Wireless services

This century has seen the development of a public wireline network that allows reliable and affordable communication of voice and low-rate data around the globe. The goal of wireless communication is to allow the user access to the capabilities of the global network at any time without regard to location or mobility.

Different types of wireless services exist:

· Cordless telephone
The basic cordless telephone (for example, CT0, CT1) provides a wireless counterpart to the standard telephone. The handset typically operates within 50 to 100 m of the user's base station, which is connected to the public switched telephone network (PSTN).

· Cordless systems
With the advent of digital cordless telephony, cordless systems with enhanced functionality (DECT, PHS) have been developed that can support higher data rates and more sophisticated applications such as use of multiple handsets with one home base station. Cordless Telephone-2,
also a digital cordless system, has less functionality as DECT or PHS, the user is not capable of moving out of his home base station range and roam in the public network as is possible with PHS (future enhancement for DECT). To setup a call in the public network the user needs to be in the area of special base stations. An example is public access Telepoint systems (Greenpoint).

· Wireless PBX
Wireless private branch exchanges have similar functions as PHS and DECT but limited to the premises of the PBX owner.

· Cellular systems
Analog Cellular systems (for example, AMPS,TACS and NMT) and Digital Cellular systems (for example, GSM and CDMA IS-95) currently are limited to voice and low-speed data within areas covered by base stations.

· Airphone
Airphone is used in airplanes where the calls are initiated from.

· Paging
Paging covers all public messaging services. Radio messaging services offer the possibility of transmitting short messages in one direction to a specific user whose location is unknown. The message may be limited to a tone signal or may consist of alphanumeric characters.

· Mobile satellite service
There are some situations in which providing radio coverage with cellular like terrestrial wireless networks is either not economically viable (such as in remote, sparsely-populated areas), or physically impractical (such as over large bodies of water). In these cases, mobile satellite services (MSS) could fulfill the gap, allowing complete global coverage. Spectrum has been designated by the ITU for MSS, and there are many MSS systems in various stages of concept, design and operation.

Wireless systems evolution

The evolution of wireless systems takes place in three generations:
· Generation 1: Analog wireless systems
· Generation 2: Digital wireless systems
· Generation 3: Integration of all kinds of wireless systems into one universal mobile telecommunication system

Generation 1 systems:
Cellular system design was pioneered during the '70s by Bell Laboratories in the United States, and the initial realization was known as AMPS (Advanced Mobile Phone Service). The AMPS cellular service has been available in the United States to the public since 1983. Systems similar to AMPS were soon deployed internationally.

Generation 2 systems:
The development of low-rate digital speech coding techniques and the continuous increase in the device density of integrated circuits have made completely digital second-generation systems viable. Digital systems can support more users per base station per MHz of spectrum than analog systems, allowing wireless system operators to provide service in high density areas more economically.

To meet the growing need to increase cellular capacity in high-density areas, different standardization bodies developed their own standard:

· The Electronic Industries Association (EIA) and the Telecommunications Industry Association (TIA) in the USA adopted the IS-54 standard (DAMPS) and later on the CDMA IS-95 standard.
· The European Telecommunications Standards Institute (ETSI) adopted the GSM standard.

Generation 3 systems:
Work is continuing in the European research consortium, RACE, and in ETSI towards developing UMTS (Universal Mobile Telecommunication System) on a joint European basis. At the same time, the ITU is working globally towards IMT-2000 (International Mobile Telecommunications-2000) with mutual agreement and information exchange. Technically, these systems by offering bandwidths of more than 2 Mbit/s, open new possibilities for additional services in mobile communication networks, such as full motion picture transmission.