Cdma vs. Gsm Docx

CDMA vs. GSM: What's the Difference?

If you're shopping for a mobile phone, you're in for a lot of acronyms. Here's what you need to know about two basic, yet important, terms.

Two basic technologies in mobile phones, CDMA and GSM represent a gap

you can't cross. They're the reason you can't use AT&T phones on Verizon's

network and vice versa. But what does CDMA vs. GSM really mean for

you?

CDMA (Code Division Multiple Access) and GSM (Global System for

Mobiles) are shorthand for the two major radio systems used in cell phones.

Both acronyms tend to group together a bunch of technologies run by the

same entities. In this story, I'll try to explain who uses which technology

and what the real differences are.

Which Carries are CDMA? Which are GSM?

Five of the top seven carriers in the U.S. use CDMA: Verizon Wireless,

Sprint, MetroPCS, Cricket, and U.S. Cellular. AT&T and T-Mobile use GSM.

That means we're mostly a CDMA country. It also means we're not part of

the norm, because most of the world is GSM. The global spread of GSM

came about because in 1987, Europe mandated the technology by law, and

because GSM comes from an industry consortium. What we call CDMA, by

and large, is owned by chipmaker Qualcomm. This made it less expensive

for third parties to build GSM equipment.

There are several variants and options carriers can choose, like toppings on

their technological ice cream. In this story we'll be talking about U.S.

networks.

What CDMA vs. GSM Means to You

For call quality, the technology you use is much less important than the way

your carrier has built its network. There are good and bad CDMA and GSM

networks, but there are key differences between the technologies. Here's

what you, as a consumer, need to know.

It's much easier to swap phones on GSM networks, because GSM carriers

put customer information on a removable SIM card. Take the card out, put

it in a different phone, and the new phone now has your number. What's

more, to be considered GSM, a carrier must accept any GSM-compliant

phone. So the GSM carriers don't have total control of the phone you're

using.

That's not the case with CDMA. In the U.S., CDMA carriers use

network-based white lists to verify their subscribers. That means you can only switch

phones with your carrier's permission, and a carrier doesn't have to accept

any particular phone onto its network. It could, but typically, U.S. carriers

choose not to.

In other words, you can take an unlocked AT&T phone over to T-Mobile

(although its 3G may not work well because the frequency bands are

different). You can't take a Verizon phone over to Sprint, because Sprint's

network rejects non-Sprint phones.

3G CDMA networks (known as "EV-DO" or "Evolution Data Optimized")

also, generally, can't make voice calls and transmit data at the same time.

Once more, that's an available option (known as "SV-DO" for

"Simultaneous Voice and Data Optimization"), but one that U.S. carriers

haven't adopted for their networks and phones.

On the other hand, all 3G GSM networks have simultaneous voice and data,

because it's a required part of the spec. (3G GSM is also actually a type of

CDMA. I'll explain that later.)

So why did so many U.S. carriers go with CDMA? Timing. When Verizon's

predecessors and Sprint switched from analog to digital in 1995 and 1996,

CDMA was the newest, hottest, fastest technology. It offered more capacity,

better call quality and more potential than the GSM of the day. GSM caught

up, but by then those carriers' paths were set.

It's possible to switch from CDMA to GSM. Two carriers in Canada have

done it, to get access to the wider variety of off-the-shelf GSM phones. But

Verizon and Sprint are big enough that they can get custom phones built for

them, so they don't see the need to waste money switching 3G technologies

when they could be building out their 4G networks.

GSM and CDMA are competing wireless technologies with GSM enjoying about an 82% market share globally. In the U.S., however, CDMA is the more dominant standard. Technically GSM (Global System for Mobilecommunications, originally from Groupe Spécial Mobile) is a specification of an entire wireless network infrastructure, while CDMA relates only to the air interface — the radio portion of the technology.

Code division multiple access (CDMA) describes a communication channel

access principle that employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code). CDMA also refers to digital cellular telephony systems that use this multiple access scheme, as pioneered by QUALCOMM, and W-CDMA by the International Telecommunication Union (ITU), which is used in GSM’s UMTS.

Comparison chart

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CDMA

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GSM

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Stands for: Code Division Multiple Access Global System for Mobile communication

Storage Type: Internal Memory SIM (subscriber identity module) Card

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CDMA

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urrently 3.63/5

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GSM

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urrently 3.92/5

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Dominance: Dominant standard in the U.S. Dominant standard worldwide except the U.S.

Data transfer: Faster on EVDO platform which is applicable in CDMA only

GPRS is again very slowforward

Network: There is one physical channel and a special code for every device in the coverage network. Using this code, the signal of the device is

multiplexed, and the same physical channel is used to send the signal

Every cell has a corresponding network tower, which serves the mobile phones in that cellular area.

International roaming:

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CDMA

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urrently 3.63/5

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GSM

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urrently 3.92/5

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Frequency band: Single(850 MHz) Multiple(850/900/1800/1900 MHz)

Network service: Handset specific SIM specific. User has option to select handset of his choice.

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Subscriber Identity Module (SIM Card)

SIM (subscriber identity module) card, the onboard memory device that identifies a user and stores all of his information on the handheld. You can swap GSM SIM cards between

handsets when a new one is necessary, which enables you to carry all of your contact and calendar information over to a new handset with no hassle. CDMA operators answer this flexibility with their own service that stores user data, including phone book and scheduler information, on the operator’s database. This service makes it possible to not only swap over to a new handset with little trouble, but it also gives users the ability to recover contact date even if their phone is lost or stolen.

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International Roaming with GSM and CDMA

Where international business travel is an issue, GSM leaps forward in the race for the title of “Most Accessible.” Because GSM is used in more than 74% of the markets across the globe, users of tri-band or quad-band handsets can travel to Europe, India, and most of

Asia and still use their cell phones. CDMA offers no multiband capability, however, and therefore you can’t readily use it in multiple countries. However, certain phones like

the iPhone 5 now have Quad-band GSM built in so they can be used overseas with special calling plans from carriers.

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Data Transfer Methods in GSM vs. CDMA

Another difference between GSM and CDMA is in the data transfer methods. GSM’s high-speed wireless data technology, GPRS (General Packet Radio Service), usually offers a slower data bandwidth for wireless data connection than CDMA’s high-speed technology (1xRTT, short for single carrier radio transmission technology), which has the capability of providing ISDN (Integrated Services Digital Network)-like speeds of as much as 144Kbps (kilobits per second). However, 1xRTT requires a dedicated connection to the network for use, whereas GPRS sends in packets, which means that data calls made on a GSM handset don’t block out voice calls like they do on CDMA phones.

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Interaction between GSM and CDMA

In cities and densely populated areas, there are often high concentrations of GSM and CDMA connection bases. Intheory, GSM and CDMA are invisible to one another and should "play nice" with one another. In practice, however, this is not the case. High-powered CDMA signals have raised the "noise floor" for GSM receivers, meaning there is less space within the available band to send a clean signal. This sometimes results in dropped calls in areas where there is a high concentration of CDMA technology. Conversely, high-powered GSM signals have been shown to cause overloading and jamming of CDMA receivers due to CDMA’s reliance upon broadcasting across its entire available band.

The result of this little cross-broadcasting joust has led some cities to pass ordinances limiting the space between cell towers or the height they can reach, giving one technology a distinct advantage over the other. This is something to note when choosing a wireless provider. The distance between towers will severely affect connectivity for GSM-based phones because the phones need constant access to the tower’s narrow band

broadcasting.

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Popularity and Market Share

GSM is a lot more widespread in Europe and Asia. In the United States, Sprint and Verizon networks are CDMA whereas AT&T and T-Mobile are on GSM. Most of Europe uses GSM and so does China. In India, Hutch, Bharti and BSNL are on GSM whereas Reliance and Tata Tele are on CDMA networks.