samsung galaxy tab2 10.1 features and helps

Battery

Battery - Charge

To charge the battery, follow these steps:

Note: If the battery level is below 25%, use the AC adapter instead of a car charger.
Note: You cannot charge your tablet by plugging the USB cable into your computer.

 

1. Gently slide the outlet connector into the charging head, making sure that the connection is secure.
   
   
2. Insert the USB cable into the charging head.
   
   
3. Plug the USB cable into the tablet’s charger/accessory port (3).
4. Plug the charging head into an electrical wall outlet.

 

Battery – Insert / remove – Not Supported

• Note: You cannot remove your tablet’s battery.

 

We’re sorry, but this feature is not available on this device.

 

Battery Manager – Access

To access the Battery Manager, follow these steps:

 

1. From any Home screen, tap the Apps icon.
2. Tap Settings.
3. Tap Power saving.

 

Battery Manager – Change battery profile

To change the Battery Manager profile, follow these steps:

 

1. From any Home screen, tap the Apps icon.
2. Tap Settings.
3. Tap Power saving.
4. To enable power saving mode, tap Custom power saving to select the check box and enable. 
5. To disable power saving mode, tap Custom power saving to clear the check box and disable.

 

Battery Manager – Set battery profile options

To set the options for the Battery Manager profile, follow these steps:

 

1. From any Home screen, tap the Apps icon.
2. Tap Settings.
3. Tap Power saving.
4. If necessary, tap the switch in the upper right-hand corner of the screen to enable power saving mode. (Switch turns green.)
5. Tap to select and enable the following options:
   • CPU power saving
   • Screen power saving

 

 

 

 

 

SIM card

Related error: 'Insert SIM'

 

Important: Turn off the tablet before installing or removing the SIM card.

 

To insert the SIM card, follow these steps:

 

1. Detach the SIM card from its packaging.
2. With the screen facing up, open the SIM card slot cover.
3. Push the SIM card into the slot with the gold contacts facing down, as shown, until it clicks into place.
   
   
4. Close the SIM card slot cover.

 

To remove the SIM card, follow these steps:

 

1. Open the SIM card slot cover.
2. Gently press the SIM card into the slot until it clicks.
3. Let go of the SIM card and it will pop out slightly.
4. Gently pull to remove the SIM card and close the SIM card slot cover.

 

 

 

 

 

Indications / functions / menu

Button functions

To identify buttons and their functions, refer to the following:

 

Front Features:

 

1. External speakers
2. Front-facing camera
3. Display screen
4. Charging port
5. Microphone

 

 

Side features

1. Micro SIM card slot
2. Headset connector
3. Infrared blaster
4. MicroSD card slot
5. Volume key
6. Power/lock key
7. Charging port

 

Display screen icons

To understand the meaning of display screen icons and indicators, refer to the following:

 

Status Bar icons

To understand the meaning of the Status Bar icons and indicators, refer to the following:

 

 

Home screen

Review the following information about the home screen:

 

 

1. Google Search
2. Home screen
3. App shortcuts
4. Current screen
5. Widgets
6. Apps
7. Back key
8. Home key
9. Navigation
10. Quick launch
11. Primary shortcuts
12. Mini App Tray
13. System bar
14. Notification icons
15. Time
16. Status icons

 

 

 

 

Memory

Set default memory location - Not Supported

We’re sorry, but this feature is not available on this device.

 

Task Manager

The Task Manager application shows the amount of free and used memory on the tablet, and it can be used to stop running applications to free up memory. To use the Task Manager, follow these steps:

 

1. From any Home screen, tap the Apps   icon.
2. Tap Settings.
3. Tap Application manager.
4. Tap one of the following options:
   • Downloaded
   • Running
   • All
5. Tap an item in the list.
6. View application information or tap to stop or disable the application.

 

View device memory – Phone book

To view the amount of free memory and used memory in the phone book, follow these steps:

 

1. From any Home screen, tap the Apps icon.
2. Tap Settings.
3. Tap Storage.
4. Tap Apps.
5. Tap the Menu icon.
6. Tap Sort by name.
7. Tap Contacts storage.
8. View the Total and Data values.

 

View device memory

To view the tablet memory status (the amount of free memory and used memory), follow these steps:

 

1. From any Home screen, tap the Apps icon.
2. Tap Settings.
3. Tap Storage.
4. Under Device memory, view the Total space.

 

View device memory – Pictures, videos

To view the memory status (the amount of free memory and used memory), follow these steps:

 

1. From any Home screen, tap the Apps icon.
2. Tap Settings.
3. Tap Storage.
4. Under Device memory, view Pictures, videos.

 

 

 

 

 

Memory card & transfer

Access files – On tablet using computer

To view files on the tablet using a computer, follow these steps:

 

Note: Depending on your operating system, you may need to download and install Samsung Kies 2.0 before sharing files.
On a Windows computer

1. Connect the included USB cable to the tablet, then to a computer.
2. When a Removable Disk window appears on the computer, double-click Open folder to view files using Windows Explorer.
3. Double-click Tablet.
4. Double-click the folder that contains the file you want to access.
5. When you are finished, click the Safely Remove Hardware icon in the system tray of your computer.

 

On a Macintosh computer

1. Connect the included USB cable to the tablet, then to a computer.
2. If a “Samsung Modem” pop-up appears on your computer, click Cancel.
3. In the Applications folder, double-click Kies and wait for it to connect with the tablet.
4. Under SGH-T869, click Music, Photos, Videos, or Podcast to access those types of files on your tablet.
5. When done, click on the Kies drop-down menu and click Exit.
6. Safely disconnect the tablet from the computer.

 

Access files – On card using device

To access files on a memory card, follow these steps:

 

1. From any Home screen, tap the Apps icon.
2. Tap Files.
3. Tap extStorages.
4. Tap SdCard.
5. Tap the folder containing the file you want to access.

Delete files – On card using computer

To delete files on a memory card using a computer, follow these steps:

 

Note: Depending on your operating system, you may need to download and install Samsung Kies 2.0 before sharing files.
On a Windows computer

1. Connect the included USB cable to the tablet, then to a computer.
2. When a Removable Disk window appears on the computer, double-click Open folder to view files using Windows Explorer.
3. Double-click Card.
4. Double-click the folder that contains the file you want to delete.
5. Right-click the file you want to delete.
6. Click Delete.
7. Click Yes.
8. When you are finished, click the Safely Remove Hardware icon in the system tray of your computer.

On a Macintosh computer

1. Connect the included USB cable to the tablet, then to your computer.
2. If a “Samsung Modem” pop-up appears on the computer, click Cancel.
3. In the Applications folder, double-click Kies and wait for it to connect with the tablet.
4. Under SGH-T869, click Music, Photos, Videos, or Podcast to access those types of files on your tablet.
5. Select the check box of each file you want to delete.
6. Click Delete.
7. When done, click on the Kies drop-down menu and click Exit.
8. Safely disconnect the tablet from the computer.

 

Delete files – On tablet using computer

To delete files on the tablet using a computer, follow these steps:

 

Note: Depending on your operating system, you may need to download and install Samsung Kies 2.0 before sharing files.
On a Windows computer

1. Connect the included USB cable to the tablet, then to a computer.
2. When a Removable Disk window appears on the computer, double-click Open folder to view files using Windows Explorer.
3. Double-click Tablet.
4. Double-click the folder that contains the file you want to delete.
5. Right-click the file you want to delete.
6. Click Delete.
7. Click Yes.
8. When you are finished, click the Safely Remove Hardware icon in the system tray of your computer.

On a Macintosh computer

1. Connect the included USB cable to the tablet, then to your computer.
2. If a “Samsung Modem” pop-up appears on the computer, click Cancel.
3. In the Applications folder, double-click Kies and wait for it to connect with the tablet.
4. Under SGH-T869, click Music, Photos, Videos, or Podcast to access those types of files on your tablet.
5. Select the check box of each file you want to delete.
6. Click Delete.
7. When done, click on the Kies drop-down menu and click Exit.
8. Safely disconnect the tablet from the computer.

 

Delete files – On card using tablet

To delete files on a memory card using the tablet, follow these steps:

 

1. From any Home screen, tap the Apps icon.
2. Tap Files.
3. Tap extStorages.
4. Tap SdCard.
5. Tap the folder containing the file you want to delete.
6. Tap the check box next to the files(s) you want to delete.
7. Tap the Trash Can icon.
8. Tap Yes.

Insert / remove card

To insert a memory card, follow these steps:

 

1. Open the microSD card slot cover.
2. Gently press the memory card into the slot, as shown, until it clicks into place.
   
   

 

To remove a memory card, follow these steps:

 

1. Open the microSD card slot cover.
2. Gently press the memory card into the slot until it clicks and pops out slightly.
3. Slide the memory card from the slot.

 

Move files – Card to computer

To move files from a memory card to a computer, follow these steps:

 

On a Windows computer

1. Connect the included USB cable to the tablet, then to a computer.
2. When a Removable Disk window appears on the computer, double-click Open folder to view files using Windows Explorer.
3. Double-click Card.
4. Double-click the folder that contains the file you want to move.
5. Drag and drop the file from the folder onto your computer desktop or into another folder on the computer.
6. When you are finished, click the Safely Remove Hardware icon in the system tray of your computer.

On a Macintosh computer

1. Connect the included USB cable to the tablet, then to your computer.
2. If a “Samsung Modem” pop-up appears on the computer, click Cancel.
3. In the Applications folder, double-click Kies and wait for it to connect with the tablet.
4. Under SGH-T869, click Music, Photos, Videos, or Podcast to access those types of files on your tablet.
5. Select the check box of each file you want to delete.
6. Click Delete.
7. When done, click on the Kies drop-down menu and click Exit.
8. Safely disconnect the tablet from the computer.

 

Move files – Card to tablet

To move files from a memory card to the tablet, follow these steps:

 

1. From any Home screen, tap the Apps icon.
2. Tap Files.
3. Tap extStorages.
4. Tap SdCard.
5. From the memory card, tap the folder containing the file(s) you want to move.
6. Tap the check box next to the files(s) you want to move.
7. Tap the Cut icon.
   • Note: Tap the Copy icon to duplicate the file and create two of the same file.
8. From the left column, tap Root at the top of the column.
9. Tap to open the desired folder.
10. Tap the Paste icon.

Move files – Computer to card

To move files from a computer to memory card, follow these steps:
On a Windows computer

1. Connect the included USB cable to the tablet, then to a computer.
2. When a Removable Disk window appears on the computer, double-click Open folder to view files using Windows Explorer.
3. Double-click Card.
4. On the computer, locate the file(s) you want to move.
5. Drag and drop the file(s) into the desired location on the memory card.
6. When you are finished, click the Safely Remove Hardware icon in the system tray of your computer.

On a Macintosh computer

1. Connect the included USB cable to the tablet, then to your computer.
2. If a “Samsung Modem” pop-up appears on the computer, click Cancel.
3. In the Applications folder, double-click Kies and wait for it to connect with the tablet.
4. Under SGH-T869, click Music, Photos, Videos, or Podcast to access those types of files on your tablet.
5. Select the check box of each file you want to delete.
6. Click Delete.
7. When done, click on the Kies drop-down menu and click Exit.
8. Safely disconnect the tablet from the computer.

Move files – Tablet to card

To move files from the tablet to a memory card, follow these steps:

 

1. From any Home screen, tap the Apps icon.
2. Tap Files.
3. Tap Root.
4. Tap the folder containing the file(s) you want to move.
5. Tap the check box next to the files(s) you want to move.
6. Tap the Cut icon.
   • Note: Tap the Copy icon to duplicate the file and create two of the same file.
7. Tap extStorages.
8. Tap SdCard.
9. Tap to open the desired folder.
10. Tap the Paste icon.

 

Move files – Tablet to computer

To copy files from the tablet to a computer using a USB cable, follow these steps:

 

Note: Depending on your operating system, you may need to download and install Samsung Kies 2.0 before sharing files.
On a Windows computer

1. Connect the included USB cable to the tablet, then to a computer.
2. When a Removable Disk window appears on the computer, double-click Open folder to view files using Windows Explorer.
3. Double-click Tablet.
4. Locate the file(s) you want to move.
5. Drag and drop the file(s) into the desired location on the computer.
6. When you are finished, click the Safely Remove Hardware icon in the system tray of your computer.

On a Macintosh computer

1. Connect the included USB cable to the tablet, then to your computer.
2. If a “Samsung Modem” pop-up appears on your computer, click Cancel.
3. In the Applications folder, double-click Kies and wait for it to connect with the tablet.
4. Under SGH-T869, click Music, Photos, Videos, or Podcast to access those types of files on the tablet.
5. Select the check box of each file you want to copy to your computer.
6. Click Save to PC.
7. Browse to the folder on the computer where you want to save the file.
8. Click Save.
9. When done, click on the Kies drop-down menu and click Exit.
10. Safely disconnect the tablet from the computer.

 

Move files – Computer to tablet

To copy files from a computer to the tablet using a USB cable, follow these steps:

 

Note: Depending on your operating system, you may need to download and install Samsung Kies 2.0 before sharing files.
On a Windows computer

1. Connect the included USB cable to the tablet, then to a computer.
2. When a Removable Disk window appears on the computer, double-click Open folder to view files using Windows Explorer.
3. Double-click Tablet.
4. On the computer, locate the file(s) you want to move.
5. Drag and drop the file(s) into the desired location on the tablet.
6. When you are finished, click the Safely Remove Hardware icon in the system tray of your computer.

On a Macintosh computer

1. Connect the included USB cable to the tablet, then to your computer.
2. If a “Samsung Modem” pop-up appears on your computer, click Cancel.
3. In the Applications folder, double-click Kies and wait for it to connect with the tablet.
4. Under Library, click Music, Photos, Videos, or Podcast to access those types of files on your computer.
5. Select the check box of each file you want to copy to your tablet.
6. Click Transfer to device.
7. When done, click on the Kies drop-down menu and click Exit.
8. Safely disconnect the tablet from the computer.

 

View available memory

To view the amount of free and used space on the tablet, follow these steps:

 

1. From any Home screen, tap Apps.
2. Tap Settings.
3. Tap Storage.
4. Under Device memory, view Available.

How to hard reset samsung galaxy tab 2 10.1

step 1:-
   press power button and volume down button together
step 2 :-
  

Side features

1. Micro SIM card slot
2. Headset connector
3. Infrared blaster
4. Micro SD card slot
5. Volume key
6. Power/lock key
7. Charging port

 

 

 

 

 

 

 

 

 

 

 

 

 

step 3 :-

   Now the display will show service menu

navigate to  "wipe factory data" from menu using volume keys

step 4 :-

    press power on button to select option

step 5:-

   Now tab will show wiping data. After  that select "restart now " option from the menu

the tab will restart

 

GPRS(General Packet Radio Service)

General Packet Radio Service is a technology that allows your phone to transfer data at moderate speeds.

The benefits of GPRS

GPRS lets you send data faster than over a GSM data network, and it's also a lot more efficient. But "data" sounds pretty vague, right?

 

How GPRS works

To use GPRS, you need a phone that supports it, a subscription from your network operator that supports GPRS, and the proper settings.

General Packet Radio Service does what it says: it sends "packets" of data over a radio wave (on the GSM network). Packet switching works like a jigsaw puzzle: your data is split into many pieces, then sent over the network and reassembled at the other end. GPRS is just one of the ways to transport these jigsaw puzzles.

What you can do with GPRS

• Connect to your office or personal email account to get email as it arrives
• Browse the Internet on your phone
• Synchronize your phone and office calendar while you're out of town
• Download ringing tones, graphics, and games
• Play online games 
• Send and receive MMS messages
• Use your phone as a modem to connect your laptop to the Internet
• Subscribe to mobile services that bring you personalized information like sports updates, breaking news, horoscopes, share prices, the daily trip-hop-country single...
• Use Java™-based applications that require a network connection
• Chat using instant messaging on your phone
• Update your friends' Presence status
• Transfer data up to three times faster with an EGPRS (Enhanced GPRS) phone

 

GPRS is better than a GSM connection for data that's transferred in larger "chunks." And unlike voice calls and dial-up Internet connections, you pay for how much you transfer, not for how long you're connected. You can have an active GPRS connection all the time if you like, which is nice if you need to synchronize periodically with a network or if you're expecting an important email.

How it Works

When you talk on a mobile phone, a continuous connection to a channel is reserved for you on the GSM network, which means nobody else can use that channel. With GPRS, you can still have a continuous connection, but you only use the channel when you're sending data.

So, you might be connected to a channel all the time, but you only actually use it when you're sending data. One channel can be shared by many people. This is why you're billed for data transferred, not for time.

GPRS is significantly faster than CSD (Circuit Switched Data, sometimes just called GSM Data). However, you may find transfers slower than the maximum GPRS data rate during peak hours in busy cell networks, because voice connections usually take precedence. The data transfer rate also depends on your device's multislot class, which brings us to the next section.

What does "Class 10 (4+2, 5)" mean?

GPRS classes refer to the slots allocated for uploading and downloading data. The class number, in this case 10, signifies the multislot class. The number 4 in (4+2, 5) refers to the maximum number of slots that can be used for downloading - the more slots used, the faster the data transfer. The second number (2) refers to uploading, and the final number (5, which may or may not be shown), refers to the maximum number of slots that can be used at any one time, both uploading and downloading.

So in this case, we could have 4 downloading and 1 uploading (4+1=5), or 3 downloading and 2 uploading (3+2=5), as a slot can only be used for uploading or downloading at one time. However, you couldn't have 2 downloading and 3 uploading, because that would exceed the maximum number of slots for upload.

Here are some common GPRS classes for Nokia phones - but it's not an exhaustive list:

GPRS Class 2 (2+1, 3)
You guessed it, 2 slots for download and 1 for upload. It's a simple class of GPRS that's found in many phones.

GPRS Class 8 (4+1)
Class 8 reserves 4 slots for downloading and 1 for uploading. This is suitable for Web browsing, and also if you read more email than you send.

GPRS Class 10 (4+1, 3+2)
This profile, which is in the example above, is better for back-and-forth use of GPRS, like instant messaging.

EGPRS (EDGE)
EGPRS (Enhanced GPRS or EDGE) uses a slightly different technology based on what's called 8PSK, or 8-Phase Shift Keying.In practice, it makes GPRS transfers about three times faster, and makes downloading larger files like video less frustrating.

 

 

FORUM

How to Manually Backup Your iPhone Using iTunes

　
 These are instructions on how to manually backup your iPhone using iTunes.

Step One
Launch iTunes from your dock.

Step Two
Connect your iPhone to the computer via the USB cable and select it from the iTunes sidebar or at the top right of the screen if you're using the new layout.

Step ThreeMake sure you are on the Summary tab and click the large Back Up Now button.

Step FourNotice the progress bar will tell you the status of your backup.





Step FiveOnce complete the date and time of your last backup will be updated.

Step SixTo see all the device backups on your system select Preferences from the iTunes menu.

Step SevenYou can find the list of backups in the Device tab.

INTRODUCTION ABOUT CELL PHONE WORKING

INTRODUCTION ABOUT CELL PHONE WORKING

 

Millions of people in the United States and around the world use cellular phones. They are such great gadgets -- with a cell phone, you can talk to anyone on the planet from just about anywhere!

These days, cell phones provide an incredible array of functions, and new ones are being added at a breakneck pace. Depending on the cell-phone model, you can:

• Store contact information
• Make task or to-do lists
• Keep track of appointments and set reminders
• Use the built-in calculator for simple math
• Send or receive e-mail
• Get information (news, entertainment, stock quotes) from the Internet
• Play simple games
• Integrate other devices such as PDAs, MP3 players and GPS receivers

But have you ever wondered how a cell phone works? What makes it different from a regular phone? What do all those confusing terms like PCS, GSM, CDMA and TDMA mean? In this article, we will discuss the technology behind cell phones so that you can see how amazing they really are.

The Cell Approach

 

One of the most interesting things about a cell phone is that it is actually a radio -- an extremely sophisticated radio, but a radio nonetheless. The telephone was invented by Alexander Graham Bell in 1876, and wireless communication can trace its roots to the invention of the radio by Nikolai Tesla in the 1880s (formally presented in 1894 by a young Italian named Guglielmo Marconi). It was only natural that these two great technologies would eventually be combined!

In the dark ages before cell phones, people who really needed mobile-communications ability installed radio telephones in their cars. In the radio-telephone system, there was one central antenna tower per city, and perhaps 25 channels available on that tower. This central antenna meant that the phone in your car needed a powerful transmitter -- big enough to transmit 40 or 50 miles (about 70 km). It also meant that not many people could use radio telephones -- there just were not enough channels.

The genius of the cellular system is the division of a city into small cells. This allows extensive frequency reuse across a city, so that millions of people can use cell phones simultaneously. In the next section, we'll look closer at these cells.

Cell Engineering
In a typical analog cell-phone system in the United States, the cell-phone carrier receives about 800 frequencies to use across the city. The carrier chops up the city into cells. Each cell is typically sized at about 10 square miles (26 square kilometers). Cells are normally thought of as hexagons on a big hexagonal grid, like this:

 

Cool Facts Most newer digital cellular phones have some sort of entertainment programs on them, ranging from simple dice-throwing games to memory and logic puzzles. Approximately 20 percent of American teens (more girls than boys) own a cellular phone. Cellular phones are more popular in European and Asian countries than they are in the United States -- more than 90 percent of Europeans or Asians own a cell phone, compared to about 50 percent of Americans.

Because cell phones and base stations use low-power transmitters, the same frequencies can be reused in non-adjacent cells. The two purple cells can reuse the same frequencies.

Each cell has a base station that consists of a tower and a small building containing the radio equipment (more on base stations later

Frequencies
A single cell in an analog system uses one-seventh of the available duplex voice channels. That is, each cell (of the seven on a hexagonal grid) is using one-seventh of the available channels so it has a unique set of frequencies and there are no collisions:

• A cell-phone carrier typically gets 832 radio frequencies to use in a city.
• Each cell phone uses two frequencies per call -- a duplex channel -- so there are typically 395 voice channels per carrier. (The other 42 frequencies are used for control channels -- more on this on the next page.)
• Therefore, each cell has about 56 voice channels available.

In other words, in any cell, 56 people can be talking on their cell phone at one time. With digital transmission methods, the number of available channels increases. For example, a TDMA-based digital system can carry three times as many calls as an analog system, so each cell has about 168 channels available.

Transmission
Cell phones have low-power transmitters in them. Many cell phones have two signal strengths: 0.6 watts and 3 watts (for comparison, most CB radios transmit at 4 watts). The base station is also transmitting at low power. Low-power transmitters have two advantages:

• The transmissions of a base station and the phones within its cell do not make it very far outside that cell. Therefore, in the figure above, both of the purple cells can reuse the same 56 frequencies. The same frequencies can be reused extensively across the city.
• The power consumption of the cell phone, which is normally battery-operated, is relatively low. Low power means small batteries, and this is what has made handheld cellular phones possible.

The cellular approach requires a large number of base stations in a city of any size. A typical large city can have hundreds of towers. But because so many people are using cell phones, costs remain low per user. Each carrier in each city also runs one central office called the Mobile Telephone Switching Office (MTSO). This office handles all of the phone connections to the normal land-based phone system, and controls all of the base stations in the region.

 

Cell Phone Codes
All cell phones have special codes associated with them. These codes are used to identify the phone, the phone's owner and the service provider.

Cell Phone Codes   Electronic Serial Number (ESN) - a unique 32-bit number programmed into the phone when it is manufactured Mobile Identification Number (MIN) - a 10-digit number derived from your phone's number System Identification Code (SID) - a unique 5-digit number that is assigned to each carrier by the FCC While the ESN is considered a permanent part of the phone, both the MIN and SID codes are programmed into the phone when you purchase a service plan and have the phone activated.

Let's say you have a cell phone, you turn it on and someone tries to call you. Here is what happens to the call:

• When you first power up the phone, it listens for an SID (see sidebar) on the control channel. The control channel is a special frequency that the phone and base station use to talk to one another about things like call set-up and channel changing. If the phone cannot find any control channels to listen to, it knows it is out of range and displays a "no service" message.
• When it receives the SID, the phone compares it to the SID programmed into the phone. If the SIDs match, the phone knows that the cell it is communicating with is part of its home system.
• Along with the SID, the phone also transmits a registration request, and the MTSO keeps track of your phone's location in a database -- this way, the MTSO knows which cell you are in when it wants to ring your phone.
• The MTSO gets the call, and it tries to find you. It looks in its database to see which cell you are in.
• The MTSO picks a frequency pair that your phone will use in that cell to take the call.
• The MTSO communicates with your phone over the control channel to tell it which frequencies to use, and once your phone and the tower switch on those frequencies, the call is connected. You are talking by two-way radio to a friend!
• As you move toward the edge of your cell, your cell's base station notes that your signal strength is diminishing. Meanwhile, the base station in the cell you are moving toward (which is listening and measuring signal strength on all frequencies, not just its own one-seventh) sees your phone's signal strength increasing. The two base stations coordinate with each other through the MTSO, and at some point, your phone gets a signal on a control channel telling it to change frequencies. This hand off switches your phone to the new cell.

As you travel, the signal is passed from cell to cell.

Roaming
If the SID on the control channel does not match the SID programmed into your phone, then the phone knows it is roaming. The MTSO of the cell that you are roaming in contacts the MTSO of your home system, which then checks its database to confirm that the SID of the phone you are using is valid. Your home system verifies your phone to the local MTSO, which then tracks your phone as you move through its cells. And the amazing thing is that all of this happens within seconds!

Cell Phones and CBs
A good way to understand the sophistication of a cell phone is to compare it to a CB radio or a walkie-talkie.

• Full-duplex vs. half-duplex - Both walkie-talkies and CB radios are half-duplex devices. That is, two people communicating on a CB radio use the same frequency, so only one person can talk at a time. A cell phone is a full-duplex device. That means that you use one frequency for talking and a second, separate frequency for listening. Both people on the call can talk at once.
• Channels - A walkie-talkie typically has one channel, and a CB radio has 40 channels. A typical cell phone can communicate on 1,664 channels or more!
• Range - A walkie-talkie can transmit about 1 mile (1.6 km) using a 0.25-watt transmitter. A CB radio, because it has much higher power, can transmit about 5 miles (8 km) using a 5-watt transmitter. Cell phones operate within cells, and they can switch cells as they move around. Cells give cell phones incredible range. Someone using a cell phone can drive hundreds of miles and maintain a conversation the entire time because of the cellular approach.

In half-duplex radio, both transmitters use the same frequency. Only one party can talk at a time.

In full-duplex radio, the two transmitters use different frequencies, so both parties can talk at the same time. Cell phones are full-duplex

 

 

Inside a Cell Phone
On a "complexity per cubic inch" scale, cell phones are some of the most intricate devices people play with on a daily basis. 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

On the Circuit Board
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 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 microprocessor

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!

AMPS

Photo courtesy Motorola, Inc. Old school: DynaTAC cell phone, 1983

In 1983, the analog cell-phone standard called AMPS (Advanced Mobile Phone System) was approved by the FCC and first used in Chicago. AMPS uses a range of frequencies between 824 megahertz (MHz) and 894 MHz for analog cell phones. In order to encourage competition and keep prices low, the U. S. government required the presence of two carriers in every market, known as A and B carriers. 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 832 frequencies: 790 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 395 voice channels, as well as 21 data channels to use for housekeeping activities like registration and paging.

A version of AMPS known as Narrowband Advanced Mobile Phone Service (NAMPS) incorporates some digital technology to allow the system to carry about three times as many calls as the original version. Even though it uses digital technology, it is still considered analog. AMPS and NAMPS only operate in the 800-MHz band and do not offer many of the features common in digital cellular service, such as e-mail and Web browsing.

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 . This compression allows between three and 10 digital cell-phone calls to occupy the space of a single analog call.

Many digital cellular systems rely on frequency-shift keying (FSK) to send data back and forth over AMPS. 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.

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 utilize each cell.

 

Cellular Access Technologies: FDMA
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.

In FDMA, each phone uses a different frequency

 

 

Cellular Access Technologies: TDMA
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.

Cellular Access Technologies: TDMA/GSM
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 same processor, 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 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.

GSM is the international standard in Europe, Australia and much of Asia and Africa. In covered areas, cell-phone users can buy one phone that will work anywhere where the standard is supported. To connect to the specific service providers in these different countries, GSM users simply switch subscriber identification module (SIM) cards. SIM cards are small removable disks that slip in and out of GSM cell phones. They store all the connection data and identification numbers you need to access a particular wireless service provider.

Unfortunately, the 1900-MHz GSM phones used in the United States are not compatible with the international system. If you live in the United States and need to have cell-phone access when you're overseas, the easiest thing to do is to buy a GSM 900MHz/1800MHz cell phone for traveling. You can get these phones from Planet Omni, an online electronics firm based in California. They offer a wide selection of Nokia, Motorola and Ericsson GSM phones. They don't sell international SIM cards, however. You can pick up prepaid SIM cards for a wide range of countries at Telestial.com.

Cool Facts The GSM standard for digital cell phones was established in Europe in the mid-1980s -- long before digital cellular phones became commonplace in American culture. It is now possible to locate a person using a cellular phone down to a range of a few meters, anywhere on the globe. 3G (third-generation wireless) phones may look more like PDAs, with features such as video-conferencing, advanced personal calendar functions and multi-player gaming

 

 

Cellular Access Technologies: CDMA
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.

In CDMA, each phone's data has a u 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. Cellular vs. PCS Personal 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 use frequencies 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. Now let's look at the distinction between "dual band" and "dual mode" technologies. Dual Band vs. Dual Mode If you travel a lot, you will probably want to look for phones that offer dual band, dual mode or both. Let's take a look at each of these options: Dual band - A phone that has dual-band capability can switch frequencies. This means that it can operate in both the 800-MHz and 1900-MHz bands. For example, a dual-band TDMA phone could use TDMA services in either an 800-MHz or a 1900-MHz system. Dual 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. Dual band/Dual mode - The 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. Sometimes you can even find tri-mode phones. This term can be deceptive. It may mean that the phone supports two digital technologies, such as CDMA and TDMA, as well as analog. 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. In the next section, we'll touch on some of the problems encountered with cellular phones Problems with Cell Phones A cell phone, like any other consumer 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 and MIN 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 nefarious sort to make calls on your account. Check out the next section to find out about cell-phone towers Cell-phone Towers A cell-phone tower is typically a steel pole or lattice structure that rises hundreds of feet into the air. This cell-phone tower along I-85 near Greenville, SC, is typical in the United States: This is a modern tower with three different cell-phone providers riding on the same structure. If you look at the base of the tower, you can see that each provider has its own equipment, and you can also see how little equipment is involved today (older towers often have small buildings at the base): Here is the equipment owned by one of the providers: 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. For example, the plate in this shot with the green wires bolting onto it is a solid copper grounding plate: One sure sign that multiple providers share this tower is the amazing five-way latch on the gate. Any one of five people can unlock this gate to get in! Cell-phone towers come in all shapes and sizes, but I do believe this one in Morrisville, NC, is one of the weirdest looking! That is one tall, ugly tree!     nique code.