Mobile phone Era

Inside a Digital Cell Phone

On a "complexity per cubic inch" scale, cell phones are some of the most intricate devices people use on a daily basis. Modern digital cell phones can process millions of calculations per second in order to compress and decompress the voice stream.

If you take a basic digital cell phone apart, you find that it contains just a few individual parts:

• A 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

Inside a Cell phone Image Gallery

Inside a digital cell phone, youll find a circuit board, battery, speaker and more. Look inside a digital cell phone with photos and explanations of each part.

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The circuit board is the heart of the system. 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. You can learn more about A-to-D and D-to-A conversion and its importance to digital audio in How Compact Discs Work. The digital signal processor (DSP) is a highly customized processor designed to perform signal-manipulation calculations at high speed.

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 amplifiershandle signals traveling to and from the antenna.

The display has grown considerably in size as the number of features in cell phones has increased. Most current phones offer built-in phone directories, calculators, games, calendars, notes, Web browsers, and cameras, as well as countless other applications, or apps, to serve practically any need or want.

The SIM card on the circuit board

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Some phones store certain information, such as the SID and MIN codes, in internal Flash memory, while others use external cards that are similar toSmartMedia cards.

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 FDMA, each phone uses a different frequency.

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Cell Phone Network Technologies: 2G

Cell phone networks fall into three categories: 2G, 3G and 4G. In 2G networks, there are three common technologies used 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.

The first word tells you what the access method is. The second word, "division," lets you know that it splits calls based on that access method.

• FDMA puts each call on a separate frequency.
• TDMA assigns each call a certain portion of time on a designated frequency.
• CDMA gives a unique code to each call and spreads it over the available frequencies.

The last part of each name is "multiple access." This simply means that more than one user can use each cell.

FDMA separates the spectrum into distinct voice channels by splitting it into uniform chunks of bandwidth. To better understand FDMA, think of radio stations: Each station sends its signal at a different frequency within the available band. FDMA is used mainly for analog transmission. While it is certainly capable of carrying digital information, FDMA is not considered to be an efficient method for digital transmission.

TDMA is the access method used by the Electronics Industry Alliance and the Telecommunications Industry Association for Interim Standard 54 (IS-54) and Interim Standard 136 (IS-136). Using TDMA, a narrow band that is 30 kHz wide and 6.7 milliseconds long is split time-wise into three time slots.

Narrow band means "channels" in the traditional sense. Each conversation gets the radio for one-third of the time. This is possible because voice data that has been converted to digital information is compressed so that it takes up significantly less transmission space. Therefore, TDMA has three times the capacity of an analog system using the same number of channels. TDMA systems operate in either the 800-MHz (IS-54) or 1900-MHz (IS-136) frequency bands.

TDMA splits a frequency into time slots.

In CDMA, each phone's data has a unique code.

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GSM and CDMA
TDMA is also used as the access technology for Global System for Mobile Communications (GSM). However, GSM implements TDMA in a somewhat different and incompatible way from IS-136. Think of GSM and IS-136 as two different operating systems that work on the sameprocessor, like Windows and Linux both working on an Intel Pentium III. GSM systems use encryption to make phone calls more secure. GSM operates in the 900-MHz and 1800-MHz bands in Europe and Asia and in the 850-MHz and 1900-MHz (sometimes referred to as 1.9-GHz) band in the United States. It is used in digital cellular and PCS-based systems. GSM is also the basis for Integrated Digital Enhanced Network (IDEN), a popular system introduced by Motorola and used by Nextel. AT&T and T-Mobile use GSM.
CDMA takes an entirely different approach from TDMA. CDMA, after digitizing data, spreads it out over the entire available bandwidth. Multiple calls are overlaid on each other on the channel, with each assigned a unique sequence code. CDMA is a form of spread spectrum, which simply means that data is sent in small pieces over a number of the discrete frequencies available for use at any time in the specified range. Verizon, Sprint and most other U.S. carriers use CDMA, which means no SIM card.
All of the users transmit in the same wide-band chunk of spectrum. Each user's signal is spread over the entire bandwidth by a unique spreading code. At the receiver, that same unique code is used to recover the signal. Because CDMA systems need to put an accurate time-stamp on each piece of a signal, it references the GPS system for this information. Between eight and 10 separate calls can be carried in the same channel space as one analog AMPS call. CDMA technology is the basis for Interim Standard 95 (IS-95) and operates in both the 800-MHz and 1900-MHz frequency bands.Ideally, TDMA and CDMA are transparent to each other. In practice, high-power CDMA signals raise the noise floor for TDMA receivers, and high-power TDMA signals can cause overloading and jamming of CDMA receivers.2G is a cell phone network protocol. Click here to learn about network protocols for smartphones.
Next, we'll look at 3G.Queen of the selfie, Kim Kardashian, takes a picture with her smartphone of herself and friend La La Anthony at a New York Knicks game.Digital Vision/ThinkstockCell-phone Network Technologies: 3G3G technology came along to support increased data needs. 3G stands for "third generation" -- this makes analog cellular technology generation one and digital/PCS generation two. 3G technology is intended for the true multimedia cell phone -- typically called smartphones -- and features increased bandwidth and transfer rates to accommodate Web-based applications and phone-based audio and video files.3G comprises several cellular access technologies. Common ones include:·         CDMA2000 - based on 2G Code Division Multiple Access
·         WCDMA (UMTS) - Wideband Code Division Multiple Access
·         TD-SCDMA - Time-division Synchronous Code-division Multiple Access
3G networks have potential transfer speeds of up to 3 Mbps (about 15 seconds to download a 3-minuteMP3 song). For comparison, the fastest 2G phones can achieve up to 144Kbps (about 8 minutes to download a 3-minute song). 3G's high data rates are ideal for downloading information from the Internet and sending and receiving large, multimedia files. 3G phones are like mini-laptops and can accommodate broadband applications like video conferencing, receiving streaming video from the Web, sending and receiving faxes and instantly downloading e-mail messages with attachments.3G is a cell phone network protocol. Click here to learn about network protocols for smartphones.Next we look at the latest network technology: 4G.A woman displays a fourth-generation WiMAX device during a exhibition at a convention centrer in Taipei in 2010.SAM YEH/AFP/Getty ImagesCell-phone Network Technologies: 4GThe "4G" cell phone has been around for years – at least since 2006, if you go by Sprint's definition of 4G [source: Segan]. That original 4G network used a technology called WiMAX, one of several approaches to 4G implementation. Like previous generations, 4G is not a standardized designation. It's simply the next step up in speed.All the top service providers have some type of 4G network now, in various stages of development and coverage, built on one of three main cellular-access technologies: LTE, HSPA+, and WiMAX [source: Gaylord].WiMAX is somewhat unique among cell phone access methods in that it's based on 802.16 wireless standards – aka wireless broadband Internet which is used for homes and offices. The WiMAX approach takes the second iteration of those standards, 802.16e, which supports mobile access, and applies it to the cell phone realm [source: Phone Scoop]. Transmissions use orthogonal frequency division multiplexing, or OFDM, a method of dividing signal data into multiple channels to speed up delivery and then combining all the bits back into a single unit at the destination [source: 4G Americas]. WiMAX transmission can theoretically top out around 40 Mbps, but in reality it is much less [source: Segan].HSPA+, on the other hand, is an upgrade to a long-existing approach to cellular: HSPA, or High-Speed Packet Access. HSPA builds on the 3G WCDMA infrastructure, which carries signals in either one or two frequency bands depending on mode [source: Tech FAQ]. In 3G form, HSPA networks have peak data-transfer speeds of 14.4 Mbps [source: 4G Americas]. By using higher-order QAM (quadrature amplitude modulation, which encodes multiple data streams into a single transmission, mimicking increased bandwidth), carriers can achieve HSPA+ speeds of up to 21 Mbps [sources: Tech Target, 4G Americas,Ruddock]. Antenna improvements may further increase HSPA+ transmission rates [source: 4G Americas].Despite the obvious gains in speed, many in the cell phone world consider both WiMAX and HSPA+ to be transitional technologies [source: Gaylord]. The 4G most people are waiting for is LTE.ACTUAL 4G LTE SPEEDSPromises of 86 Mbps may be fulfilled someday, but in the initial stages of LTE, actual speeds are well below that theoretical peak. In 2013, LTE users in Houston, Texas, are seeing an average upload rate of 8.4 Mbps and download rate of 7.3 Mbps; in San Diego, 7.1/9.6; in NYC, 8.4/6.7; and in L.A., 7.2/7.5 [source: Osborne].4G LTEFor decades, the mobile world has pushed for industry-wide standards to sync up the technology and allow for definable advances. Many see LTE, or Long Term Evolution, as the first real chance at standardization, as many top carriers have signed on to adopt the technology [source: 4G Americas].LTE is being developed as the 4G standard, which is why you sometimes see "4G LTE" as opposed to simply "4G." 4G could mean support for any speed above 3G; 4G LTE means support for up to 86 Mbps based on specific technology and software infrastructures [source: 4G Americas].The LTE network is based on Internet Protocol (IP) standards, the kind that delivers Web pages to your computer, and adds voice data to the transmission streams [source: 4G Americas]. It uses a schematic called OFDMA, or Orthogonal Frequency Division Multiple Access, which is similar to the OFDM approach in WiMAX. OFDMA also separates the bits in a single data transmission into multiple subcarriers to increase speed, reassembling it at the destination. The LTE protocol, though, has the added ability to assign particular data paths to particular users on the fly, optimizing the bandwidth available at any given time [source: 4G Americas].LTE can operate on a wide range of radio frequency bands, which will allow many mobile carriers to switch over to LTE without starting from scratch [source: 4G Americas]. The migration has already begun: 4G LTE is operating in many U.S. and European cities in 2013 [source: Osborne]. It doesn't require a new phone. LTE can operate alongside 2G and 3G networks, and multi-mode phones can access any of them, using LTE where it's available and, say, HSPA where it's not [source: 4G Americas].Having a multi-mode phone, then, is a huge benefit as LTE towers start popping up around the country and around the world.CELLULAR VS. PCSPersonal Communications Services (PCS) is a wireless phone service very similar to cellular phone service, but with an emphasis on personal service and extended mobility. The term "PCS" is often used in place of "digital cellular," but true PCS means that other services like paging, caller ID and e-mail are bundled into the service.
While cellular was originally created for use in cars, PCS was designed from the ground up for greater user mobility. PCS has smaller cells and therefore requires a larger number of antennas to cover a geographic area. PCS phones usefrequencies between 1.85 and 1.99 GHz (1850 MHz to 1990 MHz).Technically, cellular systems in the United States operate in the 824-MHz to 894-MHz frequency bands; PCS operates in the 1850-MHz to 1990-MHz bands. And while it is based on TDMA, PCS has 200-kHz channel spacing and eight time slots instead of the typical 30-kHz channel spacing and three time slots found in digital cellular.Multi-band vs. Multi-mode Cell PhonesIf you travel a lot, you will probably want to look for phones that offer multiple bands, multiple modes or both. Let's take a look at each of these options:·         Multiple band: A phone that has multiple-band capability can switch frequencies. For example, a dual-band TDMA phone could use TDMA services in either an 800-MHz or a 1900-MHz system. A quad-band GSM phone could use GSM service in the 850-MHz, 900-MHz, 1800-MHz or 1900-MHz band.
·         Multiple mode: In cell phones, "mode" refers to the type of transmission technology used. So, a phone that supported AMPS and TDMA could switch back and forth as needed. It's important that one of the modes is AMPS -- this gives you analog service if you are in an area that doesn't have digital support.
·         Multiple band/Multiple mode: This best of both worlds allows you to switch between frequency bands and transmission modes as needed.
Changing bands or modes is done automatically by phones that support these options. Usually the phone will have a default option set, such as 1900-MHz TDMA, and will try to connect at that frequency with that technology first. If it supports dual bands, it will switch to 800 MHz if it cannot connect at 1900 MHz. And if the phone supports more than one mode, it will try the digital mode(s) first, then switch to analog.You can find both dual-mode and tri-mode phones. The term "tri-mode" can be deceptive. It may mean that the phone supports two digital technologies, such as CDMA and TDMA, as well as analog. In that case, it is a true tri-mode phone. But it can also mean that it supports one digital technology in two bands and also offers analog support. A popular version of the tri-mode type of phone for people who do a lot of international traveling has GSM service in the 900-MHz band for Europe and Asia and the 1900-MHz band for the United States, in addition to the analog service. Technically, this is a dual-mode phone, and one of those modes (GSM) supports two bands.Of course, none of this would be possible without those soaring towers that carry cell phone signals from phone to phone.Cell phone Tower Image GalleryCell phone towers come in many shapes and sizes.HowStuffWorksProblems with Cell PhonesA cell phone tower is typically a steel pole or lattice structure that rises hundreds of feet into the air.Pictured here is a tower with three different cell phone providers riding on the same structure. If you look at the base of a tower, you can see provider equipment.The box houses the radio transmitters and receivers that let the tower communicate with the phones. The radios connect with the antennae on the tower through a set of thick cables.If you look closely, you will see that the tower and all of the cables and equipment at the base of the tower are heavily grounded.One sure sign that multiple providers share a tower is a five-way latch on the gate. Any one of five people can unlock this gate to get in.Like all consumer electronics, cell phones come with their share of problems. Next, we'll take a look at some of them.Cell-phone TowersA cell phone, like any other electronic device, has its problems:·         Generally, non-repairable internal corrosion of parts results if you get the phone wet or use wet hands to push the buttons. Consider a protective case. If the phone does get wet, be sure it is totally dry before you switch it on so you can try to avoid damaging internal parts.
·         Extreme heat in a car can damage the battery or the cell phone electronics. Extreme cold may cause a momentary loss of the screen display.
·         Analog cell phones suffer from a problem known as "cloning." A phone is "cloned" when someone steals its ID numbers and is able to make fraudulent calls on the owner's account.
Here is how cloning occurs: When your phone makes a call, it transmits the ESN (electronic serial number) and MIN (mobile identification number or phone number) to the network at the beginning of the call. The MIN/ESN pair is a unique tag for your phone -- this is how the phone company knows who to bill for the call. When your phone transmits its MIN/ESN pair, it is possible for nefarious sorts to listen (with a scanner) and capture the pair. With the right equipment, it is fairly easy to modify another phone so that it contains your MIN/ESN pair, which allows the crook to make calls on your account.For more information about cell phones and related topics, check out the links on the next page and be sure to read How Buying a Cell phone Works for loads of helpful consumer tips.