Evolved Packet System (EPS): The LTE and SAE Evolution of 3G UMTS

1.4 Spectrum

The radio spectrum is the most critical resource in radio communication systems, making frequency regulation and allocation a complex issue:

• A scarce resource: because of physics laws, the amount of spectrum that can actually be used for mobile (possibly high-speed) and high bit rate applications is quite limited. The lower part of the spectrum (starting at 400 MHz) is already overcrowded with digital, analogue, public and military applications. The upper part of the spectrum, above 2 GHz, offers more possibility for extensions and high bit rate-demanding applications, at the cost of a shorter cell range because the propagation loss increases with the frequency.
• Lack of harmonization: because of the history of and disparities in regulation rules, spectrum allocation is not consistent between countries. This complicates worldwide system spectrum definition.

Coming back to cellular system history, GSM (the most popular 2G technology) was initially built to work on a single 900-MHz frequency band. The way it was introduced in the core specifications of GSM left quite limited possibilities for extension to other frequency bands. However, as GSM became largely accepted, the need for additional frequencies appeared as a requirement to support the increasing number of customers and operators. GSM was therefore modified to be able to support other frequencies on the request of specific countries, first in the 1800 and 1900-MHz bands, and then in the 450, 480 and 850-MHz ...