LOS ANGELES � In DRU, we�ve covered many stories on the development of technology that makes use of millimeter wave bands (between 30 and 300 GHz).� (Here�s one aboutFacebook;here�s one aboutBoeing�s satellite system.)� Many of you have probably thought, as I have, that this is going to be tough, just based on what little we know of propagation in these bands.�
An article inrcrwireless.comsummarized the physical issues thus:
- �� � ��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 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�� Raindrops are roughly the same size as the millimeter 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 must use alternative ways to reach the receiver, such as diffraction, reflection or bending. Diffraction in millimeter waves is scarce due to the short wavelengths.
�The difficulties associated with mmWave means standards organizations and mobile operators will continue to rely heavily on sub-6 Ghz spectrum,� according to the same article.
The International Telecommunications Unionat WRC-15 reached agreements and identified new spectrum for mobile communications for International Mobile Telecommunications, the collective term for 3G, 4G and 5G:�� � ��
- A decision was reached to make the L-Band (1427 � 1518MHz) and part of the C-Band (3.4 � 3.6GHz) available for mobile broadband on a global basis.
- �� � ��The 700MHz band (694 � 790MHz) is now also globally harmonized following the initial decisions made at WRC-12 and the follow-up action at WRC-15 for its use in Europe, Middle East and Africa.
- �� � ��Additional spectrum is identified in some countries in the frequency bands 470 � 694/698MHz, 3.3-3.4GHz, 3.6-3.7GHz and 4.8 � 4.99GHz.
- �� � ��Spectrum at higher frequencies in the range from 24.25GHz up to 86GHz will be subject to study work for 5G (IMT-2020) usage in ITU, providing one of the cornerstones for future 5G services.
WRC-19, to be held in 2019, will decide millimeter wave spectrums allocations.��