CDMA vs. GSM: What’s the difference between these cellular standards?

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Jan Jirous/Shutterstock
If you’re in the market for a new smartphone or carrier — or you’re simply interested in cell phone networks — you’ve likely encountered the acronyms CDMA and GSM before. But what are they, and how do they affect your phone?

The two cellular standards function in different regions and allow for global communication between individuals, and each converts incoming and outgoing data into radio waves differently. Neither should be a huge factor when buying a cell phone (unlike 4G and LTE), but it’s definitely worth knowing your stuff, since not all cell phones are guaranteed to work on both standard. It depends on where you are, what you’re looking for, and who you’re with.

GSM explained

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The iPhone 7 is a smartphone that typically functions on a GSM network.

GSM stands for Global System for Mobile Communication, and unless you live in the United States or Russia, this is probably the technology your phone network uses, given it’s the standard system for most of the world. GSM networks use TDMA, which stands for Time Division Multiple Access. TDMA works by assigning time slots to multiple conversation streams, alternating them in sequence and switching between each conversation in very short intervals. During these intervals, phones can transmit their information. In order for the network to know which users are connected to the network, each phone uses a subscriber identification module card, or SIM card.

SIM cards are one of the key features of GSM networks. They house your service subscription, network identification, and address book information. The cards are also used to assign time slots to the phone conversation, and moreover, they tell the network what services you have access to. They store your address book, too, along with relative contact information. They can even be used to pass information between phones, if a carrier allows it.

CDMA explained

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The Google Pixel XL is a smartphone that runs on a CDMA network.

CDMA — or Code Division Multiple Access — is often found in the U.S and Russia, though GSM is also present in those countries. The Allied Forces developed the technology during World War II, primarily as a method to prevent Nazi forces from jamming radio signals. Unlike GSM, CDMA grants users full access to the entire spectrum of bands, thus allowing more users to connect at any given time. It also encodes each user’s individual conversation via a pseudo-randomized digital sequence, meaning the voice data remains protected and filtered so that only those participating in the phone call receive the data.

Phones on CDMA networks do not use SIM cards. Instead, each phone is built specifically to work on that carrier’s network. What does this mean for consumers? For starters, it means that phones are tied to a carrier and their bands, so if you decide to change providers, you’ll have to buy a new phone.

Is one better than the other?

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Huawei’s phones very rarely support CDMA Julian Chokkattu/Digital Trends

Not necessarily. Both are the global standards for cell communication. The major factor affecting call quality is the network itself, not the method it uses to transmit information. Of course, there are some things to keep in mind when it comes time to choose between CDMA and GSM phones. For starters, CDMA phones without SIM slots are tied to their carriers, and cannot be transferred to other networks. A Verizon phone could not be transferred to Sprint’s network, for instance, or vice versa. But sometimes it’s not as cut and dried as all that — although some Verizon devices do use CDMA, they also have an unlocked SIM slot, so could be unlocked for use on other networks. Sprint is less forthcoming with unlocked SIM slots when its devices do contain one, but you can usually find ways get your carrier to unlock your phone when you’re done with them.

In contrast, GSM phones are fairly easy to unlock and transfer to other networks. Additionally, third-party manufacturers often sell phones designed for GSM networks, since they don’t require access to a specific carrier’s bands. GSM phones will even work in countries with compatible GSM networks.

CDMA networks allow for a greater number of users, meaning their capacity for communication is greater than that of GSM networks. Moreover, CDMA is the infrastructure on which all 3G networks are based — for both GSM and CDMA carriers. However, there’s now a third type of network that is quickly becoming the frontrunner in terms of quality, with many major cell phone companies quickly adopting it. Dubbed LTE for Long-Term Evolution, the technology represents an evolved form of GSM, and uses a similar technology as GSM networks. The new standard boasts enhanced voice quality and functions as the base of high-speed, 4G data networks. In this case, LTE does have an edge over the competition in terms of overall speed and quality.

If you’re a U.S. customer and wondering what companies use which type of network, the split is right down the middle: AT&T and T-Mobile are GSM carriers, while Verizon and Sprint are CDMA. In truth, picking a new phone or carrier solely based on what standard it adheres to doesn’t necessarily matter because the services, features, phones, and service quality a network offers aren’t solely dependent on their network infrastructure. So unless you have a particular need for choosing one over the other, go with the carrier that best fits your tastes, needs, and budget.

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