Why is mobile hard?
Last updated
Last updated
Mobile communications are hard to handle, specially because spectrum is a scarce good.
One critical economic issue from the governments point of view.
Also the whole nature of mobile systems is problematic – including the device specific issues.
Although it is improving, power is still a problem.
As mobile systems became dominant (even into broadband!), scaling is a problem.
We never dreamed with such a large success.
RF Spectrum = Radio Frequency allocation.
Electromagnetic signal that propagates through “ether” at the speed of light.
Ranges 3 KHz .. 300 GHz
Omnidirectional applications;
Directional applications (above 5/10 GHz);
Or 100 km .. 0.1 cm (wavelength).
300 GHz is huge amount of spectrum!
Spectrum can also be reused in space.
Not quite that much:
Most of it is hard or expensive to use!
Noise and interference limits efficiency;
Most of the spectrum is allocated by Regulators;
ISM bands unlicensed – but subject to multiple constraints;
Governments control who can use the spectrum and how it can be used.
(ITU-T WRC. Anacom, Oftel, FCC…);
Need a license for most of the spectrum;
Limits on power, placement of transmitters, coding, ...
Need rules to optimize benefit: guarantee emergency services, simplify communication, return on capital investment, …
1 GHz to 40 GHz and higher.
Directional beams possible.
Suitable for point-to-point transmission.
Used for satellite communications.
30 MHz to 1 GHz.
Suitable for omnidirectional applications.
Roughly, 3x10 11 to 2x10 14 Hz.
Useful in local point-to-point multipoint applications within confined areas.
Industrial, Scientific, and Medical (ISM) bands.
Unlicensed, 22 MHz channel bandwidth.
