If There Is A Will

[chandramauli 0]

IF THERE IS A WiLL / Know your technology

This article is quite old but its worth a read ...chech it here The Week

Know your technology

While making your telephone wire-free, you have two competing technologies to select from-Code Division Multiple Access (CDMA) and Global System for Mobile Communication (GSM). In India, limited mobility service providers opt for CDMA while cellular operators use GSM technology.

In CDMA, the data is digitised, each packet is given a unique sequence code and spread on the entire bandwidth. On reaching the receiver, it is reassembled. In effect, every call uses the full available frequency spectrum, thereby enhancing capacity.

CDMA, patented by US-based Qualcomm, is projected as the technology of the future because it is still evolving and so, can accommodate nuances.

The technology, though ideally suited for data transfer, has its own share of limitations, the important one being its inability to offer add-ons such as SMS and roaming facilities.

GSM uses the narrowband Time Division Multiple Access technology. Here, each call is assigned a frequency and so, the number of calls that can pass through a spectrum is limited. Its biggest strength is the capability to offer add-on services like SMS and roaming. It is a mature technology. That 70 per cent of the approximately one billion cell phones in the world use GSM is testimony to it.

Now the most important question: why is the coverage limited for CDMA phones and why can't they offer SMS? This is not the technology's fault. The government has restricted the WiLL operators from offering their service beyond the Secondary Distance Charging Area. Besides, mobile operators have jointly decided not to give inter-connectivity to WiLL operators.

A customer who goes in for the rock bottom rates WiLL operators offer should realise that some of them are introductory in nature. Besides, the regulatory body, TRAI, is yet to approve them. They should also be prepared to shell out whatever rates they decide once the first three years, for which the up front amount is paid, gets over.

And if you have already invested in a GSM phone, don't lose heart-it is a foregone conclusion that the GSM cellular rates will also crash now

[Utsav 0]

>>>>>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.

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.

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 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. 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.

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.

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.

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.

[Utsav 0]

You'll find a lot more information here:How Cellphone Works

[chandramauli 0]

good stuff of info...

[city02 63]

It is now possible to locate a person using a cellular phone down to a range of a few meters, anywhere on the globe.

Only if it has a GPS built in.

Otherwise the best resolution is via triangulation of the nearest towers and only narrows it down to the size of a cell site... (about 0.5-1km)

[Utsav 0]

Without GPS, you can locate the Cell phone user as per signal response and positional calculation may be calculated by adjascent towers. But can anyone tell me the Signal Strenth comparison between CDMA and GSM towers?

I mean which one uses more towers and less burden on each?

[biosbhai 0]

GSM uses more towers than CDMA.

[Utsav 0]

That means each CDMA tower covers more individuals... right?

Another thing, RIM and RIP(FWP/FWT) share same tower right?

[t9en 0]

Yes... turbasu...... u r right... RIM & RIP using same towers.......