3G Networks

The year 1980 observed the first commercial mobile networks. This was based on analog communication in the radio path and was termed as first generation network (1G). 1G network were confined to national boundaries. In 1990, second generation (2G) networks came with the replacement of analog networks with the digital second generation networks. The most popular 2G technology is GSM- Global System for Mobile communication. The specification of GSM was developed in the year 1989 by the European Telecommunication Standards Institute (ETSI). The 2G technology employed by Japan was PDC- Personal Digital Communication. The main limitation of 2G networks are low transfer rates, low efficiency for packet-switched services and multiple standards. Modification of 2G resulted in 2.5 Generation networks which include High Speed Circuit-Switched Data (HSCSD), General Packet Radio Services (GPRS) and Enhanced Data rates for Global Evolution (EDGE). Third generation partnership program (3GPP) emerged in the year 1998. Here a mobile competence centre has been established to ensure day-to-day running of the 3GPP. Both frequency division duplex (FDD) mode and time division duplex (TDD) mode are employed in the access network which is based on Universal Terrestrial Radio Access (UTRA) radio interface.

Radio wave propagation

There exist two ways of radio wave propagation. They are ground wave propagation and ionospheric propagation. If the electromagnetic waves are propagating near the surface of the earth, it is called ground wave propagation. This includes propagation of radio waves through troposphere too. Electromagnetic waves can travel in different ways (multiple paths) between transmitter and receiver antenna. A direct path can be established by fixing transmitter and receiver antenna in the line of sight of each other.  A wave which propagates along this path is called direct wave. The different mechanisms for electromagnetic energy transfer are direct, reflection, scattering and diffraction. The direct, reflected, scattered and diffracted waves are collectively known as space wave. When an electromagnetic wave reaches an interface between two dissimilar media, a part of the energy flows along the interface. This is known as surface wave. For a vertically polarized electromagnetic radiation, surface wave is predominant at low and medium frequencies.