Modern digital cell phones can process millions of calculations per second in order to compress and decompress the voice stream. The parts of a cell phone If you take a cell phone apart, you find that it contains just a few individual parts: An amazing circuit board containing the brains of the phone An antenna A liquid crystal display LCD A keyboard not unlike the one you find in a TV remote control A microphone A speaker A battery The circuit board is the heart of the system. Here is one from a typical Nokia digital phone: The front of the circuit board The back of the circuit board In the photos above, you see several computer chips.
Let's talk about what some of the individual chips do. The analog-to-digital and digital-to-analog conversion chips translate the outgoing audio signal from analog to digital and the incoming signal from digital back to analog. The digital signal processor DSP is a highly customized processor designed to perform signal-manipulation calculations at high speed. The microprocessor The microprocessor handles all of the housekeeping chores for the keyboard and display, deals with command and control signaling with the base station and also coordinates the rest of the functions on the board.
The ROM and Flash memory chips provide storage for the phone's operating system and customizable features, such as the phone directory. The radio frequency RF and power section handles power management and recharging, and also deals with the hundreds of FM channels.
Finally, the RF amplifiers handle signals traveling to and from the antenna. The display and keypad contacts The display has grown considerably in size as the number of features in cell phones have increased. Most current phones offer built-in phone directories, calculators and even games. And many of the phones incorporate some type of PDA or Web browser. The Flash memory card on the circuit board The Flash memory card removed Some phones store certain information, such as the SID and MIN codes, in internal Flash memory, while others use external cards that are similar to SmartMedia cards.
The cell-phone speaker, microphone and battery backup Cell phones have such tiny speakers and microphones that it is incredible how well most of them reproduce sound. As you can see in the picture above, the speaker is about the size of a dime and the microphone is no larger than the watch battery beside it.
Speaking of the watch battery, this is used by the cell phone's internal clock chip. What is amazing is that all of that functionality -- which only 30 years ago would have filled an entire floor of an office building -- now fits into a package that sits comfortably in the palm of your hand!
In order to encourage competition and keep prices low, the U. One of the carriers was normally the local-exchange carrier LEC , a fancy way of saying the local phone company. Carriers A and B are each assigned frequencies : for voice and 42 for data. A pair of frequencies one for transmit and one for receive is used to create one channel.
The frequencies used in analog voice channels are typically 30 kHz wide -- 30 kHz was chosen as the standard size because it gives you voice quality comparable to a wired telephone. The transmit and receive frequencies of each voice channel are separated by 45 MHz to keep them from interfering with each other. Each carrier has voice channels, as well as 21 data channels to use for housekeeping activities like registration and paging.
Even though it uses digital technology, it is still considered analog. Along Comes Digital Digital cell phones use the same radio technology as analog phones, but they use it in a different way. Analog systems do not fully utilize the signal between the phone and the cellular network -- analog signals cannot be compressed and manipulated as easily as a true digital signal. This is the reason why many cable companies are switching to digital -- so they can fit more channels within a given bandwidth.
It is amazing how much more efficient digital systems can be. Digital phones convert your voice into binary information 1s and 0s and then compress it see How Analog-Digital Recording Works for details on the conversion process. This compression allows between three and 10 digital cell-phone calls to occupy the space of a single analog call. FSK uses two frequencies , one for 1s and the other for 0s, alternating rapidly between the two to send digital information between the cell tower and the phone.
Clever modulation and encoding schemes are required to convert the analog information to digital, compress it and convert it back again while maintaining an acceptable level of voice quality.
All of this means that digital cell phones have to contain a lot of processing power! Cellular Access Technologies There are three common technologies used by cell-phone networks for transmitting information: Frequency division multiple access FDMA Time division multiple access TDMA Code division multiple access CDMA Although these technologies sound very intimidating, you can get a good sense of how they work just by breaking down the title of each one.
In recent years, other technologies have emerged and enriched mobile uses:. Radio Waves how does a mobile phone work? A GSM phone can provide up to a maximum power of 2W during a call, and in the best reception conditions, the power can be a thousand times lower about 0.
This technology is also far more effective in signal processing, because in optimal conditions for receiving, a 3G mobile can operate at power levels several million times less than its maximum power its maximum power is 0.
In recent years, other technologies have emerged and enriched mobile uses: DECT Digital Enhanced Cordless Telecommunications , formerly Digital European Cordless Telephone, is a wireless digital telephone standard aimed at both private individuals and companies, which operates on a frequency range between 1, and 1, MHz.
Even though this standard was designed for a wide variety of uses, it is now mainly used for voice calls. In additional to the basic function of voice calls, most modern cell phones come with additional functions such as web surfing, taking pictures, playing games, sending text messages and playing music.
More sophisticated smart phones can perform similar functions of a portable computer. Cell phones use radio waves to communicate. Radio waves transport digitized voice or data in the form of oscillating electric and magnetic fields, called the electromagnetic field EMF.
The rate of oscillation is called frequency. Radio waves carry the information and travel in air at the speed of light. Cell phones transmit radio waves in all directions. The waves can be absorbed and reflected by surrounding objects before they reach the nearest cell tower. Cordless telephones , commonly used in homes, have base units that are plugged into telephone jacks and wired to local telephone service; these are not considered "cellular" phones.
Transportable phones are also known as "bag phones. Because they are most commonly stored inside the car with the phone user, or carried by the phone user, bag phones can be a greater source of RF exposure than mobile phones. Transportable telephone use is declining as portable phones become more popular. Mobile phones , also called "car phones," usually have an antenna mounted on the outside of a car-on the window, fender, roof, or trunk. The antenna of a cellular phone is the phone's primary source of radio frequency.
The metal surface of a car provides a shield between the mobile phone user and the energy associated with the antenna. The physical distance between the mobile phone user and the antenna also serves as protection against RF energy.
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