difference between GSM-CDMA

[kristof.vanriet]

I know what CDMA is and what GSM is and how it basicly works, but what are the benefits of a CDMA network vs GSM and otherwise
And why are there used 2 technologies, and not one global...
As we all know GSM started several years before CDMA.

SO what are the + and - of a CDMA?
and what are the + and - of GSM?

[Michael]

Well, I am no expert, but I can probably fill in a few details.

One of the basic things that differentiates GSM (based on TDMA) and CDMA is the way the carve up bandwidth.

Each bit of radio spectrum used by a handset has to be shared with other people in the area. It is more or less the same as multiplexing for normal data land lines.

The major difference between GSM/TDMA and CDMA is in the way they divide up those signals between multiple users.

GSM/TDMA uses a Time Division method. TDMA, in fact, stands for Time Division Multiple Access. Simply put, this means that each device on the local network is allocated a time slice where it "owns" the bandwidth, and it can send/receive its data.

So lets just pick a number and say there are 30 available time slices in a given cycle. Each phone would then get 1/30th of every cycle that it could send and receive data (aka, voice).

CDMA uses a different method, called Code Division Multiple Access. The specifics of how it breaks the cycle up are beyond me, but how it works out is that the phones only get a slice of the bandwidth cycle when they actually need one. So if you are not talking, and the other person is not talking, nothing is transmitted.

With GSM/TDMA, each phone is transmitting and receiving during its slices of the bandwidth cycle, whether it needs it or not.

Since most coversations are comprised largely of silence, the end result is that CDMA phones have to transmit less data. They don't have to send silence, like GSM/TDMA phones do.

This means a few things. More CDMA calls can be fit into a given amount of frequency spectrum (ie. it is more efficient for the network), less radiation is being created from the phone towards the user (you only get radiation when you are talking, basically), and battery power is conserved since the handset only transmits when it actually has something to send.

There are other differences, too, that I can't get into. For one, it is harder to implement a CDMA network. The tower placement is more difficult. Dealing with hills is more difficult than with GSM/TDMA. Things like that.

But in general, CDMA is vastly superior technology. Not surprising since Qualcomm's version of it (that which is used in CDMA and WCDMA phones) is newer technology, even if the basics were in use by the US military as far back as the 40s.

The important thing for me, though, is the SIM card. Had CDMA implemented the use of a SIM card (something it very easily could have done), then the North American market would be very different today, and there would be more CDMA networks in other countries. The SIM card allows people to easily switch phones, and that helps the market.

Anyway, I hope that gives you a basic overview.

[3ple4]

Huh? :confused: You mean countries that use CDMA don't use SIM cards? Then what's the equivalent of the SIM card in a CDMA network?

Another stupid question: Then why are there different frequencies (eg. 900, 1800, 1900) in a GSM network? Can a mobile operator support 2 frequencies?

Lastly in CDMA, does it also have different frequencies?

[Michael]

Originally posted by 3ple4
Huh? :confused: You mean countries that use CDMA don't use SIM cards? Then what's the equivalent of the SIM card in a CDMA network? The phones have something called an ESN programmed into them. A serial number, if you will. The network assigns an ESN to an account. If you want to change phones, you call them and tell them the ESN of the new phone.

Originally posted by 3ple4
Another stupid question: Then why are there different frequencies (eg. 900, 1800, 1900) in a GSM network? Can a mobile operator support 2 frequencies?

Lastly in CDMA, does it also have different frequencies? What do you mean? There are different frequencies because different areas of the world use different frequencies for different things.

Mobile operators can support multiple frequencies, but it is not in their best interest to do so. This ususally only happens after a merger.

And yes, CDMA works on different frequencies. Sprint uses 1900Mhz, Verizon 800Mhz, for example.

[14charusername]

In South America CDMA is generally 1900MHz, elsewhere generally 800MHz. Brazil seems to have nothing but 1800MHz GSM. ALL US mobile services (CDMA, iDEN, GSM, analog, whatever) are 800 or 1900 or both becuase those are the only licensed bands. In Eastern Europe there are plans to use licenses for an old 450MHz band for CDMA networks. Theoretically any technology can be made to work on any band. But there are other pratical issues in terms of band choice, licensing and availability of compatible phones. iDEN phones are only made to work at 800MHz becuase of the licensing the largest operator: Nextel, was able to obtain. Even iDEN networks in Israel are 800MHz despite the general trend in Israel to license radio the way Europe licenses radio. (GSM in Israel is 900/1800.) I thought with WCDMA everyone in the world was going to be using 2100MHz to simplify things, but apparently ATTWS is planning 1900MHz WCDMA. That would mean that to build a 3G truly world phone with a SIM card, you'd need to include 5 bands (4GSM bands and 2 WCDMA bands). That's just a little silly. Anyone know if the FCC is licensing for WCDMA 2100? That would be good news.