The in a system known as CDMA One (a

The key requirements for any
telecommunication system are the efficient use of the available radio frequency
spectrum. The main technologies used in mobile radio include cellular frequency
reuse. The first generation systems (1G) are characterized by the fact that
they were fully based on analogue technology every user in the same cell were
allocated different channels. This technique also known as Frequency Division
Multiple Access (FDMA) where the frequency divided among multiple users. These
include systems such as the Advanced Mobile Phone System, Nordic Mobile
telephone, Total Access Communication System, etc. the analog first generation
systems  designed for voice calls. All
these systems offered handover and roaming capabilities but the cellular
networks were unable to communicate with other countries. This was one of the main
disadvantages of first generation mobile networks. When the demand grew up, the
available spectrum became progressively more congested. As a result, it quickly
became required that a less frequency spectrum technique would be required.
This led to the introduction of the second generation systems. 2G systems enabled
digital technology to provide the high levels of efficiency. The  early 2G systems were GSM and US-TDMA as well
as its derivative Pacific Digital Cellular, these used a combination of FDMA
and another technique where by every users were allocated different time frames
on the same channel. This is also known as Time Division Multiple Access.
Second generation systems offered limited data facilities, therefore interim
solutions were brought 2.5G systems provided higher data accessible rates than
the existing 2G systems. It known as General Packet Radio Service (GPRS) used
with GSM to provide an increased in data rates. Here the main change was the
use of packet switched radio systems rather than using circuit switch which
were used in the earlier systems. A data rate of up to115kbps was gained. A
further high speed improvement was provided by another technique known as
Enhanced Data rate for GSM Evolution (EDGE).Although the above systems also
used time-division approach; another system used a different technique Based on
a spread spectrum technology, it used different codes to provide access to each
users, known as Code Division Multiple Access (CDMA);this technology was
originally used in a system known as CDMA One (a full 2G Technology). The
concept is introducing a third generation systems (3G systems). CDMA2000 1X
provided better evolutionary path to 3G systems. The CDMA20001xEV-DO stands for
Evolution Data Only was designed for data only package and provides a high data
rate capability of over 2.4Mbps on the  downlink channel. It was followed by CDMA2000
1xEV-DV another 3G system EV-DV stands for Voice and Data only is an evolution
of CDMA2000 that can simultaneously handle both voice and data. Its high rate
is limited to about 384 kbps on the uplink and 3.1Mbps on the downlink. The
Universal Mobile Telecommunication System (UMTS) uses wideband CDMA offers data
rates of up to 2Mbps. Another 3G system is the Time Division Synchronous CDMA
(TD-SCDMA), which uses the same time slot for base stations and mobiles to
communicate among them. Unlike other 3Gsystems which uses time division
duplexing technique to communication. Other solutions were sought as the need
for more spectral efficient technologies and very high speed data transfer rates
were introduced. The system known as High Speed Packet Access (HSPA) was developed;
it’s referred as 3.5G system. This gives a highest data rate of about 14.4Mbps
on the downlink using packet data. Finally, the above technologies were not
fully utilized, attention was diverted to the next generation systems such as the
Ultra-Mobile Broadband which is 3.99/4G evolution cellular technology for CDMA
2000, the Long Term Evolution also 
3.99/4G technology. These systems would be much highly spectral
efficient and provide improved capabilities in terms of high speed data rates