Spectrum:  It is a condition that is not limited to a specific set of values but can vary infinitely within a continuum.

Spectrum 2G:  It was developed in the year 1993.
Signals are transmitted in the form of digital format.
It improves the quality of calls and reduce the complexity of data transmissions.
It enables the connectivity all over the world.
Speed is 14.4 kbps.
Internet service is narrow band.
Bandwidth is 25 mega hertz.
Carrier frequency is 200 kilo hertz.

Advantages:  Short message service.
Multimedia messaging service.
Internet access.
Sim introduction.

Disadvantages:  Slow data rate.
Low network range.

Spectrum 3G:  It was developed in the year 2001.
It has packet switching except for air interface.
Speed rate is 3.1 Mbps.
Internet service is broadband.
Bandwidth is 25 M hertz.
Frequency is 5 M hertz.

Advantages:  International roaming.
High security.

Disadvantages:  High power consumption.
Low network coverage.
High spectrum license.

Spectrum 4G:  It was developed in 2009.
It has packet switching.
Speed rate is 100 Mbps.
Internet service is ultra broad band.
Bandwidth is 100 M hz.
Frequency is 15 M hz.

Advantages:  Global mobility.
High speed MIMO technology.

Disadvantages:  Hard to implement.
Complicated hardware required.