Brighthand FAQ: What's the Difference Between CDMA and GSM?

[Adama D. Brown]

Often when a new member of the Brighthand forum asks for advice on which device to buy, one of the questions that trips them up has to do with cell phone technologies: which is better, and what these various acronyms and technologies even mean.

CDMA and GSM are the names of competing cellular phone standards. They're about equal in the U.S. in terms of users, but overseas there's only GSM other than a few places like Japan, India, and Korea. Out of the four national carriers in the U.S., two -- Sprint and Verizon -- use CDMA, the other two--AT&T and T-Mobile -- use GSM.

The two biggest differences between these standards are international compatibility, and how the networks handle activating phones. Outside the U.S. and Canada, most GSM phones will still work, while almost all CDMA phones simply can't be used overseas. The only ones that can are those that also have a GSM radio. These are sold for people regularly traveling overseas on business, and are priced accordingly.

CDMA phones are activated remotely, by the carrier, using the phone's serial number, known as the ESN. Since each carrier has a database of all the ESNs that are approved for its network, this lets most CDMA carriers refuse to activate phones not originally intended for their network.

GSM phones are activated differently. Each account is associated with what's called a SIM card, or Subscriber Identity Module. This card, about the size of a fingertip and the thickness of a piece of paperboard, carries an encrypted version of all the information needed to identify your wireless account to the network. You slip it into the appropriate slot on a GSM phone (usually under the battery) and that phone is ready to use.

Naturally, this means that you can use pretty much any compatible phone on a GSM network, with or without the carrier's permission. This is limited only by the phone supporting the right radio frequencies (850 and 1900 MHz for North America, 900 and 1800 MHz for overseas), and on the phone not being "locked" to a provider other than the one you're trying to use it with.

Not only can you use a wider variety of phones with your service, it also allows you to take any GSM hardware and make it "your phone" instantly, including the ability to carry your contacts right on the SIM card. You could literally take your phone, smash it with a hammer, extract the SIM card, and with a backup phone in your glove compartment be back up and running in 30 seconds. Or you could carry a pre-paid SIM with you and pop it into your phone in case there was ever a time when you wanted to have phone service but not be reachable by your usual number. GSM's strength is in its flexibility.

That's not to say CDMA providers don't have advantages. In the U.S., at least, Sprint and Verizon are well ahead of AT&T and T-Mobile on deploying high-speed Internet: both of the CDMA carriers have reasonably extensive wireless broadband footprints, while AT&T's is relatively small, and T-Mobile is still preparing to launch such a system. Thus, some users in the U.S. have to chose whether flexibility now is worth having to wait for the broadband coverage to catch up.

Related Articles:

• Brighthand FAQ: Which Is Better, EV-DO, HSDPA, or Wi-Fi?

 

[holvoetn]

Good explanation Adama

One minor addition though: CDMA is used in a bit more countries then generally assumed.
Large parts of Russia and Scandinavian countries also use CDMA, as well as some areas in Europe, Africa and AsiaPac. (source: cdg.org)
So that's not really 'a few places'

[r0k]

Good explanation Adama.

Another thing to consider is the performance of the networks in your area. Att and Tmo networks are not as widely available as the existing CDMA infrastructure. A few years ago, driving through the corn fields of Indiana, Ohio, Illinois, Minnesota, Wisconsin, Pennsylvania, New York, Michigan, Ontario and Quebec gave me a pretty good survey of the availability of GSM and at the time the answer was "don't get off the interstate". Nextel uses a step-child of GSM called IDEN which supports that walkie-talkie feature. It is the most poorly built out infrastructure available and is really only marginally useful in central cities where utilities rely on the walkie talkie feature. The most annoying feature of Nextel is being bumped (dropping a call) in a 5 bar reception area. To me it seems like they kick off existing calls to let new calls through. Very annoying.

Dropped Calls:
1 Nextel (twice an hour)
2 Tmo
3 MetroPCS (Att's leftover TDMA network)
4 Att (more bars in more places is merely a commercial)
5 Sprint
6 Verizon (twice a year)

Signal strength:
1 Verizon (especially in rural areas)
2 Sprint
3 Att
4 Tmo
5 MetroPCS
6 Nextel (don't stray from downtown/interstates)

Low Cost:
1 MetroPCS ($40 a month unlimited everything)
2 Tmo
3 Att
4 Nextel
5 Sprint
6 Verizon (PAYG data can lead to a huge bill!)

So it's not quite as simple as who has data built out. Deciding on a carrier requires doing research on who has the better infrastructure in the area you live, work or travel. Many find that GSM works better indoors than CDMA. I have friends who are on the fringe between 2 CDMA towers and have given up on Verizon and Sprint and get great reception from the GSM providers. Some Sprint users roam Verizon towers and get identical reception to what I get while others do not. In the arena of RF (Radio Frequency) performance YMMV. A good summary of communication types (though somewhat biased toward non-technical readers) is available at http://www.wirelessguide.org/communication/index.php

Remember, it doesn't matter who consumer reports or wireless guide likes. What matters is which carrier works for you in the places you go.

[AKAJohnDoe]

I now have two wireless carriers (GSM for voice; CDMA for data), and I am dropping my landline and associated DSL.

[maceyr]

The only reason why I'm not on a CDMA network is mainly because of the agreement between most CDMA carriers to refuse activation of CDMA phones from other carriers mainly and forcing customers to sign another contact. If they didn't have this practice, I may have gone CDMA as well since they do offer better coverage where I am. But GSM is very nice when traveling since I simply buy a local SIM and pop it in my unlocked GSM Treo.

I equate the CDMA vs GSM debate similar to Betamax vs VHS.

[ampermc]

Any discussion of CDMA v. GSM needs to mention the annoying squawk of GSM phones through audio systems that possess less than ideal shielding. I understand that articles like this primarily focus on the benefit to the end user, but I also think it's worth mentioning some of the more technical details about the two systems.

Personally, I believe that CDMA is technically superior to GSM. The only real advantages to GSM are the ability to change SIM cards, overseas availability, and device choices due to the somewhat larger market. If I'm not mistaken, it's primarily the Qualcomm licensing fess which prevented CDMA from capturing more of the market.

Of course, in my personal situation, GSM has the iPhone, CDMA does not. I also don't travel overseas much, so CDMA's reach doesn't bother me, and my iPhone squawks through my car's Kenwood EZ-500 stereo (though not through my Kenwood TM-D700A(G) and Yaesu FT-100 amateur radio sets).

[holvoetn]

Originally Posted by ampermc

Any discussion of CDMA v. GSM needs to mention the annoying squawk of GSM phones through audio systems that possess less than ideal shielding.

Ah, you mean that funny sound just before a call comes in ? I know what you mean, LOL
But that's more an issue of the audio system, not the GSM device.

[maceyr]

I agree that CDMA is the "better" network which is why I brought up the Betamax reference, and even the HD-DVD vs Blu-Ray debate, but that doesn't mean much in real life when the more popular or adapted product is the one that wins.

[Adama D. Brown]

Originally Posted by holvoetn

So that's not really 'a few places'

Perhaps not, but the bulk of coverage and compatibility overseas is GSM; widespread use of CDMA is limited to a relative few countries.

Originally Posted by r0k

Another thing to consider is the performance of the networks in your area.

Indeed. Of course, signal availability varies so widely that to try comparing it in more than the vaguest terms is useless to the end user. In my area, for instance, the only native carriers are Verizon and AT&T, though they extend roaming rights to Sprint and T-Mobile. The AT&T footprint is still a bit smaller than Verizon, though I suspect that if you did the same survey today you'd find much less difference in coverage.

Some Sprint users roam Verizon towers and get identical reception to what I get while others do not.

They should update their PRLs, as to my knowledge all Sprint customers should be able to roam onto Verizon.

Originally Posted by ampermc

Any discussion of CDMA v. GSM needs to mention the annoying squawk of GSM phones through audio systems that possess less than ideal shielding.

This is true, though a minor point relative to the major technical considerations. It's also signal and device dependent--the better a signal, the lower the transmit power, and thus the lesser the beeping.

Personally, I believe that CDMA is technically superior to GSM. The only real advantages to GSM are the ability to change SIM cards, overseas availability, and device choices due to the somewhat larger market. If I'm not mistaken, it's primarily the Qualcomm licensing fess which prevented CDMA from capturing more of the market.

Umm, you just said it's only real advantages are it's advantages.

In all seriousness, I really don't see what's superior about CDMA. It's biggest claim to technical superiority was the ability to roam back to analog, but that's become almost irrelevant these days. The network size and speed is controlled by carrier buildout, not inherently by the technology.

[ve7mdt]

I did not expect the discussions going technical but it did (which I had not done anything to trigger that). So anyway, might as well put in my 2 cents and see if I get more negative rep power or not :-) .

Ok, technically speaking, CDMA and GSM are the common layman's terms, which came out from technical terms, but weren't originally meant to be that. However, using terms which can be intepreted in strict industry lingo, or in layman's tongue would easily result in arguments and misunderstanding. You only have to go to HowardForums for example to see every other week of such posts as "CDMA sucks", or "GSM will take over the world", and such nonsense.

What we are trying to describe is a type of system, and in the industry, it's designated as IS-??(?), at least for standards that came from North America. Yes, engineers like numbers and types. At least for them, they don't have the ambiguity, and gladly so so they can do their job.

When layman talks about CDMA, they are actually talking about IS-95, which, of course, uses "CDMA" technology.

CDMA stands for Code Division Multiple Access, which is a form of spread spectrum coding method. Many things uses CDMA (the coding, not the cellphone), not just "CDMA" phones or systems. As a matter of fact, the earlier usage of CDMA is in the military, in order to have better security (and not for a better voice quality, better things that you would think). Qualcomm, a big proponent of CDMA (both the native technology, and later the cellular technology), had been doing military contracts using this technology before there was CDMA cellular, and they use that to make a competing system to GSM (to replace analog).

GSM is an acronym for Global System for Mobile (in French), and came from Europe (and you can see why Qualcomm pushed something different). GSM uses TDMA as a base technology, but has a lot more complex and well thought out system design than the "TDMA" cellular technology (which is IS-136 that North America has seen). You can see why things can be confusing here, because if GSM uses TDMA then, isn't TDMA = GSM and things like that will go on and everyone got confused.

CDMA is not unique to have hands off capability to analog, TDMA had it also. It was a necessity because of those "growing pains" any carriers would endure.

It is true that GSM causes more interference to electronics that process audio etc, compared to CDMA. It is not only just the power, but because of how the signal is designed / coded. GSM has a signal that is a SAW wave, and that means it is suspectable to be picked up by analog gain circuitry by means of a diode rectifier effect. CDMA on the other hand, has a signal more like a background noise, very evenly spreaded out to a large frequency range, and thus does not have a strong "hot point" in the band to be picked up (rectified). This is why GSM causes more interference.

BTW, iDEN system also uses TDMA based coding method, however, is a completely different system to TDMA or GSM.

I remember seeing in other forums where those "fanboyz" were heating up the bashing etc, when WCDMA came out, and some thought that GSM carriers were changing to CDMA.

UMTS / HSDPA (and whatever follows etc) is the 3G standard that most, if not all GSM carriers have adopted as the next generation of system, however, what is confusing is that UMTS uses WCDMA as the coding method. So when WCDMA became the new 3G standard, people were confused, and then those "fanboyz" were saying this and that. Unfortunately, despite the name, WCDMA is not CDMA, but it is not TDMA either. As a matter of fact, it is a combination of something here, and something there. So how do you define it? A bastard? :-) .

It does not help when each generation of technology might be given a new name, and there might be more than 1 name. Name could be given from standard organizations, or be branded, or something that falls in between, to become a layman's term etc. e.g. CDMAOne is a brand name, but 1xRTT was originally a technical name (which the layman's term would be, yes, you guess it right, 1x). Names names names.

And don't even get me started as to what constitutes 3G.

Back to the original subject. Some of the differences are not necessarily so. For example, "CDMA" can have something that GSM enjoys: SIM card. It is called R-UIM but it is not implemented in North America. Some people were totally confused when they saw a slot inside their CDMA Nokia phones and thought that the phone can be used on the GSM network, and asked on forums how they can get it unlocked :-) . In other countries, those "CDMA" phones can be swapped around like we use GSM ones here.

The SIM flexibility is a big thing to many, including myself. If my battery runs out, or if my device breaks down, I don't have to panic. Just take the SIM out and put it in some other device.

One thing is certainly nice about CDMA though, is its inherent noise cancelling technology (a by-product of the coding method / codec, not as truly intended), such that when you driving with the window down, the other party doesn't really hear the noise.

But as far as Smartphone and PDA aficionados' concern, neither "CDMA" or "GSM" would satisfy any of us nowadays. We want 3G, and neither one is 3G. Ev-DO or UMTS/HSPDA/HSPA is what we should be discussing here :-) .