Why is mobile hard?

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

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, …

General Frequency Ranges

Microwave frequency range

1 GHz to 40 GHz and higher.

Directional beams possible.

Suitable for point-to-point transmission.

Used for satellite communications.

Radio frequency range

30 MHz to 1 GHz.

Suitable for omnidirectional applications.

Infrared frequency range

Roughly, 3x10 11 to 2x10 14 Hz.

Useful in local point-to-point multipoint applications within confined areas.

Frequency Bands

Industrial, Scientific, and Medical (ISM) bands.

Unlicensed, 22 MHz channel bandwidth.