The Mobile Telephone System

The traditional telephone system (even if it some day gets multi-gigabit end-to-end fiber) will still not be able to satisfy a growing group of users: people on the go. People now expect to make phone calls from airplanes, cars swimming pools, and while jogging in the park. Within a few years they will also expect to send e-mail and surf the Web from all these locations and more. Consequently, there is a tremendous amount of interest in wireless telephony.
Wireless telephones come in two basic varieties: cordless phones and mobile phones (sometimes called cell phones). Cordless phones are devices consisting of a base station and a handset sold as a set for use within the home. These are never used for networking. And mobile phones are used for wide area voice and data communication. Mobile phones have going through 3 distinct generations, with different technologies:
1. Analog voice (1st Generation)
2. Digital voice (2nd Generation)
3. Digital voice and data (3rd Generation with Internet, e-mail, etc)
The first generation of mobile phones was analog, dominated by Advanced Mobile Phone System (AMPS). In all mobile phone systems, a geographic region is divided up into cells, which is why the devices are sometimes called cell phones. In AMPS, the cells are typically 10 to 20 km across; in digital systems, the cells are smaller. Each cell uses some set of frequencies not used by any of its neighbors. The key idea that gives cellular systems far more capacity than precious systems is the use of relatively small cells and the reuse of transmission frequencies in nearby (but not adjacent) cells.
The second generation of mobile phones was digital. Just there was no standardization during the first generation; there was also no standardization during the second, either. Four systems are in use: D-AMPS, GSM, CDMA, and PCA.
PCA is used only in Japan and is basically D-AMPS modified for back-ward compatibility with the first-generation Japanese analog system. Personal Communications Services (PCS) originally meant a mobile phone using the 1900 MHz band, but that distinctions rarely made now. The second generation of the AMPS systems is D-AMPS and is fully digital. D-AMPS is widely used in the U.S. and (in modified form) in Japan. Virtually everywhere else in the world, a sstem called GSM (Global System for Mobile Communication) is used, and it is even starting to be used in the U.S. on a limited scale. GSM channels are much wider than the AMPS channels (200 kHz versus 30 kHz) and hold relatively few additional users (8 versus 30, giving GSM a much hither data rate per user than D-AMPS. Global system for mobile communications (GSM) was developed on TDMA protocol in Europe; GSM is now the worldwide standard technology for mobile communications.

The advantage of GSM is that it provides a high level of security, globally accepted technology standards and superior sound quality. For any GSM phone to work, it requires a Subscriber Identity Module (SIM), a card that contains your telephone account information. Thus, a national GSM phone can be used in other foreign countries too.
What is the future o mobile telephony? High quality voice transmission, Messaging (replacing e-mail, fax, SMS, chat etc.), Multimedia (playing music, viewing videos, films, television, etc.) and Internet access (Web surfing, including pages with audio and video). GPRS, short for General Packet Radio Services, is an enhancement to GSM technology that integrates GSM and IP technology. GPRS offers always-on, high speed connectivity to the Net. Thus you can check your email on the move and surf the Web at high speeds. In this hi-tech age, people on the move need any-time access to the Net. This is where WAP comes in.
It provides Internet access to cell phones. It is an open standard for wireless protocols that is independent of the service providers. To display Web content, the cell phone must have a WAP browser. Nowadays, cell phones often come with GPRS and WAP technology. WAP and GPRS also allow you to download games, send mail and even transfer your messages to your PC. The new EDGE ((Enhanced Data GSM Environment) interface has been developed specifically to meet the bandwidth needs of 3G. Promoted by Ericsson, it offers high-speed data transfers over GSM networks with just a software upgrade to the handset. EDGE allows speeds up to 384 kbps.
Now it’s the time of 3rd generation mobile communication.