Question

Question about networks and 5G.

Millimeter waves can be used for 5G cellular systems.

What are some challenges we may face if millimeter waves are used for communication?

Answer 1

Answer:

Challenges we may face if millimeter waves are used for communication:

The major challenge has been the travelling media due to the poor penetration attributed to atmospheric and free-space path loss.

Some of the challenges faced by millimeter waves include

Free space loss – The free space loss in dB is calculated with:
L(Transmission loss) = 92.4 + 20log(f) + 20log(R)

Atmospheric absorption – The atmosphere absorbs millimeter waves, thus restricting their transmission range. Rain, fog, and moisture in the air make the signal attenuation very high. Oxygen (O₂) absorption is especially high at 60 GHz.

Mechanical resonance – The mechanical resonance frequencies of gaseous molecules also coincide with the millimeter wave signal. For current technology, the important absorption peaks occur at 24 and 60 GHz.

Scattering – Millimeter wave propagation is also affected by rain. Raindrops are roughly the same size as the radio wavelengths and therefore cause scattering of the signal.

Non-line of sight issues – When a line-of-sight path between transmitter and receiver isn’t present, the travelling signal still has alternative ways to reach the receiver, be it through diffraction, reflection or bending. Diffraction in millimeter waves is scarce due to the short wavelengths.

Brightness temperature – When millimeter waves are subjected to absorption by water vapor, oxygen and rain, these molecules absorb high frequency electromagnetic radiation. This absorption subsequently leads the molecules to emit higher frequency EM radiation (closer to the infrared spectrum). This energy emission, when received by a receiver antenna, is called brightness temperature and it degrades system performance. Any Earth-based antenna aimed at a satellite with a high elevation angle, for example, will suffer signal degradation caused by picking up brightness temperature emanating from atmospheric constituents.

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