Wireless Standards: What's the difference?

TDMA http://en.wikipedia.org/wiki/Time_division_multiple_access

CDMA http://en.wikipedia.org/wiki/CDMA

GSM http://en.wikipedia.org/wiki/GSM

 

Sorry, I guess I am not intelligent enough to still understand the difference. :O

Can you break it down even further?

 

In the simplest terms they are different technology interfaces to interact with their network. This is why handsets for one technology will not work on the other technnology's networks. The links provided tell you what the different technologies are and give a basic explanation on how they work. If the provided links and my simple explanation are not what you want you're going to have to explain what you do want. Hope this helps.

 

AMPS- Advanced Mobile Phone System
Primary analog standard used in US. Only on 850 mHz. 30 kHz spectrum needed per call.

IS-136 "TDMA"- Time Division Multiple Access
First widespread digital standard. Can be on 850 and 1900. 10 kHz spectrum needed per call.

GSM- Global System for Mobile Communications
Uses TDMA air interface. Needs 25kHz of spectrum per call. Runs on 450/850/900/1800/1900 mHz. Only 850 and 1900 in the U.S.

CDMA- Code Division Multiple Access
Assigns each transmission a code and spreads it out over a wide range of spectrum.

iDen- Intregrated Digital Enhanced Network
Uses TDMA air interface. Is considered Specialized Mobile Radio.

W-CDMA- Wideband Code Division Mutiple Access
For high-speed data transmissions. Not sure how to explain it.


BY CARRIER

Cingular- AMPS, TDMA, GSM, W-CDMA

Verzion- AMPS, CDMA

Sprint Nextel- CDMA, iDen

T-Mobile- GSM

Alltel- AMPS, CDMA, TDMA, GSM

U.S. Cellular- CDMA

Cell One (Dobson)- TDMA, GSM

Cell One (4 Corners Wireless)- AMPS, GSM

First Cellular of Southern Illinois- GSM, CDMA

Midwest Wireless- CDMA

Bristol Bay Cellular- AMPS

Unicel- TDMA, CDMA, AMPS, GSM

Commnet- GSM, AMPS, CDMA, TDMA

Southern Cellular- iDen

 

This is a very simplified explanation and I am either glossing over or distorting some of the details, but here goes!

If you consider wireless communication of any kind (radio, TV, mobile telephony, etc.), in the simplest abstraction, you have a trasmitter and a receiver. The trasmitter converts the voice or video (or data) baseband signal into a form that can be broadcast into the air (the technical term for this is modulation) and the receiver receives the signal and demodulates it back into the baseband.

If you simply stopped there, you could have for example, only 1 radio station within the range of that radio station. People realized that since the human ear can only hear sounds from about 20Hz to about 20KHz, you could for example have a radio station that uses the frequency band from 0 to 20KHz, another that goes from 20KHz to 40KHz, etc. etc. In effect you are taking the entire radio spectrum available and chopping it up into smaller segments and assigning each to a different radio station. The center of this smaller range is called the carrier frequency and it is what the station is known as, for example, 1010AM, 970AM, etc. This kind of system where the available spectrum is divided into smaller frequency bands is called Frequency Division Multiplexing or Frequency Divison Multiple Access (FDMA). It is the general multiplexing scheme used for radio and television.

As people started researching digital communication, they realized that there are other ways than frequency to multiplex multiple signals. For example, you can sample each signal at a rate that is related to the maximum frequency in that signal. If you have voice communication for example, the maximum frequency is rather low and you don't have to sample very fast to re-create the original signal. In other words, you can fit multiple voice calls into the same band by interleaving the samples. Of course you need some way to unravel the interleaved conversations at the receiving end. This form of multiplexing is called Time Division Multiple Access or TDMA. It is the underlying modulation scheme for IS-136, which is eponymously called TDMA in common parlance, iDEN which is the air interface for Nextel phones and GSM which is the air interface for Cingular, T-Mobile, etc. in the US and in much of the rest of the world.

TDMA has several limitations that are a bit too messy for this discussion, but suffice it to say that it will be largely supplanted in the world by a system called Code Division Multiple Access or CDMA. As the name suggests, this modulation scheme multiplexes multiple calls by assigning codes to each of them. It has its own complications, but largely addresses the issues that limit TDMA. It is the modulation scheme of the future. There are several air interfaces that utilize the CDMA modulation scheme. These include the so-called "second generation" air interfaces like IS-95 which is the original air interface used by Verizon, Sprint, etc. and is called CDMA by the general public, IS-2000 which is also called CDMA2000 1xRTT. All so-called "third generation" air interfaces like 1xEVDO (Sprint, Verizon, etc.) or WCDMA/UMTS (Cingular, T-Mobile, etc.) are evolutionary paths from the older IS-95/IS-2000 or GSM air interfaces but they all use CDMA as the modulation scheme.

It is important to distinguish the modulation scheme from the air interface. All of digital telephony is moving towards CDMA as the modulation scheme - TDMA is a dead end. The precise nature of the air interface is what is different. The majority of folks will end up with either UMTS/HSDPA (from GSM) or with 1XEVDO (from CDMA2000).

Which is better? Clearly, as a modulation scheme, CDMA is better. That is why everyone is going to use CDMA as the modulation scheme in the future and all TDMA-based schemes like GSM will disappear. However, that is not important.

It does not matter whatsoever what modulation scheme or air interface you choose. This is only deemed important by techies of the kind that inhabit boards like these . Simply worry about whether the company has enough towers to give you a good signal where you need it and whether (and this may or may not be important to you) the company has the kinds of phones/features you wish to have.

Hope this helps!

 

As an end user, you wouldn't need all the technical jargon unless you are interested in exploring the technical differences between them. Therefore, as an end user, you'll notice these differences between the technologies:

TDMA or CDMA: 3-way calling is very simple and consists of the use of the traditional Send and End keys. 3-way can only be accomplished by initiating the 3rd call. Once you are all linked, you can't unlink someone in the conference. They have to hang up. If you hang up, everyone gets disconnected. Cannot join someone in call waiting to a conference. You can complete a 3-way call before the 3rd party answers. You can send DTMF tones while being the 3-way call host. Call timer begins when you press Send. Roaming is controlled partly by the phone and partly by the network. No SIM card is required for the phone to operate. Call Waiting is not configurable from your phone. Call Forwarding can be partially configured from your phone. There is no provision in the Call Forwarding feature to forward when the line is busy. Time for voicemail to answer cannot be configurable from your phone. You have to call your provider. Caller ID can only be blocked per call. If you want to block it permanently, you have to call your provider. You can always call customer service even if your phone is deactivated.

GSM/UMTS: 3-way calling is smarter and allows up to 6-way calling (if your carrier allows), switching between parties, individually hanging up on each party, putting someone on hold while talking to someone else. All this requires the use of the phone menus. You can join someone in call waiting to a conference. DTMF tones cannot be sent by the conference call host. Cannot complete the 3-way link until the 3rd party answers the phone. The call timer on the phone starts when the call is completed (answered in the other end). Roaming is controlled entirely by the network. A SIM card is required for the phone to operate. Also, you can activate/deactivate or configure features such as Call Waiting, Call Forwarding and Forward when Busy, time for voicemail to answer, Caller ID (per call, or permanent), right from the phone menus (on some phone models). If the phone does not include the menus to do all this, there are codes you can enter. You cannot call customer service from a GSM phone if the SIM card is bad, or if your service is disconnected (SIM card inactive) because you didn't pay the bill. However, it is always possible for carriers to let SIM cards allow calls to Customer Service when the SIM card is inactive, but they just don't do it.

 

Less technically than the previous posts, GSM is the dominant interface around the world, meaning that with a Triband or Quadband frequency GSM phone (from Cingular or Tmobile), you can roam around most of the world with the same phone and the same phone number. There are a two billion GSM users worldwide, covering 82% of cell phone market worldwide. For someone to reach you while you vacation in Italy, they just dial your local US number, and only pay the local charge:you pay for the call, typically $1.29/minute. Or they can text message you for 20 cents.

You cannot do that with CDMA phone interfaces. The number of CDMA users is less than 300 million, globally. CDMA companies (Verizon/Sprint) will give their customers a GSM phone for global roaming (the exceptions being mostly in south america). As a result, most all businesses with global interests give their employees GSM phones for international travel.

GSM providers are upgrading, globally, to a new interface called W-CDMA (also called 3GSM, or UTMS). This is for faster data services like web browsing. The new phones have GSM and W-CDMA so they work both systems and arre therefore considered 'backward compatible'.

Verizon/Sprint is upgrading from CDMA to CDMA20001x (or called EVDO) for faster data rates. However, and this is an important point, these phones or interfaces are NOT compatible with GSM's W-CDMA (UTMS) systems, even though the name sounds the same and the core technology is the same. So once again, after the upgrades for faster data speeds (not voice), there will be mainly two world systems, with GSM's sibling being projected as the dominant player, globally, once again.

By this narrow, but important, definition of using a phone for voice communication around the world, GSM is currently, and it's upgrade path is projected to be the doinant universal standard in the near future.

There is a heated discussion whether this is the right thing to do, but the reality is that the numbers project that this will be the case. There is some hope that a 4th or 4G standard will emerge that will combine the two, but there is some heated mercantile ($$) competition on whether this will ever happen, and could be a decade into the future.

The thing to remember, is that newer or better, does not always project to the widest use by the consumer. If your interests are mainly limited to phone use in the USA,then either standard GSM or CMDA, is your choice. If you lived in the UK or Germany, you really have no choice...there is really only GSM and it is used throughout europe, into the middle east, china,and the rest of asia.

Maybe this targets your question from a different angle. The reference to wikipedia by the other posters are excellent.

I may have 'GSM' logo in my picture avatar at the left, but I chose GSM not because it is better than CMDA, nor because CDMA is inferior to GSM, but because my business takes me around the world and I need that kind of phone. Fortunately over the last 3 years, with the merger of Cingular and ATT, Cingular has made GSM an equal competitor to Verizons CDMA system in the USA. The voice quality is more than acceptable by both systems. TDMA is being was abandoned by Cingular and will disappear in 2007.

 

I would argue the difference in conference call set up and the like is more a function of the specific Carrier RAN and handset capabilities. The other things you lay out are a function of over the air capabilities that aren't fundamental differences between interface/OTA technologies (CDMA, TDMA, GSM, etc...)

 

Cingular will support TDMA and AMPS until March 2008.

 

The may charge you $20 for the privilege

 

That is true, in fact starting with September bill, Cingular is charging TDMA users $4.95 extra per month. Not to mention that TDMA service/coverage has not remained static over the last 3 years...it has been reduced to the minimum, with GSM replacing some of the multiple transmitters at each tower.

 

Nope, they aren't charging me anything. My AMPS StarTAC is on Beyond Wireless. Beyond Wireless will support existing TDMA/AMPS customers until January 2008.

 

Thanks for all the excellent responses and links posted to my son's original question. It's been over a month and I wasn't aware he'd asked this. I have the same questions too. I'll have to reread this thread to digest all that help!

For us, the problem is living, working, and camping in thinly populated, (and served) parts of Maine. All the small villages we know are well served by the new standard, but in the woods or hills we have to fall back on our old phones, which we still have (and even that isn't a sure bet.) We entered a new family plan with Cingular in August, (3 Razr phones) and are thrilled with what can be done with them, in the villages, but the reality here is very large dead zones.

It will get better as time goes on. I think.

 

None of the MVNO's who use the IS-136 network charge their subscribers an extra fee. I do not know of any MVNO (such as Beyond Wireless) who will activate any new IS-136 accounts.

 

I think Tracfone will.

 

I currently have full bars (signal) with GSM.

What I have been hearing (and this is purely unofficial) is that because UMTS/W-CDMA uses the same over the air interface as CDMA, where I get full bars now with GSM, I will NOT get full bars with UMTS/W-CDMA.

Is this true, or would I continue to have full bars with UMTS/W-CDMA?

 

It shouldn't make any difference at all. What makes the difference is where you are and where the nearest base station is located. The nearer you are to a base station the higher your RF reception will be. I don't think that concept is hard to understand. Also, whatever affects reception (trees, mountains, other obstructions) makes a difference as to how you receive a signal..

 

Wirelessly posted (T-Mobile: Nokia6800/2.0 (5.58) Profile/MIDP-1.0 Configuration/CLDC-1.0)

OK, I'll throw T-Mobile into this...

I have full bars literally everywhere with T-Mobile.

If the new equipment is in the same cell locations as it currently is with GSM, then should I continue to have full bars with UMTS/W-CDMA?

 

Whether you get full bars or not has nothing to do with GSM vs CDMA or WCDMA. It depends on how strong the signal is on your phone at your specific location. If you are using GSM and you get full bars, when switching to a UMTS device, chances are you will still have full bars at the same location. That's because when transfering the network from GSM to UMTS, the coverage patterns must be preserved, otherwise there will be coverage holes created and increased indoor reception problems. I am sure that's not what GSM carriers want.

 

To back up bobolito on this, the difference between CDMA, W-CDMA, GSM, etc is a matter of protocol (think languages, it's comparing English, German, and Japanese basically) not a matter of Equipment so much, at least not as far as this conversation is concerned. The signal is still amplified and carried so and so far, granted there are some minor differences between 1900mHz GSM and 850mHz UMTS but it shouldn't be detectable by the general public as far as Signal strength is concerned outside of building penetration in which case the phone should change back to 1900mHz GSM should it have been originally availabe in the area.

 

Thanks for the responses, it's understood now.

Once UMTS/W-CDMA goes live, I don't think GSM will be going anywhere anytime soon afterwards.

 

Wow Bandwidth Hogs, CATV only needs 6 MHz per Video Channel
and there are Hundreds of Digital Channel from Regular Broadcast
to Premium HBO or Pay per View or even HDTV,
but can you call it TDMA?

 

Agreed , it's deployed in 213 Countries.

 

Well jones A.K.A. GSM fanboy I hate to inform you that GSM uses more bandwidth than TDMA.

 

HDTV required a larger chuck of spectrum/bandwidth than other digital video....by far, due to the resolution.

Using a packet protocol, for example: DVB-ASI would be in the range of 270 MBPS while HDTV composite is upwards of 1480 MBPS (which I believe equates to about 25 MHZ of RF signal).

 

Well CDMA Fanboy, No wonder GSM sound is the Clearest.
But the other Difference between them is that GSM is in 213 Countries
w/ GSM users approaching 3 Billion.

 

Which is the precise reason why in certain places it is difficult to complete a GSM call. A friend and I in Shanghai this month had to resort to SMS or a landline. We would call each other 5 or 6 times to get a total of 30 s of voice calling. That is if we were lucky.

China really needs 3G licenses awarded to add some bandwidth.

 

I used to use GSM and I can't tell a diffrence. Also my phone will make calls in places where your phone will have a blank screen.

Also, I said something good about TDMA. How does that make me a CDMA fanboy?

 

Sorry AG8000 but GSM does NOT use more bandwidth than TDMA. In fact is uses the same bandwidth but has more call capacity.:lmao: