# Mobile Technologies



## ravimevcha (May 11, 2005)

From the heavy cordless phones of the 1980's to the smart phones of today, cellular phone technology has undergone a tremendous change.
But have you ever wondered how you can call someone across the world using a tiny phone? You might have heard of features like WAP and GPRS from cell phone vendors and service providers. But are you aware of what they really mean? Well, as far as   I think this articles gives you , all you need to know about the present mobile technologies.

For the convinience of you people I have described   each technology in two parts:

Part 1: ( Non- Technical )
For those who donâ€™t have a technical background .


Part 2: ( Technical )
For those who are from technical background.

So now lets start with the discussion

Generations of mobile communications
The first generation (1G) of mobile communications was introduced in the late 1970s; it was primarily used for voice transfer. In the early 1990s, second generation (2G) systems came into existence and was further developed to 2.5G, which includes GSM, TDMA and CDMA. These were used for voice and data.
The next generation of mobile communications is 3G and this delivers data speeds from 384 kbps to 2 Mbps and over wireless interfaces such as GSM, TDMA and CDMA.

Technologies used in Mobile communication


*Frequency division multiple access (FDMA)*

*( Non- Technical )*

The first-generation mobile access method, FDMA uses separate frequencies for each call. For example if there are four stations, each will receive their own frequency. Thus there is no interference between them. This reduces interference, but limits the number of users.
It uses Analog transmissions, Analog transmission is considered an "older" cellular phone technology. Analog is considered an older method of modulating voice or data information radio signals.And this technology is considered the least efficient way
Of mobile communication.

*( Technical )*

FDMA is used exclusively for analog cellular systems, even though in theory FDMA can also be used with digital. Essentially, FDMA splits the allocated spectrum into many channels. In current analog cell systems, each channel is 30 kHz. When a FDMA cell phone establishes a call, it reserves the frequency channel for the entire duration of the call. The voice data is modulated into this channelâ€™s frequency band (using frequency modulation) and sent over the airwaves. At the receiver, the information is recovered using a band-pass filter. The phone then uses a common digital control channel to acquire channels.
FDMA analog transmissions are the least efficient cellular networks since each analog channel can only be used one user at a time. Analog channels don't take full advantage of band-width. Not only are these FDMA channels larger than necessary given modern digital voice compression, but they are also wasted whenever there is silence during a cell phone conversation. Analog signals are especially susceptible to noise and the extra noise cannot get filtered out. Given the nature of the signal, analog cell phones must use higher power (between 1 and 3 watts) to get acceptable call quality. Given these analog features, it is easy to see why FDMA is being replaced by newer digital networks such as TDMA and CDMA.


*Time division multiple access (TDMA)*

*( Non-Technical )*

TDMA allocates unique time slots to each user within each channel, thus allowing many users to access the radio frequency without anyone's interference. Each mobile conversation uses only a particular frequency slot of the time.

The TDMA system is designed for use in a range of environments and situations, from hand portable use in a downtown office to a mobile user traveling at high speed on the freeway. The system also supports a variety of services for the end user, such as voice, data, fax, short message services, and broadcast messages. TDMA offers a flexible air interface, providing high performance with respect to capacity, coverage, and unlimited support of mobility and capability to handle different types of user needs. TDMA is the leading digital technology in cellular phones today.

While TDMA is a good digital system, it is still somewhat inefficient since it has no flexibility for varying digital data rates (high quality voice, low quality voice, pager traffic) and has no accommodations for silence in a telephone conversation. In other words, once a call is initiated, the channel/timeslot pair belongs to the phone for the duration of the call. TDMA also requires strict signaling and timeslot synchronization. A digital control channel provides synchronization functionality as well as adding voice mail and message notification. Due to the digital signal, TDMA phones need only broadcast at 600 milliwatts.

Compared to analog FDMA transmissions, TDMA offers a cellular carriers a efficient bandwidth option. TDMA is more secure, and has better quality of voice transmissions over longer and shorter distances. Due to lower cost savings compared to CDMA, TDMA is the digital transmission of choice in today's cellular world. TDMA is more popular with cellular carriers and manufactures and is the adopted digital standard for most phones. TDMA can be viewed as modern technology, FDMA/Analog as older technology.

*( Technical )*

Time division multiple access (TDMA) is digital transmission technology that allows a number of users to access a single radio-frequency (RF) channel without interference by allocating unique time slots to each user within each channel. The TDMA digital transmission scheme multiplexes three signals over a single channel. The current TDMA standard for cellular divides a single channel into six time slots, with each signal using two slots, providing a 3 to 1 gain in capacity over advanced mobile-phone service (AMPS). Each caller is assigned a specific time slot for transmission.
Time Division Multiple Access (TDMA) is one of several technologies used in digital wireless transmissions that increases the efficiency of the network by allowing a greater number of simultaneous transmissions. Networks using TDMA assign 6 timeslots for each frequency channel. Devices using the wireless network send bursts of information that are reassembled at the receiving end.
TDMA builds on FDMA by dividing conversations by frequency and time. Since digital compression allows voice to be sent under 10 kilobits per second (equivalent to 10 kHz), TDMA can fit three digital conversations into a FDMA/Analog channel (which is 30 kHz). By sampling a personâ€™s voice for, say 30 milliseconds, then transmitting it in 10 milliseconds; the system is able to offer 3 timeslots per channel in a round-robin fashion. This technique allows compatibility with FDMA while enabling digital services and easily boosting the system by 3 times capacity. This leads to increase calls, more users on the network and better cellular quality.

*Code division multiple access (CDMA)*

*( Non- Technical )*

Commercially introduced in 1995 by Qualcomm, CDMA quickly became one of the world's fastest-growing wireless technologies. 3G CDMA networks provide more capacity for voice traffic, along with high-speed data capabilities, hence many cellular service providers are now building or upgrading to it.
For cellular phone users, it's a transparent interface for a wireless digital network. CDMA was original developed by the military in the early 1960's
For a non-technical definition, CDMA channels the packets of voice and data over wireless radio frequencies so a cellular user can hear better, quicker and with more quality then ever before.

*( Technical )*

CDMA uses wide-band spread spectrum techniques for signal transmission, as opposed to narrow-band channel techniques used in conventional analog systems. . CDMA uses sequential code frequencies to funnel traffic channels within the same radio channels.
CDMA is used in both 2G and 3G wireless technologies. Indian Cell operators like Reliance IndiaMobile, TATA Indicom, BSNL and MTNL's Garuda all use CDMA2000 technology and its variant CDMA1x
As far as I think , CDMA is the latest, greatest cellular technology.

One of the main problems facing CDMA technology these days is channel pollution, and signal deterioration inside buildings. But CDMA really comes into its elements when you are out in the countryside with few sites covering large expanses of land. CDMA also has a very high data transmission rate, from 153.6 to 614 kbps. Hence the Reliance India Mobileâ€™s claim to supply internet at 144 kbps speed.

Last but not the least , I would like to discuss few words about the GSM technology used in mobile phones.

*Global system for mobile communications (GSM)*

*( Non-Technical )*

Developed on TDMA protocol in Europe, GSM is now the worldwide standard technology for mobile communications. The advantage of GSM is that it provides a high level of security, globally accepted technology standards and superior sound quality.
For any GSM phone to work, it requires a Subscriber Identity Module (SIM), a card that contains your telephone account information. Thus, an Indian GSM phone can be used in USA and other countries too

The battle between GSM and CDMA technologies in India is hotting up! While the initial tilt was towards the GSM with players like Bharti, Hutch, Spice, BPL, Essar and BSNL preferring it, the TATAs and the Reliance have now entered the market putting their bets on CDMA.

Ideally, the GSM (TDMA) technologyâ€™s talk-range from a tower is 35 kms in comparision with CDMAâ€™s 110 kms, and the power output of a GSM (TDMA)phone is 2W, in comparision with CDMA phoneâ€™s 200 mW i.e., CDMA implies lesser radiation hazard. But the talk time is generally higher in a GSM (TDMA) phone due to its pulse nature of transmission, in comparision with a CDMA phone which transmits all the time.

CDMAâ€™s flaws are not yet known to the engineering community. Also, as CDMA is relatively new, the network is not set up to provide as many facilities as GSM (TDMA). Being the standard for mobile communication in very few countries, CDMA also cannot offer international roaming, a large disadvantage.

*( Technical )*

GSM (TDMA)phone determines that there is no intelligent data to transmit, it blanks out the audio, but to keep the listener comfortable, it inserts what is known as Comfort Noise, which mimics the volume and structure of the real background noise. This fake background noise assures the caller that the connection is alive and well. On the otherhand, in CDMA phones, background noise can be effectively suppressed even while the user is talking, so that Comfort Noise, as it is, is unnecessary

The GSM is built around the TDMA, or the Time Division Multiple Access concept.
Basically, the two technologies address differently the same fundamental problem of mobile communication, how to divide the finite frequency of airwaves between multiple users at the same time, or, how to make more than one person to carry on a conversation on the same frequency without causing mutual interference

In technical jargon, GSM (TDMA) does it by chopping up the channel into sequential time slices. Each user of the channel takes turns transmitting and receiving in a round-robin fashion. In reality, only one person is actually using the channel at any given moment, but he only uses it for short bursts. CDMA on the other hand, uses a special type of digital modulation called Spread Spectrum, which takes the userâ€™s voice stream bits and splatters them across a very wide channel in pseudo-random fashion. The receiver undoes the randomization in order to collect the bits together in a coherent order.

But the GSM (TDMA), which can provide only 56 kbps data transmission speed today, is also catching up very fast, and moving towards the next generation protocols, the GPRS and the EDGE.

Wireless technology platforms: GPRS, EDGE and WAP
GPRS
GPRS, stands for General Packet Radio Services, is an enhancement to GSM technology that integrates GSM and IP technology. GPRS offers an always-on, high speed connectivity to the Net. Thus you can check your email on the move and surf the Web at high speeds. Currently BPL Mobile and Hutch (Orange in Mumbai) offer GPRS services in India.

*WAP*

In this hi-tech age, people on the move need any-time access to the Net. This is where WAP comes in. It provides Internet access to cell phones. It is an open standard for wireless protocols that is independent of the service providers. To display Web content, the cell phone must have a WAP browser. Nowadays, cell phones often come with WAP and GPRS technology.
WAP and GPRS also allows you to download games, send mail and even transfer your messages to your PC.

*EDGE*
The new EDGE ((Enhanced Data GSM Environment) interface has been developed specifically to meet the bandwidth needs of 3G. Promoted by Ericsson, it offers high-speed data transfers over GSM networks with just a software upgrade to the handset. EDGE allows speeds up to 384 kbps.

*Conclusion*

The final conclusion is that it is not so much over technology that a customer decides which network to adopt. It is basically performance! Whichever mobile communication provider puts in better efforts in giving a higher performance, the subscriber is bound to follow that path! 


Source : *www.krify.com/


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## imcool (May 12, 2005)

The reality with EDGE, don't be fooler, practical speeds are nowhere near those i 3G, belive me i wasted 25000 bucks, max you get is 60-100 kbps, nothing more. check this

*cyberia-gen.blogspot.com/2005/05/edge-is-overhyped.html


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