In 1946, the first car-based telephone was set up in St. Louis, Missouri, USA. The system used a single radio transmitter on top of a tall building. A single channel was used, therefore requiring a button to be pushed to talk, and released to listen. This half duplex system is still used by modern day CB radio systems utilized by police and taxi operators. In the 1960s, the system was improved to a two-channel system, called the improved mobile telephone system (IMTS). Since frequencies were limited, the system could not support many users.
Cellular radio systems, implemented for the first time in the advanced mobile phone system (AMPS), support more users by allowing reuse of frequencies. AMPS is an analogue system, and is part of first generation cellular radio systems. In contrast, second generation systems are digital. In the USA, two standards are used for second generation systems: IS-95 (CDMA) and IS-136 (D-AMPS). Europe consolidated to one system called the global system for mobile communications (GSM). Japan uses a system called personal digital cellular (PDC).
Present Day
Cellular radio is the fastest growing segment of the communications industry. Cellular companies reported a subscription base of more than 200 million people in 1997. This figure grows by an average of 150,000 new subscribers every day.
Because of Europe's early commitment to one system, it is leading the field in both its subscriber base and data transmission capabilities. GSM is used in over 100 countries by over 215 operators inside and outside of Europe. The Japanese PDC system is the second largest digital cellular system, followed by the IS-54/136 and IS-95 systems used in North America.
Current cellular radio systems are in their second generation (2G). The third generation of cellular systems (3G systems) will allow different systems to interoperate in order to attain global roaming across different cellular radio networks. The International Telecommunication Union (ITU) has been doing research on 3G systems since the mid 1980s. Their version of a 3G system is called international mobile telecommunications - 2000 (IMT-2000).
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