Giz Explains: What’s the adaptation between GSM and CDMA? [Giz Explains]

America is divided! One faction is strong and entrenched. The opposite is respected by the remaining of the area, but can’t seem to seize power here. I’m talking, obviously, about our cellphones.

Buying a phone is a difficult choice. No wait, scratch that: It’s a difficult set of selections, a dozen decisions wrapped into one, made just once every two years. Once you decide it’s time to buy, you’ve got to pick out between operating systems, hardware, and feature lists. Just as importantly, you’ve got to make your mind up a network, with its distinct coverage areas, rate plans and customer service. But built into your choice of network, is one more dilemma: network technology. GSM or CDMA? These inconspicuous acronyms, which a whole lot of folks deem fit to ignore, define probably the most basic functions of your phone

What, Which, and Who

GSM and CDMA both serve as shorthand for different cell phone technologies. GSM stands for Global System for Mobile Communications; it’s the area’s most prolific mobile standard (a conventional being a fixed of rules and recommendations about how a mobile network should work). CDMA stands for Code Division Multiple Access -within the context of cellphones and mobile networks, people are inclined to use it interchangeably to check with two different mobile standards: CDMAOne or CDMA 2000.

What’s the core difference? It all has to do with the manner your data is converted into the radio waves that your cellphone broadcasts and receives. To keep from lulling you to sleep with the deep dive, I’ll just scratch the outside and say that GSM divides the frequency bands into multiple channels so that multiple user can place a decision through a tower simultaneously; CDMA networks layer digitized calls over one another, and unpack them on the back end with sequence codes.
Image courtesy of National Instruments

CDMA was a late response to GSM, and in 1995 this more complex and modern channel access promised better security, fewer dropped calls, and more efficient infrastructure. But that was 1995, when car phones were still regularly spotted on city streets.

America is unique is that it’s home to more CDMA users than GSM users, with the two largest CDMA carriers accounting for over 43% of the market. The two largest GSM carriers barely break 37%; worldwide, CDMA accounts for around 13% of phones, with GSM and its successor, UMTS making up of the rest.

Of course, none of this tells us anything at all about what it means to take advantage of networks on either standard. Standards being basically a collection of guidelines that participating companies abide by, many of the differences between CDMA and GSM are small details that you simply’ll never ought to concern yourself with: frequency bands, audio codecs, the physical specifications of the network infrastructure, the way in which a user is linked to a phone, etc.

But these rules are essential to the AT&Ts, Verizons, Apples, and Samsungs of the sector: They outline quite often every technical aspect of a cellular network, and, to a lesser extent, the phones which can be used on it. Inside the same way that web standards make sure that webpages render properly in our browsers, the GSM and CDMA standards give carriers a collection of instructions to (for probably the most part) follow, and cellphone makers a guide for making devices that’ll work on the area’s wireless networks.

The Differences

Most of us will never ought to consider whether or not our phones are CDMA or GSM-based. These acronyms are meant to be transparent, a bit like so many other tech standards are. (Most HDTV owners don’t really care much if their images are delivered via Component or HDMI cable, nor do most music listeners mind if their music was encoded as a AAC file or an MP3-so long as the quality doesn’t suffer.) But that’s not to assert that they aren’t different.

First, let’s get this out of ways: I’ve been using GSM and CDMA as blanket names for a hard and fast of standards that have changed over the years. Most new phones on AT&T and T-Mobile actually adhere to both GSM and the newer UMTS (Universal Mobile Telecommunications System) standards. UMTS isn’t an official element of the GSM standard, but it surely is what GSM carriers use for 3G data transmission. Likewise, CDMA2000, based more directly on its predecessor incorporates a range of improvements over the original CDMAOne, key among them 3G data speeds. Though both GSM and CDMAOne standards are on their way out, I fully expect their names to live to tell the tale as shorthands for what comes next. Of course , they were the premise of the complete cellular industry as we knew it for decades.

Back in 1995, CDMA was an insurgent standard looking to supplant the dominant GSM, and the variations between the two technologies were more obvious. Old-school, 2G GSM phones worked better inside buildings (neat trick: In case you’re having trouble getting a signal indoors, switch off your 3G), but caused interference in unshielded speakers (side-effect of aforementioned ‘neat’ trick). Concurrently, CDMA phones had a marginally more refined method for handing off calls from tower to tower, in order that they dropped fewer calls. This can be still true. It’s also still true that 2G GSM networks can offer better coverage in mountainous terrain, since they utilize taller cell towers, though range of said towers is otherwise a touch shorter. Additionally, GSM (and UMTS) phones can send and receive data packets while making a choice, which most CDMA networks still don’t support.

Such were the arguments for and against CDMA when it barged into the scene in 1995, at time when GSM was the best game in town and most of the people didn’t even own cellphones. So it follows that these original performance differences, which have been striking at the time, now don’t matter matter quite so much anymore. If a Droid gets better reception at your property than an iPhone, it’s not because one is a CDMA2000 phone and the opposite is a GSM/UMTS phone. It’s certainly because Verizon has a tower towards your pad, and the backhaul to support your calls.

The real differences-the ones that you can care about-are more obvious.

Both GSM and CDMA standards outline a method that phones are identified by carriers. In GSM phones, it’s a removable chip called a SIM card. In theory, that you would be able to pop a SIM card out of a GSM phone and stick it in any other GSM phone. (Although numerous phones are ” locked” to a particular carrier, that is majorly annoying.) The CDMA standard describes something similar, called the RUIM (removable user ID module), but that hasn’t really caught on. Instead, CDMA phones ship locked to 1 network, and may only be switched to another with the cooperation of both the old and new carriers.

This isn’t so important in a place like America, where phones are sold with contracts and discarded with after two years. Nevertheless it’s a big deal within the developing world, where phones are sold unlocked, independently of carriers, and wish to work with any and all local networks. And even inside the first world, sometimes it’s nice so that you can just switch numbers every now and again. (a neighborhood pay-as-you-go SIM saved me a boatload of money on a up to date trip overseas.)

And that leads us to the key reason you’ll must consider when choosing between CDMA vs. GSM: travel. Basically, CDMA phones suck at this. A CDMA-only phone from Verizon or Sprint is solely in a position to roam on other CDMA networks, which simply don’t exist in much of the area. Both carriers offer phones with built-in GSM support just for travelling, but this selection is missing from their preferable handsets.

Subtle as they’re, the outward differences between CDMA and GSM can inform you plenty about your phone, from where you should use it to how well it holds a choice on the highway. I’m not saying so you might place more weight on a carrier’s choice of wireless tech standards that its phone choice, customer service or coverage for your area. I’m just saying that you simply shouldn’t ignore it.

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This post is tagged: code division multiple access, global system for mobile communications, mobile standards, national instruments, network technology