$
$= 8.854 \cdot \10^{-12} F/m$.

The unit of $\varepsilon_0$ is Farad/m: $F/m = A s/V = A^2 s^4/(kg m^2)$

# Diffraction

Diffraction is the transforming of a wave at an object, typical edge of a house ("edge diffraction") or the roof-top

# Scattering

Interaction with object being about the same size as the wavelength, $lambda...$