Licensed vs Unlicensed Spectrum
Radio Spectrum, in general, can be categorised into two types, a) licensed - assigned exclusively to operators for independent usage, b) unlicensed - assigned to every citizen for non-exclusive usage subject to some regulatory constraints, like restrictions in transmission power etc.
What is the advantage of a licensed spectrum?
It can be used more efficiently. Why? The reason is simple - the operator can exercise more flexibility in deploying his network to manage interference. The base stations (transmitting signals to devices) can be spaced apart, thereby optimising network costs - making services affordable.
What is the disadvantage of a licensed spectrum?
No one else, other than the licensee has the right to offer services in the licensed spectrum. Hence, the user is totally dependent on the operator for using it.
What is the advantage of an unlicensed spectrum?
Users are not dependent on any operator to use an unlicensed spectrum. It is free for all.
What is the disadvantage of an unlicensed spectrum?
Managing interference between adjacent users is more difficult in unlicensed than licensed spectrum. Why? As the usage is totally uncoordinated and haphazard with no regulatory restrictions other than a restriction in the transmission power.
How to manage interference between adjacent users in an unlicensed spectrum?
It can be done using the following strategies:-
a) Reducing transmitting power - Radio waves will die quickly before its collides with adjacent users.
b) Use higher frequency bands - Radio waves travelling at higher frequency bands die much faster (at an exponential rate) compared with those travelling at lower frequency bands.
c) Use frequency hopping - Transmitting equipment are empowered with intelligence to select a specific block of spectrum (out of a large number) which is relatively interference free than others. This ends up wasting a lot of spectrum, as only a fraction of the total assigned is used at a time.
Why are unlicensed bands at higher frequencies?
This is due to the following reasons:-
a) Higher frequency bands help in managing interference between adjacent users, as the radio waves traveling in it die out much faster compared to other bands at lower frequencies (explained above).
b) Higher frequency bands have a large amount of spectrum (compared to lowers bands). Hence, using techniques like "frequency hopping" is easy compared to lower bands - which have a significantly lower amount of spectrum.
Why are unlicensed bands not at lower frequencies?
This is due to the following reasons:-
a) Radio waves in the lower frequency bands travel far, and therefore more prone to interfering with adjacent users.
b) One cannot find a large amount of spectrum for using techniques like "frequency hopping" to manage interference between adjacent users.
Hence, the lower frequency bands are best used if assigned for licensed operations.
Why should 60 GHz band be used for unlicensed operations?
60 GHz band (V band) is the best band to support unlicensed operations. This is due to the following reasons.
a) Radio waves travelling in this band die out 100 times faster compared to neighbouring frequencies, due to the "oxygen molecule" interference. See my note titled - Valuation of 60 GHz spectrum (V Band).
b) A lot of spectrum is available (9000 MHz) for supporting all kinds of interference mitigation techniques like frequency hopping etc.
c) Valuation of this band (if assigned through auctions) will be much lower compared to other similar bands. See my note titled - Valuation of 60 GHz spectrum (V Band).
d) Internationally this band is not auctioned but used for unlicensed operations.
Hope you find this FAQ useful. Thanks.
(Views expressed are of my own and do not reflect that of my employer)
PS: Find the list of other relevant articles in the embedded link.
Ingénieur en Systèmes Réseaux et Télécommunications option Technologies Mobile, Système et Services Réseaux . NSE 1,2 &3 | ePMP | PMP 450 | CCNA | LinkPlanner | CCNA SECURITY | CCNP in progress | Chef de Projet | ITIL?4
3 年Great article thanks Parag Kar
Bhawani traders Ashta
7 年My home
State Resource Person at BIHAR Institute Of Public Administration Patna Bihar
7 年License
Transmission Planner
7 年licensed spectrum can be assigned to the operator for countrywide, regional, or even individual radio use. there is also option for light licensing, which is a faster and cheaper way of licensing in the mmwave bands. the success of unlicensed spectrum usage depends on the application: wi-fi is excellent for indoor, or limited outdoor use. but using it above rooftop level in urban area is only making a mess. using proper antennas is a key factor for minimizing interference. unfortunately unlicensed is often a synonym of cheap bad quality radios, antennas, and incompetent istallation/settings. 60GHz band has the advantage because of the specific propagation due to O2 absorption. but the same reason brings on, that the distance is limited. also the reflection, diffraction, and penetration features are far worse than lower bands.