Why a Cell Phone?

Cell phones are used by millions the world over. Because you can use a cell phone from just about anywhere to talk to anybody it is one of the greatest inventions for social and business life today.

Many functions are available for convenient and efficient cell phone usage. They are growing so fast that the cell phone was noted by Forbes ( September 20, 2004 ) to become the PERSONAL CONTROLLER FOR ANYTHING humans come in contact with.”

For instance, you can use cell phones to:

• Keep a list of tasks
• Manage e-mail
• Surf the Internet and get the information you need
• Keep your contact list
• Enjoy a large number of games on your cell phone
• Hook up with accessories like MP3 players, GPS receivers, and PDAs

Because cell phones are increasingly important, it's good that you are checking up on them. What follows should clear up some misconceptions about cell phones and make you more of an expert than the average person.

Did you ever ask yourself, “What's inside the box?” Let's take a look at how the cell phone differs from a traditional phone. We will learn what the important acronyms mean; i.e., TDMA, CDMA, PCS, and GSM. The way you will know how to buy and use the best cell phone for you is to know the nitty-gritty. It will save you money and lots of grief!

  of the 19 th century. By combining the telephone with the radio, we essentially have a wireless phone!

Like cell phones, when old-fashioned telephone-radios were installed in cars, they greatly helped people on the move to communicate. They utilized a central tower in each city, having around 20-25 channels. Of course, the towering antenna had to transmit signals some 50 miles (approximately 70 km). That meant great power was needed. Its nature also was that only a few people could access these 20-some channels.

The cell phone miracle is that an area can now be divided into many smaller cells. This enables frequency to be reused many times over, and allows millions of people to take advantage of the cell phone's convenience and efficiency.

Cell phone carriers usually get about 800 frequencies to use throughout a city, in the typical analog cell phone system. The city is divided into numerous cells of about 10 square miles (26 square kilometers). Usually, we conceive these as hexagons in a huge hexagonal grid.

Having low-power transmitters in the cell phones and base stations permits identical frequencies to be reused in non-adjacent cells. Within each cell is its own base station that is made of a little building, some radio equipment inside of it, and a tower.

Cell Phone Transmission
Low-strength transmitters in cell phones are the reason they can send signals. Cell phones in general have a couple of signal strengths: six-tenths of a watt and three watts. Along with the base station transmitting at low power, being lower than the four watts of the average citizen's band radio provides two advantages for cell phones:

First, it is not necessary for the transmissions to exceed the boundaries of the cell, and indeed they don't go too far out. That enables each cell to reuse the 56 frequencies.

Second, low-power transmissions keep the battery consumption low, permitting the installation of ever smaller cell phone batteries.

Regardless of the city size, numerous base stations are required in the cell phone system. Several hundred towers are necessary in the average large city. The cost is kept low for the users through economies of scale; i.e., lots of people are using their cell phones.

In addition to the above, the cell phone system requires a Mobile Telephone Switching Office (MTSO). All base stations are under its control, and every phone connection to the land-based phone system is also managed by it.

Codes that Cell Phones Use

Unique codes are integrated into all cell phones. By these codes, the cell phones can be positively identified, along with their respective service providers and owners. These codes are described now:

• Electronic Serial Number (ESN) – every cell phone has a special 32-bit number programmed into it when made
• Mobile Identification Number (MIN) – the phone number of the device helps generate this 10-digit number
• System Identification Code (SID) – the FCC assigns this unique 5-digit number to each carrier.

When you buy a service plan and have the cell phone activated the Mobile Identification Number and the System Identification Code get programmed onto it. The Electronic Serial Number, however, is permanently affixed to the phone during manufacture.

When switched on, your cell phone listens to hear an SID. The hope is that the SID will be heard on the specific frequency (called a control channel) that the cell phone and base station use to set things up. When no control can be found, the cell phone concludes that it is out of range and will generate a “no service” message.

However, when it does receive the SID, the cell phone tries to match it with the preprogrammed SID in the unit. In case of a successful match, the cell phone sends a registration request, and the phone's location is entered into a database. By using this database, the MTSO can always be aware of which cell you are in.

When the MTSO receives the call, it looks for you in the database and identifies your cell location. Then it selects a frequency pair for your phone to use in that particular cell, notifies your phone of it, and both your phone and the tower switch on those frequencies. This is a connection.

A weakening signal is detected by the base station as you travel toward the boundary of the cell. Likewise, the base station of the adjacent cell picks up a strengthening signal among all the frequencies it is monitoring. In a concerted effort with the MTSO, both base stations coordinate a change in frequencies. They let your phone know about it through the control channel, so that you can enter the new cell without interruption.

Let's suppose the SID in your cell phone doesn't match the SID on the control panel. This signals the MTSO of that cell you are roaming in to contact the MTSO of your home system. In turn, your home system MTSO examines its database to verify the validity of your cell phone's SID. Once confirmed, your home system notifies the local MTSO, which begins to trace your cell phone's movement.

Comparing Cell Phones and Citizens' Band Radios

Knowing something about a CB radio or walkie-talkie will be very helpful in grasping the facts about cell phones.

When only one person can talk at a time, such as on a walkie-talkie or CB radio, we call that “half-duplex.” On the other hand, a cell phone is “full duplex,” meaning that two people can talk at once. This is made possible by using two separate frequencies, one for talking, and the other for listening.

Channels

You cell phone can communicate on many more channels than a walkie-talkie, which normally only has a single channel. Your cell phone can even outdo a CB radio, with typically 40 channels. Your cell phone can communicate on at least 1,664 channels!

How about range?

Because cell phones function in and among cells they have extraordinary range. For instance, hundreds of miles often can be covered with a traveling cell phone without losing a connection. This advantage of the cellular approach dwarfs the 1 mile (1.6 kilometer) range of a .25-watt transmitter walkie-talkie. Moreover, the 5-watt transmitter CB radio has only a fraction of the cell phone's range: approximately five miles (8 kilometers)!

Few gadgets that we toy with on a daily basis are as technically complex as the cell phone. Applying compression and decompression to the voice stream demands that in each second the device will process calculations numbering in the millions.

Cell Phone Components

There aren't many parts to a cell phone. A look inside would review mainly these: Battery
Speaker
Antenna
Display (LCD)
Microphone
Speaker
Keyboard
Circuit board Here's a circuit board that does the millions of calculations per second.

Something has to keep things coordinated, and that task is handled by the microprocessor. Besides the keyboard's and display's dependency on it, the microprocessor's importance also lies in command and control signaling with the base station.
Your cell phone's microprocessor contains memory chips, such as read-only-memory (ROM) and Flash memory chips. These provide space to store the operating system and a customizable phone directory. Another section manages power and recharging. It's called the radio frequency (RF) and power section. Additionally, it handles the FM channels that number in the hundreds.

Flash memory inside cell phones provide storage for the SID and MIN codes. External SmartMedia cards are also used in some cell phones.

The cell phone's internal clock chip uses a watch battery to keep it running.

Cell phones were originally analog devices. The first standard was approved in 1983 by the Federal Communications Commission, called AMPS (Advanced Mobile Phone System). It operated on the range of 824 megahertz (MHz) and 894 MHz. The federal government mandated that, in order to foster competition and benefit the consumer, at least two carriers needed to be in each market. They were called A and B carriers. The local phone company was generally one of them, and was the designated local exchange carrier (LEC).

As mentioned earlier, a pair of frequencies (one for transmission and the other for reception) represents a channel. Analog voice channel frequency ranges are normally 30 kHz wide because that supplies enough voice quality to be on par with a landline telephone. Each carrier, A and B, are apportioned 832 frequencies: 42 for data and 790 for voice.

To prevent cell phone interference among the transmission and reception frequencies, a separation of 45 MHz is in place. Each carrier, A and B, has 395 voice channels, along with 21 data channels that accommodate maintenance activities such as paging and registration.

Some digital technology has been integrated into a new version of AMPS. The result is Narrowband Advanced Mobile Phone Service (NAMPS), which accommodates approximately three times as many connections as the original version. Though this digital technology is incorporated, it is still considered an analog system. Operating in the 800-MHz band, AMPS and NAMPS cell phone services don't offer some features like email and Web surfing that digital cellular service does.

Analog phones and digital cell phones use the same radio technology in different ways. Because analog signals cannot be compressed and manipulated in a manner as simple as a digital signal, they cannot completely utilize the signal between the phone and the cellular network. Hence, lots of cable companies are migrating to digital, because more channels can fit into a given calls sometimes take up only 1/10 the space of a single analog call is efficient compression. Your voice gets converted into binary information (ones and zeros) and then gets compressed.

Frequency-shift team (FSK) is used by many digital cell phone systems to digital data were data back and forth over AMPS. FSK rapidly alternates between two frequencies, one that uses 1s and the other that uses 0s to transmit the digital data between the cell phone and the cell tower. Much processing power and goes into using modulation and encoding schemes to convert analog access to digital, compressed at, and convert it back to analog. The amazing thing is that the level of voice quality remains acceptable.

Technologies for cellular access

Cell phone networks use three common technologies to transmit data:

Frequency division multiple access (FDMA)

Time division multiple access (TDMA)

coated division multiple access (CDMA)

FDMA assigns each called to a separate frequency.

TDMA assigns each call a certain portion of time on a designated frequency.

CDMA assigns a unique code to each call in spreads it over the available frequencies.

The phrase "multiple access" simply means that each cell can be utilized by more than one user.

In order to separate the spectrum into distinct voice channels, FDMA splits the spectrum into uniform chunks of bandwidth. Like radio stations, each station transmits its signal at a different frequency within the available band. FDMA does not have a reputation for being an efficient way to transmit digital information, and is used primarily for analog transmission. In FDMA a different frequency is used for each cell phone.

Understanding TDMA cellular access technology:

TDMA splits the narrowband that is 30kHz wide and 6.7 ms long into three times slots. This is the access method and utilized by the Electronics Industry Alliance and the Telecommunications Industry Association for Interim Standard 54 (IS --54) and interim standard 136 (IS --136).

The traditional meaning of the terms "narrowband" is channels. Because less transmission space is required due to the conversion to digital formats and compression, each conversation uses the cell phone for one third of the time. In this way, TDMA has triple the capacity of an analog system using the same number of channels. Frequency bands used for TDMA systems are either the 800MHz (IS-54) or 1900 -- megahertz (IS-136) frequency bands. TDMA causes the frequency to be split into times slots.

The global system for mobile communications (GSM) also uses TDMA as the access technology. But the implementation is significantly different and incompatible with IS-36. It is somewhat akin to different operating systems working on the same computer; for instance, LINUX and Windows working in the same box. GSM utilizes the 900-megahertz and 1800-megahertz bands in Asia and Europe , and then 1900-megahertz (sometimes referred to as 1.9-gigahertz) band in the United States . Both PCS-based systems and digital cellular systems use it. It also provides the basis for integrated digital and enhanced network (IDEN), Motorola's creation that is used by Nextel.

Europe , Australia and much of Asia and Africa utilize the GSM international standard. In covered locations, cell phone users can buy one phone that functions anywhere that the standard has support. Subscriber identification module (SIM) cards enable GSM users to connect to the specific service providers in these countries by switching cards. Small removable disks, SIM cards slide in and out of GSM cell phones. In the SIM cards identification numbers and connection data are stored so that you can access any particular wireless service provider.

Due to the incompatibility of the United States and international systems, their 1900-megahertz GSM phone devices won't work together. So, when traveling from the United States , you will need to buy a GSM 900MHz/1800MHz cell phone. Although you can buy these cell phones in the United States , you can buy them in the other countries, as well.

CDMA, which digitizes data and spreads it out over the entire available bandwidth, is significantly different from TDMA. Numerous calls are layered upon one another on the channel, each having a unique sequence code assigned to it. With CDMA, data is transmitted in small pieces over a number of the discrete frequencies that exist in the specified range at the time. This is a form of spread spectrum.

The same wide-band piece of the spectrum is utilized by all users. This signal of each user is spread over the complete bandwidth by a unique spreading code. This same unique code is utilized at the receiver to recover the signal. Referencing the GPS system, CDMA systems attach an accurate time-stamp on each piece of a signal. Within the same channel space as one analog apps call, eight to 10 individual calls can be carried by a CDMA system. CDMA technology operates in both the 800-megahertz and 1900-megahertz frequency bands, and is the basis for interim standard and 95 (IS-95).

CDMA and TDMA are ideally transparent to each other. However, in practice, this is not the case. High-power TDMA signals may cause overloading and jamming of CDMA receivers, and high-power CDMA signals raise the noise floor for TDMA receivers.

Adding special services like paging, caller ID, and e-mail makes an ordinary cell phone service become a personal communications service (PCS). This added and this is on personal service and extended mobility can also be called "digital cellular".

Although cellular was originally created for automobiles, the focus of the new PCS was a design for greater mobility. It requires smaller cells and a larger number of antennas to service a geographic region. The frequencies that PCS cell phones use are between 1.85 and 1.99GHz (1850MHz to 1990MHz). Other cellular phones in the United States function in the 824MHz to 894MHz frequency bands.

 

if you are frequently on the move would probably prefer a cell phone that offers dual band, dual mode, or both.

Dual band is able to operates in both the 800MHz in 1900MHz bands.

In other words, by dual-band capability to cell phone can switch frequencies. For instance, a dual band TDMA cell phone could use TDMA services in either an 800MHz or a 1900MHz system.

A dual mode cell phone can switch back and forth as needed between types of transmission technology. For instance some cell phones can support AMPS and TDMA. AM PS is especially useful because it provides analog service in case you are in a region that doesn't have digital service.

Dual band/dual mode provides both of the above, and lets you automatically alternate between frequency bands and transmission moments as required. Such cell phones will normally first try to connect at the default option set such as 1900MHz TDMA. Likewise, it will try to digital mode first if the cell phone supports more than one mode, and then switch to analog if needed.

Changing bands or modes is done automatically by cell phones that support these options. Usually the cell 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 cell phone supports more than one mode, it will try the digital mode(s) first, and then switch to analog if needed.

Tri-mode cell phones are also available. This could mean that it supports one digital technology in two frequency bands and also offers analog support. One version that is popular among international travelers has GSM service in the 900MHz band for Europe and Asia and the 1900MHz band for the United States . It also provides analog service. Tri--mode can also mean that the cell phone supports two digital technologies, such as TDMA and CDMA, in addition to analog.

like other electronic devices, cell phones that get wet can suffer internal corrosion of parts. Rain and wet hands can contribute to this but if it does get doused ensure that it is completely dry before using it again in order to avoid serious damage.

Both without cell phone electronics and the battery can suffer damage from extreme heat. Likewise in extremely cold situations there could be a temporary loss of the screen display.

"Cloning" is occasionally a problem with analog cell phones. It means that someone has stolen in its ID number and can now make fraudulent calls on the owners account. It happens when your cell phone transmits the ESN and MIN to the network at the start of the call. The phone company uses the MIN/ESN couplet as a unique identifier for your cell phone to assist in the billing process. With standard technology an eavesdropper can monitor your cell phone and capture the couplet. It can then be reinserted into a different cell phone, and calls can be made on your MIN/ESN couplet.

How to buy a cell phone

Walk downtown in any major city in the United States and you're bound to see many people gabbing on their cell phones. They are ubiquitous for a reason -- they are great tools that are often very fun!

Some of the many functions that are now available include:

Contact information for merchants

to-do lists

appointments and reminders

built-in calculator

e-mail sending and receiving

Internet surfing (financial news, entertainment, news)

games

integration and to PDAs, MP3 players and GPS equipment

If this list looks appealing to you, then you might consider the following factors before you buy:

Price

Size

Service Plan

Mode

Battery Type

Display

Functions Included

Special Features

Service Plan

One of the more vital factors to consider would be the service plan, because not all types of cell phones accommodate all service plans.

Mode

The mode can make a big difference in the usability of your cell phone. Make up their mind if you prefer PCS or cellular. You will also need to choose between analog or digital, and TDMA or CDMA. Dual mode/dual band cell phones are best for frequent travelers.

Battery type

There are two major battery types used in cell phones. The more commonly used NiMH (nickel-metal hydride) high-capacity battery gives extra power for extended use. Lithium ion batteries (Li-ion) normally costs more because a lot of power is packed in a lightweight container. When you compare cell phones, consider both the talk time and the standby time. It will also help to know how long it takes the battery to charge and whether you can get a rapid charger. Although most cell phone batteries are removable, there are some smaller styles that incorporate built-in batteries.

There are several important factors to consider with displays:

size -- if you plan on using the cell phone for wireless Internet, you will definitely want a large, multi-line display.

Monochrome or color -- the more common cell phones have monochrome (16 grays) displays, but color displays are becoming more in vogue. These cost more and require more memory.

Reflective or backlit -- the latter will help you see more clearly in dim light

features -- if you want more, you'll pay more:

• Phone directory
• Call forwarding
• One-touch dialing/speed dialing
• Incoming-number storage
• Automatic redial
• Last-number recall
• Multi-party calls
• Hands-free headset/speakerphone
• Personalized/custom sounds
• External volume/ringer control
• Mute/hold button
• Clock
• Rapid charger/built-in charger
• Calculator
• Games
• Appointment reminder/calendar
• Voice-activated functions
• Vibrate mode
• Lock/alarm
• Car adapter

Top of the Line Features

Some cell phones even have distinctive features such as:

• MP3 player
• Text messaging
• Wireless Internet
• GPS receiver
• Modem function
• PDA
• PC synchronization

When considering cell phones with a headset or speakerphone connection, note whether the plug is proprietary or generic. If it is proprietary, then find out the cost and availability of the headset or speakerphone. A charger will come with the cell phone, but it may not be a rapid charger.

Size

where and how you will need the cell phone will play a part in determining the size. Some people prefer to use it as a car phone, while others. In their purse or pocket all day. You can save money by purchasing a heavier one, but you pay a price in lugging it around.

Price

pay only for features that you will use only people who are interested in wireless Internet would shell out extra cash for a WAP-enabled cell phone.

When You Shop

many cell phone feature comparison charts are available for researching the numerous makes and models available.

Watch out!

Here are a few other things you want to pay attention to as you look for a cell phone:

if you are a frequent traveler you may need a cell phone that will work in another country. Therefore, it is important to know whether the cell phone you are considering is analog, digital, or both (dual-mode). Using a digital signal, your cell phone could work only over a certain area, or over the complete country, and that depends on your provider. What makes this things out is that there are several digital systems in competition with one another. Each system works with several different frequencies. Try to obtain a map of exactly where the digital signal you will be accessing is available. Your provider should have one for you.

Although an analog cell phone will usually work over most areas, they are usually short on features and clarity. If you travel extensively, perhaps your best bet would be a dual-mode cell phone that can access a digital signal when available,

Research results are inconclusive on the effects of cell phone radiation on the human body. Although the degree of radiation coming from most cell phone is minuscule, close proximity to the head could cause some concern. Perhaps the only precaution you can take toward minimizing radiation effects would be to hold the antenna away from your head as much as possible. One of the best ways to do this would be to obtain a hands-free kit, or on a car-kit antenna.

Long-distance charges

The term "long-distance" is nebulous when you examine fees across the board. It is important to inquire what vendors mean when they say "free long-distance." Get and their definition of "long-distance" and the facts on the duration of any special rates, as well as surcharges.