Nov 22, 2004 12:03 AM
218580 Views
(Updated Nov 22, 2004 12:03 AM)
Dear friends,
Most of you posted a request for a review covering all aspects of GSM and CDMA phones. And all of you needs a non technical review. But as GSM and CDMA are very technical terms in nowadays electronics I must say something about the technical aspects too.
HISTORY
The GSM was originated in Europe (Global System for Mobile) in the year 1990 and gained world wide popularity because of its modern network features which are available to the individual mobile phone user. CDMA or code division multiple access was developed by Qualcomm Inc. and it became an international standard in 1995.
TECHNICAL ISSUES
As you know the mobile personal communication systems uses microwave frequencies above 800MHz for their transmission and reception purposes. They all are operating in some predefined or pre allocated frequency bands according to the international standards.
For operating in these microwave frequencies they all need some access methods. And these methods are:
- Frequency division multiple access (FDMA)
2.Time division multiple access (TDMA)
3.Code division multiple access (CDMA)
Thus CDMA is one access technology which cell phones uses to transmit and receive data. You can understand the meaning of FDMA, TDMA and CDMA eazily by just noting the word meaning for ezch letter. That is FDMA puts each call on a separate frequency and TDMA assigns each call a certain portion of time on a designated frequency for the above mentioned purpose. But CDMA gives a unique code to each call and spreads it over the available frequencies. All these are multiple access systems because more than one user can use the specified CELL ( not cell phone!) at a time.
But GSM or Global System for Mobile uses the above mentioned TDMA ( Time Division Multiple Access ) for mobile communication purposes ! In other words GSM is a global standard based on TDMA and a very popular one in the entire Europe, Middle East, Asia and Africa and not an access code as CDMA but one global standard.( Remember it always....CDMA vs GSM is really misleading! it is CDMA vs TDMA..!)
GSM operates in the 900 MHz band (890 MHz - 960 MHz) in Europe and Asia and in the 1900 MHz band in the United States. Besides these facts we must know the limitations and advantages of each systems in a brief way. All these facts are highly technical but I will try my best to write the details suite for all the mouthshut readers.
First TDMA of GSM.
The data transmission in TDMA is actually not continuous. It occurs in bursts. But the time between these bursts for a single mobile phone user is very very short, so that he never knows that the speech of the other person is discontinuous!
As TDMA uses different time slots for transmission and reception your handset never need a duplexer. But it simply need a switch to transfer between transmission and reception sesseions!
But the CDMA system has a soft capacity limit. That is increasing the number of users will decreases the system performance.( any comments Reliance users..?..!!).
Channel data rates are very high in CDMA systems. But sel-jamming is a major problem.
AND NOW SOME INTERESTING FACTS
Above are the technical facts you must know. But as you are very familiar with GSM of BSNL, AIRTEL, ESCOTEL etc. and the CDMA of Relience I know you are also eager to know about some commonly misunderstood things.
GSM is a widely spread standard and CDMA is a patented technology. That is you must pay a royalty for using CDMA! Also GSM covers the entire Europe , Asia except Korea, Africa and Middle East. So being a GSM user you have virtually an international roaming. You can eazily use a GSM phone in any of these countries while roaming.
GSM users are almost 8 times in number than CDMA users worldwide. By being a GSM user you will be part of the largest mibile community.
And coming to voice quality GSM is far better than CDMA, as I mentioned it earlier. CDMA base stations consumes less power than GSM and also covers a large distance. That is the cell size in CDMA is larger compared to GSM.
In general I say both GSM and CDMA are frontier technologies and both have good and bad qualities. And in the case of mobile handsets the fact is that GSM handsets are very popular and many of the new facilties are readily available in GSM phones with lesser price. The reason is simple...nokia and motorola needs profit...and they will invest more in GSM because GSM has 8 times more users than CDMA.
In the case of data rates also GSM is nowadays improving with their new GPRS. With GPRS it is expected that a data rate of about 171 kbps may be provided however on a shared basis between multiple users. GPRS enables an existing GSM system to communicate with any application or network that uses packet switching. GPRS thus allows subscribers to connect to the Internet to access applications as web browsing, mail and FTP.
So answering the question, CDMA vs GSM is not like Relience vs BSNL...! In the later case you can easily pick one first..!
Thank you.
Kannan.
