The unlicensed spectrum has no associated licensing and bandwidth fees. Since there are no licensing fees and less usage regulations, unlicensed spectrum has a much higher chance of interference by other users. Typically unlicensed frequency bands have a narrow, more controlled bandwidth usage. The 60 GHz, 70/80 GHz and 90 GHz frequency band are the exception having wide channel bandwidths.
The licensed spectrum typically has associated fees for spectral and bandwidth usage. There is typically less chance of interference and congestion with less users operating in the same spectral band. Typically a licensed band offers more available bandwidth than a comparable unlicensed band. Licensed spectrum typically offers higher reliability and greater transmission distances.
Why use 60 GHz for wireless video transmission?
60 GHz is a globally allocated unlicensed spectrum.
- UK 57-64 GHz License Exempt, 64-66 GHz Light License
- ETSI 57-66 GHz License Exempt
- FCC/IC 57-64 GHz License Exempt
The 60 GHz spectrum or V band offers 7 GHz of usable spectrum between 57 GHz and 64 GHz. This provides high-bandwidth capability for the transmission of uncompressed 1.485 Gbps 720p or 1080i HD SDI video.
The 60 GHz oxygen absorption and attenuation “feature” enables it to be used for secure and highly sensitive DOD satellite to satellite communications systems. It is not possible to eavesdrop on a 60 GHz signal outside the Earth’s oxygen atmosphere as the signal will be absorbed and dissipated.
There are a variety of environmental factors that affect the choice between 60 GHz, 70/80 GHz, and 90 GHz bands including oxygen absorption, rain, and fog. The 60 GHz band is more readily absorbed and attenuated by oxygen molecules which can limit the transmission distance in some applications when compared to the 70/80 GHz and 90 GHz bands. The 60 GHz frequency, however, is less susceptible to rain and fog when compared to the 70/80 GHz and 90 GHz bands making it a better choice in humid and wet environments. Understanding these limitations can be used as an advantage in certain applications.
A 60 GHz signal also does not travel far beyond the intended user. This makes the signal difficult to detect and ideal for secure communications. In military and battlefield operations a command vehicle can communicate with a soldier on the front line with line of sight a kilometer away. The transmission will not give away the command vehicle’s position as the propagation distance of the 60 GHz signal is quickly attenuated by the oxygen in the air. Encryption is also often not necessary because of this propagation distance limitation.
A 60 GHz wireless system has a narrow transmission beam width of approximately 4°. The beam width of an RF transmission signal is inversely proportionate to the frequency as shown in table 1.
|Frequency||99.9% Beam Width|
|2.4 GHz||117 degrees|
|24 GHz||12 degrees|
|60 GHz||4.7 degrees|
Table 1 – Beam Width for Several Unlicensed
Frequency Bands for 30 cm diamter antennas