It was only at the beginning of the 1980s when mobile phone technology started to be introduced and accepted in a large way. Since then there have been many new cell phone or mobile phone systeith a real need for their employees to be able to keep in touch all the time. Now they are an almost essential personal belonging for most people. In many countries market penetration has exceeded 70%, and it is not uncommon for many people to have one phone for business and another for personal use. Accordingly in some segments of the population the market penetration is very much higher than 70%.
Development overview
The phones themselves have undergone many changes. The technologies used have improved. The first systems to be launched were based on analogue technology. The early phones were very large and could certainly not be placed in a pocket like the phones of today.
The first generation (1G) phone systems as they are now known were overtaken in the early 1990s by the first digital systems.
The high levels of use and limited frequency allocation meant that greater spectrum use efficiency was needed. Accordingly the next or second-generation (2G) phone systems were introduced to meet this need.
As the usage of phones increased and people became more mobile, new possibilities emerged for using the phones for data transfer. They could be used to download information from the Internet, or to send video. The first stage in this migration was to provide a medium speed data transfer capability. These systems were accordingly known as 2.5G.
However the ultimate aim was to provide a relatively high-speed data transfer capability. These full third generation (3G) systems took longer to develop and roll-out than had been originally anticipated as a result of higher development costs and a downturn in the global economy. However they are able to provide a significant improvement in capability over the 2.5 G systems
Analogue Systems
There was an enormous variety of first generation systems that were introduced. Much of the early development of cellular systems had been undertaken in the USA, but the first fully commercial system to be launched was the Nordic Mobile Telephone (NMT) system. Shortly after this a system known as the Advanced Mobile Phone System (AMPS) was launched commercially. This was developed primarily by Bell and was introduced in the USA although many other countries used this system later. A further system known as Total Access Communication System (TACS) developed by Motorola was introduced in the UK and many other countries.
These were the main systems that were developed, although around the globe many variants were developed to suit the needs of the individual countries.
Although there were differences in the specifications of the systems, they were all very similar in concept. The voice information was carried on a frequency-modulated carrier. A control channel was also used to enable the mobile to be routed to a suitable vacant channel. The channel spacing for each system was different. NMT used a 12.5 kHz channel spacing, AMPS, a 30 kHz spacing and TACS a 25 kHz spacing. A later development of AMPS called NAMPS or narrowband AMPS used a 10 kHz channel spacing to conserve spectrum.
Digital systems
The analogue systems were very successful, but their very success started to show some of their shortcomings. The main one was the inefficient way in which they sued the spectrum. With the growth rates that were being seen, there was insufficient spectrum to support the quality of service that was required. By converting to a digital system, considerable savings could be made. A number of systems arose from this initiative. These second-generation systems as thems introduced, and many improvements have been made in the technology. The mobile phones themselves as well as the associated equipment including base stations and the other network equipment has become much cheaper and far smaller.
One of the major changes is the level of market penetration that has been achieved. Around one in six of the worlds population now has a mobile phone. When the first systems were introduced the operating and ownership costs were such that they were only used by businesses wy were termed, started to be deployed in the early 1990s.
The system that was developed in Europe was the result of 26 telecommunications companies working together. Work actually started in 1982, and the roll-out commenced in 1991. The system known by the letters GSM was originally called Groupe Speciale Mobile but this was later changed to Global System for Mobile communications in view of the wide involvement in its development. It used time division multiple access (TDMA) to allow up to eight users to use each of the channels that are spaced 200 kHz apart. The basic system used frequencies in the 900 MHz band, but other bands in the 1800 and 1900 MHz (USA) bands were added. New bands in the 850 MHz region were also added.
In the USA a system specially designed to operate alongside their AMPS system was devised. The system was known under a variety of names including Digital AMPS or DAMPS, and US Digital Cellular (USDC), although it is normally known just as TDMA today as it relies on TDMA technology. The system was originally defined under standard number IS-54, although this was later updated to IS-136 and it uses a 30 kHz channel spacing to make it compatible with the existing AMPS systems in operation.
Another development in the USA from Qualcomm took a major leap in technology. It introduced a totally new concept for multiple access. Based on direct sequence spread spectrum (DSSS) that had previously been used for military transmissions, it used a multiple access system known as code division multiple access (CDMA). The new system offered far greater levels of spectrum efficiency although it required more complicated circuitry in the handsets. The system was defined under standard IS-95 and each carrier had a bandwidth of 1.25 MHz, although many users could use the same channel. The specification was updated from IS-95A to IS-95B. It was this later standard that went under the trade name cdmaOne.
2.5G
Once the second-generation systems became established it soon became apparent that the limited data capabilities of some of the 2G systems were a significant disadvantage. Many applications for data transfer with the increased use of the Internet and laptop computers were seen. Even though the third generation systems were on the horizon, developments were needed to provide a service before they entered the market. One of the first was the General Packet Radio Service (GPRS) development for the GSM system. Its approach centred on the use of packet data. Up until this time all circuits had been dedicated to a given user in an approach known as circuit switched, i.e. where a complete circuit is switched for a given user. This was inefficient when a channel was only carrying data for a small percentage of the time. The new packet switched approach routed individual packets of data from the transmitter to the receiver allowing the same circuit to be used by different users. This enabled circuits to be used more efficiently and charges to be metered according to the data transferred.
Further data rate improvements were made using a system known as EDGE (Enhanced data Rates for GSM Evolution). This basically took the GPRS system and added a new modulation scheme, 8PSK, to enable a much higher data rate to be achieved. Whilst the symbol rate remained the same at 270.833 samples per second, each symbol carried three bits instead of one.
Whilst GPRS and EDGE were applied to GSM networks, enhancements were also applied to the CDMA system that originated in the USA. Here an evolutionary path from 2G through 2.5G to 3G was created. The intermediate stage was development of cdmaOne was CDMA2000 1X. This scheme retained the 1.25 MHz bandwidth of IS95 / cdmaOne, but by adding further channels enabled data transfer rates of 307 kbps to be achieved, thereby doubling the capacity of IS95B.
Third Generation
Although technologies such as GPRS, EDGE and CDMA2000 1X were able to deliver significantly higher data rates than their predecessors, the final migration was to the full 3G service. There were three main technologies.
From Europe there was the UMTS (Universal Mobile Telecommunications System) using wideband CDMA (W-CDMA). This system used a 5 MHz channel spacing and provided data rates of up to 2 Mbps.
Then there were the CDMA2000 evolutions. The first to be launched was CDMA2000 1xEV-DO. Here the letters EV-DO stood for Evolution Data Only. The idea for this system was that many of the applications would only need a data connection, as in the case of a data card for use in a PC to provide a wireless Internet capability over a mobile phone system. For any applications needing both data and voice a standard 1X channel would be required in addition. Although using CDMA technology, the EV-DO system also used TDMA technology as well to provide the throughput whilst still maintaining backward compatibility with IS95 (cdmaOne) and CDMA2000 1X.
The next evolution of the CDMA2000 family was CDMA2000 1xEV-DV. This was an evolution of the 1X system, and totally distinct from 1xEV-DO and it provided a full data and voice capability. Again this system was able to provide backward compatibility with IS95 (cdmaOne) and CDMA2000 1X whilst still being able to provide a data capability of 3.1 Mbps in the forward direction.
These major two players in the 3G scene both used what is called frequency division duplex (FDD) where the forward and reverse links used different frequencies. Within UMTS there is a specification covering a time division duplex (TDD) system where the forward and reverse links used the same frequency but use different timeslots. However the TDD version is not being deployed for some time.
A third 3G system that originated in China uses TDD. Known as time division synchronous CDMA (TD-SCDMA) this system used a 1.6 MHz channel spacing and was thought to be likely to take a significant portion of the Chinese market along with those in neighbouring countries
Summary
It took just over 20 years to migrate from the first analogue systems to the 3G systems capable of high data rate transfers. Now people are working on the 4G standards and it remains to be seen what new services and capabilities this new technology will offer
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