Cell Phone Codes
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.
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.
* 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
How Mobile Phone Works
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.
In other words, in any cell, 56 people can be talking on their mobile phone at one time. Analog cellular systems are considered first-generation mobile technology, or 1G. With digital transmission methods (2G), 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.
Mobile phones have low-power transmitters in them. Many mobile 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.
In a typical analog cell-phone system in India, the mobile-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 26 square kilometers. Cells are normally thought of as hexagons on a big hexagonal grid, like this:
In full-duplex radio, the two transmitters use different frequencies, so both parties can talk at the same time.
Cell phones are full-duplex.
In half-duplex radio, both transmitters use the same frequency. Only one party can talk at a time.
Thousands of people in the Bhilai and around the world use Mobile Phones. They are such a great gadgets, with a mobile phone, you can talk to anyone on the earth from just about anywhere!
These days, Mobiles provide an incredible array of functions, and new ones are being added at a breakneck pace. Depending on the Mobile phone model, you can:
* Store contact information
* Make task or to-do lists
* Keep track of appointments and set reminders/scheduler
* Use the built-in calculator for simple mathematics
* Send or receive e-mail
* Get information (news, jokes, entertainment, astro, stock quotes) from the Internet
* Play simple/3D games
* Chat, Surf the internet.
But have you ever wondered how a mobile works? What makes it different from a regular phone? What do all those terms like PCS, GSM, CDMA and TDMA mean? Below, we will discuss the technology behind cell phones so that you can see how amazing they really are.
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.
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.
A good way to understand the sophistication of a mobile phone is to compare it to 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 1.5 km using a 0.25-watt transmitter. A CB radio, because it has much higher power, can transmit about 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.
