It is very often we hear 3G and 4G technology.. and we use to speak more about it.. but when some one ask us what is the technical work behind it? we will be blinking for it...
so being a electronic and communication engineer i shouldn't blinking so i learned few about it and that is here...
1G TECHNOLOGY- ANALOG TECHNOLOGY
The first generation in mobile communication technology is analog communication..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.
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 Narrow band 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.
This uses FDMA (frequency division multiple access) -FDMA separates the spectrum into distinct voice channels by splitting it into uniform chunks of bandwidth.

2G TECHNOLOGY-GLOBAL SYSTEM FOR MOBILE COMMUNICATION (GSM)
This second generation in mobile communication technology is digital communication.GSM (Global System for Mobile Communications: originally from Groupe Spécial Mobile) is the most popular standard for mobile telephony systems in the world.  the world’s most widely used cell phone technology. Cell phones use a cell phone service carrier’s GSM network by searching for cell phone towers in the nearby area.
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 uses TDMA- Time Division Multiple Access:
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.
CDMA-Code Division Multiple Access:
Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne and CDMA2000 (which are often referred to as simply CDMA), which use CDMA as an underlying channel access method.
CDMA uses a “spread-spectrum” technique whereby electromagnetic energy is spread to allow for a signal with a wider bandwidth. This allows multiple people on multiple cell phones to be “multiplexed” over the same channel to share a bandwidth of frequencies.
With CDMA technology, data and voice packets are separated using codes and then transmitted using a wide frequency range. Since more space is often allocated for data with CDMA, this standard became attractive for 3G high-speed mobile Internet use. While CDMA and GSM compete head on in terms of higher bandwidth speed (i.e. for surfing the mobile Web), GSM has more complete global coverage due to roaming and international roaming contracts.

GSM technology tends to cover rural areas in the U.S. more completely than CDMA. Over time, CDMA won out over less advanced TDMA technology, which was incorporated into more advanced GSM.
3G :
3G is the third generation of mobile phone standards and technology.3G allows simultaneous use of speech and data services and higher data rates (at least 200 kbit/s peak bit rate to fulfill to IMT-2000 specification). Today's 3G systems can offer practice of up to 14.0 Mbit/s on the downlink and 5.8 Mbit/s on the uplink. since the bandwidth is high,greater network capacity and rate of data transfer is also high..
The first pre-commercial 3G network launched in May 2001 by NTT DoCoMo in Japan. The network was branded as FOMA. Following the first pre-commercial launch, NTT DoCoMo again made history with the first commercial launch of 3G in Japan on Oct. 1, 2001.
EDGE-Enhanced Data rates for GSM Evolution 
EDGE  is a backward-compatible digital mobile phone technology that allows improved data transmission rates, as an extension on top of standard GSM. EDGE is considered a 3G radio technology and is part of ITU's 3G definition. EDGE was deployed on GSM networks beginning in 2003— initially by Cingular (now AT&T) in the United States.

^4G: 
4G, which is also known as “beyond 3G” or “fourth-generation” cell phone technology, refers to the entirely new evolution and a complete 3G replacement in wireless communications.
Just as data-transmission speeds increased from 2G to 3G, the leap from 3G to 4G again promises even higher data rates than existed in previous generations. 4G promises voice, data and high-quality multimedia in real-time (“streamed”) form all the time and anywhere.
Various standardization and regulatory bodies estimate the launch of 4G networks commercially between 2012 and 2015.


^{THAT IS ALL I KNOW ABOUT THE 4 GENERATION OF THE MOBILE TECHNOLOGIES... STILL I NEED TO LEARN MORE ABOUT 3G AND 4G... I WILL TRY TO LEARN IT SOONER..}

CELL PHONE

   "NECESSITY IS THE MOTHER ON INVENTION"

Today, every human has an extra organ called cell phone... which is of variety of models and size...i say it as organ since it is being with us all around the clock..
 Every one is using it but very few know how it works..
as i said already i love to again knowledge... i put little effort to understand it... here is that...

CELL PHONE

This is the advanced version of radio,but sophisticated and secured one... As like as the radio each network operator gets their own unique carrier frequency with which they modulate the signals...

• A cell-phone carrier typically gets 832 radio frequencies to use in a city.
• Each cell phone uses two frequencies(one to receive and other to transmit) 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 later.)      

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:

The about 395 channels are divided into 7. each cell has about 56 channels (i.e. 56 people can be talking on their cell phone at a same time). the cell around will not have this same 56 channel.. but the cell outside the cells around the center can have the same this same 56 channel.. this is to avoid the repetition of channel
.

when the customer goes from one cell to another the signal to the current base station will diminish and the base station of the next cell will find the arrival of other channel with in its range and 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.

Let's say you're on the phone and you move from one cell to another -- but the cell you move into is covered by another service provider, not yours. Instead of dropping the call, it'll actually be handed off to the other service provider.this is roaming

once the mobile is switched ON... our mobile will search for same SID(system identification number).. once the same SID is found, it will setup a connection with the base station using the control channels.. else it will say "NO SERVES" or " NO NETWORK COVERAGE"..

our mobile will communicate with base station using the control channels about call set up and channel changing.. for this communication sets up only if our phone system identification number(SID) should match with the base station SID... always there will be a connection between our mobile phone and the base station..with this the mobile telephone switching office(MTSO) will maintain a database of their customers..

once a call arrives.. the MTSO will find the location of the specific customer with the help of the data base.. and divert the call to the nearest base station... then the base station will allocates two frequency(one freq. to receive and another to send the date) which is support by the customer's phone.. then the call will be transferred..

when the customer wants to make a call the reverse operation will be done..