CellPhoneInfo

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The problem with early radio telephones was that they quickly ran out of available frequencies, i.e. channels. Often a wealthy individual with a radio telephone in his car would have one of his employees make a series of calls starting very early in the morning to reserve a channel for himself and guarantee that he could have his radio telephone available as he was being driven to work, just like Humphrey Bogart in the original movie "Sabrina".

The problem was that to be useful, a radio telephone had to work throughout a whole metropolitan area, and a large area even back then made for a large number of users. The problem could be solved by having many small areas (now called cells) which all shared the same frequencies. A small area only had a small number of users so that the number of frequencies was adequate. What would happen, however, when a user drove from one of the areas to another? In principle this problem could be solved by doing automatic switchovers from one cell to another, but such automatic switches were very complicated to implement. Enter the digital computer. It was capable doing the complex job of managing the switchover so that the call would not be lost, and the modern cell phone was born.

At first the speech was analog, and the logic to manage the switchover was digital (i.e. done by a digital computer). These types of cell phones are known today as analog phones even though the switching is digital. A true all-digital cell phone, however, would also represent the speech as a series of numbers, i.e. in digital form. A cell phone which also digitizes the speech improves the sound quality, gets rid of static on the line, and incidentally, increases the battery life by 3 to 5 times. (Also see the article on the difference between analog and digital systems.)

Since also making the speech digital was even more complicated than just making the switchover digital, the true all-digital cell phone had to wait for microprocessors to get smaller and more powerful. This has now been achieved, and one can have truly high quality cell-phone service with the new digital units. All-digital cell phones have now become so capable, the call rates so low, and the battery life so long that it makes sense for some businesses to have only cell phones for their business extensions.

To have a rough idea of how rapidly cell-phone use has grown, the first commercial cell phone service was started by NTT in Japan on December 3, 1979. The commercial AMPS (Advanced Mobile Phone Service) began in the U.S. in 1983. By the late 1980s the GSM (Global System for Mobile communication) all-digital system based on TDMA was introduced in Europe. TDMA stands for Time Division Multiple Access. The Multiple Access part simply means that many people can use the system at once, i.e. it provides the channels. Time Division means that each user is separated from another by having pieces of their conversations go through at different times.

TDMA all-digital systems became available in the U.S. in the early 1990s, and CDMA (Code Division Multiple Access) all-digital systems began to be offered around 1995. Code Division Multiple Access is based on the highly secret technology which has been used in limited form by the U.S. military since the 1950s to keep their communications, radar, and sonar secret. It was invented among others by the actress Hedy Lamar in the mid 1940s.

CDMA gives superior digital service; and because of its greatly increased capacity to handle large numbers of channels, probably is the future of cellular communications. Because of this TDMA phones are now obsolete.

If you wish the best digital performance and the fewest dropped calls, I recommend CDMA digital cell phones. The cell-phone service providers have chosen not to market the concept CDMA since they believe that the idea is too complex for the average user. For this reason it is often difficult to tell if a digital cell phone is truly CDMA since often even the sales people are confused. CDMA cell phones can be recognized by their service providers. These are: ALLTEL, Cricket Wireless, Qwest, Sprint, Verizon, and Virgin Mobile. Also see the page, Choosing a Cell Phone.

Verizon and AirTouch offer dual-mode CDMA cell phone service at the normal cell phone frequencies around 850 MHz. Dual-mode means that the phone can be both analog and digital in case one travels to an area which has no digital service. Sprint offers pure digital at the PCS frequency of approximately 1900 MHz and analog service in the 850 MHz bands. GSM is TDMA and is limited to digital-only areas.

Satellites are used to provide coverage where there is now no cell phone service (mountains, dessert, Siberia, third world, etc. Globalstar, Inmarsat, and Iridium provide satellite phone service. Also see the page on satellite phone

Who invented the CellPhone

The cell phone was invented by Bell Labs from about 1947 to 1967, but a controversy has arisen about this. . Read more about the Invetor of the cell phone.