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Early History of Mobile Communication Networks
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| Australia has nearly 15 million mobile phone subscribers |
The first car based telephone mobile, implemented in the city of St Louis (USA) dates back to 1947. This system allowed wireless and mobile telephone handsets to be connected to the Switched Telephone Network (PSTN) via a single antenna (Base Station) located on a tall building. This early implementation proved that the concept of mobile communications where users could be contacted any time anywhere was feasible. This very basic system relied on a half duplex communication where a single frequency (or channel) had to be shared among potential users. In the late 1960s, this system was upgraded to a full duplex system, the Improved Mobile Telephone System (IMTS) where 2 different channels were used for communications between the base station and the mobile users (downlink) and the communication between the mobile users and the base station (uplink).
First Generation of Mobile Communication Systems
The main limitation of the IMTS which still relied on a single base station was the poor capacity since only 2 channels had to be shared among all potential users in the system. In order to solve this capacity problem, the concept of cellular network was introduced: the coverage area was split into cells, each served by their own base station operating on frequencies that could be re-used by other distant cells. The Advanced Mobile Phone System (AMPS) was the first example of such a cellular network and relied on analog communication. AMPS, the first generation cellular radio system started experiencing rapid growth in the 1980s.
Second Generation of Mobile Communication Systems
The first Second generation system based on a digital transmission was developed initially in Europe in the early 1990s by a study group called the "Group Special Mobile" (GSM). The responsibility of the GSM was transferred in 1989 to the European Telecommunication Standard Institute (ETSI) and commercial service started in 1991, initially in Europe and later on extended to 110 countries around the world. The acronym GSM now stands for Global System for Mobile communications. The choice of digital communications as opposed to analog was made in order to support a wider range of services requiring higher data rates. At that time, significant advancements were made in the area of Digital Signal processors and compression algorithms. However, due to radio transmission limitations, the expected 64kb/s was not achieved. GSM relies on a combination of Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) where users share a pool of available frequencies and are allocated time slots within frames. It was claimed that TDMA was not resilient towards multipath propagation and required the use of equalizers. Code Division Multiple Access (CDMA) seemed to be more robust towards these impairments and it was chosen by Qualcomm for their second generation IS95 which was implemented in the USA.
Third Generation (3G) of Mobile Communications Systems
One of the major goals of 3G systems is to allow different systems to interoperate in order to obtain global roaming. The International Telecommunication Union (ITU) has been doing research on 3G since the mid 80s and their system is called International Mobile Telecommunication 2000 (IMT 2000). European countries are also researching on the implementation of 3G and their system is called Universal Telecommunication Systems (UMTS) which has the same goals as the IMT 2000.
- Universal roaming
- Standardization of radio interfaces
- High data rate transmission for both circuit and packet switched systems
- High bandwidth efficiency
CDMA was chosen as a basic building block for UMTS and IMT2000. Research is still active to solve the many issues associated with the idea of supporting high data rates in a multi user and limited bandwidth environment. In Australia, a consortium, m.Net Corporation, comprising many telecommunication companies and service providers, was created to provide a proof of concept of 3G systems. Despite such isolated initiatives aimed at convincing that 3G is a reality, there is a growing concern that these advanced systems will never be implemented in various countries. Some attribute this delay of implementation to the fact that different standards are still being used throughout the world which makes global roaming difficult to achieve. A more fundamental problem is the lack of clarity as to whether users are prepared to pay a high cost for services that are not really needed.
Fourth Generation Systems
While 3G technology is still to convince users, there has been a growing interest in 4G technology and in fact, 4G systems have already been deployed in many countries. 4G systems are IP-based and provide access through a collection of radio interfaces. They promise global roaming, wireless internet combining multiple radio interfaces (such as Wireless LAN, Bluetooth, GPRS, Hiperlan) into a single network.
More Information
- International Engineering Consortium (IEC) tutorials on Cellular Communications, Wideband CDMA and GSM
- Sun Microsystems' article on 4G Wireless
- 3G standards consortia, including 3GPP, 3GPP2 and ETSI
Australian Mobile Communications Researchers
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